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6 Organometallic Chemistry Part (i) The Transition Elements By R. PEARCE D. J. THOMPSON and M. V. TWlGG ICI Corporate Laboratory PO Box 7 7 The Heath Runcorn Cheshire WA7 4QE 1 Introduction Most recent publications fall into two broad areas the larger concerned with preparations structures and properties of complexes and the smaller with applica- tions in organic synthesis. It is with the latter that we are principally concerned. While advances continue on all fronts the most exciting developments have taken place in transition-metal-catalysed olefin metathesis where we now have a better understanding of the reaction pathway (see Section 7). The more important review articles are given below. Of a general nature publications have included a special editioc of J.Orgunornetdic Chern. (Vol. 100) which is a collection of personal reflections by leading researchers; a comprehensive handbook of data on syntheses physical constants and reactions of complexes that appeared in the literature in the period 1965-1968;’ and a further volume of a multi-author book dealing with a number of applications of transition-metal complexes in homogeneous catalysis.* More specific articles have dealt with trans- ition-metal catalysis of pericyclic reaction^;^ metathesis4 (see also ref. 3);olefin poly- meri~ation;~applications of metal vaporization to organometallic synthesis;6 organo-chromium compound^;^ the roles of nickel’ and palladium’ complexes in catalysis; reactions of hydrido-nickel -palladium and -platinum complexes;” 1 K.Bauer and G. Haller ‘Organometallic Compounds. Methods of Synthesis Physical Constants and Chemical Reactions Second Edition. Volume 1 Compounds of the Transition Metals First Supple- ment’ ed. M. Dub Springer-Verlag Berlin 1975. 2 ‘Aspects of Homogeneous Catalysis’ ed. R. Ugo Reidel Dordrecht Holland Vol. 2 1974. 3 F. D. Mango Coordination Chem. Rev. 1975,15 109. 4 R. J. Haines and G. J. Leigh Chem. SOC.Rev. 1975,4 155; J. C. Mol and J. A. Moulijn Adv. Catalysis 1975 24 131; W. B. Hughes Chemtech. 1975,486; L. Hocks Bull. SOC.chim. France 1975 1893. ‘Co-ordination Polymerisation a Memorial to Karl Ziegler’ ed. J. C. W. Chien Academic Press New York 1975; D. G. H. Ballard J. PoZymer Sci. Polymer Chem. Edn. 1975,13 2191. P. S.Skell and M. J. McGlinchey Angew.Chem. Internat. Edn. 1975,14 195; P. L. Timms ibid. p. 273; E. A. Koerner von Gustorf 0.Jaenicke 0.Wolfbeis and C. R. Eady ibid. p. 278; K. J. Klabunde and T. 0. Murdock Chemtech. 1975,624; K. J. Klabunde Accounts Chem. Res. 1975,8,383. R. P. A. Sneeden ‘Organochromium Compounds’ Academic Press New York 1975. * P. W. Jolly and G. Wilke ‘The Organic Chemistry of Nickel’ Academic Press New York Vol. 2,1975. P. M. Henry Ado. Organometallic Chem. 1975 13 363. lo D. M. Roundhill Adv. Organometallic Chem. 1975 13 274. 119 120 R. Pearce,D.J. Thompson,and M. V.Twigg reactions of Na,Fe(CO),; ''homogeneous catalytic activation of carbon-hydrogen bonds;12 activation of Grignard reagents by transition-metal complexe~;'~ and metal v-complexes (arene cyclopentadienyl and ally1 group^).'^ 2 Hydrogenation Advances in homogeneous catalytic hydrogenation have been in the areas of selective hydrogen addition and asymmetric synthesis Futher details have appeared on [Co(q3-C,H,){P(OMe),},] which among homogeneous catalysts is unique in selectively hydrogenating arenes to cyclohex- anes.15 Selectivity is such that benzene is hydrogenated to cyclohexane at a rate some three to four times greater than is cyclohexene.Neither cyclohexadiene nor cyclohexene are important intermediates. Once transfer of the first hydrogen has taken place the arene must remain tightly bound to the metal centre until the sixth has been added. This tight binding is well demonstrated in the hydrogenation of [2HJbenzene which affords the first synthesis of pure all-cis-[2&]cyclohexane.It was suggested that an important intermediate is the complex [Co(q1-C3H5)-(H),{P(OMe),}(q4-C6H6)].The ally1 group is not lost during reaction and indeed the corresponding hydrido-cobalt complex is inactive. [RuCl,(PPh,),] effects reduction of both aliphatic and aromatic nitro-compounds to amines.I6 For the alphatic compounds this method appears to be the preferred reduction procedure catalyst turnover is high reaction conditions are mild; and aqueous work-up procedures are not necessary.'6a For aromatic compounds high selectivity is observed other substituents e.g. halogen ester or nitrile are not affected and reduction of dinitro-compounds proceeds at a higher rate affording a procedure for the sequential hydrogenation of nitro-amines and diamines.I6' [RuCl,(PPh,),] is an efficient catalyst for the reduction of cyclic carboxylic acid anhydrides to y-lactones the reaction being one of the few examples of transition-metal-catalysed homogeneous hydrogenolysis of a carbon-oxygen bond.17 Other conventional hydrogenation catalysts were ineffective.Carboxylato-rhodium(1) species e.g. [Rh(OCOPh)(cyclo-octa- 1,5-diene)(PPh3)] in the presence of base were highly active in the selective hydrogenation of alk-1-ynes to alk-1-enes." [RhCl(PPh,),] in combination with H202gives an undefined heterogeneous catalyst that is active in the selective conversion of mesityl oxide into methyl isobutyl ketone.l9 Important pointers to the design of ligands particularly those related to diop (1 ; Ar =Ph) for use in asymmetric hydrogenations come from a study of the effect on catalytic activity of changes in the ring size of chelating diphosphine ligands 11 J.P. Collman Accounts Chem. Res. 1975 8 342. 12 G. W. Parshall Accounts Chem. Res. LY7.5 8 113. 13 H. Felkin and C. Swierczewski Tetrahedron 1975 31 2735. l4 W. E. Silverthorne Ado. Organometallic Chem. 1975 13 48; M. A. Bennett Organometallic Chem. 1975 3 290; M. Choke ibid.,p. "!7 W. E. Watts ibid. p. 342. (a)F. J. Hirsekorn M. C. Rakowski and E. L. Muetterties J. Amer. Chem. SOC.,1975,97,237; (6)E. L. Muetterties M. C. Rakowski F. J. Hirsekorn W. D. Larson V. J. Basus andF. A. L. Anet ibid.,p. 1266. l6 (a) J. F. Knifton J.Org. Chem. 1975,40 519; (b)J. F. Knifton Tetrahedron Letters 1975 2163. l7 J. E. Lyons J.C.S. Chem. Comm. 1975,412. Is R. H. Crabtree J.C.S. Chern. Comm.. 1975,647. 19 W. Strohmeier and E. Hitzel J. Orp9iometallic Chem 1975,102 C37. Part (i) The Transition Elements Ph2P(CH2),PPh2 in combination with a Rh’ centre.” Activity was high for n =3 less good for n =4,5,or 6 and poor for n =2 [or in cases where (CH,) was replaced by the groups CH,OCH or cis-CH=CH] (cf. ref. 56). Chiral phosphine-rhodium(1) complexes predominate in reports on catalytic asymmetric hydrogenation. Efficient asymmetric reduction of ketones has been achieved using e.g. [Rh(hexa-Z,5-diene)Cl] +diop with optical yields of up to Using the chiral diphosphine (2) as ligand Knowles has achieved enan- tiomeric excesses of 96% in the reduction of a-acylamido-acrylic acids to a-amino- acids rivalling the stereospecificity observed with enzyme systems.22 Importantly the high optical yields were not markedly sensitive to temperature and pressure.H OMe (1) (2) Chiral diphosphines related to diop (1; Ar = Ph) have been in~estigated.~~ In combination with Rh’ species higher optical yields have been obtained for (1; Ar =C6H4Me-m)23a and (3),23bwhereas when the oxygen-containing ring is substi- tuted by a cyclopentane or a bicyclo[2,2,2]octane ring yields are lower. Using space-filling models the chirality of the major products of asymmetric hydrogena- tion and hydrosilylation using diop-rhodium complexes has been predi~ted.’~ In all but three cases the correct product was predicted.OPPh CI CI n Ru-P P-RU P P = (+)-diop ‘OPPh (3) (4) First reports have appeared on the use of ruthenium complexes in asymmetric hydr~genation.’~ Both mono- and di-nuclear diop complexes of RuII were prepared but of these only the dinuclear (4) was effective. Optical yields up to 60% were [Ru,H,(CO),{( -)-diop},] has been used for the high-temperature and high-pressure hydrogenation of carbon-oxygen and carbon-nitrogen double bonds but optical yields were Further work on the asymmetric hydrogenation catalysed by the bis(dimethylglyoximato)cobalt(II)-chiral amino-alcohol system has shown that asymmeric induction is brought about by amino-alcohol molecules that are not 20 J.-C.Poulin T.-P. Dang and H. B. Kagan J. Organornetullic Chern. 1975,84,87. 21 B. Heil S. Toros S. Vastag and L. Marko J. Organornetullic Chem. 1975 94 C47; J. Solodar Cherntech. 1975 42 1. 22 W. S. Knowles M. J. Sabacky B. D. Vineyard and D. J. Weinkauff J. Amer. Chem. Soc. 1975,97,2567. 23 (a)T. P. Dang J.-C.Poulin and H. B. Kagan J. Organornetullic Chem. 1975,91,105; (b)M. Tanaka and I. Ogata J.C.S. Chern. Cornrn. 1975 735. 24 R. Glaser Tetrahedron Letters 1975 2127. 25 (a)B. R. James D. K. W. Wang and R. F. Voigt J.C.S. Chem. Grnrn.,1975,574; (6) C. Botteghi M. Bianchi E. Benedetti and U. Matteoli Chirniu (Switz.) 1975 29 256. 122 R. Pearce,D.J. Thompson andM. V.Twigg co-ordinated to the cobalt atom.26 This system was compared to oxido-reductases where the catalytic site and stereospecificity-determiningsite are generally sepa- rated.3 Hydrosilylation Rhodium(1) complexes containing chiral phosphines effect catalytic asymmetric hydrosilylation of ap-unsaturated carbonyl c~mpounds.~' The nature of the pro- duct depends on the silane with monohydrosilanes 1,4-addition takes place to give the useful silylenolates which hydrolyse to optically active saturated carbonyl dihydrosilanes undergo 1,2-addition at the carbonyl group to give optically active ap-unsaturated Optical yields were generally low. A problem related to hydrosilylation is the conversion of 'direct process residues' by-products from the direct synthesis of halogenoalkylsilanes containing mixed disilanes into useful products.Two recent disclosures point to a possible solution.28 Nickel palladium and platinum complexes catalyse the reaction of halogenoalkyl- disilanes R,Si2C16-x with alkyl and aryl halides to give monosilanes. For example [Pd(PPh,),] effects essentially quantitative conversion of CIMe2SiSiMe2C1 and PhBr into PhMe,SiCl and Me,SiBrCl. 4 Metal-catalysedHydrogen-transfer Reactions Earlier indications that amines are highly efficient reagents in hydrogen-transfer reactions have been confirmed.29 These reactions generally employ hydrocarbons (e.g. tetralin) or primary or secondary alcohols as donors. With RhC1(PPh3) as catalyst cyclic amines (e.g.piperidine pyrrolidone and indoline) are more reactive than the above donors in transfer hydrogenation to ~ycloheptene.~~" Simple amines (e.g.tri-isopropylamine) are effective in the [RuH,(PPh,),]-catalysed reduction of aldehydes or ketones to Furthermore H2N(CH2)3NH2 or HN(CH,),NHCHEt in combination with a palladium catalyst effect selective reduc- tion of cyclo-octa-l,5-diene to cyclo-octene; this is the first example of a selective reduction of a diene to a monoene via a metal-catalysed hydrogen-transfer reac- ti~n.~~~ Although we are concerned with transition-metal-catalysed reactions it is noteworthy that a metal-free hydrogen-transfer reaction system has been dis- clo~ed.~~ The reagent is dehydrated alumina that has been treated with isopropyl alcohol and it is specific for the reduction of aldehydes to primary alcohols; other functional groups (e.g.ketones esters) are not affected. [Ru(OCOCF,),CO(PPh,),] is reportedly the most efficient homogeneous catalyst for the dehydrogenation of primary and secondary alcohols to aldehydes and z6 Y. Ohgo Y. Natori S. Takeuchi and J. Yoshimura Chem. Letters 1974 1327. z7 (a)T. Hayashi K. Yamamoto and M. Kumada TetrahedronLetters 1975,3;(21) I. Ojima T. Kogure and Y. Nagai Chem. Letters 1975,985. 28 H. Matsumoto S. Nagashima K. Yoshihiro and Y.Nagai J. Organometallic Chem. 1975,85 C1; U.S. P. 3 772 347 (Chem. Abs. l974,80,3625v). 29 (a)T. Nishiguchi K. Tachi and K. Fukuzumi J. Org. Chem 1975,40,237;(6)H. Imai T. Nishiguchi and K. Fukuzumi Chem. Letters 1975,807; (c)S.-I. Murahashi T. Yano and K.-I. Hino Tetrahedron Letters 1975,4235. 3O G. H. Posner and A.W. Runquist Tetrahedron Letters 1975,3601. Part (i) The Transition Elements ketones re~pectively.~’ P-Elimination from an alkoxy-ruthenium intermediate is proposed in the reaction pathway. Rhodium has joined platinum and iridium as an homogeneous catalyst in the form of RhCl, for the isotopic hydrogen-exchange reaction.32 Significantly while it is less active than platinum strong acid is not required to stabilize the catalyst solution. The results from studies of H/D exchange in alkanes and aromatic hydrocarbons point to a common mechanism for all three metals and give added support to the role of n-complexes as intermediates. 5 Oligomerization Oligomerizationof alkenes dienes and alkynes continues to be a productive field. Cyclo-oligomerization to give four- five- or six-membered rings provides the main area of interest.An improved synthesis of benzocyclobutenes indanes and tetralins involves the [Co(q5-C,H,)(C0),]-catalysed cyclo-oligomerizationof a,@-diynes and substituted acetylenes [equation (l)].” The most versatile synthesis involves Me,SiCGCSiMe,. This alkyne shows little tendency to undergo homocyclotrimerization and produces the versatile reagent (5a; R =Me,Si) which isomerizes readily to (5b; R= Me,Si) with acid. The trimethylsilyl groups are readily substituted by electrophiles. (54 (5b) Bonnemann has extended his work on the organocobalt-catalysed 2 1 cyclo-trimerization of alk-l-ynes with nitriles which gives 2,4,6- and 2,3,6-substituted pyridines to the preparation of bipyridyl~.~~ From the readily available cyanopyridines and alk- l-ynes (RC-CH) the corresponding bipyridyls (6a) and (6b) are obtained in almost quantitative yield.The reaction of a,@-dinitriles with alkynes proceeds stepwise to give 2-cyanoalkylpyridines and 2,2‘-dipyridylalkanes. 1,3-Dienes undergo cyclodimerization with nitriles to give dihydropyridines which readily dehydrogenate to the corresponding pyridine. This substitution of alkynes by 1,3-dienes considerably increases the scope and utility of these syntheses and we can expect further useful developments in heterocyclic synthesis with such cobalt- based systems. It is interesting to speculate that in the 1980’s pyridines and bipyridyls may be synthesized industrially in this manner with 2,2’-bipyridyls coming from the inexpensive starting materials butadiene and cyanogen.An interesting five-membered-ring formation has been observed in the [NiCl,(PPh,),]-catalysed telomerization of butadiene with PrMgBr which reacts as a 31 A. Dobson and S. D. Robinson J. Organometallic Chem. 1975,87 C52. 32 M. R. Blake J. L. Garnett I. K. Gregor W. Hannan K. Hoa and M. A. Long J.C.S. Chm. Comm. 1975,930. 33 R. L. Hillard tert. and K. P. C. Vollhardt Angew. Chem. Internat. Edn. 1975 14 712; W. G. L. Aalbersberg A. J. Barkovich R. L. Funk R. L. Hillard tert. and K. P. C. Vollhardt J. Amer.Chem. SOC. 1975,97,5600. 34 H. Bonnemann Seventh Internat. Conf. Organometallic Chem. Venice 1975 abstr. 132. R. Pearce,D.J. Thompson and M. V.Twigg (64 (6b) (7) source of [HMgBr].Both cis-and by thermal isomerization trans-(2-vinylcyclopenty1)methylmagnesium bromide [cis-and trans-(7)]were obtained in high stereochemical X-Ray structures of intermediates have provided further insights into reaction pathways. Confirmation that dienylpalladium complexes are intermediates in [PdClJ-catalysed cyclotrimerization of alkynes comes from the study of (8) an intermediate in the reaction of [PdCl,(PhCN),] with BUT-CH that can be trapped by addition of MeS(CH,),SMe.36 Nickel species are active in the cyclodimerization of 3,3-dimethylcyclopropene. From the reaction with 2,2’-bipyridyl(cyclo-octa-1,5-diene)nickel the active intermediate (9)was is~lated.~’ This is the first example of metallo-ring formation by oxidative dimerization of an olefin at a metal centre presumably related to the ring strain in the cyclopropene which imparts alkyne-type reactivity.(Cf.ref. 38for recent work on the formation of nickelocycles via oxidative dimerization of alkynes). Bu‘ Q Me / Me CI Me (8) (9) Improvements have been made in the selectivity of catalyst systems to the production of linear dimers. [NiBr,(PPh,),] in combination with NaBH, gives high yields of (E,E)-octa-1,3,6-triene in the dimerization of butadiene and overcomes the strong tendency for the production of cyclic products with organonickel cata- lyst~.~~ Isomeric hexenes have been obtained in good selectivity (up to 95% linear products) using the catalyst system [Pd(acac),)-EtAlCl,-PR,.40The reaction rate was however relatively low.Full details have appeared on the catalytic activity towards butadiene oligomeriza- tion shown by diarenetitanium compounds and catalyst systems obtained from condensed vapours of the first-row transition metals Ti V Cr Mn Fe Co and Ni41 3s H. Felkin L. D. Kwart C. Swierczewski and J. D. Umpleby J.C.S. Chem. Comm. 1975 242. 36 B. E. Mann P. M. Bailey and P. M. Maitlis J. Amer. Chem. SOC.,1975 97 1275. 37 P. Binger J. McMeeking U. Schuchardt and M. J. Doyle ref. 34 abstr. 129. 38 J. J. Eisch and C. A. Damasevitz J. OrgunometullicChem.,1975,96 (219; J. J. Eisch and J. E. Galle ibid. p. C23. 39 C. U. Pittman jun. and L. R. Smith J. Amer. Chern. SOC.,1975,97 341. 4O C. Henrici-OlivC and S. Olivk Angew.Chem. Internat. Edn. 1975,14 104. 41 V. M. Akhmedov M. T. Anthony M. L. H. Green and D. Young J.C.S. Dalton 1975 1412. Part (i) The Transition Elements 125 An interesting pointer to the role of metal clusters in catalysis comes from a study of the fluxional tetranickel species [Ni4(CNCMe,),].42 This complex is an active catalyst in the cyclotrimerization of acetylene and in the dimerization of butadiene to cyclo-octadienes (no other cyclo-dimers or linear dimers being produced) whereas the monometallic [Ni(CNCMe,),] is inactive. The authors suggest that more than one metal may be involved in these transformations as in a 'template synthesis'. We look forward to further developments in this field with extensions to the preparation of discrete supported clusters of varying nuclear (M,) sizes.6 Isomerization The conversion of 4-vinylcyclohexene into cyclo-octa- 1,5-diene on reaction with [PdCl,(PhCN),] one of the few reported skeletal rearrangements initiated by a palladium complex has been reinvestigated. Although a variety of experimental conditions were employed no cyclo-octa- 1,5-diene was detected.43 A new process for the cis-trans interconversion of olefins involves formation of an epoxide its ring-opening (with inversion) by [Fe(q '-CsHS)(CO)J and heating the intermediate alkoxide to give the desired olefin. This sequence is not complicated by the presence of an olefin group in the epoxide and is well suited to dialkyl and diary1 epoxides but is less effective for CU,~ -epoxycarbony1 'H N.m.r.of the olefinic molybdenum complexes [MoH(C,H4),(Ph,PCH2CH,PPh,),]' and [MoH(~~-C,H,)(P~~PCH,CH,P~,)~] have provided an insight into reaction pathways in olefin isomerization. For the former rapid exchange of the Mo-H with half of the hydrogens in the bound ethylenes is observed this being the first direct observation of a reversible insertion process of this type. For the latter exchange of the Mo-H with the terminal protons in the co-ordinated ally1 group is observed giving a direct observation of the 1,3-hydride shift mechanism via a hydrido-ally1 intermediate. 7 Olefin Metathesis There has been a high level of interest on all fronts in olefin metathesis this year including the publication of several reviews.374 Much of this work is concerned with elucidating the mechanism of this intriguing reaction and here we concentrate on this aspect.Previously it had been demonstrated that some rhodium-carbene complexes are active in homogeneous metathesis of a number of electron-rich 01efins.~~ The generality of such a mechanism involving metal-carbene intermediates to the metathesis of simple olefins has been questioned. Such doubts have for example been expressed by a reviewer (Mango3) in 1975. Subsequently a number of independent workers have presented evidence4' supporting such a catalytic cycle. 42 V. W. Day R. 0.Day J. S. Kristoff,F. J. Hirsekorn and E. L. Muettertes J. Amer. Chem. SOC.,1975,97 2571. 43 W. T. Wipke and G. L. Goeke J. Org. Chem 1975,40 3242. 44 M. Rosenblum M.R. Saidi and M. Madhavarao Tetrahedron Leners 1975,4009. 45 J. W. Byrne H. U. Blaser and J. A. Osborn J. Amer. Chem. Soc. 1975,97,3871. 46 D. J. Cardin M. J. Doyle and M. F. Lappert J.C.S. Chem. Comm. 1972 927. 47 (a)E. L. Muetterties Znorg. Gem. 1975,14,951; (b)M.F. Farona and W. S. Greenlee J.C.S. Chem. Comm. 1975,759;(c) R. H. Grubbs P. L. Burk and D. D. Carr,J. Amer. Chem. Soc. 1975,97,3265; (d)T. J. Katz and J. McGinnis ibid.,p. 1592. R.Pearce D.J. Thompson and M. V. Twigg Space does not permit a detailed review of all of this evidence but the essential cycle of the carbene mechanism based on the presentation by M~etterties,~~" is shown in Scheme 1. Reagents i R2HC=CHR2; ii R'HC=CHR' Scheme 1 Although intermediates (or transition states) involving cyclobutanes have previ- ously received the major attention five-membered metallocyclic species have also been considered.Unlike the present metal-carbene mechanism these involve the simultaneous interaction of the metal with two olefin molecules. Direct evidence for this scheme comes from initial product analysis of a reaction using an interesting new stable rhenium catalyst system [Re(CO),X]-EtAICl in chloroben~ene,~'~ the ratio of deuteriated ethylenes from specifically deuteriated octa-l,7-diene on treatment with WC1,-LiBu or PhWC13-AlC13,47C and the results of the mixed metathesis of cyclo-octene trans-but-2-ene and trans-oct-4-ene as well as cyclo-octene and hex- 2-ene with [MoCl,(NO),(PPh,),] and Et,AI,CI in chl~robenzene.~~~ It is also pertinent that tungsten-methylene species have been proposed4' as intermediates in other reactions e.g.in the reaction of [W(q-C,H,),Me(C,H,)]+ with phosphines and that the first stable and fully characterized (X-ray) transition- metal-methylene complex [Ta(q5-C5H5)Me(CH,)] has been rep~rted.~' Adsorbed methylene is also thought to be involved in heterogeneous metathesis Last year the WC16-EtAlC1 system originally classified as a homogeneous catalyst was reclassified as a heterogeneous ~atalyst.~' This year further studies have shown that the heterogeneous part of the system is inactive and that the activity resides in the homogeneous solution.52 Two groups53 have examined the unusual catalyst system formed by U.V. irradia-tion of [w(co)6]in CCI,.No activity was observed in hexane chlorobenzene or CHCI,. Although the involvement of [W(CO),Cl] is suggested it is tempting to speculate that a dichlorocarbene complex is the active intermediate. 48 N. J. Cooper and M. L. H. Green J.C.S.Chem. Comm. 1974,761; L. Farrugia and M. L. H. Green ibid. 1975,416. 49 R. R. Schrock,J. Amer. Chem. SOC.,1975,97,6577; L. J. Guggenberger and R. R. Schrock ibid.,p. 6578. J. I. C. Archibald J. J. Rooney and A. Stewart J.C.S. Chem. Comm. 1975 547. 51 E. L. Muetterties and M. A. Busch J.C.S. Chem. Comm. 1974,754. 52 R. Wolovsky and Z. Nir J.C.S. Chem. Comm. 1975,302. 53 P. Krausz F. Granier and J. E. Dubois J. Amer. Chem. SOC.,1975,97,437;A. Agapiou and E. McNelis J.C.S. Chem. Comm. 1975 187. Part (i) The Transition Elements 8 Carbonylation There has been a high level of interest this year in carbonylation using palladium catalysts.Severai groups of workers have reported the catalytic carbonylation of aryl and benzyl halides under mild conditions [equation (2)].54 Yields are generally best for iodides but bromides and chlorides have also been successfully carbonylated. If the reaction is carried out with a primary or secondary amine in place of the methanol the corresponding amide is Pd complex R'X+ CO +MeOH +R:N ______* R'C0,Me +[RzNH]+X-(2) In the carbonylation of styrene using palladium-phosphine complexes it was found that the product depended on the phosphine Using [PdCl,(PPh,),] ethyl 2-phenylpropionate was selectively obtained whereas [PdCl,{Ph,P(CH,),PPh2}] gave ethyl 3-phenylpropionate.The complexes [PdCl,{Ph,P(CH,),PPh,}] (n= 1,2 or 3) were inactive. This variation in catalytic activity with ring size has a parallel with some recently reported hydrogenation studies.20 Mixtures of PdCl and thiourea catalyse in high yield and under mild conditions the carbonylation of appropriate acetylenic alcohols to Q -methylene-lactones e.g. (10)to (11).57 (10) (1 1) Although platinum hydroformylation catalysts are relatively unusual a report has appeared on the use of [PtH(SnCl,)(CO)(PPh,),] for the hydroformylation of pent-1-ene.58 The catalyst is extremely selective giving more than 95% of the straight- chain aldehyde in almost quantitative yield. Pentacarbonyliron has been shown to react with either Q -or p -pinene to give the ring-expanded ketones (12) and (13).59The reaction takes place stereospecifically and represents the first metal-induced ring expansion of a monovinylcyclobutane.s4 A. Schoenberg I. Bartoletti and R. F. Heck J. Org. Chem. 1974,39,3318; J. K.Stille and P. K. Wong ibid. 1975,40 532; M.Hidai T.Hikita Y. Wada Y. Fujikura aild Y. Uchida Bull. Chem. SOC.Japan 1975,48,2075. 55 A. Schoenberg and R. F. Heck J. Org. Chem. 1974,39,3327. 56 Y.Sugi K. Bando and S. Shin Chem. and Ind. 1975,397. 57 J. R.Norton K. E. Shenton and J. Schwartz Tetrahedron Letters 1975,51. 58 C.Y.Hsu and M. Orchin J. Amer. Chem. SOC.,1975,97,3553. 59 A.Stockis and E. Weissberger J. Amer. Chem. SOC.,1975,97,4288. R.Pearce,D.J.Thompson andM. V.Twigg The reaction of NN-dichloro-amines or -amides with Fe,(CO) yields the corre- sponding isocyanate in reasonable yield.60 The reaction is envisaged as going via carbonylation of a nitrene intermediate ta give complexes of the type (14). Oxidative demetallation with Ce4' then liberates the isocyanate. 9 Heterogeneous Catalysts Derived from Known Homogeneous Systems Interest in this area is continuing to grow. Although the majority of the work has been undertaken using cross-linked polystyrene as the heterogeneous support other supports which have been used to anchor catalysts include poly(methally1 and phosphinated (diace tylene) .6 '* Several papers have described the increased activity and selectivity of supported catalysts over their homogeneous counterparts.62 Polymer-supported [IrCl(CO)- (PPh,),] selectively catalyses the hydrogenation of 4-vinylcyclohexene to 4-ethylcyclohexene and the hydrogenation of cyclo-octa- 1,5-diene to cyclo-octene.62u Moreover in the latter case the rate of hydrogenation was significantly greater using the anchored catalyst than using its homogeneous counterpart,62b and it could be recycled without loss of activity or selectivity.The complex [RhH(CO)(PPh,),] was anchored to a polymer support and found to be an active catalyst for the hydroformylation of pent-1-ene giving high yields of both normal and branched aldehyde.62c By varying the phosphine/rhodium ratio the ratio of normal to branched aldehyde could be varied. Butadiene was selectively dimerized to 4-vinylcyclohexene using polymer-supported [Ni(CO),(PPh,),] in high The reduction with sodium borohydride of aromatic nitro-derivatives in the presence of nickel-phosphine catalysts has been studied.62d Whilst the homogene- ous catalyst gives a mixture of products the polymer-supported catalyst shows a high selectivity for the preparation of aromatic azoxy-compounds in good yield.The selective hydrogenation of cup -unsaturated carbonyl and nitrile compounds has been achieved using polymer-supported [Rh6(C0),6].62" Polymeric amines were used as the support and the rate ofhydrogenation was higher for the resin-supported catalyst than for the homogeneous catalyst. This greater rate is attributed to the presence of a higher concentration of Rh6 species the dimerization of the Rh to Rh, species being prevented by polymer attachment.An interesting development of the work of Pittman was the first example of sequential multistep organic reactions carried out by attaching two catalysts to the same Thus the sequential cyclo-oligomerization of butadiene to 4- vinylcyclohexene followed by hydrogenation to ethylcyclohexane was accomplished using a single styrene-divinylbenzene resin to which [Ni(CO),(PPh,),] and [RhCl(PPh,),] had been anchored. 6o H. Suzuki K. Itoh I. Matsuda and Y. Ishii Chem. Letters 1975 641. (u)W. R. Cullen D. J. Patmore A. J. Chapman and A. D. Jenkins J. Orgunomerullic Chem. 1975,102 C12; (b)J. Kiji S. Kadoi and J. Furukawa Angew. mukromol. Chem 1975,46 163.62 (a)S. E. Jacobson and C. U. Pittman jun. J.C.S. Chern. Comm. 1975,187;(b)C. U. Pittman jun. S. E. Jacobson and H. Hiramoto J. Amer. Chem. Soc. 1975,97,4774;(c)C. U. Pittman jun. L. R. Smith and R. M. Hanes ibid. p. 1742; (d) B. Loubinoux J. J. Chanot and P. Caubere J. Orgunometullic Chem. 1975,88 C4; (e)T. Kitamura T. Joh and N. Hagihara Chem. Letters 1975 203. C. U. Pittman jun. and L. R. Smith J. Arner. Chern. Soc. 1975,97 1749. Part (i) The Transition Elements 129 By the reaction of a divinylbenzene-styrene resin with [Cr(CO),] a polymer- anchored tricarbonylchromium moiety bonded to the polymer's phenyl ring was This complex catalysed the selective hydrogenation of methyl sorbate to methyl (Z)-hex-3-enoate. Cyclopentadienyl compounds of titanium have been attached to a styrene-divinylbenzene cop01ymer.~~ The compounds are related to [TiCl,( 17 -C5H5)J and can be reduced apparently without undergoing dimerization to give very active catalysts for the hydrogenation of olefins.The polymer-bound catalysts are much more active than the corresponding reduced non-attached [TiCI,(q-C,H,),] for the reduction of olefins but are not as active for the reduction of dinitrogen. A disadvantage when using insoluble polymers as carriers is the differing accessi- bility of the catalytic functions. With this in mind a series of soluble metal complexes of polymers @ typically a non-crosslinked phosphinated polystyrene was syn- thesized.66 The complexes e.g. [RhCl(CO),@] were active for catalytic hydrogena- tion and hydroformylation but do not appear to be any more active than the normal insoluble polymer-supported catalysts.The soluble macromolecular catalysts were separated from the reaction products by membrane filtration or by precipitation with hexane. An interesting approach to using supported homogeneous catalysts is to conduct the metal-ion-catalysed reactions in the intracrystal space of a swelling layer lattice silicate.67 Using this technique the hydrogenation of hex- 1-ene catalysed by rhodium-phosphine complexes was studied. Since the mineral-bound rhodium complexes showed no activity toward hydrogenation of benzene the reduction is due to metal hydride formation and not to trace amounts of metallic rhodium which is an excellent catalyst for the reduction of aromatics as well as for olefins.10 Reactions of Co-ordinated Ligands Additions and Substitutions at Co-ordinated Ligands.-Interest in the reactions of iron carbonyl complexes has continued. Although the addition of nucleophiles to co-ordinated olefins or dienes normally occurs in an em-fashion it has been shown that the reaction of (tricarbony1)cyclohexadienylironwith MeO- gives the 5-endo- derivative as the ultimate product.68 Work on the reaction of diene-Fe(CO) complexes with Lewis acids has been extended to provide the synthesis of a variety of new ketonic complexes e.g. (16) from (15).69 Although the reaction formally involves the addition of carbon monoxide the yield is independent of the presence of gaseous CO. The synthesis of cis-alk-2-enes by alkylation of tetracarbonyliron complexes using organocadmium reagents has been de~cribed.~' Thus the reaction of the 64 C.U. Pittman jun. B. T.Kim and W. M.Douglas J. Org. Chem 1975 40 590. 65 W. D. Bonds jun. C. H. Brubaker jun E. S. Chandrasekaran C. Gibbons R. H. Grubbs and L. C. Kroll J. Amer. Chem. SOC., 1975,97 2128. E. Bayer and V. Schurig Angew. Chem. Internat. Edn. 1975,14,493. 67 T. J. Pinnavaia and P. K. Welty J. Amer. Chem. Soc. 1975,97 3819. 68 K. E. Hine B. F. G. Johnson and J. Lewis J.C.S. Chem. Comm. 1975,81. 69 B. F. G. Johnson J. Lewis D. J Thompson and B. Heil J.C.S. Dalton 1975,567. 'O A. J. Pearson Tetrahedron Letters 1975 3617. R. Pearce D.J. Thompson,and M. V.Twigg methylallyl-Fe(CO) complex (17) wth Ph2Cd gave the alkene (18)in 60% yield.In all cases the major product was derived by attack at the unsubstituted terminus of 0 (17) (18) The reaction of tropone-Fe(CO) with diazoalkanes has led to a new synthesis of homotropones in good yield (Scheme 2).71 The reaction goes via the stable pyrazoline (19) which is isolated during the reaction. R Fe(COl3 (19) Reagents i R,CN,; ii A; iii Me,NO. Scheme 2 The use of organometallic complexes as protecting groups for olefins and acetylenes has been de~cribed.'~ Olefins co-ordinated to the protecting group [(q-CsHS)Fe(CO),]' are unreactive toward many reagents which attack olefins thus permitting selective transformations at other reactive centres in polyfunctional alkene~.'~~ Moreover the complex selectively co-ordinates to less substituted or strained olefins in a variety of dienes.The free alkene is readily regenerated by the reaction of the complexes with NaI. The CO~(CO)~ group has been used as a protecting group for acetylenes.72b Diarylacetylenes which cannot be acetylated directly undergo nuclear acylation readily as their CO~(CO)~ complexes. Oxidation of the acetylated complex with ceric ammonium nitrate releases the acetylated acetylene in good yield. The regio- and stereo-selective reactions of palladium n-ally1 complexes have been studied.73 In the alkylation of the n-ally1 complex (20) in the presence of 71 M. Franck-Neumann and D. Martha Tetrahedron Letters 1975,1759. 72 (a) K. M. Nicholas J. Amer.Chem. Soc. 1975 9'1 3254; P. F. Boyle and K. M. Nicholas J. Org. Chem. 1975,40,2682; (b)D. Seyferth,M. 0.Nestle and A. T. Wehman J. Amer. Chem. Soc.,1975,97 7417. 73 (a)B. M. Trost and P. E. Strege J. Amer. Chem. Soc. 1975,97,2534; (b)D. N. Jones and S. D. box J.C.S. Chem.Comm. 1975,166. Part (i) The Transition Elements PdC1/2 (20) various ligands it was shown that the nucleophile normally attacks the primary carbon atom but when bulky activating ligands are used the predominant reaction is at the secondary carbon atom.73a Steroidal palladium .rr-allyl complexes are oxidized regiospecifically and with high stereoselectivity to allylic alcohols by 3-chloroperbenzoic acid the hydroxy-group being delivered preferentially to the same diastereotopic face of the .rr-ally1 system as that originally occupied by palladium.736 The use of tricarbonylchromium intermediates in the activation of arenes towards alkylation has been described.74 The readily made arene-Cr(CO) complexes react with a variety of carbanions e.g.LiCH,Cn to give the expected alkylated complexes in high yield.The free alkylbenzene can be liberated in quantitative yield by reaction with iodine or by aerial oxidation. By replacing one of the CO groups in the arene-Cr(CO) complex with other ligands e.g. PPh, the activating power of the Cr(CO) group could be Although a lot of work has been done on metal carbene complexes very little use has been made of them for organic synthesis. A report this year however describes the synthesis of a-methylene- y-butyrolactones uia chromium-carbene complexes of the type (21).75 Although only low to moderate yields were obtained it does indicate the promising nature of these reagents.(21) Generally co-ordinated dinitrogen in metal complexes is inert to chemical attack but this year two reports have appeared on the reaction of co-ordinated dinitrogen in the complex [Mo(N,),(P~,PCH,CH,PP~,),].~~ Alkylation leads to the alkylazo- complexes [MoB~(N~R)(P~~PCH~CH~PP~~)~]~~~ while reaction with trimethylsilyl azide followed by protonation gives the imido-complex [Mo(NH)Cl,-(Ph,PCH,CH2PPh,),].76* Synthesis involving Carbonylferrates.-The application of carbonylferrate species in organic synthesis continues. A number of useful new reactions have been described and earlier work has been reviewed." Two ketone-forming reactions have been reported in which the product contains three additional carbon Ethyl ketones result from treating alkyl halides (or 74 (a)G.Jaouen A. Meyer and G. Simonneaux,J.C.S. Gem. Comm.. 1975,813; (b)M. F. Semmelhack H. T. Hall M. Yoshifuji and G. Clark J. Amer. Chem. Soc.,1975,97 1247. 75 C. P. Casey and W. R. Brunsvoid J. OrgunornefulficChern. 1975,102 175. 76 (a)A. A. Diamantis,J. Chatt G. J. Leigh and G.A. Heath J. OrgunomefuflicChem. 1975,84 C11; (b) J. Chatt and J. R. Dilworth J.C.S. Chem. Comm. 1975,983. 77 (u) M. P. Gmke and R. M. Parlman J. Amer. Chem. Soc. 1975 97 6863; (b) M. Yamashita Y. Watanabe T. Mitsudo and Y. Takegami Tetrahedron Lettern 1975,1867.R. Pearce D.J. Thompson and M. V.Twigg tosylates) with Na,Fe(CO) in the presence of ethylene under ambient conditions [equation (3)].77" This reaction is thought to involve insertion of C2H4 into an C2H4 RX+ Na,Fe(CO) --+RCOCH2CH (3) iron-acyl bond but unfortunately this does not take place with higher olefins. Methyl ketones are obtained from reduction with [HFe(CO),]- of unsaturated pentane-2,4- diones [RCH=C(COMe), products of the reaction of the pentanedione with aldehydes RCHO] under mild conditions.77b The reaction of [RCOCH,Fe(CO),]- with an acid chloride does not produce a 1,3-diketone but the corresponding enol ester.78 By varying the amine reagent ratio selective N-methylation and NN-dimethytation of aliphatic and aromatic amines can be effected by treatment with formaldehyde in the presence of [HFe(C0),]-.79 Substituted aldehydes can be used; for example H0,CCHO gives RNHCH2C02H with [HFe(CO),]- and RNH,.Secondary amines undergo reductive N-alkylation with ketones under an atmos- phere of CO; under these conditions enamines are smoothly reduced to the tertiary amine.80 The reductive amination of glutaraldehyde provides a rapid convenient synthesis of N-alkyl- and N-aryl-piperidines." During an investigation on the facile reduction of nitro- and nitroso-compounds excellent yields of quinoline were obtained from o-nitrocinnamic aldehyde.82 Desulphurizationof thioketones with [HFe(CO),]- gives the parent hydrocarbon; [DFe(CO),]- affords the deuteriated derivative this being a particularly attractive route to geminal dideuterio-species (R'R2C=S -+R'R2CD,).83 Insertion.-Full mechanistic details of insertion reactions into Pt-H bonds in square-planar platinum complexes are not completely resolved.Frequently pro- posed steps are ligand dissociation followed by co-ordination of the incoming molecule (e.g. C,H4) and cis-trans isomerization of intermediates so that the unsaturated ligand becomes cis to the Pt-H bond. Studies on insertion reactions of trans-[(phosphine),PtHL]' have shown that with L = CO the carbonyl group does not leave the co-ordination sphere of the metal during the insertion process with ethylene.84 The complex trans-[(PP)PtH(acetone)J' undergoes ethylene insertion I I PhzP PPh 78 T. Mitsudo Y. Watanabe T.Sasaki H. Nakanishi M. Tamashita and Y. Takegami Tetrahedron Letters 1975,3163. 79 Y. Watanabe T. Mitsudo M. Yamashita S. C. Shim and Y. Takegami ref. 34 abstr. 138. 80 T. Mitsudo Y. Watanabe M. Tanaka S. Atsuta Y. Yamamoto and Y. Takegami Bull. Chem. SOC. Japan 1975,48 1506. 81 Y. Watanabe S. C. Shim T. Mitsudo M. Yamashita and Y. Takegami Chem. Letters 1975,995. 82 Y. Watanabe T. Mitsudo M. Yamashita and Y. Takegami Bull. Chem. SOC.Japan 1975 48 1478. 83 H. Alper J. Org. Chem. 1975,40 2694. 84 H. C. Clark C. R. Jablonski and C. S. Wong Znorg. Chem. 1975,14 1332. Part (i) The Transition Elements 133 into the Pt-H bond even though it is not possible for hydrido and olefin ligands mutually to adopt cis-~rientations.~~ The first fully characterized products from the insertion of an acetylene into an alkynyl carbon-metal bond have been reported;86 earlier work yielded polymeric material [equation (4)].The products isolated are thermally stable and unaffected by dry HCl in ether. Methyl and cr-vinyl complexes undergo similar insertion reactions. [(Et,P),PdCl(C-CPh)] +Me02CC-CC02Me 4 [(Et3P)2PdCIC(C02Me)=C(C02Me)C~CPhl (4) A series of musk compounds were prepared from 12-and 14-membered ring systems obtained from the insertion of MeO,CCECCO,Me into a,w-dodecatrienediylnickel. The metal was removed as [Ni(CO),]."' Schwartz and co-workers8* have found that the readily available [Zr(q- C,H,),HCl] undergoes insertion-isomerization reactions with olefins (alicyclic or cyclic) to form alkylzirconium(1v) complexes.n-Alkyl derivatives are obtained from terminal and internal linear olefins. The subsequent clean high-yield reactions of these complexes with a variety of electrophiles are of potential use in synthesis and have practical advantages over hydroboration and hydroalumination routes. The Zr-R bond is readily cleaved by a variety of electrophiles88" (e.g. H' Br, I, CH,COCl). Since Zr'" is a doelectron system it is possible that these reactions do not proceed by the normally envisioned oxidative addition at the metal but rather by direct attack on the carbon. Alcohols are obtained by reaction with peroxides peracids or even dioxygen though this is a slower process (hours) that involves the formation of [Zr(q -CsHs),C1(OOR)]. Apparently a chiral alkyl complex affords the optically active alcohol on reaction with Bu'OOH but oxygen gives 50% retention and 50% racemization.88b The ready carbonylation (20 p.s.i.room temperature) of [Z~(T~C~H~)~C~R] and subsequent reaction of the acyl complex with electrophiles provides a convenient route to terminal carbonyl derivatives from internal olefins.88c Reactions are summarized in Scheme 3. [Zr(q-C,H,),HCI] also reacts with dialk- ylacetylene to form a mixture of cis-vinylic complexes. After standing for several hours at room temperature an equilibrium mixture containing a high proportion of the sterically favoured complex is obtained. This is the basis of a potential pfepara- tive method for specific tri-substituted olefins since treatment of the equilibrium mixture with N-bromosuccinimide produces a good yield of vinyl bromides with the same stereochemistry and isomer ratio as in the precursor Oxidative Addition.-Halogen-exchange Reactions.Co-ordinatively unsaturated transition-metal complexes catalyse halogen-exchange reactions of alkyl halides.89 The proposed mechanism involved oxidative addition of the organic halide to the metal complex followed by substitution of co-ordinated halide and reductive 85 G. Bracher P. S. Pregosin and L. M. Venanzi Angew. Chem. Internat. Edn. 1975,14,563. 86 Y. Tohda K. Sonogashira and N. Hagihara J.C.S. Chem. Comm. 1975 54. 87 R. Baker P. Bevan and R. C. Cookson J.C.S. Chem. Comm. 1975,752. 88 (a)D. W. Hart and J. Schwartz,J. Amer. Chem. Soc.,1974,% 81 15; (b)T.F. Blackburn J. A. Labinger and J. Schwartz Tetrahedron Letters 1975,3041; (c) C.A. Bertelo and J. Schwartz J. Amer. Chem.Sac. 1975,97 228; (d) D. W:Hart T. F. Blackburn and J. Schwartz ibid. p. 679. Hq J. E. Lyons J.C.S. Gem. Comm. 1975,418. R.Pearce D.J. Thompson and M. V.Twigg ,R COR \ RCOX RX (XU = HCI MeOH-Br, or HONa-H20,) (XU = HCl Br, Cl, C121Ph MeCOCI or H00Bu‘) Reagents i olefin; ii CO; iii XY Scheme 3 elimination of the halogen-exchanged product. However a more recent report” shows that the true catalyst is halide ion formed by quaternization of phosphines derived from the complex. Indeed quaternary ammonium and phosphonium halide salts catalyse exchange in the absence of metal complex. The displacement of iodide from aryl iodides by CN- is strongly catalysed by [Pd(PPh3)4] and in contrast to the alkyl halogen-exchange reactions most probably involves oxidative/reductive elimination Alkyl halides including fluorides also undergo reaction with MoCl in CH2C12 at room temperature to give the corresponding The mechanism of this interesting process is not clear and strangely it is not effective for n-bromoalkanes.Formation of Carbon -Carbon Bonds. Nickel(o) complexes [e.g. Ni(CO),] are re- agents for the production of cyclic systems from a,@-dihalides. They are particularly useful for the production of large-ring Several preparations of biaryls from iodo-aryls have been reported. Ring closure of 1,n -bis-(iodoary1)alkyls to give ortho-bridged biaryls of pharmacological interest can require forcing conditions with the classic copper catalysts.However [Ni(PPh,),] has been found to be a particularly effective catalyst for this A convenient in situ method of generating [Ni(PPh,),] from [NiCl,(PPh,),] zinc and added PPh in DMF has been described.946 This is a particularly useful reagent for coupling aryl vinyl and allylic halides. Biaryls are formed from idobenzenes and catalytic quantities of Pd(OAc) in NEf,.’,‘ The mechanism of this reaction is incompletely understood but it appears to involve the interaction of two arylpalladium species. 90 D. Foster J.C.S. Chem. Cbmm. 1975 917. 91 A. Sekiya and N. Ishikawa Chem. Letters 1975 277. 92 J. San Filippo A. F. Sowinski and L. J. Romano J. Org. Chem. 1975,M.3295. 93 S. Takahashi Y. Suzuki and N. Hagihara Chem.Letters 1974; 1363; E. J. Corey and P. Helquist Tetrahedron Letters 1975,4091. 94 (a)M. F. Semmelhack and L. S. Ryono J. Amer. Chem. Soc. 1975,97 3873; (b) A. S. Kende L. S. Liebeskind and D. M Braitsch Tetrahedron Letters 1975,3375; (c)F. R. S. Clark,R. 0.C. Norman and C. B. Thomas J.C.S. PerkinI 1975 121. Part (i) The Transition Elements Acetylenic hydrocarbons can be substituted by aryl iodides bromoalkenes or bromopyridines under very mild conditions in the presence of [PdCl,(PPh,),] and CuI in Et2NH.95 The active species is thought to be [Pd(PPh,),]. Oxidative addition of organic halide is followed by addition of acetylene with CuI promoting loss of HX in the basic solvent. Subsequent reductive elimination of the monosubstituted acetylene regenerates the active species.K. Sonogashira Y. Tohda and N. Hagihara Tetrahedron Letters 1975,4467.

ISSN:0069-3030    

DOI:10.1039/OC9757200119

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

6 Organometallic Chemistry Part (ii) Main-group Elements By K. SMITH Department of Chemistry University College of Swansea Swansea SA2 8PP 1 Introduction As in the previous Annual Report on main-group element organometallic com- pounds,' B Si and As will be included but not P Se and Te. Perusal of the relevant 1975 literature prompts a feeling of dkjk ufi with the appearance of a number of papers whose titles recall some of the highlights from the literature of the past decade or so. The classic example is a paper by Seebach and Corey on the generation and synthetic applications of 2-lithio- 1,3-dithian (Scheme 1).2 It seems incredible that these reactions3 had not previously been reported in full detail.3 The importance of the compounds derives of course from their role as acyl carbanion equivalents (the carbonyl group is subsequently generated by mercury- catalysed hydrolysis of the dithian moiety).Scheme 1 Hardly less well-known are the hydroboration reactions of 1,1,2-trimethylpropylborane (thexylborane Scheme 2).4 New and more detailed investi-gations reveal that careful attention to experimental procedure can maximize yields of the synthetically valuable organoborane prod~cts.~ Full details of hydroborations using catecholborane have also appeared.6 1 K.Smith Ann. reports (B),1974,71 195. D. Seebach and E. J. Corey J. Org. Chem. 1975,40 231. 3 E. J. Grey and D. Seebach Angew. Chem. Internat. Edn. 1965,4,1075 1077. G.Zweifel and H. C. Brown J. Amer. Chem. Soc. 1963,85 2066. 5 H. C. Brown E.Negishi and J.-J. Katz J. Amer. Chem. Soc. 1975,97,2791; H. C. Brown J.-J. Katz C. F. Lane and E. Negishi ibid.,p. 2799. H. C. Brown and S. K. Gupta J. Amer. Chem. SOC.,1975,97,5249. 136 Part (ii) Main -group Elements Reagents i alkene A -20 "C;ii alkene B. Scheme 2 The initial communications on the synthetically important reactions of trialkyl- cyanoborates with electrophiles (e.g.Scheme 3)7 signalled a major shift in research into applications of organoboranes as reagents. Whereas in 1970 reports of reactions RB-CR2 R,B -1 Na+[R,BCN]-A 1 ,>N 0-c R,COH ' R,C=O /B-CR3 Reagents i NaCN; ii (CF,CO),O 1 mole; iii excess (CF,CO),O; iv H,O,-OH-. Scheme 3 of four-co-ordinate ('ate'-complex) organoboron compounds with electrophiles were rare chemical curiosities of little synthetic value today such reactions provide most of the new applications of organoboranes and are intensively studied (see p.143). Included with details of the original cyanoborate work are studies of solvent effects and of reactions with other electrophiles and methods for the preparation of highly hindered tertiary alcohols.' A clearly presented review of the present deliberations about the vexed problem of which factors control the stereochemistry of addition of organometallic reagents to cyclic ketones makes it clear that the 'product development' part of the 'steric approach and product development control' rationalization must finally be put to rest.' Where steric interactions are substantial hindrance to approach is clearly a major factor in determining product distributions but it is of questionable value in the light of our present understanding to discuss product distributions of ca.60:40 (i.e.transition-state energies differing by ca. 0.25 kcal mol-' at 25 "C or around one tenth of the barrier to rotation about the C-C bond in ethane); such small differences may result from factors (the phase of the moon?) quite beyond our ken. Organometallic compounds containing element-carbon pT-pT bonds for elements such as As Sb Bi Si Ge and B have been reviewed." It may be surprising to those not familiar with this area of chemistry to discover the number of such compounds which have been isolated. Compounds of Si continue to defy isolation though they are abundantly postulated as transient intermediates (see p.146). 'A. Pelter M. G. Hutchings and K. Smith Chem. Comm. 1970 1529; ibid. 1971 1048. * A. Pelter K. Smith M. G. Hutchings and K. Rowe J.C.S. Perkin I 1975 129 138. E. C. Ashby and J. T. Laemmle Chem. Rev. 1975,75,521. lo P. Jutzi Angew. Chem. Zntemat. Edn. 1975,14 232. 138 K. Smith A new general method for the synthesis of trifluoromethyl organometallic com- pounds involves the reaction of trifluoromethyl radicals generated in the glow discharge of GF6,with metal halides." Yields are good [e.g. (CF,),Hg 95% from HgI; (CF,),Sn 90%from SnI,; (CF,),Ge 64% from GeBr,). 2 Group I Lithium.-There has been much interest in 'masked' lithium-containing synthons. For example (l) formed by reaction of (2) with lithium bis(prop-2-yl)amide behaves as a masked version of LiCOCH2CH0.'2 On the other hand compounds of type (3) Li Li + CH,SC=C=CHOMe MeSCECCH,OMe -VoMe behave as masked Wittig reagents corresponding to (4)in their reactions with carbonyl compo~nds,'~ whereas (5) is a masked 3-carboxycarbanion.l4 Compound (5) is of course similar to a vinylogous protected cyanohydrin anion. Cyanohydrin anions protected by an 0-SiMe group have been shown to be comparable with those protected by an 0-methoxymethyl group." The latter compounds as well as other acyl carbanion equivalents can be used in the synthesis of small-ring ketones by reaction with a,o-dihalogenoalkanes.'6 Dianions of a -methylthio- or a-phenylthio-acetic acids also behave as acyl carbanion equi~alents,~~ whilst the dianion of a-trimethylsilylacetic acid is a masked analogue of the Wittig reagent R,P=CHCO,H in its reactions with carbonyl compounds.'8 In contrast to 2-lithio- 1,3-dithian bulky sulphur-stabilized carbanions such as (PhS),CLi (LiC0,Me equivalent) or (6; M =Si,Sn) useful for further modifications after introduction of a masked acyl group undergo conjugate addition to cyclohex-2-enone." Sulphur-stabilized carbanions of a different type have been employed in 11 R.J. Lagow L. L. Gerchman R. A. Jacob and J. A. Morrison J. Amer. Chem. Soc. 1975,97 518. 12 R. M. Carlson R. W. Jones and A. S. Hatcher Tetrahedron Letters 1975 1741. 13 E. J. Corey and P. Ulrich Tetrahedron Letters 1975 3685. l4 H.Ahlbrecht and C. Vonderheid Synthesis 1975 512. S. Hiinig and G. Wehner Synthesis 1975 180. l6 G. Stork J. C. Depezay and J. d'Angelo Tetrahedron Letters 1975,389; K. Ogura M. Yamashita S. Furukawa M. Suzuki and G. Tsuchihashi ibid. p. 2767. B. M. Trost and Y. Tamaru Tetrahedron Letters 1975 3797; P. A. Grieco and C.-L. J. Wang J.C.S. Chem.Comm. 1975,714. l8 P. A. Grieco C.-L. J. Wang and S. D. Burke J.C.S. Chew. Comm. 1975,537. l9 A.-R. B. Manas and R. A. J. Smith J.C.S. Chem. Comm. 1975,216; D. Seebach and R. Biirstinghaus Angew. Chem. Internat. Edn. 1975,14,57. Part (ii) Main -group Elements a versatile synthesis of thiirans which are of course readily converted into alkenes by sulphur extrusion (Scheme 4 X =0,S).*' -OLi 0 + LiCH2SCf] 11 -78°C I /c\ N N temp.S \ /C=CH 4 Ph,P \ 1\ C-CH + LiOC / N Scheme 4 1-Lithio-1,l-dibromoalkanesdecompose above ca. -70 "C but their formation and reactions with electrophiles occur in high yield below ca. -90 OC.*l As a general method for the introduction of ortho-substituents into a benzene ring bearing an oxygen function lithiation of methoxymethoxy-compounds is superior to lithiation of methoxy-compounds on three counts (i) faster lithiation (ii) greater positional selectivity (with BuZi) and (iii) easier removal of the protecting group (e.g. Scheme 9.'' ortho-Substituted benzoic acid derivatives may be obtained by selective ortho-lithiation of 2-aryloxazolines reaction with an electrophile and hydrolysis of the oxaz01ine.~~ OCH,OMe OCH,OMe i ii iii w DO," __* flC0,H / / / /o 95 % this isomer Reagents i Bu'Li; ii CO,; iii H,O+.Scheme 5 Amine-free monolithioacetylene may be prepared and used at low temperature in THF though it disproportionates on ~arming.'~ It is more reactive towards nu- cleophiles than the tmeda complex and adds to ketones to give essentially quantita- tive yields of alkynylmethanols. Consecutive lithiation-alkylations of allene lead to mono- di or tri-substituted allenes also in good yields.25 Reactions of organolithium compounds with water are usually thought to be extremely fast and D,O quenching is often quoted as a method of determining equilibrium proportions of interconverting organolithiums so it is particularly 20 A.I. Meyers and M. E. Ford Tetrahedron Letters 1975 2861; C. R. Johnson A. Nakanishi N. Nakanishi and K. Tanaka Tetrahedron Letters 1975 2865. 21 J. Villieras C. Bacquet and J.-F. Normant Bull. SOC. chim. France 1975 1797. 22 H. Christensen Synthetic Comm. 1975,5,65; R.C. Ronald Tetrahedron Letters 1975 3973. 23 H. W. Gschwend and A. Hamdan J. Org. am.,1975,40,2008;A. I. Meyers and E. D. Mihelich ibid. p. 3158. 24 M. M. Midland J. Org. Chem. 1975,40 2250. 25 G. Linstrumelle and D. Michelot J.C.S. Chem. Comm. 1975 561. 140 K. Smith interesting to read two reports relying upon the slowness of the reactions between organolithium compounds and water for their interpretations. Thus addition of Bu"Li to a mixture of a bromoarene and tritiated water in Et20 at -70°C is a convenient method for preparation of tritiated arenes which implies that Bu"Li reacts with the bromoarene faster than it reacts with water.26 Reaction (1)gives good yields of ketones after extended periods of reflux but if prematurely quenched with water much less of the ketone and more of the tertiary alcohol are produced implying that the excess R2Li reacts with liberated ketone faster than it reacts with Shall we await the day when reactions of organolithiums are routinely performed in aqueous solution? R'CH2C02Li +R2Li-+ R'CH2C(OLi)2R2 R'CH2COR2 (1) On the whole 1975 has been a disappointing year for mechanistic organolithium studies though a few interesting points have emerged.The reaction of (7) with MeLi to give (8) occurs with retention of configuration and without loss of deuterium so cycloalkyne or carbene intermediates are ruled out though the mechanism of the direct coupling remains unclear.28 cis-Enones of type (9; R =Bu',Ph) rapidly equilibrate with the trans-isomers via their anion radicals so they can be used to test for anion radical mechanisms in reactions of a@-unsaturated ketones with organometallic Methyl-lithium and dimethylmagnesium react with- out causing equilibration but anion radicals are clearly implicated in reactions of Me2CuLi.Sodium Potassium Rubidium and Caesium.-Benzylcaesium compounds can be prepared by direct metallation of the appropriate hydrocarbons with Cs metal in THF.30 3Group I1 Magnesium.-Transition-metal catalysis of reactions of organomagnesium com- pounds presumably involving intermediate transition-metal organometallics (though these have not been identified) can lead to some useful synthetic proce- dures.Thus the Ni-complex-catalysed reaction of 1,5-dichlorobenzenes or 2,6- dichloropyridines with XMg(CH2) MgX gives metacyclophanes in a single step albeit in yields ranging from only ca. O-lO% to ca. 30% as n is varied from 6 to ca. 12.31 Unsymmetrical ethers are obtained in high yields by reaction of alkyl 2,4-dichlorophenyl acetals with Grignard reagents under TiC1 catalysis (e.g. Scheme z6 R. Taylor Tetrahedron Letters 1975,435. 27 R. Levine M. J. Karten and W. M. Kadunce J. Org. Chem. 1975,40 1770. 28 P. G. Gassman and T. J. Atkins Tetrahedron Letters 1975 3035.29 H. 0.House and P. D. Weeks J. Amer. Chem. SOC.,1975,97 2770. 3O N. Collignon J. Organometallic Chem. 1975,% 139. 31 K. Tamao S. Kodama T. Nakatsuka Y. Kiso and M. Kumada J. Amer. Chem. SOC.,1975,97,4405. Part (ii) Main -group Elements 141 6),32whereas the regioselective insertion of isoprene into allyl-Mg bonds again Ti-catalysed is useful in the synthesis of ter~enoids.~~ TiCI, THF + PhCH,CH,MgBr . 98 7"yield CH,CH2 Ph Scheme 6 The initial product of the reaction of ethyl LY -(t-butylsulphiny1)acetate with EtMgBr reacts with carbonyl compounds to give adducts which eliminate the elements of t-butylsulphinic acid on treatment with sulphuryl ~hloride.~ The overall result is a high-yield synthesis of ap-unsaturated esters and the reagent could be considered as a masked Wittig reagent R,P=CHCO,Et.A Mg-acetylene compound of approximate composition Mg(C-CH) ,,,formed by reaction of Mg or MgSO with Na in liquid NH3 is reported to resemble LiC=CH in its reactions but to be much cheaper.35 The addition of Grignard reagents RMgX to Me,SiNCO followed by hydrolysis provides a convenient and direct method for preparation of RCONH2,which is applicable even for cases where R is an alkynyl The reaction of NN-dimethylhydrazone methiodides with Grig- nard reagents gives a more efficient synthesis of aziridines than the previously reported reaction involving oximes and is applicable to vinyl-substituted aziridines (Scheme 7) in yields around 50-75%.37 r 1 R3CCHR'R2 R3 NII \+ NMe I- H2C=CH w::N H Reagents i H,C=CHMgBr; ii H,O +.Scheme 7 Competition between 1,2- and 1,4-addition reactions of Grignard reagents with arP-unsaturated ketones is well known but a major product from the reaction of ButMgCl with ethyl cinnamate is ethyl 2-t-butyl-3-phenylpropanoate,apparently a product of €,3-additi0n.~~ Rearrangement of a cyclopropanone hemiketal inter- mediate is suggested as the likely route to this unusual product. Reactions of organomagnesium reagents with thiocarbonyl compounds have been reviewed.39 In recent years the mechanism of formation of Grignard reagents from organic halides and Mg has been shown to involve initial electron transfer from Mg to RX followed by loss of halide to give a radical R. However it was uncertain whether the 32 H.Ishikawa and T. Mukaiyama Chem. Letters 1975 305. 33 S. Akutagawa and S. Otsuka J. Amer. Gem. Soc.,1975,97 6870. 34 J. Nokami N. Kunieda and M. Kinoshita Tetruhedron Letters 1975 2179. M J. N. Gardner Canad. J. Chem. 1975,53 2157. 36 K. A. Parker and E. G. Gibbons Tetrahedron Letters 1975,981. 37 R. Chaabouni and A. Laurent Synthesis 1975,464. 38 I. Crossland Acra Chem. Scund. (B).,1975 29 468. 39 D. Paquer Bull. SOC. chim. France 1975 1439. 142 K. Smith Grignard reagent was formed directly from R and 'MgX (path a Scheme 8) or from R2Mg and MgX via the Schlenk equilibrium (path b). In the cases R =But or C,F the Schlenk equilibria are established relatively slowly and n.m.r. methdds can be used to observe the initial products; it is clear that in these cases at least RMgX is the primary product not R2Mg4* RX +Mg ARX' +Mg' Ml3s 1 RMg; t-R' +'MgX combine path b\ Ipath a 1+J 1 R2Mg +MgX2 +RMgX subscript s =surface bound Scheme 8 Zinc,Cadmium and Mercury.-Activated Zn prepared by refluxing ZnC1 with K metal in THF can be used for Reformatsky reactions in Et,O at low temperatures with excellent The reaction of Et,Zn with CHBr in the presence of air (radical initiator) provides a bromocarbenoid of Zn which in the presence of alkenes produces monobromocyclopropanes in good yields.42 Previously such compounds have usually been obtained by partial reduction of gem-dibromocyclopropanes.Homogeneous catalysts overcome the problems previously encountered in cataly- tic hydrogenolysis of organomercury compounds when heterogeneous catalysts were employed.Furthermore carbonylation of the intermediate in the presence of MeOH gives good yields of carboxyl derivatives [(Ph,P),RhCl ~atalyst].~ Carbonylation of vinylmercurials is easier occurring at -20 "C with a PdC1,-LiCI catalyst and is stereospecific(e.g.Scheme 9).44 R' H R' H \/ i\/ c=c -+ c=c /\ /\ H HgX H CO,RZ Reagent i CO(1 atm) R20H,PdC1,-LiCl -20 "C. Scheme 9 Trihalogenomethylmercury compounds are well known as dihalogenocarbene precursors but extended periods at elevated temperatures are generally necessary for their complete decomposition. Iododihalogenomethylmercurycompounds (10; X =Cl Br; Y =C1 Br) however generate the corresponding dihalogenocarbenes 40 H.W. H. J. Bodewitz C. Blomberg and F. Bickelhaupt Tetrahedron Letters 1975 2003. 41 R. D. Rieke and S. J. Uhm Synthesis 1975,452. 42 S. Miyano Y. Matsumoto and H. Hashimoto J.C.S. Chem. Comm. 1975,364. 43 W. C. Baird and J. H. Surridge J. Org. Chem. 1975,40 1364. 44 R. C. Larock J. Org. Chem. 1975,40,3237. Part (ii) Main -group Elements 143 slowly at 20°C or within minutes at 80°C.45By analogy with ketone analogues HgC1,-catalysed hydrolysis of compounds of type (11) to aldehydes (12) had generally been considered as a formality with synthesis of (11)being thought of as synonymous with synthesis of (12) but it has been shown that the usual conditions are not successful in these cases.46 Successfu! hydrolysis is achieved by prior addition of either HCl or PhSH.SPh \/ PhHgCXYI c=c ‘CHCHO / ’ ‘H (10) (11) (12) Use of the system Hg(OAc),-Bu‘O,H for peroxymercuration of alkenes suffers from competitive acetoxymercuration resulting in mixtures which are difficult to separate but use of Hg(OCOCF,) (CF,CO; is less nucleophilic than CH,CO,) overcomes this difficulty and high yields of 2-peroxyalkylmercurials or their bromodemercuration products may be thus ~btained.~’ The displacement of alkali metals from their organcmetallic compounds by Hg metal4’ and the role of Hg‘ intermediates in reactions of related types4’ have been reviewed. 4 Group I11 Boron.-An excellent book on synthetic reactions of organoboranes which has appeared is especially valuable for the non-specialist ; it contains many detailed experimental procedures and a whole chapter is devoted to techniques useful for handling organ~boranes.~~ Reactions of allylboranes with unsaturated com-pound~,~~ arid applications of methane-tetra- and -tri-boronic esters5 and of organoborates and organoboranesS3 as synthetic reagents have been reviewed.Of the wealth of new synthetically useful reactions of organoboranes the majority involve the reactions of four-co-ordinate (‘ate’-complex) boron compounds with electrophiles. Trialkylalkynylborates (1 3) continue to be involved in the lion’s share and further studies of their behaviour [reaction (2)] have been numerous. Protona- tion of (13; R2=H) can be controlled to give either a single migration (leading to ‘Markovnikov’ vinylboranes) or two rnigration~.’~ Functionalized electrophiles react with (13)to give functionalized products.Thus methyleneimmonium salts give cis-trans mixtures of (14; E =CH2NMe2),55 whereas iodoacetonitrile and propargyl bromide undergo a stereospecific reaction to give (14; E =CH,CN or CH,CrCH) 45 D. Seyferth and C. K. Haas J. Org. Chem. 1975,40 1620. 46 A. J. Mura G. Majetich P. A. Grieco and T. Cohen Tetrahedron Lerters 1975 4437. 47 A. J. Bloodworth and I. M. Griffin J.C.S. Perkin I 1975 195 695. 48 A. A. Morton Chem. Reo. 1975,75767. 49 0.A. Reutov and K. P. Butin J. Orgunometallic Chem. 1975,99 171. H. C. Brown ‘Organic Syntheses via Boranes’ Wiley-Interscience New York 1975. s1 B. M.Mikhailov Pure Appl. Chem. 1974,39 505. 52 D. S. Matteson Synthesis 1975 147. 53 E. Negishi J. Chem. Educ. 1975,52 159. 54 H. C. Brown A. B. Levy and M. M. Midland J. Amer. Chem.Soc. 1975,97,5017;M. M. Midland and H. C. Brown J. Org. Chem. 1975,40,2845. 55 P. Binger and R. Koster Chem. Ber. 1975,108 395. 144 K. Smith with E and R1 cis (not trans as wrongly reported for the reaction with a-bromocarbonyl compounds) .56 Li+[R:BC-CR*]-+ EX +RiBCR'=C R2E +further? (2) (13) (14) A reaction of type (2) between (13; R1=Pr" R2=SiMe3) and TsO(CH,),CZX(CH,),OTHP (Ts = tosyl THP = tetrahydropyranyl) is a key step in a new synthesis of propylure the sex attractant of the pink bollworm A modification of reaction (2) involves the reaction of di-sec-alkyldialkynylborates with iodine; this provides a convenient synthesis of conjugated diynes (Scheme R',BX + 2LiCGCR2 -+ Li+[R1 2B(CrCR2),]- 1 R~C~C-C~CR~ (ca.90%) R' = 1,2-dimethylpropyl cyclohexyl ; X = C1 Br Scheme 10 Reactions of trialkylvinylborates with aldehydes provide a direct route to 1,3-diols though yields are whilst trialkyl-isopropenylboratesreact with iodine to give 2-alkylpropenes in good yields.60 Lithium tetra-alkylborates and trialkylarylborates react with acyl halides to give ketones by intermolecular transfer of an alkyl or aryl group.61 Since ketones rather than tertiary alcohols are obtained the trialkylborane may be said to 'moderate' the reactions of the organolithium compounds used to form the organoborates.The major products in the reactions of magnesium trialkylarylborates with acyl halides are ortho-alkylaryl ketones formed by attack of the acyl group on the aromatic ring and intrumoleculur transfer of an alkyl group.62 The reasons for the differences are not clear but may have something to do with the relative solubilities (Li > Mg). Borate complexes may be key intermediates in the synthesis of (E,E)-dienes by MeCu-induced coupling of dialkenylchloroboranes,63the production of 'mixed' trialkylmethanols from lithioaldimines and dialkylchloroboranes,64 the formation of alkyl phenyl ketones from trialkylboranes and Q -azido~tyrene,~~ and the homologa- tion of organoboranes with sulphur-stabilized anions (Scheme 1 1).66 Whereas Scheme 11 leads to a particular type of 'mixed' trialkylborane a two-step process [reaction (3)] involving bromination of dialkyl(methy1thio)boranesand 56 A.Pelter K. J. Gould and C. R. Harrison Tetrahedron Letters 1975 3327. 57 K. Utimoto M. Kitai M. Naruse and H. Nozaki Tetrahedron Letters 1975,4233. 58 A. Pelter K. Smith and M. Tabata J.C.S. Chem. Comm.,1975 857. 5q K. Utimoto K. Uchida and H. Nozaki Chem. Letters 1974 1493. 6o N. Miyaura H. Tagami M. Itoh and A. Suzuki Chem. Letters 1974 1411. 61 E. Negishi K.-W. Chiu andT. Yoshida J. Org. Chem. 1975,40,1676;E. Negishi A. Abramovitch and R. E. Merrill J.C.S. Chem. Comm. 1975 138. 62 K. Utimoto K. Okada and H. Nozaki Tetrahedron Letters 1975,4239. 63 Y.Yamamoto H. Yatagai and I. Moritani J. Amer. Chem. SOC.,1975,97 5606.64 Y. Yamamoto K. Kondo and I. Moritani J. Org. Chem. 1975,40 3644. 65 A. Suzuki M. Tabata and M. Ueda Tetrahedron Letters 1975 2195. 66 E. Negishi T. Yoshida A. Silveira and B. L. Chiou J. Org. Chem. 1975,40,814. Part (ii) Main-group Elements 145 R',B +LiCH2SR2 Li+[R',BCH,SR']-'3 R',BCH2R' +MeSR2 +LiI Scheme 11 reduction-hydroboration of the product provides a more general approach to these A general synthesis of cis-alkenyldialkylboraneshas also beenyeported.68 NaH RiPiSMe 3MeSSMe +R;BBr -R:BR2 (3) alkeneZ A different kind of borate complex (15) a complex of borabenzene is obtained by treatment of the Co derivative (16) with KCN.69 Another type sodium diphenyl- borate(1) (17) has been postulated as an intermediate in the formation of yet a further type (18) formed on photolysis of NaBPh in the presence of PhCZCPh.70 Aliphatic analogues of (17) have previously been postulated in the reactions of alkali metals with dibutylchloroborane but it has been shown that subsequent reaction with benzoyl chloride does not give the previously claimed boryl ketones.'l The actual product is a mixture of Bu2BOCH2Ph and PhC02CH2Ph [reaction (4)] and it seems very unlikely that aliphatic analogues of (17) are the stable intermediates in these reactions.Ph Ph co K+ [Q-R] -<F>B Ph2B-Na+ B-Na' -R /\ Ph Ph PhCOCl Bu,"BCI %K [Bu,"B-M'] -BuqBOCH,Ph +PhC02CH2Ph (4) alloy Reactions of alkeneboronic acids with Br in the presence of MeO-MeOH provide simple one-stage syntheses of a-brom~acetals,~~ whilst reactions of aldehydes with bis(ethylenedioxybory1)methyl-lithium followed by oxidation give the homologated aldehydes in high yields.73 An earlier report that mercurideboro- nation at C-2 of the norbornyl system involved retention of configuration is not general inversion occurring to 3 95% in an open-chain example.74 Aluminium Gallium Indium and Thallium.-A convenient method of attaching a t-alkyl group to an alkyne is provided by the reaction of a t-alkyl halide with a trialk~nylalane.~~ Only one of the three alkynyl residues is utilized but the other two 67 A.Pelter K. Rowe D. N. Sharrocks and K. Smith J.C.S. Chem. Comm. 1975,53 1 ;A. Pelter K. Rowe and K. Smith ibid. p. 532. 68 E. Negishi R. M. Williams G. Lew and T.Yoshida J. Organometallic Chem. 1975,92 C4. 69 G. E. Herberich and H. J. Becker Angew. Chem. Internat. Edn. 1975,14 184. 'O 3. J. Eisch K. Tamao and R. J. Wilcsek J. Amer. Chem. Sac. 1975,97 895. 71 K. Smith and K. Swaminathan J.C.S. Chem. Comm. 1975 719. 72 T. Hamaoka and H. C. Brown J. Org. Chem. 1975,40 1189. 73 D. S. Matteson R. J. Moody and P. K. Jesthi J. Amer. Chem. SOC.,1975 97 5608. 74 M. Gielen and R. Fosty Bull. SOC.chim. belges 1974,83 333. 75 E. Negishi and S. Baba J. Amer. Chem. SOC. 1975,97,7385. 146 K. Smith cm be recovered as alkyne. The lower basicity of the aluminium reagents compared with e.g. lithium compounds may be responsible for the success of this method and for the successful synthesis of ketones by Ni(acac),-catalysed reactions of Me,Al with nitriles even when the latter contain highly acidic hydrogens (e.g.PhCH,CN).76 Nickel compounds also catalyse conjugate addition reactions of Me& to aP-unsaturated or cyclopropyl ketone^.'^ Whereas previous studies showed little reaction between tetra-alkylaluminates and oxiransjn ether solvents the reactions occur readily in hydrocarbons especially under Ni ~atalysis.~’ High yields of alcohols are obtained and the regiochemistry is opposite to that obtained in the corresponding reactions of trialkylalanes. Scrambling of stereochemistry in the addition product of an optically active organoaluminium compound and an aromatic ketone indicates a non-synchronous transfer whereas the same aluminium compound abstracts a deuterium atom from [2&]acetone with complete retention of ~tereochemistry.~’ In favourable cases nitrodethalliation of arylthalliumbis(trifluoroacetate)swith NO in CF,CO,H gives high yields of nitroarenes.80 On the other hand acetyl nitrate causes ring nitration without dethalliation and subsequent iododethalliation provides a useful synthesis of nitroaryl iodides.81 5 Group IV Silicon.-Interest in transient silicon analogues of unsaturated compounds continues to gather momentum and a fine review of the subject has Unfortunately the topic is getting out of hand in the sense that many papers whose specific purpose is to ‘show’ the presence of such intermediates contain little or no evidence to support the claims the inferences arising from ‘reasonable’ mechanistic rationaliza- tions for the formation of identified products.A timely reminder of the dangers of such overassumption is provided by a reinvestigation of the reactions of (19) generated in the presence of alcohols. The production of (20) in MeOH had previously been attributed to the intermediacy of a sila-alkene (path a Scheme 12) but in other alcohols the product is not (21) but (22) now rationalized according to pathway b.’ Despite the above reservations it is interesting to record the first claims for Si=S speciess4 and for the parent sila-ethene and silanone ~ystems.’~ Some effort including the use of labelling techniques was used to try to eliminate non-sila-alkene 76 L. Bagnell E. A. Jeffery A. Meisters and T. Mole Austral.J. Chem. 1974 27 2577. 77 L. Bagnell E. A. Jeffery A. Meisters and T. Mole Austral. J. Chem. 1975 28 801; L. Bagnell A. Meisters and T. Mole ibid. pp. 817 821. 78 G. Boireau D. Abenhaim C. Bernadon E. Henry-Basch and B. Sabourault Tetrahedron Letters 1975 2521. 79 J. J. Eisch and K. C. Fichter J. Amer. Chem. SOC.,1975,97 4772. B. Davis and C. B. Thomas J.C,S. Perkin I 1975,65. 81 E. C. Taylor H. W. Altland and A. McKillop J. Org. Chem. 1975,40,3441. 82 L. E. Gusel’nikov N. S. Nametkin and V. M. Vdovin Accounts Chem. Res. 1975,8 18. W. Ando A. Sekiguchi T. Migita S. Kammula M. Green and M. Jones J. Amer. Chem.SOC.,1975,97 3818. 84 L. H. Sommer and J. McLick J. OrganometullicChem.,1975,101 171. 85 C. M. Golino R. D. Bush and L. H. Sommer J. Amer.Chem. SOC. 1975,97,7371. 147 Part (ii) Main -group Elements Me,SiC(N,)CO,Me Me,Si=CMeCO,Me J$ Me,SiCHMeCO,Me I OMe pa/ (20) ;I \ Me SiCCO Me Me,SiCHMeCO,Me I OR ... path b \ (21) Me I Me,SiC=C=O 3Me,SiCHMeCO,R I I OR Reagents i A; ii MeOH; iii ROH. Scheme 12 pathways in the proGaction of disilacyclobutanes on thermal decomposition of Me3SiCHN2.86 Labelling also shows that production of (23)by rearrangement of the carbene (24) does not involve the previously suggested siliran intermediate but rather it proceeds by a well-documented set of phenylcarbene rearrangement^.^' The isolable siliran (25) provides a convenient method for low-temperature (60-80 "C) thermal generation of :SiMe, but is itself very reactive with many types of compounds.88 After 25 years of unsuccessful attempts to prepare tri-t-butylsilane derivatives such compounds have been independently reported by three laboratorie~.~~ The most successful approach involves the reaction of Bu'Li with fluorosilane~.~~~*~ Organic 1,2-disilane derivatives undergo Pd-complex-catalysed reactions with aryl halides giving the corresponding arylsilanes and halogeno~ilanes,~~ whilst cyclic examples add across CrC bonds to give cyclic cis-disilylethenes." Acyclic cis-disilylethenes are obtained by a novel dehydrogenative double silylation of alkynes by hydrosilanes catalysed by a Ni complex.92 Reductive silylation of anisole using R.L. Kreeger and H. Shechter Tetrahedron Lefrers 1975,2061. 87 T.J. Barton J. A. Kilgour R. R. Gallucci A. J. Rothschild J. Slutsky A. D. Wolf and M. Jones J. Amer. Chem. SOC. 1975,97,657. 88 D. Seyferth and D. C. Annarelli J. Amer. Chem. SOC.,1975,97,7162. 89 (a)M. P. Doyle and C. T. West J. Amer. Chem. Soc. 1975,97,3777;(b)M. Weidenbruch and W. Peter Angew. Chem. Internat. Edn. 1975,14642;(c)E. M. Dexheimer and L. Spialter Tetrahedron Letters 1975 1771; (d) E. M. Dexheimer L. Spialter and L. D. Smithson J. Organometallic Chem. 1975 102 2 1. 90 H. Matsumoto S. Nagashima K. Yoshihiro and Y. Nagai J. Organometallic Chem. 1975,85 C1. 91 H. Sakurai,Y.Kamiyama and Y. Nakadaira J. Amer. Chem. Suc. 1975,97,931. 92 K. Tamao N. Miyake Y. Kiso and M. Kumada J. Amer. Chem. SOC.,1975,97,5603. 148 K. Smith the system Me,SiCl-Li-THF under mild conditions gives (26) in high yield.Hydrolysis then gives (27).93 SiMe3 OoMeoo SiMe Si SiMe3 8 NMe2 (28) (29) Silicenium ions have proved elusive but now a particularly favourable example (28) has been demonstrated in the reaction of (29; R=H) with Ph3C+ at low temperature. Addition of NaBD to the green solution without prior warming gives (29; R =D).94 Since (28) presumably owes its stability (? !) albeit at relatively low temperature to extensive conjugation with the aromatic rings could it justifiably be claimed as a Si=C species stable at such temperatures? Treatment of vinylsilanes with halogenocarbenes followed by elimination of halogenotrimethylsilane under the action of fluoride ion produces cyclopropenes which can be identified as benzofuran addition Friedel-Crafts reactions of alkenes with acyl halides and AlCl usually give low yields of a@-unsaturated ketones but use of vinylsilanes instead of simple alkenes gives both good yields and site-specificity the carbonyl group becoming attached to the carbon which initially held the silyl group.96 A number of 6-silasteroids have been synthesized and investigated for ant if ertili ty activity .97 Germanium Tin and Lead.-Bis(triethylgermy1)keten has been isolated from the reaction of Et,GeC(N,) Et with (Et,Ge),Hg.98 A review of industrial applications of organotin compounds has appeared.99 Compound (30),available by a hydrostannylation reaction is a useful purveyor of a sterochemically defined -CH=CHCH20H group via the corresponding Cu ate complexes,1oo whereas (31) reacts with ketones to give y-hydroxyalkyltin com-pounds which can be converted into cyclopropane carbonitriles.lo' Although tetra-alkyltin compounds generally show no Lewis acidity the reaction of l,l-dibromo-2,3,4,5-tetraphenylstannolewith cyclopentadienyl-lithium seems to give (32),a five-co-ordinate tin compound. lo2 A convenient method for generation of dialkylstannylenes :SnR, involves photolysis of cyclopolystannenes (R,Sn), in 93 M. Laguerre J. Dunogues R. Calas and N. Duffaut J. Organometallic Chem. 1975,93 C17. 94 J. Y. Corey J. Amer. Chem. SOC.,1975,97 3237. 95 T. C. Chan and D. Massuda Tetrahedron Letters 1975,3383. 96 I. Fleming and A. Pearce J.C.S. Chem. Comm. 1975 633.97 S. Barcza and C. W. Hoffman Tetrahedron 1975,31,2363; C. G.Pitt A. E. Friedman D. Rector and M. C. Wani. ibid. p. 2369. 98 0.A. Kruglaya I. B. Fedot'eva B. V. Fedet'ev and N. S. Vyazankin Zzvest. Akad. Nauk S.S.S.R. Ser. khim.,1975 199 (Chem. Abs. 1975.82 171 157d). 99 P. Smith and L. Smith Chem. in Britain 1975 11 208. loo E. J. Corey and R. H. Wollenburg J. Org. Chem. 1975,40,2265. Io1 S. Teratake Chem. Letters 1974 1123. 102 W. Z. M. Rhee and J. J. Zuckerman J. Amer. Chem. SOC.,1975,97,2291. Part (ii) Main -group Elements H \ /CH20THP /c=c\ HBu,Sn Bu,SnCH,CH,(CN)Li Li' THP = tetrahydropyranyl (30) (31) (32) benzene and in the absence of any suitable reactant the starting material is simply re-formed.lo3 Peroxides and disulphides react to give RiSn(OR2) and R;Sn(SR2), whereas two molecules of a ketone react wi?h one of a stannylene to give a 1,3,2-dioxastannolan.6 Group V Arsenic @timony and Bismuth.-Compounds such- as (33; X =CO,Et OH) cannot be obtained by electrophilic substitution reactions of arsabenzene but may be obtained by sequences involving As-Sn exchange of appropriately substituted organotin intermediate^."^ A compound previously reported (in 19 12!) to be (34) has now been shown to be the reductive dimer (35).lo5 (33) (34) H (35) +-Crystallinemethylenetriphenylarsorane Ph3As-CH, has been isolated from the reaction of methyltriphenylarsonium bromide with sodamide. lo' *03 W. P. Neumann and A. Schwarz Angew. Chem. Internat. Edn.1975,812. lo4 G. Markl H. Kellerer and F. Kneidl Tetrahedron Letters 1975 2411; G. Markl H. Baier and S. Heinrich Angew. Chem. Internat. Edn. 1975 14 710. lo5 H. Vermeer R. Lourens and F. Bickelhaupt Tetrahedron 1975,31 2529. lo6 Y. Yamamoto and H.Schmidbaur,J.C.S. Chem. Comm. 1975,668.

ISSN:0069-3030    

DOI:10.1039/OC9757200136

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

7 Electro-organicChemistry ByJ. H. P. UTLEY Departmentof Chemistry Queen Mary College Mile End Road London E 1 4NS 1 Introduction In this Report the emphasis is on new and preparatively significant reactions and related observations.* Two authoritative and comprehensive books have appeared during 1975.Iv2 2 Anodic Processes Oxidationof Neutral Organic Compounds.-Full details have been reported3 of the construction and use at 20-50 A of an undivided 800 cm2concentric capillary-gap cell which uses a graphite anode. A 3000 cm2 version with a production volume of cu. 1kg h-’ has also been built and tested. These cells may be purchased and can be used in combination with standard large-scale glassware and commercially available power supplies. Progress continues to be made on the functionalization viu anodic oxidation of normally unreactive aliphatic molecules.In fluorosulphuric acid solution containing potassium fluorosulphate alkanoic acids are converted4 at a platinum anode and at 273 K into lactones and unsaturated cyclic ketones. Proton loss is at positions remote from the carboxylic acid group. Immediate work-up allows isolation of lactones but delay leads to further chemical reaction (Scheme 1).In MeCN-LiC10 solutions U Me(CH,),CO,H work-up 1 ‘Techniques of Chemistry Vol. 5 Parts 1 and 2 Techniques of Electroorganic Synthesis’ ed. N. L. Weinberg Wiley-Interscience New York 1974. 2 S. D. Ross M. Finkelstein and E. Rudd ‘Anodic Oxidation’ Academic Press New York 1975. 3 L. Cedheim L. Eberson B.Helgee K. Nyberg R. Servin and H. Sternerup Actu Chem. Scand. (B), 1975,29,617. D.Pletcher and C. Z. Smith J.C.S. Perkin I 1975,948. * Help in locating the several hundreds of references which were reviewed came from a current-awareness service provided by Anne Jarvis and Stephen Shaw (Queen Mary College Library). 151 152 J.H.P. Utley containing a little water aliphatic ketones are oxidized5 at relatively low anodic potentials [ca. 2.2 V (us. AglAg+)]. As with carboxylic acids proton cleavage from straight-chain compounds is remote from the carbonyl group and the expected acetamides are formed.5a However from the radical-cations of cy -branched ketones comparatively stable carbenium ions may be produced by carbon-carbon bond cleavage.5b Similar considerations apply to the oxidation of secondary and tertiary alkylphenylcarbinols.For instance,5c acetophenone (83%)is obtained from the anodic oxidation in acetonitrile of 1-phenylethanol (via H' loss) whereas benzaldehyde (61%) and N-t-butylacetamide (47%) are obtained from l-phenyl- 2,2-dimethylpropanol (via Me$' loss). Examples of these reactions are given in Scheme 2. MeCO(CH ,),Me 2.2 V (us. AglAg') + MeCO(CH,),CH(Me)NHCOMe MeCN-LiCIO (40%) 2.5 V (us. AglAg+) Bu'NHCOMe + MeC0,H Bu'CO Me ---+ MeCN-LiCIO (80% (25 %) Scheme 2 A clean and simple alternative to cleavage of glycols using lead tetra-acetate and periodic acid has been suggested by Shono and co-workers.6 Anodic cleavage at readily accessible potentials at a carbon rod anode gives respectable yields of the corresponding acetals (e.g.Scheme 3). 2.02 V (us s.c.e.) CH(OMe) MeOH-Et,NOTs graphite anode (51 %) (14 %) Scheme 3 Since P. S. Skell's early work on the anodic cleavage of alkyl halides [cf. Ann. Reports (B),1969,66,2197] much work has been directed towards elucidating the detailed mechanism of the reaction. Skell's work suggested that a 'hot' lightly solvated carbenium ion was formed following ejection of halogen atom from the alkyl halide radical-cation. Laurent's more recent and comprehensive studies involving comparisons of anodic and solvolysis reactions [cf.Ann. Reports (B),1974 71,2231 suggest that for iodides in acetonitrile the halogen loss is solvent-assisted. This theme is continued in an investigation7 of the products of anodic oxidation in MeCN-LiClO of the series of 2-adamantyl bromides (1)-(3).Compound (3)is not Me Me Me ..iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii &NHCOMe gBr &Br DBr Me MeCONH (1) (2) (3) (4) (5) (a)J. Y. Becker L. R. Byrd and L. L. Miller J. Amer. Chem. Soc. 1975,97,853;(b)J. Y. Becker L. L. Miller and T. M. Siegel ibid. p. 849; (c)E. Mayeda ibid. p. 4012. T. Shono and Y. Matsumura J. Amer. Chem. SOC.,1975 97 2546. F. Vincent R. Tardivel and P. Mison Tetrahedron Letters 1975 603. Electro -organic Chemistry oxidized at S3.1 V (us.AglAg’). Compounds (1)and (2) are oxidized at 2.5 V but whereas (2) predominantly undergoes one-electron cleavage to give after work-up the acetamide (4),the unsubstituted bromide (1)undergoes two-electron cleavage to give the acetamide (5);from which the bromine is not lost.It has been pointed out that (2) is solvolysed thirty times faster than (1);this result has been interpreted in terms of Laurent’s hypothesis. However for the iodides an alternative mechanism has been shown to be worth very serious consideration (Scheme 4).Iodine is oxidized in acetonitrile consuming 2 F mol-’ and giving an ill-defined ‘iodinium species’ that can be loosely represented as ‘I”. Addition of 2-iodo-octane to a freshly electro- lysed solution of iodine in acetonitrile resulted* in the regeneration of iodine and the formation after work-up of 2-acetamido-octane (6)(54%) and 3-acetamido-octane (7) (22%). The plausibility of the mechanism in Scheme 4 is thereby established although both direct and indirect oxidation must presumably operate at the begin- ning of an electrolysis.1.8v Me(CH,),CH(MeU ‘2 MeCN ’ ’I + Me(CH,)&HMe 2F mol~’ JMeCN-H,O Me(CH,),CH(Et)NHCOMe + Me(CH,),CH(Me)NHCOMe (7) (6) Scheme 4 The oxidation of aliphatic amines has also been much studied and at conventional electrochemical concentrations amine radical-cations can undergo cleavage’ to carbenium ions (Scheme 5). At very high concentrations of t-butylamine a useful preparation of 2,2‘-azobutane (8) results’’ from the enhanced effectiveness of nucleophilic trapping of the radical-cation uis h vzs cleavage (Scheme 5). What is H2N + Me,e -+ Me,COH + Me,C=CH Me,&H / Me3&d l:bMe,C N =NC Me (8) Scheme 5 probably the first example of the capture of the hitherto unknown aza-ally1 cation (10)comes from a study” of the anodic oxidation of the aziridine (9).At 3 F mol-’ propiophenone is the major product of constant-current oxidation at platinum in methanol-NaC10,-Na2CO at 273 K. (It is readily oxidized further to the corre- sponding acetal). Treatment of a freshly electrolysed solution in the manner described in Scheme 6 gave (12) which suggested the initial formation of (11)via the L. L. Miller and B. F. Watkins Tetrahedron Letters 1974 4495. K. K. Barnes and C. K. Mann J. Org. Chem. 1967,32 1474. lo A. U. Blackham S. Kwak and J. L. Palmer J. Elecfmchern. Soc. 1975,122 1081. l1 P. G. Gassman and I. Nishiguchi J. Amer.Gem. SOC.,1975 97 1600. 154 J. H.P.Utley H N 3Frnol-I LiAIH,, R anode (11) Et20 PhCH(Et)NHMe + PhC(OMe),Et qpr 0 "C MeOH-NaCIO, (12) Na,CO . + 7 Ph(Et)C-N=CH2 ----*Ph(Et)C=NCH,OMe MeOH (10) (11) Scheme 6 aza-ally1 cation (10). Many attempts to purify an unstable product of electrolysis to 3 F mol-' gave material of 60-70% purity and the spectral data were consistent with structure (11).One of the limitations of the use of N-methyl-amides as solvents for anodic electrolyses is the ready oxidation to the isomerically stabilized cations of the type R'CONR2CH2+.This reaction has been put to good preparative use in the formation12of novel phosphonium salts and cyclic oxammonium salts (Scheme 7). + HCON(Me)CH,PPh ClO Scheme 7 Shono's work on the oxidative cleavage of enol acetates has been extended [cf.Ann. Reports (B) 1974 71 2231 and it is particularly noteworthy that the competition between two mechanistic pathways is greatly infl~enced'~ by the choice of supporting electrolyte (Scheme 8). Unsaturated ethers may also be cleaved K" Et,NOTs; nil KOAc; 60% HOAc KOAc or Et,NO% -H+,X Et,NOTs ;90 % KOAc; 25% Scheme 8 l2 M. Genies Bull. Soc. chim. France 1975 389. l3 T. Shono M. Okawa and I. Nishiguchi J. Amer. Chem. Soc. 1975,97,6144. Electro-organic Chemistry anodically. For instance cis-or trans-dimethoxystilbenes are oxidized' at platinum [1.8 V (us. AglAgI)] in MeCN-LiClO or DMF-LiC10 to (13)and (14). In this case (13) (14) the proportions of products are markedly dependent on concentration.From electrolysis of the cis-isomer in DMF the ratio of (13):(14) is ca. 1 at a starting concentration of 2.5 X lo-' mol I-l whereas the ratio is 6.5 at 0.5 X lo-' mol I-'. A variant of the long-established anodic substitution of furans has been introduced and presented as a new route" to substituted maleic anhydrides (Scheme 9). The method seems to be simple and to offer soinewhat better yields than previously used chemical methods. Several examples are given other than that illustrated in Scheme 9. Et Et Et Et Pt anode Jones Oxidation' NaHCOJaq.) 6 (84%) Scheme 9 Several interesting applications have been reported of the anodic addition of alkoxide to aromatic compounds.The synthesis of 1,4,9,12-tetraoxadispiro[4,2,4,2]tetradeca-6,13-diene (15) has been repeated,'6a and it appears that the reaction does not go to completion by electrolysis as originally reported.'6b The intermediate formed anodically must be converted by acid into the desired product (Scheme 10). Virtually identical conditions of electrolysis were II MeO. ,OCH,CH,OH nn k.2 MeOH-KOH(l%) \ ).' Et,O W OCH,CH,OH 0x0 Scheme 10 chosen for the key cyclization and addition step in an elegant and short synthesis" of 4a,Sa-homonaphthodiquinone(16) (Scheme 11). In similar vein amperostatic anodic oxidation in an undivided cell of 4-methoxyphenol in MeOH-LiClO led to l4 M. A. Michel P. Martigny and J. Simonet Tetrahedron Letters 1975 3143. J.Froborg G. Magnusson and S. Thoren J. Org. Chem. 1975,40 122. l6 (a)P. Marguretha and P. Tissot Helu. Chim. Actu 1975,58 933; (b) C. G. Fink and D. B. Summers Trans. Electrochem. Soc. 1938,74,325. f7 W. Bornatsch and E. Vogel Angew. Chem. Internat. Edn. 1975,14,420. 156 J. H. P.Utley f Me0 OMe Pt anode Mt:O&Me H,O+ & + MeOH-KOH(l%) Me0 OMe c 55 % Scheme 11 the preparation" of 4,4-dimethoxycyclohexa-2,5-dienone(17) in 97% isolated yield and with high purity. It is claimed that this procedure is much better than the alternative oxidation with Ce'". 0 Me0 OMe 0 (17) Many bright ideas for electrochemical reactions are foiled because during the key electrolysis fouling of the electrode prevents the passage of current.In this context a remarkable claim has been made. For the oxidation at platinum of benzhydrol to ben~ophenone,~~ in strongly alkaline solution the addition of cationic surfactants increases current efficiency from 1% to an unbelievable 326% (presumably based on 2 F mol-l although this is not clear). Excluding the sort of explanation which also allows Saints to cross the Irish Sea on floating altar stones it may well be that the cationic surfactant is in alkaline solution merely promoting a hydride transfer (Scheme 12). H OH-/J Ph,CHOH Ph,C \>-S"' -+ Ph,CO + SH('-')+ SH("-I)+ anode __* S"+ + H'; S"' = surfactant. Scheme 12 Anodic cleavage of the carbon-oxygen bond is well established and a useful example is the electrolysis of 4-methoxybenzyl ethers (Scheme 13).Such ethers of a range of alcohols are cleaved" under relatively mild conditions and in high yields MeCN-H,O, ROCHz00.. + 1.65 V (us. s.c.e.) ROH + OHCQOMe LiCIO Scheme 13 A. Nilsson A. Ronlan and V. D. Parker Tetrahedron Letters 1975 1107. I9 T. Franklin and L. Sidarons J.C.S. Chem. Comm. 1975,741. 2o S. M. Weinreb and G. A. Epling J. Org. Chem. 1975,40 1356. Electro -organic Chemistry (75-98%). Work-up is simple; the unwanted aldehyde is removed by extraction with saturated aqueous sodium bisulphite. The mechanism is assumed to be that proposed by earlier workers [Ann. Reports (B) 1972 69 3101 which involves proton loss from the initially formed radical-cation followed by a second electron transfer to give stabilized carbenium ions such as (18).Whilst plausible there is little + ArCHOR evidence that this mechanism holds generally; indeed for electrolysis of dibenzyl ether in dry acetonitrile detailed coulometric and '80-labelling experiments have shown that it is the ether radical-cation that undergoes cleavage.2' An interesting advance in anodic substitution reactions is the realization of trifluoroacetoxylation of usually unreactive substituted benzenes.'* Some key results are given in the Table and it seems that electron transfer from the aromatic Table Anodic trifluoroacetoxylation 22 of substituted benzenes PhX YieldsOf XC6H4OH (UkZ XC6H40COCF3) X o (%) rn (Yo) p (%) Current yieZd (YO) H - - - 27 C02Me 51 34 15 65 NO2 22 59 19 60 CF3 35 47 18 31 COMe 54 32 14 67 COPh 70 18 12 21 CN 45 30 25 10 compound is the prior step.The initialiy formed trifluoroacetates are hydrolysed during work-up to produce phenols and these reactions provide an effective means of anodic hydroxylation. In related oxidation of aromatic carbonyl com- pounds in CH,CI,-CF,CO,H solvent gives nuclear hydroxylation and nuclear acetamidation occurs in wet acetonitrile. Comparison of the results of these two studies reveals an interesting medium effect. For acetophenone and methyl ben- zoate oxidation in CF3C02H-CF3C02Na (1mol I-') gives2' substantial amounts of the rnetu-substituted products whereas oxidation in CH,C1,-CF3C0,H-Et4NBF4 (0.1mol I-') gives23 no detectable metu-substitution.Full details have now appeared of the preparatively useful inn~vation'~ of anodic cyanation of aromatic compounds in aqueous emulsions of methylene chloride containing phase-transfer agents. The possibility of an indirect route for the conversion of benzene into phenol has led to a detailed study of the optimization of yields for formation of diphenyliodonium salts from anodic oxidation of i~dobenzene~~ in the presence of 21 R. Lines Ph.D. Thesis London University 1975. 22 Z. Blum L. Cedheim K. Nyberg and L. Eberson Acru Chem. Scund. (B),1975,29 715. 23 Y.-H. So J. Y. Becker and L. L. Miller J.C.S. Chem. Comm. 1975,262. 24 L. Eberson and B. Helgee Actu Chem. Scand. (B),1975,29,451. 25 H. Hoffelner H. W. Lorch and H. Wendt J. Electroanulyt.Chem. Interfacial Electrochem. 1975,66 183. 158 J. H. P.Utley benzene. Such salts may be hydrolysed to phenol and iodobenzene can be re- covered. At low temperatures (303K) low potentials and high ratios of concentra- tions of iodobenzene and benzene chemical yields of 95% are achieved for the diphenyliodonium cation. Examples of useful anodic intramolecular coupling in the synthesis of phenolic alkaloid intermediates are becoming commonplace.26 In this context the elec- trochemical preparations of (f)-kresiginone26" and (f)-cryptopleurine (19)26bare noteworthy (Scheme 14). MeCN-HBF Pt anode 1.07 V (us. s.c.e.) OMe OMe 31% Meow OMe Scheme 14 Oxidation of Organic Anions.-An important correction has been made to the literature concerning the Kolbe reaction.It has always seemed unlikely that the of the detection of the anodically generated triphenylacetoxyl radical could be correct and assessment of the work is hampered because the key e.s.r. spectrum was not published. In a reinve~tigation~~~ it has been shown that in situ,controlled-potential oxidation at platinum of triphenylacetate in acetonitrile solution does not give rise to an e.s.r. signal. However if an anodic pulse of sufficient duration is applied and the circuit is opened the e.s.r. spectrum of the triphenylmethyl radical is obtained. Alternatively if a cathodic pulse to GO.35V is applied following the anodic pulse the same spectrum results. The rationalization of this behaviour is given in Scheme 15. 26 (a)J.M. Bobbit I. Noguchi R. S. Ware K. N. Chiong and S. J. Huang J. Org. Chem. 1975,40,2924; (b)E. Kotani M. Kitazawa and S. Tobinaga Tetrahedron 1974,30 3027. 27 (a)N. B. Kondrikov V. V.Orlov V. 1. Ermakov and M. Ya. Fioshin Elekirokhimiya 1972,8,920;(b) R. D. Goodin J. C. Gilbert and A. J. Bard J. Electroanalyt. Chem. Interfacial Electrochem. 1975,59 163. Electro -organic Chemistry anode cathode Ph ,CCO ,-s,"d,+ Ph3C+ +e-Ph,C' Scheme 15 The retention of stereochemistry at sites other than the a-carbon atom is an important feature of the Kolbe reaction and one of the reasons for its usefulness in the synthesis of naturally occurring compounds. Species other than Homo supiens now appreciate the implications of this because the reaction has recently proved useful for the syntheses of the housefly sex attractant muscalure [Ann.Reports (B) 1973,70,302] and of brevicomin (20) the sex attractant of the western pine beetle. This latter28 very elegant synthesis is outlined in Scheme 16. A two-electron EtCHkHCH,CO; + MeCO(CH,),CO; Pt anode MeCO(CH,),CHkHEt (20)42 % Scheme 16 oxidative decarb~xylation~~ has proved to be an efficient method for the preparation of the bicyclic ketone (2 l) which has the correct stereochemistry for ring opening via Baeyer-Villiger oxidation and subsequent conversion into methyl (f)-jasmonate (22)-3 Cathodic Processes Radical-anions as Bases Nucleophiles and Electron-transfer Agents.-There is growing interest in the possibility of using electrogenerated bases [cf.Ann.Reports (B),1969,66 2391. Dianions may be generated cathodically according to Scheme 17 and either the radical-anion or preferaMy the dianion may be strong bases II M + M2-Scheme 17 ** J. Knolle and H. J. Schafer Angew. Chem. Znternat. Edn. 1975 14 758. 29 S. Torii H. Tanaka and T. Mandai J. Org. Chem. 1975,40,2221. 160 J. H. P. Utley useful for initiating further chemical reaction. For cyclic voltammetry on the phenyl-substituted ethylenes (23) and (24) the transfer of the first electron is Ph,C=CHPh Ph MeC=CHPh (23) (24) reversible and that of the second irreversible. The ratio of peak currents [ip(l)/ip(2)] is in HMPA independent of sweep but for (24)in DMF the ratio can vary from 45 at 0.1 V s-l to 1.1at 30 V s-l i.e.at slow sweep speeds and in the solvent that is less able to stabilize the counterion disproportionation to the dianion is significant. Thus conditions may be set up for the generation of the strongly basic dianion at the potential of the first electron-transfer reaction. A similar study31has compared the effectiveness of water and methyl iodide in reacting with azobenzene radical-anion. Methyl iodide is very much better than water at quenching reversibil-ity of the first electron-transfer reaction. N-Methylation and NN-dimethylation are observed following electrolysis at the first peak potential and the proportions are dependent on the electrolyte and solvent. The extremes are N-methylation (90%)in moist DMF-LiCl and NN-dimethylation (loo”/,)in dry HMPA-LiC1.Cyclic volt-ammetry has also been to detect chemical reaction that is initiated by the cathodic generation of azobenzene dianion. Addition of azobenzene to solutions of acetophenone or benzophenone in acetonitrile causes diminution of the peak currents for reduction of the ketones. Azobenzene is reduced at less cathodic potentials than the ketones in question and it is supposed that azobenzene dianion abstracts a proton from the solvent and that the nucleophile thus formed (NCCH,) adds to the ketones thereby decreasing their concentration at potentials prior to Ph Ph (25) their reduction potentials. Benzil (25) and benzil dianil (26) are methylated by cathodic reduction at the potential of first electron-transfer in DMF containing methyl chloride33 [exemplified for (26) in Scheme 181.The products are highly -._-phHph Ph >=( Ph + Ph )=( Me DMF MeCl + NPh + PhNH(Ph)C=C(Ph)NHPh Hgcathode PhN NPh 2Fmol-’ PhN NPh PhN Ph cis and trans Me Me Me (24) Bu,NCl 12”/ 88 ”/ none LiCl 20 ”/ trace >60% Scheme 18 dependent on the cation; with LiC1 hydrogenation is preferred and this may be an example of the lithium cation carrying (by hydration) a proton donor to the vicinityof 30 T. Troll and M. M. Baizer Electrochim.Acru 1974,.19 951. 31 T. Troll and M. M. Baizer Electrochim.Acta 1975,20 33. 32 A. J. Bellamy J.C.S. Chem. Comm. 1975 944. 33 J. Simonet and H. Lund Bull. SOC.chim. France 1975 2547. Electro-organic Chemistry the cathode.Acetic anhydride is also a useful electrochemically inert electrophile which may react with electrogenerated nucleophiles. Thus the of benzophenone in MeCN containing acetic anhydride gives the acetate (27) in ca. 70% isolated yield. Ph2C-0Ac I COMe (27) Several paper^^'-^' have appeared which describe further the consequences of electron transfer by the homogeneous electron-exchange processes outlined last year [Ann. Reports (B) 1974 71,2261. For reactions which give a polarographic catalytic wave electron transfer to BX may be effected at the (lower) potential that corresponds to electron transfer to A provided that further reaction of BX' is rapid (Scheme 19). Thus the electrochemically inert ether (28) is cleaved3' at an accessible potential by the intermediacy of the radical-anion of 1-methylnaphthalene (Scheme 19).A' + PhCH,OPr' A + [PhCH,OPr']= (BX) (28) (BXL) BXI A Pr'O-+ PhCHi e- H+ b PhMe 93% w-1 (B') (BH) Scheme 19 Cathodic Cleavage.-Hydroxy-groups may be cleaved38 from unsaturated alcohols in DMF solution at a mercury cathode and at very negative potentials [ca. -2.6 to -2.9V (us. s.c.~.)]. Phenol is used as the proton donor and certainly for the reactions given in Scheme 20 loss of hydroxyl ion is faster than protonation of the -2.9 V (us. s.c.e.) Ph,COH DMF-BudNI b Ph,CH 2Frnol-' 95 % Ph,C=CHCH,OH Ph,C=CHMe 95 % -Ph2CHEt Ph,C(OH)C-CH -2.6 V 95 % Scheme 20 34 T. J. Curphey L. D. Trivedi and T. Layloff J. Org. Chem. 1974,39 3831. 35 H.Lund and J. Simonet J. Electroanalyt. Chem. Interfacial Electrochem. 1975,65,205. 36 J. Simonet M.-A. Michel and H. Lund Acta Chem. Scand. (B) 1975,29,489. 37 H. Lund M.-A. Michel and J. Simonet Acta Chem. Scand. (B),1975,29 217. 38 H. Lund H. Doupeux M.-A. Michel and G. Mousset Electrochim. Acta 1974,19,629. 162 J.H.P. Utley multiple bonds. Pinacols may also be cleaved3' cathodically provided there is at least one electro-active group that is a to the hydroxy-group. In protic media both C-0-and C-C- bond cleavage are observed e.g. from (29). In aprotic media it (29) (30) (31) is likely that C-C- bond cleavage is initiated by strong bases that are generated at the cathode with subsequent loss of hydroxyl radical from the ketone radical anion [e.g.(30) is formed in 90% yield from (31) in dry DMF at -2.3 V 0s. (AglAgI)]. Highly branched a-acetoxy-ketones are produced4' in good yield by cathodic removal of bromine from CYCY -dibromo-ketones. Straight-chain act -dibromo-ketones are reduced to the corresponding ketones but for highly branched molecules the loss by cathodic cleavage of the first bromine gives rise to an enolic intermediate (32) which is rapidly solvolysed (in acetic acid) to an a! -acetoxy-ketone (Scheme 21). This scheme is consistent with the known solvolytic behaviour of a -branched allylic bromides. BrABr -1.8V(AglAg+) &J3r Hg pool Ah HOAc-NaO Ac (32) 0 OH 78 % Scheme 21 An interesting mechanistic distinction may be made for the reductive cleavage of carbon-halogen bonds from benzenoid compounds.For electrolysis in DMF-D,O YO) the incorporation of deuterium depends on whether or not th? radical anion (MXL) diffuses from the cathode. Cleavage in bulk solution (to M ) results in H abstraction (no D incorporation) whereas cleavage at the electrode allows further electron transfer (to M-) and hence deuterium incorporation. Thus c1eavage4l from (33) gives benzophenone with no deuterium incorporation whereas (34) is reduced with loss of bromine to a product with ca. 60%deuterium incorporation. Consistent with this hypothesis is the observation of reversible one-electron transfer in the cyclic voltammetry of (33) i.e.the radical-anion has a lifetime which permits diffusion from the cathode. 39 M.-A. Michel G.Mousset and J. Simonet Electrochim. Acta 1975 20 143. 40 A. J. Fry and J. J. O'Dea J. Org. Chem. 1975,40,3625. 41 J. Grimshaw and J. Trocha-Grimshaw,J.C.S. Perkin 11 1975,215. Electro -organic Chemistry Cathodic Hydrogenation and Cydization.-Alkynes are less easily reduced than alkenes and consequently cathodic hydrogenation of alkynes usually results in complete four-electron reduction to alkane. A recent systematic of the cathodic reduction in DMF of 1-phenylhex-1-yne shows that although at low (polarographic) concentrations there is four-electron reduction to 1-phenylhexane preparative-scale electrolysis (0.002-0.01 M in alkyne) leads predominantly to PhCH=C=CHPr (35) the allene (35). The rearrangement is presumably bimolecular involving electro- generated base and therefore favoured by higher concentrations.A similar concen- tration dependence attends the cathodic reduction43 of 6-chloro- 1-phenylhex- 1-yne (36). At low concentrations (ca.2.5 X 10-4mol l-') controlled-potential electrolysis leads to the cyclic compound (37) i.e. from intramolecular displacement of chloride PhCrC(CH,),Cl x (36) U (37) in the alkyne radical anion. At higher concentrations intermolecular isomerization to the allene (see above) occurs at a potential which initiates further reduction to a complex mixture of products. For the reactions depicted in Scheme 22 the competition between hydrogenation and cyclic hydrodimerization on structure and in particular on the bulk of R; dimerization is inhibited where R is t-butyl or phenyl.H+,e- H+ Ph(R)C=C(CN) 5 Ph(R)k-C(CN) Ph(R)CHCH(CN) (R = Ph or Bu') 1 Ph cis and trans (R = H or Me) Scheme 22 42 W. M. Moere and D. G. Peters J. Amer. Chem. SOC.,1975,97 139. 43 W. M. Moore and A. Salajegheh J. Amer. Chem. SOC.,1975,97,4954. 44 A. L.'Avaca and J. H. P. Utley J.C.S. Perkin 11 1975 161. 45 A. L. Avaca and J. H. P. Utley J.C.S. Perkin 1 1975,971. 164 J. H.P. Utley StereoselectiveCathodicReactions.-Significant progress has been made recently in understanding and accomplishing stereoselective reduction. A particularly signifi- cant advance is the preparation of a chiral electr~de.~~ Graphite rods were baked in air (160°C for 36 hours) and the surface carboxylic groups so produced were converted into acid chloride groups (using SOCl in dry benzene) and then into chiral amide [viu S( -)-or R( +)-phenylalanine methyl ester].The chiral electrodes cannot be distinguished from the original carbon electrodes either by eye or by their cyclic voltammetric behaviour. Reduction of (38) at such pre-treated electrodes at -1.05 V (vs. s.c.e.) in ethanolic acetate buffer gives the optically active alcohol with an enantiomeric excess of the (-)-isomer if pre-treatment is with S(-)-phenylalanine ester and an excess of the (+)-isomer if R(+ )-phenylalanine ester is PhCOC0,Et (39) used. The optical yield is not given because there is no reliable value for the specific rotation of the optically pure alcohol. However similar reduction of (39) gives the corresponding optically active alcohol in 9.7% optical yield.The electrodes are re-usable. Stereoselectivity may also be a consequence of electron transfer under the influence of a chiral double layer and a possible example4' of this is the reduction of cobalt(rI1) trisacetylacetonate (Scheme 23). In this case the key observation is that if Hg pool -1.0 V (US.AglAgCI) ( ')-Co(acac)3 M&N-tri-N-methyl-'tco(acac),l (-)-menthylammonium = 14 perchlorate Scbeme 23 the reaction is halted before completion the recovered starting material has become optically active and furthermore the optical activity is larger the longer the reaction is allowed to continue. The supposition is that the rate of electron transfer in the chiral double layer is different for the two enantiomers.However reaction in bulk solution containing chiral salts may also result in asymmetric induction and an interesting comparison of stereoselective photochemical and electrochemical pinacolization has been made.48 Acetophenone is pinacolized stereoselectively at 25 "Cin a methanolic solution of (+)-1,4-bis(dimethylamino)-2,3-dimethoxybutane containing lithium bromide by irradiation (optical yield 3.3% ;meso-:(&)-isomer = 0.5)or cathodically (optical yield 5.6%; meso-:(*)-isomer =0.35). The similarity of these results suggests that interactions at the electrode environment are not essential for asymmetric induction. Hydrogen transfer from chiral donors is another possible mechanism for asymmetric reduction and the cathodic hydrogenation of a malononitrile adduct (Scheme 22; R =But) was from this viewpoint.This 46 B. F. Watkins J. R. Behling L. L. Miller and E. Kariv J. Amer. Chem. SOC.,1975 97 3549. 47 S. Mazur and K. Ohkubo J. Amer. Chem. SOC.,1975 97,2911. 48 D. Seebach and H. A. Oei Angew. Chem. Internat Edn. 1975,14 634. Electro -organic Chemistry compound is particularly suitable for probing the possibility because its radical- anion is produced at povtentials well clear of those required for discharge of chiral proton donors such as ephedrine hydrochloride or quinidine sulphate. This pre- cludes hydrogen-atom transfer [cf. Ann. Reports (B) 1970 67 2341 and ensures proton transfer. Within experimental error no induction of asymmetry was found for this system.In a pragmatic of the asymmetric reduction of phenylglyox-ylic acid (40)to mandelic acid (41),many experimental parameters have been varied PhCOC0,H PhCH(OH)CO,H (40) (41) systematically. In this case the hypothesis advanced is that optimum stereoselectivity (ca. 20% optical yield) is found for conditions (e.g. temperature pH nature and concentration of alkaloid inducer current density) which most favour the formation between carbanionic intermediate and alkaloid of diastereoisomeric adsorbed complexes which protonate with retention of configuration and presumably at different rates. A similar conclusion comes from the work of Horner's group and a recent and very detailed account of their studies has a~peared.~' For racemic ethylenic ketones such as (42) highly stereoselective reductive coupling has been achieved51 by careful control of pH resulting in the predominant (42) (43) formation of only the cis-threo-cis-isomers e.g.(43).The overall yields of glycols are highly dependent on pH but fall within the range 60-90%. 4y M. Jubault E. Raoult and D. Peltier Electrochim. Actu 1974 19 865. L. Horner and D. Degner Electrochim. Acru 1974,19,611. 51 E. Touboul and G. Dana Tetruhedron 1975,31 1925.

ISSN:0069-3030    

DOI:10.1039/OC9757200151

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

8 Photochemistry By W. M. HORSPOOL Department of Chemistry The University Dundee DO7 4HN Benzene photochemistry is an area which continues to provide interesting results. Barltrop and Day' have suggested that permutational analysis may be useful in recognizing which path has been followed in the transposition of groups in the rearrangement of aromatic systems e.g. the conversion of o-xylene into rn-xylene. They point out that there are twelve permutation patterns in the six-membered ring systems and the two which would account for the xylene transformation are shown in (1)and (2). In no case has it been established which of the 12 patterns actually occurs R3 R'OR' R'\+ 0 R5 in the transpositions since most of the experiments so far described in the literature have had insufficient labelling of atoms.They' also suggest that there are no cases where a connection has been established between benzvalene or Dewar and pris- mane isomers and the occurrence of photo-transposition. This statement has been challenged by Chambers et uZ.,~ who cite the photochemical rearrangements of perfluoroalkyl-pyridines. Permutation patterns for the transposition of ring-carbons have been used to analyse the photo-reactions of alkyl hydroxypyrilium cations (3)3 and of 2qanopyrr0les.~ J. A. Barltrop and A. C. Day J.C.S. Chem. Cbmm. 1975,177. * R. D. Chambers R. Middleton and R. P. Corbally J.C.S. Chem. Cbmm. 1975,731. J. A. Barltrop R. Carder A. C. Day J. R. Harding and C.J. Samuel,J.C.S. Chem. Comm. 1975,729. J.A. Barltrop A. C. Day P. D. Moxon and R. R. Ward J.C.S. Chem. Cornrn. 1975,786. 167 168 W.M. Horspool The interest in the photoaddition reactions of benzene and substituted derivatives has been maintained. Typical of this is the report of the 1,3-addition of diphenylacetylene to trimesic trimethyl ester to afford the adduct (4).' 1,2-Dimethylenecyclohexane has also been added to benzene photochemically to yield the first example (5) of 1,4-1',3'-additi0n.~ Compound (6) a 1,4-lf,4'-adduct was also isolated. Bryce-Smith et a1.' have published work which shows that the bicyclo-octadiene (7) is the immediate precursor of the 2 :1adduct in the benzene- maleic anhydride system. The diene (7) is the precursor in both the sensitized and direct reactions [in direct irradiation the zwitterion (8) is precursor to the diene (7)].0 0 0 0-(7) (8) The influence of diluents upon the reaction path has demonstrated that di- bromoethane can act as an aid to intersystem crossing (S +T,).A further report* on the photochemical addition of furan to benzene has explained that the differences between the original reports were due to different experimental The formation of (9) and (10) as the main products is dependent upon the use of a virtually monochromatic light source of low intensity. The formation of (1 1) requires a high-intensity source. (9) (10) (11) The influence of xenon on the fluorescence efficiency of benzene in oxygen-free cyclohexane has been studied. l1 Under these conditions the fluorescence intensity is decreased; however the photochemical yield of benzvalene is not affected.The results support the assumption that benzvalene formation arises from a non-relaxed state before the fluorescent level is reached. The photochemistry of benzvalene (12a) is inefficient with a quantum yield of 0.1. This inefficiency is a result of the degenerate photovalence isomerization (12b) +(13).12 This isomerization can be brought about by direct irradiation at 254nm or else by triplet sensitization providing that the sensitizer energy is <272 kJ mol-' but >222 kJ mol-'. When the triplet energy is >272 kJ rno1-l the photolysis affords benzene. The authors12 5 T. Teitei and D. Wells Tetrahedron Letters 1975 2299. 6 J. C. Berridge D.Bryce-Smith and A. Gilbert Tetrahedron Letters 1975 2325. 7 D. Bryce-Smith R. R. Deshpande and A. Gilbert Tetrahedron Letters 1975 1627. 8 J. C. Berridge D. Bryce-Smith A. Gilbert and T. S. Cantrell J.C.S. Chem. Cornm.,1975 6 11. 9 J. C. Berridge D. Bryce-Smith and A. Gilbert J.C.S. Chem. Cornm. 1974 965. 10 T. S. Cantrell Tetrahedron Letters 1974 3959. 11 Y. Ilan and G. Stein Chem. Phys. Letters 1975 31 441. 12 C. A. Renner T. J. Katz J. Pouliquen N. J. Turro and W. H. Waddell J. Arner. Chern. SOC.,1975,97 2568. Photochemisfry suggest that the higher energy sensitizers populate the benzvalene T2state which ring-opens to benzene triplets whose energy is sufficient to decompose a second benzvalene molecule i.e. a quantum chain process is in operation.The dependence on sensitizer concentration is in agreement with this proposal. D (12) a; R = H b;R=D Exciplex formation in arene-diene systems continues to be an area of active investigation. In this area Lewis and Hoyle13 have examined temperature depen- dence and have established that reversible exciplex formation is important. Thus it is possible to explain the decrease in the fluorescence quenching rate constants with diene ionization potential in terms of increased reversibility of exciplex formation rather than simply a decrease in the rate of exciplex formation. Similar observations have been made in a kinetic analysis of the a-cyanonaphthalene-olefin systems.14 Exciplexes are also involved in the reaction of 9-cyanoanthracene with furans,” and of anthracene with dienes.“J’In another report the piperylene-sensitized dimeriza- tion of 9-phenylanthracene has been shown to be a quite general process and several dienes show the ability to sensitize the dimeri~ation.~’,~~ The reaction mechanism apparently involves deactivation of the anthracene excimer by the diene. A similar effect has been observed in the dimerization of the parent anthracene. However in this case the authors2* conclude that an exciplex between the diene and the excited-state anthracene is involved. The generation of radical cations of 1-phenylcyclopentene 1-phenylcyclohexene and 2-phenylnorbornene has been reported in the photolysis of these olefins in the presence of 1-cyanonaphthalene as an electron acceptor.21 Photo-dehydrocyclizations of cis-stilbene analogues have long been an area of considerable activity.In the past year activity has been maintained and the R3 (14) a; R = a-C,,H (15) a; R2-R3 = (CH=CH),; R’ = H b; R = B-CloH b; R1-R2 = (CH=CH) ;R3= H l3 F. D. Lewis and C. E. Hoyle J. Amer. Chem. SOC.,1975,97,5950. l4 W. R. Ware D. Watt and 3.D. Holmes J. Amer. Chem. Soc. 1974,96,7853. l5 K. Mizuno C. Pac and H. Sakurai J.C.S. Perkin I 1974,2360. l6 N. C. Yang D. M. Shold and J. K. McVey J. Amer. Chem. SOC.,1975,97,5004. N. C. Yang K. Srinivasachar,B. Kim and J. Libman J. Amer. Chem. Soc. 1975,97,5006. R. 0.Campbell and R. S. H. Liu Mol. Photochem. 1974,6 207. l9 R. 0.Campbell and R. S. H. Liu Chem. Comm. 1970,1911. 2o J. Saltiel and D.E. Townsend J. Amer. Chem. SOC.,1973,95 6140. 21 Y.Shigemitsu and D. R. Arnold J.C.S. Chem. Comm. 1975,407. 170 W. M. Horspool photochemical cyclization of the benzothienylnaphthalenes (14) has been reported.22 The a-naphthyl isomer (14a) cyclizes normally to afford (15a) while the p-isomer (14b) yields (15b). This result is in contrast to normal cyclization paths encountered in other P-styrylnaphthalene cyclizations. Another interesting applica- tion of the photo-cyclization is in the formation of the bridged [18]annulene (16) which was obtained from the low-temperature (-80 "C)irradiation (254 nm) of a THF solution of (17).23 RR RR (16)a; R = H b;R-R = CH2CH2 Attention is still being focussed on photochemical reactions of dienes (either conjugated or not).The photochemical excitation either direct or sensitized of allenes (18) in acetic acid affords the enol acetates (19). The photo-addition to these substrates takes place in the reverse sense from the ground-state process.24 The penta-173-dienes have been the subject of attention over the past few years in reports which showed that direct irradiation (253.7 nm) of cis-and trans-penta-1,3-dienes R' R3 H R2 OAC R2Fc=( RkcR3 (18) a; R' = Ph; R2 = Me; R3= H b; R' = Ph; R2 = R3 = Me c; R' = rn-MeOC6H4; R2 = Me; R3 = H d; R' = n-C6H13; R2 = R3 = H in solution led to 3-methylcyclobutene 1,3-dimethylcyclopropene,as well as the geometric isomer of the diene.25 A recent study26 has now shown the presence of a wavelength effect in this system which was made evident by the lack of cyclobutene and cyclopropene products when the penta-1,3-dienes were irradiated at 228.8 nm.Interest has still been maintained in the photochemistry of non-conjugated dienes particularly the di-w-methane systems. In this respect the photochemistry of (20) and (21) which yield (22) and (23) respectively has shown that there is no demand on the di-w-methane reaction for either a cis-or a trans-rearrangement in the intermediate biradical [e.g. (24) which is the biradical proposed for the rearrange- ment of 1,1,5,5-tetraphenyl-3,3-dirnethylpenta-l74-diene into the vinylcyclo-propane].*' The replacement of one of the double bonds in the di-7r-methane 22 A. Croisy P. Jacquignon and F. Perin J.C.S. Chem.Comm. 1975 106. 23 R. B. Vernet T. Otsubo J. A. Lawson and V. Boekelheide J. Amer. Che.m. SOC.,1975,97 1629. 24 K. Fujita K. Matsui and T. Shono J. Amer. Chem. SOC.,1975,97 6256. 25 S. Boue and R. Srinivasan J. Amer. Gem. SOC.,1970 92 3226. z6 P. Vanderlinden and S. Boue J.C.S. Chem. Comm. 1975,932. z7 H. E. Zimmerman and L. M. Tolbert J. Amer. Chem. Soc. 1975,97,5497. Photochemistry 171 system by a cyclopropane ring as in (25) does not curtail photochemical reactivity and several products are formed.28 The path by which the bicyclopropenyl (26a) photochemically rearranges to a benzene derivative was originally thought to involve a prismane ir~termediate.~' However a reinvestigation of this process using suitably labelled bicyclopropenyls (26b c) has shown that a prismane intermediate does not account for the conversion R4 R' RZ R3 R Ph Ph Ph (26) a; R' = R2 = H; R3= R4 = Ph b; R1= H; R2 = Me; R3= R4 Ph c; R' = R2 = Me; R3 = R4 = Ph d; R' = R2 = Ph; R3 = H; R4 = Me e; R' = R2 = Ph; R3= R4 = Me R 2 v Ph (27) P h into the toluenes (2,3,4,5-tetraphenyltolueneand 2,3,4,6-tetraphenyltoluene)or for the isomerization of bicyclopropenyl (26b) into (26d) and of (26c) into (26e).The suggest that a biradical(27) is involved which can either aromatize into the toluenes or else revert to bicyclopropenyls. Hixson aEd Borovsky3' have established in the photoisomerization of the cyclo- propane (28a) that rupture of both bond 'a' yielding (28b) and bond 'b' yielding (29) cccurs. The analysis shows that upon direct irradiation 81% of the isomeriza- tion arises by bond 'a' fission while in sensitized photolysis 98% of the isomerization arises by bond 'a' fission.This indicates that the triplet state shows a greater preference for outside bond fission. Direct irradiation of either of the two alcohols (28) a; R' = H; R2 = CH,OH (29) (30) a; R' = OH; R2= H b; R' = CH20H; R2 = H b; R' = H; R2 = OH 28 H. E. Zimmerman and C. J. Samuel J. Amer. Chem. SOC.,1975,97,448,4025. 29 R. Breslow P. Gal H. W. Chang and L. J. Altman J. Amer. Chem. Soc. 1965,87,5139. 30 R. Weiss and H. Kolbl J. Amer. Gem. Soc. 1975 97 3222 3224. 31 S. S. Hixson and J. Borovsky J. Amer. Chem. Soc. 1975,97 2930. 172 W. M.Horspool (28a) or (28b) also affords ring-opened products (30)32 by a mechanism involving carbocation intermediates.Ring-opening in another system (3 1) has permitted the recognition of the fact that 1,5-hydrogen migration is an important feature in the photolysis of benzon~rcaradienes.~~ (31) In the review of the photochemistry of last year (1974) the report of the photoisomerization of alkenes into carbenes was mentioned.34 This past year (1975) has seen the publication of other reports of this conversion. Thus the direct irradiation of cycloheptene at moderate pressures in the gas phase affords methylenecyclohexane and bicyc1o[4,l70]heptane (32a) which are formed via the carbene (33a).35 The irradiation of 3-phenylcycloheptene in benzene (triplet ?) afforded products (32b c) and 2-phenylmethylenecyclohexane in a total yield of R' ,R2 b (32) a; R' = R2 = H (33) a; R = H (34) (35) b; R' = Ph; R2 = H b; R = Ph C; R' = H; R2 = Ph 20% as well as dimeric or polymeric material.A route to products involving the Hixs0x-1~~ carbene (33b) was post~lated.~~ has shown that irradiation of 1,l-diphenyl-3,3-dimethylbut-l-enein solution phase probably involves a carbene (34) intermediate which subsequently yields 1,2-diphenyl-3,3-dimethylbut-l-ene(not isolated) and the cyclopropane (35). The feasibility of the carbene scheme was demonstrated by deuterium-labelling studies. A re-interpretation of the photochemical conversion of triptycene (36a) into (37) by Iwamura et al.38,39 has implicated a carbene intermediate (38). Originally this reaction was thought4' to be another example of the di-n-methane reaction.Wheeler et d41 have joined in the fray and have examined the photochemistry of the dimethoxytriptycene (36b) which is converted into the aceanthrylene (39). No evidence for the intermediacy of carbenes was obtained. Iwamura and Tukada4* 32 S. S. Hixson and J. Borovsky J.C.S. Chem. Comm. 1975 607. 33 J. S. Swenton K. A. Burdett D. M. Madigan T.Johnson and P. D. Rosso J. Amer. Chem. Soc. 1975,97 3428. 34 T. R. Fields and P. J. Kropp J. Amer. Chem. SOC.,1974,96 7559. 35 Y. Inoue S. Takamuku and H. Sakurai J.C.S. Chem. Comm. 1975,577. 36 S. J. Cristol and C. S. Ilenda J. Amer. Chem. SOC., 1975,97 5862. 37 S. S. Hixson J. Amer. Chem. SOC., 1975,97 1981. 38 H. Iwamura and K. Yoshimura J.Amer. Chem. SOC.,1974,96,2652. 39 H. Iwamura Chem. Letters 1974 5. 40 T. D. Walsh J. Amer. Chem. SOC.,1969,91,515;N. J. Turro M. Tobin L. Friedman and J. B. Hamilton ibid.,p. 516. 41 R.0.Day V. W. Day S. J. Fuerniss and D. M. S. Wheeler J.C.S. Chem. Comm. 1975,296. 42 H. Iwamura and H. Tukada J.C.S. Chem. Comm. 1975,969. Photochemistry 173 .H (36) a;R = H (37) b; R = OMe C; R = OH have suggested that car "enes could be involved in the plotoreaction of (36b) and they have studied the closely related triptycene (36c) which is converted into (40)by a route thought to involve carbenes. The introduction of polar substituents into a 0" (39) (40) barrelene (41) has an effect on the sensitized photochemistry which yields 1,2- dicyanocyclo-octatetraene (20%) (the sole product from the direct irradiation) and two dicyanosemibullvalenes (42a 56%)and (42b 4%).This latter minor product is thought to involve a carbene (43) intermediate.43 (41) (42) a; R' = CN; R2 = H (43) b;R' = H;R2 = CN The intramolecular hydrogen-abstraction reaction encountered44 in the photo- chemistry of the N-(diphenylmethy1ene)acetamides (44a) is reminiscent of Norrish Type I1 hydrogen abstraction in o-methylbenzophenone~~~ or in the reactions of 1-o-tolyl- l-~henylethylene.~~ Hydrogen abstraction by the imino-group in (44a) leads /' ,'NHAc \\ (44)a;R=H (45) b;R=D 43 K. Saito and T. Mukai Bull. Chem. SOC.Japan 1975,48,2334. 44 M. Saeki N. Toshima and H. Hirai Bull. Chem.SOC.Japan 1975,48,476.45 e.g. H. Lutz E. Breheret and L. Lindqvist J.C.S. Faraday I 1973,69,2096. 46 A. C. Pratt J.C.S. Chem. Cornm. 1974 183. 174 W. M.Horspool to an o-quinomethide (45) which in MeOD will deuteriate by exchange on the N-H. Subsequent tautomerization affords the deuterium-incorporation product (44b). Another report on the photochemistry of imines has suggested that the low reactivity of the imine double bond towards hydrogen-abstraction reactions is due to rapid radiationless decay and twisting about the C=N double bond.47 Interest in the photochemistry of sulphur analogues of ketones has been con- tinued. One synthetic application in this area is the synthesis of (*)cuparene (1,2,2- trimethyl-1-p-tolylcyclopentane)by a route involving the desulphurization of the thiol(46) obtained from the photochemical cyclization of the thione (47) in benzene Remote oxidations in steroidal systems continue to be studied.In this p-MeC,H p-MeC,H respect the novel remote oxidation of the C-4 P-methyl group of the steroidal derivative (48) has been A further use of aryl iodide dichlorides for remote oxidation has been published for the photolysis of the cholestanyl aryl iodide (49) in the presence of PhIC12. After work-up unsaturation in the steroidal skeleton was found at the C-16/C-17 site." Irradiation of the esters (50) using the lSO-labelled compounds has demon- strated a previously undetected scrambling of the oxygen This indicates that radical recombination occurs in competition with decarboxylation in ester photolysis.The irradiation of the optically active ester (50b) ([a]i3:-121.8") showed that although the scrambling reaction was taking place the group migration occurred with considerable retention of the stereochemical integrity ([ax; -118.0O). A previous study on the photochemical reactions of benzofuran with sensitizers suggested that dimers were obtained when high-energy sensitizers were used while 47 J. M. Hornback G. S. Proehl and I. J. Starner J. Org. Chem. 1975,40 1077. 48 P. de Mayo and R. Suau J.C.S. Perkin I 1974,2559. 49 J. A. Nelson S. Chou and T. A. Spencer J. Amer. Chem. SOC.,1975,97 648. 5O B. B. Snider R. J. Corcoran and R. Breslow J. Amer. Chem. SOC.,1975,97,6580. 51 R. S. Givens and B. Matuszewski J.Amer. Chem. SOC.,1975,97 5617. Photochemistry 175 (50) a; R = H (51) a; R = Me b;R=Me b; R = Et oxetans were formed from lower-energy sen~itizers.~~ The reinvestigation of the reaction has shown that the high-energy sensitizers (propiophenone and acetophenone) also yield oxetans (51a b) the ratio of products (oxetans dimers) being sensitive to the ratio of the reactants a dependence which has been rationalized in terms of a reversible energy-transfer step in competition with oxetan formation. The results obtained from the study suggest that the energies of pro-piophenone and acetophenone are closer than previously established by low- temperature phosphorescence measurements. In fact the authorss3 suggest that in benzene solution at room temperature the triplets of acetophenone and pro- piophenone are iso-energetic.A study of the photochemistry of the keto-olefins (52),(53) has shown that the inefficiency in product (54) formation is a result of inefficient formation of the biradical (55).54 This biradical is the intermediate which either yields photoproduct (54) or brings about isomerization by a Cope process of (52)to (53) or vice versa. The inefficiency of the biradical formation is due to exciplex formation between the singlet n7r* state and the olefin. (52) (53) (54) (55) The cycloaddition reactions of enones and related systems still constitute a popular area of research. A reinve~tigation~~ of the photochemical reaction of coumarin with tetramethylethylene has confirmed that the photoproduct is the (2 +2) adduct (56),56 formed from both the triplet and the singlet state of the coumarin.Surprisingly the tetramethylethylene completely suppresses the dimerization of the singlet coumarin. (56) (57) a; X = 0 (58) a; X = 0 b; X = CH b; X = CH 52 C. H. Krauch W. Metzner and G. 0.Schenck Chem. Ber. 1966,99,1723. 53 S. Farid S. E. Hartman and C. D. DeBoer J. Amer. Chem. SOC.,1975,97,808. 54 J. C. Dalton and S. J. Tremont J. Amer. Chem. Soc. 1975,97,6916. s5 J. W. Hanifin and E. Cohen TetrahedronLetters 1966 1419. 56 P. P. Wells and H. Morrison J. Amer. Chem. Soc. 1975,97 154. 176 W. M. Horspool Previous work has shown that the dimerization of coumarin from the singlet arises from an exciplex. To account for the suppression of the dimerization the suggest that the mechanism involves the interception of the singlet exciplex by the olefin.The problem associated with charge distribution of cycloadditions to cyc- lohexenones has been examined further using the intramolecular additions encoun- tered in the enones (57) and (58).57 Padwa and DehmS* have reported phenyl migration arising on photochemical excitation of the furanones (59a b) yielding (60) in benzene solution. An odd- electron process (checked by migratory aptitude experiments) is indicated permit- ting phenyl migration to the enone terminus. ."a0 R (59) a; R = H (60) a;R = H b; R = Ph b; R = Ph P,y-Enones have had a special place in organic photochemistry for some time. The interest in these systems was heightened by the publication of theoretical predictions concerning their excited-state reactivity.P,y-Enones in the triplet excited state mainly undergo 1,2-acyl-migrations (an 0x0-di-v-methane reaction) affording cyclopropanes [e.g. (61a) and (61b) are converted into (62a) and (62b) respectively upon acetone sensiti~ation].~~,~~ The singlet reactivity is such that 1,3-acyl shifts result [e.g. the conversion of (61b) into (63)J6' Other work has shown that in some instances 1,3-acyl-migration can occur upon sensitization as well as upon direct irradiation. Thus enone (64) is converted into (65) upon direct as well as (61) a;n = 1 (62) a;n = 1 (63) b;n=2 b;n=2 acetone-sensitized irradiation. In the triplet reaction this product is accompanied by the usual 1,2-acyl-migration prod~ct.~' A further example of sensitized 1,3-acyl- migration has been detected in a reinve~tigation~~ of the photochemistry of the norbornenone (66) which is converted into (67).63This product is also photolabile and is converted by a 1,2-acyl shift into product (68).The reaction of the enone (66) can be sensitized by acetone acetophenone or benzophenone. However the efficiencyof the reaction falls off dramatically in the case of the last two sensitizers. It is particularly surprising that acetophenone should be so inefficient since it has been 57 D. Becker Z. Harel and D. Birnbaum J.C.S. Chem. Comm. 1975,377. 58 A. Padwa and D. Dehm J. Amer. Chem. SOC.,1975,97,4779. 59 R. K. Murray jun. T. K. Morgan jun.and K. A. Babiak J. Org. Chem. 1975,40 1079. 6o R. K. Murray jun. D. L. Goff and R. E. Ratych Tetruhedron Letters 1975,763. 61 P. S. Engel and M. A. Schexnayder J. Amer. Chem. SOC.,1975,97 145. 62 J. Ipaktschi Tetrahedron Letters 1969 2153; Chem. Ber. 1972,105 1840. 63 M. A. Schexnayder and P. S. Engel Tetrahedron Letters 1975 1153. Photochemistry (66) (67) (68) that the triplet energy of (66) is 291.2 kJ mol-’. This value was based on phosphorescence studies but the present paper points out that the enone (66) has no phosphorescence when it is pure. Thus the previous value is in some doubt. Kinetic studies have shown that triplet sensitizers (benzophenone and acetophenone) can form an excited-state complex with the enone and this competes favourably with energy transfer.The problem of interaction other than energy transfer between acetophenone and the enone (69) has also been 0m (69) In an earlier study of the photobehaviour of the cyclohexadienone (70)Schuster et .~~ ~1 interpreted the results from quenching studies using cyclohexa-1,3-diene in terms of two excited states. The nm* state was thought to be responsible for hydrogen abstraction from solvent yielding p-cresol while the mm* state formed the lumiketone. This interpretation was contrary to earlier proposals concerning the excited state responsible for the rearrangement. However in a re-interpretation of the photochemistry of the dienone (70)the recognition of a free-radical process casts doubt on the original p~stulate.~’ Closely associated with the problem of which excited state of a dienone is responsible for the rearrangement is the report of the thermal decomposition of the dioxetans (71).68 This decomposition yields 4,4-diphenylcyclohexa-2,5-dienone 6,6-diphenylbicyclo[3,l,O]hex-3-en-2-one (the usual photoproduct from the photolysis of the dienone) and the corresponding (j CCI Ph ‘Ph (71) a; R = Ph b; R = m-MeOC,H C; R = P-CloH arylmethyl ketone (acetophenone m-methoxyacetophenone or p- acetonaphthone).The authod8 reason that the decomposition of the dioxetan must yield the nn* triplet state of the dienone and it is this which is responsible for the formation of the bicyclic photoproduct in ca. 17% yield. 64 K. G. Hancock and R. 0.Grider J.C.S.Chem. Comrn. 1972,580. 65 P. S. Engel M. A. Schexnayder W. V. Phillips H. Ziffer and J. I. Seeman Tetrahedron Letters 1975 1157. 66 D. I. Schuster and K. V. Prabhu J. Amer. Chem. Soc. 1974,96 3511. 67 D. I. Schuster G. C. Barile and K. Liu J. Amer. Chem. SOC. 1975,97,4441. 68 H. E. Zimmerman and G. E. Keck J. Amer. Chern. Soc. 1975,97,3527. 178 W.M.Horspool An 0x0-di-n-methane rearrangement yielding (72) has been reported from the triple t-sensi tized pho to1 ysis of 2,2,7,7-te trame t h ylcyclo hep ta-3,5 -dien- 1-one .69 Direct irradiation of this dienone yields 2,7-dimethylocta-2,4,6-triene the product of decarbonylation. Population of the S (nn*)state by irradiation of the dienone at 254 nm also yields (72) (from the TI,nn* state) and the triene (from S1 nn*state) but two additional products (73)and (74) are also formed from the upper (S,) (72) (73) (74) Decarbonylation is also found on photolysis of the squaric acid derivative (75).The decarbonylation yields (76a) which is readily desilylated to the deltic acid (76b).70 Other 1,2-dicarbonyl compounds have also been studied particularly where they are known to undergo hydrogen-abstraction reactions. Ogata and Me,SiO OSiMe (75) (76) a; R = SiMe b;R=H Takagi7' recently published results which suggested that a photo-enol was involved in the photochemical conversion of the diones (77) into the hydroxyindanones (78). Hamer7* has suggested however that a triplet biradical (79) is involved in this conversion and by the use of SO as a radical trap (SO2 is a poor dienophile and would not capture the photo-enol) has isolated the adducts of this biradical from the photolysis of the dione in the presence of SO,.R R (77) R = H or Me (78) (79) Research has continued on the photochemical generation of nitrile ylides from azirines. Padwa and Carl~en~~ have examined the photochemistry of the substituted azirines (80) and have observed that the products (81) formed are the result of 1,l-addition. The suggest that molecular constraints prevent the normal addition of the ylide intermediate to the olefin. However rehybridization as 69 J. Eriksen K. Krogh-Jespersen M. A. Ratner and D. 1. Schuster J. Amer. Chem. Sac. 1975,97,5596. 70 D. Eggerding and R. West J. Amer. Chem. SOC.,1975,97 207.71 Y. Ogata and K. Takagi Bull. Chem. SOC.Japan 1974,41,2255;J. Org. Chem. 1974,39 1385. 72 N. K. Hamer J.C.S. Chem. Comm. 1975,557. 73 A. Padwa and P. H. J. Carlsen J. Amer. Chem. SOC.,1975 97 3862. Photochemistry suggested by Salem,74 would permit addition of a bent ylide to the isolated double bond. Interestingly this carbene-like addition takes place with the inversion of the Ph fl H' P(0Et) phYN ;y R' R2 NXo RT+ (82) a; R' = RZ= Me R 1-R2 (80)a; R' = R2 = H R' R2 R2 b; R' = H; R2 = Me b; R' = H; R2 = Ph c; R' = Me;R2 = H (81) c; R' = H; R2 = Me (83) geometry of the rr-system. Schmid and his co-worker~'~ have extended further the scope of the addition of nitrile ylides from the azirines (82) and have studied the addition to diethylbenzoylphosphonate,yielding (83).The addition is regiospecific but not stereospecific. The photoreaction (at 350 nm) of the betaine (84)in ethyl acetate yields a valence isomer (85) and a dimer (86) as the primary photo product^.^^ 00-P T0 03. ) F \+ N N Ph Ph ; NPh H H (84) (85) (86) 74 L. Salem J. Amer. Chem. Soc. 1974,% 3486. ?5 N. Gakis H.Heimgartner and H. Schmid Helv. Chim. Acta 1975 58 748. 76 A. R. Katritzky and H. Wilde J.C.S. Chem. Comm 1975 770.

ISSN:0069-3030    

DOI:10.1039/OC9757200167

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

9 Aliphatic Compounds Part (i) Hydrocarbons By D. R. TAYLOR Department of Chemistry University of Manchester Institute of Science & Technology Manchester M60 1 Acetylenes The chemistry of alkynylarsines' and nitroacetylenes* and the addition reactions of dialkylaluminium hydrides including those to acetylene^,^ have been reviewed. New catalysts which promote coupling between relatively unreactive halides and acetylenes under mild conditions will make the synthesis of mono- and di-substituted For example CUI(P~~P)~P~C~ acetylenes ea~ier.~ catalyses the reaction of phenylacetylene and bromobenzene to give tolan in diethylamine. Diyne synthesis has also been advanced by the report of a simple procedure for making the trialkylsilyl-protected terminal diynol (1) and the corresponding 5-halides (2) from 1,4-dichlorobut-2-yne5 (Scheme 1).ClCH,C-'CCH,Cl A H[C-C],CH,OSiMe A Me,Si[C-C],CH,OSiMe J. 111 Me,Si[CrC],CH,X Me,Si[CrC],CH,OH Reagents i. NaNH, (CH,O), Me,SiCI; ii EtMgBr Me,SiCI; iii acid; iv SOCI (X = C1) or PBr (X = Br) Scheme 1 Excellent yields of long-chain (up to G4)a,w-terminal diynes can now be achieved using improved techniques for handling lithium acetylide e.g. in hexamethylphosphoramide-THF.6 Lithium alkynides and reactive 1-chloroalkynes have been generated by a route which avoids the parent acetylene it starts with a Wittig-Horner reaction (Scheme 2) and is easily adapted to a molar scale prepara- tion.' Acetylenic dianions are also useful starting materials for syntheses.For example propyne can be dilithiated and then by treatment with first one and then I. N. Azerbaev Z. A. Abramova and Yu. G. Bosyakov Russ. Chem. Rev. 1974,43 657. R. B. Rall A. I. Vil'davskaya and A. A. Petrov Russ. Chem. Reu. 1975 44 373. E. Winterfeldt Synthesis 1975 617. K. Sonogashira Y. Tohda and N. Hagihara Tetrahedron Letters 1975 4467; L. Cassar J. Organo-metallic Chem. 1975,93 253; H. A. Dieck and F. R. Heck ibid. p. 259. 5 B. F. ales and D. R. M. Walton Synthesis 1975 390. W. Beckmann G. Doerjer E. Logemann C. Merkel G. Schill and C. Ziircher Synthesis 1975,423. J. Villieras P. Perriot and J. F. Normant Synthesis 1975. 458. 181 182 D. R. Taylor RCHO A RCH=CCI RC-CX Reagents i (EtO),P(O)CCl,Li; ii Bu"Li -70°C (X = Li) or Et,NLi (X = C1) Scheme 2 another electrophile it can be converted into a variety of alkynes.' The dianion of but-2-ynoic acid undergoes mainly y-alkylation; subsequent esterification and alkylation of the conjugated triple bond therefore provides a means for stereospecific isoprenoid homologation as for example in the synthesis of nerol (Scheme 3).9 Reagents i R,NLi THF-HMPA; ii Me,C=CHCH,Br; iii MeI; iv LiCuMe, MeCu; v AlH Scheme 3 The conversions of lithium 1-alkynyltrialkylboratesinto ketones and disubstituted acetylenes were noted in an earlier Report;" more papers on these reactions have now emerged which include techniques for preparing tertiary alcohols11 and 1,l-dialkyl-'* and trialkyl-01efins.l~ The key step in all these methods is migration of one or more alkyl groups from boron to adjacent carbon followed by oxidative or electrophilic removal of boron (Scheme 4).R' R1 I I [RlBCECR2]Li -b R:BC=CR2R3 -% R'COCHR2R3 R2CH2CR$OH R:C=CHR2 R:CH=CR2R3 Reagents i R3Hal; ii H,O, NaOH; iii H,O+; iv I (R3 = H); v aq. HCl (R3 = H) Scheme 4 Suitable modification of the alkynyltrialkylborate can provide (i) a chloroalkynyl- borate which enables the conversion of 1,2-dichloroethylene into either symmetri- cally substituted alkynes or alkenes,14 (ii) lithium dialkyldialkynylborates,which are 8 S. Bhanu and F. Scheinmann,J.C.S. Chem. Comm. 1975,817. B. S. Pitzele J. S. Baran and D. H. Steinman J. Org. Chem. 1975,40 269. lo R. S. Atkinson Ann. Reports (B),1973,70 348. l1 M. M. Midland and H.C. Brown J. Org. Chem. 1975,40,2845. H. C. Brown A. B. Levy and M. M. Midland J. Org. Chem. 1975,40,5017. l3 A. Pelter C. Subrahmanyam R. J. Laub K. J. Gould and C. R. Harrison Tetrahedron Letters 1975 1633;A. Pelter K. J. Gould and C. R. Harrison ibid. p. 3327; G. Zweifel and R. P. Fisher Synthesis 1975,376. l4 K.Yamada N. Miyaura M. Itoh and A. Suzuki Tetrahedron Letters 1975 1961. Aliphatic Compounds-Part (i) Hydrocarbons 183 excellent precursors of symmetrical diynes,15 and (iii) dilithium ethynylbis(trialky1- borates) (3) which are obtainable from Li,C and act as a source of trans-disubstituted and tri- or tetra-substituted olefins16 (Scheme 5). yRCH=CHR CHCl=CHCI -+ [R,BC-CCI]Li RCrCR [R,BCrCBR,]Li 3RCH=CHR + R,C=CHR + R,C=CR (3) [RiB(CGCR2),]Li -$R’CrCCZCR’ Reagents i I, [O];ii H+ [O]; iii BrCN Me0 %heme 5 Further details have also emerged of the reactions of the promising new synthon catecholborane (4) with alkynes giving cis-alkeneboronic esters which are easily converted into ketones and cis-alkenes.” Alk-1-ynes react faster than internal acetylenes in which steric effects appear to dominate the regioselectivity of addition.The usefulness of hydroboration-mercuration of acetylenes which gives vinylmer- curials has been enhanced by the finding that the mercurials undergo smooth carbonylation with CO-PdC1,; the products are unsaturated acids of known geometry.l8 Such esters can also be obtained with improved stereochemical control by conjugate alkylation of acetylenic esters using polymeric copper complexes derived from lithium alkyls instead of conventional lithium dialkylcuprates.This technique was successfully applied to the synthesis of the juvenile-hormone analogue (5).19 ‘0 H (4) (5) The stereochemistry and mechanism of the acylation of acetylenes by RCOC1- AlC1 and by acyl triflates RCOOS02CF3 have been investigated.20 A four-centre cis-addition pathway predominates with electron-deficient acyl halides or triflates but otherwise acylation is almost wholly truns and intermediate vinyl cations are implicated because indenones and other rearrangement products arise. Surpris- ingly acylation by cycloalkanoyl tetrafluoroborates affords none of the expected cyclopentenones (6) but after formation of the vinyl cations a [1,5]hydride shift leads to the cycloalkyl cations (7) which in non-nucleophilic solvents are captured by fluoride ion giving the fluorides (8).21 l5 A.Pelter K. Smith and M. Tabata J.C.S. Chem. Comm. 1975 857. l6 N. Miyaura S. Abiko M. Itoh and A. Suzuki Synthesis 1975,669. l7 H. C. Brown and S. K. Gupta J. Arner. Chem. SOC.,1975,97 5249. la R. C. Larock J. Org. Chem. 1975,40 3237. l9 R. J. Anderson V. L. Corbin G. Cotterrell G. R. Cox C. A. Hendrick F. Schaub and J. B. Siddall,J. Amer. Chem. Sac. 1975,97 1197. zo H. Martens F. Janssens and G. Hoornaert Tetrahedron,1975,31 177. 21 A. A. Schegolev W. A. Srnit V. F. Kucherov and R. Caple J. Amer. Chem. SOC.,1975,97,6604. 184 D.R. Taylor f 1‘ The predilection of ynamines for [2 + 21 cycloaddition recurs in the synthesis of two relatively long-lived monomeric cyclobutadienes (10) which result when the cyclobutenyl cation (9) is deprotonated by sodium hydride.Cation (9) stems from the dimerization (catalysed by Lewis acid) of the ynamine RCICNEt (R = Ph or PhS).22 Et,N R R NEt (9) (10) The reactivity towards carbocations of acetylenes is comparable to that of similar- ly substituted trans-olefins (kcsc.kc=c = 0.4-3.2),23 a finding which echoes previ- ous data for ease of protonation. Protonation of alkynes with FS0,H has been studied in S02C1F and SO at low temperature^.,^ Terminal alkynes undergo syn :anti-addition in the ratio 4 1,but the strange result was that but-2-yne (7 1) behaves differently to hex-3-yne (1 1); both are believed to react via proton-bridged vinyl cations.Stereoselective cis-or brans-halogenation of alkynes can be achieved using respectively molybdenum penta~hloride~’ or cupric chloride.26 The regio- and stereo-selectivity of acetoxymercuration of acetylenes has been st~died.~’ The site of attack by AcOHg’ depends upon the chain length of the substituent groups but addition is always wholly trans. The astonishing superbase KNH(CH2)3NH2 has been termed the ‘acetylene zipper’ because it leads to virtually instantaneous migration of a triple bond from an internal to a terminal position.28 It converts tetradec-7-yne for example into tetradec-1-yne within seconds at 0 “C,even though the number of individual proton transfers must be enormous on a random-walk basis.22 R. Gompper S. Mensch and G. Seybold Angew. Chem. Internat. Edn. 1975,14 704. 23 F. Marcuzzi and G. Melloni Tetrahedron Letters 1975 2771. 24 G. A. Olah and R. J. Spear J. Amer. Chem. SOC.,1975,97 1845. 25 J. S. Filippo A. F. Sowinski and L. J. Romano 1.Amer. Chem. SOC.,1975 M 1599. 26 S. Uemura A. Onoe and M. Okano J.C.S. Chem. Comm. 1975,925. 27 S. Uemura H. Miyoshi K. Sohma and M. Okano J.C.S. Chem. Comm. 1975 548. 28 C. A. Brown and A. Yamashito J. Amer. Chem. SOC.,1975,97,891. Aliphatic Compounds-Part (i) Hydrocarbons 185 Terminal diynes and mono- or di-substituted acetylenes are codimerized catalyti- cally in a new general synthesis of indans and tetralins which can be qdapted to provide a variety of substitution patterns in the benzene ring (Scheme 6).29a!-Diynes also feature as substrates in cyclic oligomerizations with 24 molecules per diyne of butadiene over nickel catalysts.Simple sequences of reactions then lead to products of ring enlargement by from 8 to 16 carbon atoms; cyclotriacontane (C30&0) was synthesized for example .30 Reagents i (n-Cp)Co(CO),; ii H,O’ Scheme 6 Three different groups have reported instances of [2,3] sigmatropic shifts in propargyl compounds of oxygen and sulph~r.~’-~~ Two were base-initiated rear-rangements of anionic intermediates; more novel was that which occurred on pyrolysis of the sulphite (1 l),which yielded the new ring system (12)after the initial [2,3] shift (Scheme 7).33 In contrast base-initiated rearrangements of propargyl -0 RC=CCH R “0 (11) R = Bu‘ Scheme 7 ethers thioethers and amines have also been postulated to occur by prototropic shifts rather than [2,3] sigmatropy; there is also an unresolved dispute as to the exact nature of the primary 2 Alkanes Relevant reviews are those which discuss reactions of saturated hydrocarbons on membrane catalysts35 and progress in the specific activation of C,3-H The behaviour of alkanes on metallic and oxide catalysts continues to receive attention.Carbenes are definitely implicated in the cyclization of hexanes” to cyclopentanes on films of iridium gold et~.~~ The hypothesis that carbanionic species are involved in the D for H exchange reactions of alkanes adsorbed on 29 R.L. Hillard and K. P. C. Vollhardt Angew. Chem. Infernut. Edn. 1975,14,712. 30 W. Brenner and P. Heimbach Annalen 1975,660. 31 M. Hucht and P. Gresson Tetruhedron Letters 1975 367. 32 G. Pourcelot L. Veniard and P. Cadiot Bull. SOC.chim. France 1975 1275. 33 T. Beetz R. M. Kellogg C. Th.Kiers and A. Piepenbrock J. Org. Chem. 1975 40 3308. 34 P. J. Garratt and S. B. Neoh J. Amer. Ckm.SOC.,1975,97,3255; see also A. J. Bartlett T. Laird and W. D. Ollis J.C.S.Perkin I 1975 1315. 35 V. M. Gryaznov and V. S. Smirnov Russ. Chem.Rev. 1974,43,821. 36 Y. Mazur Pure Appl. Chem. 1975,41 145. 37 Z. Karpinski and J. K. A. Clarke J.C.S. Faruday I 1975 71 2310. 186 D.R. Taylor y-alumina has been confirmed and a Brsnsted relationship shown to hold.38 Rearrangements and hydrogenolysis of 13C-labelled pentanes on platinum-alumina are claimed to proceed via adsorbed cyclic and a,?-diadsorbed species; 13C n.m.r.spectra were not available.39 A modified procedure for photo-oximation of alkanes with NOCl led to the isolation of the initially formed oximes and revealed that attack at methyl groups competes effectively with abstraction of secondary CH's (relative reactivity of primary :secondary is between 3 and 10) even in acyclic alkanes. Thus 2,2,4- trimethylpentane gave 57% of (13) 24% of (14) and 19% of (15).40 (13) Phosphorus penta- and tri-chlorides are excellent catalysts for chlorination of alkanes and arylalkanes at room temperature in the dark in spite of their weak Lewis acidity. Since compounds such as cumene give over 90% side-chain chlorination an ionic pathway is ruled out in favour of a free-radical me~hanism.~~ 3 AUenes An attractive new method for converting propadiene into 1,3-dialkylallenes involves stepwise metallation and alkylation (Scheme 8).42 Other new methods include the CH,=C=CHR' CH,=C=CH CH,=C=CHLi + +R~CH=C=CHR~ R'CH,CrCH Reagents i Bu"Li; ii R'X Scheme 8 displacement-rearrangement of propargylic esters with alkyl~oppers,~~ and the conversion of ketones into allenes via enol triflate~.~~ A fresh approach to the problem of the asymmetric synthesis of chiral allenes chose the optically active (at phosphorus) ester (16) as a substrate for the Wittig- Horner reaction.With ketoketens it gave optically active allenic esters (17).45 Propargylic displacement of a quaternized amine function by hydride ion was used in H Ph&O)(OMe)CH,CO,Me + Phs(O)(OMe)CHCO,Me -R 1161 PhWO*Me (17) 38 P.J. Robertson M. S. Scurrell and C. Kemball J.C.S. Furuduy I 1975,71,903. 3g F. Garin and F. G. Gault J. Amer. Chern. Soc. 1975,97,4466. 4O E. Miiller and A. E. Bottcher Chem Ber. 1975,108 1475. 41 G. A. Olah P. Schilling R. Renner and I. Kerekes J. Urg. Chern. 1974,39 3472. 4* G. Linstrumelle and D. Michelot J.C.S. Chem. Comm. 1975 561. 43 P. Vermeer J. Meijer and L. Brandsma Reu. Truu. chim. 1975 94 112; see also J. L. Luche E. Barreiro,J. M. Dollat and P. Crabbk TetruhedronLetters 1975,4615. 44 P. J. Stang and R. J. Hargrove J. Org. Chern. 1975,40,657.4s S. Musierowin A. Wrobliewski and H. Krawnyk Tetrahedron Letters 1975,437. Aliphatic Compounds-Part (i) Hydrocarbons 187 another asymmetric synthesis in this case of chiral allenic &alcohols the optical purity of which was monitored by means of a chiral lanthanide-shift reagent.46 The chiral heptatetraene (18) is now available being prepared by the base- catalysed isomerization of the isomeric dienyne (19),using (-)-mentholate as the base.47 Like most vinylallenes (18) undergoes Diels-Alder reactions; with N-phenyltriazolinedione it does so twice over yielding the spiro-adduct (20). 0. -=== <NPh 0 (20) Coupling reactions of a -bromo-allenes can lead to unsaturated allenes. For example they react with acetylenes in the presence of Cu' a reaction which has now been applied to the synthesis of naturally occurring allenediynes and related model compounds.Other reactive sites can advantageously be protected with trialkylsilyl groups (Scheme 9).48 Alternatively a-bromo-allenes undergo self-coupling with Me,SiOCH,CH=C=CHBr -$ HOCH,CH=C=CH[C-C],SiMe lii HOCH,CH=C=CH[CrC],H Reagents i H(C-C),SiMe, Cu,Br, Bu,N; ii NaOH MeOH Scheme 9 Cu' in DMF a very simple way to make bis-allenes; propargyl acetates apparently serve equally well as substrates in this reaction.49 Whereas base-catalysed rearrangement of tetra-alkynes of type [21; R =But X =S(CH,),S n = 1 or 21 in which the two halves of the molecule are well-spaced yields bis-allenes which dimerize internally to give heterocycles (22) similar treat- ment of tetra-alkynylethanes (21; R =But Ph or Me X = u-bond) affords mainly the (E)-and (2)-isomers of the trialkynylbutadiene (23) accompanied when R=Bu' and a one-molar ratio of PhLi is used by the remarkably unsaturated compound (24).50 Skatteba 1's synthesis of allenes via dihalogenocarbene addition to olefins con- tinues to find new applications.One of the most determined examples featured the stepwise insertion of three carbon atoms into the m-bond of bicyclobutylidene to give (25) (26) and (27)!51Cyclopropylallene (28) has also been prepared in this way from vinylcyclopropane; it rearranges above 300°C to (30) with E, ca. A. Claesson L. Olsson G. R. Sullivan and H. S. Mosher J. Amer. Chem. SOC.,1975,97 2919. 47 U.Modlhammer and H. Hopf Angew. Chem. Internut. Edn. 1975,14 501. 48 P. D. Landor S. R. Landor and P. Leighton J.C.S. Perkin I 1975 1628. 49 F. Toda and Y. Takehira J.C.S. Chem.Comm. 1975 174. 50 H. Hauptmann Tetrahedron Letters 1974,3589; 1975,1931. 5l L. K. Bee J. Beeby J. W. Everett and P. J. Garratt J. Org. Chem. 1975,40 2212. 188 D. R. Taylor RC-CCHCECR +IXIRC=CCHCECR RCrCC=C=CHR RCZCC=C=CHR (21) R (22) CH=CHR / \(RCrC),C=C CGCR (23) 50 kcal mol-’. Deuterium labelling showed that isomerization within the cyclo- propyl ring occurs 4-5 times faster than ring enlargement indicating the participa- tion of diradical (29) rather than a [1,3] sigmatropic shift.52 Electrophilic additions to propadiene are of interest because their orientations depend to an unusual degree upon the electrophile protons attack at a terminal carbon to give a vinyl cation whereas halogenonium mercurinium and sulphenium attack the central carbon presumably via stable bridged ‘onium’ ions (31) which are certainly detectable in superacid.Kinetic isotope effects the study of which has been so successful in probing the mechanism of allene dimerization have now been used + X /\ H,C-C=CH (31) + to confirm that (31) and not a genuine open-chain allylic cation (CH,CX=CH,) is involved in the addition of HOBr to pr~padiene.~~ These findings are reinforced by direct observation of the ion (31; X =HgMe) in the gas phase using ion cyclotron resonance mass ~pectrometry.~~ Allenes bearing electron-withdrawing substituents at C-1 are attacked nuc- leophilically at C-2 by organocuprates.When the reagent contains two different 52 W. R. Roth T. Schmidt and H. Humbert Chem. Ber. 1975 lQfI 2171. 53 W. R. Dolbier and B. H. Al-Sader TefruhedronLetters 1975 2159. 54 R. D. Bach J. Patane and L. Kevan J. Urg. Chem. 1975,40 257. Aliphatic Compounds-Part (i) Hydrocarbons 189 groups (R1R2CuLi) the group mainly transferred can be predicted from considera- tion of the sequences But > Ph > Pr' > Bun> Me > CECR. It adopts a position anti to the largest substituent at C-3.55 The regio- and stereo-selectivity of heterogene- ous catalytic semihydrogenation of allenes has been exhaustively studied confirming the expectation of a simple cis-1,2-hydrogenation governed mainly by steric Hence it is in theory possible to establish the absolute configuration of a chiral allene by catalytic semihydrogenation provided that the absolute configura- tion of the olefin produced can be determined.Oxidation of dissymmetric allenes by lead tetra-acetate also occurs stereospecifically (Scheme Me CPb(OAc) / OAc Me Pb(OAc) MeToA-+ MeC-C-C--H H HFi-H -* S(+) Me S(+) Me Me ACO/+H M~ \ Scheme 10 The reactions of allenes with carbenes (e.g. ref. 58) are unexceptional but their behaviour towards nitrenes was largely unknown until recent work on reactions between etho~ycarbonylnitrene~' and phthalimidonitrene6' and propadiene 3- methylbuta-l,2-diene and methyl 2-methylbuta-2,3-dienoate.It appears that the primary reaction mode even with ethoxycarbonylnitrene is by 1,2-addition to give alkylideneaziridines (32) which may isomerize thermally to oxazolines (33).C0,Et I N R2L1=CH2 (32) (33) An extraordinarily simple route to alkylidenecyclobutanes is available following the interesting observation that Lewis-acid-catalysed cyclodimerization of simple allenes and olefins occurs at room temperature. Nearly quantitative yields of the adducts (34) were obtained within a few minutes.6f Cyclopropylideneallenes react R4 55 K. Koosha J. Berlan M. L. Capmau and W. Chodkiewin Bull. SOC.chim.France 1975,1284,1291. 56 L. Crombie P. A. Jenkins and D. A. Mitchard J.C.S. Perkin I 1975,1081; L. Crombie P. A. Jenkins and J. Roblin ibid. p. 1090.57 R. D. Bach R. N. Brummel and J. W. Holubka J. Org. Chem. 1975,40,2559. 58 R. R. Kostikov V. S. Aksenov and I. A. D'yakonov J. Org. Chem. (U.S.S.R.),1974,10 2115; R. R. Kostikov I. A. Vasil'eva and Ya. M. Slobodin ibid. p. 2339. 59 E. M. Bingham and J. C. Gilbert J. Org. Chem. 1975,40 224. 60 R. S. Atkinson and J. R. Malpass Tetrahedron Letters 1975,4305. 61 J. H. Lukas A. P. Kouwenhoven and F. Baardman,Angew. Chem.Infernat. Edn. 1975,14,709;J. H. Lukas F. Baardman and A. P. Kouwenhoven Ger. Offen. 2 422 349 1974 (Chem. Abs. 1975,82 72 569). 190 D.R. Taylor straightforwardly in [2 +21thermal cycloadditions with electron-deficient acetylenes and give mainly spirocyclobutenes (35) .62 Attempts to catalyse this reaction with Lewis acids seem doomed to failure in view of the acid-catalysed rearrangement of such allene~.~~ Photochemical reactions of allenes are at long last receiving the attention they merit.Acetophenone-sensitized photolysis of propadiene yields an interesting range of products (37)to (41),which are presumed to arise via the planar triplet (36) formed by non-vertical triplet-triplet energy transfer (Scheme 11).64The dimer and trimers are not those obtained as major products thermally. H,C=C=CH ' fi+ 49 I (37) H PhCMe=CHCOMe + (39) (40) COMe Reagents i PhCOMe hv; ii C,H Scheme 11 The photochemically initiated isomerizations of 1,2-dial kylidenecyclo butanes (allene dimers) have been examined using deuterium and alkyl labelling to distin- guish the competing pathways.Ring-opening appears to display at least an 80% preference for conrotation but leads to a 2,2'-bisallyl biradical which rotates freely about the central bond.65 Thermal cycloadditions of ketens to allenes have received further attention. They are regioselective the central carbons of the keten and the allene are invariably joined but differently substituted allenes show different preferences for the other site at which ring closure shall occur and most give mixtures of isomeric alkylidenecyclobutanones (42) and (43). They are also stereoselective in that an R4 (42) (43) (R)-l93-dialkyla1lene gives only adducts with (R)-configuration at the new asym- metric centre (though usually mixtures of E-and 2-geometric isomers are 62 T.Sasaki S. Eguchi and T. Ogawa J. Amer. Chem. Soc. 1975,97,4413. 63 L.Fitjer Angew. Chem. Intenat. Edn. 1975 14 360. 64 H. Gotthardt and G. S. Hammond Chem. Ber. 1975,108,657. 65 P.A.Kelso A. Yeshurun C. N. Shih and J. J. Gajewski J. Amer. Chem. Soc. 1975 97 1513. Aliphatic Compounds-Part (i) Hydrocarbons 191 formed).6h These experimental features have been rationalized hitherto on the basis of a mechanism in which zwitterionic intermediates are first formed [e.g.(44)]; one must be cautious however since 1,3-diphenylallene and t-butylcyanoketen give only the (E)-isomers (43 and the major isomer is the more hindered one. This reaction bears the hallmarks of a concerted [,2 + ,2,] pathway.67 Bu' H 4 Olefins Relevant reviews noted are those covering synthetic methods,68 metathesis,6" catalysis of pericyclic reactions,70 reactions of metal atoms with ole fin^,^' Grignard-olefin reaction^,^^ ozon~lysis,~~ intermediates in oxidation of strained ~lefins,~~ addition reactions,75 and ammoxidation of pr~pene.'~ Some useful new techniques for olefin synthesis have appeared besides those involving alkynyltrialkylborates (see p.182). Organoselenides are involved in three of them perhaps the most elegant being a new route to very hindered olefins e.g. (46) via selenoketones (Scheme 12).77 The attraction of selenium seems to be its R1 R' N=N R' iii \ \ & \ R'A)Ph2 -+ C="=PPh C=Se / / R2 Se RZ/C=CPh2 R2 R2 1iv (46) Reagents i. Se. Bu;N 120°C; ii Ph,CN, 0°C; iii heat; iv R3R4C=Se Scbeme 12 66 M.Bertrand R. Maurin J. L. Gras and G. Gil Tetrahedron 1975,31,849; M. Bertrand J. L. Gras and J. Gore ibid. p. 857. 67 H. A. Bampfield P. R. Brook and W. S. McDonald J.C.S. Chem. Comm. 1975 132. 68 I. Fleming Chem. and Ind. 1975,449; A. H. Davidson P. K. G. Hodgson D. Howells and S. Warren ibid. p. 455. 69 R. J. Haines and G. J. Leigh Chem. SOC.Rev. 1975.4 155. 70 F. D. Mango Co-ordination Chem. Rev. 1975,15 109. 71 P. S. Skell and M. J. McGlinchey Angew. Chem. Znternat. Edn. 1975 14 195. '2 H. Felkin and G. Swierczewski Tetrahedron 1975 31 2735. 73 R. Criegee,Angew. Chem. Znternat. Edn. 1975,14,745. 74 V. V. Voronenkov Russ. Chem. Rev. 1975,44,333. 75 F. Freeman Chem. Rev. 1975,75,439. 76 I. M. Kolchin Russ. Chem.Rev. 1974,43 475. 77 T. G. Back D. H. R. Barton M. R. Britten-Kelly and F. S. Guziec J.C.S. Chem. Comm. 1975 539. 192 D.R. Taylor ease of elimination; the spontaneous decomposition of selenirans features in a method for converting trims- into cis-isome~s,~~ and facile syn-elimination of PhSeOH occurs in a route from halides to mono- and di-substituted olefins which commences with nucleophilic substitution by the anions PhSecHR or PhSe(O)CHR.79 Potassium selenocyanide can be used for stereospecific &oxygenation of epox-ides," a reaction also achieved with complete retention of geometry using the anion [CpFe(CO),]-uia acidification of the ring-opened alkoxide (47). Since virtually 100% cis-elimination occurs if the alkoxide (47) is heated it constitutes a common precursor for both cis-and trans-isomers of an olefin (Scheme 13)." H R2 'c=c' H Y R '/' \ H -L ..p-\/ R R2 -Fe R2 H // \ /H R'/c=c\R' (47) Reagents i NaCpFe(CO),; ii reflux THF; iii H,O'; iv 1-Scheme 13 A silicon analogue of the Wittig reaction involves the decomposition of a 2-hydroxyalkylsilane (48) instead of a phosphonium betaine.These silanes (48) are also common precursors for either geometric isomer of an olefin because exclusively syn -elimination occurs in basic conditions and exclusively anti-elimination in acid (Scheme 14).82 The method of producing the required silane (48) shown is a new one reported to be both regio- and stereo-~pecific.~~ Reagents i R,BH AcOH; ii 3-CIC6H,CO,H; iii LiRzCu -78°C; iv H,O+; v KH THF Scheme 14 78 D.Van Ende and A. Krief Tetrahedron Letters 1975,2709. 79 H. J. Reich and S. K. Shah J. Amer. Chem. SOC., 1975,97 3250. J. M. Behan R. A. W. Johnstone and M. J. Wright' J.C.S.Perkin I 1975 1216. 81 M. Rosenblurn M. R. Saidi and M. Madhavarav Tetrahedron Letters 1975 4009. 82 P. F. Hudrik and D. Peterson J. Amer. Chem. SOC.,1975,97 1464. R3 P. F. Hudrik D. Peterson and R. J. Rona J. Org. Chem. 1975,40 2263. Aliphatic Compounds-Part (i) Hydrocarbons In a reaction reminiscent of the behaviour of Grignard reagents towards esters an excess of triphenylphosphinemethylene has been found to convert a variety of carboxylic esters into 2-substituted p~openes.'~ An alternative route to such olefins effectively achieves the addition of propene to a C=C double bond using lithium prop-2-enyltrialkylborates (49) generated from propenyl-lithium (Scheme 15).85 Reagents i 9BBN; ii CH,=CMeLi; iii I Scheme 15 There is currently much interest in the stereoselective synthesis of dienes quite understandable in view of their importance as a structural unit in juvenile hor- mones,86 insect pheromone~,'~ and terpenoids.'8 One approach uses the Horner reaction of allylic phosphine oxides to overcome difficulties which arise in analogous Wittig reactions;" the intermediate hydroxyphosphine oxides decompose spontane- ously and need not be isolated.Direct conversion of allylic halides into 175-dienes without loss of stereochemistry is effectively promoted by Cu' in the presence of lithium dialkylamides.Hitherto the main product of such reductive coupling (e.g. over nickel carbonyl) was the (E,E)-isomer irrespective of starting material. Now (2,E)-farnesyl bromide (50) can be coupled to give the (E,Z,Z,E)-squalene (51).90 Corey's group have applied the (51) Nio-promoted allylic coupling to the synthesis of large-ring methylenecycloal- kanes?l but of more interest to-prostaglandin enthusiasts could be the discovery of a nickel complex which stereoselectively catalyses the conversion of butadiene and 84 A. P. Vijttewaal F. L. Jonkers and A. van der Gen Tetrahedron Letters 1975 1439. 85 N. Miyaura H. Tagami M. Itoh and A'. Suzuki Chem. Letters 1974,12 1411. R6 C. A. Hendrick W. E. Willy J. W. Baurn T. A. Baer €3. A.Garcia T. A. Mastre and S. M. Chang J. Org. Chem. 1975,40 1. 87 R. J. Anderson and C. A. Hendrick,J. Amer. Chem. Soc. 1975,97,4327; J. N. Labovitz C. A. Hendrick and V. L. Corbin Tetrahedron Letters 1975,4209; K. Mori M. Tominaga and M. Matsui Tetruhedron 1975,31 1846. 88 S. Tanaka A. Yasuda H. Yamamoto and H. Nozaki J. Amer. Chem. Soc. 1975,97 3252. 89 B. Lythgoe T. A. Moran M. E. N. Narnbudiry S. Ruston J. Tideswell and P. W. Wright Tetrahedron Letters 1975,3863. yo Y. Kitagawa K. Oshima H. Yamarnoto and H. Nozaki Tetrahedron Letters 1975 1859. 91 E. J. Corey and P. Helquist Tetruhedron Letters 1975 4091. 194 D.R. Taylor n-propylmagnesium bromide into 2-vinylcyclopentylmethylmagnesiumbromide (52) (Scheme 16).92Methylenecyclopentanes can be obtained from appropriate 1,4-and 1,S-dienes and catalytic amounts of trialkylal~minium.~~ (52) Reagents i Pr"MgBr (PPh,),NiCI,; ii CL-70 "C Scheme 16 A unique gap in the array of functional groups was closed by the discovery that long-lived olefinic diazonium salts can be prepared by two routes (Scheme 17).The double-bond substituents were so chosen that they either rendered the vinyl cations R'RZCCR3=NNHTos 6 R1R2C=CR3N R1R2C=CR3N=C=0 I Hal 1 iii c1 Me0 \C=CHNl 3 \C=CHN / / Ar Ar (53) (54) Reagents i AICl or SbCl,; ii NO' SbCI;; iii PhOMe (=ArH) R1 = RZ = C1 R3 = H; iv MeOH. Scheme 17 arising by loss of nitrogen unstable or stabilized the diazonium ion by resonance. Nucleophilic displacement of one or both @-halogens was possible giving further diazonium salts e.g.(53) and (54).94 One of the outstanding mechanistic problems still facing olefin chemists is that of the metathesis reaction. This is reviewed in the organometallic section (p. 125). There have been several physical organic studies of ionic halogenation of ~lefins.~',~~ Molybdenum pentachloride is proposed as a reagent for cis-chlorination of acyclic and cyclic olefins.26 Continuous n.m.r. monitoring of the addition of dry HCI to propene revealed that surface and gas-phase reactions were both first-order in olefin and third-order in HCl suggesting a slow step in which an olefin-HC1 complex collides with (HCl)2.97 Additions of perdeuterioacetic and deuterio- trifluoroacetic acids to norbornene and 7,7-dimethylnorbornene occur with very 92 H.Felkin L. D. Kwart G. Swierczewski and J. D. Umpleby J.C.S. Chem. Comm. 1975 242. 93 K. W. Eggar Annalen 1975,521. 94 K. Bott Chem. Ber. 1975,108,402. 95 For chlorination see Yu. A. Serguchev and V. P. Konyushenko J. Org. Chem.(U.S.S.R.),1975,11,463; W. M. Baluzov Ch. Duschek G. Just W. Pritzkow and H. Schmidt J. prakt. Chern. 1975,317 53. 96 For bromination see M. F. Ruasse and J. E. Dubois J. Amer. Chem. Soc. 1975 97 1977; E. Bienvenue-Goetz and J. E. Dubois J. Org. Chem. 1975,40,221;P. L. Barili G. Bellucci F. Marioni and V. Scartoni ibid. p. 3331. 97 M. J. Haugh and D. R. Dalton J. Amer. Gem. SOC.,1975,97 5674. Aliphatic Compounds-Part (i) Hydrocarbons high exo-selectivity (99.92-99.98'/0) and at rates sufficiently similar to exclude a concerted cis-addition which invariably occurs more slowly in 7,7-dimethylnorbornene.Nucleophilic capture by a rapidly equilibrating pair of classical cations was advocated as the best e~planation.~~ Hydroboration of unsaturated hydrocarbons has been advanced by the publica- tion of detailed papers on the use of 9-borabicyclo[3,3 llnonane (9BBN),99 thexyl- borane,'" and the newer catecholborane (4). l7 Trimethylamine N-oxide is useful as an especially mild reagent for the B-C cleavage step in hydroboration."' A new high-yield synthesis of ketones from olefins involves the versatile trialkylcyanobo- rates in which the cyanide's carbon becomes the terminus for electrophilically promoted migration of unhindered (i.e.not thexyl) alkyl groups (Scheme 18).If all R3 R2 R2 CF3 R3 R2 // I\ 1-1 R'-B -C=N:T&O -+ RI-B-C -+ RIB,c N 3 R2R3C=0 \ I-\ R3 (-OCOCF3 0-cII PN \ 2/ o=c CF3 \ CF3 Scheme 18 three alkyl groups are mobile trialkylcarbinols result; these two procedures are seemingly more convenient than carbonylation. lo2 Considerable progress has been made in catalysis of amine additions to olefinslo3 and dienes.lo4 If 2 1adducts are formed from dimes like isoprene such reactions are ideal for the synthesis of compounds like linalool (Scheme 19).lo5 Reagents i Bu"Li Et,NH; ii H,O,; iii AcOH. Scheme 19 Lithium reacts with ethylene in aprotic solvents if activated by naphthalene or biphenyl giving vinyl-lithium and 1,4-dilithiob~tane.'~~ Highly lithiated species are 98 H.C. Brown and K. T. Liu J. Amer. Chem. SOC.,1975,97,2469;H. C. Brown and J. H. Kawakami ibid. p. 5521. 99 H. C. Brown E. F. Knights and C. G. Scouten J. Amer. Chem. SOC.,1974,96,7765. loo H. C. Brown E. Negishi and J. J. Katz J. Amer. Chem. Soc. 1975,97,2791. lo* G. W.Kabalka and H. C. Hedgecock J. Org. Chem. 1975,40,1776. *M A. Pelter K. Smith M. G. Hutchings and K. Rowe J.C.S. Perkin Z 1975 129; A. Pelter M. G. Hutchings K. Rowe and K. Smith ibid.,p. 138. lo3 B. Akermark and J. E. Backvall Tetrahedron Letters 1975,819. Io4 R. Baker A. Onions R. J. Popplestone and T. N. Smith J.C.S. Perkin I 1975 1133; G. K. Noren J. Org. Chem. 1975,40,967. Io5 K. Takabe T. Katagiri and J. Tanaka Tetrahedron Letters 1975 3005.lo6 V.Rautenstrauch Angew. Chem. Znternat. Edn. 1975,14,259. 196 D. R. Taylor produced if lithium vapour is contacted with olefins or dienes,lo7 but more useful in synthesis are species generated from alkyl-lithium and olefins such as 1,3-dilithiopropene which reacts with n-butyl bromide for example to give undec-5- ene.lo8 The regioselectivity of the addition of Grignard reagents to terminal olefins varies from 99% attack at C-1 (Mg attached to C-2) by Bu'MgX to 100°/~attack at C-2 by PhMgX and can be correlated with the sum of the Taft u*values of the substituents R in R1R2R3CMgX.lo9 This work is part of a major analysis of organometallic additions to olefins. New evidence on ozonolysis paths has been obtained which explains away one of the main experimental challenges to the Criegee mechanism.Oxygen exchange between 180-labelled aldehyde and ozone occurs faster than other reactions of the aldehyde.'" This can explain how l80becomes incorporated into the peroxide bridge of an ozonide (55)when labelled aldehyde is added to the ozonolysis it enters as part of the ozone molecule! Some ingenious experimentation has shown that but- 2-yne and ozone produce an ozonide possibly (56) or (57) which is capable of 4\ /o\ 0 -0-C,p +O/ I1 MeC Me/c=c\ (55) \ Me epoxidizing olefins at -70 "C with almost complete (95-99%) stereospecificity." A polymer-bound peracid suitable for olefin epoxidation has been developed it did not appear to be explosive. Alkylamido-osmium trioxides are convenient reagents for czs-oxyamination of olefins.They are quite simple to make from osmium tetroxide and an amine and their initial adducts at the C=C bond are smoothly cleaved by lithium aluminium hydride. Acid-catalysed Diels-Alder reactions are emerging as a growth area. Correct choiceof catalyst can reverse the normal regioselectivity of the Diels-Alder reaction; thus without catalyst penta-l,3-diene adds to 1,5-dimethylbenzoquinoneto give (58) but in the presence of BF etherate the reaction gives exclusively (59) and at Io7 J. A. Morrison C. Chung and R. J. Lagow J. Amer. Chem. SOC., 1975,97,5015. 108 J. Klein and A. Medlik-Balan J.C.S. Chem. Comm. 1975 877. lO9 H. Lehmkuhl 0.Olbrysch D. Reinehr G. Schomburg and D. Henneberg Annalen 1975 145.G. Klopman and C. M. Joiner J. Amer. Chem. SOC.,1975,97,5287. 111 R. E. Keay and G. A. Hamilton J. Amer. Chem. Sm. 1975,97,6876. 11* C. R. Harrison and P. Hodge J.C.S. Chem. Comm. 1975,1009. lI3 K. B. Sharpless D. W. Patrick,L. K. Truesdale and S. A. Biller,J. Amer. Chern. Soc. 1975,97,2305. Aliphatic Compounds-Part (i) Hydrocarbons 0 OC.'14 An attempt has been made to rationalize these reversals by the frontier- orbital treatment.lI5 Such reactions are finding synthetic applications exemplified by the acid-catalysed additions of mesityl oxide and 3-halogenomesityl oxide to penta- 173-diene used in the elegant syntheses of damascone (60) damascenone (61) and edulan I1 (62).'16 An intriguing problem in the Diels-Alder reaction is the extent to which minot products arise by a stepwise path or by a concerted but non-allowed one.Interesting contrasts in results cloud the answer at present for example the [Z7Z-ZH,Jbutadiene (63) dimerizes to give besides the expected products [(64) and (65)]of em-and endo-concerted suprafacial-suprafacial addition some 10%of material arising by antarafacial addition to the ,2-component and identified as (66) and (67). These were considered to arise by the non-allowed pathway.'" On the other hand dimerization of the [E,E-2H,]pentadiene (68)gave only products of fully suprafacial I I D D D cycloaddition and it was concluded that no common intermediate existed between this reaction and isomerization of trans-1,2-bisprop- 1-enylcyclobutane (69) in which inversion dominates."s Z.Stojanac R. A. Dickinson N. Stojanac R. J. Woznow and Z. Valenta Canad.J. Chem.,1975,616; N. Stojanac A. Sood Z. Stojanac and Z. Valenta ibid. p. 619. 115 P. V. Alston and R. M. Ottenbrite J. Org. Chem. 1975 40 1111. 116 K. S. Ayyar R. C. Cookson and D. A. Kagi J.C.S.Perkin I 1975,1727; D. R.Adams S. P. Bhatnagat and R. C. Cookson,ibid. p. 1736. L. M. Stephenson R. V. Gemmer and S. Current J. Amer. Chem. Soc. 1975,97 5909. 11* J. A. Berson and R. Malherbe J. Amer. chem.Soc. 1975,97,5910. 198 D.R. Taylor Amongst many interesting developments in the study of the physical properties of olefins are reports on chirality in skewed dienes,'" the use of 13C-H coupling constants to distinguish cis-from trans-isomers,'20 and the use of mixtures such as Ln(fo~)~-C~F~ COzAg as shift reagents for a1 kenes without other functionality .* 21 N.m.r.studies have confirmed that the conformation of highly hindered tetra- alkylethylenes is 'geared' as in (70) with high rotational barriers leading to non-equivalen t a1 kyl groups. 122 c=c \./ \ ,I-/ ,c ; llp 0.Korver Rec. Trav. chim. 1975,94 125. 120 J. E. Anderson Tetrahedron Letters 1975,4079. D. F. Evans J. N. Tucker and G. C. de Villardi J.C.S. Chem. Comm. 1975,205. lZ2 D. S. Bomse and T. H. Morton Tetrahedron Letters 1975,781; R. F. Langler and T. T. Tidwell ibid.,p. 777.

ISSN:0069-3030    

DOI:10.1039/OC9757200181

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

9 Aliphatic Compounds Part (ii) Other Aliphatic Compounds By E. W. COLVIN Chemistry Department University of Glasgow Glasgow G12 8QQ 1 Carboxylic Acids The degree of acidity of carboxylic acids has been correlated' with their core- electron ionization potentials; a similar study2 of the proton affinity of esters has been reported. One of the biochemical functions of vitamin BIZ,in the form of its coenzyme is to isomerize acids such as p-methylitaconic (1) and a-methyleneglutaric (2) by reversible conversion of an apparently unactivated methyl group into a methylene group followed by incorporation of the latter into the backbone chain; Dowd3 has succeeded in performing this remarkable process in vitro,in an enzyme-free system (Scheme l),opening the way to a detailed study of the rearrangement mechanism unencumbered by the enzyme.C0,H (2) Scheme 1 Pyrolysis of the doubly labelled chiral ether (3) leads by way of an ene reaction followed by reductive elimination to a product containing a chiral methyl group of predictable configuration thus providing a new route4 to chiral acetic acid (Scheme J. S. Jen and T. D. Thomas J. Amer. Chem. Soc. 1975,97 1265. T. X. Carroll S. R. Smith and T. D. Thomas J. Arner. Gem. Soc. 1975,97,659. P. Dowd M. Shapiro and K. Kang J. Amer. Chem. Soc. 1975,97,4754. C. A. Townsend T. Scholl and D. Arigoni J.C.S. Chem. Comm. 1975,921. 199 200 E. W.Colvin 2). An efficient synthesis' of (R S)-[5-'sO]mevalonolactone' has been described as has an improved route6 to (3R S; 5S)-[5-3H,]mevalonic acid.OCD,OMe heat /D -+ 0 H0 C-C--T \ H Scheme 2 2 Lactones and Macrolides Based on the result of a synthesis7 of optically active avenaciolide from D-glucose the chirality of the naturally occurring enantiomer must be revised to (3aR ; 4R ; 6aR) as shown in (4);consequentially the configurational assignments of this entire series of fungicides are probably incorrect since they have all been related to avenaciolide itself. An efficient synthesis' of (R,S)-4-iso-avenaciolide has been described as have new routes to carolic acid' and the tetronic acids.1° (4) Pig liver esterase hydrolyses the diester (5) to the chiral half-ester (6);differential reduction with LiBH or diborane allows obtentionll of either (R)-or (S)-mevalonolactone (Scheme 3).The electronic rotatory strengths of the n -+ T* transition in saturated chiral y-and &lactones have been measured." Biosynthetic st~dies'~ on some sixteen-membered macrolides have indicated the involvement of butyrate as a four-carbon building block. I3Cn.m.r. spectral4 of J. W. Cornforth and R. T. Gray Tetrahedron 1975,31 1509. J. W. Cornforth F. P. Ross and C. Wakselman J.C.S. Perkin I 1975,429. R. C. Anderson and B. Frazer-Reid J. Amer. Chem. SOC.,1975 97 3870; see also H. Ohrui and S. Emoto Tetrahedron Letters 1975,3657. * R. E. Damon and R. H. Schlessinger Tetrahedron Letters 1975 4551. A. Svendsen and P. M. Boll Acta Chem. Scand. (B),1975,29 197. lo J. V. Greenhill M. Ramli and T.Tomassini J.C.S. Perkin I 1975 588. F.-C. Huang L. F. Hsu Lee R. S. D. Mittal P. R. Ravikumar J. A. Chan C. J. Sih E. Caspi and C. R. Eck J. Amer. Chem. SOC. 1975,9? 4144. l2 F. 5. Richardson and W. Pitts J.C.S.Perkin 11 1975 1276. I3 S. Omura A. Nakagawa H. Takeshima K. Atsumi J. Miyazawa F. Piriou and G. hkacs J. Amer. Chem. Soc. 1975,97,6600; S. Omura A. Nakagawa H. Takeshima J. Miyazawa C. Kitao F. Piriou and G. Lukacs Tetrahedron Letters 1975,4503 l4 J. G. Nourse and J. D. Roberts J. Amer. Chem. Soc. 1975 97 4584. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds 201 HO bo R-( -1 -* 1 "X ' Hb Me02C C0,Me Me0,C CO,H\ (5) (6) 0 S-(+ 1 Reagents i pig liver esterase; ii LiBH,; iii B2H Scheme 3 some macrolides have been determined as have the conformation and conforma- tional flexibility of inter ah the pikromycin aglyconesl' and erythronolide B.16 Methymycin (7) has yielded to an elegant total synthesis," as has the simpler vermiculine18(8).Data on the complexation reactions between alkali-metal cations and polyether hydroxy-acids such as monen~in'~ and grisorixin2' have been pre- sented; such organic species act as specific sodium- or potassium-ion 'pumps' transporting the ions across the lipid portions of cell membranes. The first synthesis of a macrotetrolide nonactin (9) has been achieved independently by two 0 "0 0 0 (9) Is H. Ogura K. Furuhata H. Kuwano and N. Harada J. Amer. Chem. SOC.,1975,97 1930. Ih R. S. Egan J. R. Martin T.J. Perun and L. A. Mitscher J. Amer. Chem. SOC.,1975,97 4578. S. Masamune H. Yamamoto SXamata and A. Fukuzawa J. Amer. Chem. SOC.,1975 97 3513. E. J. Corey K. C. Nicolaou and T. Tom J. Amer. Chem. SOC.,1975,97 2287. l9 E. M. Choy D. F. Evans and E. L. Cussler J. Amer. Chem. SOC. 1974,96 7085. P. Gachon G. Chaput G.Jeminet J. Juillard and J.-P. Morel J.C.S. Perkin ZZ 1975 907. 202 E. W.Colvin groups.21722 The structures of the polyether hydroxy-acid antibiotic mould metabo- lites alb~rixin,~~ and lonomycinZ5 have been solved by X-ray analysis lyso~ellin,~~ and the structure of antibiotic X-20626has been corrected by the same technique. 3 Functional Derivatives of Carboxylic Acids Spectroscopic evidence27 for the formation of diethylmalonic anhydride (Scheme 4) has been presented; i.r.absorption bands at 1980 and 1900 cm-'were observed the latter being slightly more intense. 0 Reagent :i dicyclohexylcarbodi-imide-CC1 Scheme 4 The E-enol of methyl acetoacetate obtainable in up to 15%yield by distillation of the ester at atmospheric pressure is estimated28 to be 10 kcal mol-' less stable than the H-bonded 2-isomer. A non-polar transition state (10) is proposedz9 for the decarboxylation of P-keto-acids in which the acid proton sits in a stable potential well during cleavage of the C-C bond; low isotope effects are therefore to be expected. An evaluation of kinetic deuterium isotope effects has produced a new transition-state for peracid olefin epoxidation characterized as (11).Ar' I 0-H-0 c=o (1 1) The Qiels-Alder adducts between nitrosocarbonylarenes and 9,lO-dimethylanthracene decompose in the presence of Ph3P to give aryl isocyanates in high yield; kinetic evidence has been presented3l supporting the involvement of free 21 J. Gombos E. Haslinger H. Zak and U. Schmidt Tetrahedron Letters 1975 3391; J. Gombos E. Haslinger A. Nikiforov H. Zak and U. Schmidt Monatsh. 1975,106 1043. 22 H. Gerlach K. Oertle A. Thalmann and S. Servi Helu. Chim. Acta 1975 58 2036. 23 M. Alltaume B. Busetta C. Farges P. Gachon A. Kergomard and T. Staron J.C.S. Chem. Comm. 1972,411. z4 N. Gtake M. Koenuma H. Kinashi S. Sato and Y. Saito J.C.S. Chem. Comm. 1975,92. 25 N. Otake M. Koenuma H. Miyamae S. Sato and Y. Saito Tetrahedron Letters 1975,4147.26 J. F. Blount and J. W. West J.C.S. Chem. Comm. 1975 533. 27 G. Resofszki M. Huhn B. Hegedus P. Dvortsik and K. KB16y Tetrahedron Letters 1975 3091. 28 R. Matusch Angew. Chem.Internat. Edn. 1975 14 260. 29 M. W. Logue R. M. Pollack and V. P. Vitullo J. Amer. Chem. SOC.,1975,97 6868. 30 R. P. Hanzlik and G. 0.Shearer J. Amer. Chem. Soc. 1975,97,5231. 3l J. E. T. Corrie G. W. Kirby and R. P. Sharma J.C.S. Chem. Comm. 1975,915. Aliphatic Cumpounds-Part (ii) Other Aliphatic Compounds nitrosocarbonylarenes (12) (Scheme 5) N-arylnitrosoimines (13) have now been prepared.32 / HNAr R-C \ ArN=C=O + Ph,PO NO (13) Scheme 5 Aliphatic thioacyl chlorides,33 a -sulphinyl P-oxo-thi~nesters,~~. and acetylene dicarbonyl have been synthesized and their properties studied.An improved liquid-phase to acyloxynitrates biologically deleterious con- stituents of photochemical smog has been described. An ab initio study of acyloxy cations (14) possible intermediates in Kolbe electrolysis has revealed38 that the isomeric dioxiryl cations (15) are the lowest energy species (Scheme 6). 0' [." \ HR-C / Of Rf + CO Scheme 6 The preparation and 'H and l3Cn.m.r. spectra of the acetoacetylium (16) and diacetoa~etylium~~ (17) ions have been reported; halogenoacetylium40 ions and some diacid-derived dications41 have also been studied. + + CH,COCH,CO (CH,CO),CHCO (16) (17) 32 T. L. Gilchrist M. E. Peek and C. W. Rees J.C.S. Chem. Comm. 1975,913 914. 33 G. Seybold Angew.Chem. Internat. Edn. 1975 14,703. 34 J. J. A. van Asten and R. Louw Tetrahedron Letters 1975 671. 35 A. J. Bridges arid G. H. Whitham J.C.S. Perkin I 1975 1603. 36 F. E. Herkes and H. E. Simmons J. Org. Chem. 1975,40,420;F. E. Herkes ibid. p. 423. 37 R. Louw G. J. Sluis and H. P. W. Vermeeren J. Amer. Chem. SOC.,1975,97,4396. 38 W. F. Maier and M. T. Reetz J. Amer. Chem. SOC. 1975,97,3687. 39 G. A. Olah A. Germain H. C. Lin and K. Dunne J. Amer. Chem. SOC.,1975,97 5477. 40 G. A. Olah A. Germain and H. C. Lin J. Amer. Chem. SOC.,1975,97 5481. 41 J. W. Larsen and P. A. Bouis J. Amer. Chem. SOC.,1975,97 6094. 204 E. W.Colvin 4 a-Amino-acids With the increasing natural occurrence of D-amino-acids a rapid method of establishing the absolute configuration of a new amino-acid is of obvious utility; such a method42 is seen in the conversion of the amino-acid into the pyrrolinone derivative (18) (Scheme 7) whose c.d.spectrum shows a negative wavelength extremum for a D-amino-acid and vice versa. * RCHCO + 0 0 Scheme7 Cram43 and continue to develop optically active cyclic polyether hosts which exhibit chiral recognition in complexation in solution with the enantiomers of primary amine and a-amino-acid ester salts as guests; in suitable cases total optical resolution can be achieved by chromatography. A new route45 to chiral a-amino- acids has been described in which a recyclable chiral induction reagent (S)-proline (19) is employed (Scheme 8). co Reagents i dicyclohexylcarbodi-hide ;ii NH Scheme 8 42 V.Toome S. De Bernardo and M. Weigele Tetrahedron 1975,31,2625. 43 G. Dotsevi Y. Sogah and D. J. Cram J. Amer. Chem. Soc. 1975,97,1259; G.W. Gokel J. M. Timko and D. J. Cram J.C.S. Chem. Comrn. 1975,394,444. 44 W. D. Curtis D. A. Laidler J. F. Stoddart and G. H. Jones J.C.S. Chem. Comrn. 1975 833 835. 45 B. W. Bycroft and G. R. Lee J.C.S. Chem. Comm. 1975,988. Aliphutic Compounds-Part (ii) Other Aliphatic Compounds 205 5 Amides and Peptides Tetrahedral Intermediates and Protonation Sites.-In one of the first Tetrahedron Reports Deslong~hamps~~ has given a full account of his stereoelectronic approach to tetrahedral intermediates in ester and amide hydrolysis in which the precise conformation of the intermediate hemi-orthoester or hemi-orthoamide controls the nature of the hydrolysis products the particular mode of breakdown reflecting the orientation of the lone-pair orbitals of the heteroatoms; other have supported and extended these concepts.Further of the A,,2 hydrolysis of benzimidate esters have been described. Acid-catalysed hydrolysis of "0-enriched benzarnide in a small but detectable amount of exchange implying the involvement of tetrahedral intermediates in such hydrolysis; the N+ correlation of nucleophilic reactivities has been shownso to apply to the reactions of nucleophiles with esters when explicit consideration of a tetrahedral intermediate is included. The first direct n.m.r. spectroscopic observationS1 of a potassium alkoxide adduct (20) of an amide has been reported; based on lineshapeanalysis a minimum lifetime of 2.3 s is deduced (Scheme 9).0 OK I CF,C // + EtC(Me),OK CF,-C-NMe, \ I NMe 0 I Me-C-Me I Et An example of arnide hydrolysis proceeding via an N-conjugate acid species has been detected5' in the acid-catalysed decomposition of N-nitroso-2-pyrrolidone; the preference for this particular pathway is ascribed to the cyclic amide structure rather than to the presence of an N-nitroso-group. A of the contribution of N-protonation to the overall acid hydrolysis of NN-dialkylacetamides has indicated not surprisingly that this route will predominate for amides of highly basic amines. While N-ammonioamidates undergo methylation at either 0 or N depending on whether the carbonyl group carries a methyl or a methoxyl substituent n.m.r.spectroscopic evidence54 has indicated that protonation occurs on N; in more acidic media dications are observed. General Properties 8nd Reactions.-The c.d. spectra of a-substituted &lactams may be to determine the configuration of the a-carbon atom. The 46 P. Deslongchamps Tetrahedron 1975 31 2463; see also P. Deslongchamps R. ChCnevert R. J. Taillefer C. Moreau and J. K. Saunders Canad. J. Chem. 1975 53 1601. 47 V. F. Smith and G. L. Schmir J. Amer. Chem. Soc. 1975,97 3171. 48 R. A. McClelland J. Amer. Chem. SOC.,1975,97 3177. 49 R. A. McClelland J. Amer. Chem. SOC. 1975 97 5281. so C. D. Ritchie J. Amer. Chem. SOC.,1975,97 1170. 51 G. Fraenkel and D. Watson J.Amer. Chem. SOC.,1975,97 231. 52 B. C. Challis and S. P. Jones J.C.S. Perkin IZ 1975 153. s3 A. Williams J. Amer. Chem. SOC.,1975 97 6278. 54 M. Liler and D. G. Morris J.C.S. Chem. Comm. 1975 93. ss H. Meguro T. Konno and K. Tuzimura Terruhedron Letters 1975 1309. 206 E. W.Colvin conformational states and biological of cyclic peptides have been reviewed as have rearrangement^^^ of penicillanic acid derivatives. The structure of a highly modified peptide althiomycin (2l),has been established5* by detailed spectral and degradative studies. 0 CH,OH 0 (21) Acid chlorides acylate secondary amides in non-polar solvents at moderate rates in the presence of a neutral scavenger for HCl such as activated molecular sieves.59 Exposure of NN-dichloroamides6' to sodium methoxide produces the correspond- ing methyl esters and nitrogen perhaps uia the sequence shown (Scheme 10).R'C //O + R20-+ R1C0,R2 + NC12 \ NCI I-.'- NCl -+CIN=NCI -''' N2 Scheme 10 The isoimide (22) is remarkably stable,61 possibly due to the nitrogen lone-pair electrons and the acetate function being trans. Further INDO configurational studies6*on the succinimidyl radical have been reported. AcO R2 )=Y' R' 6 Aldehydes and Ketones The inability of the Criegee ozonolysis mechanism to explain the observation that addition of 180-enriched aldehyde to an ozonolysis reaction resulted in some of the label turning up in the peroxide bridge of the ozonide has tended to invalidate this attractively simple mechanism (Scheme 11).It has now been that aldehydes undergo a rapid exchange reaction with ozone resulting in the case of 180-enriched 56 Yu.A. Ovchinnikov and V. T. Ivanov Tetrahedron 1975,31 2177. 57 R. J. Stoodley Tetrahedron 1975,31 2321. 58 B. W. Bycroft and R. Pinchin J.C.S. Chem. Comm. 1975 111. 59 L. M. Weinstock S. Karady F. E. Roberts A.M. Hoinowski G. S. Brenner,T. B. K. Lee W. C. Lumma and M. Sletzinger Tetrahedron Letters 1975 3979. 6o R. E. White and P. Kovacic J. Amer. Chem. SOC.,1975,97 1180. 61 A. F. Hegarty and M. T. McCormack J.C.S. Chern. Comm. 1975 168. T. Koenig and R. A. Wielesek Tetrahedron Letters 1975 2007. 63 G. Klopman and C. M. Joiner J. Amer. Chem. SOC.,1975,97 5287. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds H -4-0 '80 0-0 180-I Scheme 11 aldehydes in equilibration of the label into the ozone thus accounting for peroxide- bridge labelling by the Criegee mechanism.Ab initiio MO-LCAO-SCF calculation^^^ on the enol tautomer of malondial-dehyde have indicated that the energy potential of the intramolecular H-bond is of the double-well type (Scheme 12) with a barrier height of 11kcal mol-I rather than the partially bonded (23) which would have a single potential well. H H H (23) Scheme 12 The formaldehyde cation radical (24) isoelectronic with the well-characterized iminoxyl radical (25),has been detected65 and studied by e.s.r. spectroscopy; it behaves as a strong acid decay occurring by proton transfer (Scheme 13). H\ + H \ 0' + H,SO -+ HCO + H,SO H Scheme 13 64 G.Karlstrom H. Wennerstrom B. Jonsson S. ForsCn J. Almlof and B. Roos J. Amer. Chem. Soc. 1975,97,4188; see also A. D. Isaacson and K. Morokuma ibid. p. 4453. 65 S. P. Mishra and M. C. R. Symons J.C.S. Chem. Comm. 1975,909. 208 E. W.Colvin 13 Cn.m.r. spectra of a variety of conjugated enones have been analysed66 to provide a measure of the relative contributions of the valence-bond canonical structures. has extended his studies on the correlation between conjugate addition to and polarographic reduction of @-unsaturated ketones when radical anions are initially produced. Treatment of dibromide (26) under Reformatsky conditions68 gives the Favorsky rearrangement product (27) via the cyclopropanone (28) and not the oxyallyl zwitterion (29) (Scheme 14) casting some doubt on the necessity of oxyallyl 0 OZnBr 0-ZABr Ph,CHCH,CO,Me PhyA (27) Ph (29) Scheme 14 zwitterions in the Favorsky rearrangement.It has been suggested6’ that both radical and ionic mechanisms can operate simultaneously in the bromination of ketones so that the ratio of brominated products may not be a true measure of the relative proportions of the enols. A ~ynthesis’~ of 2-6-heneicosen-ll-one the principal component of the sex attractant of the Douglas fir tussock moth which is a severe defoliator of firs has been described. The sex pheromone of the German Cockroach 3,l l-dimethyl-2-nonacosanone has been prepared as a diastereoisomeric mixture.” The a! -diketone thioether (30) is the main volatile component72 of the anal scent-gland secretion of 0 both the male and female striped hyena; material was collected daily (from caged animals) with great courage.66 R. H. Levin and L. Weingarten Tetrahedron Letters 1975,611. 67 H. 0.House and P. D. Weeks J. Amer. Chem. SOC.,1975,97 2770 2778,2785. 6s H. M. R. Hoffmann and T. A. Now J.C.S. Chem. Comm. 1975,37. 69 V. CaIb and L. Lopez J.C.S. Chem. Comm. 1975,212. 70 R. G. Smith and G. D. Daves and G. E. Daterman J. Org. Chem. 1975,40 1593. 71 M. Schwartz J. E. Oliver and P. E. Sonnet J. Org. Chem. 1975,40 2410; A. W. Burgstahler L. 0. Weigel W. J. Bell and M. K. Rust ibid.,p. 3456. 72 J. W. Wheeler D. W. von Endt and C. Wemmer J. Amer. Chem. SOC.,1975,97,441.Aliphatic Compounds-Part (ii) Other Aliphatic Compounds 209 Reviews have appeared on the chemistry of of halogenomalondial- dehyde~,~~ and of the reactions of Grignard reagents with of vicinal polyketone~,~~ thiocarbonyl 7 Alcohols Full details have been given of the appli~ation~~ of the exciton chirality method7* for the determination of absolute configuration of vicinal glycols and amino-alcohols. Vicinal diesters show a preference for gauche oxygen functions with respect to the ethane backbone nearly as large as that shown by the parent diols; this conforma- tional preference is ascribed,79 at least in the case of erythro diesters to some intrinsic attraction related to electronegativity. A quantum-mechanical study" of the effects of alkyl substituents on the acidity or basicity of alcohols or amines has been described.Preferential complexation of one component of a binary alcohol mixture with calcium chloride or manganese chloride offers'' an attractive purification method; the alcohol with the longer chain is clearly favoured the degree of selectivity increasing with the difference in chain length between the competing components. Protonated chloromethyl alcohol (3l),a suggested intermediate in chloromethyla- tion with formaldehyde and HCl has now been observed8* by low-temperature n.m.r. spectroscopy (Scheme 15). + -CH,O + 2HC1 + ZnC1 + ClCH,OH ZnC1 (31) Scheme 15 8 Amines The absolute configurations of chiral sterically non-hindered primary and secondary amines can be determined by direct inspections3 of the sign of the longer-wavelength c.d.spectral bands of their neutral complexes with copper(I1). Chiral polyether host molecules capable of resolving racemic amine salts by specific molecular complexa- tion have been des~ribed.~~,~~ 'H Dynamic n.m.r. spectroscopy has provideds4 a general picture of the rotation-inversion dichotomy in alkyl-amines. If the barrier to nitrogen inversion is greater than that for isolated rotation about the C-N bond then the process having the lowest barrier that is available for equilibrating the '3 F. I. Luknitskii Chem. Rev. 1975,75 259. 74 C. Reichardt and K. Halbritter Angew. Chem. Internat. Edn. 1975 14 86. 75 M. B. Rubin Chem. Rev. 1975,75 177. 76 D.Paquer Bull. SOC.chim. France 1975 1439; see also R. Couturier D. Paquer and A. Vibet ibid. p. 1670. 77 J. Dillon and K. Nakanishi J. Amer. Chem. Soc. 1975,97 5409 5417. 78 N. Harada S. L. Chen and K. Nakanishi J. Amer. Chem. Soc. 1975,97,5345. 7y C. A. Kingsbury and C. R. Cowles J. Org. Chem. 1975,40 1302. 8o R. F. Hudson 0.Eisenstein and N. T. Anh Tetrahedron 1975,31 751. K. B. Sharpless A. 0.Chong and J. A. Scott J. Org. Chem. 1975,40 1252. 82 G. A. Olah and S. H. Yu J. Amer. Chem. SOC.,1975,97 2293. 83 F. Kerek and G. Snatzke Angew. Chem. Internat. Edn. 1975 14 109. 84 C. H. Bushweller,W. G. Anderson P. E. Stevenson and J. W. O'Neil J. Amer. Chem. Soc. 1975,97 4338. 210 E. W.Colvin environments of the alkyl substituents on carbon is simple rotation with no inversion; if on the other hand the barrier to inversion is lower than that for isolated C-N bond rotation the lowest-barrier process available for equilibrating such environ- ments involves concomitant C-N bond rotation and inversion at nitrogen.A general methodg5 for the conformational analysis of aliphatic hydrazines has been presented based on a direct correlation of the dihedral angle between the two electron lone-pairs with the split As of the n-orbitals obtained from photoelectron spectra. ‘H N.m.r. spectroscopic evidence has indicateds6 that the monoprotonated forms of 1,3-and 174-diamines exist largely as cyclic H-bonded species in which the added proton is attached to both amino-groups simultaneously. 173-Diaminopropane reacts with KH to give a new ‘superbase’ highly soluble in and stable towards excess amine which can accordingly be used as solvent for a variety of prototropic processes .87 N-Nitrosamines are biologically important owing to their extreme carcinogenic- ity.The solution chemistry of methyl(aceroxymethy1)nitrosamine (32) the acetate of the presumed carcinogenic metabolite cf dimethylnitrosamine has been studied;” the parent alcohol is highly unstable in aqueous solution transferring a methyl group to any suitable nucleophile thus mimicking its proposed metabolism. SeebachS9 has minimized handling procedures in his method for the a-alkylation of amines via nitrosamines by making the process ‘one-pot’. The energetic ordering of the molecular orbitals of nitrosamines has been determined” by photoelectron spectroscopy and quantum chemical analysis.9 Diazoalkanes Ab initio generalized V.B. and configurational interaction calculations have indi- cated” that the ground state of diazomethane is better represented as a singlet biradical (33) than as a zwitterion (34). H \ H \. + /C-N=N:H H/C-N=N 8s P. Rademacher Chem. Ber. 1975,108 1548; P. Rademacher and H. Koopman ibid. p. 1557. eb J. Hine and W. S. Li J. Org. Chem. 1975,40 1795. 87 C. A. Brown J.C.S. Chem. Comm. 1975 222. 8H P. Roller D. R. Shimp and L. K. Keefer Tetrahedron Letters 1975 2065. 89 D. Seebach andD. Enders Angew. Chem. Internat. Edn. 1975,14,15; Chem. Ber. 1975,108,1293. 90 D. R. Battiste L. P. Davis and R. V. Nauman J.Amer. Chem. Soc. 1975,97 5071. 91 S. P. Walch and W. A. Goddard J. Amer. Chem. SOC. 1975,97 5319. Aliphatic Cbmpounds-Part (ii) Other Aliphatic Compounds The syntheses and reactivities of a-diazo-y-butyr~lactone~~ (35) and of a@-epoxydiazomethyl ketones93 (36) have been investigated and the chemistry of phosphoryldiazoalkanesy4(37) has been reviewed. 0 RACOCHN, R2P-CR II RR II 0 N2 The first example of a reversible photochromic valence between diazo-compounds- and diazirines has been described (Scheme 16). hv d -do R heat R Scheme 16 10 Alkyl Halides An n.m.r. spectroscopic inve~tigation~~ of the role of solvent in acyclic carbonium ion-cyclic halonium ion equilibria (Scheme 17) has indicated that cyclic halonium ions become relatively more stable as the solvent becomes less capable of nucleo-philic solvation.The numerous literature reports of increased stereoselectivity in electrophilic alkene halogenations in non-polar solvents and at low temperatures serve as qualitative examples of this effect. Scheme 17 Olah" has detected both alkyl and aryl hydridohalonium ions (38) and methyl methylene halonium ylides (39)by n.m.r. spectroscopy; he has also written a booky8 on cyclic and acyclic halonium ions. + +-RXH Me-X-CH (38) (39) y2 A. Schmitz U. Kraatz and F. Korte Chem. Ber. 1975,108 1010. 93 P. M. M. van Haard L. Thijs and B. Zwanenburg Tetrahedron Letters 1975 803; A. C. Brouwer L. Thijs and B. Zwanenburg ibrd.,p. 807. 94 M. Regitz Angew.Chem. Internat. Edn. 1975 14 222. 95 E. Voigt and H. Meier Chem. Ber. 1975,108 3326. y6 S. P. McManus and P. E. Peterson Tetrahedron Letters 1975 2753. 97 G. A. Olah Y.Yamada and R. J. Spear J. Amer. Chem.SOC.,1975,97,680. 98 G. A. Olah 'Halonium Ions' John Wiley and Sons New York 1975. 212 E. W.Cblvin The precise structure and anchimeric intermediacy of halogeno-alkyl radicals continue to generate considerable controversy. Absolute rate constants99 for the reaction of the t-butylperoxyl radical with 1-bromo- and 1-chloro-2-methylpropane have provided kinetic evidence for anchimeric assistance in the abstraction of a hydrogen atom from these substrates. a-Bromo- and a! -iodo-carboxylate deriva- tives can apparently'" give rise to either a -halogenocarboxylate radicals (40) or rearranged P-halogeno-radicals (41); a -chloro-carboxylates form only the radicals (40) (Scheme 18).Hal = 1 or B y HalCH,COX H,CCOX + Hal- HalCHCOX (40) Scheme 18 It has been suggested'" that the species detected by e.s.r. spectroscopy on X-irradiation of isobutyl chloride or bromide in a [2Hl,]adamantane matrix at 77 K was not a P-halogeno-t-butyl radical (42) but was the t-butyl radical itself; the original authors in a full account'02 of their work do detect the disproportionation reaction shown in Scheme 19 but only at temperatures above 209 K. > 209 K BrCH,kMe -DCH,CMe + Me,C C,oD, (42) Scheme 19 The force-field method of conformational analysis has been successfully applied103 to alkyl halides.An alkyl perbromate (43) has been preparedlo4 (Scheme 20). AgBrO + Pr'Br -200c R Pr'OBrO 20"c MeCOMe (43) Scheme 20 11 Miscellaneous Force-field calculations105 on alkanethiols and thioethers have been described as have generalized V.B. descriptions of formaldehyde and formarnide.'O6 Synthese~"~ yy J. H. B. Chenier J. P.-A. Tremblay and J. A. Howard J. Amer. Chem. SOC.,1975,97 1618. loo R. J. Booth S. P. Mishra G. W. Neilson and M. C. R. Symons Tetrahedron Letters 1975 2949. Io1 D. Nelson and M. C. R. Symons Tetrahedron Letters 1975 2953. lo* R. V. Lloyd and D. E. Wood J. Amer. Chem. SOC.,1975,97 5986. Io3 A. Y.Meyer and N. L. Allinger Tetrahedron 1975,31 1971. Io4 K. Baum C. D. Beard and V. Grakauskas J. Amer. Chem. Soc.1975,97 267. *05 N. L. Allinger and M. J. Hickey J. Amer. Chem. SOC.,1975,97 5167. 106 L. B. Harding and W. A. Goddard J. Amer. Gem. SOC.,1975,97,6293,6300. lo7 B. W. Christensen and A. Kjaer J.C.S. Chem. Comm. 1975,784. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds of the chiral sulphimide (44) and sulphodi-imide (45) have been reported and the stability of NN-dialkylthiohydroxylamineshas been explored. log (44) (45) The relevance of the hard-soft acid-base theory to organic chemistry has been the subject of a review.lo9 log D. H. R. Barton S. V. Ley and P. D. Magnus J.C.S. Chem. Comm. 1975 855. Io9 T.-L. Ho Chem. Rev. 1975,75 1.

ISSN:0069-3030    

DOI:10.1039/OC9757200199

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

10 Aromatic Compounds By R. G. COOMBES Department of Chemistry The City University St.John Street London EC1 V 4PB 1 Introduction It has been suggested' that the contribution to the magnetic susceptibility component perpendicular to the molecular plane serves as a more reliable aromaticity index than that based on magnetic anisotropy or n.m.r. data and that high magnetic anisotropy does not necessarily imply aromaticity. The approach seems similar to that in more recent papers by Flygare and co-workers* than those cited where the importance of relating to a hypothetical localized model is also emphasized. A small advanced text on aromaticity3 is worthy of attention particularly for its laudable separation of experimental and theoretical aspects. The full details of the preparation of cyclo-octa[def]biphenylene have a~peared.~" This molecule which might be expected to have simultaneously olefinic aromatic and antiaromatic properties exhibits a marked paramagnetic ring shift indicative of the planar 4n7r rings but is thermally stable and seems to exhibit a high reactivity towards electrophiles.A related compound (1) has three linearly fused 4n7r rings is thermally stable and is diatropi~.~~ It is concluded that the application of the simple n.m.r. criterion of aromaticity to polycyclic systems is hazardous. The importance of the local aniso- tropic contribution to proton shieldings has also been emphasized this being held responsible for the observed shifts in paratropic [4n]annulenes.' R. Benassi P.Lazzeretti. and F. Taddei J. Phys. Chern. 1975,79,848. 2-(a)T. G. Schmalz C. L. Norris and W. H. Flygare J. Amer. Chem. SOC.,1973 95 7961; (b) T. G. Schmalz T. D. Gierke P. Beak and W. H. Flygare Tetrahedron Lerters 1974 2885. D. Lewis and D. Peters 'Facts and Theories of Aromaticity,' Macmillan London 1975. (a)C. F. Wilcox jun. J. P. Uetrecht G. D. Grantham and K. G. Grohmann J. Arner. Chern. SOC.,1975 97 1914; (b) C. F. Wilcox jun. and G. D. Grantham Tetrahedron 1975,31,2889. M. Barfield D. M. Grant and D. Ikenberry J. Amer. Chem. SOC.,1975,97,6956. 215 216 R. G. Coombes Details of the improved version of the MIND0 semi-empirical SCF-MO method (MIND0/3) have been published6 and the approach has been criticized.' A general rule of aromatic stability of non-alternant polycyclic conjugated hydrocarbons has been proposed' and supported by aromatic stability indices.The application of PMO theory to homoaromaticity has been developed,' and the paper contains a useful review of homoaromatic systems. Application of MIND0/3 to the homo- tropenylium cation" indicates a long homoconjugate linkage and deformation of the seven-membered ring leading to an energy gain of 3 kcal mol-I. Full details of the study of cyclobutenyl cations have appeared.'' The 1,3-diphenyl-2,4-di-R-cyclobutenyl cations (R =Ph Me or H) have negligible contributions from 1,3-~ overlap but greater overlap occurs for exclusively methyl-substituted cations. The parent cyclobutenyl cation (2) exhibits truly aromatic delocalization is the simplest homoaromatic system and has AG* = 8.4kcal mol-' for the ring-flipping process.N.m.r. data on symmetrically trisubstituted 1,3,5-trineopentylbenzenescan be consistently interpreted in terms of the predominance of a rotamer with all three neopentyl groups on the same side of the ring thus providing evidence for attractive steric effects amongst the alkyl groups.l* The barrier to rotation of the dimethylamino-group in NN-dimethyl-2,4-dinitroaniline(7.1 kcal mol-') is similar to that calculated for NN-dimethyl-4-nitroaniline,indicating little mesomeric interaction of the out-of-plane ortho-nitro-group. l3 N.m.r. measurement~~~ indicate that trans-stilbenes become more nearly coplanar if a vinylic hydrogen is replaced by deuterium whereas the corresponding cis-stilbenes differ little from one another.This suggests that a C-*H bond has a smaller steric requirement than a C-'H bond presumably due to the smaller vibrational amplitude. ESCA measurement^'^^ show that the carbon adjacent to a trifluoromethyl group substituted in a benzene ring is negative in agreement with earlier CND0/2 predictions and more surprisingly that the group donates electrons to the ring overall. The fact that this charge is localized at the ipso-position is suggested as an explanation of the apparent contradiction to chemical evidence. The use of the aryl fluorine atom as a probe for investigating electronic effects of substituents must involve some qualifications. 15' 19Fchemical shifts involve factors different from and of a different order of complexity to those encountered in the study of substituent effectson conventional chemical properties.One problem is their apparent sensitiv- ity to substituent-induced structural distortions which are not necessarily a function of substituent size. The earlier demonstration that linear free-energy relationships and the Hammond Postulate are incompatible [Ann. Reports (B),1973,70,74,392] has been expanded R. C. Bingham,M. J. S. Dewar andD. H. L0,J.Amer. Chem. SOC.,1975,97,1285,1294,1302,1307. J. A. Pople J. Amer. Chem. SOC.,1975,97,5306;W. J. Hehre ibid. p. 5308; cf. M. J. S. Dewar ibid.,p. 6591. 8 J. Kruszewski and T. M. Krygowski Canad. J. Chem. 1975,53,945. R. C. Haddon J. Amer. Chem. SOC.,1975,97,3608. lo R.C. Haddon Tetrahedron Lefters 1975,863. G. A. Olah J. S. Staral R. J. Spear and G. Liang J. Amer. Chem. SOC.,1975 97 5489. l2 R. E. Carter B. Nilsson and K. Olsson J. Amer. Chem. Soc. 1975,97,6155. l3 D. D. MacNicol Tetrahedron Leners 1975 2599. l4 P. J. Mitchell and L. Phillips J.C.S. Chem. Comm. 1975 908. l5 (a) S. A. Holmes and T. D. Thomas J. Amer. Chem. SOC.,1975 97 2337; (b)W. Adcock M. J. S. Dewar R. Golden and M. A. Zeb J. Amer. Chem. SOC.,1975,97,2198. Aromatic Compounds 217 in an important analysis by C. D. Johnson.16 It is noted that free-energy relation- ships are linear over very wide ranges and that selectivity is clearly independent of reactivity which may lead to the deduction that transition-state structure is indepen- dent of reaction rate; a conclusion which may also be drawn from isotope studies.The question remains of whether this deduction is correct or whether transition-state structures do vary but selectivity parameters and isotope effects fail to respond in the expected manner. The long-standing problem of the extent of dissociation of the triphenylmethyl dimer has been res01ved.l~ 2 Benzene Isomers Oxides and Homobenzenes Gas-phase electron-diffraction studies of the structures of benzvalene,lga and hexa -methyl prismane,186 hexaAuoroDewarbenzenel8‘and a microwave study” of pris- mane have been performed. A complete assignment of the fundamental vibrations of Dewarbenzene and benzvalene has been reported.20 Both molecules exhibit abnor- mal C=C stretching frequencies indicative of o-.rr interaction between the strained bridge bonds and the ?r-bonds.The first reports have appeared of bicyclopropenyl Cope rearrangements. Pyrolysis of (3a) gave (3b) which exists as two diastereomers2* Compound (3b) was mainly responsible for the rn-and p-xylenes observed amongst the products of the thermal aromatization of (3a). Compounds (4a) and (4b) also rearranged thermally to give (5a) and (Sb) respectively and the reverse of these reactions (5)+(4) R Ph Ph Ph Ph R MePh Ph Me Ph Ph (3) a; R’ = H R2 = Me (4) a; R = Me (5) a; R = Me b; R’ = Me R2 = H b;R=H b;R=H occurs photochemically.22 In the latter case however it seems that only a chair transition state is involved and that the product is the d,Z-isomer. Supporting evidence has been presented to confirm that thermal bicyclopropenyl to benzene rearrangements proceed via Dewarbenzene~.~~’~~ Chemiluminescence and kinetic techniques were used to identify 1,4-dimethyIDewarbenzeneas an intermediate in the aromatization of 3,3’-dimethylbi~yclopropenyl.*~ A study of the photochemical rearrangement of (5b) into 2,3,4,6- and 2,3,4,5-tetraphenyltol~enes~~ has clearly l6 C.D. Johnson Chem. Rev. 1975,75 755. l7 K. S. Colle P. S. Glaspie. and E. S. Lewis J C.S. Chem. Comm. 1975,266. l8 (a)R. R. Karl jun. and S. H. Bauer J. Mol. Structure 1975,25 1; (b)R. R. Karl jun. Y. C. Wang and S. H. Bauer ibid. p. 17; (c) K. L. Gallaher Y. C. Wang and S. H. Bauer ibid.,p. 35. l9 R. D. Suenram J. Amer. Chem. SOC.,1975,97,4869.*O D. W. T. Griffith J. E. Kent and M. F. O’Dwyer Austral. J. Chem. 1975,28 1397. 21 W. H. de Wolf 1. J. Landheer and F. Bickelhaupt Tetrahedron Leners 1975 179. 22 R. Weiss and H. Koelbl J. Amer. Chem. SOC.,1975,97 3224. 23 N. J. Turro G. B. Schuster R. G. Bergman K. J. Shea and J. H. Davies J. Amer. Chem. Soc. 1975,97 4758. z4 R. Weiss and H. Koelbl J. Amer. Chem. Soc. 1975,97 3222. 218 R. G.Coombes demonstrated that prismanes are not intermediates in the photochemical rearrange- ment either and the suggestion has been made22 that species analogous to (6) are important in both photochemical Cope and aromatization processes. (6) (7) (8) 1,4-TrimethyleneDewarbenzene,which remains intact at 300 "C has been prepared'' by the silver-ion-catalysed valence isomerization of 1,l'-trimethylenebicyclopropenyl(7) and in methanol as solvent trapping of the inter- mediate cation (8)was observed in support of the previously suggested mechanism for these reactions [Ann.Reports (B),1973,70,390].Further confirmation26 comes from capture by the solvent of the other proposed intermediate in the reaction of 1,l'-dimethylenebicyclopropenyl. 1,4-PentamethyleneDewarbenzene has been prepared by a similar method to that mentioned above and on thermal aromatiza- tion it gave the unexpected rearrangement product benzo~ycloheptene.~' Me (9) The syntheses and resolutions of the Dewarbenzene (9),28"the first optically active derivative of a valence-bond isomer of benzene and related compounds286,c have been reported.Compound (9) undergoes a remarkably high-yield photochemical conversion into the corresponding achiral prismane. Further examples of the unusually stable Dewarbenzene isomers of perfluorohexa-alkylbenzeneshave been prepared,29" and a detailed of the hexakis(pentafluoroethy1)benzenesystem shows that the equilibrium favours the Dewar isomer above 551 K. The application of MIND0/3 theory to the conversion of benzvalene into benzene suggests an extremely exothermic 'allowed' The photoreactions of benzvalene involve several unusual processes in which the extraordinary unreac- tivity of the benzvalene skeleton is notew~rthy.~' Hexakis(trifluoromethy1)-25 1. J. Landheer W. H. de Wolf and F. Bickelhaupt Tetrahedron Letters 1975 349; see also L. A.Paquette Synthesis 1975,347. 26 F. C. Peelan G. G. A. Rietveld I. J. Landheer W. H. de Wolf and F. Bickelhaupt Tetrahedron Letters 1975,4187. 27 J. W. van Straten I. J. Landheer W. H. de Wolf and F. Bickelhaupt Tetrahedron Letters 1975,4499. 28 (a) J. H. Dopper B. Greijdanus and H. Wynberg J. Amer. Chem. Soc.,1975,97,216; (b)J. H. Dopper B. Greijdanus D. Oudman and H. Wynberg Terruahedron Letters 1975,4297; (c) J. H. Dopper B. Greijdanus D. Oudman and H. Wynberg J.C.S. Chem. Comm 1975,972. 29 (a) M. G. Barlow R. N. Haszeldine and M. J. Kershaw Tetrahedron 1975 31 1649; (b) A. M. Dabbagh W. T. Flowers R. N. Haszeldine and P. J. Robinson J.C.S. Chem. Comm. 1975,323. 3O M. J. S. Dewar and S. Kirschner J. Amer. Chem. Soc.,1975,97,2932. 31 C.A. Renner T. J. Katz J. Pouliquen and N. J. Turro J. Amer. Chem. SOC.,1975,97,2568. Aromatic Compounds 219 benzvalene ozonide has been prepared32" and in contrast to the unsubstituted analogue is stable at room temperature. Photolysis of this compound to yield the syn-tetrakis(trifluoromethy1)cyclobutadiene dimer (10) involved the free cyc- lobutadiene which could be trapped by diethyl azodicarboxylate. Flash thermolysis of (1l) prepared by a route involving cycloaddition to the benzvalene also yielded (10) via the same intermediate cy~lobutadiene.~~' (10) R = CF (11) R = CF Prinzbach and co-workers have continued their studies of benzene oxides and related compounds. These have led to simple syntheses of ~treptamine,~~" 2-de~xystreptamine,~~' ~is-trithia-,~~" (f )-hy~samine,~~~ trans-a,a -dioxa-P -thia-,33d and trans -p -oxa-a,a-di thia- tris- a-homo benzenes33 (12a) (13 a) and (13 b) and two to trans-trioxatris-a-homobenzene(13c).The reaction of cis-trioxatris-u-homobenzene (12b) with hydrobromic acid has been as has the thermal isomerization of cis-triazatris-a-homobenzene to the 1,4,7-triazacyclonona-2,5,8-triene The cis -diazabis-a -homobenzenes undergo rapid 2a-27r valence isomerization to give 1,4-diaza[8]annulenes (14) and it appears that (14c) sustains a diamagnetic ring current in contrast to (14a) and (14 b) .34c R R \ / xvXNuN X- (12) a;X = Sx Y b;X=O (13) a; X = 0,Y = S (14) a; R = Ts b;X=S,Y=O b; R = C0,Me c;X=Y=O c;R=Me trans-Bishomobenzene is readily available35 by the reaction of dibromocarbene with 3-norcarene followed by methyl-lithium-promoted carbenoid cyclization and acid-catalysed ring opening of the resultant bicyclobutane (13 which also provides a preferred route to 2,3-homotropilidene by silver-ion-catalysed rearrangement.In 32 (0) Y. Kobayashi I. Kumadaki A. Ohsawa Y. Hanzawa and M. Honda Tetrahedron Letters,1975 3001; (6) ibid. p. 3819. 33 (a) R. Schwesinger and H. Prinzbach Angew. Chern. Internut. Edn. 1975,14,630; (6) H. Prinzbach R. Keller and R. Schwesinger ibid. p. 632; (c) S. Kagabu and H. Prinzbach ibid. p. 252; (d) H. Prinzbach C. Kaiser and H. Fritz ibid. p. 253; (e)H. Prinzbach R. Keller and R. Schwesinger ibid. p. 633; cf)H. Prinzbach and H.-W. Schneider Tetrahedron Letters 1975,3073.34 (a)L. Knothe and H. Prinzbach Tetruhedron Letters 1975,1319; (b) H. Prinzbach R. Schwesinger M. Breuninger B. Gallenkamp and D. Hunkler Angew. Chern. Internat. Edn. 1975 14 347; (c) H. Prinzbach M. Breuninger B. Gallenkamp R. Schwesinger and D. Hunkler ibid. p. 348. 35 R. T. Taylor and L. A. Paquette Angew. Chem. Internut. Edn. 1975,14 496. 220 R. G.Coombes contrast to previously known trans-a-homobenzenes the hexamethyl derivative undergoes reversible valence isomerization and skeletal rearrangement to (16) above 120°C presumably because of steric interaction between the cis-isopropylidene moieties.36 3 Benzene and its Derivatives General.-A useful review of the photosubstitution reactions of aromatic com- pounds has appea~ed.~' It has been pointed out that there is sparse evidence concerning the nature of the intermediates in phototransposition reactions of six-membered aromatic rings and that attempts to trace the bonding relationships of all six atoms should provide informative restrictions on the possible intermediates The immediate precursor of the 2 1photoadduct of maleic acid and benzene is the originally proposed bicyclo-octadiene (17) which is formed from the zwitterion (18) in unsensitized reactions.39 Heavy-atom solvents induce an alternative triplet pathway to (17).The conflicting reports on the photoaddition of furan to benzene have been largely rec~nciled,~~ and the proportions of adducts are dependent on the light source and the reactant concentrations.Compound (19) and its Cope- rearranged isomer are the major products with high concentrations of benzene if a 0 +&o 0-& (17) (18) (19) low-intensity near-monochromatic source (254 nm) is used. The fixed cis -diene 1,2-dimethylenecyclohexaneadds photolytically to benzene to produce the novel 1,4-1',3'-benzene adduct (20) and the 1,4-1',4'-add~ct,~l" whereas the latter type of adduct was the only one isolated from the reaction of benzene and cis-1,2- dihydrophthalic anhydride.416 The truns-diene 3-methylenecyclohexene gave only very low yields of unidentified product^.^^‘' Benzene has been forced to act as a dienophile towards hexachlorocyclopentadieneat 220-240 "Cunder extreme pres- sure (10000 atm) to give the 1,2-adducts (21).42 36 P.Binger and J. McMeeking Angew. Chem. Internat. Edn. 1975,14 371. 37 J. Cornelisse and E. Havinga Chem. Rev. 1975,75 353. 38 J. A. Barltrop and A. C. Day J.C.S. Chem. Comm. 1975 177. 39 D. Bryce-Smith R. R. Deshpande and A. Gilbert Tetrahedron Letters 1975 1627. 40 J. C. Berridge D. Bryce-Smith A. Gilbert andT. S. Cantrell J.C.S. Chem. Comm. 1975,611. 41 (a)J. C. Berridge D. Bryce-Smith and A. Gilbert Tetrahedron Leners 1975,2325;(b)N. C. Yang C. V.Neywick and K. Srinivasachar ibid. p. 4313. 42 W. Jarre D. Bieniek and F. Korte Angew. Chem. Internat Edn. 1975,14 181. Aromatic Compounds 221 (21) R' and R2 = H or C1 The first spirocyclopropabenzenes (22) have been ~ynthesized~~ by 1,3-dipolar cycloaddition of diazocyclopentadienes to cyclo-octyne and subsequent photofrag- mentation.Compounds (22a) and (22c) are thermally stable but (22b) rearranges to the 1-arylcyclo-octene rapidly at room temperature. The benzene ring has been subjected to further strain and the synthesis of cyclopropa[4,5]benzocyclobutene (23) has been acc~mplished.~~ (22) a; R = Ph b;R=H (23) c; R = p-BrC,H4 The new soluble catalyst q3-C3H,Co[P(OMe),] leads to specific cis-hydrogenation of arenes and pure all-cis-[2HJcyclohexane has been prepared for the first time by hydrogenation of [*H,]ben~ene.~~ Transition-metal catalysis is also involved in a new general of indans and tetralins by acetylene cyclization (Scheme 1). Reagents i (n-Cp)Co(CO,)-n-C,HI Scheme 1 The rate coefficient for reaction of phenyl radicals from phenylazotriphenyl- methane and benzene has been measured4' by a technique involving competition with N-(t-buty1)-a-phenylnitrone.The value of ca.lo5dm3 mol-* s-' suggests that the rate of decarboxylation of the benzoyloxy radical is considerably faster than previously assumed. Studies of the dependence of product ratios on temperature and on the addition of Cu" salts in the phenylation of 0-and p-dichlorobenzenes support the contention that the formation of the cyclohexadienyl radical inter- mediate may be reversible particularly when the incoming radical is ortho to a 43 H. Durr and H. Schmitz. Angew. Chem. Internat. Edn. 1975,14 647. 44 D. Davalian and P. J. Garratt J. Amer. Chem. SOC.,1975,97,6883;See also C. J. Saward and K.P. C. Vollhardt Tetrahedron Letters 1975 4539. 45 E. L. Muetterties M. C. Rakowski F. J. Hirsekorn W. D. Larson V. J. Basus and F. A. L. Anet J. Amer. Chem. Soc. 1975,97 1266. 4h R. L. Hillard tert. and K. P. C. Vollhardt Angew. Chem. Infernat. Edn. 1975 14,712. 47 E. G. Janzen and C. A. Evans J. Amer. Chem. SOC.,1975,97,205. 222 R. G.Coombes sub~tituent.~~ A variety of persistent cyclohexadienyl radicals have been generated by addition of some carbon- silicon- oxygen- and phosphorus-centred radicals to various sterically hindered aromatic Species(24) was stable for several days at room temperature. Bu Bu' (24) A preferable alternative to the Rosenmund reduction for aromatic acid chlorides has been described?' Their reactions with phospholens give arlyphospholenium salts which yield the corresponding aldehydes and phospholen oxides on hydrolysis.The reaction of acyl halides with lithium aryltrialkylborates readily available from the reaction of aryl-lithium with trialkylboranes produces the corresponding aryl ketones in high yields.51 The demonstration that N-tosyloxyphthalimide readily undergoes photolysis in aromatic solvents to give the N-arylphthalimides by a radical path has opened up a Gabriel-type route to primary aromatic amine~.~~ The Schiemann reaction does not involve prior dissociation of the fluoroborate anion but involves direct reaction of the anion probably with the singlet aryl cation (see p. 227).53An example of the unknown possibly aromatic benzochlorophenium ions (25) is implicated as an intermediate in the thermal dediazoniation of o-(@,p-dichloroetheny1)phenyldiazonium hexafluorophosphate to give chloro(o-chloropheny1)e thyne .54 (26) An interesting report is of the selective aliphatic hydrogen exchange in 2,4,6-tri- isopropyltoluene on treatment with deuteriated trifluoroacetic acid in carbon tetrachl~ride.~~ In addition to aromatic exchange the @-hydrogen atoms in the 4-isopropyl substituent only were exchanged and a mechanism involving exchange in the most stable tertiary carbonium ion (26) formed by oxidation was suggested.48 R. Henriquez and D. C. Nonhebel Tetrahedron Letters 1975,3855,3857. 49 D. Griller K. Dimroth T. M. Fyles and K. U. Ingold J. Amer. Chem. SOC.,1975,97,5526. 50 D.G.Smith and D. J. H. Smith J.C.S. Chem. Comm. 1975,459. 51 E.-I. Negishi A. Abrarnovitch and R. E. Merrill J.C.S. Chem. Comm. 1975 138. 52 J. I. G. Cadogan and A. G. Rowley J.C.S. Perkin I 1975 1069. 53 C.G.Swain and R. J. Rogers J. Amer. Chem. SOC.,1975,97 799. 54 G.A.Olah and Y. Yamada J. Org. Chem. 1975,40 1107. 55 A.Nilsson and K. Olsson Acra Gem. Scand. (B),1975,29,752. Aromatic Compounds 223 Electrophilic Substitution.-The kinetically controlled gas-phase reaction of the t-butyl cation with rn-xylene gives predominantly 1,3-dimethyl-4-t-butylbenzene, in contrast to the orientation observed in conventional Friedel-Crafts alkylati~n.~~ Photochemically induced nitrosation reactions of phenols and naphthols in neutral solution in the presence of sodium nitrite have been rep~rted.~' It is questionable whether this is due to the enhanced acidity of 2-naphthol on excitation to the excited singlet state producing a local increase in acidity which allows protonation of nitrite ion and consequent nitrosation of 2-naphthol at the 1-position.The presence of a cation radical under conditions appropriate to the side-chain chlorination of polyalkylbenzenes in acetic acid has been reported (twice!)'" and the involvement of such species in the side-chain process has been suggested. The high positional selectivity and the product distribution from for example 1,2,3,5- tetramethylbenzene is evidence against this hyp~thesis,~'" and detailed studies of the products have been interpreted in terms of ion pair involvement after loss of chloride ion from the cyclohexadiene intermediate.59b The full report6' of the nitration of $-cumene in aqueous sulphuric acid convinc- ingly demonstrates that selectivity may remain between positions in a molecule of similar steric requiremects but of different intrinsic reactivity when reaction is occurring at the encounter rate.The selectivity however was not found to be sufficient to require the presence of any intermediate involving attractive interaction prior to the Wheland intermediate. The rates of nitration of the acids Ph(CH,),SO,H indicate that the sulphonate anions are the reactive species in <98% sulphuric acid and that even when n =3 the sulphonate ion exerts a deactivating influence.61 Tertiary aromatic phosphine oxides [ArP(O)R,] react as their conjugate acids leading to metal ortho-orientation with considerable discrimination against para -substitution.62A rein~estigation~~" of the temperature dependence of the HR acidity scale has revealed that contrary to an earlier report the graph of -HR versus %H,SO does indeed become less steep with increasing temperature and hence the apparent qualitative difference from the behsviour of rate profiles for nitration disappears.A compilation of the extensive literature data on nitration reactions in aqueous sulphuric acid has been presented with rates extrapolated to similar reaction conditions.636 Nitration of p-t-butyltoluene in acetic anhydride yields inter alia the first characterized 1,2-adduct (27) presumably because of steric inhibition of nucleo- philic capture at the 4-po~ition.~~ The adducts (28) from 3,4-dimethylaceto- or benzo-phenone form the 2- and 5-nitro-derivatives in strongly acidic solution by 1,2- or 1,3-nitro shifts from the intermediate cyclohexadienyl cation which can be 56 P.Giacomello and F. Cacace J.C.S. Chem. Comm. 1975,379. 57 F. D. Saeva and G. R.Oh 3. Amer. Chem. Soc.,1975,97,5631. 58 J. K. Kochi Tetrahedron Letters 1974,4305; 1975,41. 59 (a)E. Baciocchi and G. Illuminati Tetrahedron Letters 1975,2265; (b)E. Baciocchi L. Mandolini and A. Patara ibid. p. 2268. 6o J. W. Barnett R. B. Moodie K. Schofield and J. B. Weston J.C.S. Perkin XI 1975 648. 61 R. B. Moodie K. Schofield and T. Yoshida J.C.S. Perkin XI 1975,788.62 E. Malinski A. Piekos and T. A. Modro Canad. J. Chem. 1975,53 1468. 63 (a)M. J. Cook N. L. Dassanayake C. D. Johnson A. R. Katritzky and T. W. Toone J. Amer. Chem. Soc. 1975,97,760; (b)A. R. Katritzky B. Terem E. V. Scriven S. Clementi and H. 0.Tarhan J.C.S. Perkin ZX 1975 1600; A. R. Katritzky S. Clementi and H. 0.Tarhan ibid. p. 1624. 64 A. Fischer and R. Roderer J.C.S. Chem. Comm.,1975 798. 224 R. G.Coombes trapped by reactive arenes to give biphenyl derivative^.^' @so-Nitration and subse- quent nucieophilic capture is indicated in the observation66 of 2-cyclopropyl-4- hydroxytoluene amongst the products of nitration of 2-cyclopropyltoluene. Nuclear and side-chain nitrates have been isolated from the reactions of tetrachloro-o- and -p-xylenes respectively with fuming nitric Compound (29) is claimed as the first nuclear nitrate ester from nitration reactions.Bu' H OAc 0 (27) (28) (29) A thorough study of the nitration of pentamethylbenzene by impure nitronium hexafluorophosphate in nitromethane indicates two modes of nitration.68 The first involves the nitronium ion produced in the rate-limiting stage and the second involves attack by the incipient nitronium ion formed by oxidation by nitrogen dioxide of the molecular complex formed between the arene and the nitrosonium ion. Both processes form products uia ipso-substituted cT-complexes. Selective nitration can be achieved by electrophilic displacement of thallium(rr1) from aryl thallium(rII) trifluoroacetates with dinitrogen tetr~xide.~~ High proportions of p-nitroalkylbenzenes can be prepared in this way but arenes with substituents orienting thallium(1Ir) to the ortho-position failed to react.A study7' of the effect of nitrous acid on the nitration of 2,4-di-iodomesitylene and 2,4-di-iodo-3,5-dimethylanisole concludes that in the former case nitrodeiodination occurs whereas in the latter nitrosodeiodination and oxidation is the preferred pathway perhaps due to the greater aromatic reactivity of the substrate. The formation of 4-cyclopropyl-3-nitrobiphenyl as a significant product of nitration of 4-cyclopropylbiphenyl with no report of the 4,2-isomer may suggest a very large discrimination between ortho- and rneta-activation by the cyclopropyl gr~up.~' The prevalence of side-chain substitution in the sulphonation of 9-methyl- and 9,lO-dimethyl-anthraceneshas been inter~reted~~ in terms of loss of a proton from the 9-methyl group in the Wheland intermediate formed by electrophilic attack at the 10-position.Side-chain substitution however is not significant for nitration of toluene in acetic anhydride as has been believed.73 Considerable deviations from additivity on sulphonation of trimethylbenzenes have been inter~reted~~ in terms of 65 A.Fischer C.C. Greig and R. Roderer Canad. J. Chem. 1975 53 1570. 66 Yu. S.Shabarov,S. S. Mochalov N. B. Matveeva and I. P. Stepanova J. Org. Chem. (U.S.S.R.),1975 11 565. 67 H. Suzuki,K. Ishizaki S. Maruyama and T. Hanafusa J.C.S. Chem. Comm. 1975,5 1 ;Bull. Chem. SOC. Japan 1975,48,2112.6s E. Hunziker P.C. Myhre J. R. Penton and H. Zollinger Helv. Chim. Acta 1975,58 230. 69 B.Davies and C. B. Thomas J.C.S. Perkin I 1975 65. 70 K. Olsson Acta Chem. Scand. (B),1975,29,405. 71 S. A. Ermishkina S. S. Mochalov and Yu. S. Shabarov,J. Org. Chem. (U.S.S.R.),1975,11 369. 72 H. Cerfontain A. Koeberg-Telder C. Ris and C. Schenk J.C.S. Perkin 11 1975,966. 73 S. C. Narang and M. J. Thompson Austral. J. Chem. 1975,28,385. 74 H. Cerfontain A. Koeberg-Telder k. Ris and Z. R. H. Schaasberg-Neinhuis J.C.S. Perkin 11 1975 970. Aromatic Compounds 225 steric effects and the postulated early position of the transition state along the reaction co-ordinate compared with that for toluene. It has been ~uggested~~ that in non-catalytic bromination reactions the power- series rate equation is the mathematical equivalent of that expected from a conven- tional A-S,2 process in which the rate of the reverse of the first step becomes significant during the course of the reaction and need have no other special mechanistic significance.Evidence from uncatalysed para-bromination of N-methylacetanilide was interpreted in this way. from the diazo-coupling reactions of 4-substituted phenolate anions suggest that the methoxy-group activates the position meta to it to electrophile attack in contrast to the behaviour expected from its u+value. This was associated with the presence of a strongly activating substituent and the weak electrophilicity of the reagent. A new value of 'u+'for the metu-methyl substituent (-0.098) determined from the pyrolysis of 1-arylethyl acetates gives better correlations of electrophilic substitution reaction~.~~ Friedel-Crafts reactions involving alkanes and cycloalkanes have been ~eviewed.~' The catalysed alkylation of chlorobenzene by cyclopropane gives n-propyl- and isopropyl-chlorobenzenes.79The high proportion of rneta-substitution under some circumstances was presumably due to thermodynamic control.A kinetic study of Friedel-Crafts alkylation in n-hexane indicates that previous values had been affected by the heterogeneity of reaction solutions.8o The new results for toluene accord with the Brown Selectivity Relationship. The role of solvation energy in related reactions has been emphasized." The alkylation of benzene with t-butyl chloride in the presence of aluminium trichloride and a saturated hydrocarbon containing a tertiary carbon atom leads not only to t-butylbenzene but also to alkylation by a moiety derived from the saturated hydrocarbon.82 Nucleophilic Substitution.-Gas-phase reactions of fluorine-substituted aromatics with hydroxide and alkoxide ions have been interpreted in terms of two reaction pathway^.'^ The Meisenheimer complex can either lose fluoride ion to give the phenol or ether or can lose an alkyl fluoride or hydrogen fluoride to give the phenoxide ion.Short-lived radical species formed in reactions of para -substituted nitrobenzenes with nucleophilic reagents have been trapped by t-nitrosobutane to give nitroxide radical^.'^ The normally difficult formation of the complex (30)from aniline and trinitroben- zene is catalysed by the presence of a tertiary amine (e.g.DABCO)." Equilibrium and kinetic measurements on the formation of 1,l-dimethoxy-complexes from activated anisoles and sodium methoxide in the presence and absence of 18-crown-6 ether suggest that the sodium ion is normally associated with the anion by interaction 75 W. M. Schubert and J. L. Dial J. Amer. Chem. SOC.,1975 97 3877. 76 J. KuliE M. Titz and M. VekrB Coil. Czech. Chem. Comm. 1975,40,405. 77 E. Glyde and R. Taylor J.C.S. Perkin 11 1975 1463. R. Miethchen and C.-F. Kroger 2. Chem. 1975,15 135. 79 M. Khosrovi I. Partchamazed and M. Fakhrai Tetrahedron Letters 1975 2619. 8o B. J. Carter W. D. Covey and F. P.DeHaan J. Amer. Chem. Soc.,1975,97,4783. C. Decoret J. Royer and 0.Chalvet Tetrahedron,1975,31 973. 82 L. Schmerling J. Amer. Chem. SOC.,1975,97,6134. S. M. J. Briscese and J. M. Riveros J. Amer. Chem. Sac. 1975 97 230. 84 I. I. Bilkis and S. M. Shein Tetrahedron,1975,31,969. 85 E. Buncel and H. W. hung J.C.S. Chem. Comm. 1975 19. R. G.Coombes with the oxygen atoms of the C-1 methoxy-groups and the ortho-substituents.s6 In the presence of a crown ether in benzene solution trinitrobenzene gives Meisenheimer complexes with a number of anions some of which (e.g. F-) do not react in aqueous The anion from cyclohexanone reacts with 33-dinitrovenzoic acid and derivatives to form 2-and 4-substituted complexes.88 The more stable 2-complex is formed more quickly.The spiro-complex anion (31) has been spectrophotometrically observeds9 as an intermediate in the Smiles rearrange- ment of N-acetyl-@ -aminoethyl 2,4-dinitrophenyl ether and (32) is formed at -70 "C by the reaction of 4-(4-~hlorobutyl)biphenylwith lithium." n 0 NCOMe . I QN02. fj. I.-' NO* Ph (31) (32) A kinetic investigation of the displacement of halide from 0-and p-bromo- and p-fluoro-nitrobenzenes by thiophenoxide ion has shown that a crown ether consider- ably accelerates reaction in t-butyl alcohol but not in mefhan01.~~ This is interpreted in terms of nucleophile ion pairing in the former solvent. Phenoxide and thiophenoxide ions interact strongly with micelles of cetyltrimethylammonium bromide which also strongly catalyses reactions of these ions with 2,4-dinitroflu~robenzene.~' Thiophenoxide ion can rather surprisingly cause aryl- oxygen bond fission in competition with attack at the carbonyl group on reaction with some nitrophenyl The products of reaction of the ambident nitrite nucleophile with halogeno- nitrobenzenes are nitrophenols whether initial attack is by the oxygen or nitrogen centre.94 Nitrogen attack has been demonstrated and is preferred for displacement of C1 Br and I.Oxygen attack which is favoured for fluorine displacement is also 86 M. R. Crampton J.C.S. Perkin ZZ 1975 825. 87 A. R. Butler J.C.S. Perkin Z 1975 1557. A. Ashiaq V. MachiEek and V. Sterba Coll. Czech. Chem. Comm. 1975,40,1910. 89 S. Sekiguchi and K. Okada J. Org. Chem. 1975,40 2782.90 E. Grovenstein jun. and S. Akabori J. Amer. Chem. SOC.,1975,97,4620. 91 G. Guanti C. Dell'Erba S. Thea and G. Leandri J.C.S. Perkin ZZ 1975 389. 92 H. Chaimovich A. Blanco L. Chayet L. M. Costa P. M. Monteiro C. A. Bunton and C. Paik Tetrahedron 1975,31 1139. 93 G. Gaunti C. Dell'Erba F. Pero and G. Leandri J.C.S. Chem. Cumm. 1975,823. 94 T. J. Broxton D. M. Muir and A. J. Parker J. Org. Chem. 1975,40,2037 3230. Aromatic Compounds 227 enhanced more than nitrogen attack by transfer to a dipolar aprotic solvent. The ratios of rate coefficients for reactions of 6-substituted 2,4-dinitrochlorobenenes with aniline and N-methylaniline can be attributed to the steric effect of the substituent the ratio increasing with the size of the 6-s~bstituent.~~ The correspond- ing rates for the 4-substituted analogues show that the faster aniline reaction is subject to considerably larger substituent effects than the N-methylaniline reaction.An earlier transition state caused by a primary steric effect for the slower N-methylaniline reaction is suggested in apparent contradiction to the expectations of the Hammond Postulate. The specific catalysing effect of copper(1) salts exemplified in the displacement of iodide ion from 2-iodoazobenzene by cuprous cyanide or alkoxide has been attri- buted to ~helation.~~ The nickel-catalysed displacement reactions of aryl halides have also been in~estigated.~' Direct substitution by an alkyl group from an alkyl-lithium into a benzenoid ring can be achieved by carrying out the reaction with m-benzenetricarbonylchromium(0) and subsequently adding iodine to give the alkylben~ene.~~ The full report implicating the phenyl cation as the reactive intermediate in dispiacement reactions of phenyldiazonium salts in the absence of bases reducing agents or light has appeared,"" and this interpretation is supported by nitrogen isotope-eff ect measurements on the dediazoniation of phenyl diazonium boroflu~ride~~~ and by the largest secondary aromatic hydrogen isotope effect yet Ab initiu calculations suggest that the p-amino-substituent will stabilize a singlet phenyl cation but probably not to the extent that the ion would be expected to be formed in solvolytic reactions.loo The heterolytic dediazoniation of some substituted phenyldiazonium ions with halide ions in pyridinium polyhydrogen fluoride solution has been studied.The o-nitrophenyldiazonium ion gives isomeric chloronitrobenzenes (48% u- 44% rn- and 8% ps and these results were discussed1o1u partly in terms of the ambident nature of the diazonium ions."" Biaryk-Tris(triphenylphosphine)nickel(O) the presumed reactive species from the reagent tetrakis(triphenylphosphine)nickel(O) may now be conveniently gener- ated in situ by reduction of bis(triphenylphosphine)nickel(rI) dichloride with zinc in the presence of triphenylphosphine."* Treatment with aryl halides produces biaryls in good yields. The earlier method has been applied to a synthesis of cyclic ortho-bridged biphenyls with rings of up to 14 member^."^ Aromatic iodides couple readily when treated with a catalytic quantity of palladium(@ acetate in triethylamine or tri-n-butylamine at 100OC,'04 and rapid Ullmann couplings of 95 W.Eggiman P. Schmid and H. Zollinger Helv. Chim. Acfa 1975,58 257. 96 P. V. Roling J. Org. Chem. 1975 40 2421. 97 R. Cramer and D. R. Coulson J. Org. Chem. 1975,40,2267. 98 M. F. Semmelhack H. T. Hall M. Yoshifuji and G. Clark J. Amer. Chem. Soc. 1975,97 1247. 99 (a)C. G.Swain,J. E. Sheats and K. G. Harbison J. Amer. Chem. Soc. 1975,97,783; (b)C. G. Swain J. E. Sheats and K. G. Harbison ibid. p. 796; (c)C. G. Swain J. E. Sheats D. G.Gorenstein and K. G. Harbison ibid. p. 791. loo J. D. Dill and P. von R. Schleyer Tetrahedron Letters 1975,2857. Io1 (a)G.A. Olah and J. Welch J. Amer. Chem. SOC. 1975,97,208; (b)G. A. Olah and J. L. Grant ibid. p. 1546. *02 A. S. Kende L. S. Liebeskind and D. M. Braitsch Tetrahedron Letters 1975 3375. lo3 M. F. Semmelhack and L. S. Ryono J. Amer. am.SOC.,1975,97 3873. lo4 F. R. S. Clark R. 0.C. Norman and C. B. Thomas J.CS. Perkin I 1975 121. 228 R. G.Cbombes activated aryl halides at room temperature in homogeneous solution can be accom- plishedlo5 by reaction with copper(1) trifluoromethylsulphonate in aqueous ammoniacal acetone. Diarylthallium(m) derivatives are not as inert as previously believed and the trifluoroacetates are useful synthetic intermediates for the synth- esis of unsymmetrical biphenyls. '06 Conclusive evidence has been presented to rule out ionization as the process responsible for the dynamic n.m.r.behaviour of some 9-arylfluorenes. lo' Mechan-isms involving change of configuration at C-9 or intramolecular hydrogen shifts were discounted and all the evidence is consistent with simple hindered rotation about the aryl-C-9 bond. The two rotamers of 9,9':9',9"-terfluorenyl(33)formed on Michael addition of fluorene to 9,9'-bifluorenylidene have been assigned the s-cis,s-cis-and s-cis,s-trans-conformations.'08The bis(propel1ane) (34) has been ~ynthesized.'~~ Quinones and Related Compounds.-An authoritative collection of reviews of quinonoid chemistry has appeared. lo The microwave spectrum of o-benzoquinone is consistent with an essentially planar classical o-quinonoid structure in the gas phase."' Cerium(1v) oxide-hydrogen peroxide is a useful reagent for the conver- sion of phenols into hydroperoxycyclohexa-2,5-dienones.112a Diphenylselenic anhydride [(PhSeO),O] reacts with phenols under neutral conditions to give 0-and p-hydroxycyclohexadienones whereas with the phenolate anions only the ortho-orientation is observed. ''2b The N-chlorosuccinimide-triethylaminecomplex is an effective oxidizing agent for the conversion of catechols into o-quinones and hydroquinones into p-q~inones."~ Oxidative demethylation of 2,5-dimethoxybenzaldehyde by the silver(I1) oxide method was unsuccessful but the corresponding diacetate gave 1,4-benzoquinone aldehyde diacetate quantita- tively.' l4 Io5 T. Cohen and J. G. Tirpack Tetrahedron Letters 1975 143.lo6 E. C. Taylor H.W. Altland and A. McKillop J. Org. Chem. 1975,40 2351. lo7 W. T. Ford T. B. Thompson K. A. J. Snoble and J. M. Timko J. Amer. Chem. Soc. 1975,97,95. lo8 M. Minabe and K. Suzuki J. Org. Chem. 1975,40 1298; Bull. Chem. SOC.Japan 1975,48 1480. Io9 G. Wittig and W. Schoch Annalen 1975,600. ]lo 'Chemistry of Quinonoid Compounds' Part I ed. S. Patai Wiley Chichester England 1974. G. L. Blackman R. D. Brown and A. P. Porter J.C.S. Chem. Comm. 1975,499. lI2 (a)D. H. R. Barton P. D. Magnus and J. C. Quinney J.C.S. PerkinI 1975,1610; (b)D. H. R. Barton P. D. Magnus and M. N. Rosenfeld J.C.S. Chem. Comm. 1975,301. 113 H. D. Durst M. P. Mack and F. Wudl J. Org. Chem. 1975,40 268. D. V. Rao H. Ulrich and A. A. R. Sayigh J. Org. Chem. 1975 40 2548.Aromatic Compounds (35) (36) The singlet m-quinone (35) is s~ggested''~ as an intermediate in the oxidative decarbonylation of 2,4,6- tri- t -butylresorcinol to give 2,3,5-tri- t- butylcyclopentadienone. p-Quinones co-ordinated to palladium(0) show distinctive behaviour and in the case of p-benzoquinone its reaction with butadiene forms a complex (36)where two molecules of butadiene are cyclized across one double bond.' l6 Lewis-acid catalysis reverses the regiospecificity of the Diels-Alder addition of alkylated 1,4-quinones to certain substituted 1,3-dienes. 'I7 p-Benzoquinones undergo photochemical addi- tion to tetramethyl- or 1,l -dimethyl-allene to form 5-hydroxyindan-2-one deriva- tives by a mechanism involving subsequent rearrangement.ll8 The Thiele-Winter acetoxylation of a series of methoxyphenyl- hydroxyphenyl- and aryl-substituted p-benzoquinones has been studied.The acetoxy-group always enters ortho or para to the phenyl or aryl group and never ortho to the hydroxy- or methoxy-substituent. A related study involves analogues bearing both bromine and phenyl groups. 'lY6 Chloro-p-benzoquinone reacts with veratrole both in aqueous sulphuric acid'20a and in the presence of aluminium chloride'206 to give various triphenylene derivatives. The thermal behaviour of diazido- 1,4-quinones has been studied.'" The 2,5- and 2,6-compounds undergo a unique thermal cleavage via a cyclopentene- 1,3-dione intermediate to give the very reactive cyanoketens. The He(r1) photoelectron spectrum of p-quinodimethane formed by the flash vacuum pyrolysis of [2,2]paracyclophane has been observed and it indicates that the ground-state structure is that of a polyene.'22 Photodecarbonylation of 1,3-diphenylinden-2-one-substitutedmaleimide adducts gave the o-quinodimethanes (37) which undergo a thermal 1,5-sigmatropic shift of the imido-group rather than alkyl migration.'23a Compounds analogous to (37a) but with less than two of the sterically stabilizing phenyl substituents are unstable but undergo photochemical conversion into cyclobuta[3,4]cyclobuta[1,2]benzenes which revert to o-quinodimethanes on heating.1236 The intermediacy of the twisted and strained o-quinodimethane (38) is indicated in a study of the photochemical decarbonylation W.H.Starnes jun. D. A. Plank and J. C. Floyd J. Org. Chem. 1975,40 1124. 116 H.Minematsu S.Takahashi and N. Hagihara J.C.S. Chem. Comm. 1975,466. 117 Z. Stojanac R.A. Dickinson N. Stojanac R. J. Woznow and Z. Valenta Canad. J. Chem. 1975,53 617. N. Ishibe K. Hashimoto and Y. Yamaguchi J.C.S.Perkin I 1975 318. Ily (a)J. M. Blatchly. R. J. S. Green J. F. W. McOmie and S. A. Saleh J.C.S.Perkin I 1975,309;(b)J. F. W. McOmie J. B. Searle and S. A. Saleh ibid. p. 314. 120 (a)R.Buchan and 0.C. Musgrave J.C.S. Perkin I 1975 811; (6)ibid. p. 2185. lz1 D. S. Pearce M. J. Locke and H. W. Moore J. Amer. Chem. SOC.,1975,97,6181; W. Weyler jun. W. G. Duncan and H. W. Moore ibid. p. 6187. lZ2 T. Koenig R.Wielesek W. Snell and T. Balle J. Amer. Chem. Soc. 1975,97 3225.123 (a)D. W.Jones and G. Kneen J.C.S. Perkin I 1975 171; (b) ibid. p. 175. 230 R. G. Cbornbes of the methyl benzobicyclo[3,2,l]octen-8-one-3-endo-and -exo-~arboxylates.~~~ The isoindenes [e.g. (39)]previously proposed as intermediates in the photo- rearrangement of 1,l-diarylindenes have been directly observed by flash photo- lysis.12' (37) a; R' = R2 = Me b; R'-RZ = (CH,) A synthetically useful route to p-benzoquinone ethylene acetal the approaches to which were previously limited is provided'26 by the photolysis of 2-phenoxyethanol in the presence of mercuric oxide and iodine via 2-(p-iodophenoxy)ethanol. Diquinocyclopropanones are formed by oxidation of bis(hydroxyaryl(cyc1opro-penones from the reaction of trichlorocyclopropenium tetrachloroaluminate with the appropriate hindered phen01s.l~~" They undergo spontaneous decarbonylation to the corresponding cumulene derivatives (40).Compound (40c) dimerizes thermally to the tetraquinocyclobutane (4 1). R R .(I)=C=COO R R (40) a; R = Me b; R = Pr' C; R = Bu' (41) Cyclophanes.-The reaction involving thermal extrusion of sulphur dioxide to form ethano-bridges has been extended to give a new method for synthesis of medium and large hydrocarbon rings,128 and this has been applied to the synthesis of [4](4,4")-orthoterphenylophane. Some [2,2]cyclophanes are now much more readily prepared.12'" The experimental procedure for production of dithia[3,3]cyclophanes has been markedly improved and subsequent Wittig rearrangement to substituted [2,2]cyclophanes is a route to be preferred to that involving Stevens rearrangement.For paracyclophanes and metacyclophanes where 1,6-elimination is a possibility the conversion is best accomplished by the 'benzene-Stevens' route (Scheme 2).129b Iz4 D. S. Weiss J. Amer. Chem. SOC.,1975,97 2550. Iz5 J. J. McCullough and A. J. Yarwood J.C.S. am. Comm. 1975 485. A. Goosen and C. W. McCleland J.C.S. Chem. Comm. 1975 655. (a)R. West D. C.Zeder S. K. Koster and D. Eggerding J. Org. Chem.,1975,40,2295; (b)S. K. Koster and R. West ibid. p. 2300. F. Vogtle and J. Grutze Angew. Chem. Znternat. Edn. 1975,14 559. (a)R.H. Mitchell T. Osubo and V. Boekelheide TetrahedronLetters 1975,219; (b)T. Otsubo and v. Boekelheide ibid. p. 3881. Aromatic Compounds 231 Ph-S PhSO 1 to1 I -CHZ-S-CHz-Benzyne+ -CH-CH,-+ -CH-CH2-% -CH=CH-Scheme 2 A simple synthesis of [2,2,2,2]paracyclophane-1,9,17,25-tetraene from terephthalaldehyde and p-bisbromomethylberzene by a Wittig procedure has been rep~rted,'~' and the series of [2"]paracyclophanes has been extended131 to include n =5,6 and 8.Energies for the axial-equatorial conformational change of the ethylene bridge protons have been established for the series. Studies of a series of new disubstituted [2,2]paracyclophanes in which each ring bears one substituent have been carried out. 132 Spectral characteristics of such compounds were attributed to transannular electronic effects but no transannular directive effects were observed for the nitration of 4-cyano- or 4-acetyl-[2,2]paracyclophane.Tetra- and octa-fluoro[4,2]paracyclophanes have been prepared,'33 and comparison with the corresponding octafluoro[2,2]paracyclophane may indicate ring distortions in the latter with the increased proximity of the aromatic rings. A one-step synthesis of [nJmetacyclophanes(n= 8-12) and 2,6-pyridinophanes by nickel catalysis of the cyclocoupling of diGrignard reagents with aromatic dihalides has been rep~rted.'~~ A new preparative route to metacyclophanes (Scheme 3) can be applied even to [6]-and [7]-metacyclophane~.~~~ Various (42) Reagents i CHBr,-Bu'OK. Scheme 3 derivatives are then available via the (6 +n)-lithio[n]metacyclophane. Photolysis of (42) produces transannular products. Studies of transannular reactions of [2,2]metacyclophane have revealed'36 a new type of disproportionation reaction with aluminium chloride giving rise to hydropyrenes and pyrene.Metacyclo-polynuclear carbophanes can be synthesized by the transannular reaction of mul- tilayered metacy~lophanes'~~ [e.g. (43)-+(44) and (45)]. The quadruply bridged [2,2,2,2]( 1,2,4,5)cyclophane (46) has been re~0rted.l~~ Two bridges were formed I3O B. Thulin 0.Wennerstrom and H. E. Hogberg Acta Chem. Scad. (B),1975,29,138. 131 I. Tabushi H. Yamada and Y. Kuroda J. Org. Chem. 1975,40 1946. 132 H. Allgeier M. G. Siegel,R. Helgeson E. Schmidt and D. J. Cram J. Amer. Chem. Soc. 1975,97,3782. 133 R. Filler and E. W. Choe Canad. J. Chem. 1975,53 1491. 134 K. Tamao S.-I. Kodama T.Nakatsuka Y. Kiso and M. Kumada J.Amer. Gem. Soc. 1975,97,4405. 135 S. Hirano H. Hara T. Hiyama S. Fujita and H. Nozaki Tetrahedron,1975,31 2219. 136 K. Nishiyama K. Hata and T. Sato Tetrahedron,1975,31,239. 137 T. Umemoto T. Kawashima Y. Sakata and S. Misumi Tetrahedron Letters 1975,463. 138 R. Gray and V. Boekelheide Angew. Chem. Zntemat. Edn. 1975,14 107. R. G.Coombes (45) by the photochemical sulphur-extrusion procedure and two by transannular car- benoid insertion reactions. [2,2](2,7)Pyrenophane (47) and [2,2]( 1,3)pyrenophane (48) have been prepared by routes initially involving [2,2]metacyclophane deriva- tives and the formation of the pyrene structure by transannular ~eacti0n.l~~ Attempts14' to synthesize the triple-layered compound (49) produced the com-pound with structure (50).This may be formed via (49) if the strained inner benzene nucleus reacts intramolecularly as a dienophile with the anthracene nucleus. The triply clamped helical compound (51)has been prepared via the trithia-compound and Stevens rearrangement.I4l The two triphenylethane systems are fixed in propel- ler form but mutally displaced giving a new type of helically chiral molecular skeleton. 139 T. Umemoto S. Satani Y. Sakata and S. Misumi Tetrahedron Letters 1975 3159; T. Umemoto T. Kawashima Y. Sakata and S. Misumi Chem. Letters 1975 837. 140 T. Toyoda A. Iwama Y. Sakata and S. Misumi Tetrahedron Letters 1975,3203. l4I F.Vogtle and G. Hohner Angew. Chem. Internut. Edn. 1975 14,497. Aromatic Compounds Me I .C C I Me (49) (51) (50) 4 Molecular Rearrangements The Claisen rearrangement has been reviewed,14* as has the multiplicity of rear- rangement paths undergone by cyclohe~adienones.~~~ The naphthalenone (52a) rearranges in acidic acetic anhydride to give (53) in good yield the product of a 'forbidden' suprafacial [1,4] shift whereas it gives symmetry-allowed products arising from [3,4] and [1,5] shifts in aqueous sulphuric acid as does the allyl analogue (52b) under both sets of ~0nditions.l~~ The thermal rearrangement of (I?)-1- propenyl-2-naphthyl allyl ether to give (54) proceeds by a double [3s,3s] path no d y d;(eCH=CH2 \/ \/ I (52) a;X =H,Y =Me Me (54) b; X =Y =H or D (53) evidence for a sigmatropic [1,5s] allyl shift being Ally1 groups in some ortho-semibenzenes [e.g.(55)] rearrange so rapidly [to (56)]that it is not possible to isolate the former.146 This process involves a [3,3] sigmatropic shift rather than the radical-chain mechanism favoured with para-semibenzenes. 1,3-Benzyl migration in analogous compounds that are stable however presumably proceeds by the free-radical process. The Stevens rearrangement of benzyldimethylphenacylammonium ylide does not proceed by consecutive [1,4] and [1,3] shifts.'47 Stere~chemical'~~~ and quantitative CIDNP on the rearrangement of closely related ylides are compatible with two possible mechanisms (a) the generally accepted radical-pair mechanism but with an average geminate recombination which is extremely fast or (b) dual 14* S.J. Rhoads and N. R. Raulins org. Reactions 1975 22 1. 143 B. Miller Accounts Chem. Res. 1975 8 245. 144 B. Miller and M. R. Saidi Tetrahedron Letters 1975 1365. 145 M. Muelly J. Zsindely and H. Schmid Heiv. Chim. Acta 1975 58 610. 146 B. Miller and M. R. Saidi Tetrahedron Letters 1975 1691. S. H. Pine and J. Cheney J. Org. Chem. 1975 40 870. 148 (a)W. D. Ollis M. Rey I. 0.Sutherland and G. L.Closs J.C.S. Chem. Comm. 1975,543; (6)U. H. Dolling G. L. Closs A. H. Cohen and W. D. Ollis ibid. p. 545. 234 R. G.Coombes (55) R = H or Me (56)R = H or Me pathways involving concurrent radical-pair and concerted processes where the latter predominates. The extent (7%) of 1,2-phenyl shift in the triphenylvinyl cation during silver-ion- catalysed acetolysis of the corresponding bromide is similar to that observed during acetolysis of the t~iflate.'~~' The second example of a 1,2-hydride shift in a vinyl cation has been noted 1496 during the acetolysis catalysed by silver ion of cis-or trans-p-bromostyrene.The data again precluded the intermediacy of a hydrogen- bridged ion. The ratios of benzaldehyde to substituted benzaldehyde from the reactions of substituted benzhydryl azides with nitrosonium tetrafluoroborate and with substituted benzhydryl tetrafluoroborates are similar and provide confirmation that aldehyde products are formed from benzhydryl azide by a Curtius rearrange- ment with the benzhydryl ~ati0n.l~' There is steric interference to the aryl migration by the benzhydryl group.Products of the acid-catalysed rearrangement of N-acetylhydrazobenzene have been interpretedl'l in terms of the involvement of phenylnitrene in either the rearrangement or disproportionation reactions. These data are quoted in support of one variant of the controversial C-N diprotonation hypothesis [cf. Ann. Reports (B) 1972,69,263]. A kinetic study of the two-proton-catalysed rearrangement of hydrazobenzene to benzidine in moderately concentrated acid suggests that the second protonation may well be part of the rate-limiting No conclusion could be drawn from this work on the site of protonation. E.s.r. studies that cation radicals are involved in the mechanism of reductive scission of NN'-dimethylhydrazobenzenes which occurs concurrently with rearrangement.The rates of reactions proceeding by both one- and two-proton-catalysed mechanisms were enhanced by anionic micelles of Na' -O,SO(CH,) ,Me.'54 A kinetic study of the unusal Wallach rearrangement undergone by 2,2',4,4',6,6'- hexame thylazobenzene to 4- h ydroxyme t hyl- 2,2',4',6,6'-pen tamet hylazobenzene 149 (a)F H. A. Rummens R. D. Green A. J. Cessna M. Oka and C. C. Lee Canad. J. Chem 1975,53 314;(b) C.C. Lee and E. C. F. KO J. Org. Chem. 1975,40,2132. 150 M. P. Doyle D. M. Hedstrand S. C. Busman and D. Alexander,J. Amer. Chem. SOC.,1975,97,5554. 151 Z.J. Allan Monatsh. 1975,106 429. 152 C. A. Bunton and R. J. Rubin Tetrahedron Letters 1975 59. 153 J.-D. Cheng and H. J. Shine J. Org. Chem 1975,40,703.C. A. Bunton and R. J. Rubin Tetrahedron Letters 1975,55. Aromatic Compounds 235 has demonstrated the operation of two mechanistic pathways depending on solvent a~idity.’~’” One involves a dicatonic intermediate and the other a quinoid species. This dichotomy of mechanism has been further illustrated in conventional rearrange- ments in the azoxynaphthalene series. ”” Interestingly in moderately concentrated sulphuric acid both (57) and (58)yield (S9) the former via a quinoid intermediate and the latter via the dicationic mechanism.155c The rearrangement has been reviewed.lSsd The evidence concerning the mechanism of the Fischer-Hepp rearrangement of N-nitroso-amines has been discu~~ed.”~” The intramolecular nature of the rear- rangement process occurring concurrently with a reversible denitrosation reaction has been further demonstrated by studies of halide-ion catalysi~’’~~ and of the rearrangement :denitrosation ~atio.”~~ The latter study has yielded quantitative information on the efficacy of various nitrite traps.The denitrosation process in hydrochloric acid solution involves nucleophilic attack on the protonated nitro- samine and the rate is strongly dependent upon the nucleophile Denitrosation in sulphuric acid solution is not due to the hydrogen sulphate ion but both water and H30+ are suggested to be reactive entities. Protonated N-methyl-N- nitrosoaniline transfers a nitroso-group directly to thiourea without the intermediacy of a free nitrosating 5 Condensed Systems Resonance and localization energies of benzenoid hydrocarbons can,be obtained by an algorithm based on counting resonance structures and the results are in good agreement with those from highly parametrized SCF-LCAO-MO calculation^.^^^ It has been by the graph-theoretical approach that the early success of resonance theory rested on the fortunate fact that all KekulC structures for ben- zenoid hydrocarbons and acyclic polyenes have the same parity and a similar has yielded an explanation for the success of the theory for predicting relative rates of aromatic substitution.An index based on counting Kekul6 structures has been propo~ed”~ which describes the local benzenoid character of individual rings in condensed benzenoid hydrocarbons and which when summed over all rings indicates the degree of ‘benzenoidicity’ of the molecule.5-Methylene-l,2-benzocyclohexa- 1,3-diene (60) has been synthesized by the reaction of 3,4-benzotricyc10[4,1 ,O,O*”]heptene with v-allylpalladium(II) chloride dimer in chloroform.’60 It is sufficiently stable to permit isolation but in the pure liquid it undergoes valence isomerization to 2-methylnaphthalene at a moderate rate at room temperature. Substituted 1,2-dihydronaphthalenes can be synthesized in good yield by con- trolled gas-phase pyrolysis of the appropriate l-phenylbuta- l,3-diene.l6’ A route to lS5 (a)R. A. Cox and E. Buncel J. Amer. Chem. SOC.,1975,97,1871; (b)R. A. Cox A. J. Dolenko and E. Buncel J.C.S. Perkin fI 1975,471 ;(c) E. Buncel R. A. Cox and A.Dolenko Tetrahedron Letters 1975 215; (d)E. Buncel Accounts Chem. Res. 1975,8 132. lS6 (a)D. L. H. Williams Tetrahedron,1975,31 1343; (b)D. L. H. Williams Internut. J. Chem. Kinetics 1975,7,215; (c)D. L. H. Williams J.C.S. Perkin If 1975,655;(d)I. D. Biggs and D. L. H. William< ibid. p. 107; (e)D. L. H. Williams J.C.S. Chem.Comm. 1975 375. 157 R. Swinborne-Sheldrake W. C. Herndon and I. Gutman TetrahedronLetters 1975,755. 158 (a)J. Gutman N. Trinajstic and C. F. Wilcox jun. Tetruhedron 1975,31 143; (b)ibid. p. 147. lS9 M. Randic Tetrahedron,1975,31 1477. lM) I. Murata J. Nakazawa M. Kato T. Tatsuoka and Y. Sugihara Tetrahedron &tters 1975 1647. P. B. Valkovich J. L. Conger F. A. Castiello T. D. Brodie,and W. P. Weber J. Amer. Chern.Soc. 1975 97 901.236 R. G. Coornbes 3-substituted 1-methylnaphthalenes is provided by the reaction of substituted 1-methylindenes with dibromocarbene,'62 and the reaction of pentacar-bonyl[methoxy(phenyl)carbene]chromium(0) with diphenylacetylene yields the complex (61) in which the naphthol skeleton has been ~ynthesized.'~~ A new approach to functionalized naphthalene^'^^ involves the reaction of substituted benzaldehydes with the appropriate Grignard derivative followed by the cyclization (62) -+(63). Phenyl radicals react with dimethyl but-2-ynedioate to give tetramethyl n 00 H' OH naphthalene-1,2,3,4-tetracarboxylatevia intermediate styryl radi~a1s.l~~ A direct method for the preparation of substituted naphthalenes and naphthols from benzenes and conjugated ketones and esters respectively uiu dienolate anions has been described.'66 The same benzyne is formed from both 2-and 3-bromoanisole and this reacts with the anion from mesityl oxide to give 8-methoxy-1,3- dimethylnaphthalene both ct-and y-attack by the anion on the rnetu-position being important.Symmetrical 9,lO-unsubstituted anthracenes can be synthesized in one step in good yield from substituted bromobenzenes by using N-lithio-2,2,6,6- tetramethylpiperidine in THF.167 The sequence of reactions involves benzyne and the enolate ion of acetaldehyde arising from the base-catalysed cleavage of the solvent. 162 S.J. Gillespie jun. S. P. Acharya and D. A. Shamblee J. Org. Chem. 1975,40 1838. K. H. DOG,Angew. Chem.Internat.Edn. 1975,14,644. 164 H.J. J. Loozen J. Org. Chrn. 1975,40 520. 165 B. D. Baigrie J. Brenan J. I. G. Cadogan,J. Cook and J. T. Sharp J.C.S. Perkin I 1975 1060. 166 P. G. Sammes and T. W. Wallace J.C.S. Perkin I 1975 1377. 167 I. Fleming and T. Mah J.C.S. Perkin I 1975 964. Aromatic Compounds 237 The first unequivocal 1,5-naphthoquinone (64) has been synthesized16* and 1,6-methano[ 101annulene has been converted into 9,lO-homonaphthodiquinone (65) by a pathway entailing electrochemical reaction. 16' The reaction of some naphthalenes containing more than two methyl substituents with dichlorocarbene yielded relatively stable polymethyl-substituted 1,2-benzoheptafulvenes as well as bis(dichloromethano)tetrahydronaphthalene~.'~~~ Naphthalene underwent ring opening to 6-chlorobenzocycloheptatrienes anthracene to 6-chloro- 11H-dibenzo[a,e]cycloheptatriene and phenanthrene gave the 9,10-nor~aradiene.'~~~ The efficient photocyanation of phenanthrene and naphthalene with sodium cyanide in the necessary presence of 1,4-dicyanobenzene has been rep~rted,'~' and irradiation of phenanthrene in the presence of various amines causes the photofixation of carbon dioxide to yield 9,lO-dihydrophenenthrene-9-carboxylicacid.172 Measurements of enthalpies of activa- tion are held to provide proof that the Diels-Alder reaction of tetracyanoethylene with 9,lO-dimethylanthracene passes through the formation of a complex between the reactants.173 Kinetic of the reaction of sodium naphthalene with n-hexyl halides accord with the usual electron-transfer mechanism but the hexyldihydronaphthyl anion is a discrete intermediate and reacts relatively slowly with the halide in contrast to the corresponding reaction with water.With n-hexyl fluoride the solvent effects are opposite to those with the other halides and it is that in the former case the negative charge in the transition state is slightly localized relative to that of the naphthalene radical anion. Low-field CIDNP studied7& of the reactions of sodium naphthalene and anthracene with water provide evidence not observed at high field and suggest that a significant fraction of the reaction proceeds through direct radical-anion protonation. Pyrene-like molecules [e.g. (66)] have been prepared from corresponding mul- tilayered metacyclophanes by routes involving transannular reaction and subsequent dehydr~genation'~' (see also refs.137 and 139). A new synthesis of mronene from 168 H. L. K. Schmand and P. Boldt J. Amer. Chem. SOC.,1975,97,447. 169 W. Bornatsch and E. Vogel Angew. Chem. Internat. Edn. 1975,14,420. 170 (a)A. Oku T. Hino and K. Matsumoto J. Org. Chern.,1975,40,695;(b)G. Blume T.Neumann and P. Weyerstahl Annalen 1975,201. 171 K. Mizuno C. Pac and H. Sakurai J.C.S. Chem. Cbmm. 1975,553. 172 S. Tazuke and H. Ozawa J.C.S. Chem. Cbmm. 1975,237. 173 V. D. Kiselev and J. G. Miller J. Amer. Chem. SOC.,1975,97,4036. 174 (a)S. Bank and D. A. Juckett J. Amer. Chem.Soc. 1975,97,567; (b)J. F. Garst R. D. Roberts and B. N. Abels ibid. p. 4925; (c)J.F. Garst and J. A. Pacifici ibid. p. 1802. 175 T. Umemoto T. Kawashima Y.Sakata and S. Misumi TetrahedronLetters 1975 1005. 238 R. G.Coombes readily available starting materials has been reported.176 3,6-Bis(bromome thy1)phenan threne reacts with p -xylene-a,a '-di thiol and after photochemical sulphur extrusion to form a cyclophane intermediate treatment with aluminium trichloride in carbon disulphide and dehydrogenation yields coronene. The cyclohepta[def]phenanthrenylium ion the second 14~-perimeter cationic species has been synthesized. 177u The indications are that (67) contributes largely to its ground state structure and that a peripheral diamagnetic ring current is of no consequence. By contrast studies of the cyclopenta[cd]phenalenyl anion indicate that a reasonable representation of the ground state is the delocalized (68) a perturbed [13lannulenide ion.1776 The properties of various derivatives support the utilization of a peripheral electronic model which describes the dibenzo[ cd,gh]pen- talene system as a perturbed [121ann~lene.~'~ [8H]-Cyclopent[a]acenaphthylene (69) is a new example of the relatively small group of planar acidic hydrocarbon^.'^^ @ / \ (67) (68) (69) N.m.r. studies of its anion which takes up a deuteron at C-8 suggest that the charge resides not only on the cyclopentadienyl moiety but also to an extent on the naphthalene skeleton. T-SCF force-field calculations of [5]- [6]- and [7]-helicenes have yielded geometries and energies of racemization the latter showing agreement with experi- mental data.'" A novel simple synthesis of [6]helicene in 55% yield from a 2-naphthaleneacetonitrile by a route involving initial condensation with 2-dimethylamino-1,l-bis(dimethyliminomethy1)ethene diperchlorate has been described,'" and [6]helicene has also been prepared by photochemical ring closure of polymer-supported 1,2-diarylethenes lS2 The all-benzene helicene series up to [14]helicene is now c~mplete."~ Examples of [11]- [121- and [14]-helicenes have been synthesized in one operational step by the previously used photo-induced double cyclodehydrogenations of bis(arylviny1)arenes.183u A systematic study of these photochemical ring closures using circularly polarized light has been reported,183b although no asymmetric syntheses were observed in the cases of the higher benzoiogues of [lO]helicenes.1-Hydroxymethyl[6]helicene rearranges to the spiroindene (70)on treatment with and the corresponding aldehyde yields 176 J. T. Craig B. Halton and S.-F. Lo,Austral. J. Chem. 1975,28 913. 177 (a)I. Murata K. Yamamoto Y. Kayane and H. Ori Tetrahedron Letters 1975 131; (b)I. Murata K. Yamamoto M. Morioka M. Tamura and T. Hirotsu ibid. p. 2287. 178 B. M. Trost and P. L. Kinson J. Amer. Chem. SOC.,1975 97 2438. 179 K. Yamamoto M. Morioka and I. Murata Tetrahedron Letters 1975 3009. 180 H. J. Lindner Tetrahedron 1975,31 281. l*l C. Jutz and H.-G. Liibering Angew. Chem. Znternat. Edn. 1975,14,418. IS2-J. M. Vanest M. Gorsane V. Libert J. Pecher and R. H.Martin Chimiu (Switz.) 1975 29 343. IS3 (a)R. H. Martin and M. Baes Tetrahedron 1975,31,2135;(b)A. Moradpour H. Kagan M. Baes G. Morren and R. H. Martin ibid. p. 2139. Aromatic Compounds indene (70) on treatment with acid,'84a and the corresponding aldehyde yields mainly (71) on trwtment with the ylide of (EtO)2POCH2C0,Et.'84b 1,16-Didehydrohexahelicene (hexa[7]circulene) (72) has been synthesized by a cyclo- phanediene route.185 This molecule is probably saddle-shaped and consequently dissymmetric. (71) R = C0,Et 6 Non-benzeneSystems The first volume of a proposed series of compilations of topics in non-benzenoid aromatic chemistry has appeared.186 Three and Four-membered &@.-The simplest known antiaromatic system is now claimedlg7 to be the di-t-butyl-(3,5-di-t-butylphenyl)cyclopropenylradical (73).The (73) antiaromaticity of the 3~-electron system is held to be demonstrated both by the fact that delocalization of the unpaired electron in the cyclopropenyl ring is less than in the allylic portion of an open-chain analogue and also by the fact that the unpaired electron resides to a greater extent in the phenyl ring of (73) than does that of the benzyl radical. An improved synthesis of tris-dialkylaminocyclopropeniumchlorides involving an exchange procedure has been reported and oxidation of these ions by anhydrous antimony pentachloride leads to the precipitation of brick-red stable salts of the radical dications (74).'88 Total ferrocenyl substitution has been shown to be an alternative to using dialkylamino-groups for example as stabilizing substituents in the cyclopropenium ion and triferrocenylcyclopropenium perchlorate has been prepared.'89 The tri-t-butylcyclopropenium ion substitutes electrophilically in the cyclopentadienyl of some Group VI metal carbonyl derivatives {e.g.[(q'-(a)R.H.Martin J. Jespers and N. Defay TetrahedronLetters 1974,1093;(6)Helv. Chim.Acra 1975 58 776. 185 P. J. Jessup and J. A. Reiss Tetrahedron Letters 1975 1453. 'Topics in Nonbquenoid Aromatic Chemistry' ed. T. Nozoe R. Breslow K. Hafner S. Ito and I. Murata Wiley New York 1975. lg7 K. Schreiner W. Ahrens and A. Berndt Angew. Gem. Internat. Edn. 1975,14 550. IE8 R.Weiss and K. Schloter Tetruhedron Letters 1975 3491. 189 1. Agranat and E.Aharon-Shalom J. Amer. Chern. SOC.,1975,97 3829. 240 R. G.Coombes (74) (75) R = Pr' C,H,)M(CO)J} and in other cases forms the oxocyclobutenyl ligand.lgO Reactions of the 1,2-bis(di-isopropylamino)-3-chlorocyclopropeniumion with the cyclopen- tadienide and indenide ions lead to what is c1aimedl9la as a new type of tripolar compound [e.g. (75)]. However similar compounds containing a cyclopentadienide ring that is 1,3-linked to two N-alkylpyridinium rings have been prepared,"lb and evidence has been presented that these at least are best represented as hybrids of monocationic forms. MINDO/3 calculations agree with some earlier results in predicting a singlet ground state for cyclobutadiene and the suggestion has been made that the square or effectively square species obtained by the matrix-isolation technique [Ann.Reports (B) 1973 70 4151 is the excited triplet.19* Another theoretical treatment,193 however suggests that when cognizance is taken of the effects of electron repulsion in open-shell systems the ground state of the species can be a square or effectively square singlet. An X-ray analysis of the cyclobutadiene (76) chosen to be as stable but as unperturbed as possible provides clear evidence that the most stable conformation is a rectangle distorted slightly by the substituent~.~~~ A comparative photoelectron spectroscopic study of tri-t-butylcyclobutadiene and (77) for which Me0,C DBU' Bu' Bu' (76) u = 1.506A b = 1.376.A c = 1.547.A (77) d = 1.4068 an X-ray analysis is available suggests a rectangular structure of the butadiene ring here al~0.l~' INDO calculations on the stable donor-acceptor cyclobutadienes suggest that their most stable geometry is that of the D2,, paralle10gram.l~~ A new method has been described'97 for the detection of reaction intermediates involving the generation of an intermediate from an insoluble polymer-bound precursor and its trapping by a second solid phase suspended in the same medium.190 M. Green and R. P. Hughes J.C.S. Chem. Comm. 1975,862. 191 (a)Z. Yoshida S. Araki and H. Ogoshi Tetrahedron Letters 1975 19; (b)W. D. Erhardt and H. L. Amrnon ibid. p 3997. 192 M. J. S. Dewar and H. W. Kollmar J. Amer. Chem. SOC.,1975,97 2933. 193 W. T. Borden J. Amer. Chem. SOC.,1975,97 5968.194 L. T. J. Delbaere M. N. G. James N. Nakamura and S. Masamune J. Amer. Chem. SOC.,1975,97 1973. 195 G. Lauer C. Muller K. W. Schulte A. Schweig G. Maier and A. Alzerreca Angew. Chem. Internat. Edn. 1975 14 173. 196 C.U. Pittman jun. K. L. Douglas Q. Y. Ng W. Hunter D. Pace and L. D. Kispert J. Org. Gem. 1975 40 2121. 197 J. Rebek and F. Gavina J. Amer. Chem. SOC.,1975,97 3453. Aromatic Compounds 241 Oxidation of a polymer-bound derivative of cyclobutadieneiron carbonyl in the presence of a polymer-bound maleimide derivative has been shown by this technique to proceed with 96% transfer of free cyclobutadiene. Stereochemical studies on the oxidation of the tricarbonyl(cyclobutadieny1)iron complex (78) in the presence of dimethyl maleate to give the bicyclo[2,2,0]hexene have also implicated the inter- mediacy of a strongly selective free cy~lobutadiene.'~~ Tetrafluorocyclobutadiene has been revealed'- as an intermediate in the photolysis of (79) from the nature of transformation and trapping products.1,3-Bis(diethylamino)-2,4-diphenylcyclobutadiene which does not fit the usual donor-acceptor substituent structure for stability has been synthesizedzm and is stable for more than 1h in the solid at room temperature. E! (78) (79) Tri-t- butylcyclobutadiene undergoes ionic as well as synchronous and radical additions and it exhibits unusual activation parameters for its dimerization reaction in accord with an extremely sterically hindered transition state.20' Thermolysis of syn-and anti-dimers of cyclobutadiene to yield cyclo-octatetraene and the activa- tion parameters obtained have been discussed2o2a in terms of a biradical mechanism rather than the unusual major direct triplet pathway proposed elsewhere.202b Butalene (80),which has two fused 4nm rings is a transient intermediate in some reactions of 3-chloro[2,2,0]bicyclohexane induced by certain bases at moderately low The vigorous conditions necessary support the conclusion that such fused ring systems are not strongly stabilized by their overall content of (4n+2) m-electrons.The second benzocyclobutadiene (81) has been as blue needles on heating the cyclobutene (82). It is fairly stable in the absence of oxygen and e.s.r. and magnetic measurements indicate a singlet ground state.204b Bu' Bu' 19* E.K. G. Schmidt Chem. Ber. 1975,1OS,1609. 199 M.J. Gerace D. M. Lemal and H. Ed,J. Amer. Chem Sm. 1975,97,5584. R. Gompper S. Mensch and G. Seybold Angew. Gem. Intemat. an. 1975,14,704. 201 G.Maier and W. Sauer Angew. Chem. Intemat. Edn. 1975,14,648. 202 (a)H. M. Frey H. D. Martin and M. Hekman J.C.S. Chem Cornm. 1975,204;(6)R.S.Case M. J. S. Dewar S.Kirschner R.Pettit and W. Slegeir J. Amer. Chem Soc. 1975,196 7581. *03 R.Breslow J. Napierski and T. C. Clarke 3. Amer. chehz. Soc. 1975,97,6275. 204 (a)F.Toda and M. Ohi J.C.S. Chem Comm. 1975,506;(b)F.Toda and K. Mukai Chem.Letters 1975, 777. 242 R. G.Coombes Five-and Seven-membered Rings.-Ionization potential measurements on cyclo- pentyl and cyclopentadienyl radicals confirm2o5 that the cyclopentadienyl cation is antiaromatic and that it is destabilized by 7.6 kcal mol-' with respect to the cyclopen- ty1 cation.A convenient synthesis of alkylated fulvenes (83) from a,P-unsaturated acid chlorides (R'CH=CR2COCI) and alkynes (R3CH,CECH) via the 4-alkylidene-2-cyclopentenoneand a lithium alkyl (R4Li) has been reported.206 6,6-Dimethylfulvene dimerizes on the metal template on direct reaction with iron vapour using a low-temperature co-condensation procedure to give 1,l'- tetramethylethyleneferrocene (84) accompanied by 1,l-di-isopropylferro~ene.~~~ Me Fe Me Me (84) The first example of isomerization of 1,4-endoperoxides into 1,2-dioxetans with characterization and isolation of intermediates has been observed2'* in the sensitized photo-oxygenation of polyarylfulvenes.X-ray analysis of a series of pentafulvalenes [e.g. (SS)] has been used to develop relationships between the charge density on the five-membered ring and carbon-carbon bond lengths.209 The 2- and 3-halogenotropone radical ions are generally unstable and give tropone uia a radical path that is of potential synthetic utility.210 The previously unknown 'p-tropoquinone' cyclohepta-3,6-diene- 1,2,5-trione (86) has been pre- pared2'la by several routes the most convenient of which involves chemical oxida- tion of 5-hydroxytropolone. Attempts to prepare '0-tropoquinone' by a similar method led to the 2-hydrate. Spectral evidence however was obtained for the unhydr ated species in solution.lb The bicyclo[ 3,2 ,O]hepta- 3,6-dien-2-one photo- chemical rearrangement products of some 2,S-disubstituted troponoids with electron-withdrawing groups at the 5-position revert to the original troponoids in the dark even below room temperature presumably by an ionic process.212 205 F. P. Lossing and J. C. Traeger J. Amer. Chem. Soc. 1975,97 1579. 206 C. Rabiller and G. J. Martin Tetrahedron Letters 1975,3713. 20' T. S. Tan J. L. Fletcher and M. J. McGlinchey J.C.S. Chem. Comm. 1975 771. 208 J. P. Le Roux and C. Goasdoue Tetrahedron 1975,31,2761. 209 H. L. Ammon and G. L. Wheeler J. Amer. Chem.Soc. 1975,97,2326. 210 M. Martinelli L. Nucci L. Pardi F. Pietra and S. Santucci Tetruhedron Letters 1975 2089. 211 (a)S. Ito Y.Shoji H. Takeshita M.Hirama and K. Takahashi TetrahedronLetten,1975,1075; (b) M. Hirama and S.Ito ibid. p. 1071. 2** T. Kobayashi T. Hirai J. Tsunetsugu H. Hayashi and T. Nozoe Tetrahedron 1975,31 1483. Aromatic Compounds The intermediacy of A’-pyrazoline species in the aerobic reaction of tropones with diazoalkanes to yield cyclo-octatrienones has been dernon~trated,’’~~ and this reaction with the tropone-tricarbonylion(0) complex to yield a stable A’-pyrazoline has been as part of a new synthesis of 2,3-homotropones (Scheme 4). Hexame thyl- tris-cr-homotropone is formed from 3,3-Reagents i R,CN,; ii Me,NO. Scheme 4 dimethylcyclopropene and carbon monoxide in the presence of a p hosphine- modified palladium(0) catalyst.214 The first syntheses of the oxygen analogues of homotropones uiz.tropone 2,3-oxide and 4,5-oxide have been described.215 An efficient synthesis of 4,5-benzotropone from o-xylylene dibromide involving bisalkylation with lithio-t-butyl acetate and Dieckmann cyclization to 43-benzocycloheptenone has been reported.216 The second benzo[3,4)-cyclobuta[l,2Jtropone (87) has been ~ynthesized,~” and n.m.r. studies indicate that the benzenoid protons resonate in the normal aromatic region. This suggests that there is no paramagnetic contribution from the four-membered ring. The formation and trapping of the benzyne analogue 4,5-didehydrotropone has been repOrted218 from the lead tetra-acetate oxidation of 1-amino-1H-cycloheptatriazol-6-one. It forms a 9,lO-adduct with anthracene. The properties of 2-hydroxy-2,4,6- and -2,4,7-cyclo-octatrienoneprovide some evidence for homoaromatic interaction and they have accordingly been termed ‘homotropolones’.219 Heptafulvene (88) has been synthesized2” and normally decomposes in a few seconds at room temperature whereas the 1,8-condensed heptafulvene (89)is stable 213 (a)M.Franck-Neumann and D. Martina Te@ahedmnktters 1975,1755; (b) ibid. p. 1759. 214 P. Binger and U. Schuchardt Angew. Gem. Infernat. Edn. 1975,14 706. ,15 R. Miyamoto T. Tezuka and T. Mukai Tetrahedron Letters 1975,891. 216 G. D. Ewing and L. A. Paquette J. Org. Chem. 1975,40 2966. 217 L. Lombard0 and D. Wege Tetrahedron Letters,1975,115. T. Nakazawa and I. Murata Angew. Chem. Znremaf. Edn. 1975,14,711. 219 Y. Kitahara M.Oda and S. Miyakoshi Tetrahedron Letters 1975 4141; Y. Kitahara M. Oda S. Miyakoshi and S. Nakanishi ibid. p. 4145. 220 W. K. Schenk R. Kyburz and M. Neuenschwander Helu. Chim. Acm,1975,58,1099. 244 R. G.Coombes 0 (88) (89) for several days.221 X-ray analysis of cu-(6-fulvenyl)diben[u,e]heptafulvene indi-cated222a boat-shaped seven-membered ring and a pronounced alternation of bond lengths. Photochemical dimerization of 1,4-dialkynylbenzenes gives azulene~~~~ [e.g. (90) from 1,4-bis(phenyIethynyl)benzene]. The remarkable anchimeric assistance shown by the 1-azulyl substituent in arylethyl arenesulphonate solvolysis is not shown224 by the 2-azulyl group and the relative abilities of the ring positions 1> 2> 6=r 4 to participate is also the order of HMO cation localization energies for these positions.The thermal rearrangements of azulenes to naphthalenes have been the subject of and it is suggested that most products can be accommodated by a mechan- ism involving attack of a radical (R.) on the seven-membered ring migration of the attacked carbon and substituents (i.e. CHRor CRMe) into the other ring and loss of R H or Me. Azulene is nitrosated at the 1-position at a rate which is that of encounter of the reactants but the reaction of 1-nitroazulene which shows a primary .kinetic isotope effect involves rate-limiting proton loss from the Wheland inter- mediate.226 AMulenes.-An account of the renaissance in cyclo-octatetraene chemistry has appeared227" and two examples of stable cyclo-octatetraene bond-shift isomers have been reported.Compounds (91) and (92)were prepared2276 by Mo(CO),-catalysed rearrangement of the propellatriene (93),which also forms (94),the product of a unique two-fold circumambulatory rearrangement. The former rearrangement probably proceeds by [1,5]-sigmatropic shift of a trigonal cyclobutene carbon within a molybdenum complex.227c 1,2,3,4-Tetramethylcyclo-octatetraeneand the bond- shift isomer 1,2,3,8-tetramethylcyclo-octatetraenehave also been prepared,227d 221 S. Kuroda M. Funamizu Y. Kitahara anbT. Asao Tetrahedron Letters 1975,3197. 222 H. J. Lindner K. Hafner M. Romer and B. Von Gross Annalen 1975,731. 223 G. Clauss and W. Ried Chem. Ber. 1975,108,528. 224 R. N. McDonald and J. M. Richmond J.Org. Chem. 1975,40 1689. 225 R. W. Alder and G. Whittaker J.C.S. Perkin II 1975,714; R. W. Alder and C. Wilshire,ibid. p. 1464. 2z6 B. C. Challis and R. J. Higgins J.C.S. Perkin II 1975 1498. 227 (a)L. A. Paquette Tetrahedron 1975,31,2855; (b) L. A. Paquette J. M. Photis K. B. Gifkins and J. Clardy J. Amer. Chem. Soc.,1975,97,3536; (c) L. A. Paquette and J. M. Photis TetrahedronLetters 1975,1145; (d)L. A. Paquette J. M. Photis and G. D. Ewing J. Amer. Chem.Soc. 1975,97,3538. Aromatic Compounds 245 Me + (93) (92) (94) and the activation energies for ring inversion and bond shifting are sufficiently large to be attainable only with difficulty. The reaction of cyclo-octatetraene with liquid sulphur dioxide promoted by antimony pentafluoride leads228a to the formation of 9-thiabarbaralane 9,g-dioxide (95) by an unprecedented 1,5-cycloaddition.Studies of the hydrolysis of cyclo-octatetraenylcarbinyl chloride have produced2286 no evidence for the involvement of the homotropylium ion but allylic stabilization as in (96) is more likely. Evidence has been presented228c that #I-cyclo-octatetraenylethylbrosylates undergo solvolysis to give initially spiro[7,2]nonatrienyl cations [e.g. (97)] and finally tetrahydro- azulenyl acetates. Whether the ring in (97) retains its tub conformation or partially (95) (96) (97) flattens to permit homoaromatic stabilization remains an open question. 1,4-Dinitrocyclo-octatetraene,the first example of this type of compound has been Nonafulvene has been prepared230 by the reaction of lithium cyclononatetraenide with acetoxybromomethane at low temperatures followed by elimination of acetic acid.It seems that the non-planar compound which shows no ring current exists as a racemic mixture of two enantiomeric conformers. 1,6-Methano[lO]annulene is a product of the hydrolysis of (98).231 An ub initio theoretical study of this molecule it to be of weak or intermediate aromaticity contrasting somewhat with its known properties. Indeed the first quantitative of the aromatic reactivity of annulenes has involved the H Br (98) (99) z28 (a)L. A. Paquette U. Jacobsson and M. Oku J.C.S. Chem. Comm 1975,115; (b)W. Kitching K. A. Henzel and L. A. Paquette,J. Amer. Chem. SOC.,1975,M 4643; (c) L. A. Paquette and K.A. Henzel ibid. p. 4649. 2z9 N. N. Podgornova E. S. Lipina and V. V. Perekalin J. Org. Chem.(U.S.S.R.),1975,11,209. 230 M. Neuenschwander and A. Frey Chimia (Switz.) 1975,29,212. 231 D. B. Ledlie and L. Bowers J. 0%.Chem.,1975,40,792. z32 G. L. Grunewald I. M. Uwaydah R. E. Christoffersen and D. Spangler TetrahedronLetters 1975,933. 233 R.Taylor J.C.S. Perkin IZ 1975 1287. 246 R. G. Coombes detritiation and desilylation of 1,6-methano[ lolannulene and its 11,l l-difluoro- derivative and has demonstrated that the reactivities and response to demand of electrons at the 2-positions of these molecules are closely similar to corresponding quantities for similar positions in the very reactive aromatics thiophen and diben- zofuran respectively.The 107r analogue (99) of a-tropolone has been synth- e~ized~~~ and it shows close similarity in behaviour to its analogue. However this analogy does not extend to ring contraction in the presence of strong bases. The steric compression of the two inner bridge hydrogen atoms has been overcome and the elusive syn-1,6:8,13-bismethano[14lannulene (100) has been prepared.235a It is clearly an arene having very similar properties to the 1,6:8,13-propanediylidene[ 14lannulene (101; n = 1).The contrast with the cyclopolyolefinic anti-isomer provides a most impressive demonstration that molecular geometry is of crucial importance for the occurrence of aromaticity in cyclically conjugated ring systems. In a series of related compounds (101) no indications of a significant (101) reduction of 7r-electron delocalization with bridge size were found and in the case of (101; n =5)a conformational mobility of the bridge was An X-ray analysis of the related 15,16-dimethyl-l,6:8,13-ethanediylidene[14lannulene indi- cates a nearly planar annulene ring with a C-C bond length (1.39 A) close to the ‘aromatic’ The effects of annelation on the properties of annulenes have been the subject of considerable study.Annelation of a 61r ring onto monodehydro[ 12lannulene and bisdehydro[ 14lannulenes reduces the paratropicity and diatropicity respectively,236 and the latter effect is also observed with tran~-lS,16-dihydropyrene.~” Benzanne-lation of the conformationally fixed protonated bisdehydror 1Slannulenone ring (102) (103) 234 E.Vogel J. Ippen andV. Buck Angew. Gem. Internat. Edn. 1975,14,566. 235 (a)E. Vogel J. Sombroek and W. Wagemann Angew. Chem. Inkmar. Edn. 1975,14 564; (6)A. Alscher W. Bremser D. Cremer H. Guenther H. Schmickler W. Sturm and E. Vogel Chem. Ber. 1975 lOS 640; (c) R.Bianchi G. Casalone and M. Simonetta,Acta ctysr. 1975 B31 1207. 236 R. H. Wightman and F. Sondheimer Tetrahedron Letters 1975,4179;R.R.Jones J. M. Brown and F. Sondheimer ibid. p. 4183. 237 R.H.Mitchell and R. J. Carruthers Tetrahedron Letters 1975,4331. Aromatic Compounds 247 reduces the diamagnetic ring current and (102) is in fact atropi~.’~~ Double benzannelation reduces the paramagnetic ring current in the bisdehydro[ 17lannulenone (103).239 The n.m.r. spectrum of the highly unstable dinaphtho-di-t-butyldidehydro[18lannulene (104) indicates a diatropicity compara- ble to that of a non-annelated analogue.24oa This behaviour is similar to that of the [14]annulene series [Ann.Reports (B) 1974,71 3081 where the mono-annelated derivative was less diatropic and is contrary to the usual effect of annelation. The dibenzobisdehydro[ 14lannulene (105) was too unstable for n.m.r. study but the (104) (105) benzo-naphtho-analogue was a little more diatropic than the mononaphtho- derivative,240b The unusually high diatropicity of these conformationally stable diannelated systems was attributed to the fact that it is possible to draw two equivalent Kekul6 structures. In accord with this idea the diatropicity of a dinaphthotetradehydror 18]annulene where this is not possible was strongly sup- A trisdehydro[16]annulene (106; n = l) containing formal acetylenic and cumulenic linkages has been and the strong paratropicity of the compound was attributed to the planar structure and the decrease in bond alterna- tion.The trisdehydro[2O]annulene (106; n = 2) had a lower paramagnetic ring Some 13Cn.m.r. spectroscopic analyses of these compounds suggested the presence of two types of acetylenic carbon atoms,indicating that (106a) may be the better structural representation. A study of three new bridged [18]ann~lenes~~~ has provided important evidence that apart from planarity the overall shape of the annulene loop is a factor in the magnitude of the detected ring current which was greatest in (107).The strong ring current detected in (107) appears to contradict the predictions of MIND0/3 calculations on [18lannulenea itself [Ann. Reports (B) 1974,71 3101. Finally macrocyclic analogues of naphthalene have been prepared for the first time. A study of the tetrakisdehydro[ 14]annuleno[ 14lannulene (108) demon- that strate~~~~the annelation reduces the diamagnetic ring current of the 238 R. T. Weavers R. R. Jones and F. Sondheimer Tetrahedron Letters 1975,1043. 239 J. Ojima A. Kimura and T. Tokoyama Chem. Leners 1975,207. 240 (a) M. Morigaki M. Iyoda and M. Nakagawa Tetrahedron Letters 1975 2315; (6) A. Yasuhara M. Iyoda T. Satake and M. Nakagawa ibid. p. 3931; (c)M. Iyoda and M. Nakagawa Chem.Letters 1975 815. 241 (a)S.Nakatsuji M. Morigaki S. Akiyama and M. Nakagawa TetrahedronLeners 1975,1233; (b)S. Nakatsuji and M. Nakagawa ibid. p. 3927. 242 R. B. DuVernet T. Otsubu J. A. Lawson and V. Boekelheide J. Amer. Chem. Soc. 1975,97,1629. 243 T. M. Cresp and F. Sondheimer J. Amer. Chem. Soc. 1975,97,4412. 248 R. G.Cbombes @-H (106a) Bu' w B u t \/ (106b) bisdehydro[l4]annulene ring but to a lesser extent than the reduction caused by annelation of benzene. The second example (109) consists of two tetradehydro[l8]annulene systems which n.m.r. measurements suggest are best regarded as two fused aromatic nuclei.244 Me -Me II Ft I II F II C \-But 244 T. Kashitani S. Akiyama M. Iyoda and M. Nakagawa J. Amer. Chem. Soc.,1975,97 4424.

ISSN:0069-3030    

DOI:10.1039/OC9757200215

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

11 Heterocyclic Chemistry By 0. METH-COHN and R. K. SMALLEY The Ramage Laboratories University of Salford Salford M54W 1 Three-memberedRing Compounds 2H-Azirines continue to be used as versatile synthetic reagents. In addition to a full report' on the intramolecular cycloaddition reactions of substituted 2H-azirines noted last year, further preparative uses have been outlined. Photolysis of 3-crotyl-2H-azirine (1)yields the endo-cyclopropanopyrrolesystem (2) which on heating epimerizes to the more stable exo-form. This reaction involves a cycloaddition of the carbenoid mesomer of a nitrile ylide and is apparently the first example of this type involving a 1,3-dipolar specie^.^ (1) (2) But-2-enyl-2H-azirines are thermally decomposed via vinyl nitrenes e.g.(3; R = CO,Me) which undergoes a novel 1,4-hydrogen transfer to give an @-unsaturated imine (4; R =C0,Me). A 1,5-H shift followed by electrocyclic ring-closure and loss of ammonia yields the biphenyl (5)(12%) or by intramolecular Michael addition and loss of methyl acetate 3-methyl-2-phenylpyridine(58%).4 Ph (3) (4) (5) Vacuum pyrolysis of 2-aminoazirines provides a useful sourceof 2-azabutadienes e.g. CH,=C(Me)N=CHNMe, which readily enter into Diels-Alder cycloaddition with suitable dienophiles to give di- and tetra-hydropyridines in practicable yields.' A. Padwa J. Smolanoff and A. Tremper J. Amer. Chem. Soc.,1975,97,4682. Ann. Reports (B),1974,71,319. A. Padwa and P. H. J. Carlsen J. Amer. Chem. Sue. 1975,97,3862. A. Padwa and N. Kamigata J.C.S.Chem. Comm. 1975,789. A. Demoulin,H. Gorissen A.M.Heshin-Frisque and L. Ghosez,J. Amr. am. Soc. 1975,97,4409. 249 0.Meth-Cbhn andR. K.Smalley Pyrazines and dihydropyrazines result from the metal-carbonyl-induced dimeriza- tion of 2H-azirines6 Azirines are useful precursors of nitrile ylides which in turn react via 1,3-dipolar cycloaddition to give a wide variety of five-membered heterocycles. For example azirines on photolysis in the presence of ketones yield A3-~~az~line~?9b whereas with esters or thio-esters the hitherto scarcely known 5-alkoxy-A3-oxazolines are formed.*= Photolysis of p-benzoquinone and 2,3-diphenylazirine in benzene yields the 2H-isoindolo-4,7-dione (6). The quinol precursor of (6) a tautomer of the initially formed quinone-nitrile ylide adduct is isolable in the absence of oxygen.8b 11 Ph R (6) (7) (8) The first example of carbon disulphide addition to an azomethine bond has been recorded during the regioselective cycloaddition of carbon disulphide to 2 H-azirines.' Thiazolo-thiones e.g.(8) are formed by ring-expansion of primary adducts e.g. (7). 2-Chloro-N-acylaziridines available by addition of acyl chlorides to 3,3-dimethyl-2-phenylazirines undergo nucleophilic displacement of halogen in methanol and rearrangement to yield 5-methoxy-A2-oxazolines (9; R' =MeO) whereas with lithium azide in methanol the azido-compound (9; R'=N,) is obtained." In contrast the chloroaziridines undergo only nucleophilic substitution of halogen with silver acetate in acetonitrile to give 2-acetoxy-N-acylaziridines.The preparation of aziridines by the action of Grignard reagents or organolithiums on ketoximes" appears to be of limited synthetic utility and a more reliable versatile variant involves treating ketone dimethylhydrazone methiodides with a Grignard reagent.'* A facile synthesis of 1,2-disubstituted aziridines has been described which employs the lithium aluminium hydride reduction of aa-dichloroanils,e.g. (lo) formed by the action of N-chlorosuccinimide on the appro- priate t-butylidene compound. l3 The trans-2,3-disubstituted 1-t-butylaziridine (1 1) thermally rearranges via an azomethine ylide to 1-t-butyl-3-phenylpyrole some forty times faster than the corresponding cis-isomer. Apparently the thermally required conrotatory ring- opening of the cis-isomer involves unfavourable stereochemical interactions 6 H.Alper and S. Wollowitz J. Amer. chcm. Soc. 1975,97,3541. (a)P. Claus P. Gilgen H. J. Hansen H. Heimgartner B. Jackson and H. Schmid Hefu. aim. Acta 1974,57,2173; (b)A. Orahovats H. Heimgartner H. Schmid and W. Heinzelmann ibid. p. 2626. 8 (a)P. Gilgen H. J. Hansen H. Heimgartner W. Sieber P. Uebelhart H. Schmid P. Schonholzer and W. E. Oberhansli Helu. Chim. Acttr 1975 58 1739; (b) P. Gilgen B. Jackson H. J. Hansen H. Heimgartner and H. Schmid ibid. 1974,57,2634. 9 V. Nair and K. H. Kim J. Org. Chem. 1975,40,1348. A. Hassner S. S. Burke and J. Cheng-fan J. Amer. Chem. Soc. 1975 97,4692. Ann.Reports (B),1974,71,321. It G. Alverhne S. Arsenyiadis R.Chaabouni and A. Laurent Tetrahedron Letters 1975,355. I3 N. De Kimpe R. Verht L. De Buyck and N. Schamp Synrhetic Cornrn. 1975,5,269. Heterocyclic Chemistry 25 1 R2 c1 H. ,Me AN Bu'-N=CH-C-R II PhCO N ini c1 I R1-)-(Me Me Bu' Ph (9) (10) (11) between the 2-and 3-substituents and the bulky t-butyl group a problem absent with the trans-i~omer.'~ In accord with this idea it was found that cis-trans isomerization of (11) proceeds via enolization rather than azomethine ylide participation. Attempts to synthesize diazaspiropentanes (14) by methods analogous to those successfully employed for the preparation of l-azaspiropentanes" have failed. 16a Azides add to methylenoaziridine (12) to give the expected spiroaziridinotriazolines (13) which on thermolysis yield not the hoped-for diazaspiropentanes (14) but a mixture of triazoles (15) and the cyclic amidines (16) (Scheme 1).The latter (15) (16) Scheme 1 compounds (R = Ph p-tosyl or C0,Et) appear to be the first recorded examples of four-membered cyclic amidines.'66 However a 14% yield of the diazaspiropentane (17; R = phthalimido) has been achieved by treating N-phthalimidonitrene with an allene (Scheme 2).l7 Scheme 2 Tetrazolines continue18 to be a convenient source of diaziridines. Photolysis of tetrazolines of type (18;X = 0or NMe) provides a useful synthesis of diaziridinones l4 A. Padwa D. Dean and T. Oine J. Amer. Chem. SOC.,1975,97,2822. Is Ann. Reports (B),1974,71,321. lC (a)J. K. Crandall,L. C.Crawley and J. B. Komin J. Org. Chem. 1975,40,2045;(b)J. K. Crandall and J. B. Kornin J.C.S. Chem. Comm. 1975,436. l7 R. S. Atkinson and J. R. Malpass Tetrahedron Letters 1975 4305. l8 Ann. Reports (B),1974,71,321. 0.Meth -Cbhn and R.K.Smaiiey (19; X=0)and diaziridimines (19; X= NMe). The tetrazoline (18; X = CMe,) however yields not diaziridine (19; X = me,) but rather the isomeric aziridine- imine (20).19 Me ,Me MeN NMe \I MeN-NMe N=N (18) (19) (20) 1,3,5-Triazabicyclo[3,1 ,O]hexane-2,4-dione (21) available in near quantitative yield from the addition of ethoxycarbonylcarbene to the triazolinedione (Scheme 3) represents the first example of carbene addition to an azo linkage.,' h N,CHCO,Et -PhNP, l,y phNk& CH,CI ; 0 "C kNC0,Et 0 0 Scheme 3 3-Acyldiazirines and 1,2,3-oxadiazoles are cyclic valence isomers of a!-diazocarbonyl compounds.Whereas 1,2,3-0xadiazoles are as yet unknown the diazirine isomer has been detected for the first time in the thermally reversible thermochromic system (22) (23).21 N. N=N A newly developed route to oxirans involves highly nucleophiiic selenocarbanion intermediates e.g. (24) (Scheme 4). Originally phenyl selenide (PhSeH) was used,,," but subsequently methyl selenide (MeSeH) has been shown to be a superior reagent.22* A convenient route to trans-trioxa-tris-o-homobenzene(25; X = Y = 0)has been de~cribed,,~" while cis-benzene trioxide (26; X = 0)has been used in a simple total synthesis of ~treptamine,~~ and in the synthesis of (*)-hyo~cyamine.~~" l9 H.Quast and L. Bieber Angew. Chem. Internat. Edn. 1975,14,428. 20 R. A. Izydore and S. McLean J. Amer. Chem. SOC.,1975,97,5611. z1 E. Voight and H. Meier Angew. Gem. Internat. Edn. 1975,14 103. z2 (a) W. Dumont and A. Krief Angew. Chem. Internat. Edn. 1975 14 350; (b) D. Van Ende W. Dumont and A. Krief ibid. p. 700. z3 (a) H. Prinzbach R. Keller and R. Schwesinger,Angew. Chem. Internat. Edn. 1975 14,633; (b)R. Schwesinger and H. Prinzbach ibid. p. 630; (c)H. Prinzbach R. Keller and R. Schwesinger ibid. p. 632. Heterocyclic Chemistry R2 R2 R2 \ I I CO + MeSeH -+ MeSe-C-SeMeB* MeSe-C' I I R'/ R' R' (24) i R3R4C0 ii Me1 I R2 R3 R2 R4 +II Me,Se -C -C -OH R 1 v R4 dl 63 Scheme 4 Thiirans may be synthesized by treating lithium alkylthio-~xazolines~~ (27; X =0) or thia~olines~~ (27; X =S) with ketones at -78 "C.Quantitative stereospecific xQx Y (25) (26) (27) conversion of oxirans into thiirans is possible by treatment with 3-methylbenzothiazole-2-thionein the presence of trifluoroacetic acid.26 Alkenes react with methyl(bismethy1thio)sulphonium hexachloroantimonate (28)at 0 "Cin methylene chloride to give thiiranium salts (29;X= S) in high yield.27 The corre-spondingseleniranium salts (29;X = Se) and selenirenium salts (30)can be similarly prepared by treating alkenes or alkynes respectively with areneselenyl hexa-fluoro-phosphates or -antimonates (ArSe'XF,-; X =P or Sb).** MeS SbC1,-SbFi \x! Y-y+ \S+ I Me Ar MeS/\Me I (28) (29) (30) The electronic structure of thiiren dioxide (31; R =H) has been investigated theoretically and by U.V.photoelectron spectroscopy.29The results indicate that the dioxide is less aromatic than cyclopropenone or tropone. Diphenylthiiren dioxide (31;R =Ph) adds to cyclicenamines to give bicyclicsystems(32; n =6,7 or 8) which can by cyclobutanering scission,yield sulphur-containingheterocycles(33;n =6,7 or 8).30 With acylic enamines thiophen dioxides (33;n = 0)are obtained. 24 A. I. Meyers and M. E. Ford Tetrahedron Letters 1975,2861. *5 C. R. Johnson A. Nakanishi N. Nakanishi and K. Tanaka Tetrahedron Letters,1975,2865. 26 V. Calo L. Lopez L. Marchese and G. Pesce J.CS. Chem. Comm 1975,621. 27 G. Capozzi 0.De Lucchi V.Lucchini and G. Modena Tetrahedron Letters 1975,2603. 28 G. H. &hid and D. G. Garratt Tetrahedron Letters 1975,3991. 29 C. Miilier A. Schweig,and H. Vermeer J. Amer. Chem. Soc.,1975,97,982. 30 M. H. Rosen and G. &net J. Org. Chem. 1974,39,3805. 0.Meth -Cohn and R.K.Smalley Ph R. po +O R The previously unknown cis-benzene trisulphide (26; X =S) has been prepared and shows a pronounced tendency towards polymerization both in the solid state and in a Also act -dioxa-@-thia- and @-oxa-act -dithia- tris-o -homobenzenes (25; X =0,Y =S) and (25; X =S Y =0)have been synthesized from cis-benzene trioxide (26; X =O).31b The monothia-compound reacts with trimethyl phosphite at 20 "Cto give benzene dioxide whereas the dithia-compound under similar condi- tions yields the benzene oxide-oxepin system.2 Four-membered Ring Compounds [3+13 Cycloadditions are comparatively rare events in synthetic heterocyclic chemistry. It is of interest therefore that azetidine-imines e.g. (34) are formed by [3+ 13 cycloaddition of azomethine ylides to various i~ocyanides.~~ Azetidinones (36) are available in good yield (R =Ph 72%) by a new ring-contraction method involving mercuric oxide oxidation of N-aminopyrazolinones (35)and extrusion of nitrogen from the resulting N-nit~ene.~~ COR I (34) Photolysis of (37) the cycloadduct of tetracyclone and the photoisomer of N-methyl-2-pyridone in methanol results in stepwise loss of carbon monoxide and tetraphenylbenzene to give the thermally labile non-isolable N-methylazetinone (38),34 which is converted in methanol into a mixture of methyl cis-and trans-@-methylaminoacrylate by way of its imino-keten valence isomer (39).Ph NMe Ph 31 (a)S. Kagabu and H. Prinzbach Angew. Chem. Internat. Edn. 1975,14 252; (6) H. Prinzbach C. Kaiser and M. Fritz ibid. p. 253. 32 K.Burger F.Maw and A.Braun Synthesis 1975,250. 33 P. Y. Johnson N. R. Schmuff and C. E. Hatch Tetrahedron Letters 1975,4089. 34 G. Kretschmer and R. N. Warrener TetrahedronLetters 1975 1335. Heterocyclic Chemistry Nitrile oxides and 2-phenylbenzazete react to give the highly strained adduct (40) which rearranges uia a non-isolable 2,3,5-oxadiazepine (41) to the more stable isomeric 1,3,5-oxadiazepine (44).35 This remarkable rearrangement is thought to proceed via oxaziridine intermediates (42) and (43) (Scheme 5) since (44) is also obtained on photolysis of the quinazoline N-oxide (45).The reaction is of particular interest since it supports the popular view that oxaziridines are intermediates in the photo-induced rearrangement of many heteroaromatic N-oxides. Ar (40) Ar (45) (44) (43) Scheme 5 2-Alkoxyazirines readily yield new synthetically useful 1,4-dipolar intermediates with acetylenedicarboxylate~~~" With p-tosyl isocyanate the 1:1 and keten~.~~~ adduct (46)is obtained which is claimed as the first stable isolable cross-conjugated 1,4-dipolar species.36c Excess of isocyanate leads to formation of the 2 1adduct (47) in near quantitative yield.Ts OMe MeG,co,fiTS Me Me Me 0 (46) (47) Benzoazetirres (49) are the major products from the photochemical isomerization of 1,2-dihydroquinolines (48) when irradiation is carried out for 5 h in ethan01.~' Further irradiation of the benzoazetines produces the indolines (50). I Ac (48) 3s C. W. Rees R. Somanathan R. C. Storr and A. D. Woolhouse J.C.S. Chem Cornm. 1975,740. 36 D. H. Aue and D. Thomas (a)J. Org. am. 1975,40,2360; (b) ibid. p. 2552; (c) ibid. p. 2356. 37 M. Ikeda S. Matsugashita F. Tabusa H. Ishibashi and Y.Tamura J.C.S. Chem. Comm. 1975,575. 0.Meth-Cohn and R. K. Smalley 1,2-Oxazete N-oxides with one exception are known only as reactive inter- mediates in the thermal and photochemical cleavage of cup-unsaturated nitro- compounds.However a new method involving addition of nitrogen tetroxide at 0 "C to readily accessible 1,l-di-t-butylallenes now permits isolation of the ther- mally labile 4H- 1,2-oxazete N-oxides (51;R =H Br or Cl),which on standing are converted into the more stable crystalline derivatives (52).38a Bu' Bu'77 0-N HH 0-N +\ Bu' NO -0 R (53) (54) I (51) X =CHNO (52) X =COR The parent 4H-l,2-oxazete (54) hitherto known only as a reactive intermediate has been prepared by vacuum pyrolysis (220 "C; Torr) of the remarkably stable nitrosoalkene (53).38bThe oxazete which condenses on a cold-finger trap at -196 "C in 54% yield decomposes on heating to yield di-t-butylketone and hydrogen cyanide which are the sole products if pyrolysis of (53)is carried out at 240 "Cor above.Vacuum pyrolysis (140 "C; 12 Torr) has also proved to be an efficient method of producing 2H- 1,3-thiazetes (56) a new four-membered heterocyclic The 1,3,5-0xathiazine precursors (55) are readily obtained by condensing perfluoroacetone with a thioamide in phosphorus oxychloride-pyridine mixture at -20 "C. The thiazetes exhibit thermal valence isomerism with the acyclic imino- thioamide (57) which can be trapped as a [4 +13cycloadduct with isocyanides or as a [4 +2) cycloadduct with a variety of alkene~.~~' (55) (56) (57) The remarkably stable crystalline 172-oxathietan-2-oxide (59) has been isolated from the reaction of the t-butyl sulphoxide (58) with N-chlorosuccinimide in methylene chloride at room temperature or with thionyl chloride at -70 0C.40At 30 "C (59) extrudes sulphur dioxide to give 2,2-dimethyl-l7l-dipheny1ethylene.0 4 Ph,CCMe,SOBu' PhRMe 1 OH Ph Me (58) (59) 3* K. Wieser and A. Berndt (a) Angew. Chem. Internat. Edn. 1975 14,69; (b) ibid. p. 70. 39 (a)K. Burger J. Albanbauer and M. Eggersdorfer Angew. Chem.Internat. Edn. 1975,14,766; (b)K. Burger J. Albanbauer and W. Foag ibid. p. 767. *T. Durst and B. P. Gimbarzevsky J.C.S. Chem. Comm. 1975,724. 257 Heterocyclic Chemistry 3 Five-memberedRing Compounds 2-Amin0-3-cyano-~~ and 2-amin0-4-cyano-pyrroles~~ have been conveniently sydthesized commencing from malononitrile and succinonitrile respectively and their role as intermediates is exemplified in the synthesis of pyrro10[2,3-b]pyridine.~~ Barltrop has applied his novel permutation-pattern approach to the phototrans- positions of pyrroles.Thus analysis of the products from irradiation of 3- 4-,and 5-methyl-2-cyanopyrrole (in each case a p-cyanopyrrole) is consistent with only one pattern (Scheme 6).43 N-Trimethylsilylpyrrole has been suggested as the pyrrole OCN N H 1.3-walk O H CN PCN CN H H CN Scheme 6 reagent of choice for use in Diels-Alder reactions. The sensitive epi-imino- derivatives are easily isolated by subsequent removal of the protecting group with cold Further examples45 of the use of functionalized dipoles for the synthesis of fused heterocycles (56 656 5566 5666 and 6566 systems) have been reported.46 Base-catalysed rearrangement of bis-propargylamines ethers and sulphides pro- vides an entry into various fused heterocycles (Scheme ,)." Flash vacuum pyrolysis of derivatives of Meldrum's acid has proved a fruitful source of heterocycles by way XxBul (14-5 1%) r"-R Bu' KOBu' L5-R 20°C I R=Ph (12-54:;) Scheme 7 *l H.J. Roth and K. Eger Arch. Pharm. 1975,308 179. 42 A. Brodrick and D. G. Wibberley J.C.S. Perkin I 1975 1910. 43 J. Barltrop A. C. Day P. D. Moxon and R. R. Ward J.C.S. Chem. Comm. 1975,786. 44 P. S. Anderson M. E. Christy G. F. Lundell and G. S. Ponticello Tetrahedron Letters 1975 2553. 45 Ann. Reports (B),1974,71,328. 46 B. E. Landberg and J. W. Low,J.C.S. Perkin I 1975 1326. 47 P. J. Garratt and S. B.Neoh J. Amer. Chem. Soc. 1975 97,3255. 0.Meth-Cohn and R.K.Srnalley of keten intermediates. Thus hydroxy-indoles carbazoles benzothiophens ben- zofurans and dibenzofurans are obtained in 50-90% yield (Scheme 8).48 0 Scheme 8 Another route to indoles lies in the aryne cyclization of a-anions derived from ketone anil~.~' The Fischer indole reaction of the hydrazone (60)gives a rearranged product (61) which has been shown by labelling to involve two consecutive 1,2-shifts of methyl groups rather than a 1,3-shift. Analogous 1,4-shifts have also been ob~erved.~~~*~ hie I Me0,Cy~~ Me02C Me Me (60) (61) The remarkable transmogrifications of substituted indoles with oxygen have been extended by two more examples (Scheme 9).51 0 Me Scheme 9 G.J. Baxter R. F. C. Brown and G. L. McMullen Austral.J. am. 1974,27,2605. 49 L. Lalloz and P. Caub&re,J.C.S. Chem. Cornrn. 1975,745. 50 R. Fusco and F. Sannicolo (a)TefrahedronLetfers,1975,3351; (b)ibid.,p. 465. 51 I. Saito M. Imuta S. Matsugo and T. Matsuura J. Amet. Chem. Sx.,1975,97,7191. Heterocyclic Chemistry 259 A mixture of stable cis-and trans-2,3-diazido-2,3-dihydroindoles results when 1-acylindoles are treated with iodine a~ide.~* Stereospecific hydrogenation of 2,3-disubstituted indoles is observed with sodium in liquid ammonia (cis addition) and borane in THF (trans additi~n).'~ Isatin interacts with potassium cyanide and ammonium carbonate to give the spiro-indolone (62),'4 while related spiro-indolones e.g.(64) may be isolated from the excellent dienophile (63).55 The bornene (64) is readily transformed into 3- phenyl-2-indolone with alkali. The origin of carbazole from 2-azidobiphenyl is still a subject of debate and Sundberg's recent flash photolysis work casts serious doubt on the oft-mooted triplet-nitrene pathway and tends to favour a singlet process.56 H (64) Two simple high-yield routes to imidazoles have been published involving the [4+21 dimerization of the cyanoimine (65) (Scheme 10y7 0- I PhCH=NMe + ~,x CN Ph Y I k-N Ph-CENMe /&-I. Ph PhCONHMe ii. KCN. HCONH,(65) Me Scheme 10 The 2,2-diphenyl-isoimidazoleN-oxides (66) have been described and their nitrone character has been e~ploited.~' Bridged benzimidazoliurn salts (68; X =H n =6-12) benzimidazolones and thiones (68; X =0 and S respectively n =5-12) have been described and their aromaticity studied.The whole series of salts 0-I+ Ph Ph Ph 'NXPh (67) t~ = 3-12 (68) X = H.0-.or S-52 Y. Tamura S. Kwon F. Tabusa and M. Ikeda Tetrahedron Letters 1975 3291. 53 J. G. Berger S. R. Teller C. D. Adams and L. J. Guggenberger Tetrahedron Leners 1975,1807. 54 H. Otomasu K. Natori and H. Takahashi Chem. and Pharm. Bull. (Japan) 1975,23 1431. 55 D. R. Long and C. G. Richards Tetrahedron Letters 1975 1603. 35 R. J. Sundberg D. W. Gillespie and B. A. DeGraff J. Amer. Chem. Soc. 1975,97 6193. 57 N. G. Clark and E. Cawkill Tetrahedron Letters 1975 2717. 58 B. A. J. Clark T. J. Evans and R. G. Simmonds J.C.S.Perkin I 1975 1803. 0.Meth-ahn and R.K. Smalley (X=H) was aromatic but loss of aromaticity was associated with n <7 and n <7-8 in the -one and -thione series re~pectively.~~~~~ Allene carbenes show a remarkable reaction with azobenzene 2-alkenyl- 1-phenylbenzimidazoles e.g. (69) being formed.60 I Ph (69) N-(N-Arylimidoy1)sulphimides are useful photo-sources of the rare imidoylni- trenes giving 2-substituted benzimidazoles in good yield (Scheme 11).61 Various Scheme 11 2-substituted benzimidazoles particularly 2-aryloxy-derivatives trimerize by a radical process on thermolysis giving the tris(benzimidazo1o)triazine (70).622-Methylenebenzimidazolines e.g. (7l),undergo some surprising reactions and the latest example is with carbon tetra~hloride.~~ Remarkably the salts (72) and (73) are isolated! A (72) MeN NMe (73) 59 R.J. Hayward and 0.Meth-Cohn (a)J.C.S. Perkin Z 1975 212; (b) ibid. p. 219. 6o T. Sasaki S. Eguchi and T. Ogawa Heterocycles 1975,3 193. dl T.L. Gilchrist C. J. Moody and C. W. Rees J.C.S. Perkin Z 1975 1964. 62 S. Ishida Y. Fukushima S. Sekiguchi and K. Matsui Bull. Gem. Soc. Japan 1975,48,956. J. Bourson Bull. Soc. chim.France 1975 644. Heterocyclic Chemistry Conjugated diazoalkanes are known to undergo 175-cyclization to give pyrazoles. However the analogues (74) are the first examples to yield both the 1,5- (75) and 1,7-cyclization (76) products as well as the carbene-derived indenes (77).64 80°C+ + + N Me Me H Me (74) The involvement of 1H-azirines in the thermal decomposition of 1,2,3-triazoles has recently been reinforced by '3C-labelling studies6' 1,2,4-Triazoles are con- venient pyrolytic precursors of the useful isoindoles.66 Mono- and di-phenyl deriva- tives were prepared by the same method.1-Aminoalkylbenzotriazole has been shown to be in rapid solvent-dependent equilibrium with its 3-isomer probably by way of the benzotriazolyl anion.67 However 1-methylbenzotriazole 3-oxide is converted irreversibly into its 2-oxide isomer on irradiation.68 Scheme 12 The a-anions of isocyanides have been used as convenient reagents for the synthesisof 2-unsubstituted oxazoles by interaction with acyl halides.69 Oxazolones and various related systems can be conveniently prepared under ambient conditions by the interaction of amino-alcohols (or phenols or thiols) with carbon monoxide in the presence of selenium (Scheme E)." An interesting intramolecular cycloaddition has been described whereby the o-allyloxybenzonitrile oxide (78) yields the fused dihydroisoxazole (79).The corre- sponding propargyloxy-derivative similarly gives the parent is~xazole.~~ The dihy- droxyisoxazoles or disic acids e.g. (80) are amongst the strongest organic acids (78) (79) 64 J. Dingwall and J. T. Sharp J.C.S. Chem. Comm. 1975,128. 65 T. L. Gilchrist C. W. Re& and C. Thomas J.C.S. Perkin I 1975,8. 66 T. L. Gilchrist C. W. Rees and C. Thomas J.C.S. Perkin I 1975 12. 67 J. R. L. Smith and J. S. Sadd J.C.S. Perkin I 1975 1181.68 M. P. Serve W. A. Feid P. G. Seybold and R. N. Steppel J. Heterocyclic Chem. 1975,12 811. 69 R. Schroder U. Schollkopf,E. Blume and I. Hoppe Annafen 1975,533. 'O N. Sonoda G. Yamamoto K. Natsukawa K. Kondo and S. Murai Tetrahedron Leners 1975,1968. R. Fusco L. Garanti and G. Zecchi Chimica e Industria 1975,57,16. 262 0.Meth-Cohn and R.K. Smalley known the example shown having a pK of -0.1.72 o-Dinitrosobenzene is the disputed valence tautomer intermediate believed to account for isomerization of the benzofuroxans. The efficiency of nitrosobenzene as a triplet nitrene trap led Scriven and co-workers to demonstrate the corresponding role of benzofuroxan by isolation of (81).73 Similarly with diphenyldiazomethane benzofuroxan gave the isobenz- imidazole di-N-oxide (82).The usefulness of benzofuroxan in synthesis has been 0-0-OH (81) (82) (83) further extended by its interaction with barbituric acid and with NN’N‘’-trisubstituted hexahydro-syrn-triazinesto give N-hydroxybenzimidazole and 1,3- dihydroxy-2-iminobenzimidazoline(83) The interaction of nitro- compounds with tervalent phosphorus derivatives is still a fertile source of novel heterocycles the ox- and thi-azaphosphoranes (84) being recent example^.^'^^^*^^ Photolysis of the former give moderate yields of carbazole. The oxazaphosphole (85) is a versatile imidazolating agent by way of the nitrile ylide (86).77 oxAr ___* P-OR ox\ ‘NO PhP(OR) ‘ /OR N’ ‘OR Ar (84) X = 0 or S CF3 (85) The regiospecific incorporation of deuterium during the photoisomerkcation of 5-phenylisothiazole to 3-phenylisothiazole has been explained by invoking a dipolar 72 G.Zvilichovsky Tetrahedron 1975,31 1861. 73 A. B. Bulachinski E. F. V. Scriven and H. Suschitzky Tetrahedron Letters 1975,3576. 74 (a)F. Seng and K. Ley Synthesis 1975,703; (b)F. Sung,K. Ley and K. Wagner ibid. p. 703 ’I5 (a)J. I. G.Cadogan B. S. Tait and N. J. Tweddle J.C.S. Chem. Comm. 1975,847; (b)J. I. G. Cadogan and B. S. Tait J.C.S. Perkin I 1975 2396. 76 J. I. G. Cadogan R. 0.Gould and N. J. Tweddle J.C.S. Chem. Cornrn. 1975 773. K. Burger and W.-D. Roth Synthesis 1975,731. Heterocyclic Chemistry intermediate (Scheme 13).78 N-Phenylbenzothiazol-2-oneloses carbon monoxide on pyrolysis giving phenothiazine at 650°C but carbazole at 850°C whereas a mixture of both is formed at 750 "C.The corresponding benzothiazole-2-thione Scheme 13 however shows only N+S migration of the phenyl group yielding 2-phenylthiobenz~thiazole.~~ 1,2,3-Thiadiazoles are versatile synthons of thioketens by flash vacuum pyrolysis. At 30°C the products dimerize to yield the dithietans (87).**The first example of a SH-1,2,3-dithiazole (89) which exists in solution in equilibrium with the thiosulphinylaniline (88) is produced when 2,4,6-tri-t- butylaniiine is treated with sulphur monochloride and triethylamine.'l The first mesoionic selenazole derivative (90) has been reported.82 New synthetic methods are frequently published and fall into two categories those that are more complex difficult to achieve or expensive than the end-products warrant and those that reappear in the literature.Occasionally the intrinsic interest and potential of one of the former methods overcomes other disadvantages. Such an example is Gassman's extension of his indole synthesis to benzofurans (Scheme 14).83 Scheme 14 78 M. Maeda A Kawahara M. Kai and M Kojima Heterocycles 1975,3,389. 79 D. C. K.Lim M. L. Thomson and D. C. de Jongh Canud. J. Chem. 1975,53,2293. 8o G. Seybold and C. Heibl Angew. Chem. Inremat. Edn. 1975,14,248. Y. Inagaki R. Okazaki and N. Inamoto TetrahedronLetters 1975,4575. 82 M. P. Cava and L. E. Saris J.C.S. Chem. Comm. 1975,617. 83 P. G. Gassman and D. R. Arnick Synthetic Comm. 1975,5,325. 264 0.Meth-Cohn and R.K.Smalley Wynberg has previously demonstrated the t-butylation of 2,5-di-t-butylfuran yielding 2,3,5-tri-t-butylfuran. However other di- or tri-alkylfurans undergo t- butylation without ‘reversion-to-type’ (e.g.Scheme 15).84 R = H or R-R = (CH2)2-3 Scheme 15 Tetracyanoethylene oxide is a most unpredictable reagent. Reactions with furan benzofuran thiophens and selenophen give two kinds of product (91)and (92).85*86 NC CN ~. ..II Q 2 *-. c:.. ...,.. NC CN A one-step high-yield synthesis of furan-2-ones has been described by Pad~a.~’ The intermediate may be isolated and separately cyclized if required (Scheme 16). The R2 I CHO CH2Ph PhCH,CO,-+ R1-C-CHO -I C,H,. A I Br R’ R‘ Scheme 16 first general method for furan-2,3-dione synthesis has appeared.The products undergo thermal extrusion of CO (Scheme 17),88and the resulting a-ketoketen may n R2- Scheme 17 dimerize to a pyrandione or be trapped (e.g. with chloral). Brave chemists have explored the chemistry of the highly explosive photo-oxide (93) of 1,3-diphenylisobenzofuran. Amongst interesting results the thermolysis in protic sol- vents yields products (Scheme 18) believed to form from the peroxide (94).89 84 H.Wynberg and U. E. Wiersurn Tetrahedron Letters 1975,3619. 85 S. Gronowitz and B. Uppstrorn Acfa Chem. Scand. (B), 1974,28,981. 86 S. Gronowitz and B. Uppstrom Acfu Chem. Scand. (B),1975,29,441. 8’ A. Padwa and D. Dehm J. Org. Chem. 1975,40,3139. 88 S. Murai K. Hasegawa and N.Sonoda Angew. Chem. Internat. Edn. 1975,14,636. 89 G. Rio and M.-J. Scholl J.C.S. am. Cbmm. 1975,474. Heterocyclic Chemistry 265 + R R= acoph co-Scheme 18 7-Oxanorbornadiene is now readily available in two steps from furan and quantita- tively transforms into 3-oxaquadricyclane (97) on photolysis. This product thermo- lyses to yield an equilibrium of oxepin and benzene oxide (95; R=H) and (96; R = H) and isomerizes with acid to give 5-formylcyclopentadiene.90The well- known photo-conversion of stilbenes into phenanthrenes has been emulated by the transformation of diary1 oxides and sulphides into dibenzofurans and diben- zothiophens in good yield.” The first synthesis of a five-membered mesoionic system containing only oxygen and sulphur as nuclear heteroatoms e.g.(98) has been accomplished by the dehydration of acylthioacetic acids.92 O\ The discovery of thiophen resulted from the formation of the blue dye indophenine obtained by its acid-catalysed reaction with isatin. The polyin- dophenine (99) is useful as a vat dye and p-type emi icon duct or.^^ The versatile Hurtley reaction has recently been ‘rediscovered’ and provides the method of choice 90 H. Prinzbach and H. Babsch Angew. Chern. Internat. Edn. 1975,14,753. 91 K.-P. Zeller and H. Petersen Synthesis 1975,532. 92 K. T.Potts J. Kane E. Carnahan and U. P. Singh J.C.S. Chern. Comrn. 1975,417. 93 G.Kossemehl and G. Manecke Makromol. Chem. 1975,176,333. 0.Meth -Cohn and R. K. Smalley for [c]-fused thiophens as exemplified in Scheme 19.94 It also proceeds satisfactorily with 3-bromothiophen-2-carboxylicacids94 and 2-bromothiophen-3-carboxylic acids.” Interesting but unsuccessful attempts to prepare the bis-thiophen analogues X / CH \ Y ____) Cu NaOEt Bbco2H EtOH x%co2H X,Y = C02Et COR,etc.Z=NHorO Scheme 19 of biphenylene have been de~cribed.~~ The thermal cheletropic extrusion of SO2 from both cis-and trans-isomers of dihydrothiophen 1,l-dioxides (100) and from the corresponding thiepin (101)has been proved to be highly stereospecific in line with orbital symmetry ~~nsiderations.~~~~ 4.. c:i2 \ Me Me (100) (101) A simple method of conversion of 3-methyl- and 3-ethyl-thiophen into the 3-formyl and 3-acetyl derivatives respectively has been reported.” The deep-blue o-thioquinomethides (102) have been made and in the absence of dienophiles yield a coloprless dimer.They behave as interesting dienes in Diels- Alder reactions.99 (102) The 1,6-dioxa-6a-thia- (or -selena-)pentalenes (103)undergo both 0 and C-protonation with acid to give the first examples of oxathiolium and oxaselenolium (104) systems.loo The elusive four-valent sulphurane system (105) has been reported. lo’ 94 D. E. Ames and 0.Ribeiro J.C.S. Perkin I,1975 1390. 95 J. A.Clarke and 0.Meth-Cohn unpublished results. % B. E. Ayres S. W. Longworth and J. F. W. Mdhnie Tetrahedron 1975,31,1755. 97 W.L. Mock (a)J. Amer Chem. Soc.,1975,97,3666;(b) ibid. p. 3673. 98 J. A. Clarke and 0.Meth-Cohn Tetrahedron Letters 1975,4705.99 R.Okazaki and N. Inamoto Chemisfty ktters 1974 1439. loo D.H.Reid and R. G. Webster J.C.S. Perkin I 1975,2097. 101 B.S.Campbell,D. B. Denney D. Z. Denney andLi-Shang Shih J. Amer. Chem. Soc. 1975,97,3850. Heterocyclic Chemistry 267 0-x-0 0-5 0 0 Slo /\ (103) X = S or Se (104) RO OR (105) The chemistry of organic 'metals' continues to develop and conductivity records are regularly broken. The polymer (106)'02 and the complex (107)with a modified ac~eptor"~ are of interest and a simplified synthesis of (log),which is purple in the "kCN s>cs S NCHS CN solid state but pink in so1ution,'04 is noted. However the present good-conductivity prize goes to the annelated diselenadithiafulvene complex (109).'05 A safe preparation of the intermediate (110) has been described.lM The highly effective Diels-Alder diene (1 11) is conveniently availablelo7 and a new highly stereo- and regio-selective hydroboration reagent 1,3,2-benzodioxaborole (1 12) (easily prepared from catechol and borane in THF) has been described."* Thus dec-1-ene and styrene react at the terminal carbon in 98 and 92% yield respec- tively and norbornene reacts ex0 to the extent of 99.5%.lM Y. Ueno Y. Masuyama and M. Okawara Ckmistry Lettern 1975,603. lo3 J. R. Andean C. S. Jacobsen G. Rindorf H. Soling and K. Bechgaard J.C.S. clhem. Comm. 1975 883. lO4 Z. Yoshida T. Kawase and S. Yoneda Tefrahedron Letters 1975,331. lo5 H. K.Spencer,M. V. Lakshmikantham,M. P. Cava and A. F. Garit0,J.C.S.dkm.Comm. 1975,867. lo6 J. R. Anderson and K. Bechgaard J. Org. dhem 1975,40,2016. lo' T. H. Chan and K. T. Nwe Tefruhedron,1975,31,2537. lo8 H. C. Brown and S. K. Gupta J. Amer. Chem Soc. 197597,5249. 0.Meth-Cbhn and R. K. Smalley 4 Six-membered Ring Compounds The reaction of lithiated crotylimines with nitriles (Scheme 20) constitutes a new pyridine synthesis.'og R R R rCNe R +& -6 \ NBu' \ mu' NHBu' Scheme 20 Triaryl-substituted pyridines are available by treating oxazinium salts (113) with 'active' methylene and by the reaction of nitrile ylides with 2,3- diphenylmethylenecyclopropene." ' Diphenylcyclopropenone reacts similarly to yield 4-pyridones. A variation of the Hantzsch synthesis using methyl propiolate (2 moles) an aryl aldehyde (1mole) and ammonium acetate allows the preparation of 1,2,6-~nsubstituted 1,4-dihydropyridines in good yield.'l2 The Diels-Alder adduct (1 14) on treatment with an azide followed by hydrolysis and decarboxylation yields the cyclic hydrazine (1 15). Mercuric oxide oxidation of (115) is accompanied by loss of nitrogen and formation of l-substituted 1,4- dihydropyridines(116) in variable yields (11-90%).' l3 (1 13) (114) (115) (1 16) 1,4-Dialky1-1,4-dihydropyridines are obtainable in excellent yield by Birch reduc- tion of 4-alkylpyridines in the presence of an alkyl halide.'14 In the absence of ethanol superior yields of N"-substituted 4,4'-bipyridyls are claimed. The hitherto almost inaccessible 2-aza-1,4-quinones e.g.(117) are now available by thermal rearrangement of 2-azido-2-cyanocyclopenten-1,3-ones(118) which result from the controlled thermolysis of 2,3-diazid0-1,4-quinones.~~~ K. Takabe H. Fujiwara T. Katagiri and J. Tanaka TetrahedronLetters 1975,4375. 11* I. Shibuya and M. Kurabayashi Bull. Chern. Soc.Japan 1975,48,73. ll1L.Toupet and R. Carrie J.C.S. chem. Comm. 1975,384. 11* T.Cheunat and U. Eisner J.C.S. Perkin I 1975 926. l13 D.M.Stout T. Takaya and A. I. Meyers J. Org. Chem. 1975,40 563. 114 A.J. Birch and E. A. Karakhanov J.C.S. Chem. Cornm. 1975 480. 115 D.S. Pearce M.J. Locke and H. W Moore J. Amer. Oum. SOC.,1975,97,6181. Heterocyclic Chemistry Room-temperature oxidative cyclization of aP,y&unsaturated amides with lithium chloropalladite in acetonitrile solution in the presence of triethylamine provides a new 2-pyridone synthesis.' 160 The parent acids undergo similar cycliza- tions in polar solvents to give 2-pyrones.'16' A general survey of old and new methods for the synthesis of NN'-linked bi(heteroary1s) has been published,' 17a and 1-pyridino-2-pyridones (1 19) members of this class of compounds are of synthetic potential.' '7b For example (119) reacts with sodium sulphinate and with potassium cyanide to give disulphone (120) (64%) and 2-cyanopyridine (87YO),respectively.(1 19) ( 120) Triphenylphosphine in acetonitrile solution has merit as a dealkylating agent for N-alkylpyridinium salts particularly when the alkyl group is benzyL1'' A useful synthesisof 2-aminonicotinaldehydes arises from the acid-promoted ring-opening of the readily available 6,7-disubstituted pyrido[2,3-d]pyrimidines.' l9 Worthyof men-tion is the new oxidant pyridinium chlorochromate (C5H5NHCr0,CI) which is prepared simply and in high yield by adding pyridine to chromium trioxide in 6M-HCl.Under mild conditions it selectively oxidizes alcohols to carbonyl compounds in excellent yield. Further studies'*l on the 'phenylnitrene energy surface' have led to the first synthesis of cyclobuta-[2,3]- and -[3,4]-pyridines. 12* Pyrindanes (121) are obtained in good yield (65%) along with other products from the flash vacuum pyrolysis of p-phenylethylsulphonyl azides at 650 0C.123 The reaction is complex and tempera- ture dependent. At 300"C for example benzothiadiazine dioxide (122) is formed in 12.8% yield.R 3-Oxido-N-phenylpyridiniumbetaine (123) on pbtolysis (A =350 nm) in ethyl acetate yields a mixture of dimer (124) valencebond isomer (125) and the em-and l6 (a)A. Kasahara and T. Saito am. adZnd. 1975,745; (b)T.Izumi and A. Kasahara Bull. Chern.SIC. Japan 1975,48,1673. 117 (a) A. R. Katritzky and J. W. Suwinski Tetrahedron 1975,31 1549; (b) A. R. Katritzky and M. P. Sammes J.C.S. Chem. Comm. 1975,247. 11* J. P.'Kutney and R. Greenhouse Synthetic Comm 1975 119. 119 G. Evens and P. Caluwe J. Org. Chem. 1975,40 1438. IZo E. J. Corey and J. W. Suggs Tetrahedron Letters 1975,2647. lz1 Ann. Reports (B),1974,71 319. lz2 W. D. Crow A. N. Khan and M. N. Paddon-Row Austral. J. Chem. 1975,28,1741.lZ3 R. A. Abramovitch and W. D. Hoicomb J. Arner. Chem. k., 1975,97 676. 0.Meth-Cohn and R. K.Smalley endo-forms of the (3,4)-(2,6) cycloadduct of valence isomer (125) and betaine (123).124 0 (1 23) (124) (125) The variation of reactivity towards cycloaddition with structure of 3-oxidopyridinium and 3-oxidopyrazinium betaines has been rationalized. 4-Oxidoisoquinolinium betaines (127) have been synthesized via the isolable aziridine (126) (Scheme 21).126 ii RN ___ \ \ 0 0 0 -me 21 The chemical versatility of heteroaromatic N-oxides continues to be exploited. Yields in the photo-induced ring-contraction of 4-substituted pyridine N-oxides to 3-substituted pyrrole-2-aldehydes have been found to be dramatically increased if photolysis is carried out in the presence of copper ~ulphate.'~' Pyridine carbamates e.g.(128) are available in practicable yield (50-60%) by the action of cyanogen bromide on pyridine N-oxides. 12* 2-Acylpyridines 2-acylquinolines and 1-acylisoquinolines may be conveniently prepared by treating the appropriate N-oxide with o-benzoylcyanohydrins in hot acetic anhydride.'*' In a variation of a reaction reported last year,130 3,5-dichloropyridine N-oxide will react with ethynes e.g. PhC=CCN to give furo[3,2-b]pyridines e.g. (lD) in one step.'31 lz4 A. R. Katritzky and H. Wilde J.C.S. Chem. Comm. 1975,770. 125 (a)N. Dennis B. Ibrahim and A. R. Katritzky J.C.S. Clrem. Comm. 1975,425; (b)N. Dennis A. R. Katritzky and M. Ramaiah J.CS. Perkin I 1975 1506.126 P. E. Hansen and K. Undheim J.C.S. Perkin I 1975,305. I27 F. Bellamy P. Mertz and 3. Streith;Heterocycles 1975,3 395. '28 M. Hamana and S. Kumadaki J. Pharm. Soc.Japan 1975,95,87. T. Endo S. Saeki and M. Hamana Heterocycles 1975 3 19. Ann. Reports (B) 1974,71 343. 131 R. A. Abramovitch and I. Shinkai J. Amer. Chem. Soc. 1975,97 3227. Heterocyclic Chemistry 271 0 one-pot synthesis of pyrroloindolizines has been announced,*33 which involves treating 2-acetylpyridine with methyl propiolate (2 moles). The reaction can be extended to the preparation of quinolizines if 2-phenacylpyridines are employed in place of the pyridyl ketone. Treatment of acetanilides with HMPA in hot DMF yields 2-dimethylaminoquinolines(40-76%) by way of the amidine intermediates (130).134 Replacement of DMF by acetic acid results in the formation of 2-dimethylaminolepidines but in reduced yields (23-54%).The hitherto inaccessi- ble 2-acyl-3-hydroxyquinolinescan be synthesized by a novel variant of the Smiles rearrangement (Scheme 22). 13’ n Scheme 22 Interest grows in the synthetic applications of intramolecular [4 +21 and 1,3-dipolar cy~loadditions.~~~”” Of the former type mention may be made of the cis stereoselective thermal ring-closure of amides (131;n =2 or 3) to hexahydro-A6- indoles and octahydro-A7-quinolines,respectively.137 In contrast amide (I32) yields mainly the trans-product (133). The quinolyne derived by treating 5-bromoquinoline with potassium amide in liquid ammonia is claimed as the best route (47%) to the otherwise difficultly obtainable 6-aminoquinoline.138 The ring-opening of nitrogen heterocycles with 132 Ann. Repom (B),1974,71,344. 133 R. M.Acheson and J. Woollard J.C.S.Perkin I 1975,740. 134 E. B. Pedersen and S. 0.Lawesson AcfuChem. Scand. (B),1974 28 1045. 135 D. W. Bayne A. J. Niml and G. Tennant J.C.S. Chem. Comm. 1975,782. 136 (a) L. Garanti A. Sala and G. Zecchi J. Org. Chem. 1975,40,2403; (b)R. FUSCO L. Garanti and G. zecchi ibid. p. 1906. 137 W. Oppolzer and W. Frostl Helv. Chim. Acta 1975,58 590. 13* H. Poradowska E. Huakowska and W. Czuba Synthesis 1975,733. 0.Meth-Cohn and R.K. Smalley R' I H (131) (132) (133) thiophosgene reported last year 139has been applied to 4,7-dichloroquinoline and yields the synthetically useful p-(o-thiocyanatopheny1)acrylaldehyde (134).140 With nucleophiles facile cyclization to vinylbenzothiazines (135)is observed.(134) (135) (136) Hydrogenation of quinoline isoquinoline and phenyl-substituted pyridines with platinum oxide in trifluoroacetic acid results in selective reduction of the carbocyclic ring.141a The 5,6,7,8-tetrahydroquinolinesso formed can be further reduced with sodium and ethanol in a high-yield (90%) synthetic route to trans-decahydroq~inoline.'~~~ Ruthenium tetroxide produced in situ by the action of sodium periodate on ruthenium dioxide is advocated as a useful reagent for the rapid high-yield room-temperature catalytic oxidation of quinolines to pyridine- 2,3-dicarboxylic acids.142 N-Methylisoquinolone (136) is available in high yield by Vilsmeier reaction of homophthalic acid at 100 "C,followed by decarb~xylation.~~~ Ozonolysis of 2,3-diarylindoles has been used as a preparative route to o-acylbenzanilides. With potassium amide in liquid ammonia the anilides cyclize to give N-acylacridones via an aryne intermediate.'44 Addition of aromatic diazonium salts to nucleophilic dienes proceeds well in acetonitrile solution in the presence of a Lewis-acid catalyst 14'-arylpyridazinium salts may be obtained. 1and good yields of 3-Azidopyridazine 2-oxides unlike mono- and di-azine N-oxides reported previ~usly,'~~ undergo thermal decomposition to give only acyclic products. For example the azido-N- oxide (137; R =Cl) in boiling toluene loses nitrosyl chloride and gives maleonitrile in 85% yield.I4' Similarly the methoxy-azide (137; R =MeO) and the parent azide (137; R=H) yield methyl p-cyanoacrylate (89Y0) and unstable p-cyanoacry lalde h yde ,respectively.139 Ann. Reports (B),1974,71 343. 140 R. Hull P. J. van den Broek and M. L. Swain J.C.S. Perkin I 1975,922. 141 F.W.Vierhapper and E. L. Eliel (a)J. Org. am. 1975,40,2729;(b)ibid. p. 2734. D. C. Ayres and A. M. M. Hossain J.C.S. Perkin I 1975,707. 143 V. H. Belgaonkar and R. N. Usgaonkar Tetrahedron Lefters 1975,3849. 14* G.4. J. Chen and M. S. Gibson J.C.S. Perkin I 1975 1138. 145 B. A. Carlson W. A. Sheppherd and 0.W. Webster J. Amer. Gem. Soc. 1975,97,5291. 146 Ann. Reports (B) 1973,70,505. R.A. Abramovitch and I.Shinkai J.C.S. Chem. Comm. 1975,703. 14' Heterocyclic Chemistry (137) L (139) The permutation-pattern approach to explain complex photo-induced rearrange- ments of various heterocyclic systems has been applied'48" successfully to the phototransposition of 4-hydroxypyrylium cations.'48b However some aspects of this intriguing approach have been ~hallenged,'~~ that particularly the ~taternent'~~' there is no case in which any connection has been established between Dewar and prismane isomers and the occurrence of phototransposition. It has been pointed out forcibly that Dewar isomers are known in the photorearrangement of perfluoroalkyl-pyridazines to pyra~ines,'~' and examples of prismane intermediates in the photo- isomerization of perfluoroalkylpyridines have recently come to light.149 A startling synthesis of tetrahydropyridazine-metal complexes e.g.(139) has been unearthed during the reaction of dinitrogen tungsten and molybdenum com- plexes (138;M =W or Mo) with alkyl bromides in THF solution in the presence of visible light."l In a unique reaction the complexed nitrogen apparently displaces oxygen from the THFring! The role of the alkyl bromide is as yet unknown but vital since the reaction fails in its absence. Interestingly there is no analogous reaction with tetrahydrothiophen. Fluoromalonodialdehyde FCH(CHO)* is a useful reagent for the synthesis of fluoroheterocycles e.g. 5-fluoro-pyrimidines and -pyrimidone~,'~~ and pyrimidinethiones are available in excellent yield by reaction of vinyl methyl ketones with arylhydrazines in the presence of trimethylsilyl i~othiocyanate.'~~ Access to the hitherto virtually unknown pyrimidine 1,3-dioxides is now possible by manganese dioxide oxidation of the cyclic hydroxamic acid N-oxides (140) (Scheme 23).lS4 R2 RZ R2 (140) Scheme 23 The first example of a thio-Claisen rearrangement in the pyrimidine series has been announced and is worthy of mention as the reaction is a convenient mild synthetic method for 5-alkyl~racils.'~~ A high-yield regioselective alkylation of 148 (a)J.A. Barltrop R. Carder,A. C. Day J. R. Harding and C. Samuel,J.C.S. them. Comm 1975,729; (b) Ann. Reports (B),1973,70,313; (c)J. A.Barltrop and A. C. Day J.C.S. Chern. Comrn,1975,177. 149 R.D.Chambers,R. Middleton and R. P. Corbally J.C.S. Chern. Comrn. 1975,731. 150 R.D.Chambers,J. A.M. McBride J. R. Maslakiewicz and K. C. Srivastava,J.C.S.Perkin I 1975,396. A. A.Diamantis J. Chatt G. A. Heath and G. J. Leigh J.C.S. Uum. Comm. 1975,27. lS2 C.Peichardt and K. Halbritter Annalen 1975,470. R. Neidlein and H. G. Hege Synthesis 1975,50. lS4 A.Ya. Tikhonov and L. B. Volodarsky TetrahedronLetters 1975,2721. lS5 J.-L. Fourrey E. Estrabaud and P. Jouin J.C.S. Chern. Cornrn. 1975,993. 0.Meth-Cohn andR. K.Smalley xanthines and hypoxanthines at N-7 may be achieved by treating the heterocycles as a cobalt complex with an alkyl halide.156 The product from the action of acetic anhydride on o-aminobenzaldoxime long thought to be a benzo-3,1,4-oxadiazepine has now been shown by X-ray analysis to be 2-methylquinazoline 3-0xide.l" Hydroxylamine in aqueous alkali appears to be a useful aminating agent and converts 6-nitroquinoxaline into its 5-amino-derivative under mild condi- tion~.~~* High-temperature (650 "C) pyrolysis of carbamate (141) in a quartz tube provides the first synthesis of 1,3-oxazin-6-one (142) (27%).15'This ring system is of interest as a potential precursor of the as yet unknown azacyclobutadiene.However on photolysis the oxazinone yields only HCN C02,and acetylene possibly by way of the valence isomeric bicyclic system (143). Substituted 1,3-oxazin-6-ones appear as products in the reaction of diphenylketen with a variety of heterocycles,'60 and many of the current results necessitate a re-interpretation of earlier work on this reaction.(141) (142) (143) The C-nitraso-imine (147) a member of a previously unreported class of organic compounds appears to be an intermediate in the lead tetra-acetate oxidation of oxime (144) and in the reaction ofsulphimide (145) with nitrile oxide (146) (Scheme 24).161" The nitroso-imines spontaneously cyclize to 1,2,4-benzoxadiazines e.g. (148),161q6 but in the presence of thebaine an efficient trap for the dienophilic nitroso-group they yield the Diels-Alder [4 + 21 cycloadducts.'"" CO,Et Scheme 24 lS6 L. G. Marzilli L. A. Epps T. Sorrell and T. J. Kistenmacher J. Amer. Chem. Soc. 1975,97,3351. lS7 L.GoliE V. KautiE B. Stanovnik and M. TiSler Tetrahedron Letters 1975,4301. Is8 R.Nasielski-Huikens and M.Benedek-Vamos J.C.S. Perkin I 1975 1229. A. Krantz and B. Hoppe J. Amer. cham. Soc. 1975,97,6590. I6O G.A. Taylor J.C.S. Perkin I 1975 1001. 16* (a)T.L. Gilchrist M. E. Peek and C. W. Rees J.C.S. Chem. Comm. 1975,913;T,L.Gilchrist M. E. Peek and C. W. Rees; (b) ibid. p. 914;(c)T.L.Gilchrist C. J. Harris M. E. Peek and C. W. Rees ibid. p. 962. Heterocyclic Chemistry The 1,2,4-benzoxadiazines undergo a remarkable ring-contraction to benzox- azoles (Scheme 25) itprocess which may well involve a rare but in this instance geometrically favourable intramolecular [,4 +,2,] cycloaddition.16" ANRORC reactions of the type reported 'in some detail last year,'62 have been extended to include triazine and several interesting transformations of pyrylium salts.For example 2,4,6-triphenylpyrylium perchlorate with sodium nitrite in acetonitrile yields the diacylisoxazole (149),la and with guanidine 2-am1no-4,6-diphenylquinazoline,which reacts further with more pyrylium salt to give Scheme 25 the pyridinium perchlorate (150).'65 N-Arylpyridinium salts are also obtained on treating pyrylium salts with pyridinium acylylide~.'~~ In contrast with sulphonium acyl ylides ring-contraction to give furan derivatives e.g. (151) is observed. Ph Ar COAr Ar COON (149) Pyrylium salts e.g. (152; X =0),react with sodium azide to give the 2-azido- derivatives which on warming undergo RORC reactions with loss of nitrogen to yield oxazepine (154; X=O) (90%) via the isolable azirine (153; R=H).16' In contrast the analogous reaction with thiapyrylium salts (152; X =S) generates the thermally unstable thiazepines (154; X =S) which by extrusion of either sulphur or benzonitrile yield pentaphenylpyridine and tetraphenylthiophen respectively.Studies on photolytically induced ring-opening reactions of five- and six- membered oxygen heterocycles have shown that selective excitation of the enol 162 Ann. Reports (B),1974 71 347. A. Rykowski and H. C. van der Plas Rec. Truu. chim. 1975,94,204. 1b4 C. L. Pedersen and 0.Buchardt Am Chem. Scand. (B),1975,29,285. 165 M. P. Zhdanova E. A. Zvezdina and G. N. Dorofeenko Khim. geterotsikl. Soedinenii 1975,277. A. R.Katritzky S. Q. A. Rizvi and J. W. Suwinski Heterocycles 1975,3 379. Ib7 J.-P. Le Roux,J.-C.Cherton and P.-L.Desbene Compt. rend. 1975,280 C 37. 16' 0.Meth-Cohn and R. K.Smalley R Ph &h Ph phfiph Ph X Ph Ph Ph Ph Ph rather than the more usual keto tautomer can occur.'68a The reactions are highly solvent dependent. For example photolysis of chromene (155; R1= OH R2= C0,Me) in acetonitrile yields the dihydrocoumaran (159) via the o-quinonoid intermediate (156) (Scheme 26).168b*c However in benzene solution the valence h I' + q RZ OH I R' C0,Me C0,Me (157) (155) MeY I C0,Me (159) Scheme 26 tautomer (158) of dihydrofuran (157)exists long enough for further light absorption to take place so that loss of carbon monoxide occurs and the o-vinylphenol(l60) is the major product. Selective excitation of an enol tautomer is also observed during photolysis of 3-phenylisocoumaranone.169 and coumarin~~~~ New general syntheses for thiopyran-2-thione~'~~ have appeared the latter method being adaptable for preparing thiocoumarins and 2-quinolones. a-Pyrones are so far unobtainable by [4 +21 cycloaddition of carbon dioxide and dienes. However an equivalent reaction is possible using diethyl ketomalonate and the resulting cycloadduct (161) readily undergoes a bis-Curtius degradation to an a-pyrone.17* 168 (a) A. Padwa and A. Au J.C.S. Chem Gmm 1975 58; (b) A. Padwa A. Au G. A. Lee and W. Owens J. Org. Chem. 1975,40,1142;(c)A. Padwa and A. Au J. Amer. Chem. Soc. 1975,97,242. 169 A. Padwa D. Dehm T. Oine and G. A. Lee J. Amer. Chem. Soc. 1975,97,1837.170 F. Ishii M. Stavaux and N. Lozach Tetrahedron Letters 1975,1473. T. Manimaran T. K. Thiruvengadam and V. T. Ramakrishnan Synthesis 1975,739. 172 R. A. Ruden and R. Bonjouklian J. Amer. Chem. Soc. 1975,97 6892. Heterocyclic Chemistry go-Thiopyrylium-3-olate (162) on basification yields cycloadduct (163) as a mixture of syn and unti forms.173a 2-Benzothiopyrylium-4-olate (164) behaves similarly. 1736 This behaviour is reminiscent of that exhibited by 3-oxidopyridinium betaines (see p. 270). d:Cy-J ( 164) so2 00N3 4% Schmidt reaction on thiochromone SS-dioxide yields besides the expected ring- expanded product (165) the HN,-adduct (166) the first example of a stable a-azido-~ulphone.'~~ The functionalization of As-phosphorins has been reported in some detail.4- F~rrnyl-,'~'" 4-~yano-,'~'" 4-ary1az0-,'~~* and 4-acetamid0-'~'~ derivatives have been prepared and a Claisen rearrangement on the allyloxy-derivative (167; R' = OCH2CH=CH2 R2= Ph) has yielded the phosphacyclohexadiene (168). On further heating (168) undergoes [3 31 sigmatropic shift of the ally1 group and intramolecular [4 + 21 cycloaddition to give the phosphaheterocycle (169). Diphosphorus (170; X = P) and phosphorus-arsenic (170; X = As) heterocycles have been isolated as cis-truns isomers,'76 and the new phosphorus-boron hetero- cycle (17 1)is potentially aromatic. 177 The azaphospha-adamantane (172) undergoes regioselective quaternization at nitrogen with methyl iodide. 178 173 (a)S. Baklien P. Groth and K.Undheim J.C.S. Perkin I 1975,2099;(b)K.Undheim and S. Baklien ibid. p. 1366. 17* I. W. J. Still M. T. Thomas and A. M. Clish Canud. J. Chem. 1975 53,276. '75 (a)H.H. Pohl and K. Dimroth Angew. Chem. Innternat. Edn. 1975,14,11 1; (6)M.Liickhoff and K. Dimroth ibid. p. 112;(c) 0.Schaffer and K. Dimroth ibid. p. 112. 176 G. Markl D. Matthes A. Donaubauer and H. Baier Tetrahedron Letreis 1975 3171. 177 H.0.Berger and H. Noth 2. Narurforsch.,1975,30b 641. 17* D. J. Daigle and A. B. Papperman J. He&mcyclic am. 1975,12,579. 0.Meth-Ghn and R.K.Smalley R2 Ph I I CP3 X I R' NEt (172) (170) (171) 4-Hydroxyarsabenzene has been prepared and unlike 4-pyridone7 appears to exist solely as the hydroxy-form."9 Arsa-anthracenes (174; R =halogen or Me) are conveniently prepared from the readily available arsinic acid (173).lBo R 5 Seven-memberedRing Compoundsand Macrocydes One of the most characteristic and interesting reactions of singlet arylnitrenes is their transformation into their valencetautomeric azirines and thence into azepines in the presence of an amine.However azepine formation is not always observed in the bicyclic series o-diaminoarenes often being preferred. French workers'8' have reported the fist important breakthrough in this area by photolysis of bi- or tri-cyclic azides in strongly basic media. It appears that the intermediate aziridine (175)is very sensitive to acid but stable in basic solution allowing selective conversion into either the azepine or the aminomethoxyarene (Scheme 27).The methoxyazepines are /D~ .:.-..m~3 hr. H 4 dioxan ' '::*. .<.* \ /KOMe-MeOH / Scheme 27 179 G. Mlirkl H. Baier and S. Heinrich Angew. Chem. Internut. Edn. 1975,14 710. 180 R. J. M. Weustink C. Jongsma and F. Bickelhaupt Tetrahedron Letters 1975 199. lS1 J. Ftigaudy C. Igier and J. Barcelo Tetrahedron Letters,1975,3845. Heterocyclic Chemistry easily converted into aminoazepines by amines. All seven chloroacetylaminoethylindoles have been cyclized with loss of HCl by photolysis cyclization occurring preferentially at the ortho or peri position. Positions 3,4 and 6 were highly reactive while position 1was unreactive.'82"b 8 f-J-$co2Et N" H Ph (176) (177) Formation of benzazepines by ring-expansion of quinoline N-oxides (with dimethylsulphoxonium methylide)Ig3 and isoq~inolines'~~ (by art ANRORC mechanism) has been examined the latter offering a useful entry to rhoeadine alkaloid synthesis.The first examples of 3H-1,2-diazepines have been described being derived from ay-dienones and tosylhydrazine. lg5 Unlike their SH-isomers they show no tendency to exist as bicyclic valence tautomers. A simpler approach to difEcultly accessible lH-1,2-benzodiazepines (176) has been as has the preparation of the last remaining unknown benzodiazepinone (177) some derivatives of which show biological (CNS) activity as great as that of ~alium.'~' An efficient synthesis of the potentially degenerate oxepin oxide (178) has been described commencing from oxepin.'88 The small amount of ethanol in commercial chloroform often shows up unexpec- tedly in reactions.Thus the remarkable conversion in Scheme 28 results from the attempt to allylically brominate the thiazepine (179).lg9 The bromobenzothiepinone Scheme 28 (180) undergoes novel rearrangements to give the tricyclic products (181) and (182).190 The first observable silicenium ion (183) is available in solution by the action of trityl perchlorate on the corresponding hydride at -40 to -50°C.'9' Another first is the synthesis of a non-fused borepin (184).'92 la2 (a) Ann.Reports (B) 1974,71,354;(b)S.Naruto ando. Yonemitsu TetrahedronLetters,1975,3399. 183 V. N. Gogte K. M. More and B. D. Tilak Indian J. Chem. 1974,12 1238. la4 M. Shamma and L.Toke Tetrahedron 1975,31,1991. 185 C. D.Anderson J. T. Sharp H. R. Sod and R. S. Strathdee J.C.S. Chem. Comm. 1975,613. la6 L.Garanti A. Scandroglio and G. Zecchi Tetrahedron Letters 1975,3349. la' U.Golik Tetrahedron Letters 1975 1327. la8 W.H.Rastetter J. Amer. Chem. Soc.,1975,97,210. Ia9 I. It0 and T. Ueda Chem. and Pharm. Bull. (Japan),1975,23 1646. 190 P.M.Weintraub and A. D. Sill J.C.S. Chem. Comm. 1975,784. 191 J. Y.Corey J. Amer. Chem. Soc. 1975,97 3237. lg2 J. J. Eisch and J. E. Galle J. Amer. Chem. Soc. 1975,97,4436. 0.Meth -Cohn and R.K. Smalley I Ph NMe (184) (183) Kauff mann has synthesized several cyclopolyheteroaromatics (1 85) by coupling dilithio-biheteroaryls with cuprous chloride lg3 and various related systems e.g.(185) (186) by the same appr0a~h.l~~ The interesting fluxional thiabarbaralene (187) results from an unprecedented 175-cycloaddition of SO2to cyclo-octatetraene in the presence of SbF5 at -70°C. Warming transforms it into the thermodynamically favoured isomer (188; X =S02).lg5A good synthesis of 9-oxabicyclo[4,2,l]nona-2,4,7-triene (188; X = 0)has come to light by the photoinduced interaction of cyclo-octatetraene epoxide with iron pentacarbonyl. 196 N~N (186) 193 T. Kauffmann B. Greving J. Konig A. Mitschker and A. Woltermann Angew. Chem. Internat. Edn. 1975,14,713. 1g4 T. Kauhann B. Muke R. Otter and D. Tigler Angew. Chem. Internat. Edn. 1975,14,714. 195 L.A. Paquette U. Jacobson and M. Oku J.CS. Chem. Comm. 1975 115. 1% R.Aumann and H.Averbeck J. Organometallic Chem. 1975,85,C4. Heterocyclic Chemistry 281 When a bidentate nucleophile reacts with a polynitroaromatic compound the intermediate Meisenheimer-type complex can undergo a second attack leading to novel products. Thus,the benzornorphan (189) is obtainable in 80% yield (Scheme 29).lg7 Ph 'CH-C / 2 PhCH =C R \ NMe N NO2 -0' + '0-NO Scheme 29 Heteroannulenes continue to hold the stage. Thus while the all-cis azoninyl anion (19a)is aromatic its benzo-analogue lacks aromaticity (i.e. is atropic below -35 "C) 190) (191) .andis thermally unstable reverting to the isomer (191) at 0 "C.This isomer in which 19'unfavourable peri-interactions are removed is distinctly diatropic. The para- tropicity (anti-aromatic character judged by n.m.r.) and diatropicity of a series of [12~]- (192; n = 1)and [lLCnJ-annulenes (192; n =2) respectively are reduced in the same order with a series of fused rings attached reflecting the decrease in importance of different participating KekulC structures of the macrocyclic rings.'99~200 The diatropic bridged [14]annulene (193) has been prepared and shows appropriate low-field NH and Me signals in its 'H n.m.r.spectrum.2o1 The first examples of paratropic non-bridged [15 Jannulenes (16~ systems) e.g. (194) have been described.202 19' R. B. Bard and M. J. Straws J. Amer. Chem. Soc.,1975 W,3789. 198 A. G. Anastassiou and E. Reichmanis J.C.S. Gem. Comm. 1975 149. 199 R. H. Wightman and F. Sondheimer TetrahedronLetters 1975,4179.2oo R. R. Jones J. M. Brown and F. Sondheimer Tetrahedron Letters 1975,4183. 201 W. Flitzsch and H. Peeters TetrahedronLetters 1975,1461. 202 R. L. Wife P. J. Beeby and F. Sondheimer J. Amer. Chem. SOC.,1975,97,641. 0.Meth -Cohnand R. K. Smalley (193) R’ = RZ = H or Ac (194) A principal method of approach to cyclophanes lies in the preparation of a dithiacyclophane followed by contractive removal of sulphur. A new method of sulphur removal by action of benzyne has appeared and is the method of choice for [2,2]cyclophane dienes and for paracyclophane~.~’~ The conformational trithiacyclod~decene,~~~ properties of a~a~yclo-~~tane~,~~~ and NN’N”-trimethyltrianthranilide206have been reported. A new route to metacyclophanes in general and [2,6]pyridinophanes in particular involves interaction of a dichloroarene with an am-polymethylene Grignard reagent in the presence of dichloro[ 1,3-bis(diphenylphosphino)propane]nickel(~~).The reaction also has potential for mac- rocyclic pol yether synthe~is.~” Crown ethers and their analogues have become an exciting frontier in research and the year has seen particular drama in the chiral recognition possibilities of ammonium complexes.The development of enzyme-like properties is a fascinating possibility. Thus Cram’s group have developed various chiral crown ethers incor- porating binaphthyl units to enhance chiral barriers,208 and have demonstrated differential complexation of hexafluorophosphate salts of methyl glycinate and ~alinate.~” Chirality has been very conveniently introduced into 18-crown-6 analogues e.g.(195) by use of diols readily prepared from natural carbohydrates such as L-tartaric acid and D-mannitol.210 Having D symmetry the last reagents are homotopic and with enantiomeric guest ammonium salts should lead to preferen- tial diastereoisomeric complexation. This has been demonstrated by n.m.r. spectro- scopy using a-phenylethylammonium hexafluorophosphate.211 New systems 203 T. Otsubo and V. Boekelbeide Tetrahedron Letters 1975 388 1. 204 J. B. Larnbert and S. A. Khan J. Org. Chem. 1975,40,369. 205 W.D. Ollis J. F. Stoddart and M. Nbgridi Angew. Chem. Internat. Edn. 1975 14 168. 2-W. D. Ollis J. A. Price J. S. Stephanatou and J. F. Stoddart Angew.Chem.Internat. Edn. 1975,14 169. 20’ K. Tarnao S. Kodarna T. Nakatsuka Y. Kiso,and M. Kurnada J. Amer. Chem. Soc. 1975,97,4405. 208 F. de Jong M. G. Siegel and D. J. Cram. J.C.S. Chem. Comm. 1975 551. 209 G. W. Gokel J. M. Tirnko and D. J. Cram. J.C.S. Chem. Comm. 1975,444. 210 W. D. Curtis D. A. Laidler J. F. Stoddart and G. H. Jones J.C.S. Chem. Cornm. 1975 833. 211 W. D. Curtis D. A. Laidler J. F. Stoddart and G. H. Jones J.C.S. Chem. Comm. 1975 835. Heterocyclic Chemistry 283 include crown ether-esters with interesting ion-complexing a remark- able caesium-selective 'football' ligand (196)in which the cation is trapped inside the cavity giving the most stable caesium complex known to date,'13 and the non-cyclic polyethers e.g.(197) which are also good complexing agents for alkali-metal and i 0 (196) (197) alkalineearth ions.214 Reinhoudt has proposed the use of Zeise's salts (e.g. KPtCl, C2H,) as a test method for crown ether complexation with cations. The salts are insoluble in chloroform but dissolve on complexation of the cation giving an ethylene signal easily determinable by n.m.r. spectroscopy.21s 6 Reviews The synthesis of heterocycles by cycloaddition to 1-azirines,2'6 by way of ben- zofur~xans,~'~ thioureas,2'8 or cup-unsaturated carbonyl and by ring transformation of isoxazoles220has been surveyed and the chemistry of pyridine221 (final volume of the four-part supplement) non-classical condensed thiophens,222 heterocycles having 8~-electrons,~~~ oxaz~les,~~~ thiiran~,~~~ isatin,226 thio- chr~mones,~~~ various nitrogenous three-membered chromenes,228 benzof~ran,~~~ heterocycle^,^^' heterocycles containing less common heteroatom~,~~~ transition-metal complexes df synthetic macrocyclic ligand~,~,~ and new heterocyclic optical 212 J.S. Bradshaw L. D. Hansen S. F. Nielsen M. D. Thompson R. A. Reeder R. M. Izatt and J. J. Christensen J.C.S. Chem. Comm. 1975,874. z13 E. Graf and J.-M. Lehn J. Amer. Chem. Soc.,1975,97,5022. 214 E. Weber and F. Vogtle Tetrahedron Letters 1975 2415. 215 R. T. Gray and D. N. Reinhoudt Tetrahedron Letters 1975,2108. 216 D. J. Anderson and A. Hassner Synthesis 1975,483. 217 K. Ley and F. Seng Synthesis 1975,415. 218 T. S. Griflin T. S. Woods,and D. L. Klayman Ado. Heterocyclic Chem.1975,18 100. 219 G. Desimoni and G. Tacconi Chem.Rev. 1975,75651. 220 T. Nishiwaki Synthesis 1975,20. Zz1 'Pyridine and its Derivatives' in 'The Chemistry ofHeterocyclic Compounds,' ed R. A. Abramovitch Wiley New York 1975 Vol. 14 Supplement Part 4. 222 M.P. Cava and M. V. Lakshmikantham Accounts Chem. Res. 1975,8,139. 223 R. R. Schmidt Angew. Chem. Internat. Edn. 1975,14,581. 224 A. V. Fokin and A. F. Kolomiets Russ. Chem. Rev. 1975,44 138. 225 I. J. Turchi and M. J. S. Dewar Chem. Rev. 1975,75 389. z26 F. D. Popp Adv. HetermyclicChem 1975,18 1. 227 S. W.Schneller Ado. Heterocyclic Chem. 197518 60. 228 L. Merlini Adv. Heterocyclic Chem. 1975,18 159. 229 P. Cagniant and D. Cagniant Adv. Heterocyclic Chem.,1975,18,338. 230 G.L'Abbt Bull. Soc.chim. France 1975 1127. 231 P. Jutzi Angew. Chem. Internat. Edn. 1975,14232. 232 L. F. Lindoy am. Soc.Rev. 1975,4,421. 284 0.Meth -Cohn and R.K. Smailey brighteners233 has been evaluated. Reviews have appeared on heteroaromatic tautorneri~m~~~ and on the tautomerism and electronic structure of biologically important pyrimidines,235 on the reactions of natural and synthetic P-lactam~,~~~ the 1,3-dipolar cycloaddition reactions of nitrone~,~~~ on the conformation of piperidine and its heterolog~es~~~ and of pentamethylene on diazotization of heterocyclic primary amine~,~~' and on rearrangement of penicillanic acid deriva- tives.241 233 A. Dorlars C.-W. Schellhammer and J. Schroeder Angew. em. Intentat. Edn. 1975,14 665.234 J. Elguero C. Marzin A. R. Katritzky and P. Linda Adu. Heterocyclic Chem. 1976 supplement I. 235 J. S. Kwaitkowski and B. Pullmann Adu. Heterocyclic Chem. 1975,18,200. 236 A. K. Mukerjee and A. K. Singh Synthesis 1975,547. 237 D. St. C. Black R. F. Crozier and V. C. Davis Synthesis 1975 205. 238 I D. Blackburne A. R. Katritzky and Y. Takeuchi Accounts Chem.Res. 1975,8,300. 239 J. B. Lambert and S. I. Featherman Chem. Rev. 1975,75,611 240 R. N. Butler Chem.Rev. 1975,75 241. 241 R. J. Stoodley Tetrahedron 1975,31 2321.

ISSN:0069-3030    

DOI:10.1039/OC9757200249

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

12 Alicyclic Chemistry By A. COX Department of Molecular Sciences Unjvemjty of w8rwick Coventry CV4 7AL 1 Synthesis Three-and Four-membered Rings.-A review containing 142 references on the chemistry of cyclopropanols has appeared.’ The use of carbenes in the synthesis of cyclopropanes has been further developed. For example’ irradiation of fluorodi-iodomethane at 350nm in the presence of an olefin trapping agent provides a synthetically useful one-step procedure for the preparation of a variety of monofluorocyclopropanes; yields as high as 45% have been obtained. The monofluorocyclopropanes are formed stereospecifically and this is in agreement with the view that the reaction involves formation of the fluorocarbene followed by addition of the carbene to the olefin rather than addition of the fluoroiodomethyl radical followed by ring closure with loss of iodine atom.The zinc bromocarbenoid reagent prepared from diethylzinc and bromoform in the presence of oxygen also leads to conversion of olefins into the corresponding monobromocyclopropanes in good yield.3 Styrene greatly inhibits the formation of the zinc bromocarbenoid reagent and polymerizes under the reaction conditions suggesting a radical mechan- ism for the formation of the carbenoid. Carbenes have also been shown4 to be intermediates in the reduction of p-substituted aromatic aldehydes by zinc in the presence of boron trifluoride several of which cycloadd to C=C. A synthesis of fused methylenecyclopropanes employing a carbenoid ring-contraction of bicyclic cyclobutanonetoluenesulphonylhydrazoneshas been announced.’ Dehalogenation of the adduct (1)with Zn-AcOH gives the corresponding cyclobutanone.Pyrolysis of the dry Li salt of the derived toluenesulphonylhydrazonegives the methylenecyc- lopropanes (2) and (3). These are found to exhibit an extraordinarily clean thermal equilibrium. Vinylcyclopropanation of olefins by means of the copper-catalysed D. H. Gibson and C. H. DePuy Chem Reu. 1974,74,605. J. L.Hahnfeld and D. J. Burton,TetrahedronLeners 1975,1819. S. Miyano,Y.Matsumoto and H. Hashimoto J.C.S. Chem Comm 1975,364. I. Elphimoff-Felkin and P. Sarda Tetrahedron 1975,31 2785. A.S.Kende and E. E. Riecke. J.C.S. Chem. Comm. 1974,383. 285 286 A. Cox reaction with vinyldiazomethane is a short and convenient synthesis of vinylcyclo- propanes.6 With cis- and trQns-but-2-enes the vinylcyclopropanation is stereo- specific.In contrast to cyclopropanations of cyclohexane using either ethyl diazo- acetate or trimethylsilyldiazomethane,both of which give almost exclusively the exo-isomer the copper-catalysed method leads to the sterically more congested endo-isomer. Similarly the syn-isomer is preferentially formed in the reaction of vinyldiazomethane with vinyl acetate. The preparation of cis-divinylcyclopropane has been reported7 by photolysis of either cis- or trans-3,5-divinyl- 1-pyrazoline at -45°C. The product consists of a mixture of the cis-and the trans-divinylcyclopropane. The cis-isomer does not rearrange to any great extent below 0 "C but at +11"C it rearranges to cyclohepta-1,4-diene.Formation of cyclic ketens by treatment of an acid chloride with a tertiary amine fails in the case of cyclo- propane probably owing to an increase in I-strain in going from the cyclopropyl to the cyclopropylidene structure. However preparation of carbonylcyclopropane has now been reported* by pyrolysis of 2,2-dimethyl-l,3-dioxan-4,6-dione-5-spirocyclopropane (Scheme 1). At room temperature carbonylcyclopropane gives the dimer (4). Scheme 1 Although 'normal' alkenes such as cyclohexenes are known not to react with diazomethane-palladium(I1) acetate in ether strained alkenes such as bicyclo[2,2,l]heptene bicycIo[2,2,l]heptadiene and hexamethylDewarbenzene reactg with this reagent to give the corresponding cyclopropane in good yield.There is a characteristic difference" between an organocopper-phosphine complex and an organosodium intermediate in the stereochemistry of cyclopropane formation from an a-chloro-compound and an cyp-unsaturated cyano-compound. Using Buf;P-CuOBu' the cyclopropane derivative is readily formed (Scheme 2). In the HCCl(Me)CO,Me B~~u~~~Bu; Bu;P,CuCCl(Me)CO,Me JCH,=CM~CN MUM' + MuC02Me C0,Me CN I -CICu,PBu; I MeC-CH -CMe I I CN C0,Me CN Me c1 CuPBu; Scbeme 2 6 R. G. Salomon M. F. Salomon and T. R. Heyne J. Org. Chem 1975,40,756. M. P. Schneider and J. Rebell J.C.S. Chem. Comm. 1975,283. * G.J. Baxter R. F. C. Brown F. W. Westwood and K. J. Harrington Terruhedron Letters 1975,4283.J. Kottwitz and H. Vorbriiggen Synthesis 1975,636. T. Tsuda F. Ohoi S. Ito and T. Saegusa J.C.S. Chem. Comm. 1975,327. Alicyclic Chemistry organosodium system the cis :trans ratio is increased with decrease in the polarity of the solvent. Assuming that the carbanionic group of the organocopper-phosphine complex firmly co-ordinates to copper it has been suggested that intramolecular cyclization will occur without chelation involving copper producing the more favoured trans-isomer due to non-bonded interactions between substituents. Decar- boxylation of substituted lactones using NaCl in DMSO at 160 "Cyields cyclopropyl ketones (Scheme 3).11 Support for the proposed mechanism is provided by the Scheme 3 observation that the product is 4-benzoylbutyronitrile when NaCN is used.Fluoride- ion-promoted elimination of @-halogenosilanes is a powerful method for generating strained alkenes and it has now been shown'* that 1,l-dichloro-2-trimethylsilylcyclopropane reacts with caesium fluoride at 80 "C to give 1-chlorocyclopropene in 54% yield. 3-Alkoxycyclobutanones are readily accessible by [2 +21 cycloaddition of ketens to enol ethers. During column chromatography on neutral or basic alumina these adducts eliminate13 ethanol and afford pure cyclobutenones in yields as high as 80%. A potentially general synthesis (Scheme 4) of cyclobutenones e.g. (6),starts from the FS03CH3) 'l:::, )+!+0 flo +Go To MeS II c MeS Me$ /\ Scheme 4 readily available compound (5).14 Keteniminium salts derived from a-chloroenamines have been used for fabricating four-membered rings.'s For exam- ple [2 +21 cycloaddition of tetramethylketeniminium tetrafluoroborate or trichlorozincate to alkynes leads to cyclobutenylideneammoni~m salts from which in favourable cases the cyclobutenones can be obtained by hydrolysis using NaOH. A simple synthesis of dimethylenecyclobutene has appeared (Scheme 5).l6 Glow discharges normally convert acetylene completely into polymeric material but under suitable conditions17 the products include vinylacetylene diacetylene benzene phenylacetylene styrene indene and naphthalene which probably arise by the initial dimerization of acetylene to cyclobutadiene. l1 S. Takei and Y. Kawano Tetrahedron Letters 1975,4389.l2 T. H. Chan and D. Massuda Tetrahedron Letters 1975,3383. l3 H. Mayr and R. Huisgen Angew. Chem. Internat. Edn. 1975,14,499. l4 T. R. Kelly and R. W. McNutt Tetrahedron Letters,1975,285. Is C. Hoornaert A. M. Hesbain-Frisque and L. Ghosez Angew. Chem. Internat. Edn. 1975,14,569. l6 H.-D. Martin S. Kagabu and H. J. Schiwek Tetrahedron Letters 1975 3311. G. Rosskamp and H. Suhr Annalen 1975 1478. Q 0 LiAlH4 Scheme5 A reactive intermediate may be generated'' from an insoluble polymer-bound precursor and trapped by a second solid phase suspended in the same reaction mixture viz. preparation of a polymer-bound o-phenanthroline derivative of cyc- lobutadieneiron carbonyl and a polymer-bound maleimide derivative. Oxidation of the former in the presence of the latter is shown to proceed with 96% transfer of free cyclobutadiene between the two polymers.These results support the conclusion that oxidation of the iron carbonyl complexes generates free cyclobutadiene and indicate that ions derived from cerium are not required as vehicles for cyclobutadiene transport. Irradiation of tetrafluorocyclobutene-3,4-dicarboxylicanhydride (7) in the vapour phase at 253.7 nm and in the presence of 500 mmHg of N2leads via tetrafluorocyclobutadieneto octafluoro[4,2,0,02~5]cyclo-octa-3,7-diene (8) which thermally isomerizes to octafluorocyclo-octatetraene(9) (Scheme 6).l9 Irradiation F8 FF Scheme6 J. Rebek and F. Gavina J. Amer. Chem. Soc.,1975,97,3453. l9 M.J. Gerace D. M.Lemal and H. Ertl J. Amer. Chem. SOC.,1975,97,5584. Alicyclic Chemistry 289 of (7) in the presence of furan yields compound (lo) in addition to (9). The substituted cyclobutadienes (1 1)and (12) are stable at room temperature for 48 and Et2N#sph Ph NEt, Et2Nnph PhS NEt (1 1) (12) 1h respectively.20 Cyclopropa[4,5]benzocyclobutene (1 3)21,22 is the first compound in which a benzene ring is annelated by both three- and four-membered rings. Bicyclobutylidene has now been prepared (Scheme 7).23 Reagents i H,NNH,-H,S -20 "C;ii Pb(OAc),; iii Ph,P; iv Wittig reaction. Scheme7 Six-,Seven- and Eight-membered Rings.-Cyclohexadienes should in principle be available from starting materials supplying two and four carbons respectively. More specifically an enolate should add to the terminal double bond of a butadienylphos- phonium salt to produce stereoisomeric ylides.If these are in equilibrium the Z-isomer should undergo an intramolecular olefin synthesis to afford the cyclohexa- diene (Scheme 8). A number of bicyclic cyclohexadienes have been thus made.24 Cyclo-octa-2,5,7-triene- 1,4-dione has been synthesized (Scheme 9).25Photolysis of the sodium salt of 2,3-homotropone toluene-p-sulphonylhydrazoneleads to tricyclo[8,6,0,02~9]hexadec-2,5,7,1 From this result and the 1,13,16-he~aene.~~ structure of the Diels-Alder adduct with cyclic dienes it was concluded that the ** R. Gompper S.Mensch and G. SeyboId Angew. Chem. internat. Edn. 1975,14 704. z1 D. Davalian and P. J. Garrett J.Amer. Chem. Soc. 1975 97,6883. 22 C. J. Saward and K. P.C. Vollhardt Tetrahedron Letters 1975,4539. 23 L. K.Bee J. Beeby J. W. Everett and P. J. Garrett J. Org. Chem. 1975,40,2212. 54 G. Buchi and M.Pawlak J. Org. Chem. 1975,40,100. z5 M.Oda Y. Kayama H. Miyazaki and Y. Kitahara Angew. Chem. 1975,87,414. 26 M. Oda Y. Ito and Y. Kitahara Tetrahedron Letters 1975,2587. 290 A. Cox -PRe(),+Q PPh3 PPh PPh, , 0' R R Scheme8 Zn-AcOH @ -0 @ (l0 0 0 Scheme 9 highly reactive species participating in the reactions is a new strained allene cyclo- octa- 1,2,4,6-tetraene which must have been formed by rearrangement of bicyclo[5,1,0]octa-3,5-dien-2-ylidene initially generated in the photolysis. The homocyclo-octatetraene dianion has been prepared by dimetallation of (2,2,2)-cyclonona- 1,3,6-triene using n-butyl-lithium in TMEDA.*' The 'Hn.m.r.coupling constants provide evidence regarding the geometry of the anion ruling out both a norcaradiene-like structure and the angle-strainless boat conformation (14) and suggesting that the eight carbons are not coplanar. H (14) Large Rings.-The reaction of allylic halides with Ni(CO) permits the synthesis of large-ring methylene cycloalkanes (Scheme 10).**Cyclization normally proceeds in high yield but curiously fails completely for the formation of 12-membered rings. Br& +H2h -k-i"H2h Br Scheme 10 27 M. Barfield R. B. Bates W. A. Beavers I. R. Blacksberg S. Brenner B. I. Mayall and C. S. McCulloch J. Amer. Chem.Soc. 1975,97,900. E. J. Gxey and P. Helquist Tetrahedron Letters 1975,4091. Alicyclic Chemistry 291 Polycyclic Compounds.-The optically active Dewar-benzene (16) has been pre- pared29 from the menthyl bornyl or s-octyl phenylacetylenic esters and the cyc- lobutane (15) followed by hydrolysis. Evidence has been presented3' that butalene Me Me Me (15) (16) (17) can be generated and trapped below room temperature. The starting material is 3-chlorobicyclo[2,2,O]hexadiene which although quite stable to most strong bases can be dehydrohalogenated using LiNMe in HNMe,-THF. Judging from the typical free-radical reactions of (18) in the gas phase and the reactions observed for (17) the prediction that (17) and (18) have a separate existence and different Iz[] \ 0 (17) (18) chemistry is confirmed.The vigorous conditions required to generate butalene support the conclusion that such fused ring systems are not strongly stabilized by their overall content of (4n+2) w-electrons. A convenient route to truns-tricyclo[5 1,0,0274]oct-5-ene (trans-bishomobenzen) allowing access to multigram quantities has appeared.31 A route from dicyclopentadiene to trishomocubanone has been described.32 Photocyclization of dicyclopentadiene leads to 1,3-bishomocubane which with [Rh(CO),Cl] undergoes carbonylation to trishomocubanone via a rhodium-containing complex. By analogy with some other acylrhodium compounds this is assumed to have a C1-bridged polymeric structure. Despite earlier failures tetra-asterane pentacyclo[6,4,0,02~7,04~11,05~'']dodecane has been ~ynthesized.~~ Iceane (20) has been prepared34 from the olefinic ketone (19).This highly symmetrical hydrocarbon (&) possesses five six-membered rings (19) (20) of which because of the rigidity imposed by the carbon skeleton two exist in chair conformations and three in non-twist boat conformations. The 'H n.m.r. spectrum (90 MHz) shows an AM pattern centred at S 0.94 and 1.90 (J= 12 Hi),consistent *9 J. H. Dopper B. Greijdanus D. Oudman and H. Wynberg J.C.S. Chern. Grnrn.,1975,972. 30 R.Breslow J. Napierski and T. C. Clarke J. Arner. Chern. Soc. 1975,97 6275. 31 R.T.Taylor and L. A. Paquette Angew. Chern. Internat. Edn. 1975,14,496. 32 J. Blum C. Uotogorski and A. Zoran Tetrahedron Letters 1975 1117.33 H. M.Hutmacher H.-G. Fritz and H. Musso Angew. Gem. Internat. Edn. 1975,14,180. 34 D.P.G. Hamon and G. F. Taylor Tetrahedron Lerters 1974,155. 292 A. Cox with the resonances due to the axial and equatorial protons respectively of each methylene group. This difference in chemical shift is probably enhanced by van der Waals deshielding of the equatorial protons due to their position in the rings having a boat conformation. The highly strained cage hydrocarbon hexacyclo[5,4,0,02~6,04~11,05~9,08~10]~ndecane (23)has been prepared35 by reaction of the ditosylate (21) with NaI in HMPA. Control experiments indicated that (23) must be formed via (22). In the field of propellane chemistry the synthesis of 3,3- dibutynylcyclopentanone and its conversion into the [3,3,3]propellane system have been reported;36 this is a key compound from which some equally ring- functionalized propellanes can be derived.(21) (22) (23) A general method3' for the preparation of bicyclo[2,1 ,l]hexenes uses the Ramberg-Backlund rearrangement of 2-chloro-3 -thiabicyclo[ 3,l ,llheptane 3,3- oxides. The synthetic sequence starts from a mixture of cis-and trans-1,3- cyclobutane dicarboxylic acids and because of the number of 1,3-cycIobutane dicarboxylic acids known e.g. the truxinic acids this method is claimed to allow the preparation of a variety of substituted bicyclo[2,l,l]hexenes. A synthesis of the strained but stable bridgehead olefin bicyclo[4,2 llnon- l(8)-ene has been de~cribed,~' involving a Wittig reaction as the key step.Chemical and physical data suggest the compound to be less strained than the isomeric bicylo[3,3,l]non- 1-ene. The utility of the intramolecular Wittig reaction for the preparation of strained bridgehead double bonds has been further inve~tigated~~ in the attempted synthesis of bicyclo[2,2,l]hept-l-ene and bicyclo[3,2,l]oct-5-ene. When the salt (24) was stirred in a refluxing solution of potassium t-butoxide and diphenylisobenzofuran the two isomeric Diels-Alder adducts (25) were formed. This sequence constitutes the first efficient synthesis of bicyclo[3,2,l]oct-5-ene. A similar sequence starting from the cyclopentanone analogue of (24) failed to yield any detectable trace of a Diels-Alder adduct derived from bicyclo[2,2,l]hept-l-ene.0 Ph 35 A. P. Marchand and T.-C. Chou Tetrahedron Letters 1975,3359. 36 J. Drouin F. Leyendecker and J. M. Conia Tetrahedron Letters 1975,4053. 37 R. G. Carlson and K. D. May Tetrahedron Letters 1975,947. 38 K. B. Becker Tetrahedron Letters 1975,2207. 39 W. G. Dauben and J. D. Robbins Tetrahedron Letters 1975 151. Alicyclic Chemistry 293 Biogenetically patterned synthesis in the field of tetra- and penta-cyclic triter- penoids has been re~iewed.~' 2 Stereochemistry The conformational analysis and electronic structure of t-butyl cyclopropyl ketones have been investigated41 within the framework of the CND0/2 approximation. In every case the cis-isomer has been found to be preferred with an unusual conforma- tion of the substituent with respect to the cyclopropane ring.Interactions have also been observed between the oxygen of the HO or Me0 substituents and the carbonyl oxygen atom. An interesting paper the results of a crystallographic analysis of a derivative of cyclobutadiene chosen so that (i) the electronic state is minimally perturbed but yet its reactivity is suppressed by the steric blocking of the approach of another molecule by the substituents thus allowing its isolation and (ii) the substituents are such as to preserve the symmetry in an important way. The compound analysed was methyl tri-t-butyl[4 Jannulene carboxylate and the analysis shows that it is definitely not a square but a slightly distorted rectangle. Ab initio MO theory has been to study the potential surfaces associated with ring puckering in some saturated five-membered ring compounds.A geometrical model is used which has fixed bond lengths and fixed angular conformations for methylene groups but all other degrees of freedom are varied. It is found that theory predicts puckering amplitudes in fair agreement with experimental data and for cyclopentane all methods give nearly free rotation. Cyclopentanone is found to have its energy minimum in the twist form but in this case conformational interconversion occurs most easily along a path passing close to the planar skeleton form as a transition state. Although planar projection formulae have long been employed to represent ring compounds the justification for their use has seldom been satisfactory.Polya's method has been employed44 to show that their use in counting isomers is allowed because the permutation symmetry of such formulae is equivalent to that of a non-planar ring in which interconversion between conformers occurs. Ther-modynamic considerations indicate that the concentration of the twist-boat form becomes quite substantial at high temperatures. By means of a high-vacuum deposition technique in which a high-temperature equilibrium is trapped at 20 K on a CsI plate the i.r. spectrum of the mixture of chair and twist-boat conformations of cyclohexanes has been The twist-boat is present to ca. 25% in cyc- lohexane deposited from 800 "C. Thus the percentage of the twist-boat in the gas phase at 800 "C is at least 25% and possibly more depending on the efficiency of trapping of the twist-boat.The induced shift ratios for several substituted cyclohex- anones have been determined46 using tris(dipivaloy1methanato)ytterbiumand the individual shift data have been used to ascertain some rotamer populations. Exten- sive calculations based on the induced shift data have been used to obtain structures 40 E. E. van Tamelen Accounis Chem. Res. 1975,8 152. 41 F. Crasnier,J. F. Labarre H. Cousse L. D. D. Hinterland and G. Mouzin Tetrahedron,1975,31,825. 42 L. T. J. Delbaere M. N. G. James N. Nakamura and S. Masamune J. Amer. Chem. Soc. 1975,97 1973. 43 D. Cremer and J. A. Pople J. Amer. Chem. Soc. 1975,97 1358. 44 J. E. Leonard G. S. Hammond and H. E. Simmons J. Amer. Chem. SOC.,1975,97 5052.4s M. Squillacote R. S. Sheridan 0.L. Chapman and F. A. L. Anet J. Amer. Gem. SOC.,1975,97,3244. 46 K. L. Servis and D. J. Bowler J. Amer. Chem. Soc. 1975,97 80. 294 A. Cox for the ketone-lanthanide chelate complexes which give the best fit between calculated and observed induced shifts for all the ring and side-chain protons. The configurations of dimethyl cyclohexanone-2,6-dipropionate and diethyl cyclohexane-l,3-dipropionatehave been determined47 by a 13C n.m.r. study. It was concluded that the former compound has a cis configuration and that the latter consists of both cis-and trans-isomers with a molar ratio of cis :truns =3. Ab initio calculations on planar and boat conformations of cyclohexa-l,4-diene have been made.48 Total energies for (26) and (27) were calculated to be -231.5610 and (26) (27) a = 159.3" -231.5491 a.u.respectively. This corresponds to (26) being 30.96 kJ mol-' more stable than (27) and the highest occupied r-level formally the SS combination of the two olefinic r-orbitals has CQ. 91.4 kJ higher energy in both conformations than the orbital represented by the SA combination. A relatively complete calculation of the low-energy conformations of cyclohep- tane that the pseudorotation paths of cycloheptane can be visualized as occurring on a helical track wound around a torus. Comparison of the results obtained for the equilibrium conformations of cycloheptane with results of other calculations is made and qualitative agreement found. The pseudorotation of cycloheptane has been described" by means of the Fourier expansion of the endocyclic torsion angle.The topography of the pseudorotational itineraries for the chair/twist-chair and the boat/twist-boat families was also discussed. Cyclo-octa- 1,5-diene and the corresponding dibenzo derivatives have been studieds1 by means of force-field calculations. The twist-boat form is found to be the most stable conformation in both the diene and dibenzo molecules with a conforma- tional preference over the chair of 6.07 and 5.44 kJ mol-'. The twist-boat form is characterized by a w234S of 37.9" for the diene and 26.5" for the dibenzo derivative. Differences between the parent-diene and the dibenzo derivative are noted and are attributed largely to the difference in torsional barriers of a saturated carbon bond when attached to a double bond as opposed to being attached to an aromatic ring.13C n.m.r. data and iterative strain-energy calculations have been announced;'* they support the view that the presence of eclipsing strains in the C-6-7-8-1 moiety of the symmetrical boat conformation of cyclo-octa- 1,3,5-triene render this conformation unfavourable. The measurements show that a distortion to give a twist-boat relieves these strains. A paper has appeareds3 giving the results of force-field calculations of the strain energies of nine cyclodeca- 1,6-diene conformers. The difference in steric energy 47 N. Matsurnoto and J. Kumanotani Tetrahedron Letters 1975 3643. 48 G. Ahlgren B. Akermark and J.-E. Backvall Tetrahedron Lemrs 1975,3501.49 D. F. Bocian H. M. Pickett T. C. Rounds and H. L. Strauss J. Amer. Chem. Soc. 1975,97,687. 50 W. M. J. Flapper and C. Romers Tetrahedron 1975,31,1705. 51 N. L. Allinger and J. T. Sprague Tetrahedron 1975,31,21. s2 F. A. L. Anet and 1. Yavari Tetrahedron Letters 1975,4221. 53 D. N. J. White and M. J. Bovill Tetrahedron Letters 1975 2239. Alicyclic Chemistry between the preferred cis,cis-and trans,trans-isomers was calculated to be 12.34 W mol-' in excellent agreement with the observation that only the former is detectable when the two isomers are equilibrated; it was predicted that truns,trans- cyclodeca-1,6-diene should consist solely of conformer (28) in the gas phase. (28) The 'H and 13C n.m.r. spectra of cyclohexadecanes4 are temperature dependent below cu.-100°C. The 13C n.m.r. spectra of [1-13C]cyclohexadecane show the presence of three resonances in the ratio 1:2 :1at -152 "C. Iterative strain-energy calculations indicate that the [4444] conformation is 7.95 kJ mol-' more stable than the [3535] conformation and it is concluded that cyclohexadecane exists predomin- antly in the [4444] conformation with a barrier to pseudorotation of 28.0* 0.84kJmol-'. The 25.2MHz 13C n.m.r. (FFT) spectra of 1-cyanobicyclo[ l,l,O]butane have been reported," both with and without hydrogen decoupling. The chemical shifts are discussed in terms of dipolar resonance con- tributions to the ground state and the unsaturated nature of the bicyclobutane ring. 3 Structural Properties and Orbital Interactions The protonation of cyclobutane has been studieds6 theoretically using ub initio methods.The protonation energy is found to be 527 kJ mol-l but is significantly lower than that obtained for the protonation of cyclopropane by similar theoretical calculations. The protonation energies for edge and corner protonation of cyc- lobutane were found to be essentially identical. MIND0/3 calculations have been carried outs7 on cyclobutadiene by the 'half-electron' method. The heats of forma- tion of cyclobutadiene triplet and singlet (29) and (30) respectively are as follows singlet [(30) rectangular] AHf 394.9 kJ mol-l CC bond lengths 1.533 1.342 A; triplet [(29) square] AH 419.6 kJ mol-' CC bond lengths 1.433 A. A square (29) (30) singlet structure for cyclobutadiene is predicted to lie well above the square triplet (54.8 kJ mol-').The intersection of the singlet and triplet surfaces therefore lies above (29) in energy and it is concluded that conversion of (29) into (30) should require activation. Using an electron monochromator-mass spectrometer combina- tion the ionization potentials of cyclopentyl cyclopentenyl and cyclopentadienyl radicals produced in pyrolytic reactions have been rnea~ured.'~ The stabilities of s4 F. A. L. Anet and A. K. Cheng J. Amer. Chem.Soc. 1975,97,2420. s5 M. Pomerantz and D. F. Hillenbrand Tetrahedron,1975,31,217. s6 T. Pakkanen and J. L. Whitten J. Amer. Chem. Soc. 1975,97,6337. 57 M. J. S. Dewar and H. W. Kollmar J. Amer. Chem. Soc. 1975,97,2933.5.9 F. P. Lossing and J. C. Traeger J. Amer. Chem. Soc. 1975,97,1579. 296 A. ax the three cations were compared by reference to enthalpies of the general reaction RH + R++H+e and it was concluded that while the introduction of one double bond into the C ring brings about a stabilization of 100kJ the second double bond destabilizes the cyclopentenyl cation by 132 kJ. The cyclopentadienyl cation is consequently destabilized by 31.8 kJ mol-' with respect to the cyclopentyl cation a figure which closely corresponds to the solvolysis rate difference of lo5found by Breslow. An analysis of the structure of the homotropenylium cation has been undertaked9 by the MIND0/3 method. This has lead to a homoconjugate bond length which is better accommodated in terms of (31) as opposed to-(32) in agreement with the Winstein picture of an open cyclopropane unit.Consideration has been given6' to whether a cyclobutane ring (33)is able to replace the traditional cyclopropane ring as (33) a homoaromatic linkage. While not ruling out the possibility of participation of the cyclobutane ring in this way the results suggest that particularly severe conditions will have to be employed in order to force the cyclobutane ring to act as a homoconjugate linkage. This may indicate that the cyclopropane ring occupies an exclusive position in homoaromaticity and may be an essential ingredient for its occurrence. An exception to the generalization concerning the additive nature of the enhance- ment in the rate of solvolysis upon introduction of multiple cyclopropane rings at positions adjacent to an incipient carbocation centre is afforded by the introduction of a second cyclopropane system into the nortricyclyl skeleton to form the quadricyc- lyl system.This puzzle has been explained61 in terms of the combination of the HOMO of cyclopropane with the LUMO of the cyclopropylcarbinyl cation to form the quadricyclyl cation. A large bonding interaction between the carbinyl carbon and the adjacent cyclopropane carbon predominates; however this is substantially counteracted by the two antibonding interactions across the small base of the tetracyclic ring system. The net effect is a small stabilization upon introduction of this second cyclopropane. Two series of substituted ally1 cations have been studied62 59 R.C. Haddon Tetrahedron Letters 1975,863. 6o R. C. Haddon Tetrahedron Letters 1974,4303. 61 L. M. hew and C. F. Wilcox J. Amer. Chem. SOC.,1975,97 2296. 62 G. A. Olah and R. J. Spear J. Amer. Chem. SOC.,1975,97 1539. Alicyclic Chemistry by I3C n.m.r. and 'H n.m.r. spectroscopy under ion-stable conditions. The 1,3-substituted cations (34a-e) exhibit strong charge delocalization between C-1and C-3 whereas the charge in the 1,l-substituted alkenyl cations (35a-e) is substan- tially higher at C-1. 1'3-Overlap does not appear to contribute significantly to the total ion structure. H a; R' = R2 = Me R'yy b; R' = Me; R2 = cyclopropyl c; R' = R2 = cyclopropyl H H d; R' = cyclopropyl;R2 = Ph e; R' = R2 = Ph (34) (35) Acetolysis of the vinyl tosylate (37) gives products closely similar to those from (36) and (38).63 It was concluded that (37) is intimately involved in the solvolyses of (36)and (38)and that all three compounds react via the same intermediate manifold implicating homoallenic participation.products 4 Acetolysis of 3,3-diphenyl- and 3,3-dimethyl-cyclobutyl tosylate proceeds more slowly than that of the unsubstituted cyclobutyl tosylate thereby militating against concerted ring-opening to the allylcarbinyl ion accompanying ionization.64 These and other data are in line with the hypothesis that most 3-substituted cyclobutyl derivatives ionize initially to the cyclopropylcarbinyl ions which then undergo a rapid ring-opening to the corresponding allylcarbinyl ions.Synthesis has been undertaken6' of the 'parallel' and 'perpendicular' isomers of trans trans- bicyclo[6,1,0]nona-4-enes.The properties of (39) are reported to be vastly different from those of the perpendicular isomer (40) or other analogous trans-alkenes and appear to be attributable to the transannular repulsions between the .rr-bond and the cyclopropane ring which distort the .rr-bond and thus greatly alter its chemical reactivity. To probe the effect of the cyclo-octatetraene ring on the stability of an adjacent cationic centre the hydrolysis rate of cyclo-octatetraenylcarbinylchloride in 50% aqueous ethanol has been compared66 with that of A'-cyclo-octenylmethyl chloride. The relative rates of these first-order reactions are such that the cot derivative is five 63 T.Von Lehman and R. S. Macomber J. Amer. Chem. Soc. 1975,97 1531. 64 C. S. Michejda and R. W. Cornnick J. Org. Chem. 1975 40 1046. 65 J. A. Deyrup and M. F. Betkouski J. Org. Chem. 1975,40 284. 66 W. Etching K. A. Henzel and L. A. Paquette J. Amer. Chem. Soc. 1975,97 4643. 298 A. Cox times less reactive at 25 "C. The involvement of a homotropylium ion cannot be dismissed. The barrier of the degenerate valence isomerization in 3,4-homotropylidene has been determined67 by complete lineshape analysis of the 13Cdynamic n.m.r. spectra and the values of physical constants obtained are in good agreement with the results of the 'H dynamic n.m.r. lineshape analysis of the octadeuterio derivative.The influence of a methyl group in the 1-or 3-position is small. The first experimental verification has been offered68 of predictions based on Winstein's concept of homoaromaticity and the refining applications of MO theory of Goldstein and Hoffmann to longicyclic systems of potential bicycloaromaticity that electronic factors in (41) should be reversed in (42). The failure of the attempted reduction of bicyclo[4,2,l]nona-2,4,7-trien-9-oneto bicyclo[4,2,l]nona-2,4-dien-9-one by di- imide was attributed6' to homoaromatic interaction of the electrons on the isolated (41) (42) double bond at C-7-C-8 with the carbonyl at C-9 leading to sharply reduced electron density at C-7-C-8 compared with the diene moiety. The electron density in the diene may even be increased by bis(homocyclopentadieny1) interaction with the carbonyl.Optimized semiempirical MIND0/2 calculations on the transition states of (45)-(48) in the sigmatropic rearrangements of (43) and (44) have been rep~rted.~'Inversion over retention at the migrating carbon centre is only slightly favoured in (47) but retention over inversion is strongly favoured in (48). 5 67 R. Bicker H. Kessler and W. Ott Chern. Ber. 1975,108,3151. 6a J. T. Groves.and K. W. Ma J. Amer. Chem. Soc. 1975,97,4434. 69 D. I. Schuster and C. W. Kim J. Org. Chem. 1975,40,505. 'O W. W. Schoeller J. Amer. Gem. SOC. 1975,97 1978. Alicyclic Chemistry The pentacyclotetradecane rearrangement graph culminating in diamantane (49) has been analy~ed.~~ The most probable mechanistic pathways from structures (50)-(56) were deduced by graphical analysis guided by empirical force-field calculations./ \ (54) exo-trans-exo (53) (55) em-trans-endo (56) endo-trans-endo The synthesis of spiro[3,4]octa-l,5,7-triene has been carried out7’ in anticipation that the combination of spiroconjugative interaction in the 7r-system and direct a-7r overlap between the four-membered ring and the diene would produce interesting spectral and chemical properties. However in the event the U.V. spectrum showed a broad featureless maximum at h =262 nm almost identical with that observed for the analogous compound saturated in the four-membered ring. An investigation has been of the degree of interaction between Walsh orbitals of a cyclopropyl group and the 7r-orbitals of a neighbouring double bond in dispiro[2,2,2,2]deca-4,9-diene (57) as compared with that in spiro[2,4]hepta-4,6-diene (58) and dispiro[2,0,2,4]deca-7,9-diene (59).Their photoelectron spectra indicate that spirocyclopropyl groups as in (57),can transmit the electronic effect between the two n-bonds in a cyclohexa-1,4-diene far better than C-C a-bonds as in (58),and the C-H a-bonds as in cyclohexa-1,4-diene itself. 71 T. M. Gund P. von R. Schleyer,P. H. Gund and W. T. Wipke J. Amer. Chem. Soc.,1975,!W 743. 72 R.D.Miller and M. Schneider Tetrahedron Letters 1975 1557. 73 P.Asmus M. Klessinger L.-U.Meyer and A. de Meijere Tetrahedron Letters,1975,381. 300 A. Cbx 4 Reactions Metal-promoted Reactions.-Evidence has been for the mechanism of the potentially general method for preparing .rr-allylpalladium chloride complexes from the reaction of cyclopropenes with palladium(I1) chloride in which the results strongly implicate symmetrical w-complex formation as the rate-determining step (Scheme 11).Treatment of 1,l’-trimethylenebicyclopropenylwith AgCIO has been I Ph H + (PhCN),PdCl +[~~~~~~~~ 1 Ph Ph I Ph Scbeme 11 found75 to lead to 1,4-trirnethylene(Dewar benzene) as the only detectable Dewar- benzene (Scheme 12).1-Methoxy-5-vinylbicyclo[3,2,0]hept-6-ene the first exam- ple of a solvent-trapped product of a cation of type (60),is also produced and must be Ag (60) Weme12 74 M. A. Battiste L. E. Friedrich and R.A. Fiato Tetrahedron Letters 1975,45. 75 I. J. Landheer W. H. De Wolf and F. Bickelhaupt Tetrahedron Letters 1975,349 Alicyclic Chemistry considered to be direct evidence for this mechanism. The major product of the oxidative decomposition of (cyclo-octa- 1,5-diene)PdC12 using Pb( OAc) has been to be 6-and not 4-exo-chloro-2-endo-acetoxybicyclo[3,3,O~ctane (Scheme 13). This suggests that a a-bonded complex rather than a 7r-bonded complex is cis- H cis- transfex insertion OAc OAc H OAc OAc cl H scbeme13 formed as the major intermediate and that cis-intramolecular ligand transfer from metal to olefin carbon is considerably faster then the well-established addition of nucleophile to the olefin-Pd" complex under these conditions.The reactions of cyclodeca- 1,2,5,8-tetraene and cyclodeca- 1,2,5-triene with mercuric sulphate in acetic acid have been found to give only rearranged product^.'^ These are the first known examples of rearrangement during oxymercuration of an allene. Compara- tive of the nickel(0)-catalysed reactions of quadricyclane and norbor- nadiene with acrylates suggest that this and the nickel(0)-catalysed isomerization of quadricyclane to norbornadiene involve a common intermediate in the product- determining step (Scheme 14). Paquette has examined the Ag'-catalysed valence isomerization of substituted 1,8-bishomocubanes. It is established" that of the four different rearrangements leading to two isomeric snoutane diesters the distal isomer (61) is formed preferen- tially.The bond-switching process is considered" to be triggered by electrophilic 76 S.-K.Chung and A. I. Scott Tetrahedron Lerrers 1975,49. 77 R.W.Thies P.-Kong Hong R. Buswell and J. L. Boop J. Org. Chem. 1975,40,585. 78 R.Noyori I. Umeda H. Kawauchi and H. Takaya J. Amer. Chem. Soc. 1975,97,812. 79 L.A.Paquette and R. S. Beckley J. Amer. Chem. Soc. 1975,97,1084. L. A. Paquette R. S. Beckley and W. B. Farnham J. Amer. Chem. Soc. 1975,97,1089. 302 A. Cox Ni Ni Ni L/\L L" 1 Z Scheme 14 R (61) attack at the C-1 -C-5 bond with direct formation of a delocalized cyclopropylcar- binyl cation. Such edge argentation accounts for all available kinetic data and conforms to theoretical conclusions that attack by Ag+ at an edge bond is energeti- cally preferable to bidentate co-ordination with one of the cubyl surfaces.To probe the effect of such groups as phenyl vinyl cyclopropyl and ethoxy on the rate of Ag+-catalysed homocubyl rearrangements the isomerizations of 4-substituted homocubanes were compared8' with those of model compounds where direct resonance interaction in the transition state was not anticipated. The bond switch- ings appear to proceed by Ag+-induced electrophilic ring-opening of the less substituted edge bonds. The rearrangements of several 1,8-bishomocubane deriva- tives by various Rh' and Pd" catalysts are sensitive not only to the nature of the ligands attached to the metal but also to the degree of substitution at the reaction site.82 The effect of varied 4-substitution of the homocubane ring system on the course of Rh'-and Pd"-catalysed rearrangements has been probed83 by direct 81 L.A. Paquette,J. S. Ward R. A. Boggs,and W. B. Farnham J. Amer. Chem. Soc. 1975,M 1101. 82 L. A. Paquette,R. A. Boggs,W.B. Farnham and R. S. Beckley,J. Amer. Chem.Soc.,1975,97,1112. g3 L. A. Paquette R. A. Boggs and J. S. Ward J. Amer. am.Soc. 1975,97,1118. Alicyclic Chemistry examination of product ratios and kinetics. The evidence suggests that the ring- opening reaction proceeds through an intermediate (62) (Scheme 15) where the transition metal has entered into oxidative addition in the rate-determining step. (62) scheme 15 A complex series of light-induced valence isomerizations of bullvalene and related CloHlohydrocarbons with Fe(C0)' in moist benzene has been reported.84 ThermallyInduced Reactions.-It has been concluded8' from an investigation of the thermal stereomutation of optically active trans-[ 1,2-2H2]cyclopropane that a double methylene rotation mechanism operates (Scheme 16) i.e.the reaction occurs == pp D D A DD Scheme 16 via a trimethylene in which the three ring carbons and four of the hydrogens occupy a common plane. In a related papers6 it has been reported that a synchronous double rotation is also prominent in the stereomutation of l-phenyl[2-2H]cyclopropane. The ring-opening of 2,3-diphenylcyclopropyl radicals to 1,3-diphenyldlyl radicals has been inve~tigated.~~ Product analyses and the dependence of the yields of the products of cage recombination on solvent viscosity as well as kinetic measurements demonstrate that ring-opening and cage recombination are competing reactions.The results are interpreted in terms of a favoured disrotatory ring-opening. Thermal rearrangement of each of the four isomeric ethyl 2-methyl-3-(trans-propeny1)cyclopropanecarboxylates has been reported8* to result in cis-trans isomerization to the other isomers and the formation of a number of rearrangement products. The results are rationalized on the basis of a model involving C-C bond cleavage rotations around bond a and/or b in the biradical formed (Scheme 17),and closure to cyclopentenes with stereochemical discrimination occurring during the final two steps. Stereochemical dissection of the 4-cyano- 1-methylcyclopentene 84 R.Aumann Chem. Ber. 1975,108,1974. J. A. Berson and L. D. Pedersen J. Amer. Chem. SOC.,1975,97 238. 86 J. A. Berson L. D. Pedersen and B. K. Carpenter J. Amer. Chem. Soc. 1975,97,240. S. Sustmann and C. Riichardt Chem. Ber. 1975,108,3043. P. H.Mazzocchi and H. J. Tarnburin J. Amer. Chem. Soc. 1975,97,555. 304 A. cox HH rotation + Et0,C eH3H CH3CH3 -1". stereorandom biradical CH3 CH3 % Et0,C H& H rotation ' Et0,C CH Scheme 17 obtained from thermal rearrangement of cis-and trans-1-cyano-2-isopropenylcyclopropane shows8' partial retention of optical activity owing to a predominance of retention of configuration from cis and of inversion of configura- tion from trans.Pending quadrisection of the rearrangement a tentative description in terms of a not obviously concerted reaction involving rotational preference within the framework of the continuous biradical hypothesis is given. Cyclopropylallene has been foundg0 to rearrange above 300 "Cto 3-methylene-l-cyclopentene,and thermolysis of the deuterium-labelled compound (Scheme 18) shows that a 4-5 times faster geometric isomerization accompanies the rearrangement. Scheme 18 The thermal rearrangement of 1,1'-dimethylbicyclopropenyl to 2,2'-dimethylbicycloprop-2-enyl is claimedg1 to be the first experimental realization of a Cope rearrangement of bicyclopropenyls. At higher temperatures two isomers were formed. Presumably one is the dl-isomer originating from the more stable chair transition state and the other the rneso-isomer originating from a boat transition state.This may have implications for the discussion surrounding the concerted or radical nature of the Cope rearrangement. 89 W. von E. Doering and K. Sachdev J. Amer. Chem Soc. 1975,97,5512. 90 W.R. Roth T. Schmidt and H. Humbert Chem. Ber. 1975,108,2171. 91 W. H.de Wolf I. J. Landheer and F. Bickelhaupt TetrahedronLetters 1975 179. Alicyclic Chemistry The semiempirical MIND0/2 method has been used to explain9* the experimental stereochemistry in the thermal rearrangements of methylenecyclobutane. Retention of configuration is shown to be due to ‘subjacent orbital control’ and antarafacial participation of the ally1 unit due to Jahn-Teller instability in the biradical transition state.Preliminary results have been reported93 on the thermal reorganizations of 3,3-divinylmethylenecyclobutane and 3-vinylmethylenecyclobutane which undergo smooth thermal conversion into (63) and (64) respectively. Rate studies coupled with simple calculations on the ther- mochemical kinetics of the system combined with kinetic isotope results are (64) Scheme 19 claimed to provide convincing evidence for a two-step (biradical) mechanism as opposed to a concerted pathway. MIND0/3 calculations have-been reported94 for the thermal rearrangements of some bicyclo[2 1,O]pent-2-enes to cyclopentadienes. Of particular interest is the case of the unsubstituted molecules in which the transition state is predicted to have a symmetrical structure (65) implying that the transformation is a normal concerted 1.43 8 (65) electrocyclic process in spite of the fact that it violates the Woodward-Hoffmann rules.The rearrangement to the acetylcyclopentene (68) has been showng5 to occur 92 W. W. Schoeller Chem. Ber. 1975,108 1285. 93 W. R. Dolbier and G. J. Mancini Tetrahedron Letters 1975 2141. 94 M. J. S. Dewar and S. Kirschner J.C.S. Chem. Comm. 1975,461. 95 J. P. Grosclaude H. U. Gonzenbach J. C. Perlberger and K. Schaffner,J. Amer. Chem. SOC.,1975,97 4147. 306 A. Cox specifically from the endo-acetylbicyclopentane(66);this process and the endo-exo interconversion (66)&(67) do not involve a common intermediate. The 7-40 (67) (66) (68) Scheme 20 stereochemistry of the thermal reorganization of methyl-substituted 6- methylenebicyclo[3,2,0]hept-2-enesinto one another and the four methylated 5-methylenebicyclo[2,2,l]hept-2-enes has been The results are consis- tent with the assumption of a set of concurrent uncatalysed unimolecular rearrange- ments and the transformations are believed to occur by a course involving non- equilibrating biradicals.The thermal behaviour of 3-methylenebicyclo[3,2,l]oct-6-ene (69) and of 3-oxobicyclo[3,2,l]oct-6-ene (70) has been in~estigated.~~ Transformation of the former (69) into 7-methylenebicyclo[3,3,0]oct-2-ene pro-(69) X = CH (70) X = 0 ceeds cleanly via a Cope rearrangement. Thermolysis of (70) occurs only at much higher temperatures apparently indicating a non-concerted process.syn [9-2H]-Bicyclo[6,1 ,O]nonatriene has been synthesized and its rate of epimerization The epimerization proceeds via the intermediate (71) (Scheme 21). I1 D D Scheme 21 96 D. Hasselmann Angew. Gem. Zntemat. Edn. 1975,14 257. 97 J. Japenga M. Kool and G. W. Klumpp Tetrahedron Letfers 1975,1029. 98 C. P. Lewis and M. Brookhart J. Amer. Chem. Soc. 1975,97,651. G. Boche W. Weber and J. Benz Angew. Chem. Zntemat. Edn. 1974,13,207 Alicyclic Chemistry The thermal isomerization reactions of cis-9,lO-dihydronaphthaleneand deriva- tives have been studied.'00 A propensity for degenerate behaviour is established in the parent and the 1,9-products which arise on thermal reorganization of cis-9,lO- dihydronaphthalenes substituted in the 9 and 10 positions arise by [1,5]suprafacial migration of one of four identical trigonal a-carbons.Conversion into 1,5-isomers involves transient intervention of cis5-cyclodecapentaene intermediates. Pyrolysis of the appropriate tosylhydrazone sodium generates syn-and anti-tricyclo[4 1,0,02,4]heptan-5-ylidene (72)and (73) respectively which fragment'" to the highly strained cyclohepta-l,2,5-triene (74). Product ratios show a total lack of dependence upon the stereochemistry of (72) and (73) and this speaks against a synchronous pathway for the formation of (74). Scheme 22 Tricycle[7,3 ,0,04*'2]dodeca-2,5 ,7,10- te traene has been synthesized. lo2 Its H n.m.r. spectrum is unchanged up to 141 "C in agreement with a static structure.Thus Cope rearrangement of this compound is slow on the n.m.r. time-scale and as the geometry might suggest otherwise this slow rate is probably due to the absence of a small ring and its accompanying strain. Thermolysis of syn-and anti-tricycl0[4,2,0,0~~~]octane (75) and (76) leads103 to both cis,cis- and cis,trans-cyclo- octadiene (77) and (78) (Scheme 23) most likely via biradicals sufficiently long- lived to aIlow internal rotation (75) (77) 1 Scheme 23 Synthesis of 4-and S-methylspiro[2,4]hepta-4,6-dienehas been accomplished,'04 and vapour-phase pyrolysis of either provides an equilibrium mixture (60:40)of both. Kinetic analysis and other results appear most adequately accommodated by a stepwise perambulation of the GH4 fragment and a hydrogen atom about the loo L.A. Paquette and M. J. Carmody J. Amer. Chem. SOC.,1975,97,5841. Iol W. R. Dolbier 0.T. Garza and B. H. Al-Sader J. Amer. Chem. Soc. 1975,97,5038. Io2 D. G. Farnum and A. A. Hagedorn Tetrahedron Letters 1975,3987. lo3 H. D. Martin and E. Eisenmann Tetrahedron Letters 1975 661. lo4 R. A. Clark W. J. Hayles and D. S. Youngs J. Amer. Chem. Soc.,1975,97,1966. 308 A. Cox periphery of the cyclopentadiene ring. Although the stepwise process appears operative a competitive concerted [1,5]-sigmatropic methylene migration cannot be ruled out. Reaction of 1,2-bis(trifluoromethy1)-3,3-difluorocyclopropenewith cyclopen- tadiene at -78 "Chas been reported to give two adducts the major one of which has been assigned an ex0 stereochemistry and assumed to be the kinetic product since on gentle heating it progressively isomerues to the minor adduct of endo configuration.However it is claimedlo5 that direct preparation of these compounds by the carbene route using norbornadiene shows the above configurational assignments to be in error and requires them to be reversed. Reaction of cyclo-octatetraene with antimony pentafluoride in liquid SO leads directly to 9-thiatricyclo[3,3,1 ,027s]nona- 3,6-diene 9,9-dioxide by an unprecedented 1,5-~ycloaddition;'~~9-thiabicyclo[4,2,l]nona-2,4,7-triene9,9-dioxide is formed concomitantly and is the thermodynamically more stable C,H,02S isomer. 10.5 C. W. Jefford J. C. E. Gehret and J. Mareda Tetrahedron Letters 1975 823.106 L. A. Paquette U. Jacobson and M. Oku J.C.S. Chem. Comm. 1975,115.

ISSN:0069-3030    

DOI:10.1039/OC9757200285

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

13 Synthetic Methods By G. PATTENDEN Department of Chemistry The University Nottingham NG7 2RD 1 Alkanes Barton and McCombie' have shown that secondary alcohols are converted smoothly into the corresponding hydrocarbons by reduction of their 0-cycloalkyl thioben- zoates and 0-cycloalkyl-S-methyl dithiocarbonates with tributylstannane. A fea-ture of the method is that it proceeds via a radical mechanism and thus avoids rearrangements common to alternative methods involving carbocation inter-mediates. In addition the conditions are sufficiently mild to tolerate the presence of other functional groups such as carbonyl ester lactone and polyene functions and the method has been applied with particular success in sugar chemistry. Several new 'metal hydride' procedures for dehalogenating halides have emerged.A particularly convenient procedure involves simply adding a solution of NaBH in ethanol to a solution of the halide and tri-n-butyltin chloride in ethanol exposed to a 100W Hg lamp.* The iron hydride [HFe(CO),]- generated from pentacarbonyl- iron and KOH is equally effective for dehalogenating halide^.^ The system titanocene dichloride-magnesium reduces both aryl and alkyl halides;" here the reducing agent most probably originates from the cyclopentadienyl ligands. In similar transformations with the species produced from reduction of TiC13,3THF with Mg in an inert atmosphere the THF molecule and not MgH is considered the most likely source of reactive hydrogen.' The tetra-alkylborate anion (1)is useful for the selective reduction of tertiary alkyl benzyl and ally1 halides.6 (1) A new procedure for the conversion of ketones into the corresponding methylene derivatives involves reduction of the tosylhydrazone derivative with catecholborane followed by decomposition of the reduction product with NaOAc in chloroform (Scheme l).7 D.H. R. Barton and S. W. McCombie J.C.S. Perkin I 1975 1574. E. J. Corey and J. W. Suggs J. Org. Chem. 1975,40,2554. H. Alper Tetrahedron Letters 1975 2257. T. R. Nelson and J. J. Tufariello J. Org. Chem. 1975 40 3159. 'S. Tyrlik and I. Wolochowicz J.C.S. Chem. Comm. 1975 781. Y. Yamamoto H. Toi S.-I. Murahashi and I. Moritani J. Amer. Chem. SOC.,1975,97,2558. G. W. Kabalkaand J. D. Bakar J. Org. Chem. 1975,40 1834. 309 3 10 G.Pattenden R,CO + R,C=NNHTs -b R,CH-NNHTs R2CH2 I Reagents i Catecholborane;ii NaOAc Scbeme 1 The phenolic C-0 bond is smoothly cleaved by catalytic hydrogenation of the potassium aryl sulphate derivative;8 this method complements alternative methods employing isourea and carbonimidic ester derivatives but has the edge in overall convenience. The conversion of certain formates acetates and benzoates into the correspond- ing hydrocarbon by photolysis in HMPA-H20 at 254 nm has been described;' in either case the alkane is derived from the alkoxy part of the ester. A limiting feature of this method is that other groups e.g.ketones and C-halogen bonds are reduced simultaneously. Diazomethane in the presence of Pb(OAc) is a useful 'cocktail' for the prepara- tion of cyclopropyl carbonyl compounds from certain a-enones particularly in cases where the conventional Corey S-ylide method and Simmons-Smith procedures are ineffective e.g.the conversion (2)+(3)." CH,N,-Pb(OAc), L-p$ GH, + Isomer OR o 0 2 Alkenes A frequent limitation of the Wittig reaction is its lack of stereochemical integrity and considerable effort has been expended towards controlling this feature; indeed several methods and procedures are now available which enhance the proportion of either the cis-or the trans-alkene produced in the reaction. In a remarkable demonstration of the sensitivity of the steric course of the Wittig reaction towards reaction media it has been shown that when 18-crown-6 complexes of K,CO or KOBu' are used to generate non-stabilized P-ylides reaction with aldehydes in THF as solvent results predominantly in cis-olefination whereas in CH2C12 largely trans- olefination results." It is also interesting that when required reproducible 1:1ratios of cis- and truns-olefins can be obtained in Wittig reactions involving primary * W.Lonsky H. Traitler and K. Kratzl J.C.S.Perkin I 1975 169. H. Deshayes J. P. Pete C. Portella and D. Scholler J.C.S. Chem. Comm. 1975 439. lo U. Mende B. Raduchel W. Skuballa and H. Vorbruggen Tetrahedron Letters 1975,629. l1 R. M. Boden Synthesis 1975 784; cf. C. Piechucki ibid. 1974 869. Synthetic Methods aldehydes and reactive ylides by arranging for partial equilibration of the inter- mediate adducts in these reactions.12 In the silicon version of the Wittig reaction i.e.the decomposition of 2-hydroxyalkylsilanes to olefins and Me,SiOH Hudrlik and Peter~on'~ have shown that this is a syn-elimination in base but an anti-elimination in acid giving in each case isomerically pure cis-or trans-olefins. Peterson and colleague^'^ have also described a method for the regio- and stereo-specific synthesis of P-hydroxysilanes based on reaction of a,@-epoxysilanes with organocuprate reagents (Scheme 2); the overall sequence has many attractions as a useful olefination method. Me$ 0 .fi Me&-/ R-H OH Reagents i LiRiCu; ii KH-THF; iii BF Scheme 2 Esters normally react with Wittig reagents to give acylated phosphonium salts; however with an excess of Wittig reagent in DMSO preparatively useful yields of isopropenyl compounds can be obtained (Scheme 3).l5 0 II -+ fH2 R-C-OR + CH2-PPh3 -+ R-F -Me Scheme 3 Two groups have outlined the application of allylic phosphine oxides in diene synthesis.Lythgoe and co-workers16 have shown that isomerically homogeneous allylic diphenylphosphine oxides can be used in Horner reactions to provide efficient syntheses of conjugated dienes of defined geometry. An interesting new route to allyldiphenylphosphine oxides starts from alkyldiphenylphosphine oxides (Scheme 4).17 R I-POPh2 i,ii Rl>poPhl iii + R 'CH=CH-CHPOPh2 ~ I R2 OH Reagents i,BuLi; ii R'CHO; iii tosylation then acid Scheme 4 l2 R.J. Anderson and C. A. Henrick J. Amer. Chem. SOC.,1975,97,4327. l3 P. F. Hudrlik and D. Peterson J. Amer. Chem. Soc. 1975,97 1464. l4 P. F. Hudrlik D. Peterson and R. J. Rona J. Org. Chem. 1975,40 2263. A. P. Uijttewaad F. L. Jonkers and A. Van der Gen Tetrahedron Letters 1975 1439. l6 B. Lythgoe T. A. Moran M. E. N. Nambudiry S. Ruston J. Tideswell and P.W. Wright Tetrahedron Letters 1975 3863. l7 A. H. Davidson and S. Warren J.C.S. Chem. Comm. 1975 148. 312 G.Pattenden In a ‘one-pot’ synthesis of molecules containing at least three conjugated olefinic bonds an allylic P-ylide is first added in a Michael sense to P-chloroacrylate [leading to (4)];18subsequent loss of chloride deprotonation by base to (3,and treatment with a carbonyl compound then leads to (6) (Scheme 5).(4) J / (4) (5) Reagents i Clw C02R;ii R’CHO Scheme 5 The intramolecular Wittig reaction has been applied effectively in the synthesis of strained bridgehead olefins (Bredt-olefins),” and a new olefin-forming reaction (8)-+ (7)20has been applied in the synthesis of (7) (Scheme 6). (7) Scheme 6 Illustrations of the synthetic value of the intramolecular variant of the Diels-Alder reaction have blossomed in the past year. The reaction has been applied for example in the synthesis of cis-perhydroindanone (9)21and octahydroquinoline (1O),” and also in the preparation of the tricyclic dilactone (1l),an intermediate in a projected synthesis of the cyto~halasans,~~ and the tricyclic system (12) where a benzenoid double bond participates as part of the diene Intramolecular [2 +41 cycloaddition to a heterocyclic system [uiz.(13)] has also been dem~nstrated.~~ H (9) l8 E.Vedejs and J. P. Bershas Tetrahedron Letters 1975 1359. l9 W. G. Dauben and J. D. Robbins Tetrahedron Letters 1975 151; K. B. Becker ibid. p. 2207. *O M.-G. Kim and J. D. White J. Amer. Chem. SOC.,1975 97 451. 21 J. J. S. Bajorek and J. K. Sutherland J.C.S. Perkin I 1975 1559. 22 W. Oppolzer and W. Frostl Helu. Chim. Acra 1975,58,590; W. Oppolzer W. Frostl and H. P. Weber ibid. p. 593. 23 J. Auerbach and S. M. Weinreb J. Org. Chem. 1975,40 3311. 24 M. T. Cox J.C.S. Chem. Comm. 1975,903. 25 P. G. Sammes and R. A. Watt J.C.S. Chem. Comm. 1975,502. Synthetic Methods COR’ -““y -4 Ph Ph An effective method for replacing ketone carbonyl oxygen atoms by iso- propylidene groups is via dibromomethylenation using CBr,-PPh, followed by reaction of the resulting 1,l-dibromoalkene with Lic~Me,.,~ In two further illustra- tions of the versatility of lithium trialkylalkynylborates (14; R =alkyl) in synthesis protonation-iodination of (14) has been shown to lead to alkenes of type (15),27 whereas alkylation of thexyldialkylalkynylborates (16; R = alkyl) is stereospecific yielding Iargely the alkene (17)(ca.90%)in which the migrating group and the group introduced are cis to each other (Scheme 7).,’ Thiirans which are useful precursors for the synthesis of olefins by phosphine- or phosphite-mediated desulphurizations are usually obtained from carbonyl com- pounds via multistep procedures involving oxirans as intermediates.They can now 26 G. H. Posner G. L. Loomis and H. S. Sawaya Tetrahedron Letters 1975 1373 *’ G. Zweifel and R. P. Fisher. Svnthesis. 1975. 376. 28 A. Pelter C. Subrahmayam’ R. J. Laub K.J. Could and C. R. Harrison Tetrahedron Letters 1975 1633. 314 G.Pattenden R' R' '. \ Li[RiBCGCR2] A \C=CHR~ ,C=CHR~ / RiB R' (14) (15) Reagents i HCl; ii I,-NaOH; iii R3X;iv H+ (17) Scheme 7 be prepared directly however from carbonyl compounds according to Scheme 8.29 The deoxygenation of epoxides to olefins with retention of stereochemistry using the complex anion [C,H,Fe(CO),]- has been described previously. It is now found that Reagents i R,CO; ii P(OEt) Scheme 8 if the alkoxide intermediate (18)in this scheme is decomposed thermally (rather than with acid) the corresponding olefin (19)of inverted stereochemistry can be obtained Scheme 9 29 A.I. Meyers and M. E. Ford Tetrahedron Letters 1975 2861. Synthetic Methods (Scheme 9).30Where acid conditions are to be avoided epoxides can be converted stereospecifically into olefins by potassium ~elenocyanate.~~ Selenoketones have been prepared for the first time and these compounds are particularly useful in the synthesis of hindered ~lefins.~’ Reductive coupling of ketones with TiC1,-LiAlH provides another useful route to hindered olefins., The reagent produced from TiCl and LiAlH is also recommended for the reductive coupling of allylic alcohols to 1,5-diene~.,~ These dienes can also be prepared from ally1 halides using the complex produced from cuprous iodide and lithium dial- kylamide;, in the latter procedure however appreciable amounts of isomeric dienes are also formed.Treatment of vinylsilanes with hydroiodic acid results in the stereospecific exchange of Me,Si for H leading to alkenes with retention of Using a mixture of iodine and deuterium oxide deuterium can be incorporated specifically into alkenes. Another useful method for the synthesis of deuterio-olefins makes use of the reaction of ketone arenesulphonylhydrazones (20) with TMEDA (Scheme Scheme 10 An intriguing synthetic process which joins an alkene and an aldehyde in a long-chain unsaturated aldehyde is the photochemical Paterno-Buchi cycloaddition reaction followed by the retro-Paterno-Biichi reaction in the alternative sense by a thermal reaction (Scheme 1l).38 Scheme 11 Olefins can be protected with the organometallic moiety [C,H,Fe(CO),]+ as the blocking group.39 The olefin complexes are simply prepared by a thermal exchange reaction between the alkene and [C,H,Fe(CO),(isobutylene)]~BF,- and alkene is regenerated upon treatment of the complexes with NaI in acetone.30 M. Rosenblum M. R. Saidi and M. Madhavarae Tetruhedron Letters 1975,4009. 31 J. M. Behan R. A. W. Johnstone and M. J. Wright J.C.S. Perkin I 1975 1216. 32 T. G. Back D. H. R. Barton M. R. Britten-Kelly and F. S. Guziec J.C.S. Chem. Comm. 1975 539. 33 D. S. Bomse and T.H. Morton Terruhedron Letters 1975,781. 34 J. E. McMurry and M. Silvestri J. Org. Chem. 1975,40 2687. 35 Y. Kitagawa K. Oshima H. Yamamoto and H. Nozaki Tetrahedron Letters 1975 1859. 36 K. Utimoto M. Kitai and H. Nozaki Tetrahedron Letters 1975,2825. 37 J. E. Stemke and F. T. Bond Tetrahedron Letters 1975 1815. 38 G. Jones jun. M. A. Acquadro and M. A. Carmody J.C.S. Chem. Comm. 1975,206. 39 K. M. Nicholas J. Amer. Gem. Soc. 1975 97 3255. 316 G.Pattenden 3 Alkynes and Allenes A rapid and simple method for the preparation of 1,l-dichloroalkenes is by reaction between aldehydes and the diethyl dichloromethanephosphonate anion (21). Further treatment of these dichloroalkenes with alkyl-lithiums affords the cor- responding lithium alkynides which can then be hydrolysed or alkylated directly leading to the alkynes (22) and (23) respectively (Scheme 12).40 R-C-CH LiCCI,PO(OEt) A "7'' 2R-CECLi 'IY (22) Y (21) c1 R-CEC-R~ Reagents i RCHO; ii BuLi; iii H'; iv R'Br Scheme 12 Reaction of lithium 2-chloroethynyltrialkylborateswith iodine provides an alter- native approach towards the synthesis of symmetrical alkyne~.~~ Symmetrical conju- gated diynes can be obtained in excellent yields from the lithium dialkyldialkynylbo- rates (24; R'= 1,2-dimethylpropyl or cyclohexyl) by treatment with iodine (Scheme 13)..42 R,B + LiC-CCI -+ [R,BC-CCI]Li+ RCZCR -[R:B(CrCR'),]Li+ -% R2CrC-C=CR2 (24) Scheme 13 In a 'one-pot' process linear chain extensions at both termini of propyne can be carried out according to Scheme 14.43 In similar studies y-alkylation of the dianion obtained from but-2-ynoic acid leads to chain-extended ynoic acids (25) (Scheme 14).44 .-Me-r -bCH,-CEC-3 Bun*-5Bun* VOH Reagents i BuLi ;ii BuBr ;iii CHzO;iv RBr Scheme 14 40 (a) P.Savignac J. Petrova M. Dreux and P. Courot Synthesis,1975,535; (6) J. Villieras P. Perriot and J. F. Normant ibid. p. 458. 41 K. Yamada N. Miyaura M. Itoh and A. Suzuki Tetrahedron Letters 1975 1961. 42 A. Pelter K. Smith and M. Tabata J.C.S. Chem. Comm. 1975 857. 43 S. Bhanu and F. Scheinmann J.C.S. Chem.Comm. 1975,817. 44 B. S.Pitzele J. S. Baran and D. H. Steinman J. Org. Chem. 1975,40 269. Synthetic Methods Normant and co-w~rkers~~ have developed a versatile synthesis of cis-enynes which is based on a coupling reaction between a cis-vinylcopper reagent and an acetylenic bromide.The orthoester Claisen rearrangement of alkynyl allylic alcohols produces largely tr~ns-enynes.~~ A simple procedure for converting ketones into internal allenes has been achieved by heating the vinyl triflate derived from the ketone in quinoline at 100"C (Scheme 15).47 Allenic compounds can also be obtained by sequential alkylation of allenic lithium reagents derived from terminal allenic hydrocarbon^.^^ 4 Alkyl Halides A review covering the use of the tertiary phosphine-carbon tetrachloride reagent for chlorinations of alcohols has appeared.49 Two group^^^,^^ have shown that this method of chlorination can be carried out more efficiently using a polystyryl diphenylphosphine resin as the P-reagent.The principle advantage of this procedure is that it involves only a filtration and evaporation process to isolate the chloride. When low acidity and mild reaction conditions are important chlorinations of alcohols with thionyl chloride are best carried out in the presence of ZnCl as catalyst in place of ~yridine.'~ P-Halogenovinyl ketones are useful intermediates in synthesis. Two particularly convenient procedures for the preparation of cyclic P-halogenovinyl ketones involve treatment of the corresponding cyclic /3 -diketone either with triphenylphosphine dihalide53 in benzene solution in the presence of triethylamine or with triphenyl- phosphine in carbon tetrachloride (or CBr4).54 Hydrozirconation of disubstituted acetylenes is a regioselective and stereospecific process providing vinyl Zr'" complexes which are valuable precursors of vinyl halides.Thus reaction of t-butylmethylacetylene with [(q'-C,H,)ZrH(Cl)] leads to the complex (26) resulting from Zr-H cis-addition to the triple bond the Zr adding to the sterically more accessible carbon Subsequent treatment of (26) with NBS produces vinyl bromide (27) in good yield and with retention of stereochemistry. 45 J. F. Normant A. Commercon and J. Villieras Tetrahedron Letters 1975 1465. 46 K. A. Parker and R. W. Kosley Tetrahedron Letters 1975,691. 47 P. J. Stang and R. J. Hargrove J. Org. Chem. 1975,40 657. 48 G. Linstrumelle and D.Michelot J.C.S. Chem. Comm. 1975 561. 49 R. Appel Angew. Chem. Internat. Edn. 1975 14 801. S. L. Regen and D. P. Lee J. Org. Chem. 1975,40 1669. s1 P. Hodge and G. Richardson J.C.S. Chem. Comm. 1975,622. 52 T. G. Squires W. W. Schmidt and C. S. McCandlish,J. Org. Chem. 1975,40 134. 53 E. Piers and I. Nagakura Synth. Comm. 1975,5 193. 54 L. Gruber I. Tomoskozi and L. Radics Synthesis 1975,708. ss D. W. Hart T. F. Blackburn and J. Schwartz J. Amer. Chem. Soc. 1975,97,679. 318 G.Pattenden c1 Cp = cyclopentadienyl 5 Alcohols The reducing agent produced from LiAlH and two molar equivalents of 2,6-di-t- butylphenol followed by one equivalent of neopentyl alcohol shows remarkable stereoselectivity for the reduction of carbonyl e.g.3,3,5-trimethylcyclohexanone is reduced to the trans-axial epimeric alcohol with >99% stereoselectivity. Reduction of the ketone functions in a-and P-keto-esters with actively fermenting yeast like that of isolated ketone functions is an asymmetric process leading to functionalized s-alcohols of high optical p~rity.~’ Two useful procedures for the selective reduction of aldehydes in the presence of ketones have emerged. In a systematic study of the reactions of organic substrates at alumina surfaces Posner and Runqui~t~~ have shown that propan-2-01 on dehydrated Woelm chromatographic alumina is an effective ‘reagent’ for the clean and rapid (<2 h) reduction of aldehydes into the corresponding primary alcohols (65-88%); ketone functions are unaffected by the medium.Sodium triacetoxy- borohydride prepared from NaBH and acetic acid also effects selective reduction of aldehydes in the presence of Yamamoto and co-workers have extended their studies of the reaction of dialkyl-chloroboranes with lithium aldimines and have developed a new approach towards the synthesis of trialkylcarbinols (Scheme 16).60 Successive treatment of the Scheme 16 chloroborane-aldimine ‘adduct’ (28) with thioglycolic acid sodium hydroxide in diglyme and hydrogen peroxide-sodium hydroxide gives good yields of trialkylcar- binols. The most widely employed reagent for the oxidation of organoboranes to 56 H. Haubenstock J. Org. Chem. 1975 40 926. 57 D. D. Ridley and M. Stralow J.C.S. Chem. Comm. 1975,400. 58 G. H. Posner and A.W. Runquist Tetrahedron Letters 1975 3601. 59 G. W. Gribble and D. C. Ferguson J.C.S. Chem. Comm. 1975 535. 60 Y. Yamamoto K. Kondo and I. Moritani J. Org. Chem. 1975,40 3645. Synthetic Methods alcohols is hydrogen peroxide. Trimethylamine N-oxide dihydrate is a more conve- nient and safer reagent to handle than hydrogen peroxide;61 furthermore yields of alcohols are at least as good and often better with this reagent. Although carboxylate esters are not reduced to alcohols by sodium borohydride itself either sodium borohydride mixed with ethanedithio16* or sodium anilidob~rohydrides,~~ synthesized from anilides and sodium borohydride are highly effective reagents for accomplishing this transformation; e.g.,benzyl alcohol is obtained in quantitative yield from methyl benzoate.Insertion of oxygen into C-H bonds with ozone leading to alcohols and ketones has been known for a long time. The reaction has now been exploited synthetically and it is that tertiary carbon atoms are selectively hydroxylated in high yields by ozonation of organic substrates adsorbed on silica gel e.g. (29) +(30). Potassium (29) (30) superoxide in solution with 18-crown-6 is an exceedingly reactive and effective oxygen nucleophile providing an expeditious synthesis of alcohols from the corre- sponding alkyl halide. The reagent has also found application in the specific conversion of a (15R)-prostanoid structure (31) into the (15s)-system (32) via displacement of me~ylate.~~ AcO 1 AcO OH OMes (31) (32) In further applications of organoselenium intermediates in synthesis Reich and co-workers have shown that selenoxide-stabilized anions react with a variety of carbonyl compounds leading to products which readily eliminate selenium to give allyl alcohols.66 Allylic alcohol systems of the type (34) useful in natural product synthesis can be prepared from addition of the 0,2-dilithio-derivative of allyl alcohol [uiz.(33)] to carbonyl For the often difficult selective reduction of a/?-unsaturated carbonyl compounds to allyl qlcohols 9-61 G.W. Kabalka and H. C. Hedgecock J. Org. Chem. 1975,40 1776. 62 T. Maki and K. Kituchi Tetrahedron Letters 1975 3295. 63 Y. Kikugawa Chem. Letters 1975 1029. 64 Z. Cohen E. Keinan Y. Mazur and T. H. Varkony J. Org.Chem. 1975,40,2141. 65 E.J. Cory K. C. Nicolaou M. Shibasaki Y. Machida and C. S. Shiner Tetrahedronktters 1975,3183. 66 H. J. Reich and S. K. Shah J. Amer. Chem. SOC.,1975,3251; cf. D. Seebach and A. K. Beck Angew. Chem. Internat. Edn. 1974 13 789. 67 E. J. Corey and G. N. Widiger J. Org. Chem. 1975,40 2975. 320 G.Pattenden borabicyclo[3,3 lln~nane,~~ are and in some instances sodium cyan~borohydride,~~ new reagents which have advantages over earlier procedures. A complementary method to the presently used reductive procedures for cleaving the benzyl ether protecting group of alcohols is by electrochemical o~idation.~' Primary alcohols are protected with advantage as the methylthiomethyl ether;71 these derivatives are stable to both basic and nucleophilicreagents (e.g.NaH RLi or NaOR) and also fairly resistant to acid-catalysed cleavage.The ethers are prepared from the corresponding sodium alkoxide and iodomethyl methyl sulphide and are easily cleaved with HgCl in MeCN-H,O or with AgNO in buffered THF-H20. An alternative new method for the protection of alcohols is by formation of the corresponding levulinate;72 deprotection of these derivatives is accomplished with NaBH, the transformation proceeding by intramolecular lactone formation. 6 Ethers Overall yields in the Williamson ether synthesis can be increased upwards of twenty-fold using phase-transfer catalysis.73 Phase-transfer catalysis is also used with advantage in the conversion of o-dihydroxybenzenes into the corresponding methylenedio~ybenzenes.~~ have shown that alkyla- Seebach and his co-worker~~~ tion of thallium(1) alkoxides with alkyl halides constitutes a useful modification of Williamson's synthesis; yields of ethers are often excellent.A particularly conve- nient synthesis of alkyl aryl ethers involves reaction between a phenol an alcohol triphenylphosphine and diethyl azodi~arboxylate.~~ In an interesting combination of the Michael and Darzens reactions White77 has developed a new synthetic appro'ach to epoxides which proceeds in a single step involving (a) conjugate addition of nucleophile to an activated halogenoalkene (b) nucleophilic addition to a carbonyl compound and (c) epoxide formation (Scheme 17). The sequence has been applied with special success in ring synthesis e.g.(35)+(36) Another interesting synthesis of epoxides involves bis-alkylation of the dilithio-derivative of phenylthioacetic acid followed by reduction to a p-68 S. Krishnamurthy and H. C. Brown J. Org. Chem. 1975 40 1864. 69 R. 0.Hutchings and D. Kandasamy J. Org. Chem. 1975,40 2530. 70 S. M. Weinreb G. A. Epling R. Comi and M. Reitano J. Org. Chem. 1975,40 1356. 71 E. J. Corey and M. G. Bock Tetrahedron Letters 1975 3269. 72 A. Hassner G. Strand M. Rubinstein and A. Patchornik J. Amer. Chem. SOC.,1975,97 1614. 73 H. H. Freedman and R. A. Dubois Tefruhedron Letters 1975,3251. 74 A. P. Bashall and J. F. Collins Tetrahedron letters 1975 3489. 75 H.-0. Kalinowski D. Seeback and G. Crass Angew. Chem. Internut. Edn. 1975 14 762. 76 M.S. Manhas W. H. Hoffman B. Lal and A. K. Bose J.C.S. Perkin I 1975 461. 77 D. R. White J.C.S. Chem. Comm. 1975 95. Synthetic Methods Scheine 17 hydroxysulphide [e.g. (37)] and 173-elimination (Scheme Ansari et al.79have shown that glycols are smoothly converted into terminal epoxides by heating the corresponding glycol monoesters in the liquid phase at 200-250 "C. (37) +-Reagents i R'X; ii LDA ;iii RZX;iv LiAIH ;v Me,OBF ;vi NaOH Scheine 18 A novel synthesis of 2,3-dihydrofurans has been described by Dauben and Hart," which starts with sodium carboxylates and the cyclopropyl-phosphonium salt (38); the reaction proceeds with attack by carboxylate anion on (38) followed by intramolecular Wittig reaction. C02Et L 7 Amines The preparation of unsymmetrical s-and t-amines from reactions of alcohols and amines is accomplished in high yields under mild conditions in the presence of 78 P.A. Grieco and C;L. J. Wang J.C.S. Chem. Comm. 1g75,714; cf. W. Dumont and A. Krief Angew. Chern. Znternat. Edn. 1975 14 350. 79 H. R. Ansari and R. Clarke Tetruhedron Letters 1975,3085. W. G. Dauben and D. J. Hart Tetrahedron Letters 1975,4353. 322 G.Pattenden aminophosphonium salts e.g. PhN(Me)6Ph,I-.81 Lindlar’s catalyst is the catalyst of choice for the selective hydrogenation of azides to amines in the presence of C=C or C=O double bonds8* For the hydrogenation of nitro-compounds to amines a solution of [RuCl,(PPh,),] in benzene-ethanol mixtures offers several advantages over alternative homogenous catalytic procedure^.^^ Although Birch had earlier shown that imidazolidines serve as useful protecting groups for aldehydes it has now been shown that these derivatives are cleaved smoothly by borane-THF providing a useful synthesis of ethylenediamine~.~~ Lithium triethylborohydride is a very useful reagent for the selective demethylation of quaternary ammonium salts containing methyl thus dealkylation of the salt (39) produces largely the amine (40) (96%) from demethylation and very little (41) (4%) from de-ethylation.A facile method for dealkylation of tertiary-alkyl Phk(Et)Me --+ PhN(Et)Me + PhNMe (39) (41) primary amines to alkene products is by reaction of the NN-dichloro-derivatives with copper(1) chloride in DMSO at room temperature (Scheme 19).86This excep- tionally mild method has several advantages over the Cope or Hofmann elimination methods and also over alternative procedures involving the use of HNO,.R R CH R CH3 R Scheme 19 The use of ‘Umpolung’ of amine reactivity (i.e. nucleophilic carbon adjacent to nitrogen) has been excellently reviewed by Seebach and Ender~.~~ Thus lithio-derivatives of nitrosamines react with carbon electrophiles leading to substituted nitroso-compounds [e. g. (42)] which after removal of the nitroso-groups produce an amine [e.g. (43)]. Rt R2YNH R3 (43) 81 Y. Tanigawa S. I. Murahashi and I. Moritani Tetrahedron Letters 1975,471. 82 E. J. Corey K. C. Nicolaou R. D. Balanson and Y. Machida Synthesis 1975 590. 83 J.F. Knifton J. Org. Chem. 1975 40 519. R4 R. C. Northrop and R. L. Russ J. Org. Chem. 1975,40 558. 85 M. P. Cooke and R. M. Parlman J. Org. Chem. 1975,40 531. 86 J. A. Tonnis P. Donndelinger C. K. Daniels and P. Kovacic J.C.S. Chem. Comm. 1975 560. D. Seebach and D. Enders Angew. Chem. Infernat. Edn. 1975,14 15. Synthetic Methods 323 Cram and his co-workers have demonstrated that the optical resolution of racemates of primary amines can be accomplished by selective structured complexa- tion of one enantiomer with optically active crown ethers.88 8 Aldehydes and Ketones A number of new or modified procedures for the oxidation of alcohols to carbonyl compounds have been reported. Pyridinium chlorochromate C,H$JH[CrO,Cl]- is an air-stable solid which oxidizes a variety of alcohols to carbonyl compounds with very high efficiency;'' furthermore the reagent is easily and safely prepared by the addition of pyridine to a solution of CrO in 6M-HCl.In the interests of economy an important advantage that this reagent has over the Collins reagent is that it produces comparable yields of carbonyl compounds with 1.5 equivalents of reagent rather than the usual 5-6 equivalents employed with the Collins reagent. Chromyl chloride is another useful oxidizing agent;90 when used in glace of chromium trioxide in the Collins procedure only 1.1 equivalents of reagent are necessary to effect oxidation of alcohols to carbonyl compounds. Barton and Forbes9' have described an important modification of the procedure for the oxidation of alcohol chlorofor- mates to carbonyl compounds involving sequential treatment with DMSO and triethylamine.Addition of an acid scavenger conveniently 1,2-epoxypropane in the first stage of the sequence is shown to improve considerably the overall yields of carbonyl products. In contemporaneous studies it has been shown that the reagent prepared as a complex from DMSO and trifluoromethanesulphonic anhydride at -78 "C can be used with some advantages as an alternative to related sulphoxonium salt oxidants for the preparation of carbonyl compounds from alcohols.92 A useful and mild procedure for the oxidation of alkyl halides to acyl hydrazone derivatives of aldehydes involves alkylation of an N-acyl-N'- triflylhydrazine and subsequent elimination of triflate in base (Scheme 20).93 H RiCHBr -+ RiCH-N-I!IcOR2 -+ RiCH-N=NCOR2 R:C=N-NHCOR2 I SO,CF Reagents i R2CONHNHSOZCF,; ii K,CO,-MeCN Scheme 20 For most purposes the alcohol function is inert to peracid reagents and does not require prior protection before conducting peracid-mediated conversions.In the presence of catalytic amounts of nitroxide radicals and HCl or simply in THF using HC1 as the only catalyst however it has now been demonstrated that preparatively useful yields of carbonyl compounds can be obtained from alcohols by oxidation with rn-chloroperbenzoic The oxidative deamination of amines to ketones can L. R. Sousa D. H. Hoffman L. Kaplan and D. J. Cram J. Amer. Chem. SOC. 1974,96,7100. 89 E. J. Corey and J.W. Suggs Tetrahedron Letters 1975 2647. 90 K. B. Sharpless and K. Akashi J. Amer. Chem. SOC.,1975,97 5927. 91 D. H. R. Barton and C. P. Forbes J.C.S. Perkin I 1975 1614. 92 J. €3. Hendrickson and S. M. Schwartzman Tetrahedron Letters 1975 273. 93 J. B. Hendrickson and D. D. Sternbach J. Org. Chem. 1975,40 3450. 94 (a)J. A. Cella J. A. Kelley and E. F. Kenchan J. Org. Chem. 1975 40 1860; (b) B. Ganem ibid. p. 1998. 9s J. A. Cella J. P. McGrath and S. L. Regan Tetrahedron Letters 1975 4115. 324 G.Pattenden be achieved following conversion into the corresponding imine epoxidation and cleavage of the resulting oxaziridine in base.96 Two useful procedures for converting a carboxylic acid into a ketone with loss of one carbon atom involve sulphenylation of the dianion derived from the carboxylic acid followed by treatment with N-chlorosuccinimide97or reaction of the dianion with molecular oxygen followed by decarboxylative elimination (Scheme 2 l).98 73 SMe +SMe ...R,CHCO,H 3 R,C / \ r /OOH R,C\ C02H Reagents i LDA; ii MeSSMe; iii NCS-MeOH; iv 0,;v H+ ;vi DMF hcetal Scheme 21 Efficient methods for the controlled reduction of carboxylic acid derivatives to aldehydes are limited. Diaminoaluminium hydrides e.g. bis-(4-methyl-l-piperaziny1)aluminium hydride have been recommended for the reduction of both carboxylic acids and their alkyl esters to aldehydes,99 and Watanabe and co-workers'" have shown that carboxylic ethylcarbonic anhydrides are reduced smoothly to aldehydes with disodium tetracarbonylferrate.A useful alternative to the Rosenmund method and metal hydride procedures for the synthesis of aryl aldehydes from the corresponding acid chlorides is reaction with phospholens and hydrolysis of the resulting acylphospholenium salts with water (Scheme 22).lo' 6 fi -% 6 + ArCHO P P P I Ph '\ COAr Ph' Ph Reagents i ArCOCl-Et,N; ii H,O Scheme 22 The formation of carbonyl compounds by cleavage of glycols using periodate is well known. Shono and co-workers'02 have shown that this much-used synthetic 96 S. E. Dinizo and D. S. Watt J. Amer. Chem. SOC.,1975,97,6900. 97 B. M. Trost and Y. Tamaru J. Amer. Chem. SOC.,1975,97 3528. 98 H. H. Wasserman and B. H. Lipshutz Tetrahedron Letters 1975,4611.99 M. Muraki and T. Mukaiyama (a)Chem. Letters 1974 1447; (b) ibid. 1975 215. 100 Y. Watanabe M. Yamashita T. Mitsudo M. Igami K. Tomi and Y. Takegami Tetruhedron Lefters 1975,1063. '01 D. G. Smith and D. J. H. Smith J.C.S. Chem. Comm. 1975 459. T. Shono Y. Matsumura T. Hashimoto K. Hibino H. Hamaguchi and T. Aoki J. Amer. Chem. Soc. 1975,97,2546. Synthetic Methods operation can also be achieved by anodic oxidation in methanol containing tetra- ethylammonium toluene-p-sulphonate. This procedure has the advantage that ethers of glycols are also capable of being cleaved a reaction which does not take place with the normal periodate reagents. In a procedure which greatly extends the scope of the aliphatic Friedel-Crafts acylation reaction Fleming and Pearcelo3 have shown that acylations of aliphatic vinyltrimethylsilane substrates are site-selective the process taking place at the carbon atom carrying the TMS group e.g.(44) +(45) and (46) +(47). 0 Boron-substituted carbanions are useful intermediates in synthesis. The carbanion derived from tris(ethylenedioxybory1)methane for example reacts particularly smoothly with aldehydes and ketones to give consistently high yields of alkeneboronic esters [viz.(48)].'04 Oxidation of these esters with buffered H,O then HC[<)I3 Li' C[<]] A R,C=CH-B R,CHCHO 3 0 Reagents i MeLi ;ii R,CO; iii H,O Scheme 23 produces the homologous aldehyde often in better overall yield than alternative methods based on the Darzens procedure or the application of Wittig reagents such as ROCH=PPh, etc.(Scheme 23). A new sequence for converting an aldehyde into a homologous unsymmetrical ketone consists of Knoevenagel condensation with 2,4-pentanedione followed by treatment with tetracarbonylhydridoferrate(Scheme 24).lo5 YCOMe K[HFetCO),I 40 RCHO + CH,(COMe) + R R COMe Scheme 24 A number of new and useful methods for carbonyl group protection have emerged. Barton and co-workers'06 have shown that the spiroacetal(49) is a useful reagent for the protection of carbonyl compounds as their acetals and methylthio- trimethylsilane (50) effects thioacetalization of carbonyl groups at 0 "Cwithout the Io3 I. Fleming and A. Pearce J.C.S. Chem. Comm. 1975,633. (a)D. S. Matteson R. J. Moody and P.K.Jesthi J. Amer. Chem. Soc. 1975 97 5608; (6) D. s. Matteson Synthesis,1975 147. Io5 M. Yamashita Y. Watanabe T. Mitsudo and Y. Takegami Teirahedron Letters 1975 1867. Io6 D. H. R. Barton C. C. Dawes and P. D. Magnus J.C.S. Chem. Comm. 1975,432. 326 G.Pattenden apparent requirement of a catalyst."' Protection of carbonyl groups as 5-methylene-173-dioxans [viz. (5l)]has several advantages over other methods,1o8 particularly in cases where it is necessary to avoid the introduction of new chiral (50) 0 centres into the substrate. These protecting groups are most conveniently removed using Rh'-catalysed isomerization to an enol followed by hydrolysis. In some related studies on carbonyl protecting groups Corey and Haselo9 have outlined useful procedures for the facile interchange of thioacetal hemithioacetal and acetal protecting groups starting from dithioacetals and involving the sulphonium deriva- tive (52) as a pivotal intermediate (Scheme 25); the procedures greatly extend the Me / ..PMe RC;) i,RC$) RCH \ S S 0Me OMe 0 / RCH RC/H 7 '0 \SCH,CH SMe 'S Reagents i MeFSO,; ii MeOH (18 h); iii MeOH (2 h); iv HSCH,CH,OH; v HOCH,CH,OH Scheme 25 scope of these carbonyl protecting groups particularly in complex natural product synthesis. An expeditious reagent for the often difficult process of regenerating carbonyl functions from their 2,4-dinitrophenylhydrazonederivatives is aqueous titanous ion.ll0 Functionalized Aldehydes and Ketones.-The stable crystalline perbromide (54) prepared by treating the phosphonium salt (53) with bromine in acetic acid is an exceptionally useful reagent for the selective bromination of C-H bonds a to a ketonic carbonyl function."' A second new reagent which effects the same * transforma tion is 2- bromo-2-cyano-NNdime thylace tamide.Trimethylsilyl enol ethers are proving to be exceptionally versatile intermediates in organic synthesis. The principal method for their preparation has been silylation of enolate anions the scope of which is defined by the procedures for the regiospecific D. A. Evans K. G. Grirnm and L. K. Truesdale J. Amer. Chem. SOC.,1975,97 3229. lo* E. J. Corey and J. W. Suggs Tetrahedron Letters 1975 3775. lo9 E. J. Grey and T. Hase Tetrahedron Letters 1975 3267.'lo J. E. McMurry and M. Silvestre J. Org. Chem. 1975 40 1502. V. W. Armstrong N. H. Chishti and R. Rarnage Tetrahedron Letters 1975 373. M. Sekiya K. Ito and K. Suzuki Tetrahedron 1975 31,231. Synthetic Methods + H02CCH2CH2PPh3Br-H02CCH,CH,6Ph Br (53) (54) generation of enolate anions. Coates et ~2Z.l'~ have now shown that silatropic rearrangements formally analogous to known prototropic rearrangements offer new regiospecific routes to various types of trimethylsilyl enol ethers e.g. (55)-B (56);the appropriate trimethylsilyl P-keto-esters (55)are easily available via (55) (56) acylation of the reqilired carboxylic acid dianion followed by silylation. In an extension of earlier studies Hassner and co-w~rkers~~~ have shown that treatment with acetic acid and triethylamine of the protected a!-hydroxy-aldehydes resulting from peracid oxidation of trimethylsilyl enol ethers provides a mild method for the synthesis of a-acetoxy-aldehydes.A number of new and in some cases intriguing routes to a!@-unsaturated carbonyl compounds have been described during the period covered by this Report. In a sequence which is actually equivalent to a directed mixed aldol condensation Trost and Stant~n'~~ have shown that when the product produced from reaction between a carbonyl compound and vinyl-lithium is quenched with benzenesulphonyl chloride an allylic sulphoxide [viz. (57)] from [2,3] sigmatropic rearrangement is produced. Sulphenylation of the sulphoxide anion then leads to a y-hydroxy-a!P-unsaturated thioether which is hydrolysed to an trp-enone (Scheme 26).The potential for a-lithio-selenides in synthesis is further illustrated in a new synthesis of enones which 1iii iv R R SPh 1 Reagents i,pLi ;ii PhSCl ;iii LDA ;iv PhSSPh ;v HgCl Scheme 26 uses P-chloro-allylic selenides as key intermediates (Scheme 27).'16 In another route to ap-enones (Scheme 28) use is made of the sulphone acetal (58) as a R. M. Coates L. O.Sandefur and R. D. Smillie J. Amer. Chem. Soc. 1975,97,1619. 114 A. Hassner R. H. Reuss and 11. W. Pinnick J. Org. Chem. 1975,40,3427. 115 B. M. Trost and J. L. Stanton J. Amer. Chem. Soc. 1975,97,4018. 116 H. J. Reich J. Org. Chem. 1975,40,2570. 328 G.Pattenden CI R CI Reagents i LiNEt,; ii RBr; iii H,O Scheme 27 n I\ 0 PhSO A PhSO,4+PhSO,-22 (y, iii n R\ o -PhS02W d Reagents i MVK; ii Bu"Li; iii RBr; iv HOAc; v base Scheme 28 p -acylvinyl anion ~ynthon."~ Perhaps a more recognizable masked unsaturated acyl anion equivalent is the keten thioacetal (59) obtained from reaction between carboxylate esters and bis(dimethyla1uminium) propane- 1,3-dithiolate.Metallation of this molecule occurs largely at the 2-position,"* and alkylation followed by hydrolysis provides an cup-enone (Scheme 29j; the whole sequence pro- vides a particularly useful method for the conversion R1CH,CH,C0,R2+ R'CH=CHCOR3. .. ... 11 111 I Reagents i Me,AIS(CH,).,SAIMe ;ii LDA ;iii R3X; iv HgCI,-THF-H,O Scheme 29 Vinylketens are unstable compounds and often difficult to synthesize; in addition they tend to undergo [2 +21 rather than [2 +41 cycloaddition reactions with appro- priate substrates.Corey and Koziko~ski~~~ have shown that the lactone (60),which is obtained simply by dehydrating muck acid behaves as a vinylketen equivalent and K. Kondo and D. Tunernoto Tetrahedron Letters 1975 1007. 118 E. J. Corey and A. P. Kozikowski Tetrahedron Letters 1975 925. E. J. Corey and A. P. Kozikowski Tetrahedron Letters 1975 2389. Synthetic Methods 329 furthermore undergoes largely [2 +41 reactions with dienophiles providing a useful route to several cyclic enones (Scheme 30). An interesting cheletropic reaction which leads to ap-enones is gas-phase thermolysis of lactones of the types (61) and (62).l2' (60) Scheme 30 RQo 4gto (61) (62) The Claisen rearrangement of silyl enolates derived from a-phenylthioacetates provides a facile route to a-phenylthid-acids [uiz.(63)] which are useful inter- mediates in the synthesis of certain Byunsaturated carbonyl compounds (Scheme 3l).'*' Addition of methoxycyclopropyl-lithium reagents to carbonyl compounds LoKSPh iv,v *dco,H ,d:i2~r (63) AcO SOPh -C0,Me Reagents; i LDA; ii Me,SiCl A; iii 2N-HCl; iv CH,N,; v NaIO,; vi NaOAc-Ac,O; vii LiAIH Scheme 31 followed by ring cleavage and dehydration also provides a useful synthetic approach to &-unsaturated aldehydes (Scheme 32).'** Li AOMe OH RAR O M e 1ii iii 0,&& &OMe OMe Reagents i R,CO ;ii MeS0,Cl; iii MeOH ;iv H+ Scheme 32 '20 W.Skorianetz and G. Ohloff Helv. Chim.Acta 1975,58 1272. 121 B. Lythgoe J. R. Milner and J. Tideswell Tetrahedron ktters 1975 2593. E. J. Corey and P. Ulrich; TetrahedronLetters 1975 3685. -0 330 G.Pattenden Cyclopropane intermediates feature in a new route to y6-unsaturated ketones123 which has as a key step the conjugate 1,6-addition of oaganoboranes in the presence of oxygen or of lithium dialkylcuprates to 1-acyl-2-vinylcyclopropanes(Scheme 33). Scheme 33 The powerful nucleophilicity and good leaving-group properties of the iodide ion have made this ion an exceptionally useful catalyst in the specific conversion of a-bromo-ketones into 1,2-diketones by oxidation with DMSO.124 An interesting new route to 1,4-diketones has been described based on the rearrangement of protonated cyclopropyl ketones (Scheme 34); 125 rearrangement leads first to the y-hydroxy- ketone (65),presumably via the oxolanylium ion (64) which on oxidation leads to the 1,4-dione.(64) Reagents:i conc. H,SO,; ii CrO Scheme 34 Conia and his colleagues have produced two excellent reviews 126~127summarizing their elegant studies of the thermal transformations of organic substrates. An illustration of the synthetic potential provided by these studies128 is the thermal rearrangement of 1-vinylcyclopentane- 1,2-diols leading to 1,5-diones (Scheme 35). Scheme 35 A particularly versatile synthesis of cyclopropyl ketones has been reported; 129 the method is based on the decarboxylative ring contraction of a-acyl- y-butyrolactones catalysed by halide ions (e.g.NaCl) in DMSO (Scheme 36). Stork and co-worker~'~~ 0 Scheme 36 123 N. Miyaura M. Itoh N. Sasaki and A. Susuki Synthesis 1975 317. D. P. Bauer and R. S. Macomber J. Org. Chem. 1975,40 1990. 125 T. Nakai E. Wada and M. Okawara Tetrahedron Letters 1975 1531. 126 J. M. Gmia and P. Le Perchec Synthesis 1975 1. 127 J. M. Conia and M. J. Robson Angew. Chem. Internat. Edn. 1975 14 473. 128 J. P. Barnier and J. M. Conia Bull. SOC. chim. France 1975 1654. lz9 S. Takei and Y. Kawano Tetrahedron Letters 1975,4389. 130 G. Stork J. C. Depezay and J. d'Angelo Tetrahedron Letters 1975 389. Synthetic Methods have extended their studies of the application of anions derived from protected cyanohydrins of aldehydes as acyl carbanion equivalents to provide a useful synthesis of small ring compounds e.g.cyclobutanone (Scheme 37). There have been several Reagents i Me,Si,N; ii aq. acid then aq. base Scheme 37 conceptually different and beautiful syntheses of prostaglandins reported in the past decade. To add to this impressive list is one by Stork and I~obe'~' (Scheme 38). This route is distinguished by its use of the enol phosphinate (66) as precursor for the regiospecific formation of the enolate (67) which is trapped with formaldehyde leading to hydroxymethylcyclopentenone (68). Elimination of water followed by conjugate addition of a vinylcuprate to enone (69)and subsequent elaboration of the fully functionalized cyclopentanone then completes a new total synthesis of PGF,,.OP(0)Phz I ii iii ,&OH . CsH11 / / OCH,Ph OR (68) 1iv v (69) Reagents i Bu'Li; ii ZnC1 ;iii HCHO; iv MeS0,Cl; v PriNEt; vi Cu L(CH,),OR] Scheme 38 Investigations on the design and synthetic applications of acyl anion equivalents continue to attract the attention and imagination of several groups of workers. Seebach and core^'^* have provided full details of their studies of 2-lithio-1,3-dithians (70) the first examples of synthetic equivalents to acyl anions to be described (1969) and 2-methylthioacetic acid (Scheme 39) and diethyl malonate are two more acyl anion equivalent^'^^ described this year. Lithium di-(a-methoxyviny1)cuprate (71) another masked anion prepared from a-methoxyvinyl-lithium has been shown to undergo conjugate addition reactions to 131 G.Stork and M. Isobe J. Amer. Chem. Soc. 1975,97,4745,6260. 132 D. Seebach and E. J. Corey J. Org. Chem. 1975,40 231. '33 B. M. Trost and Y.Tamaru Tetrahedron Letters 1975 3797. 332 G.Pattenden MeS-CO,H . . . . . .. MeSxCO,H 0 l,il,l,lli R’ R2 Reagents i LDA; ii R’X; iii;R2X; iv NCS-NaHCO,; v HCI-H,O Scheme 39 n VS R enones and coupling reactions with halides 134~135leading to several synthetically useful products (Scheme 40); these new synthetic reactions complement those 0 0 OMe 0 OMe 0 Scheme 40 described earlier for a-methoxyvinyl-lithium itself. An alternative method of achieving conjugate addition of a masked anion to an a@-unsaturated carbonyl compound is by application of the readily accessible lithiated bis(methylthio)(silyl)- and bis(methylthio)(stannyl)-methanes (72).136The allenic anion (73)prepared (72) M = Si or Sn from 1-thiomethyl-3-methoxypropyneis an unusually interesting and at the same time synthetically useful acyl anion equivalent.Alkylation of this anion for exam- ple leads to (74)which depending on reaction conditions can be hydrolysed as either a thioenol ether or an enol ether (Scheme 41).13’ 134 R. K. Boeckman K. J. Bruza J. E. Baldwin and 0.W. Lever J.C.S. Chem. Comm. 1975,519. 135 C. G. Chavdarian and C. H. Heathcock J. Amer. Chem. SOC.,1975,97 3822. 136 D. Seebach and R. Burstinghaus Angew. Chem.Infernat. Edn. 1975,14 57. i37 R. M.Carlson R. W. Jones and A. S. Hatcher Tetrahedron Letters 1975 1741. Synthetic Methods MeS MeS MeS, -Q-OMe ewOMe \\C-OMe -MeS OMe iii R RXCvOMe R (74) Reagents i LDA; ii RX; iii HgCI,-MeOH; iv H+-H,O Scheme 41 A new 1,2-carbonyl group transposition which uses a-sulphenylated esters as key intermediates has been developed by Trost and co-worker~;~~~ the process is illustrated for cyclic ketones in Scheme 42. lv Reagents i LCPA ;ii PhSSPh ;iii NaBH ;iv TsOH ;v TiC1 Scheme 42 9 Acids and Anhydrides Meyers and his co-worker~~~~ have extended their studies on the application of lithiated chiral oxazolines to provide an asymmetric synthesis of 3-substituted alkanoic acids; the chiral oxazoline (75) was found to undergo conjugate addition with various organolithium reagents producing (76) in high enantiomeric purity (>90%).Although several workers have used hydrazides as carboxy protecting groups in the past the drawback to this method is that deprotection is frequently accompanied by undesirable side reactions. It has now been e~tablished'~' that these deprotections are effected smoothly with perchloric acid N-benzoyl-L-phenylalaninehydrazide for example yielding N-benzoyl-L-phenylalaninein quantitative yield and without 138 B. M. Trost K. Hirio and S. Kurozumi J. Amer. Chem. SOC.,1975,97,438. 139 A. I. Meyers and C. E. Whitten J. Amer. Chem. SOC.,1975,97,6266. I4O J. Schnyder and M. Rottenberg Helv. Chim. Acra 1975,58 521.334 G. Pattenden H R RH N -. +R yy\OXp" Rw\oJph -R'FCO,H N-1 i ohe OMe (75) (76) racemization. An alternative acid protecting group which can be removed under mild acidic conditions (e. g. HC1-THF) or under catalytic-reductive conditions is the benzyloxymethyl ester derivative.14' @-Unsaturated acids are produced in a Ramberg-Backlund reaction when allylic sulphones of the type (77) are treated with carbon tetrachloride containing KOH (Scheme 43);142 the requisite sulphones are easily available via rearrangement of allylic sulphinates derived from the corresponding carbinols. R RL Rb A RLS02nC02Me OH OS02CH,C02Me 1 iii (77) R Reagents i Bu'SOCH,CO,Me-NCS; ii A; iii KOH Scheme 43 A study of the site-selectivity of nucleophilic additions to unsymmetrically substi- tuted maleic anhydrides has uncovered an interesting dichotomous reaction pathway amongst the carbanion and hydride ion nucleophiles 143 e.g.hydride-ion attack in (78) and (79)takes place predominantly at C-1 whereas carbanions of the C-P ylide type attack largely at C-4. The products of such reactions e.g. (80) and (81) are useful intermediates in the synthesis of natural 4-ylidenebutenolides. OMe (80) (81) Functionalized Acids.-An efficient asymmetric synthesis of a-amino-acids from a-keto-acids and ammonia employing S-proline as the recoverable chiral reagent has 141 P. A. Zoretic P. Soja and W. E. Conrad J. Org. Chem. 1975,40 2962. P. A. Grieco and D. BoxIer Synrh. Comm.1975,5 315. 143 M. J. Begley D. W. Knight and G. Pattenden TetrahedronLerrers 1975 4279. Synthetic Methods been reported (Scheme 44);'44 the method is equally applicable to the synthesis of N-methyl-amino-acids. Ayre~l~~ has shown that oxidation of substituted amines of co2-Ohc, H' Reagents i MeCOC0,H ;ii NH3;iii CF,C02H ;iv H,-Adams catalyst ;v H+ Scheme 44 type (82) with RuO in a phosphate buffer containing periodate in the presence of RuCI3,3H2O as catalyst provides a useful synthetic route to several a-,p- or y-amino-acids. N-Acyl derivatives of a-amino-y-keto-acids can be prepared from 1,3-dicarbonyl compounds by aminoalkylation with glyoxylic acid amide deriva- tives. 146 R R (82) The potential in synthesis for silyl enol ethers is further illustrated in a new synthesis of a-hydroxy-a~ids.l~~ Oxidation of keten bis(trimethylsily1) acetals [e.g.(83)J with peracids leads first to epoxy-derivatives which by mild acid hydrolysis R OSiMe OSiMe (83) through [1,4] silatropic shifts afford the corresponding a-hydroxy-acids in excellent yield. In a second new synthesis of a-hydroxy-acids a P-keto-sulphoxide is first converted in one step by the Pummerer rearrangement into an a-acetoxy-acid thioester with Ac,O-N~OAC;'~* alkaline hydrolysis then produces the a-hydroxy- acid (Scheme 45). 144 B. W. Bycroft and G. R. Lee J.C.S. Chem. Comm. 1975 988. 145 D. C. Ayres J.C.S. Chem. Comm. 1975,440. 146 D. Ben-Ishai Z. Berler and J. Altman J.C.S. Chem. Comm. 1975 905.147.G. M. Rubottom and R. Marrero J. Org. Chem. 1975,40 3783. 148 S. Iriuchijima K. Maniwa and G. Tsuchihashi J. Amr. Chem. SOC.,1975,97 596. 336 G.Pattenden 0 Scheme 45 10 Esters and F'unctionalized Esters Esters of sterically hindered acids can be prepared from equimolar amounts of the acid and an alcohol with 1-methyl-2-halogenopyridiniumsalts in the presence of two equivalents of tri-n-butylamine. 149 In an interesting modification of the ozone cleavage reaction ozonization of vinyl chlorides in methanol is shown to lead to preparatively useful yields of methyl esters; cyclic vinyl halides produce bis-esters. 150 The series Organic Reactions now in its twenty-second year has begun a programme of updating earlier reviews and an article on the Reformatsky reaction is included in the latest volume.15' Activated indium prepared from reduction of InCl with and a new active form of zinc prepared from reduction of ZnC1 with are recommended alternatives to zinc wool etc. for the formation of Reformatsky reagents from a-halogeno-esters. In a reaction which is similar to the Darzens reaction condensation between alkyl dichloroacetate and carbonyl compounds leads to a-chloroglycidic esters [e.g. (84)].154 Reaction of these com- pounds with magnesium iodide followed by sodium bisulphite provides an expedi- tious-route to a-keto-esters. An equally useful synthesis of a-keto-esters starts from the corresponding acetate and proceeds via bis-sulphenylation to the bis-sulphide (85),followed by trans-acetalization and acid hydr01ysis.l~~ C12CHC02R -+ RiC-C + R;CHCOCO2R \ 0 COZR R'CH2C02R2 + R'C-C0,R2 -+ R'COC02R2 PhS' 'SPh (85) Ladones.-Efforts towards the development of flexible syntheses of the important a-methylene- y-butyrolactone system have continued unabated.Several new approaches to this system have been rec~rded~~~-~~' (Scheme 46) and reviews of 149 T. Mukaiyarna M. Usui E. Shimada and K. Saigo Chem. Letters 1975 1045. 150 K. Griesbaum and H. Keul Angew. Chem. Intenrat. Edn. 1975 14,716. 151 OrganicReactions Vol. 22 ed. W. G. Dauben Wiley New York 1975. I52 L. C. Chao and R. D. Rieke J. Org. Chem. 1975,40,2253. 153 R. D. Rieke and S. J. Uhrn Synthesis 1975,452. 154 P. Coutrot and C. Legris Synthesis 1975 118.I55 B. M. Trost and T. N. Salzrnann J. Org. Chem. 1975 40 148. lS6 S. M. Ali and S. M. Roberts,'J.C.S. Chem. Comm. 1975 887. lS7 N. Bensel H. Marshall and P. Weyerstahl Chem. Ber. 1975 108 2697. lS8 R. M. Carlson and A. R. Oyler Tetrahedron Letters 1975 4099. lJ9 J. R. Norton K. E. Shenton and J. Schwartz Tetrahedron Letters 1975 51. Synthetic Methods liii Rej 157 Tviii aoH Ref 158 + dco2H6 :roxo ix,x Ref:159 :roxo ArCH202C C02CH,Ar CO,H Reagents i,Me(Br)C=C=O; ii rn-CIC,H4C03H; iii DBN; iv NaCH(CO,Et) ;v -OH; vi NHEt,XH,O; vii NaOAc-HOAc; viii CO-PdCl,; ix LDA-R,CO; x Ht ;xi CF,CO,H Scheme 46 earlier routes have The a-methylenebutyrolactone system is 'protected' from Michael-type additions by preparation of the corresponding p-thiophenyl adduct using sodium thiophenoxide.162 Regeneration of the ty -methylene unit is readily accomplished following oxidation of the sulphide to its sulphoxide and thermal elimination of benzenesulphenic acid. For the preparation of the a-methylene-S-lactone system also an important structural feature in several biologi- cally active natural products Tro~t'~~ has outlined a method based upon the ring-expansion of a y-butyrolactone system (Scheme 47). Reagents i LDA ;ii MeOCHSPh ;iii AgN03-NCS ;iv pMeC6H4SOJH ;v CH26Ph3 ;vi H + ;vii MnO Scheme 47 160 P. A. Grieco Synthesis 1975 67. 161 R.B.Gammill C. A. Wilson and T. A. Bryson Synth. Comm. 1975,5,245. 162 P.A. Grieco and M. Miyashita J. Org. Chem.,1975,40 1181. 163 B.M.Trost and C.H. Miller J. Amer. Chem. Soc. 1975,97 7182. 338 G.Pattenden Although carbon dioxide does not undergo [4+2] cycloaddition reactions with dienes leading to unsaturated 8-lactones diethyl ketomalonate has been shown to serve as a carbon dioxide equivalent in [4+2] reactions leading first to adducts of type (86) which are then unmasked by double Curtius degradation followed by R R Et02C C02Et R (84) hydrolysis leading to the S-lactone. 164 Preparatively useful yields of but-2-enolides are obtained when epoxy diazomethyl ketones are irradiated in ben~ene.'~' The 4-ylidenebutenolide ring system [uiz.(88)]is found in a number of biologically active natural products. A useful synthetic route to this system is application of the corresponding 4-phosphoranylidenebut-2-enolide derivatives [uiz.(87)].'66 R' R' (87) (88) Cycloalkene-fused y-butyrolactones are also widely distributed in Nature. Two novel routes to this system involve as a key stage either Claisen rearrangement of monovinyl ethers from 2-cycloalkene- 1,4-di0ls'~' or solvolysis of cyclopropylcar- binols (Scheme 48).'68 aq. HCIO. in McOH Scheme 48 Macrolides.-Macrolide antibiotics seem destined to replace the prostaglandins as the next group of challenging substances to attract the attention of the foremost synthetic chemists. During the period covered by this Report Masamune has reported a synthesis of the macrolide antibiotic methmycin (89)'69*170 and Grey has R. A. Ruden and R. Bonjouklian J. Amer.Gem. Soc. 1975,97,6892. 165 P. M. M. van Haard L. Thijs and B. Zwanenberg Tetrahedron Letters 1975,803. 166 D. W.Knight and G. Pattenden J.C.S. Perkin I 1975 535. 16? K. Kondo M. Matsumoto and F. Mori Angew. Chem. Infernut. Edn. 1975,14 103. J. A. Marshall and R. H. Ellison J. Org. Chem. 1975,40,2070. 169 S. Masamune C. U. Kim,K. E. Wilson G. 0. Spessard P. E. Georghiou and G. S. Bates J. Amer. Chem. SOC.,1975,97,3512. 170 S. Masarnune H. Yamarnoto S. Karnata and A. Fukuzawa J. Amer. Chem. Soc. 1975,97 3513. Synthetic Methods described a synthesis of vermiculine (90);17'in addition a number of new approaches to macrolide systems have emerged. For the critical lactonization step in methmycin synthesis Masamune employed the S-t-butylthioester (88) which underwent par- ticularly smooth cyclization using mercuric ion cataly~is.'~~ Masamune's use of 0 (90) t-butylthioesters in macrolide synthesis resembles Corey's use of 2-pyridinethiol esters for the same process.Indeed Gxey has demonstrated the potential of 2-pyridinethiol esters in the synthesis of vermiculine (90)and also in the synthesis of novel macrolides in the prostaglandin and polyether antibiotic field^."^ Corey has also shown that the intramolecular version of the Diels-Alder reaction offers scope for the synthesis of macrolide~'~~ (Scheme 49). A significant aspect emanating from (cam 44%) (ca. 49 %) (cam 7%) Scheme 49 these studies was the similarity in product distribution for the intra- and inter- molecular Diels-Alder reactions; these data suggest that during the cyclization the E.J. Corey K. C. Nicolaou and T. Toru J. Amer. Chem. Soc.,1975,97,2287. 172 S. Masamune S. Kamata and W. Schilling J. Amer. Chem. Soc. 1975,97 1315. 173 E.J. Corey K. C. Nicolaou and L. S. Melvin J. Amer. Chem. Soc. 1975,97,653,654. E. J. Grey and M. Petrzilka Tetrahedron Letters 1975 2537. 340 G.Pattenden two mutually reactive units behaved almost as though they were not in the same molecule. Dean and Park175 have outlined a useful-looking approach to macrolides which is based on the stepwise insertion of ethylidene units into smaller unsaturated lactone rings by addition of diazoethane followed by elimination of nitrogen (Scheme 50). An intriguing route to the diketomacrolide (93)involves the thermolysis of the Reagents i MeCHN ;ii A Scheme 50 cyclic diperoxide (92) which is prepared by reaction of tetrahydroindane (91) with 0z0ne.l'~ 11 Amides and Nitriles '~~ Barton ~~cLZ.have published full details of their studies of the conversion of ketonic nitrones into N-alkylamides by treatment with toluene-p-sulphonyl chloride in pyridine containing water; this synthetically useful procedure provides a convenient alternative to the Beckmann rearrangement. a-Hydroxy-amides (and other carbox- ylate derivatives) can be prepared from NN-dialkylamides by treatment with alkyl-lithiums and oxidation of the resulting carbanions with molecular 0~ygen.l~~ A simple procedure for the monomethylation of amides which does not require strong basic conditions is by reaction with chloromethyl methyl sulphide in strong acid followed by treatment with Raney nickel.'79 Alkyl allyl and benzyl nitriles are conveniently prepared from their correspond- ing halides by stirring with tetraethylammonium cyanide in an appropriate solvent (CH,CI, DMSO or MeCN) between -30 and +50 OC.'*O Similar nucleophilic substitution reactions using dry KCN in the presence of 18-crown-6 as catalyst have also been reported.lsl An effective route to nitriles from the corresponding aldehyde 175 F.M. Dean and B. K. Park J.C.S. Chem. Comm. 1975 142. 176 G.L.Large and E. Neidert J. Org. Chem. 1975,40 3604. D. H.R. Barton M. J. Day R. H. Hesse and M. M. Pechet J.C.S. Perkin I 1975 1764. 178 H. H. Wasserman and B.H. Lipschutz Tetrahedron Letters 1975 1731. 179 L.Bernardi R. de Castiglione and U. Scarponi,J.C.S. Chern. Comm. 1975,320. lSo G. Simchen and H. Kobler Synthesis 1975,605. J. W. Zubrick B. I. Dunbar and H. D. Durst Tetrahedron Letters 1975 71. 1'7 Synthetic Methods is by base treatment of the 0-2,4-dinitrophenyloximederivatives.18* Aldoximes give nitriles by treatment with phenyl chloros~lphite.~~~ 12 Alkylation Vicinal bis-alkylation of enones by conjugate addition and alkylation of the resulting specific enolate [viz. (94) -B (95)-+(96)] is a sequence of considerable synthetic R' (94) (95) (96) potential. A perennial preparative limitation in the sequence however is the problem of proton exchange versus alkylation. It has been shown that this problem is largely overcome when the appropriate enolate is generated by cleavage of the corresponding trimethylsilyl enol ether with LiNH in liquid ammonia.'84 Subse- quent alkylation then proceeds in high yield in this solvent with little enolate equilibration leading to high yields of vicinal bis-alkylated products.Posner and his co-w~rkers'~~ have now published full details of their studies of the alkylation of enolate anions generated regiospecifically from a,a'-dibromo-ketones and enones using organocopper reagents; the overall results of these studies are useful in that they provide valuable information on the relative rates of enolate alkylation versus enolate equilibration amongst in particular 2-and 3-monoalkyl- and 2,3-dialliyl- cyclohexanones and 3-alkylcyclopentanones.Lithium organocuprates are now used widely in organic synthesis. To avoid side reactions resulting from the presence of Cu" compounds and other metal impurities in Cu' salts used to form the organocuprates House et uZ.lg6recommend the use of the easily prepared crystalline complex Me,S,CuBr. This complex is readily soluble in mixtures of Me$ and ethereal solvents and the sulphide ligand is easily removed from reaction products. In an interesting sequence which marries the use of organocuprates and of specific enolates in synthesis Naf et ~1.'~'have shown that when LiCuMe is added to substrates of the type (97) simultaneous conjugate addition and aldol condensation occur leading to one diastereoisomer of the product (98).The regiospecific C-acylation of organocopper enolates generated from (97) (98) 182 M. J. Miller and G. M. Loudon J. Org. Chem. 1975,40 126. 183 J. G. Krause and S. Shaikh Synthesis 1975 502. 184 E. S. Binkley and C. H. Heathcock J. Org. Chem. 1975,40 2156. 185 G.H. Posner J. J. Sterling C. E. Whitten C. M. Lentz and D. J. Brunelle J. Amer. Chem. Soc. 1975 97 107. 186 H. 0.House C. Y. Chu J. M. Wilkins and M. J. Umen J. Org. Chem. 1975 40 1460. 187 F. Naf R. Decorzant and W. Thommen Helu. Chim. Acra 1975,58 1808. 342 G.Pattenden conjugate addition of organocopper lithium reagents to ap-enones has also permit- ted the expeditious synthesis of P-diketones. '" The synthesis and evaluation of new organocuprates which might add selectively (1,2 or 1,4) to enone substrates continues to be an important area.Alkynyl groups of lithium alkynylcuprates are transferred regiospecifically to cyclic enones to afford the corresponding 1,2-adducts only in the presence of HMPA.ls9 The divinylcuprate (99) reacts with enones largely in a 1,2-~ense,~~' whereas the closely related derivative (100) does so predominantly by 1,4-additi0n;'~' lithium divinylcuprate ~e02CyCuyC02Me Li ] 2 (99) (100) itself undergoes 1,4-addition reactions to cyclohexenones. 19* A synthetically useful coupling reaction leading to P-alkyl-a@-unsaturated ketones involves addition of alkylcuprates to the corresponding P-halogeno-a-unsaturated ketones.'93 Tris(pheny1thio)methyl-lithium,in contrast to other carbanions stabilized by adja- cent sulphur atoms reacts with a-enones by 1,4-addition leading to adducts of the type (101);mild hydrolysis then provides a useful synthesis of yketo-e~ters.'~~ 0 4+ (PhS),CLi (PhS)C AA -+ -+Me02C (101) The regioselectivity of alkylation of allylic carbanions derived from CWP-unsaturated esters is remarkably dependent on the structure of the ester.Carbanions derived from crotonate and its a-isopropyl or P-propyl homologues have earlier been shown to undergo alkylation regioselectively at the a-position. Unsaturated esters which have both a-and P-carbons substituted are now shown to undergo exclusive reaction at the y-po~ition.'~~ In another illustration of allylic alkylation where the allylic carbon behaves as an electrophile reaction of the w-allylpalladium complex (102) derived from crotonate with malonate ion leads regio- and stereo- specifically to (103) in quantitative yield.'96 A synthetically valuable sequence of I CIPd/2 Et0,C *C02Et (102) (103) T.Tanaka S. Kurozumi T. Toru M. Kobayashi S. Miura and S. Ishimoto Tetrahedron Letters 1975 1535. G. Palmisano and R. Pellegata J.C.S. Chem. Comm. 1975 892. 190 J. P. Marino and D. M. Floyd Tetrahedron Letters 1975,3897. lgl J. P. Marino and J. S. Farina Tetrahedron Letters 1975 3901. 192 C. Alexandre and F. Rouessac J.CS. Chem. Cornm 1975,275. 193 E. Piers and I. Nagakura J. Org. Chem. 1975,40 2694. '94 A. R. B. Manas and R. A. J. Smith J.C.S. Chem. Comm. 1975,216. 195 A Kajikawa M. Morisaki and N.Ikekawa Tetrahedron Letters 1975,4135. 196 W. R. Jackson and J. U. G. Strauss Tetrahedron Letrers 1975,2591. Synthetic Methods 343 reactions which highlights the y-methylthiocrotonic ester anion as a bifunctional Michael nucleophile isoutlined in Scheme 5 1.197 MeSAC0,Me 2MeS&CO,Me -MeS+rCo2Me J”’,iv ,v o-YCo2H Reagents i LDA; ii MeI; iii Ba(OH) ; iv H+; v Me02CCH6Ph3 Scheme 51 The malonic ester synthesis has been a corner stone in synthesis for almost a century. A very simple alternative to the usual sequence in the synthesis starts with the half-ester (104). Preparation of the dianion (105) from (104),followed by + RCH,CO,Me C0,Me -<c02-<Co2H C0,Me Cd,Me (104) (105) alkylation in HMPA and decarboxylation can be made into a ‘one-pot’ procedure leading to better overall yields than the classical procedure.In related studies Krapcho and Ka~hdan’~~ have shown that good yields of disubstituted malonic acids can be obtained from alkylation of trianions derived from monosubstituted malonic acids with primary halides. The synthetic potential of the cyclobutanone spiroannelation sequence of Trost has been greatly extended by an investigation of methods for the ‘nucleophilicr cleavage’ of the four-membered ring (Scheme 52);200these elegant studies have 0 0 >o jii C0,Me 6iii bBr 3 cBr + --* Br Br Reagents i I);iPh2 ;ii H+; iii Br2;iv -0Me Scheme 52 resulted in synthetic methods for the replacement of both C +0bonds of a carbonyl group by several differently functionalized carbon chains.*O1 Phase-transfer catalytic procedures are featuring more and more in synthesis.202 A new class of catalysts for two-phase reactions are a-phosphoryl sulphoxides and 197 A.S. Kende D. Constantinides S. J. Lee and L. Liebeskind Tetrahedron Letters 1975,405. 198 J. E.McMurry and J. H. Musser J. Org. Chem. 1975,40 2556. 199 A.P.Krapcho and D. S. Kashdan Tetrahedron Letters 1975,707. B. M. Trost M. J. Bogdanowia and J. Kern J. Amer. Chem. Soc. 1975,97,2218. 201 B. M. Trost M. Preckel and L. M. Leichter J. Amer. Chem. Soc. 1975,97,2224. 202 H.W.Herriott and D. Picker J. Amer. Chern. Soc. 1975,97,2345. 344 G.Pattenden sulphones [uiz.(106)].203These compounds are completely different in structure to other phase-transfer catalysts such as onium salts and crown ethers.So far they have been shown to act as highly effective catalysts in the alkylation of ketones. Aza- macrobicyclic pol yethers are also highly efficient catalysts for two-phase C-alkylation reactions,2M and Fiaud has described an alkylation of 1,3-diones in the presence of the asymmetric phase-transfer catalyst (-)-N-benzyl-N-methylephedrinium bromide (107)which proceeds with a high degree of asymmetric R2 R2 13 Amelation Enolate anions from cyclic ketones and 1,3-dicarbonyl compounds feature in a number of new and modified annelation reactions leading to six-and five-membered ring systems. Thus addition of the enolate anion from (108) to the phenylthio- cyclopropylphosphonium salt (109)leads to an intermediate ylide which cyclizes by an intramolecular Wittig reaction to give after hydrolysis the cyclopentanone (1 In a similar manner (111)and (38) produce the spiro-annelated product (1 12).207 These reactions are similar in principle to those published earlier involving SPh -fi 'y C02R [)<$Ph3 C0,R C0,H OEt + 0602R 203 M.Mikolajnyk S. Grzejszczak,A. Zatorski,F. Montanari and M. Cinquini Tetrahedron Letters 1975 3757. ZOP M. Cinquini F. Montanari and P. Tunds J.C.S. Gem. Comrn. 1975 393. 205 J.-C. Fiaud Tetrahedron Letters 1975 3495. 206 J. P. Marino and R. C. Landick Tetrahedron Letters 1975,4531. 207 W. G. Dauben and D. J. Hart J. Amer. Chem. Soc. 1975,97 1623. Synthetic Methods addition of enolate anions to 1-butadienyltriphenylphosphoniumsalts and leading to cyclohexadienes e.g.(113)<3+-on(114).208 ---) X-+PPh (113) (114) Baldwin and his ~o-workers~~~ have shown that the irradiation of cr-formyl- ketones in the presence of alkenes gives rise initially to [2 +21photoproducts derived exclusively from that tautomer enolized towards the aldehyde carbonyl; in situ cleavage of the intermediate cyclobutanes followed by re-cyclization then completes a new and useful cyclohexenone annelation sequence (Scheme 53). Reagents i hv; ii H+ Scheme 53 Thermal rearrangement of trimethylsilyl enol ethers of cyclopropyl methyl ketones leading ultimately to cyclopentanones e.g. (115)4(1 16),provides a useful (1 15) (116) complementary procedure for cyclopentanone annelation2" to those published earlier based on the thermal vinylcyclopropane-cyclopentenerearrangement.Upwards of 50% yields are realized when the .Robinson annelation is effected with a P-chloro-ketone in the presence of an acid (H,SO or toluene-p-sulphonic acid).211 14 General Corey and his co-workers212 and Hendricks~n~'~ have discussed separately further procedures (computer assisted and application of graph theory) for the systematic 208 G. Buchi and M. Pawlak J. Org. Chern. 1975 40 100. *09 (a)S. W. Baldwin R. E. Gawley R. J. Doll and K. H. Lung J. Org. Chern. 1975,40 1865; (6)S. W. Baldwin and R. E. Gawley Tetrahedron Leners 1975,3969. 210 S. A. Monti F. G. Cowherd andT. W. McAninch J. Org. Chern. 1975 858.211 P. A. Zoretic B. Brauchaud and T. Moestrone Tetrahedron Letters 1975 527. 212 E. J. Corey,W. J. Howe H. W. Orf D. A. Pensak and G. Peterson J. Arner. Chern. Soc. 1975,97,6116. *I3 J. B. Hendrickson J. Amer. Chern. SOC.,1975,97,5673 5784. 346 G.Pattenden design and analysis of complex synthetic problems. Two useful article^^^^^^^^ cover-ing the applications of organic compounds of Si P and Sin synthesis have appeared and a review of the chemistry of S-ylides has been pub1ished.’l6 Brown has brought together in book form the major synthetic uses of organoborane~;~~~ the book also provides useful experimental detail for handling organoboranes. The fourth volume of Fieser’s ‘Reagents for Organic Synthesis’ has emergedz1’ and a second volume of Harrison’s ‘Compendium of Organic Synthetic Methods’ has been p~blished.’’~ Two volumes of a new series ‘Synthetic Reagents’ 220 and the first volume of ‘Creativity in Organic Synthesis’ 221 add further sustenance to the inquiring synthetic chemist.214 I. Fleming Chem. and Ind. 1975,449. 215 A. H.Davidson P. K.G. Hodgson D. Howells and S. Warren Gem. and Ind. 1975,455. 216 B. M.Trost and L. S.Melvin ‘Chemistry of Sulphur Ylides’ Academic Press New York 1975. 217 H:C. Brown ‘Organic Syntheses via Boranes’ Wiley-Interscience New York 1975. 218’M. Fieser and L. F. Fieser ‘Reagents for Organic Synthesis’ Vol. 4 Wiley-Interscience New York 1974. 219 T.T. Harrison and S. Harrison ‘Compendium of Organic Synthetic Methods’ Vol. 2 Wiley New York 1974.2t0 J. S.Pizey ‘Synthetic Reagents’ Vols. 1and 2 Wiley New York 1974. 221 J. S. Bindra and R. Bindra ‘Creativity in Organic Synthesis’ Vol. 1 Academic Press New York 1975.

ISSN:0069-3030    

DOI:10.1039/OC9757200309

出版商:RSC    

年代:1975

数据来源: RSC