摘要:

5 Free Radicals By W. T. DIXON Chemistry Department Bedford College Regent 3 Park London NW? 4NS 1 Kinetics of Free-radical Reactions There are two approaches to the measurement of kinetics in solution one direct in which the appearance and/or disappearance of species is measured as a function of time and the other indirect in which reactions are conducted competitively and relative rates are deduced from the pattern of products. The object of such studies is generally rather more to elucidate reaction mechanisms than to deter- mine individual reaction rates although there may be something of intrinsic interest in the latter. There is still muchactivity in the investigation of the reactions of phenyl radicals which may be generated in a very 'clean' way by the y-radiolysis of diazonium ions ArN,' 'zZ?p Are + N Subsequent reactions of these radicals can then be followed indirectly without the complication of molecular species required to initiate the formation of the phenyl radicals.The rate of disappearance of the diazonium ion (measured photometrically) as a function of dose rate can be used to indicate the mechanism of the overall reaction for the reduction of the diazonium salt to the parent hydrocarbon ArN,+ + AH -+ ArH + A + N + H+ The rate of hydrogen abstraction by the aryl radical is in the order hypophos- phite phosphite =-formate > methanol > formic acid. A chain reaction is in-volved thus generating further aryl radicals Ar. + AH + ArH + AH. ArN,' + AH. + Ar- +A + N + Hi The free-radical phenylation of perfluoroaromatic compounds has been studied with increasing intensity' and the results of classical kinetic studies and of product analyses seem to have shown that the reactions of these perfluorinated compounds are not strictly analogous to those of the corresponding hydrogen compounds.However the analogy is pressed home as far as possible and it seems fairly definite that there is an intermediate '0-complex' of the cyclohexadienyl type. J. E. Packer R. K. Richardson P. J. Soole and D. R. Webster J.C.S. Perkin II 1974 1472. R. Bolton J. P. B. Sandall and G. H. Williams J. Fluorine Chem. 1974 4 347 355. I35 136 W. T. Dixon *aF F F--‘F (1) One intriguing result is the occurrence of small quantities of hexafluorobiphenyl in the products of the reaction of phenyl radicals with hexafluorobenzene.This is analogous to results observed using hexadeuteriobenzene as the substrate3 and is rationalized in terms of a novel exchange in the intermediate (Scheme I). 2 Kinetics Using E.S.R. Although the slow decay of relatively long-lived species such as hindered phenoxyl radicals4 is relatively straightforward in kinetic work mainly ‘steady state’ concentrations of radicals are observed enabling relative rates of generation and termination reactions to be determined. This is true whether the steady-state concentrations are generated in a flow ~ystem,~ electrolytically,6or photolytical-Absolute rate constants can often be calculated from steady-state ex- periments provided that one of the rates involved is known but to do this directly it is necessary to disturb these conditions sufficiently e.g.by means of a rotating sector stopped flow flash photolysis constant current pulse etc. each of which may lead to a meaningful extrapolation to the start of the reaction (when the rate of radical decay is zero !). The photolysis of di-t-butyl peroxide and other peroxides has provided much of the focus in kinetic applications of e.s.r. spectroscopy. On the whole reactions ’E. K. Fields and S. Meyerson J. Amer. Chem. SOC.,1967 89 3224. R. D. Parnell and K. E. Russell J.C.S. Perkin II 1974 161. B. C. Gilbert R. 0.C. Norman and R. C. Sealy J.C.S. Perkin II 1974 824. I. R. Goldberg and A. J. Bond J. Phys. Chem..1974 78 290. ’A. G. Davies R. W. Dennis and B. P. Roberts J.C.S. Perkin 11 1974 1101. D. Griller B. P. Roberts A. G. Davies and K. U. Ingold J. Amer. Chem. SOC.,1974 96 554. D. Griller G. D. Mendenhall W. Van Hoof and K. U. Ingold J. Amer. Chem. SOC. 1974 96 lo V. Malatesta and K. U. Ingold J. Amer. Chem. SOC.,1974 96 3949. I* G. D. Mendenhall D. Griller D. Lindsay T. T. Tidwell and K. U. Ingold J. Amer. Chem. SOC.,1974,96 244 1 D. Lal D. Griller S. Husband and K. U. Ingold J. Amer. Chem. SOC..1974 96 6355. Free Radicals 137 which already have been observed have been quantified such as the dimerization of phosphorus-centred radicals,8 the disproportionation of sterically hindered alkyl radicals,' and the cyclization of the hex-5-enyl radical (2).(2) The more detailed knowledge gained by kinetic investigations shows for example that alkyl radicals leave more easily from an apical than from an equator- ial site of a phosphoranyl radical (RO),PR + (RO),PR + R-Both iminyl' and 1,l-dialkylhydrazyl radicals lo generated by t-butoxyl oxidation decay by dimerization though in the latter case there may be a radical equilib- rium as with hexaphenylethane BuO. -k RC=NH -+ R,C=N.-+ dimer 2R,NNH G R,NNHNHNR L R,NNH + R,N=NH A further important technique in kinetics is to make measurements or conduct experiments first in the presence of scavengers i.e. radical traps and secondly in their absence. This approach has made it possible to find the propagation and termination rate constants in the autoxidation of some hydrocarbon^'^ and to study the rate ofreaction oftriplet carbonyl compounds with some alcohols.14 3 Alkyl Radicals Some further interesting studies on conformation have appeared ;in particular the effect of P-substituents in the ethyl radical appears to lead to a definite preference between conformations (3a) and (3b).15916 When R = Bu' confor-mation (3b) is invariably preferred but when R = H (3a) is preferred for (34 (3b) l3 J.E. Bennett J. A. Eyre and R. Summers J.C.S. Perkin [I 1974 797. l4 P. B. Ayscough and R. C. Sealy J.C.S. Perkin II 1974 1402. D. Griller and K. U. Ingold J. Amer. Chem. Soc. 1974,96 6715; K. S. Chen and J. K. Kochi ibid. p. 794. R. V. Lloyd D. E. Wood and M. T. Rogers J. Amer. Chem. SOC.1974,96 7130. 138 W. T. Dixon X = MR, where M is in the first row of the Periodic Table (e.g. carbon). On the other hand if M is from rows 2,3 or 4 of the Periodic Table (3b) is preferred,' perhaps owing to the size of such groups. In contrast to this when R = Me and X = C1 the eclipsed conformation is preferred,16 whereas when R= Me and X = Br the favoured conformation is (3a). As one expects the stable confor- mations are observed when the speed of internal rotation is low (low temperature) and the usual cos' 8 rule is invoked for the P-proton coupling constants. An interesting attempt to put forward a formula for the angular dependence of P-I3C coupling constants has involved the use of the n.m.r. contact shifts in appropriate nickel complexes of aromatic amines.'' Analysis of the e.s.r. spectra of five- and six-membered-ring radicals'* over the temperature range 545"Chas led to the conclusion that whereas five-membered rings rapidly undergo interconversion between two 'half-chair' conformers the six-membered rings flip relatively slowly from one chair form to the other. The phenacyl radical' has been generated and trapped in matrices at low or high temperatures and the formation of benzyl during its decomposition sug-gests an intricate rearrangement mechanism 4 My1 Radicals Ally1 radicals have always been found to be remarkably resistant to rotation about either C-C bond. However a number of examples have been found where such an isomerization must occur (Scheme 2). Its occurrence has been deduced from product analyses" and it has been observed directly by means of e.s.r.spectroscopy. 9' Scheme 2 l7 G. R. Underwood and H. S. Friedman J. Arner. Chern. SOC.,1974,96,4989; L. M. Stock and M. R. Wasielewski ibid. p. 583. B. C. Gilbert R. 0. C. Norman and M. Trenwith J.C.S. Perkin ZZ 1974 1033. 19 P.H. Kasai D. McLeod,jun. and H. C. McBay J. Amer. Chern. SOC.,1974,96 6864. *O P. S. Engel A. I. Dalton and L. Shen J. Org. Chem. 1974 39 2607; R. M. Hoyle and D. B. Denney ibid. p. 2607; W. P. L. Carter and D. C. Tardy J. Phys. Chem. 1974 78 2201. 21 R.Sustman and H. Trill J. Amer. Chem. SOC.,1974 96 4343. 22 B. E. Smart P. J. Krusic R. Meakin and R. C. Bingham J. Amer. Chem. SOC.,1974 96 7382; see also ibid. p. 621 1.Free Radicals 139 5 Radicals Derived from Aliphatic Alcohols Alkoxy-radicals abstract hydrogen atoms attached to a saturated carbon atom but the presence of a sterically crowded group in an alcohol is liable to increase the reactivity of the hydroxylic hydrogen towards alkoxy- radical^.^ 3y24 Thus compare CH,OH + RO. -+ *CH,OH + ROH Bu'CH,OH + RO-+ Bu'. + ROH + CH,O The observation by e.s.r. of the hindered (or strongly delocalized) radical suggests effective abstraction of the hydroxylic proton which can be inhibited by the presence of fluoride ion with which it forms strong hydrogen bonds R'CH20H + -OR2 -+ R'CH,O. + HOR' L CH20 + R'. Whether or not this whole process is concerted remains to be established since even if it did have an independent existence the lifetime of the radical RCH20-would be too short for it to be observed by trapping.Related to these processes is the thermal decomposition of heavily substituted alcohols25 such as tri-t-butyl- methanol which because of the considerable steric strain within the molecule will fragment homolytically BU:COH + BU. + BU,COH -+ (BUH + B~,CHOH+ B~,c=o) products Similarly results have been obtained from studies of the decomposition of hypochlorites in which the chlorine atoms are trapped by halogen-substituted olefins :26 RCH20CI -+ RCH,O. + C1-3 XCl 1 R. + CH,O There is a marked polar effect in the @-scission of the alkoxy-radical. 50 % yield Scheme 3 23 I. H. Elson and J. K. Kochi J. Org. Chem. 1974,39 2091.24 D. Griller and K. U. Ingold J. Amer. Chem. Soc. 1974 96 630. " J. S. Lomas and J. E. Dubois J. Org. Chem. 1974 39 1776. 26 C. Walling and R. T. Clark J. Amer. Chem. SOC.,1974 96 4530. 140 W. T. Dixon Further examples of 1,4-hydrogen atom shifts27 are found when alkyl hydro- peroxides react with ferrous ion in the presence of cupric acetate (Scheme 3). Such a reaction would be unlikely if the chain were rigid because the formation of the six-membered transition state (which necessitates the S-hydrogen being close to the oxygen) would not be possible. The reaction between organometallic compounds and peroxides has hitherto been believed to be a heterolytic process but product studies and the observa- tion of CIDNP show that radicals are involved (Scheme 4).*’ RCH,CH,MgBr + Bu0,Bu + BuOMgBr +{::::cHz*} polarization step JL RCH,CH,OBu RCH,=CH + BuOH Scheme 4 More comprehensive studies of the interaction of radicals with maleic acid2’ and with allylic compounds30 have been carried out.In the latter case addition to the double bond is invariably preferred to proton abstraction leading to a delocalized allyl-type radical. In many of the adduct radicals long-range coupling constants are observed which are unusually large for non-rigid systems. However by suitably simplified c~mputation,~~ allowing for averaging over the possible conformations it seems that whereas 6-splittings arise from extended hyper- conjugation (of the type implied by the ‘W’ rule) E-splittings are due to a direct interaction between the &-proton and the odd electron cloud on C (4).From a rather different viewpoint the contact shifts of y-and 6-protons have been ex- plained also in terms of a generalized hyperconjugation (5).31 However whereas 6-couplings are invariably positive y-splittings may be positive or negative depending on conformation (6).31-3 This could be the explanation for the absence of y-couplings in some cases where they might have been expected2’ and can be rationalized in valence-bond terms. 2’ Z. Cekovic and M. K. Green J. Amer. Chem. SOC.,1974 96 3000. 28 W. A. Nugent F. Bertini and J. K. Kochi J. Amer. Chem. SOC.,1974 96 4945. 29 W. T. Dixon J. Foxall and G. H. Williams J.C.S. Furuduy II 1974 70 1614. 3o P. Smith R. A.Kaba and P. B. Wood J. Phys. Chem. 1974 78 117. ” G. R. Underwood and H. S. Friedman J. Amer. Chem. SOC.,1974,96,4089. 32 N. L. Bauld and F. R. Farr J. Amer. Chem. SOC.,1974 96 145. 33 G. A. Russell and A. Mackor J. Amer. Chem. SOc. 1974 96 5633. Free Radicals 141 zero spin (5) hyperconjugation (6) homohyperconjugation dependent on conformation A series of papers3L37 has appeared on semidiones RC(O* )=C(O-)R. Acyclic 1,2-semidiones can exist in cis-and in trans-form;34*35the former may be stabilized somewhat by chelation on to a metal cation although the trans con-figuration is still generally preferred. One of the interesting aspects which has appeared in the study of bicyclic aliphatic semidi~nes~~~~~ concerns some clear examples of valence isomerization (Scheme 5).38 In these radicals the odd 0-0 Scheme 5 electron occupies an orbital which is antisymmetric with respect to reflection through the plane of symmetry of the molecule and so we would expect very small if any splittings from the syn-and anti-protons.However a simple two-step model can be used to rationalize the observed splittings. First there is a spin polarization leading to negative spin density in orbital A and secondly there is hyperconjugation (7) of a similar type to that in the vinyl radical. The observed ratio leads one to expect a bridgehead angle of ca. 120" as in vinyl itself and this 34 G. A. Russell D. F. Lawson H. L. Malkus R. D. Stephens G. R. Underwood T. Takano and V. Malatesta J. Amer. Chem. SOC.,1974 96 5830.35 G. A. Russell and J. L. Gerlock J. Amer. Chem. SOC.,1974 96 5838. 36 G. A. Russell P. R. Whittle C. S.C. Chung Y.Kosugi K. Schmitt and E. Goettert J. Amer. Chem. SOC.,1974,96 7053; G. A. Russell G. W. Holland K. Y. Chang R. G. Keske J. Mattox C. S. C. Chung K. Stanley K. Schmitt R. Blankespoor and Y. Kosugi ibid.,p. 7249. 37 G. A. Russell R. L. Blankespoor J. Mattox P. R. Whittle D. Symalla and J. R. Dodd J. Amer. Chem. SOC.,1974 96 7249; R. L. Blankespoor ibid.,p. 6196. G.A. Russell J. R.Dodd T. Ku C. Tanger and C. S. C. Chung J. Amer:Chem. SOC. 1974,96 7255. 142 W. T. Dixon Usyn uanti= 1 2 is borne out by INDO calculations. Assuming an odd-electron density on C-2 of ca. 5 spin-density in A is ca. -5 & (from Q 2.5 mT) and the average splitting of the syn- and anti-protons would be cu.5 x 3%) x mT = 0.08 mT (ob- served 0.12 mT). The order of magnitude is correct and supports the mechanism proposed. * The mechanism of the Kolbe electrolysis is apparently quite strongly depen- dent on interactions between the carboxylate ions and the surface of the anode.39 A reverse-Kolbe reaction can occur at the cathode for activated olefins4' may be reduced and add on carbon dioxide (or vice versa) (Scheme 6). It would appear that a cell could be constructed in which cyclic addition and loss of CO could be achieved! -co CH,=CHX 5 CH,=CHX ee -CHXCH,CO,-'''L Jc-.H' -O,CHXCH,CO -CH XCH,CO,H Scheme 6 6 Simple Aromatic Radicals Some more phenyl-type radicals have been generated in an argon matrix$l i.e.those with 2-OH or 2-OMe substituents (Scheme 7). As might be expected radicals isomerize when the temperature is allowed to rise. Scheme 7 '9 J. P. Coleman R. Lines J. H. P. Utley and B. C. L. Weedon J.C.S. Perkin II 1974 1064. 40 D. A. Tysee and M. M. Baizer J. Org. Chem. 1974 39 2819. 4' P. H. Kasai and D. McLeod jun. J. Amer. Chem. Soc. 1974 96 2338. Free Radicals 143 When phenols or hydroxypyridines are reduced by means of photoelectrons from sodium in an inert matrix the keto-form becomes preferred so that the resultant anions can be regarded as cyclohexadienyl-type radicals (8). In the case of the anion of 4hydroxypyridine two possibilities (9a) and (9b) seem to be realized. The relative yields of phenol and biphenyl during the radiolysis of aqueous solutions of benzene in the presence of N20are affected by the presence of oxidiz- ing ions,43 and the intermediate radicals can also by means of pulses be oxidized ele~trolytically.~~ A large number of aromatic acids also give rise to hydroxy- cyclohexadienyl radicals when present in the Ti1"-H202 flow set-~p.~',~~ The effect of the acid groups seems to be to decrease the rate of acid-catalysed elimination of water46 so that the sulphonated adduct radicals can persist at lower pH's (Scheme 8).Some hydroxyl adducts with naphthalenesulphonic acids have been observed by e.~.r.,~~ and the patterns of spin densities in them are the same as those in corresponding naphthoxyl radicals.3 1 Scheme 8 Phenoxyl radicals have also been exhaustively studied using both in situ radi~lysis~~ and oxidation by Ce'V.48 Well defined trends are observed in the spin distributions of substituted phenoxyl radicals trends which extend smoothly from the nitro-derivatives to the semiquinones. These trends are useful in assign- ing the coupling constants. Different radicals from aminophenols are observed in strongly acidic solutions4* from those seen in neutral although in both cases there are two protons attached to the nitrogen atom. This may be " P. H. Kasai and D. McLeod jun. J. Amer. Chem. SOC.,1974,96 2342. 43 M. K. Eberhardt J. Phys. Chem.. 1974 78 1795; K. Bhatia and R. H. Schuler ibid. p. 2335. 44 K. M. Bansal and A. Henglein J.Phys. Chem. 1974 78 160. 45 G. Filby and K. Gunther J. Phys. Chem. 1974 78 1521. 46 W. T. Dixon and D. Murphy J.C.S. Perkin II 1974 1630. 47 P. Neta and R. W. Fessenden J. Phys. Chem. 1974 78 523. W. T. Dixon M. Moghimi and D. Murphy J.C.S. Furuduy II 1974,70 1713. 144 W. T. Dixon due to protonation on the oxygen atom at lower pH.48 This contrasts with anilino-radicals4’ observed under more alkaline conditions when there is only one proton ‘permanently’ attached to nitrogen. As one might expect the ring- proton coupling constants in the anilino-radical lie between those of phenoxyl and benzyl [(lOH12)] although the negative densities are rather large. To 0,::;; ~~~~~~ 8 066mT 0 1X mT 061 mT 0 82 mT I04 mT (10) (1 1) (12) some extent this trend has been explained by INDO calculation^.^' Benzyl itself can be trapped in an adamantane matrix” at room temperature and in such an environment it has a remarkably long half-time (ca.0.5 h). CIDNP measurementss1 have shown that F splittings of ortho and para fluorine nuclei in fluorinated phenoxyl and anilino-radicals are positive whereas meta fluorine splittings in these radicals are negative. A variety of semiquinones from polyhydr~xynaphthalenes’~ and pyridine diolsS3 have been observed by e.s.r. and the hydroxylation of activated aromatic compounds52 by alkaline hydrogen peroxide (Scheme 9) has been monitored by (observed) Scheme 9 means of autoxidation. Facile dimerization of the radicals from the oxidation of pyridine diols by Pb0,-[Fe(CN),] -leads to diazophenosemiquinones (Scheme These schemes show how e.s.r.can be used as a tool in elucidating mechanisms even of non-radical reaction steps and a further example is the autoxidation of 6-hydroxytropolone. 54 The tropolonyl radical (13)54*55itself has an e.s.r. spectrum very similar to that of phenoxyl [see (14)and (15) for MO models] and it might therefore be expected that the b-hydroxy-derivative might resemble p-benzosemiquinone from the point of view both of its spin distribution and of its stability. In alkaline water 6-hydroxytropolone gave e.s.r. spectra first 49 R.V. Lloyd and D. E. Wood J. Amer. Chem. Soc. 1974 96 659. 50 J. E. Jordon D. W. Pratt and D. E. Wood J. Amer. Chem. Soc. 1974 96 5588.51 M. L. Kaplan M. L. Marion and H. D. Roth J. Phys. Chem. 1974,78 1837. 52 P. Ashworth and W. T. Dixon J.C.S. Perkin II 1974 739. 53 P. Ashworth Biochem. J. 1974 141 577. 54 W. T. Dixon and D. Murphy J.C.S. Perkin II 1974 1430;W. T. Dixon W. E. J. Foster and D. Murphy Mol. Phys. 1974 27 1709. 55 C. A. Russell and J. Kokensgard J. Amer. Chem. SOC.,1967 89 5059. Free Radicals I45 OH semiquinone 0 OH 0-observed (obsened) dimerization + [Ol dimeric product [o] (quinone) -Scheme 10 $i;-. -(JJ / 2.5 rnT 0 I 0 m'l (13) (14) (1 5) of p-benzosemiquinone and later of the semiquinone from 1,2,4-trihydroxyben- zene. In HMPA,* in the absence of water a spectrum of two triplet splittings (0.12,0.2 mT) was observed which eventually decayed to the p-benzosemiquinone spectrum.The sequence of events suggested is as in Scheme 1 1. +co, OH gH (-j6 OH 0-0 O-\ unstable radicals observed Scheme 11 The cyclo-octatrienyne negative ion56 has been observed by e.s.r. in the reduc- tion of monobromocyclo-octatetraene by potassium metal (16) and the effect ofsubstituents on the degenerate orbitals of the planar cyclo-octatetraene negative 56 G. R. Stevenson M. Colon J. G. Concepcion and A. M. Block J. Amer. Chem. SOC. 1974,96 2283. * Hexamethylphosphoramide. 146 W. T. Dixon 0.292 mT 0.406 mT K metal .. ion has been investigated. ’’ As expected electron-releasing groups such as methyl ethyl or butoxy split the degeneracy so that they are attached to positions which have minimum negative charge (and hence maximum spin density) (see Figure).I 11 I higher in energy originally degenerate NBO’s Figure Eleotron-releasing groups decrease the rate of reduction of tropylium ions by zinc metal or chromous ion so that an amino-s~bstituent~~ stops the reaction Scheme 12 altogether (Scheme 12). Chromium(I1) is also an effective one-electron reducing agent for enones :59 R RCH=CHCOR \CHCHR RCOCH2CH2R -0/-A popular way of producing radicals is by photochemical excitation of when the triplet-state species formed can add to double bonds abstract protons (effectively giving ketyl radicals) or even undergo some other intramolecular process. Intramolecular H-abstractions may be dominated by conformational rather than by energy requirements (entropic control).60 ’’ G.R. Stevenson and J. G. Concepcion J. Phys. Chem. 1974 78 90. 58 K. Okarnoto K. Komatsu and 0. Sakaguchi Bull. Chem. Sac. Japan 1974,47 2426 243 1. 59 H. 0. House and E. F. Kinloch J. Org. Chem. 1974 39 1173. 6o F. D. Lewis R. W. Johnson and D. R. Kory J. Amer. Chem. Soc. 1974,96 6456. Free Radicals 147 4- + HBr + GH + Br. 0 0 Radical bromination by N-bromosuccinimide" involves the succinimido- radical (1 8) which acts as a chain carrier. It seems that it is still not clear whether amido-radicals are necessarily of Q-or of ~r-type.~~ Amination of aromatic compounds by analogues of Fenton's reagent (i.e. Fe" and N-chloroamines) takes place via cyclohexadienyl-type intermediates (Scheme 1 3).64 + t Fe" R,NHCl + Fe" -P R,NH termination* R,NH H C1 Scheme 13 A variety of cyclic radicals containing nitrogen have been studied by means of e.s.r.These range from alkyl hydra~yls,~~ e.g. CF,N-N(CF3)R and the related hydrazine positive ions66 of type R,NkNR, which are of ntype to a-radicals of alicycliciminoxy- derivative^,^' characterized by large 14Ncoupling constants. Particularly intriguing are radicals related to 1-aziridylmethyl(1 9).6s " N. Shimizu M. Ishikawa K. Ishikura and S. Nishida J. Amer. Chem. SOC.,1974 96 6456; M. Hoshino S. Arai and M. Imamura J. Phys. Chem. 1974 78 1473; H. A. J. Carless J.C.S. Perkin II 1974 834; H. G. Heine W. Hartmann D. R. Kory J. G. Magyar C.E. Hoyle J. K.McVey and F. D. Lewis J. Org. Chem. 1974 39 691. 62 J. C. Day M. J. Lindstrom and P. S. Skell J. Amer. Chem. SOC.,1974,96 5616; J. G. Trynham and Y. S. Lee ibid. p. 3590. 63 J. N. S. Tam R. W. Yip and Y. L. Chow J. Amer. Chem. SOC.,1974 96 4543; T. Koenig J. A. Hoobler C. E. Klopfenstein G. Hedden F. Sunderman and B. R. Russell ibid. p. 4573. A. Clerici F. Minisci M. Perchinunno and 0. Porta J.C.S. Perkin II 1974 416. 65 L. Lunassi and K. U. Ingold J. Amer. Chem. SOC.,1974 96 5558. " S. F. Nelsen and R. T. Landis jun. J. Amer. Chem. Soc. 1974,96 1788; S. F. Nelsen G. R. Weisman P.J. Hintz D. Olp and M. R. Fahey ibid. p. 2916. 67 G. A. Russell and A. Mackor J. Amer. Chem. SOC.,1974 96 145; H. Caldararn and M. Moran ibid. p. 149. 68 W.C. Daren and C. T. West J. Amer. Chem. SOC.,1974 96 2447. 148 W. T. Dixon The preferred conformation is that with the odd-electron orbital on C eclipsing the lone-pair orbital of the nitrogen (20). This contrasts with the situation in the cyclopropylmethyl radical in which the nodal plane of the odd-electron orbital bisects the ring. Further wide varieties of radicals have been added to nitroso-compounds to a, give nitroxides of the types69 !>N-O where R =alkyl or aryl and X =SO -or [C0(CN),l3- as well as more usual trapping products.'' In several paper^,^^,^^ the mechanisms of decay of nitroxide radicals have been more fully elucidated than hitherto72 (e.g. Scheme 14). In aryl nitroxides addition7 RO. +CF,NO -+ F,C-N-OR I 0 1CF,NO F3C\ N-0-N-CF3 / I RO 0.1 CF,NOR +CF,N02 I N /-'\ RO CF (analysis by m.s.) Scheme 14 occurs via coupling to the aromatic nucleus rather than on to what is usually a sterically hindered nitrogen atom. One suggested path of reaction is shown in Scheme 15. D. Mulvey and W. A. Waters J.C.S. Perkin II 1974 666 772. M. J. Perkins and B. P. Roberts J.C.S.Perkin II 1974,297; A. J. Bard J. C. Gilbert and R. G. Goodin J. Amer. Chem. SOC.,1974,96 620; J. W. Neely G. F. Hatch and R. W. Dreilick ibid. p. 652. A. Calder A. R. Forrester and G. McConnachie J.C.S. Perkin I 1974 2198 2208 2213. D. H. R. Barton R. L. Harris R. H. Hesse M. M. Pecket and F. J. Urban J.C.S. Perkin I 1974 2344. Free Radicals 149 R' Me0 0 N HBu -R' R' Scheme 15 An attempt has been made to rationalize the stability of free radicals in terms of steric hindrance and a push-pull effect designated 'rnerostabili~ation'.~~ The gist of this rationalization is that a compound such as p-nitroaniline (21a) has 'extra' stability due to favourable canonical structures [e.g.(21b)j in which (21b) one substituent donates and the other accepts an electron pair. This idea is carried over to free radicals so that high stability is expected for nitroxides and hydrazyls +' R,N-*O. ++ R2N+O--R,NANR t- R,&-+NR High stability may also be expected for suitably substituted aromatic radicals if appropriate canonical forms can be written down e.g. (22). However it seems doubtful whether anything new has really been gained by introducing the new term since these radical types are fairly well understood already.73 R. W. Baldock P. Hudson A. R. Katritzky and F. Soti J.C.S. Perkin I 1974 1422 1427. 150 W. T. Dixon Scheme 16 Thianthrene (23) can be formed by a free-radical substitution reaction74 as shown in Scheme 16 and its positive radical ion (24) can behave as an electro- ~hile.~~ it has been suggested that radicals previously From solid-state st~dies’~ identified as RS are probably cr* radicals of the type RS’SR . + Finally two systems of biological interest deserve mention. First the cation radicals of some porphyrins (25) have been ob~erved,~’ and restricted rotation is found when R is an alkyl group other than methyl.It is suggested that some -7 t (25) 74 L. Benati P. C. Montevecchi A. Tundo and G. Zanardi J.C.S. Perkin I 1974 1272. ’’ K. Kim V. J. Hull and H. J. Shine J. Org. Chem. 1974 39 2534. 76 M. C. R. Symons J.C.S. PerkinZI 1974 1618. 7’ J. Fajer D. C. Borg A. Forman A. D. Adler and V. Varadi J. Amer. Chem. SOC. 1974,96 1238. Free Radicals 151 I I I CO.C,H; I -m co‘C,H .icl-nt CO .C H; I-m Scheme 17 enzymes connected with the destruction of hydrogen peroxide function cia radicals of this type. Cortisone acetate has been ~ynthesized’~ using a radical ‘relay’ mechanism as shown in Scheme 17. If the p-iodide is used attack is on position 14 instead of position 9. R.Breslow R. J. Corcoran and B. R.Snider J. Amer. Chem. Soc. 1974,96,6791 et seq.

ISSN:0069-3030    

DOI:10.1039/OC9747100135

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

6 Arynes Carbenes Nitrenes and Related Species By R. C. STORR Robert Robinson Laboratories University of Liverpool L iverpool L 69 3BX 1 Arynes Generation.-Labelling studies have shown that the formation of benzyne from benzenediazonium acetate involves an E2 rather than Elcb elimination.' A major disadvantage in the 'one pot' formation of arynes from benzenediazonium acetates is that the diazonium compound can decompose via the normal radical route. As expected addition of alkenes which are good phenyl radical traps promotes benzyne formation by inhibiting the radical chain. This also probably explains the similar effect previously observed for tetracyclone.2 Acenaphthyne and benzyne have been implicated as intermediates in the formation of diphenylfluoroanthene and 1,4-diphenylnaphthalene from the phosphole ylides (1) and (2) respectively by reaction of the aryne with the liberated 1,2,5-triphenylphospholeoxide.Intramolecular mechanisms cannot be discounted for the above reactions however as added anthracene failed to intercept free benzyne in the latter case.3 Benzyne is produced in low yield (6%) by pyrolysis of benzene o-disulphonyl a~ide.~ The use of sodamide-containing complex bases in aryne chemistry has been re~iewed.~ Elimination-addition is largely responsible for cine substitution in the methoxydehalogenation of halogenobenzofurazans6 but different addition- elimination sequences are involved in both normal and cine substitution for thiometho~ydehalogenation.~The reaction of polyhalogenobenzenes with primary and secondary amines in the presence of NaNH2 or NaNH2-NaOBut proceeds mainly via arynes but in certain cases an S,Ar mechanism operates.8 3,4-Dehydrotoluene formed viu a sulphurane has been implicated in the reaction of p-tolylsulphoxide with p-tolyl-lithium,' and the new aryne 2,3- didehydrotriptycene has been generated." ' J.I. G. Cadogan C. D. Murray and J. T. Sharp J.C.S. Chem. Comm. 1974 133; J.C.S. Perkin 11 1974 1321. J. I. G. Cadogan C. D. Murray and J. T. Sharp J.C.S. Chem. Comm. 1974 901. J. I. G. Cadogan R. J. Scott and N. H. Wilson J.C.S. Chem. Comm. 1974.902. R. A. Abramovitch and G. N. Knaus J.C.S. Chem. Comm. 1974 238. ' P. Caubere Accounts Chem. Res. 1974 7 301. L. Di Nunno S. Florio and P.E. Todesco J.C.S. Perkin ZZ 1974 1171. L. Di Nunno S. Florio and P. E. Todesco Tetrahedron 1974 30 863. P. Caubere and L. Lalloz Bull. SOC.chim. France 1974 1983 1989 1996. B. K. Ackerman K. K. Andersen I. Karup-Nielsen N. B. Peynircioglu and S. A. Yeager J. Org. Chem. 1974 39 964. lo V. R. Skvarchenko and V. K. Shalaev Doklady Akad. Nauk S.S.S.R. 1974 216 110. 153 154 R.C.Storr I 1'1-(1) (2) (3) Thermal decomposition of benz[bd]iodolium iodide (3) in dimethyl acetylene- dicarboxylate gives some dimethyl phenanthrene-9,lO-dicarboxylate possibly via the 2,2'-dehydrobiphenyl biradica1.l ' Structure and Reactions-MIND0/3 calculations for the three didehydro- benzenes involving optimization of geometry lead to the prediction.that 1,2-didehydrobenzene has a ground singlet state a small 1,2-bond length and large 1,2,3 and 6,1,2 bond angles as expected. For 1,3-didehydrobenzene a singlet ground state with considerable bonding character between the dehydro-centres approximating to (4) and an energy similar to 1,2-benzyne is calculated and it is suggested that this species should be considered more seriously in reaction mechanisms. There are two energy minima for 1,4-didehydrobenzene corre- sponding to (5)and (6) the latter being of higher energy. Species (5)is most likely a singlet with a low singlet-triplet separation.' The small effect of pressure on the proportions of stepwise [2 + 21 and con- certed homo-Diels-Alder addition of tetrachlorobenzyne to norbornadiene runs contrary to the current idea that concerted reactions have smaller transition states.It is suggested that the [2 + 21 addition involves solvation of an inter- mediate zwitterion which causes a compensating contraction of the system.' The mode of addition of benzyne to ccg-unsaturated carbonyl compounds depends on the reactivity of the carbonyl group.14 Further examples of [2 + 21 additions of benzyne to dienes" and of ene reactions involving benzyne16 have '' T. Sato K. Shimizu and H. Moriya J.C.S. Perkin I 1974 1537. I' M. J. S. Dewar and W.-K. Li J. Amer. Chem. Soc. 1974 % 5569. l3 W. J. le Noble and R. Mukhtar J. Amer. Chem. Soc. 1974 96 6191. I4 A. T. Bowne and R. H. Levin Tetrahedron Letters 1974 2043. L. Lombard0 and D. Wege Tetrahedron 1974 30 3945; M.R. Decamp R. H. Levin and M. Jones Tetrahedron Letters 1974 3575. l6 G. Mehta and B. P. Singh Tetrahedron 1974 30,2409; H. H. Wasserman and L. S. Keller Tetrahedron Letters 1974 4355. Arynes Carbenes Nitrenes and Related Species appeared. A biradical intermediate (7) seems likely in the novel phenylation of camphene with benzyne.” The reaction of benzyne with pyridine N-oxides leads mainly to fl-hydroxyarylated pyridines (8) probably as shown.’ Benzyne reacts with CS2 to give products which can be rationalized in terms of the di- thiolium carbene (9).’g Addition of 1,2-dehydronaphthalenes to tetrahydro- benzo[b]furans provides a one-step synthesis of hexahydrochrysenes,20 and intermolecular addition of 1,2-dehydronaphthalene to enolate anions has been exploited.2 Further applications of intramolecular aryne cyclizations have appeared ;22 in the case of compound (10) the expected phenolic aryne cyclization was not observed but the benzodiazepine (1 1)was formed.23 1 17 G.Mehta and B. P. Singh Tetrahedron Letters 1974 4297. I8 R.A. Abramovitch and I. Shinkai J. Amer. Chem. SOC. 1974 96,5265. 19 J. Nakayania J.C.S. Chem. Comm. 1974 166. 20 W. Tochtermann G. Stubenrauch K. Reiff and U. Schumacher Chem. Ber. 1974 107 3340. 21 P. Caubere and M. S. Mourad Bull. SOC. chim. France 1974 1415. 22 S. Kano T. Yokomatsu N. Yamada K. Matsumoto S. Tokita and S. Shibuya, Chem. and Pharm. Bull. Japan 1974 22 1607; J. A. Skorcz J. T. Suh and R. L. Germershausen J. Heterocyclic Chem.1974 11 73. 23 R. J. Spangler D. C. Boop and J. H. Kim J. Org. Chem. 1974,39 1368. 156 R.C.Stow 2 Nitrenes Deoxygenation of nitroxyl radicals with triethyl phosphite has provided a new route to nitrenium ions.24 The dianisylnitrenium ion and its conjugate acid have been directly observed.25 Full details of the formation of triarylarsinimines from a variety of nitrene precursors have now appeared. Thermolysis of those azides which lead to electrophilic nitrenes and stabilized ylides copper-catalysed decomposition of 3-aryl-1,4,2-dioxazolidin-5-ones (12) (the value of copper in lowering the de- composition temperature is stressed) and a-elimination routes probably involve nitrenes.26 However lead tetra-acetate (LTA) oxidation of sulphonamides and amides in the presence of triphenylarsine give arsinimines uia diacetoxy-triphenylarsorane (13),the amides being unoxidized in the absence of triphenyl- arsine.The situation with N-aminophthalimide where rapid oxidation occurs in the absence of triphenylarsine is less clear. The same arsinimine acetate is formed by LTA oxidation and from heating of the aziridine (14)in the presence of acetic acid suggesting that at least some of this product in the LTA oxidation is formed by a non-arsorane route and involves a nitrene-lead complex nitrene or nitrenium ion. The last intermediate could explain the differing modes of reaction of ‘phthalimidonitrene’ with dimethoxybenzene when generated by LTA oxida- tion (nitrenium ion) and pyrolysis of aziridine (14) (free r~itrene)~~ (Ann.Reports (B),1973,70,186).A number of N-substituted 1-amino- 1,2,5-triphenylphospholes (15) have been produced by trapping of nitrene or nitrenoid species with 1,2,5-triphenylphosphole and by its reaction with azides which does not involve nitrenes.28 Nphth N-N S Ph -r( >Ph KYN\? N 0’ “0 I :N 24 J.I. G. Cadogan and A. G. Rowley J.C.S. Chem. Comm. 1974 179; J.C.S. Perkin 11 1974 1030. 25 U. Svanholm and V. D. Parker J. Amer. Chem. SOC.,1974 96 1234. 26 J. I. G. Cadogan and I. Gosney J.C.S. Perkin I 1974,460. ” J. I. G. Cadogan and I. Gosney J.C.S. Perkin I 1974 466. 28 J. I. G. Cadogan R. J. Scott R. D. Gee and 1. Gosney J.C.S. Perkin I 1974 1694. Arynes Carbenes Nitrenes and Related Species 157 Other workers assume that a nitrene is involved in the stereospecific formation of aziridines from LTA oxidation of N-aminophthalimide in the presence of alkenes.A transition state (16) involving lateral approach of an sp-hybridized singlet nitrene allows favourable interaction between the nitrene HOMO and olefin LUMO and vice uersa. The relative reactivities of different alkenes can be rationalized in terms of estimated FMO energies. Secondary interactions in this parallel-plane approach favour a syn orientation of the phthalimide and olefinic ester groups.29 Such a stereochemical preference is normally masked by rapid inversion at nitrogen in aziridines but has now been elegantly confirmed by carrying out the oxidation at low temperature where inversion is eliminated.30 A free nitrene (17) is thought to be involved in the oxidation of 4-amino-3,S-diphenyltriazole since the proportion of fragmentation to benzonitrile and intermolecular aziridine formation in the presence of olefins is the same with different oxidant^.^ N-Nitrenes have been suggested as intermediates in several other reactions.32 Photolysis of dioxazolidinones (12) and thiadioxazolidine S-oxides (18)appears to give acyl nitrene~~~ since the same reactivity pattern regarding C-H insertion is observed as with the corresponding acyl a~ides.~" There is evidence that in the photolysis of acyl azides in halogen-free solvents the photo-Curtius reaction and nitrene formation are independent and c~ncurrent.~~ Further evidence for the stabilization of singlet ethoxycarbonylnitrene by methylene chloride has been claimed.35 Detailed analysis of the thermolysis of methanesulphonyl azide in aromatic solvents with electron-withdrawing groups is consistent with initial formation of the singlet nitrene which collapses to the triplet in competition with addition to the solvent to give benzaziridines.These ring-open to give rn-sulphonamides whereas o-sulphonamides result from radical substitution by the triplet ~~itrene.~~ The trapping of azepines as the kinetically controlled products of such reactions supports the proposed intermediacy of benzaziridines. Sulphonyl azides give tetraphenyl-2-pyridone and tetraphenyl-2-pyridyl sulphonates on pyrolysis in the presence of tetracyclone most likely by 1,4- or 1,Zaddition of the nitrene followed by rearrangement.4 Detailed studies of the competition between carbazole and azepine formation in the photolysis of biphenylazides and deoxygenation of nitrosobiphenyls in the j9 H.Person C. Fayat F. Tounard and A. Foucaud Bull. Soc. chim. France 1974 635. .'' R. S. Atkinson and R. Martin J.C.S. Chem. Comm. 1974 386. " F. Schroppel and J. Sauer Tetrahedron Letters 1974 2945. 32 S. B. Matin J. C. Craig and R. P. K. Chan J. Org. Chem. 1974 39 2285; S. Mataka and J.-P. Anselme J.C.S. Chem. Comm. 1974 554; B. V. Ioffe and L. A. Kartsova Zhur. org. Khim. 1974 10 989. 33 E. E. Eibler and J. Sauer Tetrahedron Letters 1974 2565. '' E. Eibler and J. Sauer Tetrahedron Letters 1974 2569.35 R.C. Belloli M. A. Whitehead R. H. Wollenberg and V. A. LaBahn J. Org. Chem. 1974 39 2128. 36 R. A. Abramovitch G. N. Knaus and V. Uma J. Org. Chem. 1974 39 1101. '' R. A. Abramovitch T. D. Bailey T. Takaya and V. Uma J. Org. Chem. 1974 39 340. 158 R. C. Storr presence of diethylamine lead to the conclusion that the initially formed nitrene (19) can give rise to carbazoie via two intermediates. One of these can be inter- cepted with diethylamine and is assumed to be the azirine (20) the other could be the unstable species (21) or the triplet nitrene.38 9s I N: .. H 0- t 19) Thermolysis of 1-and 2-azidonaphthalenes gave dibenzo[ah]phenazine and other products typical of the triplet nitrenes. Photolysis of the azides in the presence of diethylamine in the hope of intercepting a singlet nitrene was successful for the 2- but not the 1-azide.The former gave 1-amino-2-NN-diethylamino-naphthalene in yields which were increased by the presence of singlet sensiti~ers.~’ The photolysis of 4-and 5-azidobenzo[b]thiophensis similar only the 5-azide giving products (4-amino-5-dialkylaminobenzo[b]thiophens)indicative of a singlet nitrene and an azirine intermediate.40 The first example of ring expansion via an azirine in the photolysis of bicyclic aromatic azides occurs with 6-azido- benzo[b]thiophens which give 8H-thieno[2,3-c]azepines in the presence of dieth~lamine.~ The thermal decomposition of 1-and 2-azidobenzylnaphthalenesgives almost exclusively aromatic C-H insertion products benzacridan and benzacridine (by oxidation).In contrast the tetralin analogues (22) give largely azepines the difference being attributed to the greater loss in resonance energy involved in the ring expansion of the intermediate aziridines in the case of the naphthalene^.^^ 38 R. J. Sundberg and R. W. Heintzelman J. Org. Chem. 1974 39 2546. ’’ S. E. Hilton E. F. V. Scriven and H. Suschitzky J.C.S. Chem. Comm. 1974 853. 40 B. Iddon H. Suschitzky and D. S. Taylor J.C.S. Perkin I 1974 579. 41 B. Iddon M. W. Pickering and H. Suschitzky J.C.S. Chem. Comm. 1974 759. 42 R. N. Carde and G. Jones J.C.S. Perkin I 1974 2066. Arynes Carbenes Nitrenes and Related Species HH The formation of thieno[3,2-b]quinoline (25) by thermal decomposition of 2- (2-azidobenzy1)thiophen (23) can be explained by insertion uia the aziridine (24) followed by oxidation.The thione (27) is also produced possibly via the 1,4- nitrene-thiophen adduct (26) formed either directly or from the aziridine (24).43 There has been little real evidence for nitrenes as intermediates in the gas- or liquid-phase thermolysis of alkyl azides which normally gives imines possibly by a mechanism involving anchimeric assistance. Intramolecular substitution has now been observed to compete with imine formation in the decomposition of a tertiary alkyl azide (28 ; R = Me or Ph). This competing insertion and the very narrow range of migratory aptitudes observed (Ph Me 1.9;o-PhC,H Me 2.0) argue strongly for a reactive nitrene in this case4 The photolysis of cyclopropyl azides gives a high yield of nitrile and olefin most likely via cheletropic fragmentation of a nitrene in contrast to thermolysis where ring-expansion to azetine can dominate and anchimeric assistance in the decomposition would seem to be involved.45 The formation of pyrazoles and pyrroles from thermolysis of 2-imino- and 2-vinyl-2H-azirines is rationalized as a further example of vinylnitrene formation from 2H-a~irines.~~ However activation parameters for the formation of azirines from vinyl azides argue against a free nitrene intermediate and indicate that anchimeric assistance is important.47 Similar conclusions are drawn for the thermal conversion of 2-azido-3-vinyl- 1,4-quinones (29) into indolequinones (30)."* A nitrene is also ruled out for the formation of 2-alkenyl-2,3-dihydro- indole-4,7-diones e.g.(32) from the photolysis (360nm) of 2-azido-l,4-quinones (31) in the presence of acyclic and cyclic dienes. The reaction is believed to involve addition of photoexcited azide followed by decomposition of the resulting " G. R. Cliff G. Jones and J. McK. Woollard J.C.S. Perkin I 1974 2072. 44 R. A. Abramovitch and E. P. Kyba J. Amer. Chem. Soc. 1974 % 480. 45 A. Hassner A. B. Levy E. E. McEntire,and J. E. Galle J. Org. Chem. 1974 39 585. 46 A. Padwa J. Smolanoff and A. Tremper Tetrahedron Letters 1974 29. '' G. L'abbe and G. Mathys J. Org. Chem. 1974,39 1779. 48 P. Germeraad and H. W. Moore J. Org. Chem. 1974 39 774. 160 R. C.Storr tria~oline.~~ Thermolysis of the acetoxy-azide (33) gives the iminoquinones (34) and (35).The former probably involves either direct acyl transfer to the nitrene or anchimerically assisted azide decomposition while the latter appears to require rearrangement of an azirine intermediate.50 The diazidonaphthalenes (36 ; R = OAcS0 or H5')give benzocyclobutanes via o-quinodimethanes. In each case the major isomer is that expected from orbital symmetry considerations. In addition the diacetoxy-compound (36; R = OAc) gives the quinoline (37) which suggests that a carbene Gnitrene skeletal interconversion may be occurring. O 49 P. Germeraad W. Weyler and H. W. Moore J. Org. Chem. 1974 39 781. D. S. Pearce M. S. Lee and H. W. Moore J. Org. Chem. 1974,39 1362.5L M. E. Peek C. W. Rees and R. C. Storr J.C.S. Perkin I 1974 1260. Arynes,Carbenes,Nitrenes,and Related Species A new route to nitrenes by thermal deoxysilylation of hydroxylamine deriva- tives e.g. (38) has been developed. Most of the products isolated from (38) which is more labile than phenyl azide parallel those expected from triplet phenylnitrene but in cyclohexene 2 % of aziridine is formed. It is not yet clear whether this last reaction which is most uncommon involves the nitrene.” /OSiMe3 Ph-N -+ Ph-N + Me,SiOSiMe, \ SiMe (38) NBr (39) Phosphorylnitrenes (39) have been generated from the dibromides (40)’ with zinc and by photolysis of phosphoryl a~ides.’~ They are extremely unselec- tive and undergo intermolecular reactions rather than intramolecular rearrange- ment and are therefore ideal for affinity labelling purposes.Intramolecular reactions do however occur on photolysis of the related 1-azidophosphetan oxides (41) in methanol. Ring-expansion may involve a nitrene or Curtius-like rearrangement and ring-opening to give phosphoramides may involve intra- molecular hydrogen transfer in an intermediate nitrene.’ ’ 52 F. P.Tsui T. M. Vogel and G. Zon J. Amer. Chem. SOC.,1974 96 7144. 53 A. Zwierzak and S. Zawadski Tetrahedron 1973 29 3899. 54 R. Breslow A. Feiring and F. Herman J. Amer. Chem. SOC.,1974 96,5937. 55 M. J. P. Harger J.C.S. Perkin I 1974 2604. 162 R. C. Storr 3 Carbenes The application of ab initio calculations to the understanding of the structure of methylene has been reviewed.56 Hydrogen abstraction is feasible through a least-motion approach for triplet methylene but through a non-least-motion route for the singlet species.Since the overall dynamics of the reaction favour the least motion approach hydrogen abstraction by singlet methylene is for- bidden.57 Analytic least-motion studies5 and new ab initio calculation^^^ for methylene dimerization agree with previous studies that the methylenes prefer to approach initially through a perpendicular configuration. Detailed trajectory calculations have given an insight into the dynamics of the insertion of singlet methylene into hydrogen. These reveal that although for appropriate initial conditions the reaction can follow the minimum energy path predicted in earlier static calculations the insertion can take place over a very wide range of initial conditions for some of which the dynamics may be very complicated.60 Cyclopentadienylidine (42) has been directly observed in the low-temperature matrix photolysis of diazocyclopentadiene.On warming it dimerizes or reacts with carbon monoxide present in the matrix to give the previously uncharacter- ized keten (43).6 Geometrical isomers of ground-state triplet vinyl methylene have been detected by e.s.r. spectroscopy after low-temperature photolysis of vinyl diazomethane.6 Matrix-isolated anthronylidene has been characterized as a ground-state triplet by emission63 and e.s.r. spectro~copy,~~ and the photo- electron spectrum of difl~oromethylene~~ has been recorded.There is further evidence for the reduction of methylene to a methylene radical- anion.66 1,l-Dicyclopropylethylene has been suggested a simple probe for the spin multiplicity of carbenes. Thus addition of typical singlet species gives the unrearranged cycloadduct while a typical triplet carbene gives a biradical intermediate which leads to cyclopropane-cleaved product^.^' A comprehensive review on alkoxycarbonylcarbenes has appeared.68 56 J. F. Harrison Accounts Chem. Res. 1974 7 378. 51 L. Salem J. Amer. Chem. SOC. 1974 % 3486. 58 S. Ehrenson J. Amer. Chem. SOC. 1974 % 3784. 59 P. Cremaschi and M. Simonetta J.C.S. Faraday II 1974 1801. 60 I. S. Y. Wang and M. Karplus J. Amer. Chem. SOC. 1973,95 8160. 61 M.S. Baird I. R. Dunkin and M. Poliakoff J.C.S. Chem. Comm. 1974 904. 62 R. S. Hutton M. L. Manion H. D. Roth and E. Wasserman J. Amer. Chem. SOC. 1974 % 4680; see also G. E. Palmer J. R. Bolton and D. R. Arnold ibid. p. 3708. 63 N. Filipescu J. W. Pavlik P. T. Frangopol and M. Frangopol Rev. Roumaine Chim. 1973 18 1959. 64 P. Devolder P. Goudmand and J. P. Grivet J. Chim. phys. 1974 71 899. 65 J. M. Dyke L. Golob N. Jonathon A. Morris and M. Okuda J.C.S. Faraday II 1974 1828. 66 G. D. Sargent C. M. Tetum and R. P. Scott J. Amer. Chem. SOC. 1974 96,1602. 67 N. Shimizu and S. Nishida J. Amer. Chem. SOC.,1974 96 6451. 68 A. P. Marchand and N. M. Brockway Chem. Rev. 1974 74 431. Arynes Carbenes Nitrenes and Related Species Generation.-Phase-transfer catalysis has now become standard practice in the generation of dichloro and other carbenes by a-eliminati~n.~~ Crown ethers have also been employed successfully as phase-transfer catalysts7' and in one of the most significant papers this year it has been shown that generation of phenylhalogenocarbenes from benzal halides with potassium t-butoxide in the presence of 18-crown-6-ether gives a species which shows the same selectivity as that from photolysis of the corresponding diazirine.It appears therefore that complexation of the K+ ion leaves a free carbene. In the absence of the crown ether elimination gives a species presumably a carbenoid such as (44) which shows a different ~electivity.~' In the short-wavelength photolysis of mercury bisdiazoacetate in the presence of olefins a substantial proportion of products arise from ethoxycarbonyl- methyne (45) which is formed in a doublet ground state and behaves essentially as a singlet carbene adding stereospecifically to give cyclopropyl radicals and inserting into C-H bonds to give alkyl radicals.72 Interception of this carbyne by metal complex formation has been reported.73 1,2-Ketocarbenes (46) are generated in the thermolysis of sodium o-bromo- phenoxide and trapped with added nucleophiles.There is no evidence for benzoxiren participation but benzothi-irens (47) appear to be intermediates in the same reaction of o-bromoben~enethiolates.~~ The stereospecificity observed in the photoinduced isomerization of cyclobutanone to tetrahydrofurylidine is inconsistent with the intervention of a biradical intermediate.75 An explanation has been advanced for the unique ability of cyclobutanones to undergo this rearrangement.Introduction of a 2-phenyl substituent causes C-C bond cleavage leading to an iminocarbene rather than the normal C-N cleavage in the gas-phase thermolysis of azirines (48). 69 See for example E. V. Dehmlow Angew. Chem. Internat. Edn. 1974 13 170; R. Mathias and P. Weyerstahl ibid. p. 132; T. Sasaki K. Kanematsu and Y. Yukimoto J. Org. Chem. 1974,39,455; T. B. Patrick Tetrahedron Letters 1974 1407; T. Sasaki S. Eguchi and T. Ogawa J. Org. Chem. 1974,39 1927. 70 M. Makosza and M. Ludwikow Angew. Chem. Internat. Edn. 1974 13 665. 71 R. A. Moss and F.G. Pilkiewicz J. Amer. Chem. Soc. 1974 96,5632. 12 0. P. Strausz G. J. A. Kennepohl F. X. Garneau T. Do Minh B. Kim S. Valenty, and P. S. Skell J. Amer. Chem. SOC.,1974 96 5723. 73 W. A. Herrmann Angew. Chem. Internat. Edn. 1974 13 812. 74 J. I. G. Cadogan J. T. Sharp and M. J. Trattles J.C.S. Chem. Comm. 1974 900. 75 G. Quinkert P. Jacobs and W.-D. Stohrer Angew. Chem. Internat. Edn. 1974 13 197; G. Quinkert and P. Jacobs Chem. Ber. 1974 107,2473. 76 W.-D. Stohrer G. Wiech and G. Quinkert Angew. Chem. Internat. Edn. 1974 13 199 200. 71 L. A. Wendling and R. G. Bergman J. Amer. Chem. Soc. 1974,96 308. 164 R.C. Storr Carbene/carbenoids are generated in good yield from primary vinyl triflates with KOBU'.~' Various organomercury reagents have been examined as carbene- transfer reagents.79 Dichlorocarbene appears to be formed from carbon tetra- chloride and antimony pentabutyl,80 and full details of its formation by vapour- phase decomposition of trifluoro(trichloromethy1)silanehave appeared.' Car-benes have been generated by deprotonation of benzodithiolium (49) and related (-50) salts.82 The carbene (50)has been intercepted in the photochemical rearrange- ment of tripty~ene,~~ and cyclopentadienylidene (42)produced by decarbonyla- tion of keten (43) is implicated in a minor pathway in the flash thermolysis of methyl ~alicylate.~~ Lithium dicyclohexylamide can be used as a convenient base for the in situ generation of carbenoids for reaction with carbonyl com- pounds.8s Kinetic studies reveal the complexity involved in the copper-catalysed decomposition of diazo-compounds.86 Rearrangements.-Estimated energies for phenylcarbene (5 I ) cyclohepta-trienylidene (52),and related species have been used in a detailed analysis of the rearrangements observed for aromatic carbenes and nitrenes.It is claimed that such a thermochemical approach allows a unifying explanation of the majority of available experimental data if the importance of chemical activation in the formation of the reactive species and hence its available energy for further transformations is taken into account. This review also casts doubts on the reported interconversion of aryl carbene and isomeric 1,3-biradicals (53) and argues strongly against the intermediacy of bicycloheptatriene intermediates in the rearrangement (51)G(52).87 However evidence for the trapping of such intermediates in related reactions has also appeared.* ' Other semi-empirical calculations for the phenylcarbene-cycloheptatrienylidene system also consider 78 P.J. Stang M. C. Mangum D. P. Fox and P. Haak J. Amer. Chem. SOC.,1974 96 4562. 79 D. Seyferth and R. A. Woodruff J. Organometallic Chem.. 1974 71 335. A. N. Nesmeyanov A. E. Borisov and N. G. Kizim Izvest. Akad. Nauk S.S.S.R. Ser. khim. 1974 1672. J. M. Birchall G. N. Gilmore and R. N. Haszeldine J.C.S. Perkin I 1974 2530. G. Scherowsky and J. Weiland Annalen 1974 403; G. Scherowsky Chem. Ber. 1974 107 1092; C. Th. Pedersen and 3. Mdler Tetrahedron 1974 30 553. 83 H. Iwamura and K.Yoshimura J. Amer. Chem. SOC.,1974 96 2652. 84 0. A. Mamer K. G. Rutherford and R. J. Seidewand Canad. J. Chem. 1974,52,1983. H. Taguchi H. Yamamoto and H. Nozaki J. Amer. Chem. SOC.,1974 96 3010. 85 86 D. Bethel1 and M. F. Eeles J.C.S.Perkin IZ 1974 704. *' C. Wentrup Tefrahedron 1974 30 1301. 88 T. T. Coburn and W. M. Jones J. Amer. Chem. SOC.,1974 96 5218; W. E. Billips L. P. Lin and W. Y. Chow ibid. p. 4026. Arynes Carbenes Nitrenes and Related Species the isomeric cycloheptatetraene (54). This non-planar allenic form is the most stable although the seven-membered ring systems behave only as (51) or (52). However the carbene (55) does behave as the allene (56),in which the larger ring more easily accommodates the allenic structure.The calculated effects of differing modes of annelation on the species (51) (52) and (54) are compatible with experimental observations. 89 CND0/2 and extended Hiickel calculations for the analogous phenylnitrene-azepinylidene interconversion indicate that the nitrene N moves out of the plane during the process. Recognition of this necessity for out-of-plane motion clarifies the experimental observations for certain aryl nitrenes and assuming a similar situation applies to aryl carbenes allows an explanation for new data concerning the proportions of styrene and benzocyclo- butanes from the different tolylcarb~ne~.~~ C-1 and C-2 labelled phenylacetylenes interconvert via benzylidene carbene at high temperature.” Ab initio calculations indicate that the singlet state for methylcarbene is almost degenerate with but slightly lower in energy than the triplet.The most favourable route for its rearrangement into ethylene is from the So--+ So states via a syn transition state (57).9’ The high exo endo hydrogen migration ratio observed for the carbene derived from the tosylhydrazone of ketone (58) is consistent with this analy~is.’~ Carbenes are usually assumed to react with very small or non-existent activation energies. However the two competing reactions of cyclopropyl carbene (59)(assuming both are carbene reac- tions) have measurably different activation energies.94 The fragmentation mode follows the stereochemistry of a concerted non-linear cheletropic extrusion.95 89 R.L. Tyner W. M. Jones Y. Ohm and J. R. Sabin J. Amer. Chem. SOC.,1974 96 3765. 90 R. Gleiter W. Rettig and C. Wentrup Helv. Chim. Acta. 1974 57 21 11. 91 R. F. C. Brown K. J. Harrington and G. L. McMullen J.C.S. Chem. Comm. 1974 123. 92 J. A. Altman 1. G. Csizmadia and K. Yates J. Amer. Chem. SOC.,1974 96 4196. 93 A. Nickon F. Huang R. Weglein K. Matsuo and H. Yagi J. Amer. Chem. SOC. 1974 96 5264. 94 S. S. Olin and R. M. Venable J.C.S. Chem. Comm. 1974 104. 95 S. S. Olin and R. M. Venable J.C.S. Chem. Comm. 1974 273. 166 R. C.Storr H ,c-c 0 H-H + (59) H -C rC-( CH Jn -C H =CH -CO,Et A Wolff rearrangement has been employed as the key ring-contraction step in the formation of a [7]-from an [8]-para~yclophane.’~ The diazo-compounds (60) undergo normal photo-induced Wolff rearrangement but copper-catalysed decomposition gives the product of a vinylogous Wolff rearrangement.97 p-Oxidocarbenoids eg.(61) readily formed from cyclic ketones and LiCHBr2 are useful intermediates in ring-enlargement reactions.98 2-Furylcarbene has been ruled out as an intermediate in the conversion of furan (62) into methylene- cyclobutenone and benzoic acid.99 In contrast to azidopyridine 1-oxides which undergo ring-contraction to 2-cyano-1-hydroxypyrroles on thermolysis 2- pyridyldiazomethane 1-oxides give 2-acylpyridines. O0 (60) R = H or Me n=lor2 Addition.-Non-linear cheletropic 1,2- and linear cheletropic 1,Caddition of singlet methylene to cisoid butadiene are both allowed although clear evidence for the latter mode has never been obtained.An MO study of this system has now accounted for this in terms of the greater closed-shell repulsion involved in 96 N. L. Allinger T. J. Walter and M. G. Newton J. Amer. Chem. SOC.,1974 96 4588. 97 A. B. Smith J.C.S. Chem. Comm.,1974 695. 98 H. Taguchi H. Yarnamoto and H. Nozaki J. Arner. Chem. SOC.,1974 96 6510. 99 W. S. Trahanovsky and M.-G. Park J. Org. Chem. 1974,39 1449. * O0 R. A. Abramovitch C. S. Menon M. Murata and E. M. Smith J.C.S. Chem. Comm. 1974 693. Arynes Carbenes Nitrenes and Related Species the 1,4-addition.'" Linear cheletropic homo- 1,4-addition of fluorocarbenes to norbornadiene has been observed. The nucleophilic carbene 2,3-diphenyl- cyclopropenylidene gives the product expected from 1,4-addition to tetracyclones.However addition of cycloheptatrienylidene is complex and gives benzocyclo- heptatrienes by a mechanism in which extrusion of carbon monoxide from an initial 1,4-adduct can be excluded. lo3 The 1,4-adducts from 2,6-di-t-butylcyclo- hexadienone carbene (63) and dienes arise via 1,2-addu~ts."~ Addition of cyclo- hexylidene carbene (64) to cyclopentadiene gives (65) by spontaneous rearrange- ment of the initial adduct uia a trimethylenemethane.105 .. Addition of 'carbenes' to olefins continues to be used widely as a route to cyclopropanes and an extensive review on the Simmons-Smith reaction has appeared. O6 Non-stereospecific addition of dimethoxycarbene to diethyl maleate and fumarate is explained in terms of a dipolar intermediate.'" Excep-tionally high enantioselectivity (up to 70 %) in the formation of cyclopropane-carboxylates from ethyl diazoacetate has been achieved using bis-[( + )-camphor-quinonedioximato]cobalt(~~)as catalyst."* The ready hydrolytic cleavage of 2-aminocyclopropane esters formed from carbenes and enamine esters provides the basis of an easy route from p-to y-keto-e~ters.''~ Labelling studies reveal that a carbenoid mechanism is involved in the formation of arylcyclopropanes in the acid-catalysed decomposition of aryldiazomethanes in the presence of olefins.lo The electrophilic character of cyclopentadienylidene is apparent in its reaction with alkynes to give spir0-2,4-heptatrienes,' and substituted styrenes to give spiroheptadienes.' l2 Neither singlet nor triplet carbenes such as (66) can assume the requisite geometry for intramolecular cycloaddition.113 Oxirans have been H.Fujimoto and R. Hoffmann J. Phys. Chem. 1974 78 1167. Io2 C. W. Jefford A. N. Kabengele J. Kovacs and U. Burger Tetrahedron Letters 1974 257; Helv. Chim. Acta 1974 57 104. lo' T. Mitsuhashi and W. M. Jones J.C.S. Chem. Comm. 1974 103. G. A. Nikiforov B. D. Sviridov and V. V. Ershov Bull. Acad. Sci. U.S.S.R. 1974 23 339. lo' M. S. Newman and M. C. Vander Zwan J. Org. Chem. 1974,39,761. '06 H. E. Simmons T. L. Cairns S. A. Vladuchick and C. M. Hoiness Org. Reactions 1973 20 1131. R. W. Hoffrnann W. Lilienblum and B. Dittrich Chem. Ber. 1974 107 3395. Y. Tatsuno A. Konishi A.Nakamura and S. Otsuka J.C.S. Chem. Comm. 1974,588. H. Bierangel J. M. Akkerman J. C. Lapierre Armande and U. K. Pandit Terruhedron Letters 1974 28 17. 'lo G. L. Closs and S. H. Goh J. Org. Chem. 1974 39 1717. H. Durr B. Ruge and B. Weiss Annalen 1974 1150. H. Durr and F. Werndorff Angew. Chem. Internat. Edn. 1974 13,483. 'I3 A. Viola S. Madhavan and R. J. Proberb J. Org. Chem. 1974 39 3154. 168 R. C. Stow isolated from the addition of halogenocarbenes to highly halogenated carbonyl compounds.' l4 Tetrachloroaziridines have similarly been obtained from carbonimidoyl dichlorides but with azo-arenes fragmentation of the initially formed diaziridine or ylide occurs.' .. Ph 5-Diazomethyl- 1,4-diphenyl- 1,2,3-triazole (67 ; R = H) decomposes readily in aromatic hydrocarbons to give tropylidenes as expected for a singlet carbene with high selectivity resulting from the stabilizing effect of the triazole ring.The a-phenyl derivative (67; R = Ph) gives products of the linear triplet carbene. This would be favoured by steric hindrance and independent conjugation of the orthogonal p-orbitals by the two substituents.' '' Detailed mechanistic investigation of the thermal decomposition of diphenyl diazomethane in the presence of butylamines shows that the main product N-(diphenylmethy1)butylamineis formed from the singlet carbene by nucleophilic attack of the amine followed by rearrangement of the resulting ylide. A minor hydrogen-abstraction recombination route involving the triplet carbene is detected by CIDNP but the major product from the triplet carbene is tetra- phenylethane.' '' Diacetyl- and dialkoxycarbonyl-carbenesdisplay complete selectivity for equatorial addition to 4-t-butylthiacyclohexane and high selectivity in intermolecular attack on a pair of dialkyl sulphides in contrast to toluene-p- sulphonyl- and ethoxycarbonyl-nitrenes which are non-selective.' Catalytic intramolecular cyclization of bis-a-diazo-ketones (68) has been achieved at high dilution and applied to a new synthesis of y-tropolone from glutaconic acid.' COCHN 'COAH Br Br D. Seyferth W. Tronich W. E. Smith and S. P. Hopper J. Organometallic Chem. 1974 67 341. D. Seyferth W. Tronich and H. Shih J. Org. Chem. 1974 39 158. 'I6 P. A. S. Smith and E. M.Bruckmann J. Org. Chem. 1974,39 1047. 'I7 D. Bethell J. Hayes and A. R. Newall J.C.S. Perkin II 1974 1307. 'I8 D. C. Appleton D. C. Bull J. McKenna J. M. McKenna and A. R. Walley J.C.S. Chem. Comm. 1974 140. l9 J. Font J. Valls and F. Serratosa Tetrahedron 1974 30 455. Arynes Carbenes Nitrenes and Related Species 169 Insertion.-Almost complete racemization is observed at the insertion centre in the reaction of triplet diphenylmethylene (from thermolysis of diphenyldiazo- methane) with optically active diastereoisomeric 1-methylheptyl cc-fluoro- phenylacetates. CIDNP observed for the -19F and -'H spectra of the products also shows no stereochemical preference and is consistent with recombination of radical pairs formed by hydrogen abstraction after many diffusive displacements.Significantly the slight predominance for insertion with retention may involve some reaction uia the singlet carbene.' 2o Insertion into cyclohexane of diphenyl- methylene from photolysis of diphenyldiazomethane has been observed con- trary to previous reports. ' ' Dihalogenocarbene insertion into unactivated cycloalkane C-H bonds has been achieved in respectable yields using phenyl- trihalogenomethyl mercury. '22 The products of intramolecular C-H insertion in 4-and 5-protoadamantylidenes indicate that when a carbene cannot approach with its vacant p-orbital along the C-H bond axis insertion can occur uia the most convenient triangular transition state. '' The cyclopropylidene derived from dibromide (69) undergoes intramolecular insertion into the primary rather than tertiary C-H bonds probably for steric reasons.124 Rare 1,3-intramolecular insertion of a silyl carbene occurs in the pyrolysis of phenyltrimethylsilyldiazo-methane.' 25 Various studies ofcarbene insertions into organosilanes,' 26 Group IV element- halogen bonds,' and polar X-H bonds (X = 0,s,or N)' s have been reported. 4 Silylenes Several papers concerning silylenes have appeared this year. Phenylmethyl-silylene has been produced by photolysis of the trisilane (70) and trapped with cyclohexene as the silacyclopropane.' 29 Photochemical extrusion of the central silylene fragment from the related 1,2,3-trisilacycloheptanesis highly stereo- specific configuration being retained at both Si-1 and Si-3 in the resulting disilacyclohexane.This process may therefore be a novel type of cheletropic rea~tion.'~' Silylene 31SiH2 produced by the nuclear recoil method from a 31Pprecursor gives the 1,4-adduct with b~tadiene.'~','~~ Addition of NO as ''O D. Bethel1 and K. McDonald J.C.S. Chem. Comm. 1974 467. ''I J. H. Boyer V. T. Ramakrishnan and K. G. Srinivasan Synthesis 1974 192. 12' D. Seyferth and Y. M. Cheng Synthesis 1974 114. ' D. Skare and Z. Majerski J.C.S. Chem. Comm. 1974 1000. '' D. P. G. Hamon and V. C. Trenerry Tetrahedron Letters 1974 137 1. I " W. Ando A. Sekiguchi T. Hagiwara and T. Migita J.C.S. Chem. Comm. 1974 372. H. Watnabe T. Nakano Y. Araki H. Matsumoto and Y. Nagai J. Organometallic '" Chem. 1974 69 389; W. Ando K. Konishi and T.Migita ibid. 67 C7-C9. R. N. Haszeldine A. E. Tipping and R. O'B. Watts J.C.S. Perkin I 1974 2391; M. Weidenbruch and C. Pierrard J. Organometallic Chem. 1974 71 C29. R. Paulissen E. Hayez A. J. Hubert and P. Teyssie Tetrahedron Letters 1974 607. 129 M. Ishikawa and M. Kumada J. Organometallic Chem. 1974 81 C3. H. Sakurai Y. Kobayashi and Y. Nakadaira J. Amer. Chem. SOC.,1974 96 2656. "I P. P. Gaspar R. J. Hwang and W. C. Eckelrnan J.C.S. Chem. Comm. 1974 242. I." 0. F. Zeck Y. Y. Su G. P. Gennaro and Y.-N. Tang J. Amer. Chem. SOC.,1974 96 5967. 170 R. C.Storr OM' RR R \/ 'E:{-R RISilR Me,SiSiMe,SiMe / 'OMe Si-R (70) R\ R Si R R /\ (71) (72) RR (73) scavenger indicates that the silylene is present as both triplet (80%) and singlet (20%) moderator studies suggesting a ground singlet state.132 The 1,4-addition of silylene produced by pyrolysis of disilane to trans,trans-hexa-2,4-dieneis non-stereospecific;this rules out a concerted 1P-addition but could be consistent with concerted 1,2-addition followed by rearrangement of vinylsilacyclopropane to silacyclopentene via a biradical intermediate.133 A vinylsilacyclopropane rearrangement involving C-C bond cleavage is probably involved in the formation of the silanonadiene (71) from methylmethoxysilylene and cyclo- octa- 1,3-diene.' 34 It has been suggested that 1,2-disilacyclobutene (72) which reacts with acetylenes uia its ring-opened form may be a key intermediate in the formation of 1,4-disilacyclohexa-2,5-dienes (73) from acetylenes and ~i1ylenes.l~ P.P. Gaspar and R. J. Hwang,J. Amer. Chem. SOC.,1974 % 6198. '34 M. E. Childs and W. P. Weber Tetrahedron Letters 1974 4033. ' 3s T. J. Barton and J. A. Kilgour J. Amer. Chem. Soc. 1974 96 71 50.

ISSN:0069-3030    

DOI:10.1039/OC9747100153

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

7 Organometallic Chemistry Part (i) The Transition Elements By J. D. JONES R. PEARCE and R. WHELAN ICI Corporate Laboratory PO Box 17 The Heath Runcorn Cheshire WA7 4QE 1 Introduction The year 1974 has seen a further increase in the number of publications in this field representing primarity the consolidation of existing areas rather than the announcement of new breakthroughs. As before this Report concentrates on reactions involving formation and/or cleavage of a metal-carbon bond and on those aspects most relevant to organic synthesis. Stereoselective syntheses and ‘heterogenized’ catalysts are discussed in separate sections. 2 Reviews Reviews of a general nature include a volume in the Advances in Chemistry series covering the recent advances in many areas of homogeneous catalysis,’ ‘a mechanistic approach to organotransition-metal chemistry’ concentrating mainly on reactions with unsaturated species,’ electron-transfer mechanisms for intermediates in catalysis,3 and the stereochemistry of reactions of organo- transition-metal complexe~.~ More specific reviews relate to homogeneous hydrogenation,’ ‘heterogenized’ catalysts,6 inter- and intra-molecular hydrogen transfer,’ the use of organoiron complexes’ and Collman’s Reagent [Na,Fe(CO),]’ in organic synthesis the organic chemistry of nickel (in two ’ ‘Homogeneous Catalysis-11’ ed.D. Forster and J. F. Roth Adv. Chem. Ser. No. 132 American Chemical Society 1974. R. F. Heck ‘Organotransition Metal Chemistry a Mechanistic Approach’ Academic Press New York 1974.J. K. Kochi Accounts Chem. Res. 1974 7 351. F. J. McQuillin Tetrahedron 1974,30 1661. L. Marko and B. Heil Catalysis Rev. 1973 8 269; G. Dolcetti and N. W. Hoffman Inorg. Chim. Acta 1974 9 269. J. C. Bailar jun. Catalysis Rev. 1974 10 17; Z. M. Michalska and D. E. Webster Platinum Metals Rev. 1974 18 65. ’ G. Brieger and T. J. Nestrich Chem. Rev. 1974 74 567; I. S. Kolomnikov V. P. Kukolev and M. E. Vol’pin Uspekhi Khim. 1974 43 903. * M. Rosenblum Accounts Chem. Res. 1974 7 122. E. A. Sullivan and T. F. Jula Internat. Laboratory 1974 (July-August) 51. 171 172 J. D. Jones R. Pearce and R. Whelan volumes Volume I1 discusses applications to organic synthesis),’ mono-olefin Ir-complexes,‘‘ ferrocene chemistry’ and the technology of metallocenes in general,13 the organic chemistry of the Group IV element^,'^ and the organo- metallic chemistry of uranium(rv).” The last review is timely for an area of chemistry that is destined for increasing attention over the next few years when one considers the growing stockpiles of 238U.3 Organometallic Compounds An area of organometallic chemistry that thas remained relatively neglected for many years and which is now marked for considerable expansion centres on the reactions of condensed metal vapours with organic compounds. ’ The advances that have created excitement are four-fold (i) the use of the electron-beam evaporation technique has allowed extension to the highly refractory metals (e.g.W) ;’’(ii) hitherto inaccessible complexes especially of the early transition metals have been prepared ;’7,18 (iii) the possibility exists of obtaining useful quantities of reagents especially of those unobtainable by other procedures by condensation of the metal with the organic reagent in an inert involatile (at low temperatures) solvent using a rotating reaction vessel’8a (cf.ref. 17); and (iv) the one-step generation of catalytic species from condensed metal vapours (e.g. condensation of the first-row transition elements with organoaluminium compounds affords cyclotrimerization catalysts for butadiene). l9 Some examples of new complexes prepared are M(butadiene) (M = Mo or W),18’ Ti(C,H,) ,l and bis(cyclo-octa-l,5-diene)iron.’ Advances have been made in the study of the more elusive metallocenes 13C n.m.r.has clarified the structure of the green isomer of ‘titanocene’ as (l),,’ while [M(C,H,),] (M = Mo or W) may now be conveniently prepared by photo- lysis of the corresponding carbonyls M(hs-C,H,),C0.2 ‘ lo P. W. Jolly and G. Wilke ‘The Organic Chemistry of Nickel’ Academic Press London 1974 Vol. 1 ;Vol. I1 in press. M.‘Herberhold ‘Metal n-Complexes’ Elsevier Amsterdam 1974 Vol. 11 Part 2. * ‘Gmelins Handbuch der anorganischen Chemie Erganzungswerk zur 8 Auflage Vol. 14. Eisen-Organische Verbindungen Part A Ferrocen 1’ Springer-Verlag Berlin 1974. I J. C. Johnson ‘Metallocene Technology’ Noyes Data Corporation Park Ridge New Jersey 1973. l4 ‘Gmelins Handbuch der anorganischen Chemie Erganzungswerk zur 8 Auflage Band 10 Zirkonium-organische Verbindungen ; Auflage Band 1 1 Hafnium-organische Verbindungen’ Springer-Verlag Berlin 1974; P.C. Wailes R. S. P. Coutts and H. Weigold ‘Organometallic Chemistry of Titanium Zirconium and Hafnium’ Academic Press New York 1974. E. Cernla and A. Massei Inorg. Chim. Acta 1974 10 239. I6 Cf.P. L. Timms Ado. Inorg. Chem. Radiochem. 1972 14 121. F. W. S. Benfieid M. L. H. Green J. S. Ogden and D. Young J.C.S. Chem. Comm. 1973 866. la (a) R.Mackenzie and P. L. Timms J.C.S. Chem. Comm. 1974 650; (6) P. S. Skell E. M. Van Dam and M. P. Silvon J. Amer. Chem. SOC.,1974 96,626. l9 V. M. Akhmedov M. T. Anthony M. L. H. Green and D. Young J.C.S. Chem. Comm. 1974 777. lo A. Davison and S. S. Wreford J. Amer. Chem. SOC.,1974 % 3017.K. L. Tang Wong J. L. Thomas and H. H. Brintzinger J. Amer. Chem. SOC.,1974 96,3694. Organometallic Chemistry-Part (i) The Transition Elements (1) A general and much improved synthesis of the useful n-allyl-palladium complexes derived from cycloalkenes and alkylidenecycloalkanes has appeared. The unexpected regioseiectivity of the reaction allowed the preparation of both exo- and endo-cyclic isomers.22 Use of the generally unreactive transition metal-carbene complexes in organic synthesis is limited by the lack of suitable methods for modification of the carbene fragment attached to the metal and its removal under sufficiently mild conditions. For the former continued studies of the reactions of the corres- ponding conjugate bases e.g.Cr(CO),[C(OMe)CHR] with epoxides and x-bromo-esters provide a route to some hitherto unavailable complexe~.~ For the latter reactions with oxygen (or sulphur or selenium) tertiary amines or 1-vinyl-2-pyrrolidones look promising. Thus truns-AuI,[C(NHC,H,Me- p),]CIO reacts with oxygen to give (p-MeC,H,NH),CO Cr(CO),(COMeAr) reacts with (X) (X = 0,S or Se) to give ArC(X)OMe;24b Cr(CO),[C(OMe)- CHR'R2] reacts with e.g.pyridine to give good yields of MeOCH=CR'R2;25 in the reaction of Cr(CO),(COMePh) with pyrrolidones R'R2C=CHkO(CH2)i cleavage of the C=C bond occurs with transfer of CR'R2 to the carbene moiety to give PhMeOC=CR1R2.26 Carbene complexes of Pd" have been shown to be intermediates in the PdC1,-catalysed reaction of P-amino-alcohols with iso-cyanides to give predominantly 2-0xazolines.~~ Metal-stabilized carbonium ions offer possibilities as reagents in synthesis.or-Ferrocenylalkylamines are conveniently prepared from or-ferrocenylalkyl-carbonium ions (generated from the readily accessible carbinols) this being particularly relevant to peptide synthesis using chiral ferrocenylalkylamines as templates.'* The species Co,(CO),CCH=CR 'R2 readily prepared from C(!,(CO) and R1R2C=CHCX, form very stable carbocations Co,(CO),- CCHCR'R'Z on reaction with electrophiles Z+. They add to various reagents YZ to generate the compounds CO~(CO)&CHYCR'R~Z.~~ Suitable mild conditions are then required for removal of the organic fragment from the C0,C cluster. 22 B. M. Trost and P. E. Strege Tetrahedron Letters 1974 2603.23 C. P. Casey and R. L. Anderson J. Organometallic Chem. 1974 73 C28. 24 (a) G. Minghetti and F. Bonati J. Organometallic Chem. 1974 73 C43; (b) E. 0. Fischer and S. Riedmuller Chem. Ber. 1974 107 915. 2s E. 0. Fischer and D. Plabst Chem. Ber. 1974 107 3326. 26 E. 0.Fischer and B. Dorrer Chem. Ber. 1974 107 1 156. Y. Ito T. Hirao and T. Saegusa J. Organametallic Chem. 1974 82 C47. S. Allenmark Tetrahedron Letters 1974 371. 29 D. Seyferth C. Eschbach G. H. Williams P. L. K. Hung and Y. M. Cheng J. Organu-metallic chem. 1974 78 C13. 174 J. D.Jones R. Pearce and R. Whelan Interest was generated in the popular scientific press by the reports that iridium complexes catalyse the reaction of NO with CO to give N,O and CO ; complexes of N,O bonded uia nitrogen were implicated as intermediate^.^' The reactions of organocopper compounds continue to attract much interest ; over 30 papers have come to our attention.We highlight their use in stereoselec- tive syntheses (see below) and the following general points. For the most efficient incorporation of the organic fragment R' mixed cuprates CuR'(X)Li [or CuR'(X)- MgY] are referr red.^' A range of such reagents has been studied where for example X = R'C-C R'O or Ar and R' = Bu But or Ph. The best selectivity in transfer (R1 rather than X) is achieved when the species CuX is relatively stable but this is often at the expense of overall reactivity ; maximum reactivity is obtained for X = Bu'.~~ An improved preparation of the most generally useful of these reagents CuR(SPh)Li has appeared., A good general preparation of ketones with effective utilization of the organocopper reagent involves its reaction with alkyl and aryl thio-esters R'COSR, and appears preferable to reaction with acid halides.34 Organocopper reagents have been used for the preparation of diones uia conjugate addition of complexes containing 'masked acyl anions'35 [of the type RCH=C(SiMe,)- (equivalent to RCH,CO-) and RC=CHSiMe (equivalent to REHCHO)] to cyclic enones equation ( l).36 Conjugate addition (1,6) to A2,4-dienoic esters of the hitherto uninvestigated propargylic-copper reagents provides a route to 1,5-enynes or 1,4,5-triene~.~' Finally while it has been suggested that the utility ofsuch reagents is related to the availability of the Cu"' state (i.e.oxidative addition reductive elimination sequences occur),38 a cautionary note to such generalizations comes from a study of reactions of ethylenic to~ylates.~~ 4 Hydrogenation CO(~~-C,H~)[P(OM~),]~ is a catalyst for the homogeneous hydrogenation of aromatic hydrocarbons and is the first unequivocal demonstration of aromatic hydrogenation with a discrete metal complex. Cyclohexanes are obtained without 30 B. L. HaymoreandJ. A. Ibers,J. Amer. Chem. SOC.,1974 % 3325; S. Bhaduri B. F. G. Johnson C. J. Savory J. A. Segal and R. H. Walter J.C.S. Chem. Comm. 1974,809. 3' Cf.J. D. Jones R. Pearce and G. L. P. Randall Ann. Reports (B) 1973 70 243. 32 W. H. Mandeville and G. M. Whitesides J.Org. Chem. 1974 39 400. j3 G. H. Posner D. J. Brunelle and L. Sinoway Synthesis 1974 662. 34 R. J. Anderson C. A. Henrick and L. D. Rosenblum J. Amer. Chem. SOC.,1974 96 3654. 35 C' D. Seebach Angew. Chem. Internat. Edn. 1969 8 639. 36 R. K. Boeckmann jun. Tetrahedron Letters 1974 3365. 37 B. Ganem Tetrahedron Letters 1974 4467. 38 C' T. Cohen J. Wood and A. G. Dietz jun. Tetrahedron Letters 1974 3555. 39 G. H. Posner and J.-S. Ting Tetrahedron Letters 1974 683. Organometallic Chemistry-Part (i) The Transition Elements 175 competing hydrogen exchange i.e. C6D6 gave C,H,D6 only. A clear indication of steric encumbrances to hydrogenation is shown by the very slow (but stereo- selective) hydrogenation of xylenes and mesitylene.The first step in the reaction sequence is presumed to be an h3-C3Hs into h1-C3Hs conver~ion.~' A useful demonstration of the activating effect of intramolecular co-ordination of a polar group within the substrate olefinic compound is provided by the hydro- genation of (2) in the presence of RhCl(PPh,),. For X = H no reaction takes place whereas for X = Li Na or K a useful conversion is obtained with exclusive production of the cis-isomer (3).41 Catalysts based on chromium should now be given serious consideration Cr(CO),(NCMe),42 or Cr(CO),(norbornadiene) with U.V. irradiation4 promote the 1P-addition of hydrogen to 1,3-dienes to give the corresponding cis-monoenes. Surprisingly addition of acetone to the catalysts Cr(CO) or Cr(CO),(norborna- diene) with U.V.irradiation gives both better selectivity and higher activity in the hydrogenation of trans-trans-hexa-2,4-dienein mixtures of hexadienes., Weak U.V. irradiation improves the activity of certain Group VIII catalysts RhH(C0) (PPh,) is reactivated4' while IrCl(C0) (PPh,) improves in activity by up to f~rty-fold.,~ Both RhH(PPh,) and [Rh(CO),(PPh,),J ,2C,H are unusual in selectively hydrogenating 1,3-dienes to a-~lefins.~' Stoicheiometric hydrogenation ofolefins with RuHCl(PPh,) gives the o-metallated RumPh,- o(Cl)PPh, which with hydrogen affords RuHCl(PPh,), an important species in hydrogenations using RuCI,(PPh,) [cf. RuCl,(PPh,) SRuC12(PPh,) + PPh 3. This intramolecular hydrogen transfer is unimportant in catalytic hydrogenations with molecular hydrogen ; hydrogenolysis of the Ru-alkyl bond is favoured.48 Interesting new catalysts include Ti(hs-CsHs)2CO(PhC~CPh),49 hydrido-metallocarbaboranes based on rhodium," and [2,2'-ethylene bis- 'O E.L. Muetterties and F. J. Hirsekorn J. Amer. Chem. Soc. 1974 % 4063. 41 H. W. Thompson and E. McPherson J. Amer. Chem. SOC. 1974 96 6232. 42 M. A. Schroeder and M. S. Wrighton J. Organometallic Chem. 1974 74 C29. 43 C. Platbrood and L. Wilputte-Steinert J. Organometallic Chem. 1974 70 393. " G. Platbrood and L. Wilputte-Steinert Tetrahedron Letters 1974 2507. 45 W. Strohmeier and G. Csontos J. Organometallic Chem. 1974,67 C27. 46 W. Strohmeier and G. Csontos J. Organometallic Chem. 1974,72,277; W. Strohmeier and L. Weiget ibid. 1974 82 417.47 G. F. Pregaglia G. F. Ferrari A. Andreeta G. Capparella F. Genoni and R. Ugo J. Organometallic Chem. 1974 70. 89. '* B. R. James L. D. Markham and D. K. W. Wang J.C.S. Chem. Comm. 1974 439. 49 G. Fachinetti and C. Floriani J.C.S. Chem. Comm. 1974 66. 50 T. E. Paxson and M. F. Hawthorne J. Amer. Chem. Soc. 1974 % 4674. 176 J. D. Jones R.Pearce and R.Whelan (nitrilomethylidine)iphenolato]palladium(~~) which behaves similarly to hydro- genase enzymes and is proposed as a model for such ~ysterns.~' Doubts and controversy concerning the mode of operation of RhCYPPh,) appear to have been resolved by the appearance of detailed reports on this catalyst system.52 Further evidence for the poisoning effect of molecular nitrogen on transition-metal catalysts comes from a study of the system RuH,(PPh,),- N2-pent-2-ene.5 Hydrosilylation U.V.irradiation of Cr (CO) provides a useful catalyst for the cis- 1,.l-hydrosilyla-tion of 1,3-dienes catalytic activity remaining after stopping irradiation. A range of silanes [e.g. Me,SiH Me,SiH, Ph,SiH, (EtO),SiH] is suitable although 1-or 4-substituted dienes are unreactive. The carbonyls Mo(CO) or W(CO), while active are unsuitable in that they promote competing iso- merization.54 RhCI(PPh,) is unusual in promoting the trans-hydrosilylation of acetylenes;55 CJ [PtH,CI,] which gives exclusive cis-addition. a-Silyl-propionitriles R 'CH ,CH(SiR:)CN prepared by hydrosilylation of simple ap-unsaturated nitriles using RhCI(PPh,), provide useful reagents for the preparation of higher @-unsaturated nit rile^,^^ and the same catalyst promotes the hydrosilylation of carbodi-imides to N-silylformamidines precursors to a range of for ma mi dine^.'^ Selective hydrosilylation of styrene has been achieved Ni(CO) at ambient temperature gives exclusively PhCH(SiCl,)CH while the system [PtH,Cl,] + PPh at 80 "C gives predominantly PhCH2CH,SiC1,.58 A detailed study of the ageing of the notoriously unreproducible [PtH,Cl,]/ Pr'OH catalyst system has been ~ndertaken.~~ 6 Metal-catalysed Hydrogen Exchange This year there have been several useful contributions in the area of metal- catalysed inter- and intra-molecular hydrogen exchange.RuCl,(PPh,) continues to attract most attention. Hydrogen transfer from alcohols to unsaturated substrates is believed to take place via formation of a metal alkoxide followed by rate-determining p-elimination to give a ketone and metal hydride.Good evidence for this comes from studies of the rate of equilibration of ketones and G. Henrici-Olive and S. Olivt Angew. Chem. Znternat. Edn. 1974 13 549. s2 C. A. Tolman P.Z. Meakin D. L. Lindner and J. P. Jesson J. Amer. Chem. SOC. 1974 % 2762; Y. Demortier and I. de Aguirre Bull. SOC. chim. France 1974 1614 1619. s3 F. Pennella J. Organometallic Chem. 1974 65 C17. 54 M. S. Wrighton and M. A. Schroeder J. Amer. Chem. SOC., 1974 % 6235. " I. Ojima M. Kumagai and Y. Nagai J. Organometallic Chem. 1974 66 C14. 56 I. Ojima and M. Kumagai Tetrahedron Letters 1974 4005. 57 I.Ojima S.-I. Inaba and Y. Nagai J. Organometallic Chem. 1974 72 C11. s8 M.Capka P.Svoboda and J. Hetflejs CON. Czech. Chem. Comm. 1973 38 3830. '9 V. B. Pukhnarevich B. A. Trofimov L. I. Kopylova and M. G. Voronkov Zhur. obshchei Khim. 1973 43 2691. Organometallic Chemistry-Part (i) The Transition Elements 177 alcohols" and the racemization of optically active alcohols6' by RuCl,(PPh,) . This reaction sequence may be used to good effect for the labelling of the a-carbon in alcohols (RCH,OH -+RCD,OD)andappears to be the preferred method.6 'g6' Under certain conditions reductive etherification may predominate with these catalysts e.g. reaction of RuCl,(PPh,)? with secondary alcohols which yield stabilized carbonium ions6' or with Pr'OH-cyclohexanone in the absence of water when using certain Ir"' species.63 >C=O + 2Pr'OH -+ >CHOPr' + Me,CO + H,O Intermolecular hydrogen transfer in a/?-unsaturated alcohols to give the corres- ponding ketones is effected by a number of Ru" catalysts.64 While this is the preferred method for this transformation certain drawbacks are apparent including competing intermolecular transfer and the necessities of using anaerobic conditions coupled with the need for recovery of the catalyst.These drawbacks may be overcome using Ru,(O)(OAc) but this catalyst is unfortunately limited to l-alken-3-0ls.~~" The intermediate (4) has been isolated during the exchange between Pr'OH and PhCOCH=CHPh using IrCl,H(Me,SO) .65 Ir /\ Me,SO I OSMe, CI (4) Although alcohols are in general use in intermolecular hydrogen transfer amines should not be neglected from a study of the hydrogenolysis of PPh complexes by hydrogen transfer from amines (e.g.indoline) it was concluded that they are the more reactive.66 RuCl,(PPh,) also catalyses the transfer hydrogenolysis of CC1 by alcohols giving CHCl ,HCl and the corresponding ketone which in some cases reacted further with HCl to give an alkyl halide.67 A novel system for the reduction of olefins is the hydrogen transfer from Pr'MgBr catalysed by Ti(h5-C,H,),C12 ; the catalytic species is most plausibly Ti@'-C5H5)2H.68 " Y. Sasson P. Albin and J. Blum Tetrahedron Letters 1974 833. 61 Y. Sasson and J. Blum J.C.S. Chem. Comm. 1974 309. b2 S. L. Regen J. Org. Chem.1974 39 260. b3 Y. M. Y. Haddad H. B. Henbest J. Husbands T. R. B. Mitchell and J. Trocha-Grimshaw J.C.S. Perkin I 1974 596. 64 (a)Y. Sasson and G. L. Rempel Tetrahedron Letters 1974 4133; (b) M. Dedieu and Y.-L. Pascal Compt. rend. 1974 278 C 1425 6s H. B. Henbest and J. Trocha-Grimshaw J.C.S. Perkin Z 1974 601. 66 T. Nishiguchi and K. Fukuzumi J. Organometallic Chem. 1974 80 C42. Y. Sasson and G. L. Rempel Tetrahedron Letters 1974 322 1. " E. Colomer and R. Corriu J. Organometallic Chem. 1974 82 367. 178 J. D. Jones R.Pearce and R.Whelan Full details have appeared of the homogeneous H-D exchange in alkanes and alkylbenzenes catalysed by Pt" c~mplexes.~~ NaJrCl behaves similarly with simple alkanes,70 and is the first such example outside Pt species.Rh(h5-C,H,) (CZHJ2 undergoes H-D exchange at all positions in both the cyclopentadienyl and the ethylene ligand with ['H,]benzene at ca. 130"C and is the first example of such a homogeneous exchange without added reagent.71 Of relevance to hydrogen-transfer processes are reports relating to Mom. .H-C interactions in molybdenum pyrazolylborate complexe~.'~ X-Ray structures of MO[E~~B(~Z),](~~-CH,CP~CH,)(CO)~~~~ and Mo[Et,B(pz),](h3-C7H7)-(CO)2726 clearly show this bonding situation and the latter structure also shows that it competes successfully with a Mo-olefin interaction i.e. the C7H7group is tri-and not penta-hapto. The strength of this interaction was estimated as 17-20 kcal mol-'. 72c 7 Oxidative Addition and Reductive Elimination Sequential oxidative addition and reductive elimination reactions can provide useful synthetic routes to organic products.Thus reductive elimination from complexes such as Ni(R)(C,H,F)(PEt,) gives alkyl-substituted fluoroaro-ma tic^.^ Aryl phosphonium salts are obtained74 from ArNiX(PPh,) and triphenylphosphine. Nitriles can be made from benzohydroxamoyl chlorides [ArC(Cl)=NOH] with iron pentacarbonyl in refluxing tetrahydr~furan.~ The formation of o-alkyl-substituted aromatics from o-metallated Pd complexes76 demonstrates a useful application of these well-documented reactions. Mechanistic studies of oxidative addition and reductive elimination reactions continue; it has been that the intramolecular reductive elimination of ethane from trismethyl Pt" complexes proceeds via initial phosphine dissocia- tion giving a five-co-ordinated intermediate and that a major pathway for addition of alkyl halides to Pto and Pdo complexes involves a radical chain process.Several papers deal with the stereochemical implications of these reactions. It is shown that B-bromostyrene adds oxidatively to Nio 79 and PtoBOand 69 J. L. Garnett and R. S. Kenyon Austrul. J. Chem. 1974 27 1023 1033; J. L. Garnett and J. C. West ibid. p. 129. 'O J. L. Garnett M. A. Long and K. B. Peterson Austral. J. Chem. 1974 27 1823. 7' L. P. Seiwell J. Amer. Chem. SOC.,1974 % 7134. 72 (a) F. A. Cotton T. LaCour and A. G. Stanislowski J. Amer. Chem. SOC.,1974 96 754; (b)F. A. Cotton and V. M. Day J.C.S. Chem. Comm. 1974,415;(c)F.A. Cotton and A. G. Stanislowski J. Amer. Chem. SOC.,1974 96,5074. 73 G. W. Parshall J. Amer. Chern. SOC.,1974 % 2360. 74 L. Cassar and M. FOB J. Organometallic Chem. 1974 74 75. 75 N. A. Genco R. A. Partis and H. Alper J. Org. Chem. 1973,38,4365. 76 S.-I. Murahashi Y.Tanba M. Yamamura and I. Moritani Tetrahedron Letters 1974 3749. 77 M. P. Brown R. J. Puddephatt and C. E. E. Upton J.C.S. Dalton 1974 2457. 78 A. V. Kramer J. A. Labinger J. S. Bradley and J. A. Osborn J. Amer. Chem. SOC. 1974 96,7145. 79 L. Cassar and A. Giarrusso Gazzetta 1973 103 793. J. Rajaram R. G. Pearson and J. A. Ibers J. Amer. Chem. SOC.,1974 96,2103. Organometallic Chemistry-Part (i) The Transition Elements 179 chloro-olefins add to Pt and Pdo with retention of configuration.The inversion of the configuration of (S)-(-)-a-phenethyl bromide82 and (S)-(+ )-[~t-~H]benzyl chloride,83 during reaction with Pd' suggests an h2-type mechanism for the oxidative addition with the metal serving as the nucleophile. The Pd'" inter-mediates in the halogenation of Pd" enyl complexes can either undergo reductive elimination with retention of configuration or nucleophilic attack at the a-carbon leading to inversion.84 Two reports demonstrate the promotion of oxidative addition by neighbouring- group effects. Addition to the complex trans-[IrCl(CO){ PMe,(o-MeOC,H,)) 2] is much faster than to either the p-methoxy or unsubstituted phenyl analogues. This is rationalized in terms of electron donation from the proximate methoxy oxygen to the metal increasing the nucleophilicity of the metal8' am-Di-halogenoalkyls react with two molecules of the Rh macrocycle (5).The second addition is much faster than the first indicating a remarkable neighbouring group effect by a d6 centre.86 FF \/ ONB'O I \ U An important pathway for the chemical degradation of DDT has been demon- strated" by its reaction with bis(dimethylglyoximato)pyridinecobalt(I) to give a cobalt(w) vinyl by HCl elimination. DDT is stable to base-induced elimination of HCl under the conditions used. Examples of more general oxidative addition reactions include the cleavage of C-0 bonds in acyclic anhydrides by Ir' and Pt0,88 of Me-0 bonds by Ir',89 of nitroalkanes by Pt0,90 of 0-H bonds of substituted phenols by Pt0,91 B.F. G. Johnson J. D. Jones J. Lewis and K. A. Taylor J.C.S. Dalton 1974 34. 82 K. S. Y. Lau R. W. Fries and J. K. Stille J. Amer. Chem. Soc. 1974 96 4983. 83 P. K. Wong K. S. Y. Lau and J. K. Stille J. Amer. Chem. SOC.,1974 96,5956. 84 P. K. Wong and J. K. Stille J. Organometallic Chem. 1974 70 121. E. M. Miller and B. L. Shaw J.C.S. Dalton 1974,480. 86 J. P. Collrnan and M. R. MacLaury J. Amer. Chem. SOC.,1974 % 3019. R. H. Prince G. M. Sheldrick D. A. Stotter and R. Taylor J.C.S. Chem. Comm. 1974 854. D. M. Blake S. Shields and L. Wyman Inorg. Chem. 1974 13 1595. 89 D. M. Blake J.C.S. Chem. Comm. 1974 815. 90 K. Schorppand W. Beck Chem. Ber. 1974 107 1371. 91 H. A. Tayim and N. S. Akl J. Inorg. Nuclear Chem. 1974 36 1071.180 J.D. Jones R.Pearce and R.Whelan and of the C-C bonds of cyclobutenedione derivatives," hexakis(trifluor0-methyl)ben~ene,~ by Pt'. and substituted cycl~propanes,~~ The addition of CH,SO,F or CH,SO,CF to Ir' gives highly labile products which when treated with anions give Ir" complexes that are difficult to prepare 8 Oligomerization Since there have been few significant papers published concerning polymerization this year the topic has been omitted. Several reports concern Ni catalysts which are active for the dimerization of lower olefins. (n-Cyclopentenyl) (n-cyclopentadieny1)Ni is active without recourse to Lewis acid promoters; a possible mechanism involves the reversible elimination of cyclopentadiene to give an intermediate Ni h~dride.~~ It is also reported" that hydrido Ni( +1)species are active for the linear dimerization of butadiene.Use of the air-stable Nio complex Ni[P(OPh),] obviates the use of a reducing agent and allows aluminium halides to be used as co-catalysts for propene dimerization.'* MekCorPPh3 H The complex (6) is the first example of a postulated intermediate of cobalt- catalysed oligomerization of dienes to be isolated.99 In contrast to the linear oligomers of dienes formed with organocobalt catalysts CoCl(PPh3) produces cyclic dimers. loo A novel approach to oligomerization has been described in a report" dealing with co-condensation of transition-metal atoms with butadiene and a co-catalyst such as (Et,AlCl),; products can be altered by omitting the A1 component.Methylenecyclopropane dimerization'"" and cyclotrimerization to give a compound containing a seven-membered ring,'01b is effected by modified Ni' 92 E. R.Hamner R.D. W. Kemmitt and M. A. R. Smith J.C.S. Chem. Comm. 1974,841. 93 J. Browning M. Green J. L. Spencer and F. G. A. Stone J.C.S. Dalton 1974 97. 94 M. Lenarda R. Ros,M. Graziani and U. Belluco J. Organometallic Chem. 1974,65 407. 95 D. Strope and D. F. Shriver Znorg. Chem. 1974 13 2652. 96 J. D. McClure and K. W. Barnett J. Organometallic Chem. 1974,80 385. 97 J. Furukawa J. Kiji H. Konishi K. Yamamoto S.-I. Mitani and S. Yoshikawa Makromol. Chem. 1973 174 65. 98 R. de Haan and J. Dekker J. Catalysis 1974 35 202. 99 P. V. Rinze Angew. Chem. Internat. Edn.1974 13 336. looM. A. Cairns and J. F. Nixon J. Organometallic Chem. 1974 64 C19. Io1 (a) P. Binger Synthesis 1973 427; (6) P. Binger and J. McMeeking Angew. Chem Internat. Edn. 1974 12 995. Organometallic Chemistry-Part (i) The Transition Elements 181 Me Me (7) catalysts. The formation of the cyclohexane derivative (7) from dimethylcyclo- propene in the presence of Pd' represents the first example of a smooth cyclo- hexane ring formation from an olefin.lo2 Novel alkenyl metallocycles of Ir are good catalysts for the cyclotrimerization of disubstituted a~ety1enes.l'~ The co-oligomerization of acetylenes has figured prominently in the literature this year. The reaction of (h5-C,H,)Co(CO) with diacetylenes gives inter- mediates which react further with acetylenes or nitriles to give benzocyclo- butenes and pyridines re~pectively."~ Diacetylenes of the type (8) undergo a Nio-catalysed Diels-Alder reaction with disubstituted acetylenes to give 0 0 Ph Et02C Eto2cw quinones of the type (9).lo5 The complex (lo) an intermediate in the co-oligo- merization of dienes with alkynes has been isolated.'06 A useful one-step procedure for making penta-1,Cdiene derivatives is the Pd-catalysed co-dimeriza- tion of acetylenes with ally1 halides.lo7 The primary step in the cobalt-catalysed co-oligomerization of diphenylacetylene with acrylonitrile is shown to be the formation of a cobaltacyclopentene complex lo* and intermediates of this type also figure in the preparation of substituted benzenes cyclohexadienes thiophens lo2 P.Binger G. Schroth and J. McMeeking Angew. Chem. Internat. Edn. 1974 13,465. '03 W. H. Baddley and G. B. Tupper J. Organometallic Chem. 1974,67 C16. K. P. C. Vollhardt and R. G. Bergman J. Amer. Chem. SOC.,1974 96,4996. F. Wagner and H. Meier Tetrahedron 1974 30,773. B. Biissemeirer P. W. Jolly and G. Wilke J. Amer. Chem. SOC.,1974,96 4726. lU7K. Kaneda F. Kawamoto Y. Fujiwara T. Imanaka and S. Teranishi Tetrahedron Letters 1974 1067. lo* Y. Wakatsuki K. Aoki and H. Yamazaki J. Amer. Chem. SOC.,1974 96,5284. J. D. Jones R. Pearce and R. Whelan selenophens and pyrroles from oligomerization and co-oligomerization of substituted benzenes and olefins. log The formation of 6,6-dicyano-1,2,3,4-tetra-phenylfulvene (11) from the reaction of (NC),C=C(C1)Mo(CO),(C5H5)with two diphenylacetylene units probably involves transfer of a chlorine atom to the metal to give dicyanovinylidene carbene.lo Ph CN Ph (1 1) Other synthetically useful reactions have been reported in which various moieties are incorporated between olefins during oligomerization. Olefins particularly ring-strained olefins will dimerize in the presence of Fe(CO) with concurrent CO insertion to give ketones e.g. equation (2)." 0 Pd catalyses the reaction of butadiene with Schiff bases (R1N=CHR2)to give trisubstituted piperidines of the type (12),'12and with nitroalkanes to give long- chain nitro-olefins having the nitro-group in the middle of the carbon chain.' l3 Finally pyridine derivatives result from the co-cyclodimerization of acetylenes and nitriles catalysed by reduced Co salts.'l4 R' Io9 Y.Wabatsuki T. Kuramitsu and H. Yamazaki Tetrahedron Letters 1974,4549. R. B. King and M. S. Saran J.C.S. Chem. Comm. 1974 851. 11' J. Mantzaris and E. Weissberger J. Amer. Chem. SOC.,1974 96 1873. 'I2 J. Kiji K. Yamamoto H. Tomita and J. Furukawa J.C.S. Chem. Comm. 1974 506. T. Mitsuyasu and J. Tsuji Tetrahedron 1974,30 83 1. 'I4 H. Bonnemann and R. Brinkmann internat. Symposium on Metals in Organic Chem. Venice 1974 abs. B11. Organometallic Chemistry-Part (i) The Transition Elements 9 Insertion Reactions The mechanism of olefin insertion into the Pt-H bond remains to be established. Kinetic studies' ''*'' cannot unequivocally distinguish between insertion of trans-co-ordinated C2H into Pt-H; through assisted isomerization to a cis-form or a stabilized five-co-ordinate Pt" intermediate.However a recent study"' of the reactivity of n-acetylenic methyl Pt" complexes has shown that C4F6 inserts more readily from a four-co-ordinate than five-co-ordinate geometry. The reaction of Me0,CC-CC0,Me with trans-PtMeCI(PMe,Ph) does not give the simple insertion product trans-PtCl(PMe,Ph),[C(CO,Me)=C(CO,-Me)Me] as previously reported but the P-chlorovinyl product trans-PtC1(PMe2Ph),[C(C0,Me)=C(C1)C0,Me] Pt-alkyne complex.' '* by attack of HCl on an intermediate A thorough study of the mechanism kinetics stereochemistry and direction of elimination of (Ph,P),RhCl-catalysed decarbonylation of acid chlorides has been made.* 9-' ' The first example of a stable o-bonded Pd complex resulting from the addition of Pd-CI to the ring double bond of 5-vinyl-2-norbornene has been reported,', and complex (13) is the first isolated example of an intermediate in the Pd- catalysed arylation of olefins showing a cis-insertion of the olefin (norbornene) into a Pd-Ph bond.'23 The difficulty of elimination of the Pd with Haexplains the formation of the unexpected product (14) rather than an arylated olefin. Similarly saturated products are formed with cyclo-octa- 1,Sdiene and endu-di~yclopentadiene.'~~ In contrast aryl- and vinyl-substituted olefins are pro- duced in the presence of amines and Pd acetate."' Is H. C. Clark C. R. Jablonski J.Halpern A. Mantovani and T. A. Wed Inorg. Chern. 1974 13 1541. l6 H. C. Clark and C. R. Jablonski Inorg. Chem. 1974 13 2213. *I7 H. C. Clark C. R. Jablonski and K. Von Werner J. Organometallic Chem. 1974 82 C51. 'I8 T. G. Appleton M. H. Chisholm H. C. Clark and K. Yasufuku J. Amer. Chern. SOC. 1974 96,6600. J. K. Stille and M. T. Regan J. Amer. Chem. Suc. 1974 96 1508. 120 J. K. Stille and R. W. Fries J. Amer. Chem. SOC.,1974 96 1514. I * J. K. Stille F. Huang and M. T. Regan J. Amer. Chem. SOC.,1974 96,1518. 122 W. T. Wipke and G. L. Goeke J. Amer. Chem. SOC.,1974 96,4244. H. Horino M. Arai and N. Inoue Tetrahedron Letters 1974 647. 124 A. Kasahara T. Izumi K. Endo T. Takeda and M. Ookita Bull. Chem. Sac. Japan 1974 47 1967. 125 H.A. Disk and R. F. Heck J. Amer. Chem. Soc. 1974 96 1133. 184 J. D. Jones R. Pearce and R. Wheian The irradiation of (h'-C,H,),WH with mesitylene and p-xylene gives products which appear to be the first examples of a direct insertion of a transition metal into an unco-ordinated aliphatic C-H group. 126 Reports have dealt with insertion of acetylenes'27.'28 and olefins'28,'29 into metal-hydride bonds and the insertion of dienes into Pd-ally1 bonds.'30 CO inserts into Rh-13' and Co-alky1'32 bonds and SnCI inserts into Fe-alkyl bonds.'33*'34 The insertion of CO into Fe-ally1 bonds is effected by phosphites and diphosphine,' and into Fe-alkyl bonds by amines phosphines alcohols and thiocyanates. '36 Isocyanide insertion into Fe-alkyl bonds appears to occur more readily than CO in~erti0n.l~~ The products from reaction of isocyanides with methoxyenyl Pd complexes are viewed as intermediates having relevance to Pd-catalysed transannular carbonylation reactions.'38 Whereas isocyan- isothio~yanates,'~~ ate~,~~~ is~cyanides,'~' nitric ~xide,'~' and carbodi-imide~,'~~ insert into Nb- and Ta-methyl bonds ketones1j3 and thi~cyanates'~' do not. Forcing conditions have yielded SO insertion products of W alkyls,144 and the insertion of SO into (h'-C5H,)Fe(CO),(h'-allyl) proceeds via a zwitteri- onic Fe-olefin intermediate. 145 10 Asymmetric and Stereoselective Syntheses The use of organo-copper reagents in stereoselective syntheses is well established. Recent examples include alkylation and arylation of thio-esters to give ketones,34 the reductive removal of halogeno- and mesyloxy-groups and conversion of c@-unsaturated ketones into saturated products 146the alkylation of unsaturated K.Elmitt M. L. H. Green R.A. Forder I. Jefferson and K. Prout J.C.S. Chem. Comm. 1914 747. lZ7 A. J. Deeming S. Hasso and M. Underhill J. Organometallic Chem. 1974 80 C53. IZn T. Blackmore M. I. Bruce and F. G. A. Stone J.C.S. Dalton 1974 106. M. Schneider and E. Weiss J. Organomerailic Chem. 1974 73,C7. 130 J. A. Sadownick and S. J. Lippard Inorg. Chem. 1973 12 2659. l3] I. S. Kolomnikov A. 0.Gusev T. S. Belopotapova M. Kh. Grigoryan T. V. Lysyak Yu. T. Struchkov and M. E. Vol'pin J. Organometallic Chem. 1974 69 C10. 13' 1. S. Kolomnikov G. Stepovska S. Tyrlik and M.E. Vol'pin J. Gen. Chem.(U.S.S.R.) 1974 44 1743. 133 B. J. Cole J. D. Cotton and D. McWilliam J. Organometallic Chem. 1974 64 223. L34 C. V. Magatti and W. P. Giering J. Organometallic Chem. 1974 73,85. 135 G. Cardaci and A. Foffani J.C.S. Dalton 1974 1808. 136 H. Alper W. G. Root and A. S. K. Chan J. Organometallic Chem. 1974 71,C14. 137 Y.Yamamoto and H. Yamazaki Inorg. Chem. 1974 13,2145. 13' G.Carturan R. Zanella M. Graziani and U. Belluco J. Organometallic Chem. 1974 82 421. J. D. Wilkins J. Organometallic Chem. 1974 67 269. I4O J. D. Wilkins J. Organometallic Chem. 1974 65 383. 141 J. D. Wilkins and M. G. B. Drew J. Organometallic Chem. 1974 69 1 11. J. D. Wilkins J. Organometallic Chem. 1974 80 349. 143 J. D. Wilkins J. Organometallic Chem.1974 80 357. 144 J. 0.Kroll and A. Wojcicki J. Organometallic Chem. 1974 66 95. 14' L. S. Chen S. R. Su and A. Wojcicki J. Amer. Chem. SOC. 1974 % 5655. L46 S. Masamune G. S. Bates and P. E. Georghiou J. Amer. Chem. Soc. 1974 96,3686. Organornetallic Chemistry-Part (i) The Trunsition Elements 185 cyclic ketones 14'* ' 4g the synthesis of vinylcyclopropanes,'49 the exclusive formation of cis-alkylated products from a/?-acetylenic sulphoxides,'" the selective epoxide ring-opening providing a short route to prostaglandins,' ' and the transformation of vinyl-copper reagents into vinylic products with retention of configuration.' 52,153 Various moieties can be stereospecifically introduced into organic substrates via transition-metal allylic complexes ;examples include alkylation of unsaturated ketones without CO group protection,' 54 the preparation of specific mono- methylt~cols,'~ stereoselective coupling reactions to allylic halides,' 56 and the first reported preparation of a n-(2-methoxyallyI)nickel complex which offers possibilities of stereospecific acetoxylation reactions.57 Polycyclic olefins can be exclusively cis-hydrogenated using (Ph,P),RhCl combined with alkali-metal salts,4 ' while Pd-promoted amination of 2-butenes is shown to proceed trans.'5g The catalytic activation of Grignard reagents by Cp2TiC1 offers a new highly stereospecific method for the reduction of bulky alko~ysilanes.'~~ Nickel complexes will stereoselectively isomerize 3-methylpent- 1-ene,' 6o and promote the cycloaddition of olefins and bicyclo[2,1 ,O]pentane to give bicycloheptanes with retention of original configuration;'61 this is virtually the reverse of what happens in purely thermal reactions.In contrast Co,(CO) causes inversion of stereochemistry during epoxide deoxygenation. 162 The reaction of threo-and erythro-[PhCHDCHDFe(CO),Cp] with halogens provides the first evidence for different mechanisms for two similar compounds in that the former reacts with retention of the alkyl-group configuration and the latter gives inversion.'63 Many asymmetric syntheses still rely upon complexes of the chiral diop ligand [2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] and Rh continues to be the most useful metal for example in the preparation of 14' R.K. Boeckman J. Org. Chem. 1973 38 4450. 148 G. H. Posner C. E. Whitten J. J. Sterling and D. J. Brunelle Tetrahedron Letters 1974 2591. 149 Y. Ito K. Yonezawa and T. Saegusa J. Org. Chem. 1974 39 1763. 'so W. E. Truce and M. J. Lusch J. Org. Chem. 1974,39 3174. Is' E. J. Corey K. C. Nicolaou and D. J. Beames Tetrahedron Letters 1974 2439. lS2 J. F. Normant G. Cahiez C. Chiut and J. Villieras J. Organometallic Chem. 1974 77 269. J. F. Normant C. Chiut G. Cahiez and J. Villieras Synthesis 1974 803. lS4 B. M. Trost T. J. Dietsche and T. J. Fullerton J. Org. Chem. 1974 39 737. Is' S. Inoue K. Saito K. Kato S. Nozaki and K. Sato J.C.S. Perkin I 1974 2097. F. Guerrieri and G. P. Chiusoli Gazzetta 1974 104 557."' L. S. Hegedus and R. K. Stiverson J. Amer. Chem. SOC. 1974 % 3250. 158 B. Akermark J. E. Backvall K. Siirala-Hansen K. Sjoberg and K. Zetterberg Tetrahedron Letters 1974 1363. lS9 R. J. P. Corriu and B. Meunier J. Organomeraliic Chem. 1974 65 187. I6O G. Strukul M. Bonivento R.Ros and M. Graziani Tetrahedron Letters 1974 1791. l6 R. Noyori Y.Kumagai and H. Takaya J. Amer. Chem. SOC. 1974 96,634. 16' P. Dowd and K. Kang J.C.S. Chem. Comm. 1974 384. 16' D. Slack and M. C. Baird J.C.S. Chern. Comm. 1974 701. 186 J. D. Jones R. Pearce and R. Whelan optically active organ~silanes,'~~ in the reduction of a-keto-esters 165 and in the synthesis of alcohols via hydrogenation of silyl enol ethers. 66 However Ni-diop complexes have found application in the asymmetric cross-coupling reaction of secondary alkyl Grignards with organic halides.167 This method has wide application as a route to optically active hydrocarbons. In addition the preparation of useful chiral ferrocenylphosphine ligands has been reported '" and the potential of its Rh complexes for asymmetric inductions is demonstrated by the higher optical yields compared with diop complexes achieved during hydrosilylation of acetophenone. New bifunctional organosilanes have been prepared by the asymmetric hydrosilylation of ketones catalysed by cationic chiral Rh complexes.'69 Optically active methylphenylcyclopropanes are made by reaction of phenyl- propene with a chiral Fe complex claimed to be the first example of an optically active transition-metal carbene transfer reagent.I7' Other iron complexes specifically ferrocene derivatives have found a use as stereoselective chiral templates for asymmetrically induced peptide synthesis.' The first optically active tertiary alcohol derivatives of indan-1-01 and 1- tetralol have been reported' 72 from the stereospecfic attack of Grignard reagents on optically active indan-1 -one and 1-tetralone tricarbonyl Cr complexes. 11 Isomerization Isomerization of Carbon Skeletons.-The transition-metal-catalysed ring-opening of cyclopropanes remains under investigation. The rhodium-catalysed isomerization of vinylcyclopropanes has been shown to afford conjugated dienes' 73 whilst a mechanistic study of the isomerization of the related quadri- cyclanes indicates that the Agl-catalysed reaction proceeds via an ionic mechan- ism ;the Pd" and Rh' reactions involve oxidative addition.' 74 Another cyclic organic compound whose valence isomerization may be considered to proceed via the ring-opening of cyclopropane rings is diademane (15).This reaction is unusual in that the silver and rhodium species apparently prefer different sites for atta~k.'~' The cyclic compound (16) isomerizes further in the presence of RhI 176 lh4 R. J. P. Corriu and J. J. E. Moreau J. Organometallic Chem. 1974 64 C51. 16' I. Ojima T. Kogure and Y. Nagai Tetrahedron Letters 1974 1889. 16h M. Tanaka Y. Watanabe T. Mitsudo Y. Yasumori and Y. Takegami Chem. Letters 1974 137. 16' K. Kiso K. Tamao N. Miyake K.Yamamoto and M. Kumada. Tetrahedron Letrers 1974 3. lhB T. Hayashi K. Yamamoto and M. Kumada Tetrahedron Letters 1974 4405. '69 T. Hayashi K. Yamamoto and M. Kumada Tetrahedron Letters 1974 331. lrO A. Davison W. C. Krusell and R. C. Michaelson J. Organometallic Chem. 1974 72 c7. G. Eberle D. Marquarding I. Ugi and R. Urban ref. 114 abs. C1. ''' A. Meyer and C. Jaouen J.C.S. Chem. Comm. 1974 787. 173 H. W. Voigt and J. A. Roth J. Catalysis 1974 33 91. 174 H. Hogeveen and B. J. Nusse Tetrahedron Letters 1974 159. A. de Meijere Tetrahedron Letters 1974 1845. I'l6 A. de. Meijere and L. U. Meyer Tetrahedron Letters 1974 1849. Organometallic Chemistry-Part (i) The Transition Elements The reported reaction of Feist's ester (17) with Fe,(C0)9 is also of interest in the context of cyclopropane reactions in that the three-membered ring is cleaved after formation of the (olefin)Fe(CO) complex has occurred.' 77 The C0,Me I C0,Me results obtained suggest that the stereospecific rearrangement to a co-ordinated diene involves more than one metal centre.Other work on the valence isomerization of organic compounds includes the first experimental evidence for the hypothesis that cyclobutene metal complexes in which the metal is bound to the olefin can undergo facile concerted disrotatory ring-opening 'of the ligand to give butadiene metal complexes. 78 The molyb- denum-assisted isomerization of unsaturated propellanes appears to be related in so far as the carbon skeleton of the propellane may be considered to involve a substituted cyclobutene.This reaction has been shown to consist formally of a 1,5-sigmatropic cyclobutene shift in complete contrast to the purely thermal reaction pathway.' 79 A1though numerous mechanistic studies of these skeletal rearrangements have been undertaken the results may have to be reassessed in the light of an investiga- tion into the rhodium-catalysed ring-opening of bicyclo[3,l,0]hex-2-enes.* 8o The results show a marked dependence on oxygen its presence being necessary for efficient ring-opening. Carboll-Carbon Double-bond 1somerizations.-Whilst Barnett et al. have demonstrated the dependence of the above transition-metal-catalysed isomeriza-tion on oxygen Pennella has shown that the isomerization of pent-1-ene to pent-2-ene is affected by nitrogen.I8' When ruthenium catalysts are used the reaction is inhibited by nitrogen apparently owing to competition with the olefin ''' T.H. Whitesides and R. W. Slaven J. Organometallic Chem. 1974 67 99. W. Slegeir R. Case J. S. McKennis and R. Pettit J. Amer. Chem. SOC.,1974 % 287. L. A. Paquette J. M. Photis J. Fayos and J. Clardy J. Amer. Chem. SOC.,1974 96 1217. K. W. Barnett D. L. Beach D. L. Garin and L. A. Kaempfe J. Amer. Chem. SOC. 1974 % 7127. 188 J. D. Jones R. Pearce and R. Whelan for co-ordination to the metal.18 However the activity of cobalt catalysts appears to be enhanced by nitrogen.'82 The scope of this type of isomerization continues to be extended. Rhodium catalysts with increased activity have been obtained by substitution of a phos- phine in (Ph,P),RhCl by dimethyl s~lphoxide'~~ and carbonyl substitution in RhH(CO)(PPh,) by PF The selective isomerization of a-olefins to cis-isomers has also been re~0rted.l~' Isomerizations which are of Possible Synthetic Value.-The isoaromatization of acyclic dienones has been reported,186 and a novel oxepin has been obtained from the Rh'-catalysed isomerization of oxaquadricyclanes.18' Other reactions include the ruthenium-catalysed isomerization of 2,5-divinyltetrahydropyran,88 which can be obtained from the transition-metal-catalysed reaction of butadiene with formaldehyde and the selective isomerization of epoxides to ketones rather than aldehydes. 12 Carbonylation Reactions used in Organic Synthesis Hydroformylation continues to be studied extensively.Results obtained from an i.r. spectroscopic study of the high-pressure dicobaltoctacarbonyl-catalysed reaction are consistent with the Heck mechanism for hydroformylation. 'O However the rate-determining step appears to depend on the structure of the olefin involved in the reaction. Other work suggests that the formation of iso-meric aldehydes is determined by the isomerization of alkylcobaltcarbonyl intermediate^'^' and an explanation for the inhibiting effect of p-methoxy- benzonitrile has been advanced. The related stoicheiometric acylation reac- tion has been shown to proceed in the presence of cobalt and rhodium com- ple~es'~~ whilst Tanaka et al. suggest that a 7r-benzyl intermediate may be involved in the previously reported asymmetric hydroformy lation of styrene.94 Interest in the use of the tetracarbonylferrate anion appears to have waned although a review has appeared.' Work on other iron complexes has continued ; the complex [Et,NH]+[HFe3(CO)I has been shown to be a catalyst precursor la[ F. Pennella and R. L. Banks J. Catalysis 1974 35 73. F. Pennella J. Organometallic Chem. 1974 78 C10. L. Kh. Freidlin Yu. A. Kopyttsev N. M. Nazarova B. L. Lebedev and B. L. Khusid Itvest. Akad. Nauk S.S.S.R. Ser. khim. 1974 1325. IE4J. F. Nixon and J. R. Swain J. Organometallic Chem.,1974 72 C15. la5 Yu. M. Zhorov G. M. Panchenkov A. V. Shelkov and G. V. Demidovich Kinetics and Catalysis 1973 14 809. Ia6 Y.Pickholtz Y. Sasson and J. Blum Tetrahedron Letters 1974 1263. 87 R. Roulet J. Wenger M. Hardy and P. Vogel Tetrahedron Letters 1974 1479. la' T. D. J. D'Silva W. E. Walker and R. W. Manyik Tetrahedron 1974 30 1015. Ia9 D. Milstein and 0. Buchman Tetrahedron Letters 1974 2257. R. Whyman J. Organometallic Chem. 1974 81 97. 19' V. Yu. Gankin V. A. Dvinin and V. A. Rybakov Kinetics and Catalysis 1974 15 47. A. C. Clark J. F. Terapane and M. Orchin J. Org. Chem. 1974 39 2405. 193 J. Schwartz and J. B. Cannon J. Amer. Chem. SOC. 1974 % 4721. 194 M. Tanaka Y. Watanabe T. Mitsudo and Y. Takegami Bull. Chem. SOC.Japan 1974 47 1698. Orgunometullic Chemistry-Part (i) The Transition Elements for the carbonylation of propylene. "* (Diene)irontricarbonyl complexes afford cyclopentenones according to the general equation (3).Yields of -50 % were R = H or COMe obtained. However (butadiene)Fe(CO) only gave 2-or 3-cyclopentenone in 5 "/ yield. Cyclopentanone has been synthesized from ethylene and CO in the presence of Cp2TiN=NTiCp2.19' This reaction is thought to proceed via a titanium metallocycle. Whereas previous workers have shown that diphenyl-acetylene reacts with CO in the presence of a rhodium catalyst to give cyclo-pentadienone and a quinone phenylacetylene affords (18) with the same cata-lyst.''* Phenylacetylene also undergoes an unusual carbonylation during the oxidative degradation of its dicobalt hexacarbonyl complex.' '' Ph Following the reports of Cu'-catalysed carbonylations last year Ag' in sulphuric acid has been shown to convert alcohols and olefins into tertiary carboxylic acids in the presence of C0.200 Also the oxidative carbonylation of alcohols has been reported; dialkyl oxalates are obtained from simple alcohols with a Pd-Cu redox catalyst system,201whereas a cyclic product results from the nickel-catalysed carbonylation of 2-mer~aptoethanol.~~~ 13 Reactions of Co-ordinated Ligands The Understanding and Discovery of New Reactions of Functional Groupings Promoted by Co-ordination to a Transition Metal.-A number of publications have appeared concerned with nucleophilic attack at a co-ordinated dienyl ligand.Synthesis of the complex cations [L(C,H,)Fe(CO),]+ (where L is a donor ligand other than CO) has been achieved from dicarbonyl (1-5-q-cyclo-19' Ya.T. Eidus A. L. Lapidus and E. Z. Gil'denberg Kinetics and Catalvsis 1973 14 515. 19' B. F. G. Johnson J. Lewis and D. J. Thompson Tetrahedron Letters 1974 3789. ")'J. X. McDermott and G. M. Whitesides J. Amer. Chem. SOC..1974 % 947. 198 J. Kiji S. Yoshikawa and J. Furukawa Bull. Chem. SOC.Japan 1974 47,490. '99 I. U. Khand G. R. Knox P. L. Pauson and W. E. Watts J. Organometallic Chem. 1974 73 383. 2oo Y. Souma and H. Sano Bull. Chem. SOC.Japan 1974 47 1717. D. M. Fenton and P. J. Steinwand J. Org. Chem. 1974 39 701. 202 P. Koch and E. Perrotti J. Organometallic Chem. 1974 81 1 11. J. D. Jones R. Pearce and R. Whelan heptadieny1ium)iodoiron and nucleophilic addition has been shown to occur exclusively at position 2 of the dienylium ligand.203 This contrasts with the corres- ponding iron tricarbonyl complex which nucleophiles attack at both positions 1 and 2.Addition at position 3 of a co-ordinated dienyl ligand has been reported for the first time.204 The position of attack has also been shown to depend on the nature of the n~cleophile.~~~ Although nucleophilic addition to co-ordinated olefins or dienes occurs preferentially in an exo fashion the stereospecificity of electrophilic addition appears to depend on the system under examination. For example protonation of the complex (19)has been shown to occur by endo attack in complete contrast Rh to the analogous (bicyclic) iron tricarbonyl complex.206 Indeed evidence for metal involvement in directing the proton attack has been obtained from the iridium analogue of (19).Other evidence for endo electrophilic addition has been obtained from systems where the two faces of a co-ordinated diene permit a clear differentiation between endo or exo protonation207 and from an X-ray structural analysis of a substituted tricarbonylallyliron cationic intermediate.208 A study of co-ordinatively saturated iron alkyl complexes indicates that addi- tion of an electrophile occurs at the metal and not directly on the alkyl The nucleophilic addition of phosphines to co-ordinated dienes has been ex- tended to include cyclobutadiene iron complexes2" and the nature of the nucleo- phile has a dramatic effect on addition to the bis(mesitylene)iron(II) cation.21 Whereas C-nucleophiles add in the expected exo fashion N-and 0-nucleophiles appear to abstract an or-proton followed by a reaction with further [bis(arene)- Fe"] -+ .'03 R. Edwards J. A. S. Howell B. F. G. Johnson and J. Lewis J.C.S. Dalton 1974,2105. '04 B. F. G. Johnson J. Lewis T. W. Matheson I. E. Ryder and M. V. Twigg J.C.S. Chem. Comm. 1974 269; J. Ashley-Smith D. V. Howe B. F. G. Johnson J. Lewis and I. E. Ryder J. Organometallic Chem. 1974 82 257. lo' R. Aumann J. Organometallic Chem. 1974 78 C31. 206 J. Evans B. F. G. Johnson J. Lewis and D. J. Yarrow J.C.S. Dalton 1974 2375. 207 B. F. G. Johnson J. Lewis and D. J. Yarrow J.C.S. Dalton 1974 1054. '08 E. 0.Greaves G. R. Knox,P. L. Pauson S. Toma G. A. Sim and D. I. Woodhouse J.C.S. Chem.Comm. 1974 257. '09 T. G. Attig and A. Wojcicki J. Amer. Chem. Soc. 1974 96,262. 'lo A. Efraty J. Potenza S. S. Sandhu jun. R. Johnson M. Mastropaolo R. Bystrek D. Z. Denney and R. H. Herber J. Organornetallic Chem. 1914 70 C24. 211 J. F. Helling and G. G. Cash J. Organometallic Chem. 1974 73 C10. Organometallic Chemistry-Part (i) The Transition Elements 191 Other examples of novel reactions of ligands upon co-ordination to a metal include the facile alcoholysis of the C-C1 bond in chloroplatinum(I1) chloro- vinyl compounds2 and the 1,6addition of hexafluorobut-Zyne to co-ordinated cy~lo-octa-1,5-diene.~~ Both these reactions are unknown for the free ligands. The Synthetic Use of Transition-metal-promoted Additions and Substitutions.-Nucleophilic substitution in an aromatic ring has been shown to be facilitated by the Cr(CO) moiety.2 Both (n-chlorobenzene)Cr(CO) and (n-benzene)- Cr(CO) can be attacked by nucleophiles (Nu); with regard to the latter complex two pathways are available [equation (4)].The organic product can be obtained in yields up to 90 %. The catalytic nitration of benzenoid compounds with NO in the presence of Pd" has been reported,215 and the electrophilic attack on activated arenes by [C,H,Fe(CO),]+ may prove to be synthetically useful.2 (4) I Cr (CO) (+ isomers) Since the industrially important catalytic formation of secondary and tertiary amines from or-olefins (other than ethylene) and the appropriate amine still has to be demonstrated amination reactions continue to be investigated.The production of amines in high yields from terminal olefins by a low-temperature Pd"-promoted amination reaction has been reported2' 'and trans addition to the co-ordinated olefin has been shown to occur. 58 Conjugated dienes have been synthesized by the reaction of unsaturated aldehydes and ketones with acetylenic hexacarbonyldicobalt complexes.218 Strained ring systems are available from the intramolecular reaction of cyclo- butadiene co-ordinated to an Fe(CO) moiety with attached dienophile~~'~ and cyclohexenones substituted in the 4-position can be prepared by oxidative removal of the organic ligand which results from nucleophilic attack of enamines on (cyclohexadienyl)Fe(CO) cations.220 A novel substitution at the allylic "' R.A. Bell and M. H. Chisholm J.C.S. Chem. Comm. 1974 818. 'I3 A. C. Jarvis R. D. W. Kemmitt B. Y. Kimura D. R. Russell and P. A. Tucker J.C.S. Chem. Comm. 1974 797. *I4 M. F. Semmelhack and H. T. Hall J. Amer. Chem. SOC.,1974 96,7091 7092. *Is R. 0.C. Norman W. J. E. Parr and C. B. Thomas J.C.S. Perkin I 1974 369. 216 C. A. Mansfield K. M. Al-Kathumi and L. A. P. Kane-Maguire J. Organometallic Chem. 1974 71 C11. '17 B. Akermark J. E. Backvall L. S. Hegedus K. Zetterberg K. Siirala-Hansen and K. Sjoberg J. Organometallic Chem. 1974 72 127. 'I8 I. V. Khand and P. L. Pauson J.C.S. Chem. Comm. 1974 379. '19 R. H. Grubbs T. A. Pancoast and R. A. Grey Tetrahedron Letters 1974 2425. 220 R. E. Ireland G. G. Brown R.H. Stanford and T.C. McKenzie J. Org. Chem. 1974 39 51. 192 J. D.Jones R. Pearce and R. Whelan position of an olefin has been demonstrated using palladium,22 and the synthesis of complex hydrocarbyl silicon molecules may be possible following a report of the stereospecific transfer of organosilicon ligands from ruthenium to a co- ordinated hydrocarbon.222 14 Heterogeneolls Catalysts derived from Known Homogeneous Systems Interest in this area is flourishing and two reviews have been published.6 Although various organic polymer and inorganic supports have been described a high percentage of the work has been undertaken using cross-linked polystyrene as a heterogeneous support. Rhodium and platinum hydrosilylation catalysts have been supported on functionalized polystyrene223 and inorganic supports.224 Although some of the catalysts can be re-used there is a possibility that the heterogeneous catalysts are merely acting as precursors for homogeneous species.Polymeric analogues of Wilkinson's catalyst (Ph,P),RhCI continue to be investigated as hydrogena- tion catalysts the supporting medium being either polystyrene225 or silica.226 Other examples of hydrogenation catalysts include platinum on nylon227 and Rh"' on poly(acry1ic acid).228 Also a significant increase in the rate of the platinum-catalysed hydrogenation of dienes and alkynes has been noted on the addition of phosphorus-containing polymers.229 Polymeric hydroformylation catalysts have been synthesized using cobalt and rhodium carbonyl complexes.The reaction of phosphinated polystyrene with dicobalt octacarbonyl affords a dimeric species (20) which is an active hydro- formylation ~atalyst.'~' Phosphine substitution in RhCI(CO)(PPh,) using the polymeric phosphine also results in an active catalyst which can be re-used. Silica-supported rhodium carbonyl species where the anchoring ligand can involve P N or S as a donor atom also show catalytic activity in the liquid-phase hydroformylation of hex-1-ene under mild condition^.^^ '" B. M. Trost W. P. Conway P. E. Strege andT. J. Dietsche J. Amer. Chem. SOC.,1974 % 7165. z22 J. A. K. Howard S. A. R. Knox V. Riera B. A. Sosinsky F. G. A. Stone and P. Woodward J.C.S. Chem. Comm. 1974,673. 223 I. Dietzmann D. Tomanova and J. Hetflejs Coll. Czech.Chem. Comm. 1974 39 123; M. Mejstrikova R. Rericha and M. Kraus ibid. p. 139. 224 M. Capka and J. Hetflejs Coll. Czech. Chem. Comm. 1974 39 154. 225 M. Graziani G. Strukul M. Bonivento F. Pinna E. Cernia and N. Palladino Symposium on Heterogeneous and Homogeneous Catalysis Brussels 1974 abs. D3.1; J. M. Moreto J. Albaiges and F. Camps ibid. abs. D4.1. 2z6 I. V. Howell R. D. Hancock R. C. Pitkethly and P. J. Robinson ref. 225 abs. D5.2. 227 E. N. Rasadkina A. T. Telesheva I. D. Rozhdestvenskaya and I. V. Kalechits Kinetics and Catalysis 1973 14 1065. 228 Y. Nakamura and H. Hirai Chem. Letters 1974 809. 229 R. G. Muratova R. Z. Khairullina S. V. Shulyndin B. E. Ivanov and R. I. Izmailov Kinetics and Catalysis 1974 15 115. 230 G. 0.Evans C. U. Pittman jun.R. McMillan R. T. Beach and R. Jones J. Organo-metallic Chem. 1974 67 295. 23' R. D. Hancock I. V. Howell R. C. Pitkethly and P. J. Robinson ref. 225,abs. D5.1. Organometallic Chemistry-Part (i) The Transition Elements Ph 2 P -,CO -C? -PPh I’ 1 11’ \ c’ cc c 0 00 0 Polymer-supported analogues of benzyl manganese pentacarbonyl have little activity as hydroformylation catalysts.23 However they were prepared by a novel route i.e. nucleophilic attack by manganese pentacarbonyl anion on chloromethylated polystyrene. Polymer-supported iron molybdenum and tungsten carbonyl species have been prepared by analogous routes.233 Oxidative addition represents another novel route to polymer-metal species ; iodinated polystyrene reacts with M(PPh,) (M = Ni Pd or Pt) to afford a C-M 0-bond.234 The nickel complex when activated with BF,,OEt,-H,O is a good ethylene dimerization catalyst.34b Metal hydrocarbyls have been shown to undergo the general reaction support- OH + MR -+ support-O-MR,-* + RH (M = Ti Zr Nb Cr Mo and W; R = n-ally1 or benzyl; support = silica or y-al~mina).~~~ These supported species show increased catalytic activity compared with their homogeneous precursors ; the supported zirconium species are highly active ethylene poly- merization catalysts and the supported molybdenum and tungsten hydrocarbyls are active olefin disproportionation catalysts. The increased activities of the disproportionation catalysts have been confirmed by other worker^.^ 36 Treat-ment of silica or y-alumina with a solution of WMe also affords a disproportiona- tion catalyst which is more active than previously supported tungsten catalysts.237 Preliminary studies have been reported on a system whereby h4-(hexa-2,4- dienylacry1ate)tricarbonyliron can be copolymerized with various other mono-mers and subsequently can be converted into polymer-bound n-allyliron tetra- carbonyl cation.238 These n-ally1 sites react readily with nucleophiles to give the 1,4-addition products of the diene moiety thereby functionalizing the polymer.2’2 C. U. Pittman jun. and R. F. Felis J. Orgunomefallic Chem. 1974 72 389. 233 C. U.Pittman jun. and R. F. Felis J. Organomeralfir Chern. 1974 72 399. 234 (a) N. Kawata T. Mizoroki and A. Ozaki Bull. Chem. Soc. Japan 1974 41 1807; (h) T.Mizoroki N. Kawata S. Hinata K. Maruya and A. Ozaki ref. 225 abs. D2.1. 235 J. P. Candlin and H. Thomas ref. 1 p. 212. 236 Yu. 1. Ermakov B. N. Kuznetsov and A. N. Startsev Kinetics and Catalysis 1974 15. 539. 237 W. Mowat J. Smith and D. A. Whan J.C.S. Chem. Comm. 1974 34. 238 C. U. Pittman jun. Macromolecules 1974 7 396. J. D. Jones R. Pearce and R. Whelan 15 Metathesis Reactions of Olefins and Acetylenes The competitive alkylation reaction observed with the system WCl ,EtAICI in aromatic solvents has been shown to be critically dependent on the electron- donor power of the aromatic species.239 However it has been suggested that some of the WCl,-baSed co-ordination catalysts should be regarded as hetero- geneous catalysts.240 This may account for the variations in activity which have been reported for apparently identical systems.Other Group VI systems continue to be studied as metathesis catalysts. Oxygen has a promoting effect on the W(CO),(PPh,),EtAlCl whilst CO also has a beneficial effect on other molybdenum and tungsten catalysts.242 A detailed study of molybdenum halogenonitrosyl catalysts has appeared243 and the compounds MoCI,(NO),EtAICI have been shown to be the precursors of a highly active metathesis catalyst.244 The combination of W(CO) and a phenol has afforded the first active homo- geneous catalyst for the metathesis of alkyne~.~~’ With regard to alkyne meta- thesis it has been suggested that a butadiene-metal species could be involved as a reaction intermediate.246 cis-1,3-Dialkenylcyclopentanes have been synthesized by the metathetical co-dimerization of norbornene and aliphatic olefin~.,~’ Iridium and tungsten catalysts can be used though higher yields are obtained with the former.‘” L.Hocks A. J. Hubert and Ph. Teyssie Tetrahedron Letters 1974 877. 240 E. L. Muetterties and M. A. Busch J.C.S. Chem. Comm. 1974 754. 241 J. M. Basset Y. P. Taarit G. Coudurier and H. Praliaud J. Organometallic Chem. 1974 74 167. 242 L. Bencze A. Redey and L. Marko Hung. J. ind. Chem. 1973 4 453. 243 W. B. Hughes ref. 1 p. 192. 244 R. Taube and K. Seyferth Z. Chem. 1974 14 284. 245 A. Mortreux and M. Blanchard J.C.S. Chem. Comm. 1974 786. 246 R. E. Davis B. L. Barnett R. G. Amiet W. Merk J. S. McKennis and R.Pettit J. Amer. Chem. SOC., 1974 96 7108. 247 R. Rossi P. Diversi A. Lucherini and L. Porri Tetrahedron Letters 1974 879.

ISSN:0069-3030    

DOI:10.1039/OC9747100171

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

7 Organometallic Chemistry Part (ii) Main-group Elements ~ By K. SMITH Department of Chemistry University College of Swansea Swansea SA2 8PP 1 Introduction In the last Annual Report of organometallic compounds of the main-group elements alarm was expressed- at the growth in the literature of organometallic chemistry.’ Although the new journal announced then has subsequently folded (apologies!) the total growth continues. The quantity of literature to be covered means that this must be essentially an annual report but the ‘Specialist Periodical Reports’ bridge the gap since 1970.’ For the purpose of this review B Si and As have been included as metals whilst P Se and Te have somewhat arbitrarily been excluded; a triennial report of organophosphorus chemistry was given last year.2 Only compounds in which a metal-carbon bond is directly implicated in the chemistry under consideration are included.A monograph primarily intended for teachers3 provides an inexpensive ground- ing in organometallic chemistry but compounds of the main-group elements are under-represented. A short book concerning synthetic applications has also a~peared.~ A review of the interaction of organometallics with living systems,’ in essence a review of toxicity will frighten the squeamish but dis- cussion of medical and pesticidal applications and of the biologically important vitamin B coenzymes goes some way to redress the balance. Organometallic compounds have always played a central role in the develop- ment of theories of structure and bonding and recent work with trimethyl- silylmethyl- and related derivatives of metals6 has forced further revisions of ideas this time about organometallic chemistry itself.Amongst the fallen tenets are such favourites as ‘variable valency main group metals except in Group 5 ’ D. J. Cardin M. F. Lappert J. D. Smith and D. R. M. Walton Annual Reports (B) 1970 67 271. S. Trippett Annual Reports (B) 1973 70 268. F. R. Hartley ‘Elements of Organometallic Chemistry’ The Chemical Society London 1974. ‘J. M. Swan and D. St. C. Black ‘Organometallics in Organic Synthesis’ Chapman- Hall London 1974. J. S. Thayer J. Organometallic Chern. 1974 76 265. P. J. Davidson M. F. Lappert and R. Pearce Accounts Chern. Res. 1974 7 209. 195 196 K.Smith form stable alkyls only in the higher oxidation states' and 'metal centred radicals of main group organometallic compounds are transient species of free radical character,' disproved by the preparation of stable derivatives such as (1) and (2). [(Me Si) CHI ,Sn [(Me Si),CHI Sn (1) (2) The authors are careful to point out that the increased stabilities of these com- pounds are not due to any magical 'stabilizing' effect of the ligands but to the removal of favourable reaction pathways for example because of steric hindrance to approach to the metal centre and the absence of P-hydrogen atoms.6 2 Group I Lithium.-Volume 130 of the 'Advances in Chemistry Series' reviews several aspects of organolithium chemistry and a book on the subject has also appeared.' Replacement of hydrogen in relatively strong CH-acids by Li (lithiation) using commercially available organolithium reagents continues to be explored as a convenient synthesis of organolithium compounds especially in aromatic systems.Attention to experimental detail is important for good results as is shown by the failure to lithiate 1,3,5-trifluorobenzene with Bu'Li at -78 "C although the same reagent at -115"C or Bu"Li at -78"C was successful c F (ca.95 %) (ca.65 %) Reagents i Bu'Li (3.15 equivalents) -1 15 "C;ii Bu'Li (4 equivalents) -78 "C Scheme 1 (Scheme 1).8 Also use of appropriate conditions may permit the formation of different compounds by giving thermodynamic or kinetic control. Scheme 2 rcmovc solvent add Et,O --L (4) Reagents i Bu"Li THF-hexane Scheme 2 B.J. Wakefield 'Chemistry of Organolithium Compounds' Pergamon Oxford 1974. R. D. Howells and H. Gilman Tetrahedron Lerrers 1974. 1319. Organometallic Chemistry-Part (ii) Main-group Elements 197 shows the results of a study of lithiation of 2,4-dimethylquinoline (3)by Bu”Li.’ The authors conclude that in THF (5) is the kinetic and (4) the thermodynamic product whilst in Et,O the reverse order applies. They record no experiment which would confirm (4) as the kinetic product in Et,O although the other conclusions are correct. Similarly ring uersus side-chain substitution of 2-methyl- 4-substituted-1,3-thiazolesis dependent on temperature. lo The dependence of the ratio of methyl- :ortho-lithiation of 2-methylanisole on the bulk of the organolithium reagent (a bulkier one gives more methyl lithiation) suggests that earlier conclusions regarding the importance of prior complexation of the reagent to the substrate were incorrect.‘ Experimental factors also affect the proportions of dilithiation products from N-methylpyrrole where the use of optimum conditions presents a direct synthesis of N-methylpyrrole-2,4-di-carboxylic acid (50% yield) on treatment with solid C02.12 Treatment of 1-butene or (2)-or (E)-2-butene with Bu’Li in 1,2-bis(dimethylamino)ethane (TMEDA) provides a convenient route to ‘crotyl-lithium’.l3 From n.m.r. data and the stereochemistry of the products obtained on treatment with bromo- butane the authors conclude that the major conformation of the anion is (Z) and they are at pains to point out that this differs from earlier interpretations of the major conformation in ether.A CND0/2 calculation for the free gaseous anion predict^'^ that (Z)is favoured over (E)by 0.36 kcal mol- and the energy difference in solution cannot be much larger when equilibrium proportions in the region 60 :40or 85 15 are being suggested so it would not be surprising to find a change in the major conformer in changing the solvent system. There is continued interest in reagents which act as acyl anion equivalents (‘Umpolung’ of the carbonyl group).”” In this context protected cyanohydrin anions (6)give a higher proportion of conjugate addition to aP-enonesl6 than do lithiodithian derivatives (7) in the absence of Cu salts.Particularly interesting is the direct formation of the acyl carbanion (8) by reaction of bis(prop-2-yl) OCH(Me)OMe 0 I II R-C-C=N Li’ Pr’,NC-Li v-(6) (7) (8) formamide with lithium bis(prop-2-y1)amide.I Other acyl carbanion equivalents which are sometimes useful include lithio-aldimines prepared by addition of * See ‘Synthetic Methods’ Ch. 16. E. M. Kaiser and W. R. Thomas J. Org. Chem. 1974 39 2659. lo G. Knaus and A. I. Meyers J. Org. Chem. 1974 39 1192. I T. E. Harmon and D. A. Shirley J. Org. Chem. 1974 39 3164. l2 D.J. Chadwick J.C.S. Chem. Comm. 1974 790. R. B. Bates and W. A. Beavers J. Amer. Chem. SOC.,1974 96 5001. I4 A. Atkinson A. C. Hopkinson and E. Lee-Ruff Tetrahedron 1974 2023. For a review see D.Seebach and M. Kolb Chem. andInd. 1974 687. l6 G. Stork and L. Maldonado J. Amer. Chem. SOC.,1974 96 5272. R. R. Fraser and P. R. Hubert Can.J. Chem. 1974 52 185. 198 K. Smith organolithium compounds to isocyanides lacking a-H's,' and a-lithio-enol ethers formed by direct 1ithiati0n.l~ Derivatives of type (10; R',R2 # H) cannot be prepared by direct lithiation of R'R2CHXPh but a new route from the selenoketal derivatives (9)(Scheme 3) provides them.,' Li /SePh RuLi / R'R~C -+ R1R2C \ XPh XPh (X = S or Se) (9) (10) Scheme 3 Lithium-halogen exchange has been employed for in situ production of stereochemically defined vinyl-lithium derivatives but yields of methylation products were low (30-40 %) possibly because lithium-hydrogen exchange is competitive.2 gem-Dibromocyclopropanes also undergo lithium-halogen exchange with organolithium reagents to yield synthetically useful a-bromo- lithiocyclopropanes.2 Allyl-lithium compounds are generally less basic and more nucleophilic than their saturated analogues and this combination of properties allows them to undergo a coupling reaction with cycloalkyl halides.23 In this reaction the least hindered end of the ambident anion is substituted predominantly though mixtures are obtained.With carbonyl compounds on the other hand unless hindrance is very marked reaction occurs predominantly at the more substituted carbon.24 With gem-dichloroallyl-lithiumthere is a progression from entirely CCl attack on acetone to entirely CH attack on ben~ophenone.~' The powerful influence of solvation of the allyl-lithium species (intimate or solvent-separated ion pairs or 'naked' anion) is demonstrated by a total reversal of site attack of (11) on acetone in THF as the added complexing agent is changed from DABCO to [2,2,2] crown ether.26 G.E. Niznik W. H. Morrison and H. M. Walborsky J. Org. Chem. 1974 39 600. l9 J. E. Baldwin G. A. Hofle and 0. W. Lever J. Amer. Chem. SOC. 1974 96,7125; J. Hartmann M. Stahle and M. Schlosser Synthesis 1974 888. 2o W. Dumont P. Bayet and A. Krief Angew. Chem. Internat. Edn. 1974 13 804; D. Seebach and A. K. Beck ibid. 1974 13 806. M. Schlosser and E. Hammer Heh. Chim. Acta 1974 57 2547. 22 M. Braun and D. Seebach Angew. Chem. Internat.Edn. 1974 13 277; A. Schmidt and G. Kobrich Tetrahedron Letters 1974 2561. 23 W. D. Korte K. Cripe and R. Cooke J. Org. Chem. 1974 39 1168. 24 V. Rautenstrauch Helv. Chim. Acta 1974 57 496; for a review see G. Courtois and L. Miginiac J. Organometallic Chem. 1974 69 1 25 D. Seyferth G. J. Murphy and R. A. Woodruff J. Amer. Chem. SOC. 1974 96,501 1. 26 P. M. Atlani J. F. Biellmann S. Dube and J. J. Vicens Tetrahedron Letters 1974 2665. Organometallic Chemistry-Part (ii) Main-group Elements Notable new synthetic applications of organolithiums include reactions of (12) the product of thiophilic addition of RLi to a thioketen;27 the THF-promoted coupling of RLi with ArBr ;’* and the production of alkanesulphonyl chlorides [reaction (I)].” RLi + SO,Cl -+ RS0,Cl + LiCl (1) Reactions of aromatic radical anions have been reviewed3’ and a new method for their synthesis from arene and Bu”Li in HMPT has been developed.31 There is a great need for more bond-strength data in organometallic chemistry but little effort is devoted to this goal.It is therefore pleasant to report that thermochemical studies of some organolithium compounds have been carried Assumptions made in calculating the bond strengths mean that the absolute values are only approximate but the trends are nevertheless informative. The figures suggest a decrease in Li-C bond strength going from MeLi (61 kcal mol- I) to Bu‘Li (35 kcal mol- I) whilst PhLi has a bond strength of 63 kcal mol-1.32 Sodium Potassium Rubidium and Caesium.-Pure PhNa and PhK have been prepared from PhLi and appropriate metal alkoxides in he~ane-Et,O.~~ 3 Group11 Beryllium.-R,Be reacts with ketones by reduction (predominantly when possible) enolization and addition (rarely) processes.34 Magnesium.-Failure to achieve success in preparation of Grignard reagents is often due to the inactivity of commercial Mg so two new methods for preparing the metal in active form are particularly interesting.The most convenient involves the reaction of Na or K metal with MgCl, giving a Mg black powder which may be used as a suspension at low temperature^.^^ For example PhMgBr was readily prepared from PhBr at -78°C. The second method involves co-condensation of Mgatoms and solvent at -196 0C.36The slurry produced is also 27 E.Schaumann and W. Walter Chem. Ber. 1974 107 3562. 2a R. E. Merrill and E. Negishi J. Org. Chem. 1974 39 3452. 29 H. Quast and F. Kees Synthesis 1974 489. 30 N. L. Holy Chem. Rev. 1974 74 243. 31 E. J. Panek J. Amer. Chem. SOC.,1973 95 8460. ” T. Holm J. Organometallic Chem. 1974 77 27. 33 G. Thirase and E. Weiss J. Organometallic Chem. 1974 81 C1. 34 R. A. Anderson and G. E. Coates J.C.S. Dalton 1974 1171. 35 R. D. Rieke and S. E. Bales J. Amer. Chem. SOC.,1974 96 1775. 36 K. J. Klabunde H.F. Efner L. Satek and W. Donley J. Organometallic Chem. 1974 71. 309. 200 K. Smith very active but the method of its preparation will deter its use in all but a few appropriately equipped laboratories. It is notoriously difficult to obtain rate data for the preparation of Grignard reagents because of the unknown and variable effective area of the Mg surface.However competition experiments have given reliable comparative data.37 The small influence of the organic moiety on the rate of the reaction which these studies reveal appears to correlate best with a rate-determining electron transfer from Mg to the alkyl halide. Metallation of relatively strong CH-acids by Grignard reagents is less widely used than in the organolithium series but it is significant that the major metalla- tion product of 1-phenylpyrazole was different for the two reagents (Scheme 4).38 (major,40Yo) (only identifiable product 80 %) Reagents i Bu"Li; ii EtMgBr Scheme 4 Surprisingly 1-(o-bromopheny1)pyrazolegave a mixture of metal derivatives on reaction with Mg whilst 1-phenylpyrrole was not metalated by EtMgBr.Notable new synthetic applications of Grignard reagents include the prepara- tion of ketones from S-(2-pyridyl)thiocarboxylates or 2-pyridyl esters in THF ;39 stereospecific cis-addition to 1-(methy1thio)alkynes in THF catalysed by Cu' salts;40 and reduction of aryl and vinyl bromides (not chlorides) by Pr'MgBr activated with (C5H,),TiC1 .41 The mechanisms of addition of Grignard reagents to ketones have been reviewed.42 From a study of theeffects ofsolvent and added FeCI on the products of reaction of MeMgBr with benzophenone (Scheme 9,it was concluded that the OH OH II Ph2C?--CPh2d Ph,CO Ph,MeCOH (especially in THF. not in HMPT) (399:';) (<757") Reagents i MeMgBr FeCl,; ii MeMgBr Scheme 5 37 R.J. Rogers H. L. Mitchell Y. Fujiwara and G. M. Whitesides J. Org. Chem. 1974 39 857. 38 A. Marxer and M. Siegrist Heh. Chim.Acta 1974 57 1988. 39 M. Araki S. Sakata H. Takei and T. Mukaiyama Bull. Chem. SOC.Japan 1974 47 1777. 40 P. Vermeer C. DeGraaf and J. Meijer Rec. Trav. chim. 1974 93 24. 4' E. Colomer and R. Corriu J. Organometallic Chem. 1974 82 367. 42 E. C. Ashby J. Laemmle and H. M. Neumann Accounis Chem. Res. 1974,7. 272. 0rganome ta 11ic Chemistry-Part ( ii) Main-group EIemen ts 20 I pure Grignard reagent reacts in a polar manner but that transition-metal impurities promote single-electron-transfer processes.43 Allylic Grignard- thioketone condensation^^^ and reactions of vinylallenic Grignard reagents with ketones45 both involve rearrangement of the ‘allylic’ group during reaction.Aromatic ketones such as 1-indanone and 1-tetralone form tricarbonyl- chromium complexes which can be resolved into their enantiomers ;the reaction of these complexes with Grignard reagents followed by photochemical removal of chromium gives the optically pure tertiary Clearly in cases where the complexes are more easily resolved than the product alcohols and where the photochemical step is not deleterious this technique could be of great utility. Although ate-complexes such as LiBMe and Li,MgMe2 + attack 4-t-butyl- cyclohexanone mainly from the equatorial side LiAlMe gives mainly axial attack.,’ PhMgBr and PhCH,MgBr attack (13; R’ = Me R2 = H) initially at the ketone group although it is difficult to prevent further attack.,* However (13; R’ = R2 = Me or R’ = Ph R2 = H) do show some tendency for initial attack at the ester function.Compounds (14) and (15) are the major products R1COCHR2C02Et ArRC(0H)COAr’ ArRC(OH)C(OH)Ar’R (13) (14) (15) from reactions of benzils ArCOCOAr’ with 1 mole or 2 moles respectively of RMgX.49 The chemiluminescence induced by molecular oxygen of aryl Grignard reagents appears to involve brominated biphenyls as the emitting species 50a but the newly discovered chemiluminescence on reaction with benzoyl peroxide is believed to involve triphenylmethyl radicals though no mechanism for their formation is given.50h Although (16) is a stable vinyl Grignard reagent all attempts to prepare (17) resulted in ring-cleavage product (18).51 43 E.C. Ashby and T. L. Wieseman J. Amer. Chem. SOC. 1974 96,71 17. 44 M. Dagonneau and J. Vialle Tetrahedron 1974 30 415. 45 M. L. Roumestant J. P. Dulcere and J. Gore Bull. SOC. chim. France 1974 1124. 46 A. Meyer and G.Jaouen J.C.S. Chem. Comm. 1974 787. ‘’ E. C. Ashby L.-C. Chao and J. Laemmle J. Org. Chem. 1974 39 3258. 4n F. Castelli and P. Canonne Bull. SOC.chim. France 1974 317. 49 F. G. Badder A. F. M. Fahmy and N. F. Aly J. Indian Chem. SOC. 1973,50 586. 50 P. H. Bolton and D. R. Kearns (a)J. Amer. Chem. SOC.,1974 96,4651 ; (b)J. Phys. Chem. 1974 78 1896. J.-L. Derocque and F.-B. Sundermann J. Org. Chem. 1974 39 141 1.202 K. Smith Calcium Strontium and Barium.-Readily available organocalcium compounds have been used to metallate stronger CH-acids such as fluorene indene and l-alkyne~,’~ a method which may develop into a useful synthesis of a variety of organocalcium compounds. Zinc Cadmium and Mercury.-The applications of organozinc compounds in synthesis have been re~iewed.’~ The ready dehalogenation of organic halides (40-85% yields) by treatment with Zn powder in DMF followed by water suggests a powerful effect of the solvent because organozinc compounds (the presumed intermediates) are normally difficult to prepare from the non-activated It remains to be seen for what other applications these organozinc solu- tions in DMF may be used.The system Et,Zn-CHI is a convenient reagent for iodocyclopropanation of alkenes in the absence of solvent.” The reaction is complicated by further reactions of the product so the yields are moderate (35-70”/,). Organocadmium compounds react with benzylhalides to yield predomin- antly coupled products ;some of the factors which influence the reaction have been investigated.’6 Of the two solvents studied (Et,O benzene) benzene is the better but sometimes alkylation of this solvent is a significant competing process. Perhaps an aliphatic hydrocarbon solvent or co-solvent would prove useful. Direct mercuration utilizing Hg” salts such as the trifluoroacetate acetate or chloride continues to be investigated. trans-1,2,3-Triphenylcyclopropane(19) may be successfully mercurated in a phenyl ring,” but mercuration of 0-or p-nitrophenylcyclopropane results in cleavage of the three-membered ring.” All attempts to mercurate (20)or (21) resulted in benzylmercury derivative^.^^ 52 I.E. Paleeva N. I. Sheverdina and K. A. Kocheshkov Zhur. obshchei. Khim. 1974 44 1135 (Chem. Abs. 1974 81 91 609s); K. A. Allan B. G. Gowenlock and W. E. Lindsell J. Organometallic Chem. 1974 65 I ; N. Kawabata. H. Yoshimura. and S. Yamashita Bull. Chem. SOC.Japan 1974 47 2822. 53 J. Furukawa and N. Kawabata Adv. Organometallic Chem. 1974 12 83. 54 G. Mehta and S. K. Kapoor J. Organometallic Chem. 1974 66 C33. ” S. Miyano and H. Hashimoto Bull. Chem. SOC.Japan 1974 47 1500. 56 G. Emptoz and F. Huet Bull. SOC. chim. France 1974 1695.57 Yu. S. Shabarov S. G. Bandaev and L. D. Sychkova Zhur. obshchei Khim. 1974,44 1653 (Chem.Abs. 1974,81 91 666h). 58 Yu. S. Shabarov T. S. Oretskaya and S. S. Mochalov Zhur. obshchei Khim. 1974 44 11 38 (Chem.Abs. 1974,81 91 674;). 59 V. A. Nikanorov V. I. Rozenberg Yu. G. Bundel and 0.A. Reutov Izvest. Akad. Nauk S.S.S.R. Ser. khim. 1974,486 (Chem. Abs. 1974,81,63 732h). Organometallic Chemistry-Part (ii) Main-group Elements 203 Since mercury substitution does not drastically deactivate a benzene ring to further electrophilic attack it is possible to obtain poly- and per-mercurated aromatic compounds.60 It has previously been observed in a number of reactions that aryl groups are transferred from tin more readily than are alkyl groups and this property has been utilized in the development of a process for synthesis of diarylmercury compounds without wastage of aryl groups [reaction (2)J6' Et,SnAr + Hg(OAc) -+ Et,Sn(OAc) + Ar,Hg (2) Use of mercury(I1) ( + )-tartrate in oxymercuration-demercuration of styrene gave (+)-1-phenylethanol in ca.30 % optical yield but the reaction was very slow and chemical yields were consequently low (cu. 30% after 1 month at 25 oC).62 by-Unsaturated urethanes such as (22) are regiospecifically oxymercurated (Hg goes fi-to N) by Hg(NO,) ,63 but that such a 'specific directing effect' is the result of prior co-ordination of Hg to alkoxycarbonyl- or cyano-groups is disputed in another which concludes that the stereochemistry of the major product of oxymercuration of (23) is as shown (24).OMe I Electroreduction of 1,o-dibromoalkanes at a Hg cathode yields Br-free dialkylmercury compounds in moderate to good yields.6s This poses an interest- ing mechanistic question since the same products are not formed in significant yields from monobromoalkanes. The authors speculate that disproportionation of intermediate (RHg) to R,Hg and Hgo occurs readily only near the electrode surface and that the second Br is essential to hold the molecule in position; having performed its function like the male of that notorious species of spider it is then quietly eliminated. Direct conversion of alkenylcopper compounds into bromoalkenes by treat- ment with bromine is difficult but the desired result can be achieved by first converting it into the organomercurial.66 When Br in pyridine is used to cleave 'O G.B. Deacon and G. J. Farquharson J. Organometallic Chem. 1974 67 C1. 6' 0. P. Syntkina E. M. Panov V. I. Lodochnikova and K. A. Kocheshkov Doklad-y Akad. Nauk;S.S.S.R. 1974,216 333 (Chem. Abs. 1974,81,91 673h). 62 T. Sugita Y. Yamasaki 0.Itoh and K. Ichikawa Bull. Chem. SOC.Japan 1974 47 1945. '' G. R. Krow and D. M. Fan J. Org. Chem. 1974,39 2674. b4 N. S. Zefirov and L. G. Gurvich J. Organometallic Chem. 1974 81 309. 65 J. Casanova and H. R. Rogers J. Amer. Chem. SOC.,1974 96,1942. 66 J. F. Normant C. Chint G. Cahiez and J. Villieras Synthesis 1974 803. 204 K. Smith the latter the process occurs with retention of configuration. A Pdo complex catalyses Hg extrusion from bis(alkeny1)mercury compounds to give 1,3-dienes the predominant product again having retained stereochemistry (Scheme 6).67 Scheme 6 Strangely although the authors quote high yields based on Pdo (> lOOOo;/o) they do not record yields based on what to organic chemists may often be the most critical component -the alkenyl group! A further development in the chemistry of halogenomethylmercury compounds has been the preparation of functionalized derivatives PhHgCX,Y (X = halide; Y = CO,Me CONMe, SO,Ph etc.).68These act as precursors for functional carbenes :CXY but they decompose slowly and product yields are often only moderate.The usual procedure for replacement of HgX by H after oxymercuration involves treatment with borohydride.In DMF saturated with 0, however this reagent replaces HgX by OH in good yield.69 A radical mechanism is proposed. An alternative approach to demercuration involves treatment of the organomercury compound with Li powder in THF at low temperature followed by hydrolysis with MeOH.70 4 Group I11 Boron.-Recent books’l and volume 7 (1973) of ‘Intra-Science Chemistry Reports’ have concentrated on synthetic applications of organoboranes and to some extent on hydroboration ;now a reviewer has expressed the opinion that the wealth of useful applications requires a renewed effort to discover new syntheses of organ~boranes.~ In the review of available methods there is much speculation and suggestion with the stated intention of providing a base on which future research might be founded.It is interesting therefore to record that some progress has already been made. Alkyl-lithiums react with 9-methoxy-9-bora- bicyclo[3,3,l]nonane (9-methoxy-9-BBN) without significant isomerization of the alkyl group (even with Bu‘Li) although with 9-chloro-9-BBN isomerization is a pr~blem.’~ The reaction is also applicable to other RiBR2 ;unfortunately ” E. Vedejs and P. D. Weeks Tetrahedron Letters 1974 3207. 68 D. Seyferth and R. A. Woodruff J. Organometallic Chem. 1974 71 335. 69 C. L. Hill and G. M. Whitesides J. Amer. Chem. Soc. 1974 96 870. 70 V. G. Aranda J. Barluenga A. Ara and G. Arsenio Synthesis 1974 135. ’’ H. C. Brown ‘Boranes in Organic Chemistry’ Cornell Univ. Press Ithaca New York 1972; G.M. L. Cragg ‘Organoboranesin Organic Synthesis’ Dekker New York 1973. ’* K. Smith Chem. SOC.Rev. 1974 3,443. 73 G. W. Kramer and H. C. Brown J. Organometallic Chem. 1974 73 1. Organometallic Chemistry-Part (ii) Main-group Elements no comment on degree of redistribution (to RiB R’BRZ) was made. Applica- tions of ‘1,1,2-trimethylpropylborane’(the~ylborane)~~ and the synthesis of diamondoid compounds using allylboranes’ have been reviewed. The most significant development in the hydroboration reaction has been the application of halogenoboranes e.g. ‘CIBH,’ and ‘Cl,BH’ in high-yield syntheses of alkenyl- or alkyl-halogenoboranes?6 Further results for the use of BH,-SMe in hydr~boration,’~ and full details of the preparation and reactions of 9-BBN78 are also useful.The major product from hydroboration-oxidation of l-chloronor-bornene is (25),79 in contrast to a surprising earlier claim. Interestingly though hydroboration of 2-chloronorbornene with 9-BBN proceeds mainly via (26) 2-bromonorbornene yields predominantly (27) as the first intermediate presum- ably because of the greater steric requirements of Br.” (35) (26) (27) 1,l-Bis(dialkoxybory1)alkenes are available in moderate yields from the reaction of triborylmethyl carbanions with aldehydes or ketones.’ Temperature-dependent n.m.r. studies of (28) using the Pr‘ group as a diastereotopic probe verify that triarylboranes stereoisomerize by a ‘two-ring-flip’ mechanism.82 (2x1 Since the demonstration of high-yield syntheses of ketones and tertiary alcohols by reactions of trialkylcyanoborates with trifluoroacetic anhydride,83 74 E.Negishi and H. C. Brown Synlhesis 1974 77. l5 B. M. Mikhailov and V. N. Smirnov Izvest. Akad. Nauk S.S.S.R. Ser. khim. 1974 1137 (Chem. Abs. 1974,81,49 7162). 76 H. C. Brown and N. Ravindran J. Organornetallic Chem. 1973 61 C5 and earlier work. l7 C. F. Lane,J. Org. Chem. 1974 39 1437. 7M H. C. Brown E. F. Knights and C. G. Scouten J. Amer. Chem. SOC., 1974 % 7765. 79 R. J. Muller and B. L. Murr J. Org. Chem. 1974 39 2810. Y. Yamamoto H. Toi and I. Moritani Chem. Letters 1974 485. D. S. Matteson and P. B. Tripathy J. Organometallic Chem. 1974 69 53. 82 J. P. Hummel D. Gust and K. Mislow J. Amer. Chem. Soc. 1974 % 3679. 83 A.Pelter M. G. Hutchings and K. Smith Chem. Comm. 1970 1529; 1971 1048 (two papers on the same page). 206 K.Smith much attention has been focused on ate-complexes of boron. In the cyanoborate reaction itself all migrations occur with retention of stereochemistry and migra- tory aptitudes of alkyl groups decrease primary > secondary > tertiary.84 The most widely studied analogous reactions involve trialkylalkynylborates and electrophiles [first step shown in reaction (3)] and these were widely discussed in the last ‘Annual Reports’ (1973). M+[RiBC-CR2]-+ EX -+ MX + R:BCR’=CR2E (3) The more interesting new electrophiles include acetylpyridinium chloride (regiospecific alkylation at the 4-position of the pyridine ring),85 dihalogeno- methanes (double migration leading to substituted allylboranes),86 and chloro- methoxymethane (synthesis of substituted ally1 methyl ethers).87 The iodination reaction of trialkylalkynylborates has been extended to a synthesis of terminal alkynes by use of trialkylethynylborates.88 The lithio-derivative of 3-chloropropyne reacts with trialkylboranes to give intermediates which hydrolyse to l-alkylallene~.~~ Whilst this is a convenient synthesis of such compounds the nature of the stable intermediate is open to some doubt.The authors propose (29) but such compounds should easily rearrange to (30). Since the spectroscopic evidence for (29) is not conclusive and since (29) would be expected to undergo allenyl-propargyl rearrangement on reaction with aldehydesg0 (which it apparently does not ”) (30) would at least seem to be a possibility for the intermediate.R,BCR=C=CH R,BCH,CECR (29) ( 30) The reaction of lithio-aldimines with R,BC1 and then an electrophile provides a new synthesis of unsymmetrical ketone^.^ 1-Lithio-1,l-bis(pheny1thio) alkanes react with trialkylboranes to give a spontaneous first migration,92 and a HgC1,-induced second migration (Scheme 7).93 Oxidation at the appropriate RiB + LiCR2(SPh) + R:BCR’R2SPh + LiSPh R;R~COH 2R~BXCR~R Reagents i HgCl,; ii [O] Scheme 7 84 A. Pelter M. G. Hutchings and K. Smith J.C.S. Chem. Comm. 1973 186. 85 A. Pelter and K. J. Gould J.C.S. Chem. Comm. 1974 347. 86 A. Pelter and C. R. Harrison J.C.S. Chem. Comm. 1974 828. *’ P. Binger and R.Koster Synthesis 1974 350. M. M. Midland J. A. Sinclair and H. C. Brown J. Org. Chem. 1974 39 731. ” T. Leung and G. Zweifel J. Amer. Chem. SOC.,1974 96,5620. 90 E. Favre and M. Gaudernar J. Organometallic Chem. 1974,76,297,305,and references cited therein. 9’ Y. Yamamoto K. Kondo and I. Moritani Tetrahedron Letters 1974 793. q2 S. Yamamoto M. Shiono and T. Mukaiyarna Chem. Letters 1973 961. 93 R.J. Hughes A. Pelter and K. Smith J.C.S. Chem. Comm. 1974 863. Organometrlllic Chemistry-Part (ii) Main-group Elements 207 stages gives ketones or carbinols respectively. MeOS0,F-induced rearrangement of aryltrialkylborate anions provides a convenient synthesis of ortho-dialkyl-aromatic or dihydroaromatic corn pound^.^^ Methoxide-induced rearrangement of thexylbis( 1-iodoalkeny1)boranes is followed by elimination of the boron unit to yield substituted 1,2,3-b~tatrienes,~' whilst bromination-rearrangement of some borapolycyclanes has led to some interesting new organoborane struc- ture~.~~ Trialkyl- and triallyl-boranes react with bicyclobutane according to Scheme 8 ;97 there is no allyl-rearrangement in cases where R is a substituted ally1 group.Scheme 8 Hydrolysis of trialkylboranes is catalysed by 2,2-dimethylpropanoic acid (pivalic acid) to the extent that reaction with water occurs at room temperat~re.~~ Another simple dealkylation procedure involves treatment with an alkanethiol [reaction (4)]. It has now been shown that the ease of displacement of groups RiB + R2SH -+ RlBSR2 + R'H (4) from the same boron atom in this reaction is tertiary > secondary > primary.99 The reaction involves radicals which is probably also true of the reaction of trialkylboranes with Fe"' salts which provide synthetic routes to RCl and RSCN.'" Aluminium Gallium Indium and Thallium.-Activated Al produced by reduction of AlC1 with K or Na may be used for the direct synthesis of 'Ph,Al,X,' from PhX.lo' Deuterioalumination of 1,l-dimethylindene using 'BulAlD' followed by deuterolysis gives the cis-dideuterioindane derivative suggesting that hydro- alumination of alkenes occurs cis (compare hydroboration of alkenes hydro- alumination of alkynes) and hydrolysis occurs with retention."' Al[(CH,),-94 E.Negishi and R. E. Merrill J.C.S. Chem.Comm. 1974 860. " T. Yoshida R. M. Williams and E. Negishi J. Amer. Chem. SOC. 1974 96 3688. " Y. Yamamoto and H. C. Brown J. Org. Chem. 1974 39 861. 97 B. A. Kazansky Yu. N. Bubnov S. B. Zotova N. M. Abramova V. G. Kiselev and B. M. Mikhailov Tetrahedron Letters 1974 567. R. Koster H. Bellut and W. Fenzl Annalen 1974. 54. q9 A. G. Davies T. Maki B. P. Roberts A. Pelter and D. N. Sharrocks J. Organometallic Chem. 1974 82 301. loo A. Arase Y. Masuda and A. Suzuki Bull. Chem. SOC. Japan 1974 47 251 1. lo' R. D. Rieke and L.-C. Chao Synth. React. Inorg. Metal-org. Chem. 1974 4 101 (Chem. Abs. 1974 81 25 7172). lo' J. J. Eisch and K. C. Fichter J. Amer. Chem. SOC.,1974 96 6815. 208 K. Smith CH=CH,] is monomeric whilst the saturated analogue is dimeric showing a powerful interaction of the n-bond with the metal.'03 Crystal structure analysis Ph Ph,Al-C=CPh I PhCrC-AlPh C Ill C Ph of (Ph,AlCrCPh) reveals not the presupposed structure (3l) but a structure resembling (32).'04 The presence of a normal C=C bond length suggests that the interpretation as a n-complex of A1 to the site of greatest electron density is an oversimplification.An extensive paper about heats of formation of A1 alkyls and related compounds concludes that AH,"values obtained by combustion calori- metry are unreliable because of high absolute errors in measurements.lo5 Calorimetry of redistribution reactions is advocated ;unfortunately the results have not been used to determine bond strengths.Under forcing conditions (sealed tube 100-200 "C) tertiary alcohols ketones and carboxylic acids are exhaustively methylated by AlMe .Io6 Yields are not always given but appear generally to be in the range 50-100% rearrangement or elimination products sometimes also being formed. Addition of vinylalumin-ium compounds to ally1 halides catalysed by CuCl provides a useful synthesis of trans-1,6dienes (Scheme 9). *' Trialkylgallium compounds can be prepared R' H R' H /I\/ R'C-CH + 'RSAlH' -+ \ C=C 3 c=c /\ /\ H AIR H CH,CH=CH Reagents i CH =CHCH,Br CuC1-hexane Scheme 9 free from base (e.g. ether) by reaction of GaCl with RLi in hydrocarbon sol- vents.'O8 Io3 T. W. Dolzine and J. P. Oliver J. Amer. Chem. SOC.,1974. 96,1737. Io4 G. D. Stucky A.M. McPherson W. E. Rhine J. J. Eisch and J. L. Considine J. Amer. Chem. SOC.,1974 % 1941. '05 M. B. Smith J. Organometallic Chem. 1974 76 171. Io6 D. W. Harney A. Meisters and T. Mole Austral. J. Chem. 1974 27 1639; A. Meisters and T. Mole ibid. pp. 1655 1665. lo' R. A. Lynd and G. Zweifel Synthesis 1974 658. Io8 R. A. Kovar G. Loaris H. Derr and J. 0.Callaway Znorg. Chem. 1974 13 1476. Organometallic Chemistry-Part (ii) Main-group Elements The recent surge of interest in organothallium ~hemistry'~' seems to have subsided. However the trans-diamination of alkenes with secondary aliphatic amines (or with aniline) in the presence of a molar proportion of TI(OAc) almost certainly involves an initial aminothallation process. ''O 5 GroupIV Silicon.-The stable tervalent Group IV metal alkyls M[CH(SiMe,),J (M = Si Ge or Sn) referred to previously were synthesized by irradiation (in hexane) of the product of the reaction of LiCHfSiMe,) with Si,CI, GeCl, or SnCI .' '' The reaction of (33) with Li metal produces (34);' ' the effect of ring size on the direction of ring-closure cannot be assessed because this is the more stable primary alkyl-lithium compound.However in the chloroplatinic-acid-catalysed cyclic intramolecular hydrosilylation of (35; n = 3) the product (60% yield) contained a 9 1 ratio of cyclopentane :cyclohexane whilst (35 ; n = 4)gave a 1 1 ratio of cyclohexane :cycloheptane (70"/ yield).' ' Qualitatively these results resemble those for cyclic hydroborations of dienes,' ' and probably reflect a kinetic rather than a thermodynamic product distribution.Cr(CO) acts as a photocatalyst for 1,6hydrosilylation of 1,3-dienes ; the products are allylsilanes (Scheme lo) apparently produced in almost quantitative yields although no figures are given.' l4 Scheme 10 The stereochemical course of substitution reactions at Si by RM (M = Li or MgX) may depend upon the natures of R the solvent the leaving group and the other groups bound to silicon.' '' Thus in THF or 1,2-dimethoxyethane (glyme) all types of Grignard reagent substicute Si alkoxides with retention at Si whilst in Et,O this is true for alkyl- and aryl- but not for allyl-MgBr (the latter gives See A. McKillop and E. C. Taylor Chem. in Britain 1973 9 4. 'lo V.G. Aranda J. Barluenga and F. Aznar Synthesis 1974 504. J. D. Cotton C. S. Cundy D. H. Harris A. Hudson M. F. Lappert and P. W. Lednor J.C.S. Chem. Comm. 1974 651. l2 T. W Dolzine A. K. Hovland and J. P. Oliver J. OrganometafficChem. 1974,65 Cl. 'I3 J. V. Swisher and H. H. Chen J. Organometallic Chem. 1974,69 83. 'I4 M. S. Wrighton and M. A. Schroeder J. Amer. Chem. SOC.,1974 96,6235. G. Chauviere R. Corriu A. Kpoton and G. Lanneau f. Organometallic Chem. 1974 73 305. and references cited therein. 210 K.Smith inversion).' l5 Strangely product yields (as opposed to proportions) are recorded only for reactions with allyl- and benzyl-MgBr in which cases the yields are reasonable (60-90%). A new synthesis of alkynylsilanes [reaction (5);R = Bun or Ph ; n = 1,2 or 31 proceeds in 60-80 % yields.' ' Et ?N CUCl Cdl .RCGCH + Me,,SiCl,_, --+ RC-CSiMe,Cl,- (5) 150 "C dutocl.l\e. IW llOh Reactive organosilicon species containing 'double bonds between Si and C 0,or other atoms have attracted much attention and a review of the topic has recently appeared.' l7 In the fascinating reaction of(36) with an excess of benzalde- hyde at 50O0C >Si=Si< >Si=C< and >Si=O species are all postulated as intermediates (Scheme 1 l).'l8 (36) (Me,SiO) +-[Me,Si=O] +-+ Me#-CHPh phCHO t[Me,Si=CHPh] t [ A-LHPh 1 I [Me,Si=O] -+ (Me,SiO) + PhCH=CHPh Scheme 11 Another transient Si-containing species is silylene :SiH ,generated by pyroly- sis of disilane and this adds to trans-2-trans-4-hexadiene to yield a 1 1 mixture of cis-and trans-2,5-dimethylsilacyclopent-3-enes, suggesting a biradical path- way.' l9 a-Cyanoalkylsilanes prepared by (Ph,P),RhCl-catalysed hydrosilylation of ag-unsaturated nitriles may be lithiated by LiNPri .I2' The anion reacts with 'I6 G.Deleris J. Dunogues and R. Calas J. Organometallic Chem. 1974 80 C45. l7 L. E. Gusel'nikov N. S. Nametkin and V. M. Vdovin Uspekhi Khim. 1974 43 1317 (Chem. Abs. 1974,81,91 600 g). 118 T. J. Barton and J. A. Kilgour J. Amer. Chem. SOC. 1974 96,2278. '19 P. P. Gaspar and R.-J. Hwang J. Amer. Chem. SOC.,1974 96,6198. I. Ojima and M. Kumagai Tetrahedron Letters 1974 4005. Organome talk Chemis try-Par t ( ii) Main-group Elements 21 1 carbonyl compounds to yield new a/3-unsaturated nitriles.New syntheses of vinylsilanes with a variety of substitution patterns have been developed.”’ These are easily converted into ketones by an epoxidation-hydrolysis sequence and this concept has been extended to annelation reactions (Scheme 12).12’ (-J +iSiMe,1 OLi SiMe 0 -a I epoxidize and hydrolyse Scheme 12 Treatment of cis-substituted vinylsilanes with halogens results in the formation of a dihalide by a trans-addition to the double bond ; the di-iodo-compounds are unstable and undergo a cis-elimination of R,SiI to give ~is-iodoalkenes.’~~ However the dibromides are stable until base (MeO-) is added whereupon they undergo a trans-elimination of R,SiOMe + Br -to give trans-bromoalkenes. The orientations of these eliminations (spontaneous cis ; base-induced trans) are the same as for the corresponding boron corn pound^.^' Bromoalkenes of type (37) are formed in high yield by the reaction of anhydrous HBr with alkynyl- silanes.24 Some rearrangement reactions in organosilicon chemistry [for example (38)-(39)] have been revie~ed.’’~ R OH \ I C=CH RiSiCR; RiSiOCHRf / Br (37) (38) (39) Germanium Tin and had.-A review about cycloalkanes containing Ge Sn and Pb has appeared,126 and the first authenticated stannacyclobutane (40) has since been prepared in 20% yield by the reaction of (Me,Si),CBrLi with 12’ B.-T. Grobel and D. Seebach Angew. Chem. Internat. Edn. 1974 13 83. L22 G. Stork and M. E. Jung J. Amer. Chem. SOC.,1974 96 3682.IL3 R. B. Miller and T. Reichenbach Tetrahedron Letters 1974 543. R. K. Boeckman and D. M. Blum J. Org. Chem. 1974,39 3307. 125 A. G. Brook Accounts Chem. Res. 1974 7,77. 26 B. C. Pant J. Organometallic Chem. 1974 66 321. 212 K. Smith Me,SnCl .127 P-Chlorovinyl derivatives of Ge and Sn have been obtained by the reaction of Bu,MH (M =Ge or Sn) with bis(/3-chlorovinyl)mercury,i28 Me,Si SiMe, \/ C Bu,Sn H Bu,Sn H /\ \/ \/ Me,Sn SnMe c=c \/ /\ /c=c\ C H SnBu H Li Me,Si /\SiMe (40) (41) (42) whilst monoalkyl derivatives of Sn" are obtained on reaction of alkyl iodides with Sn" bis(acetylacetonate).' 29 The readily available distannylethene (41) is easily converted into (42) by reaction with Bu"Li in THF at -78 "C; alkylation of (42) with an alkyl halide gives an alkenyltributylstannane,which on oxidation with Pb(OAc) yields an a1k~ne.l~'The reagent (42) is therefore a masked ethynyl anion and by prior conversion into the cuprate it can also be used to effect conjugate addition of an ethynyl group to ab-enones.Nitrodestannylation of ArSnMe ,by treatment with NOCl followed by oxidation is a convenient route to aromatic nitro- compounds.''Aryl-lead tricarboxylates react readily with some aromatic substrates notably polymethylbenzenes to provide a useful route to the corres- ponding mixed biaryl~.'~' The Karplus-type dependence of '9Sn-' 3C vicinal coupling constants on molecular geometry has been more precisely defined by analysis of n.m.r. data for a number of molecules with fixed geometry (Me,Sn derivatives of norbornane adamantane etc.).', 6 GroupV Arsenic Antimony and Bismuth.-Acetylenic organoarsenic compounds have been reviewed.'34 The first all-cis-cyclotriarsane (43) has been synthesized FA? MeC .,-1-AS MeC(CH,AsI,) H* AsMe, /-A; Me As (44) Me Me (43) (45) D. Seyferth and J. L. Lefferts J. Amer. Chem. SOC.,1974 96,6237. 1'8 A. N. Nesmeyanov and A. E. Borisov Izuest. Akad. Nauk S.S.S.R. Ser. khim. 1974 1667 (Chem. Abs. 1974,81 105 651p). I. Wakeshirna and I. Kijima J. Organometallic Chem. 1974 76 37. I3O E. J. Corey and R. H. Wollenburg J. Amer. Chem. SOC.,1974 96,5581. C. Eaborn I. D. Jenkins and D. R. M. Walton J.C.S. Perkin I 1974 870. 13' H. C. Bell J. R. Kalman J. T. Pinhey and S.Sternhell Tetrahedron Lerfers 1974 857. 133 D. Doddrell I. Burfitt W. Kitching M. Bullpitt C.-H. Lee R. J. Mynott J. L. Consi-dine H. G. Kuivila and R. H. Sarma J. Amer. Chem. SOC.,1974 96 1640. 134 I. N. Azerbaev Z. A. Abramova and Yu. G. Bosyakov Uspekhi Khim. 1974 43 1384 (Chem. Abs. 1974,81 136 202x). Organometallic Chemistry-Part (ii) Main-group Elements (54”//, yield) by the reaction of (44)with Na in THF.13’ Compound (45),which has been prepared by photochemical addition of Me,AsAsMe to 2,2,4,4-tetramethylbicyclobutane acts as a chelating or bridging bidentate ligand. 36 ‘35 J. Ellermann and H. Schossner Angew. Chem. Internat. Edn. 1974 13,601. 136 W. R. Cullen and J. T. Price Canad. J. Chem. 1974 52 1108.

ISSN:0069-3030    

DOI:10.1039/OC9747100195

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

8 Electro-organic Chemistry By J. H. P. UTLEY Department of Chemistry Queen Mary College Mile End Road London El 4NS 1 Introduction The choice of material in this Report is intended to highlight new developments and point but briefly at areas where consolidation has taken place. As before the chapter is organized according to the nature of the species which is believed to be involved in the initial electrode reaction. The compilation of this Report has been greatly helped by a current-awareness service provided by Ann Jarvis (Q.M.C. Library). 2 AnodicProcesses Oxidation of Neutral Organic Compounds.-Alkanes Alkenes and Alkynes. The functionalization of alkanes by anodic oxidation in strong acids such as fluorosulphonic acid was discussed in the corresponding 1973 Report (p.299). Contrary to the original report,' a suggestion has been made2 that protonation of the alkanes prior to electron transfer is not necessary. The case hinges on the observations that (i) addition of base (NaS0,F) apparently assists oxidation (E+ values become slightly less anodic) (ii) I-IF SO, and H,S04 were detected in the anolyte and (iii) the likely presence of SO (a strong Lewis acid in FS0,H) demands consideration of a chemical cleavage of alkanes to carbenium ions. However in trifluoroacetic acid solution oxidation3 of cyclohexane is assisted by the addition of a stronger acid (FS0,H). Activation towards anodic oxidation was also achieved using CF,S03H CH,SO,H and mixtures of CH,Cl and FS0,H. The product of preparative-scale electrolysis in CF,CO,H was cyclo- hexyl trifluoroacetate.A strongly acidic solution is not essential for anodic oxidation of alkanes. High anode potentials [ca.3.6 V (us. Agl Ag')] may be reached in dry acetonitrile and the usefulness of this is well demonstrated4 by the acetamidation reactions outlined in Scheme 1. The fragmentati~n~~ of branched alkanes and the position of substitution in straight-chain esters4b is consistent with the formation of J. Bertram J. P. Coleman M. Fleischmann and D. Pletcher J.C.S. Perkin If 1973 374. F. Bobilliart A. Thiebault and M. Herlem Compt. rend. 1974 278 C 1485. H. P. Fritz and T. Wiirminghausen J. Electroanalyt. Chem. Interfacial Electrochem. 1974 54 181. (a) J. Y. Becker L. L. Miller and T. Siegel J.C.S.Chem. Comm. 1974 341; (6) L. L. Miller and V. Ramachandran J. Org. Chem. 1974 39 369. 215 216 J. H. P.Utley Reagents i Pt anode 3.6 V (us. AglAg') MeCN-Et,NBF, -45 "C 2.3 F mol~; ii H,O Scheme 1 carbenium ions following electron transfer and proton loss from the hydrocarbon chain. Alkenes are more easily oxidized either directly or indirectly. For instance 3,3-dimethylbut- 1-ene is oxidized' in methanol containing either NaOMe or NaOC0,Me to a variety of products (mostly rearranged) including methoxy- lated alkylmethylcarbonates and the corresponding alcohols [e.g MeO(Me),-CCH(Me)CH,OCO,Me]. Apparently NaOC0,Me is formed in the electrolysis of NaOMe in methanol and the results have been rationalized according to an indirect mechanism which involves initial radical addition to the alkene.The direct oxidation of alkenes often results in dimerization with subsequent sub- stitution. The observation of tail-to-tail coupling is taken as evidence of initial dimerization of radical-cations. Recent examples,6 and the current mechanistic explanation are given in Scheme 2. It should be noted that the anodic dimeriza- tion of enol ethers6a in methanol provides a route to acetals of 1,4-dicarbonyl ~ dirnerize R C H=C(OEt)R2 -e R CH&( OEt)R2 -+ R2(OEt )&H( R ')CH(R ')&(OEt)R 1MeOH ere. R2COCH(R')CH(R 'FOR + R '( OEt)C(OMe)CH(R ')CH(R..')C(MeO)(Et O)R2 . PhCH=CH Ph 0 (52% current yield) Ph Reagents i graphite anode CH,Cl,-H,O-Bu,NHSO Scheme 2 compounds.The substituted tetrahydrofuran (1)is prepared' in 12 % yield by the oxidation at a graphite anode of a-methylstyrene in wet acetonitrile. The product ' R. Brettle and J. R. Sutton J.C.S. Chem. Comm. 1974 449. ' (a) D. Koch H. Schafer and E. Steckhan Chem. Ber. 1974 107 3640; (h) Angew. Chem. Internat. Edn. 1974 13 472. H. Sternerup Acta Chem. Scand. (B) 1974 28 579. Electro-organic Chemistry is unsurprising but it is noteworthy that the reaction was carried out on a molar scale (118 g) and run at 50 A using a simple capillary-gap cell.* Double-bond oxidation may also compete favourably with carboxylate oxidation in unsaturated acids. Scheme 3 displays a good exampleg of this. -e PhCH=CHCH,CH2C02-a I. cyclrzation 11. -e- MeOH 1 PhCH(OMe1LA, (> 90 %) Scheme 3 The direct oxidation of alkynes has been attempted lo using constant-current electrolysis at a graphite anode in methanol with added sodium perchlorate.Several products are obtained from phenylacetylene and the pattern can be explained in terms of initial formation of a radical-cation which is methoxylated and then further oxidized in a predictable but uncontrolled manner to produce polymethoxylated and cleaved products. For instance the most abundant products (in ca. 30 % current yield) are PhC(OMe) and HC(OMe) . Aromatic Hydrocarbons. The importance of the medium for the stabilization of cationic species is further emphasized by the Copenhagen group in the first report’ of reversible one-electron oxidation of anthracene.Reversible cyclic voltammetric behaviour is observed using tetra-n-butylammonium tetrafluoro- borate supporting electrolyte in methylene chloride that has been rigorously dried over neutral alumina or mixtures of methylene chloride trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAn). From earlier studies of the oxidation of anthracene it is known that traces of water in solvents cause irrever- sibility owing to rapid hydroxylation. In ‘super dry’ acetonitrile (with added TFAn) two-electron irreversible oxidation of anthracene is found as usual but hydroxylation is suppressed and the nitrilium ion (2) is formed. Subsequent work-up gave the corresponding acetamide (3) in 82 % isolated yield.’’ i ’ L. Eberson K. Nyberg and H.Sternerup Chem. Scripta 1973 3 12. F. M. Banda and R. Brettle J.C.S. Perkin I 1974 1907. lo M. Katz and H. Wendt J. Electroanalyt. Chem. Interfacial Electrochem. 1974 53 465. ‘I 0. Hammerich and V. D. Parker J. Amer. Chem. Soc. 1974 96 4289. 0. Hammerich and V. D. Parker J.C.S. Chem. Comm. 1974 245. J. H. P.Utley Anodic aromatic substitution generally occurs via an ECE mechanism [cf. Ann. Reports (B),1968 65 2451. It is encouraging to see that this possibility is being considered for classical electrophilic aromatic substitution reactions particularly those involving easily oxidized aromatic compounds or reactions in which side-chain substitution occurs. A case in point is the chlorination in acetic acid of hexamethylbenzene which gives the corresponding pentamethyl- benzyl chloride.When the reaction was carried out in a tube in the cavity of an e.s.r. spectrometer the well-characterized spectrum of the hexamethyl benzene radical-cation was obtained,' which suggests that serious consideration should be given to an ECE mechanism (Scheme 4).In an important practical advan~e,'~ CH ?H2 @ ' C~OP c:,-~~ec[a] 0 \ \ Scbeme 4 Eberson and Helgee have shown that oxidation of aromatic compounds in a water-methylene chloride emulsion (with added phase-transfer agent) is a con- venient way of effecting cyanation at high current densities that are not usually reached in solvents of low conductivity. The preparative consequences of anodic oxidative coupling of methoxylated aromatic compounds which form relatively stable radical-cations have been pursued.l5 More examples of the synthesis by intramolecular coupling of morphandienones have been described. 54 In methylene chloride-trifluoro- acetic acid (2 :l),biaryls are formed 5b*cin good yield following reductive work-up of solutions of radical-cations e.g.(4) of the coupled products which are stabilized " J. K. Kochi Tetrahedron Letters 1974 4305. '' L. Eberson and B. Helgee Chem. Scripta 1974 5 47. l5 (a)A. Ronlan K. Bechgaard and V. D. Parker Acra Chem. Scand. (B) 1973 27 2375; (6) A. Ronlan and V. D. Parker J. Org. Chem. 1974 39 1014; (c)J. R. Falck L. L. Miller and F. R. Stermitz J. Amer. Chem. SOC. 1974 96 2981; (d) Tetrahedron 1974 30 93 1. Electro-organic Chemistry in the acidic solution thus precluding further oxidation.Following a systematic voltammetric and u.v.-spectroscopic investigation l6 of the stability of such radical-cations of a series of substituted biphenyls it is clear that coplanarity ofthe rings is important in determining radical-cation stability. In the same paper the slow deprotonation of methoxy-substituted 9,lO-dihydrophenanthrene radical cations (4) is both confirmed and explained. It is now almost certain that the coupling reactions described above involve the intermediacy of phenoxonium ions and recent and compelling evidence' is summarized in Scheme 5. Phenols are more easily oxidized than the corres- OMe OMe HO 0 Reagents i Pt anode -e- -H+ -e- 1.25 V (us. s.c.e.1 MeCN 2 F mol-' Scheme 5 ponding methyl ethers and in the case presented the nature of the products and the absence of intermolecular coupling argues for the phenoxonium-ion route.Heterocyclic Compounds. The methoxylation of furans by anodic oxidation in methanol has been much studied [c& Ann. Reports (B),1968,65,246].A recent investigation'* of the oxidation of 2,3,4,5-tetraphenylfuran(5) in either methanol or nitromethane shows that the intermediate radical-cation (which is sufficiently stable in nitromethane to be characterized by e.s.r. spectroscopy) undergoes substitution in the normal way (in methanol) or else (in nitromethane) cleavage to (6). The anodic oxidation of nitrogen compounds usually leads to complicated product mixtures because the substrates are often basic and nucleophilic and l6 A.Ronlan J. Coleman 0. Hammerich and V. D. Parker J. Amer. Chem. Soc. 1974 96 845. l7 U. Palmquist A. Ronlan and V. D. Parker Acta Chem. Scand. (B) 1974 28 267. M. Libert and C. Caullet Bull. SOC.chirn. France 1974 805. 220 J. H. P.Utley Reagents i MeCN-pyridine-Et,NC104; ii MeCN-Et,NCIO Scheme 6 can therefore take part in substitution in and abstraction from cationic inter- mediates. The electrochemical behaviour ' of N-aryl-2-pyrazolines is therefore smprisingly straightforward (Scheme 6). The corresponding pyrazoles are obtained in good yield by o~idation'~" in acetonitrile in the presence of pyridine whereas without the base dimers such as (7) are formed" in high yield. In the more complete report of these ~tudies"~ attention has also been paid to the electrochemistry of the dimeric products as well as to the voltammetry and coulometry associated with the reactions.The anodic trimerization of 1,3-dirnethylbarbituric acid (8) has been accom- plished2' using controlled-potential electrolysis at a pyrolytic graphite anode with acetic acid as solvent. The product formed in good yield is a new cyclic barbiturate (9). Its structure was confirmed by X-ray crystallography. 0 (9) Among recent attempts at clarifying the electrochemistry of biologically im- portant nitrogen heterocycles is an investigation2 of the electrochemistry l9 (a) F. Pragst 2. Chem. 1974 14,236; (6)F. Pragst and B. Siefke J. prakt. Chem. 1974 316 267; (c) P.Corbon G. Barbey A. Dupre and C. Caullet Bull. Soc. chim. France 1974,768. 2o S. Kato M. Poling D. van der Helm and G. Dryhurst J. Amer. Chem. Soc. 1974,96 5255. 2' C. Slifstein and M. Ariel J. Electroanalyt. Chem. interfacial Electrochem. 1973 48 447. Elec tro-organic Chemistry 22 1 1 (10) M = Me P = CH,CH,CO,H V = CH=CH H (1 1) Reagents i Au anode DMSO 0.55 V (us. s.c.e.),2 F mol-' Scheme 7 of bilirubin (10) in DMSO. A variety of voltammetric techniques have been used. Controlled-potential coulometry at +0.55 V (us. s.c.e.) reveals that 2 F mol-are consumed during oxidation. The probable reaction is given in Scheme 7 although there is little direct evidence for the formation of biliverdine (11). The smooth methoxylation of (tetrapheny1porphyrin)iron chloride follows controlled-potential oxidationz2 in methanol-methylene chloride solution.The product cation (meso-tetraphenylmethoxyisoporphyrin)iron(lIr)chloride was isolated as the hexafluorophosphate salt. Acyclic Nitrogen and Sulphur Compounds. More evidence has been produced concerning the mechanism of the oxidation of NN-dimethylbenzylanine in methanol [cf Ann. Reports (B) 1968 65 2431. Mixtures containing both the a-methoxy and N-methoxymethyl products are usually obtained and it has hitherto proved difficult to distinguish between direct oxidation and indirect oxidation involving H abstraction by an anodically produced methoxyl radical. A careful study23 reveals that in Bu,NBF,-methanol controlled-potential oxidation at platinum gives a 10 :1 ratio for the N-methoxymethyl :a-methoxy products and in these conditions cyclic voltammetry suggests that oxidation of the amine occurs before solvent discharge.In the presence of alkali the corres- ponding ratio of products is cu. 2 :1 which is the expected ratio for random hydrogen abstraction. PhCH / /\ PhCH PhCH CH,Ph (12) (60-75 % depending on R' and Rz) R' R2 Reagents i Pt anode MeCN-LiCIO,; ii Scheme 8 22 J. A. Guzinski and R. H. Felton J.C.S. Chem. Comm. 1973 715. 23 J. E. Barry M. Finkelstein E. A. Mayeda and S. D. Ross J. Org. Chem. 1974 39 2695. 222 J. H. P.Utley The controlled-potential oxidation of dibenzylhydrazine is a convenient means of generating the cation (12),and Cauquis and co-~orkers~~ have used the method in performing a number of interesting cycloaddition reactions (Scheme 8).Coupling of N-alkylanilines may be achieved in acidic solution provided that the N-alkyl group is bulky.25 Similarly anodic oxidation of N-ethylbis-(4-t-butylpheny1)amine gives N-ethy1-3,6-di-t-butylcarbazolein about 15 % yield.26 The intramolecular formation of sulphur-sulphur bonds may also be brought about anodically. A number of gem-polysulphides (13) undergo’ an interesting chain contraction the final product depending on the dryness of the solvent (Scheme 9). The mechanism is not certain but the suggested intermediacy of ArS /CH2\ FH2\ /CHzNu SAr -L ArS-sp’ 2ArS-SAr (1 3) (14) 1 (Nu-= nucleophile) Nu,CH + ArS-SAr (ca.70%) Reagents i Pt anode MeCN-LiClO, 2 F mol-; ii Nu-Scheme 9 the dication (14) is plausible. A sulphur cation intermediate is also implicated in the anodic production28 in 80 % yield of the sulphurane (15) from the corres- ponding diary1 disulphide dicarboxylate. The electrochemical preparation of 0 (15) sulphonium salts has been discussed [Cf. Ann. Reports (B) 1973 70 3071. Tri-phenylsulphonium perchlorate is one of the products of controlled-potential oxidation2’ of diphenyl sulphoxide in dry acetonitrileNaC10 solution in the presence of benzene. The other major product is diphenyl sulphone which sug- gests the mechanism outlined in Scheme 10. Similar electrolysis3’ of triphenyl- phosphine gives tetraphenylphosphonium perchlorate. 24 G.Cauquis B. Chabaud and M. Genies Tetrahedron Letters 1974 2389. 25 R. L. Hand and R. F. Nelson J. Amer. Chem. Sac. 1974 96 850. 26 R. Reynolds L. L. Line and R. F. Nelson J. Amer. Chem. SOC. 1974 96 1087. 27 J.-G. Gourcy G. Jeminet and J. Simonet J.C.S. Chem. Comm. 1974 634. C. S. Liao J. Q. Chambers I. Kapovits and J. Rabai J.C.S. Chem. Comm. 1974 149. 2q G. Bontempelli F. Magno G. A. Mazzocchin and R. Seeber J. Elecrroana/yt. Chem. Interfacial Electrochem. 1974 55 109. 30 G. Schiavon S. Zecchin G. Cogoni and G. Bontempelli J. Electroanalyr. Chem. Interfacial Electrochem. 1973 48 425. Electro-organic Chemistry 223 Ph,SO -3Ph:SO 0'IA Ph,i-O-SPh -P +. Ph2S + Ph2S02 ii 1-H+. -e- Ph,i c10,- Reagents i Ph,SO; ii C,H6 Scheme 10 Miscellaneous.Many examples of the oxidative cleavage of acetate from enol esters have been ~resented.~ ' The experimental procedure is simple involving constant-current electrolysis at a carbon rod anode in an undivided cell. A good example of the usefulness of this reaction is its involvement as a key step in the conversion32 of (-)-menthone into (+)-menthone (Scheme 11). ho -*b ---* Qo*c A A (-1 (+I Reagents i Carbon anode HOAc-Et,NOTs 2.5 F mol-'; ii epoxidation; iii H,NNH2-HOAc; iv Jones reagent; v H,-Pd Scheme 11 The extent of rearrangement of carbenium ions produced by oxidation of carboxylates or alkyl iodides has been compared with that of cations produced by trifluoroacetolysis of tosylates and in a comprehensive paper33 Laurent and co-workers conclude that for iodide electro-oxidation the solvent (acetonitrile) assists cation formation.This conclusion is reinforced by the ob~ervation~~ of 207; inversion in the major product [MeCONHCH(Me)C,H,,] of anodic oxidation of optically active 2-iodo-octane. The full report35 of similar oxidative cleavage of a variety of substituted adamantanes has appeared. Me CH,-H? MeCH, I 'C' /O+' MeCONHCCH,COMe Me/\CH,-C I \ 31 T. Shono Y.Matsumura and Y. Nakagawa J. Amer. Chem. Soc, 1974 96 3532. 32 T. Shono Y. Matsumura K. Hibino and S. Miyawaki Tetrahedron Letters 1974 1295. 33 A. Laurent E. Laurent and R. Tardivel Tetrahedron 1974 30 3423. 34 A. Laurent E. Laurent and B. Tardivel Tetrahedron 1974 30,3431. 35 V. R. Koch and L. L. Miller J.Amer. Chem. Soc. 1973,95 8631. J. H. P. Utley The oxidation of 4,4-dimethyl-2-pentanone in acetonitrile yields,36 after aqueous work-up an acetamide (16) in which the carbon skeleton is altered in a way best rationalized by a McClafferty-type rearrangement via e.g. (17).An attempt to induce a rearrangement similarly inspired by mass spectrometry of dibutylamine failed3' because of the nucleophilicity of the starting material towards the radical-cation produced at the anode. Oxidation of Organic Anions.-Carboxylates. It has been a quiet year for the Kolbe reaction. A very thorough investigation3* of the products of anodic oxidation in methanol of exo-and endo-1,7,7-trimethylnorbornane-2-carboxylic acid and of exo-and endo-2,3,3-trimethylnorbomane-Zcarboxylicacid confirms that exclusively two-electron oxidation results and that the cation (18) is a (1 8) common intermediate.Two-electron oxidation is also found39 for a-alkoxy- acetates in acetonitrile and the resulting cation reacts not with the solvent but exclusively with unreacted carboxylate to form alkoxylated esters. Full reports have appeared of the oxidation of ethylenic carboxylates4' and of phenyl- acetates4' [cf Ann. Reports (B) 1971 68,3131. At a carbon anode either one- or two-electron oxidation of y-substituted paraconic acids can be effected42 by a suitable choice of solvent (Scheme 12). Reagents i Carbon anode NaOMe-MeOH 1 F mol -I ;ii Carbon anode Et ,N-pyridine- H,O 2 F mol-I Scheme 12 Miscellaneous. The anodic reactions of the enolate of dibenzoylmethane are clearly complicated but in benzonitrile (which reduces the probability of ab- straction) oxidative dimeriza tion to tetrabenzoy lethylene is encouraged.36 J. Y. Becker L. R. Byrd and L. L. Miller J. Amer. Chem. Soc. 1974,96 4718. 37 S. Wawzonek and S. M. Heilmann J. Electrochem. Soc. 1974 121 378. 38 G. E. Cream and C. F. Pincombe Austral. J. Chem. 1974 27 589. 39 H. G. Thomas and E. Katzer Tetrahedron Letters 1974 887. 40 R. F. Garwood Naser-ud-din C. J. Scott and B. C. L. Weedon J.C.S. Perkin I 1973 27 14. 41 J. P. Coleman R.Lines J. H. P. Utley and B. C. L. Weedon J.C.S. Perkin II 1974 1064. 42 S. Torii T. Okamoto and H. Tanaka J. Org. Chem. 1974 39 2486. 43 H. W. Vandenborn and D. H. Evans J.Amer. Chem. Soc. 1974,96 4296. Electro-organic Chemistry 225 A full report has appeared of Breslow's use44 of voltammetry to assess the anti- aromaticity of cyclobutadiene by measurements of oxidation half-wave potentials for substituted quinol dianions [cJ Ann. Reports (B),1970,67,226]. 3 Cathodic Processes Reduction of Neutral Organic Compounds.-Cathodic Cleavage. Following unsuccessful attempts4' at preparing substituted bicyclo[2,2,2]propellane by reduction of 9,10-dihalogenotriptycenes,Wiberg and co-workers succeeded46 by using controlled-potential electrolysis of 1,4-dibromobicyclo[2,2,2]octane at -15 "C. Subsequent addition of chlorine gave (19) an addition product which can only come from propellane (20). Similarly the cyclopentadiene adduct of the highly strained olefin (21) has been isolated47 following electrolysis at -20 "C of l-bromo-4-chlorobicyclo[2,2,0]hexane.For acyclic vicinal di- bromides reductive cleavage to alkenes under chemically mild conditions can be highly stereo~elective.~~ For example ( +)-2,3-dibromobutane gives mostly (80:<) of the cis-but-2-ene and the mesu-dibromide gives only trans-but-2-ene.Another interesting use of halogen cleavage is the efficient synthesis49 of deuterio-organic compounds by reduction of 1 -halogeno-naphthalenes in the presence of D20. These experiments also confirm the carbanionic nature of the intermediate. Contrary to conventional wisdom it has been found that with careful control of potential benzotrifluoride may be reduced in steps and the conditions max be arranged5' to optimize formation of the CHF, CH2F and CH products.A full report of earlier work on cleavage from benzylic systems has appeared" [cJ Ann. Reports (B),1970 67 2361. When alkyl halides are reduced in DMF in the presence of carbon dioxide radical-derived products (R2Hg,ROCOC02R RC0,R) are formed at mercury,52 whereas at a graphite cathode carbanion-derived products predominate. 44 R. Breslow D. R. Murayama S. I. Murahashi and R. Grubbs J. Amer. Chem. SOC. 1973,95 6688. 45 A. Bohm J. Kalo Ch. Yarnitsky and D. Ginsburg Tetrahedron 1974 30 217; G. Mark1 and A. Mayr Tetrahedron Letters 1974 1817. 46 K. B. Wiberg G. A. Epling and M. Jason J. Amer. Chem. SOC.,1974 96 912. '' J. Casanova and H. R.Rogers J. Org. Chem. 1974 39 3803. 48 J. Casanova and H. R. Rogers J. Org. Chem. 1974 39 2408. 49 R. Renaud Cunud. J. Chem. 1974 52 376. 50 H. Lund and N. J. Jensen Acta Chem. Scand. (B) 1974 28 263. '' J. P. Coleman Naser-ud-din H. G. Gilde J. H. P. Utley B. C. L. Weedon and L. Eberson J.C.S. Perkin II 1973 1903. 52 J. H. Wagenknecht J. Electroanulyt. Chem. Interfacial Electrochem. 1974 52 489. 226 J. H. P. Utley It now seems clear53 that an earlier report [cf. Ann. Reports (B) 1968 65 2581 of substantial inversion of configuration in the electrochemical reduction of 2-chloro-2-phenylpropionicacid is incorrect. Similarly the carbon-sulphur bond in ethyl 2-phenylmercaptopropionateis cleaved5 with little or no stereo- selectivity. The reductive cleavage of sulphones continues to attract attention although recent experiments are aimed at clarifying mechanistic detail.54 Cathodic cleavage in aprotic solvents of arylsulphonyl chlorides can however lead to a number of useful products. In particular yields of ArSO,SAr ArSSAr and ArSH may be optimized55 by control of the amount of electricity used. Electrolysis has also been used to cleave disulphide bridges in immunoglobulins56 and efficiently to remove benzylidine and benzoyl shields from carbohydrates. 57 Cathodic Substitution. A probably very important polarographic study'* of homogeneous electron exchange (Scheme 13) offers the hope that molecules -A 2A' A' + BX S A + BX' BXL S B' + X-Then e.g. B' +A' S AB-B' +A' $ B-+A Scheme 13 (e.g.BX) may be reduced in the presence of a more easily reduced compound (A) at a potential significantly below that normally required. The requirement is that A should form a relatively stable radical-anion and that decomposition of BXL be rapid. In a polarogram the rate of reduction of BX by A-is reflected in a catalytic increase of the height of the reduction wave for A and this is found to be dependent on the difference between the half-wave potentials of A and BX. Examples of A are aromatic hydrocarbons aromatic ketones esters and nitro- compounds and examples of BX are halides esters alcohols sulphonamides and azides. If for cleavage and substitution reactions the preparative consequen- ces of this idea are realized an electrochemical equivalent of photosensitization will result.An intriguing example of 'electrochemistry without current' has been provided by Saveant and co-~orkers~~ (Scheme 14). The key result is that in wet acetoni- 53 C. M. Fischer and R. Erickson J. Org. Chem. 1973 38 4236. 54 (a)J. A. Cox and C. L. Ozment J. Electroanalyt. Chem. Interfacial Electrochem. 1974 51 75; (b) B. Lamm and J. Simonet Acra Chem. Scand. (B) 1974 28 147. G. Jeminet J. Simonet and J. G. Gourcy Bull. SOC.chim. France 1974 1102. 56 C. Rivat M. Fontaine C. Ropartz and C. Caullet European J. Immunol. 1973 3 537. 57 V. G. Mairanovskii N. F. Loginova A. M. Ponomarev and A. Y. Veinberg Elektro-khimiya 1974 10 172. 58 H. Lund M.-A. Michel and J. Simonet Acta Chem. Scand. (B) 1974,28 900. 59 J.Pinson and J.-M. Saveant J.C.S. Chem. Comm. 1974 933. 227 Electro-organic Chemistry PhCOC6 H,Br PhC(O)C,H,Br PhCOC6H4' + PhS-Ph k(0)C 6 H,s Ph Scheme 14 trile the product (22) of nucleophilic substitution is formed in 80 % yield after the passage of only 0.2 F mol-Cyclic voltammetry confirms that at potentials required for the reduction of p-bromobenzophenone the radical-anion of (22) is oxidizable. The cathodic cleavage of disulphides6' in the presence of methyl chloride or acetic anhydride gives high (80-90%) yields of the corresponding RSMe and RSCOMe compounds. The generality of the method of synthesis of sulphones which involves alkylation of the sulphur dioxide radical-anion has been exten- ded6 to include the preparation of unsymmetrical sulphones [cf.Ann. Reports (B) 1973 70 2951. Amino-acids may be prepared62 in good yield by the con- trolled-potential reductive alkylation in DMF of Schiff's bases. The potential is selected on the basis that the halide is the first-reduced species so the reaction presumably goes via carbanionic (two-electron) or radical (one-electron) addition to the carbon-nitrogen double bond. Cathodic Addition and Oligornevization. The considerable importance of ion- pairing in electro-organic reactions is becoming clear. A simple illu~tration~~ is that a-trifluoroacetophenone gives reversible cyclic voltammetric behaviour in acetonitrile-Et4NC1O4 and its radical-anion may be characterized by e.s.r. spectroscopy. However in the presence of LiClO, the reduction potential becomes more anodic irreversible voltammetric behaviour is observed and preparative-scale electrolysis leads to the pinacol(35 % isolated yield).Similarly dimerization of dimethyl fumarate radical-ions is enhanced6 by conditions which favour ion-pairing and a simple view is that ion-pairing effectively causes charge dispersal which by reducing coulombic repulsion favours radical combination. In a careful in~estigation,~~ the many organic products of reduction of carbon dioxide in an aprotic solvent have been separated by high-pressure liquid chromatography. The optimism engendered by earlier studies [cf:Ann. Reports (B) 1969 66,2351 has not been restored but undoubtedly malic succinic and tartaric acids are among the products if some water is present.In dry DMF at a 6o P. E. Iversen and H. Lund Acta Chem. Scand. (B) 1974 28 827. 61 D. Knittel and B. Kastening Ber. Bunsengesellschaft phys. Chem. 1973 77 833. 62 T. Iwasaki and K. Harada J.C.S. Chem. Comm. 1974 338. 63 C. P. Andrieux and J.;M. Saveant Bull. SOC. chim. France 1973 2090. 64 M. D. Ryan and D. H. Evans J. Electrochem. SOC. 1974 121 881. 65 U. Kaiser and E. Heitz Ber. Bunsengesellschaft phys. Chem. 1973 77 818. J. H. P.Utley 2e 2cs * 2cs,-+ -sc-cs-& s=c-c=s II I1 I I ss ss 'C' -s/\ s-1 -s2-Reagents i CS2;ii 2MeI Scheme 15 mercury cathode up to 90% current yield of oxalic acid is achievable. Carbon disulphide is trimerized66 following electroreduction in DMF solution.The product of addition of methyl iodide to the electrolysed solution was (23) and the reaction presumably proceeds according to Scheme 15. Radical-anions formed in aprotic solvents by reduction of activated olefins will give nucleophilic addition to carbon dioxide. Useful examples of this reaction are discussed in two papers from the Monsanto Conditions may be adjusted to give carboxylation or carboxylation with dimerization. For instance methyl acrylate is reduced in acetonitrile saturated with carbon dioxide to yield,67" after methylation with methyl iodide the triester (24); dimethyl maleate may similarly be reduced at a lower potential to yield the carboxylated dimer (25). C02Me I MeO,CCH,CH(CO,Me) (MeO,C),CHCHCHCH(CO,Me) Cathodic Hydrogenution.A simple undivided cell has been described" that overcomes for reductions where the products are not easily oxidized and which require a proton source the problem of the basicity of the cathode compartment increasing during electrolysis. In essence it employs a mercury pool cathode and a platinized platinum anode over which hydrogen is bubbled. The anode re- 66 S. Wawzonek and S. M. Heilmann J. Org. Chrm. 1974 39 51 I. 67 (a)D. A. Tyssee and M. M. Baizer. J. Org. Chem. 1974 39 2819; (b) ibid.. p. 2823. " J.-M. Saveant and S. K. Binh J. Electroanalyt. Chem. Interfacial Electrochem. 1974. 50 417. Electro-organic Chemistry action is therefore production of protons at a rate which must balance the demand at the cathode. A miniature cell is described in the report of an in~estigation~~ of electrocatalytic hydrogenation of unsaturated steroids.Depending mainly on temperature isolated carbon-carbon double bonds may be reduced selectively (Scheme 16). OH ?H (70 ",") Me0& \ (96Yo) Reagents i Pd cathode EtOH-H,SO, reflux; ii Pd cathode EtOH-H,SO, room temperature Scheme 16 The importance of ion-pairing has been referred to (p.227). The stereoehemis- try of reduction of exocyclic double bonds is seemingly controlled by ion-pairing ; e.g. in ethanol the presence of zinc or magnesium perchlorate directs" the reduction of 4-t-butylcyclohexanone exclusively to the less stable axial alcohol. Under conditions of solvent less favourable to ion-pairing the equatorial alcohol is the major product.These results may be rationalized according to Scheme 17 in which the rate of protonation is assumed to be greater than the rate of inversion of the carbanionic conformers. 4 '0 Scheme 17 K. Junghaus Chem. Ber. 1974 107 3191. 'O R. J. Holman and J. H. P. Utley Tetrahedron Lerrers 1974 1553. J. H. P. Utley Miscellaneous. Breslow and co-~orkers'~ have measured the half-wave potentials for a number of annulenediones e.g. (26) p-benzoquinone (28) and dibenzoyl- diacetylene (29) in the hope that the sum of the reduction potentials for the 0 0 Ill iii I I 0 i Ill Ill PhCOC-CC-CCOPh (29) two waves (El + E2) which reflects the ease of attainment of the aromatic dianions will also indicate the degree of aromatic stabilization.The electrostatic effect on the addition of the second electron must vary however so interpretation of the results is not straightforward. However a comparison of (El + E2) for(26)and (29)shows that the annulenedione dianions e.g.(27),have considerable aromatic character. Redaction of Organic Cations.-Tropylium and triphen ylcyclopropen yl salts may be reduced cathodically and dimerization usually results. For instance tropylium tetrafluoroborate gives,72 at a mercury cathode in 50% acetic acid- acetonitrile a quantitative yield of 7,7'-bis(cycloheptatrieny1). Dimers are formed by reduction at the potentials of either the first or second voltammetric wave and the persistence of dimer formation following two-electron reduction in acidic solution is rationalized according to Scheme 18.Support for this mechanism R+ 5 R. > R-BH'CI0,-7 RH 1 lR+ 9% R BH+ = guanidinium ion (at 1st wave) (at 2nd wave) Scheme 18 comes from the use of a new proton donor guanidinium perchlorate (301 which can be expected to penetrate into the electrical double-layer and make the proto- nation step competitive. With this proton donor (0.4moll-in acetonitrile) the " R. Breslow D. Murayama R. Drury and F. Sondheimer J. Amer. Chem. SOC. 1974 96 249. 72 R. Breslow and R. F. Drury J. Amer. Chem. SOC.,1974,96,4702. Electro-organic Chemistry 231 + (H,N),C=NH,CIO,-(30) monomer product cycloheptatriene is obtained in 30% yield. Similar results are obtained for the reduction of triphenylcyclopropenyl cations.The behaviour of quinolizinium ions often resembles that of the pyridinium ion and the analogy may be extended to electroreduction. The quinolizinium perchlorate (3 1)is reduced to (32) and (33) in aqueous solvents and to a red dimer in dry DMF.73The proportions of(32) and (33) vary greatly with pH and cathode (31) X = C0,Me (32) (33) potential. Enammonium salts such as (34) are also readily reduced,74 with ring-opening to the corresponding 2-substituted cyclohexylamines and cyclo- hexanones. Again the ratio of the products is greatly dependent on pH. The highly conductive charge-transfer complexes that are formed between derivatives of tetrathiofulvalene and tetracyano-p-quinodimethane provoke interest in methods of preparation of the required sulphur compound.The cathodic dimerization of sulphonium salts is therefore of interest and in par- MeS (see Scheme 15) lii 1 Reagents i Et,OBF,-CH,CI,; ii Pt cathode MeCN 1 Fmol-'; iii CCI, 100°C Scheme 19 73 S. Kato Y. Tanaka and J. Nakaya Denki Kagatu Oyobi Kogyo Butsuri Kuguku 1974 42. 223 (Chem. Abs. 1974,81 135 919). '' P. E. Iversen and J. 0.Madsen Tetrahedron 1974 30 3477. 232 J. H. P.Utley ticular the elegant method outlined in Scheme 19 is n~teworthy.~~ Yields in excess of 75 % were achieved for each step. 4 General Of the books and reviews that have appeared attention is drawn to a which concentrates on practical aspects ofthe subject and to a long authoritative and comprehensive review which deals with the applications of electrochemistry to carbohydrate chemistry.77 ” (a)P.R. Moses and J. Q. Chambers J. Electroanalyt. Chem. Interfacial Electrochem. 1974 49 105; (6) J. Amer. Chem. SOC.,1974 96 945. 76 M. R. Rifi and F. H. Covitz ‘Introduction to Organic Electrochemistry’ Marcel Dekker New York 1974. ” M. Fedoronko Ado. Carbohydrate Chem. 1974 29 107.

ISSN:0069-3030    

DOI:10.1039/OC9747100215

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

9 Photochemistry By W. M. HORSPOOL" Department of Chemistry The University Dundee DDI 4HN Photochemistry is the subject of a Specialist Periodical Report. This article which has a definite bias towards organic aspects of photochemistry is intended to indicate those areas which in the opinion of the author are undergoing exciting developments. Ladwig and Liu' have published an account of the energy transfer from the second triplet of naphthalene (ET= 368.7 kJ mol-') using benzene as solvent (ET = 353.6 kJ mol-') and dicyclopentadiene as reactant (ET= 301.7 kJ mol-I). This system permits the transfer of energy from the excited naphthalene to the benzene which transfers its energy to the cyclopentadiene. Yields of 3.96% conversion were obtained with the solution being 1 moll-' in benzene.Interest in the use of heavy-atom solvents as an aid to intersystem crossing has been maintained. Thus the photochemistry of 1,8-divinylnaphthalene in the presence of bromocyclopropane has been reinvestigated. Under these conditions the quantum yield for intersystem crossing was 0.25. Bromocyclopropane quenches the fluorescence of the naphthalene and from a Stern-Volmer plot a fluorescent lifetime of 1.4ns was calculated.2 Zimmerman et aL3 have studied the decay of excited states as a function of twist possible in a double bond for a series of cyclic mono-olefins. The total decay rate of the excited singlet states were measured by the previously reported meth~d.~,~ Schaffner and his co-workers6 have reinvestigated the decafluorobenzo- phenone-propan-2-01 actinometer and reported that it is not as dependable as was first claimed.' * This Report was written while the author was on leave at the Department of Chemistry The University of Wisconsin Madison Wisconsin.The author expresses his sincere thanks to the University of Wisconsin for hospitality received. ' C. C. Ladwig and R. S. H. Liu J. Amer. Chem. Soc.,' 1974,96,6210. R. H. Fleming F. H. Quina and G. S. Hammond J. Amer. Chem. SOC.,1974,96,7738. H. E. Zimmerman K. S. Kamm and D. P. Werthemann J. Amer. Chem. Soc. 1974 96 7821. H. E. Zimmerman D. P. Werthemann and K. S. Kamm J. Amer. Chem. Soc. 1973 95 5094. H. E. Zimmerman D. P. Werthemann and K. S. Kamm J. Amer. Chem. SOC.,1974 96 439. ' P. Margaretha J.Gloor and K. Schaffner J.C.S. Chem. Comm. 1974 565. N. Filipescu J. P. Pinion and F. L. Minn Chem. Comm. 1970 1413. 233 234 W.M. Horspool The photochemical reactions of 1-iodo- and 1-bromo-norbornane have been studied.' For both compounds the reduction product norbornane was formed in methanol but with the iodo-compound reduction was the minor process and 1-methoxynorbornane was the main product. This is presumably formed via a cationic intermediate (l) reduction resulting from a free-radical path. Kropp and Poindexter' suggest that the difference between the reactions of the halogeno- compounds arises from an electron transfer. Thus with the iodo-compound excitation leads to fission of the C-I bond giving radicals and iodine atoms.The iodine atom remains close enough for electron transfer to result giving the cation and iodide. This is not the case with the bromo species although if the viscosity of the solvent is increased (ethylene glycol) electron transfer to yield the ion (1) becomes by far the dominant process. Photochemical homoallyl rearrangement of trans-2-arylcyclopropylcarbinyl-acetate (2a) has been reported to give via the singlet state the homoallyl product (3) (25%).9 Further study on the effect of substituents using compounds (2b-d) was not really effective in establishing a mechanism although a cationic process is favoured. OCOR (2) a; X = H,R = Me b;X = Me0,R = Me c; X = C1,R = Me d;X = H,R = CMe Several reports have appeared during the past few years dealing with the application of excited benzophenone moieties to the functionalization of remote methylene groups.A computer simulation has sought to establish the role played by the flexibility of the hydrocarbon chain in determining the specificity of the reaction.' The use of alkyl (C1-C22) benzoylbenzoates has demonstrated that the alkyl chains show no tendency to form hairpin conformations or micellar aggregations.' The remote oxidation of steroids has been examined further using the photolysis of the iododichloride (4a) in chlorobenzene. l2 After work-up the cholestenyl acetate (5) (53%) was isolated. The cholestenyl acetate (6)(43%) was obtained from irradiation of the dichloride (4b). The intriguing remote oxidation technique has been used in the synthesis of the paracyclophane (7).' 8 G.S. Poindexter and P. J. Kropp J. Amer. Chem. SOC.,1974,96 7142. 9 S. S. Hixson J.C.S. Chem. Comm. 1974,68 1. 10 M. A. Winnik R. E. Trueman G. Jackowski D. S. Saunders and S. G. Wittington J. Amer. Chem. SOC.,1974,96 4843. II M. A. Winnik C. K. Lee S. Basu and D. S. Saunders J. Amer. Chem. SOC.,1974,96 6182. 12 R. Breslow R. Corcoran J. A. Dale S. Liu and P. Kalicky J. Amer. Chem. SOC.,1974 96 1973. 13 D. Bichan and M. A. Winnik Tetrahedron Letters 1974 3857. Photochemistry This was achieved by irradiation of non-10-enyl4-benzoylbenzoate in CCl when the sole product was the oxetan (8) (83%). AcO' (4)a; R = CH2 b; R = CH IC1 Me Ph $X=O MLhSe Ph Me Me Ph (10) (11) Quinkert and his co-workers'L'8 have re-examined one of the intriguing problems associated with the photochemical ring-expansion of cyclobutanones to oxacarbenes (9) namely whether a stepwise biradical mechanism is followed as the result of Norrish type I fission of the C-CO bond.Irradiation of the methylenecyclobutanone (10)in methanol affords the tetrahydrofuran (11)without '' G. Quinkert and P. Jacobs Chem. Ber. 1974 107 2473. 15 G. Quinkert P. Jacobs and W.-D. Stohrer Angew. Chern. Internat. Edn. 1974,13 197. l6 G. Quinkert K. H. Kaiser and W.-D. Stohrer Angew. Chem. Internat. Edn. 1974 13 198. 17 W.-D. Stohrer G. Wiech and G. Quinkert Angew. Chem. Znternat. Edn. 1974,13 199. W.-D. Stohrer G. Wiech and G. Quinkert Angew. Chem. Znternat.Edn. 1974,13,200. W.M. Horspool loss of the configuration of the migrating carbon and therefore it can be con- cluded that the reaction takes place in a concerted fashion without the inter- mediacy of biradicals. The first ring-expansion of this type in the six-ring series has been rep~rted.'~ This involves the expansion of the anhydropentulose (12) into the dioxepans (13). The interest in the photochemical rearrangements of py-unsaturated ketones has been maintained. The studies to date have sought to differentiate between the excited states which bring about 1,3- and 1,2-acyl migrations. Typical of the type of reaction encountered is the acetone-sensitized 1,2-acyl shift in the enone (14) yielding the isomer tetracyclo[5,2,0,03~5,04~6]non-8-en-2-one.'o Other workers2 have studied the influence of the introduction of substituents onto the a-carbon of the enone (15) and have found that increasing methyl substitution either influences the intersystem crossing efficiency or affects the rate of a-fission.Thus direct irradiation of (15a) or acetone sensitization yields only the oxa-di-n- methane product (16a). However direct irradiation of (15c) gives the product of 1,3-acyl shift (17) while acetone sensitization yields (16b). However Schuster and (14) (15) a; R' = RZ= H (16) a; R' = R2 = H b; R' = Me R2= H b; R' = R2 = Me C; R' = R2= Me Kim22 have re-examined' the photochemistry of 2,2,7,7-tetramethylcyclohepta-3,5-dien-l-one and have postulated that regardless of the heavy a-substitution direct irradiation yields 3,3,7,7-tetramethylbicyclo[4,1,0]hept-4-en-2-onevia a barely quenchable triplet state.In this instance there is no evidence for 1,3-acyl shifts. Both 1,2- and 1,3-acyl shifts from the triplet and the singlet states respec- tively have been observed in the photorearrangements of the enone (18).24 Use l9 P. M. Collins N. N. Oparaeche and B. R. Whitton J.C.S. Chem. Comm. 1974 292. 2o K. Yano Tetrahedron Letters 1974 1861. P. S. Engel M. A. Schexnayder H. Ziffer and J. I. Seeman J. Amer. Chem. Soc. 1974 96. 924. 22 D. I. Schuster and C. W. Kim J. Amer. Chem. Soc. 1974,96,7473. 23 L. A. Paquette R. F. Eizember and 0.Cox J. Amer. Chem. SOC.,1968 90,5153. 24 R. L. Coffin R. S. Givens and R. G. Carlson J. Amer. Chem. Soc.1974,% 7554. Photochemistry of the optically active forms of (18) showed that the rearrangement to (19)from (-)-(18) occurred with inversion at C-2. This type of reaction is to be compared with that encountered by Cookson and Rogers,2s who have reported that 2-(1’- cyclohepteny1)cycloheptanoneaffords (20) the result of [2+21 addition of the carbonyl group to the double bond. This took place with both direct and acetone- sensitized photolysis. Hart et have reported a novel dimerization encountered in the irradiation (populating the triplet m* state) of the enone (21) in cyclo- hexane solution. The route to the products (22) is thought to involve [2 +41 addition producing (23) which undergoes secondary photolysis and rearranges by 1,3-acyl migration.0 (22) a; R’= a-H R2= P-H (23) a; R’ = a-H R2 = P-H b; R’ = P-H R2= a-H b; R’ = P-H R2 = a-H Further work has been carried out on the argon-laser-induced reactions of p-benzoquinones. This recent report2 records the generality of the trapping of ” R. C. Cookson and N. R. Rogers J.C.S. Perkin I 1974 1037. 26 H. Hart T. Miyashi D. N. Buchanan and S. Sasson J. Amer. Chem. Soc. 1974 96 4857. ’’ R. M. Wilson and S. W. Wunderly J. Amer. Chem. SOC.,1974,96 7350. W.M. Horspool the biradicals (24) formed by the addition of the excited quinone to cyclohexene t-butylethylene and vinyl acetate. The biradicals formed can be trapped by oxygen or sulphur dioxide. Oxygen has also been used as a trap for the enol formed by the irradiation of o-tolualdehyde in aerated cyclohexane yielding the peroxide (25).28 0 R' = R2 = (CH,) R' = H,R2 = t-Bu R' = H R2 = OAC Methanol addition to 1,2-diphenylcyclobutene has been reported to yield via the singlet excited state l-methoxy-l,2-diphenylcyclobuteneand the ring- contracted product l-phenyl-l-(methoxyphenylmethyl)cyclopropane.29Both products arise from a protonated cyclobutene.A protonation of an excited olefinic singlet state is also involved in the formation of the major product 2-methyl- 2,5-diphenyltetrahydrofuran,from the irradiation of 5-hydroxy-2,5-diphenylpent-l-ene.30 A more important result is that the same pentenol affords acetophenone and 2-phenylpropene from the triplet excited state. This reaction is considered to involve the abstraction of hydrogen by the olefinic excited state to afford the biradical(26).Proof of the mechanism was obtained by the irradiation of deuteri- ated pentenols. The products from this reaction showed that there was transfer from the y-site (C-5) of a hydrogen. Triplet-excited ethylenes have been shown by other workers to undergo intramolecular hydrogen abstraction ;however the evidence for intramolecularity was circpmstantial. Pratt3' has sought by a reinvestigation of the photochemistry of l-phenyl-l-o-tolylethylene, to establish beyond doubt that the hydrogen abstraction is intramolecular. His results show that irradiation of the ethylene affords the o-quinodimethide (27) which can be Ph Ph i\;i"Ph 28 D. M. Findlay and M. F. Tchir J.C.S.Chem. Comm. 1974 514. 29 M. Sakuragi and M. Hasegawa Chem. Letters 1974 29. 30 J. M. Hornback J. Amer. Chem. SOC.,1974,96,6773. 31 A. C. Pratt J.C.S. Chem. Comm. 1974 183. Photochemistry trapped by maleic anhydride as a Diels-Alder adduct. This evidence is conclusive. Another study of the photochemistry of 1,l-diphenylethylene this time in the presence of unsubstituted or p-substituted benzamides has provided an interesting route to 1-psubstituted phenyl-3-phenylpr0panones.~~ Fields and Kr~pp~~ have shown that the irradiation of 3,4-dimethylhex-3-ene or 3-ethyl-2-methylpent-2-eneaffords cyclopropane products such as 1,2-diethyl- 1-methylcyclopropane by way of the carbenes (28). This work follows up an (28) earlier study which suggested that photoexcitation of ethylenes led to a Rydberg state.The photo-intermediacy of carbenes was proved by the formation of the carbenes by a ground-state path and the observation that the same spread of products was found in both the ground and the photochemical reactions. Me-Et (29) (30) a; R' = H,R2 = CH< b;R' = CH< R2 = H .~~ Zimmerman et ~1have examined the di-n-methane reaction with a view to determining the stereochemistry at C-3 in the rearranged product. This question had not been resolved using an acyclic diene so the optically active diene (29) was used ;on irradiation this was converted into the cyclopropanes (30). Analysis of the products obtained showed that in this instance the configuration of the saturated carbon C-3 had been inverted (31) (32) Irradiation of the cyclic sulphone (31) is thought to yield the intermediate vinyl sulphene (32).3 Concrete evidence for the formation of this intermediate 32 Y.Katsuhara R. Tsujii K. Hara Y. Shigemitsu and Y. Odaira Tetrahedron Letters 1974,453. 33 T. R. Fields and P. J. Kropp J. Amer. Chem. Soc. 1974,% 7559. 34 H. E. Zimmerman J. D. Robbins R. D. McKelvey C. J. Samuel and L. R. Sousa, J. Amer. Chem. SOC.,1974 96,1974. 35 C. R. Hall and D. J. H. Smith Tetrahedron Letters 1974 3633. W.M. Horspool was not obtained but its formation was inferred from the types of product isolated from the reaction. Ring-opening of this type has also been studied by Padwa and Au~~ who have investigated the photochemistry of the enol(33).Irradiation of this compound or its keto tautomer with which it is in equilibrium afforded the diquinomethide derivative (34). This intermediate was not isolated since it rapidly is converted into the isolable product (35). An enol(36) is also involved in the photoisomerization of 4-phenylchroman-3-one into 4-phenyldihydro- c~umarin.~' OH OH W (33) (34) (35) A wavelength dependence thought to be conformational in origin has been observed for the photochemistry of ~Zs-2,6-dimethylhepta-1,3,5-triene.~~ When irradiated at 13. > 280nm the triene affords a mixture of three products 3,6,6- trimethylbicyclo[3,l,O]hex-2-ene 2,6-dimethylhepta-2,3,5-triene and l-methyl-3-(1'-isobutenyl)cyclobutene in a ratio of 38 :41:21. However at 254 nm the triene is converted by cis-trans-isomerization into trans-2,6-dimethylhepta-1,3,5-triene and the other products are of minor importance.The identity of the single product ion from the irradiation of protonated cyclo-octatetraene (in H2S04 at 0 "C)has been identified as (37).39 (37) A review of the elegant syntheses of helicenes many using photochemical oxidative cyclizations has been p~blished.~' Other work on simpler oxidative 36 A. Padwa and A. Au J. Amer. Chem. SOC.,1974,96 1633. 37 A. Padwa and G. A. Lee J. Amer. Chem. SOC.,1974,96 1634. 38 P. Courtot and R. Rumin J.C.S. Chem. Comm. 1974 168. 39 P. A. Christensen Y. Y. Huang A. Meesters and T. S. Sorensen Canad. J. Chem. 1974,52 3424. 40 R. H. Martin Angew. Chem. Internal.Edn. 1974 13 649. Photochemistry 24 1 cyclizations has reported that 4,4’-dialdehydostilbene cyclizes to yield 2,7-dialde- hyd~phenanthrene.~’ The reactivity of this aldehyde is to be contrasted with the failure of the cyclization of the 4-a~etylstilbene.~~ An abnormal cyclization has been reported from the irradiation of methyl 2-(a-naphthyl)-3-(4’-pyridyl)-acrylate which affords the products (38) and l-methoxycarbonyl-2-(4’-pyridyl)-acenaphthylene by cyclization at the naphthalene peri (38) Evidence has been accumulated proving the existence of n-chlorobenzene (39) the lifetime of which is estimated as > 7 x lop9s. This compound is formed by photolysis of chlorobenzene at 253.7 nm. The photochemical decomposition of chlorobenzene is solvent dependent (a= 0.38 in cyclohexane and 0.012 in Freon 113).In the former solvent the products of the irradiation are benzene and chlorocyclohexane.44 A mechanistic study of the photo-Fries reaction of phenyl acetate suggests a radical me~hanism.~’ This proposal is further sub- stantiated by a CIDNP study of p-tolyl-p-chlorobenzoate which has shown that the photo-Fries process occurs by a singlet-state reaction. The triphenylmethane sensitized reaction also takes place by a singlet The irradiation of alkyl phenyl ethers (e.g.methoxybenzene) leads to ortho rneta and para-isomeric alkyl phenols. A free-radical mechanism readily accounts for the ortho and the para products since radical recombination is most likely at these sites in the phenoxy radical.By the use of deuterium-labelled material the route to the rneta-isomer was identified as a secondary photochemical isomerization of the para tautomer 4-methyl~yclohexa-2,5-dienone.~~ Several products are formed from the photoreaction of the acetate (40).“*Of especial importance is the formation of the triene (41) and 2-acetoxy-l,5-dimethoxy-3-methylbenzene CI’ f.4 MeooFe nA 41 J. Y. Wong C. Manning andC. J. Leznoff Angew. Chem. Internat. Edn. 1974,13,666. 42 F. B. Mallory C. S. Wood and J. T. Gordon J. Amer. Chem. SOC.,1964,86 3094. 43 W. C. Fleming W. M. Lee and D. W. Henry J. Org. Chem. 1973 38,4404. 44 M.-A. Fox W. C. Nichols jun. and D. M. Lemal J. Amer. Chem. Soc. 1973,95 8164. 45 C. E. Calmus and D. M. Hercules J. Amer. Chem.SOC.,1974 96 449. 46 W. Adam J.C.S. Chem. Comm. 1974 289. 47 J. J. Houser M.-C. Chen and S. S. Wang J. Org. Chem. 1974 39 1387. 4u D. A. Jaeger J. Amer.Chem. SOC.,1974,96 6216. W.M. Horspool formed by the thermal rearrangement of (41). The exact details of the process are not known but a superficial examination suggests that the product (41) is formed by a 1,3-migration. For several years many groups have sought an explanation for the diverse addition paths of benzene. Bryce-Smith and his co-workers4’ have proposed following a close examination of their own and other research that there is a relationship between the ionization potential of olefins and their tendency to undergo 1,2- and 1,3-addition to benzene. 1,2-Addition is favoured when the olefin has either marked donor or acceptor properties otherwise 1,3-addition results.Efficient (a> = 0.17) photochemical addition of cyclopentene to anisole in cyclohexane solution has been reported to yield the adduct (42).50 Cantrell’l has examined the photochemical addition (using 253.7 nm light or a Vycor filter) of benzene toluene and xylene to furan. The benzene-furan system affords five 1 1 adducts four of which have been identified (43)-(45). These products (42) arise by the addition of the furan by 1,3- and 1,4-addition modes to benzene. The 1,4-addition product which results by the addition of furan across the 2,5- positions was not isolated since it apparently undergoes secondary photolysis to yield the cage compound (45).The unidentified product is thought to arise by secondary photolysis. Cantrel15’ reports that the reaction is efficient with a value of 0.27 for the quantum yield of formation of (43) and 0.11 for that of (45). Another report of the same addition reaction records much different results although from the information given the irradiation techniques were the same in both cases. However the Reading group5* report that the main product formed is the [4+4] product (46) which was not reported by Cantrell.” This 49 D. Bryce-Smith A. Gilbert B. Orger and H. M. Tyrell J.C.S. Chem. Comm. 1974,334. R. Srinivasan V. Y. Merritt and G. Subrahmanyam Tetrahedron Letters 1974 2715. T. S.Cantrell Tetrahedron Letters 1974 3959. 52 J. Berridge D. Bryce-Smith and A.Gilbert J.C.S. Chem. Comm. 1974 964. Photochemistry product is obtained from a mixture of five 1 1 adducts and the total quantum yield is 0.073.The main photoproduct (46)is both thermally and photochemically labile and yields the Cope-rearranged product (47). It does not yield the cage product (45). The reasons for these major differences are not obvious and further developments are awaited. Considerable interest has been shown in the involvement of exciplexes in the photoaddition of aromatic species to olefins. Thus Mizuno et aLS3have reported a highly selective addition of cis-and trans-1-phenoxypropene to 1-naphthonitrile. Creed and Caldwe1ls4 have observed an additional fluorescent emission (at 452 nm) between phenanthrene and dimethyl fumarate which can be quenched by electron donors; this is good evidence for the involvement of an exciplex.Exciplexes had previously been suggested in this system by Farid et although KauppS6 in a later publication had cast doubt on this possibility. Exciplexes are also thought to be involved in the addition of acrylonitrile to ind01e.~' In a study of the addition of cis-and trans-piperylene to acenaphthylene exciplexes have been discounted and the suggest that triplet biradicals best explain the observed products. The crystal structure of the maleimide adduct of the cis-cyclo-octene-benzene photoproduct has been determined as (48).59y60 From this it has been shown that the initial addition of the cyclo-octene to the benzene takes place in the endo fashion which is in contrast to the exo addition of maleimide to benzene.The photodimerization of2-methoxynaphthalene in benzene using Pyrex-filtered light affords both the cis and the trans-dimers.6' These dimers are both the result of [4 + 41 additions. Bichromophoric molecules and their photochemistry are still the subject of considerable interest. One particularly interesting example which has been published in the past year deals with the photochemistry of 6-phenylhex-2-yne which is transformed via a singlet excited state into the cyclo-octatetraene (49) 53 K. Mizuno C. Pac and H. Sakurai J.C.S. Chem. Comm. 1974,648. 54 D. Creed and R. A. Caldwell J. Amer. Chem. SOC.,1974,96 7369. 55 S. Farid J. C. Doty and J. L. R. Williams J.C.S. Chem. Comm.1972 71 1. " G. Kaupp Angew. Clrem. Internat. Edn. 1973 12 765. '' K. Yamasaki T. Matsuura and I. Saito J.C.S. Chem. Comm. 1974,944. W. I. Ferree jun. B. J. Plummer and W. W. Schloman jun. J. Amer. Chem. SOC. 1974,% 7741. 59 H. M. Tyrell and A. P. Wolters Terrahedron Letters 1974,4193. 6o D. Bryce-Smith B. Vickery and G. I. Fray J. Chem. SOC.(0,1967 390. " T. Teitei D. Wells and W. H. F. Sasse Terrahedron Lerrers 1974 367. W. M. Horspool (@ = 3.3 x 10-3).62Another phenyl-acetylene reaction has been described in the reinvestigation of the photochemistry of diphenylacetylene. This most recent report63 suggests that the primary photochemical product from this reaction is 2-phenylbenzocyclobutadiene. This is reported to be an unstable pale green crystalline compound which is thermally labile and readily changes into 1,2,3- triphenylazulene and 1,2,3-triphenylnaphthalenethe usual products of the photo- chemical transformation.Inoue et ~21.~~ have reported the photoreaction of the cyclophane (50) when irradiated in benzene solution using sunlight as the source of energy. This leads to the formation of the dimer (51) whose structure was deduced from spectral data. The authors suggest that the reactions may be concerted and interpret them in terms of Woodward-Hoffmann nomenclature. However it is also con- ceivable that the reactions arise by conversion of the cyclophane into a butatriene derivative which would then thermally or photochemically dimerize across the central double bond of the butatriene unit.Such an intermediate would also be implicated in the addition reactions to cyclopentadiene and furan. Two reports by Iwam~ra~~’~~ have shown that the rearrangement of trypticene does not follow the di-n-methane pathway to product as was originally reported.67 The rearrangement in fact involves bond fission to afford the carbene (52)and it is this intermehate which affords the usual photo-product or else can be intercepted by solvent. (52) 62 W. Lippke W. Ferree jun. and H.Morrison J. Amer. Chem. SOC.,1974 96 2134. 63 K. Ota K. Murofushi T. Hoshi and H. Inoue Tetrahedron Letters 1974 1431. 64 T. Inoue T. Kaneda and S. Misumi Tetrahedron Letters 1974 2969. 65 H. Iwamura Chem. Letters 1974 5. 66 H. Iwamura and Y. Yoshimura J.Amer. Chem. SOC.,1974,96,2652. ‘’ T. D. Walsh J. Amer. Chem. SOC.,1969,91 515; N. J. Turro M. Tobin L. Friedman and J. B. Hamilton ibid. p. 516. Photochemistry Chapman et a1.68have re-examined the photochemistry of the benzene oxide- benzoxepin rearrangement and at 253.7 nm obtained evidence that the deuterio isomer (53a) isomerizes into (53b) by an oxygen walk process. At low temperatures (-77 K) a keten (54) (vmax 21 12 cm-’) is obtained which is converted into phenol (54) (53) a; R’ = H R2= D b; R’ = D R2= H upon continued irradiation or warming. The low-temperature matrix isolation technique (in argon or nitrogen) has been used for the identification of the photo- product (thioketen and ethynyl mercaptan) from the irradiation of 1,2,3-thiadi- azole.69 More interest has been shown in the photochemical addition of diarylthio-ketones to both electron-rich and electron-deficient 01efins.’~ de Mayo and Ng7’ have reported the photochemical addition of the thiones (55) to cyclopentene and tetramethylethylene yielding the deep blue thiones (56).These adducts are s%;; w &s\ (55) (56) R’ = RZ= (CH,), R’ = R2 = Me in equilibrium with [4 + 41 dimers which are the isolable forms of the compounds. A hydrogen abstraction akin to a Norrish type I1 reaction of a ketone has been reported arising from the nn* triplet state for the thioketone (57).72 This reaction gave the ring-closed product l-phenyl-2,2-dimethylcyclopentane-1-thiol. Mein- wald and Kna~p’~ have reported the facile synthesis of the thiet (58) by the irradiation (Pyrex filter) of a benzene solution of the dioxide (59).s-so Ph (-5 7) (58) (59) 68 D. M. Jerina B. Witkop C. L. McIntosh and 0. L. Chapman J. Amer. Chem. SOC. 1974,96 5578. 69 A. Krantz and J. Laurent J. Amer. Chem. SOC.,1974,96 6768. ’O H. Gotthardt Chem. Ber. 1974 107 1856. 71 P. de Mayo and H. Y.Ng J.C.S. Chem. Comm. 1974,877. l2 P. de Mayo and R. Suau J. Amer. Chem. SOC.,1974,96,6807. ” J. Meinwald and S. Knapp J. Amer. Chem. SOC.,1974 96 6532.

ISSN:0069-3030    

DOI:10.1039/OC9747100233

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

10 Aliphatic Compounds Part (i) Hydrocarbons ~ ~~ By R. S. ATKINSON Department of Chemistry University of Leicester Leicester L El 7RH 1 Acetylenes Recent reviews of acetylene chemistry include those on compounds derived from alkynes and carbonyl complexes of cobalt,' per- and poly-fluorinated acetylenes,2 1,3-anionic cycloadditions of organolithium compounds to triple bonds,3 and the synthesis of alkenes allenes 1,3-dienes and enynes from alkynes oia hydro bor at ion.4 The ability of the ferrocene nucleus to stabilize electron-deficient centres has permitted the observation by n.m.r. of vinyl cations in s~lution.~ Thus the alkyne (1) dissolves in trifluoroacetic acid to give initially a purple solution of (2). The latter has two vinyl protons which appear as an AB system (6 6.75 and 6.18).Differentiation of the vinyl protons is expected in view of the restricted rotation about the ring-C + bond in ferrocenylalkylium cations. The anomalous coupling constant (J = 12 Hz) is considered to be evidence for a linear geometry in the vinyl group. Bu' Bu' ,Bu' Hex0 .OCOCF .. Fe . c=c \ I CF,C02H I Hendo -* Fe 'Me Fe ., 0 I .. R. S. Dickson and P. J. Fraser Advn. Organometallic Chem. 1974 12 323. M. G. Barlow and D. R. Taylor in 'Fluorocarbon and Related Chemistry' ed. R. E. Banks and M. G. Barlow (Specialist Periodical Reports) The Chemical Society London 1974 Vol. 2 p. 37. ' T. Kauffmann Angew. Chem. Internat. Edn. 1974 13 627. G. Zweifel Intra-Sci. Chem. Reports 1973 7 181.T. S. Abram and W. E. Watts J.C.S. Chem. Comm. 1974 857. 247 R.S. Atkinson SbF Me F MC Me (3) Attempts to obtain stable vinyl cations in superacid media have hitherto failed but the cation (3) has now been observed' in S0,ClF-SbF ;the vinyl methyl groups are equivalent by 13C n.m.r. a result consistent with the expected sym- metry of the vinyl cation. A related study' using carbon n.m.r. allows estimates to be made of the relative importance of alkynylcarbenium and the mesomeric allenylcation forms in (4). (4) Isolation of some intermediate metal complexes has assisted in unravelling the pathways along which metal-catalysed oligomerizations of acetylenes and olefins proceed. The reaction of butadiene with alkynes to give 10-membered rings is catalysed by zerovalent nickel compounds and it is believed to occur in a stepwise manner with addition of the alkyne to an am-bisallyl-C nickel system.Such a system (5) has been prepared' and reacts with dimethyl acetylene- dicarboxylate at -30 "C with formation of the yellow complex (6). Four moles of carbon monoxide are absorbed per gram-atom of nickel in (6)to give nickel tetracarbonyl and the cyclodecatriene derivative (7). -PPh, 3+ Ph,P-Ni Me0,CC-CC0,Me --+ (7) The reaction of the cobalt acetylene complex (8) with dimethyl maleate in benzene at room temperature gives (9)as a red crystalline solid whose structure has been proved by X-ray analysis.9 Treatment of (9) with acrylonitrile and diphenylacetylene results in the complexes (10)and (1l) respectively.Thus in the ' H.-U. Siehl J. C. Carnahan L. Eckes and M. Hanack Angew. Chem. Internat. Edn. 1974 13 675. ' G. A. Olah R. J. Spear P. W. Westerman and J. M. Denis J. Amer. Chem. Soc. 1974 96,5855. B. Biissemeier P. W. Jolly and G. Wilke J. Amer. Chem. SOC.,1974 96,4726. Y. Wakatsaki K. Aoki and H. Yamazaki J. Amer. Chem. SOC.,1974 96 5284. A lipha t ic Compounds- Part (i) Hydrocarbons ,PPh3 PPh3 (x-CSH )CO (n-C5 H ,)Co/ c02 Me ;.\ + MeO,CCH=CHCO,Me -+ Ph$ Y-H PhC =CCO,Me C0,Me (8) Me0,C 'H CH =CHCN (9) PhCECPh /CHzCN Ph Ph (n-C5 5 Co Me Ph C0,Me H Me0,C H H (11) (10) co ba 1t -cata1ysed oligomerization of diphenylacetylene and acrylonitrile the product (12) is presumably formed from a complex analogous to (10) with regeneration of the cobalt acetylene complex corresponding to (8).Oxidation of the iron tricarbonyl complex (13) with ceric ion yields 4-methyl- phthalan where the cyclobutadiene has been trapped intramolecularly by the acetylene." Oxidation of two equivalents of cyclobutadiene iron tricarbonyl in the presence of one equivalent of dibenzoylacetylene gave a single isomer containing four linearly-fused four-membered rings formulated' ' as (14) from n.m.r. data. Fe(CO) + PhCOC-CCOPh 3 ICOPh COPh lo R.H. Grubbs T. A. Pancoast and R. A. Grey Tetrahedron Letters 1974 2425. ' ' J. MeinwaId and J. Mioduski Tetrahedron Letrers 1974 3839. 250 R.S. Atkinson LiCrCH-EDA + RX -* RCECH + LiX + EDA (15) 2LiC-CH-EDA + X(CH,),,X -+ HCrC(CHz),C-CH + 2LiX + EDA EDA = ethylenediamine Scheme 1 The lithium acetylide-ethylenediamine complex (15) is a stable solid (up to 45 "C) and optimum conditions for its reaction with alkyl halides and am-dihalogenoalkanes (Scheme 1)have been determined.I2 Its use obviates the need for liquid ammonia in these reactions.9,lO-Dihydrofulvalene (16) undergoes a multiple Diels-Alder reaction with dimethyl acetylenedicarboxylate to give (17) and (18) (17) has been converted into the fused and functionalized five-membered ring system (19) with a view to the synthesis of dodecahedrane.I3 MeQ,CC-CCO,Me C0,Me (18) i LiAIH, ii CH,=S=O. iii. Nal-HMPA 4 Me0,C Reaction of t-butylisocyanide with dimethyl acetylenedicarboxylate at -20 "C gave a product identified as the bicyclobutane (20) whose formation may be ascribed to the carbene character of the initial isocyanide-acetylene adduct (2l).I4 The endo-configuration of the ketenimine groups was demonstrated by the formation of (22) on treatment with acid.The normally acid-sensitive bicyclo- butane survives this acid treatment due to the presence of electron-withdrawing su bstituents. W. N. Smith and 0.F. Beumel Synthesis 1974,441. l3 L. A. Paquette and M. J. Wyvratt J. Amer. Chem. SOC.,1974 % 4671; see also D. McNeil B. R. Vogt J. J. Sudol S. Theodoropulos and E. Hedaya ibid. p. 4673. l4 H. J. Dillinger G. Fengler D. Schumann and E. Winterfeldt Tetrahedron 1974 30 2553 2561.Aliphatic Compounds-Part (i) Hydrocarbons 25 1 E E -\-/E \ /E E-CGC-E + C-NBU' -+ C=C\ .C-CNc 'NBu' (22) E =CO,Me (20) Ynamines have a predilection for [2 + 21 cycloadditions and (23) reacts with 3-nitrobenzthiophen to give the adducts (24) and (25); the latter is believed to result from an initial [2 + 21 cycloaddition to the nitro-group.15 NR'R (24) 0-JNO2 + PhCrCNR1R2 + /*-Ph (23) aNy CNR'R~ II 0 (25) Cycloaddition of ynamine (26) with 5-methylcyclohexenone yields the bi- cyclic enamine (27) stereospecifically. Hydrolysis under controlled conditions ' D. N. Reinhoudt and C. G. Kouwenhoven Tetrahedron Letters 1974 2503. J. Ficini and A. M. Touzin Tetrahedron Letters 1974 1447. 252 R.S.Atkinson gives the acid (28),where three asymmetric centres have been fashioned in known relative configuration. A route to an analogue (29) of the naturally-occurring steganone (30)uses a ring-expansion of 9-pyrrolidinophenanthrene by dimethyl acetylenedicarboxy- late (Scheme 2). -I I -E=CO,Me OMe 30) Scheme 2 The cyclic diyne (31) has been synthesized as an unexpectedly stable crystalline solid (Scheme 3).18 A similar route has been used to prepare the less stable monoacetylene (32) which reacts with a potassium mirror in THF to give a di- potassium salt of the dianion (33). From the positions of benzenoid and olefinic proton resonances the eight-membered rings in (31) and (32) are responsible for paratropic contributions to the ring currents (as in biphenylene) whereas the dianion (33) is a diatropic system.' D. Becker L. R. Hughes and R. A. Raphael J.C.S. Chem. Comm. i974 430. la H.N. C. Wong P.J. Garratt and F. Sondheimer J. Amer. Chem. Soc. 1974 96 5604. AI@hatic Compounds-Part (i) Hydrocarbons A free benzocyclobutadiene (34) can be isolated by judicious heating of the trans-bisacetylene (35) since valence isomerism of (35)to (34)proceeds at a faster rate than dimerization of (34)to (36). l9 -CrCPh > 80"C > 80 "C +Me PI1 w Me C-CPh Me*ph Med Me Me Me (35) Pyrolysis of Ph13C-CH at 700 "C and 0.2 mmHg gave Ph''CC_CH and PhCG' 3CH in equal amounts. Benzylidene carbene PhCH=C is thought to be an intermediate pyrolysis of (biphenyl-2-y1)acetylenegave a small yield of 1,2-benzazulene (37).20 _-0.2 mmHg I l9 H.Straub Angew. Chem. Internat. Edn. 1974 13 405. R. F. C. Brown K. J. Harrington and G.L. McMullen J.C.S. Chem. Comm. 1974 123. A. A. Schegolev W. A. Smit G.V. Roitburd and V. F. Kucherov Tetrahedron Letters 1974,3373. R.S. Atkinson 0 I I Mi Me Me R = alkyl (39) (38) 55-73% But-Zyne and substituted acylium tetrafluoroborates react at -60 "C in CH2C1,-C2H,Cl2 giving cyclopentenones (38)' A mechanism involving electrophilic substitution at the saturated carbon as in (39)is suggested. Addition of hydrogen chloride to the deuteriated phenylacetylene (40) results in isomeric or-chlorostyrenes (41)and (42) in a ratio of 70 30. A ratio of 30 :70 is obtained in addition of deuterium chloride to phenylacetylene confirming the large contribution from a syn-addition.22 HCI + PhC-CD C1 /H \ /D (40) > >c=c + \ /c=c\ DCI + PhC-CH Ph D Ph H (41) (42) The reaction of anhydrous hydrogen bromide with terminal trimethylsilyl- alkynes is a rapid free-radical reaction resulting in the elimination of the trimethyl- silyl group and formation of 2-bromo-1-alkenes in good yield (Scheme 4).23 Br Br 3"'h% >L\ C3H,C-CSiMe3 + Br)= + Me,SiBr C3H SiMe C,H SiMe C3H Scheme 4 Pyridine N-oxide and sodium acetylide react24 to give (43) and (44) and not 2-ethynyl pyridine N-oxide as previously reported.22 F. Marcuzzi G. Melloni and G. Modena Tetrahedron Letters 1974 413. 23 R. K. Boeckmann and D.M. Blum J. Org. Chem. 1974,39 3307. lAV. Fritzsche and S. Hunig Annalen 1974 1407. Aliphatic Compounds-Part (i) Hydrocarbons 255 A route to 2-(1-alkeny1)furans involves elimination of methanol from enynes with base (Scheme 5); 2-( 1,3-alkadienyl)furans have been similarly prepared.25 00 Me R H II K 0Bu'-HO Bu' \ /Me HOCH,CH=CC-CCHOMe ,c=c, CH C \2 0-%C R \/ CHOMe Me J/ Me R Scheme 5 A detailed study has been undertaken of the reduction of hex-3-yne with sodium in HMPA-THF containing t-butanol.26 At -33 "C in the presence of excess sodium the initially formed trans-vinyl radical (45) is reduced and protonated to give the trans-olefin (46) (> 95 % of the olefinic product) at a rate slightly faster than equilibration of the vinyl radicals (45) and (47).However either an increase in reaction temperature or a reduction in sodium concentration permits nearly complete equilibration of the vinyl radicals (45) and (47) leading to an olefin Et e \ D H+ Et\ D EtCrCEt -++ Na /'='\ -+ /c=c\ Na. 'Et H' (45) 'Et iw/ -\\ Et Et Na Et \ /H H+ \ / \ /Et /c=c\ + /c=c\ H /c=cQ H Et H Et (46) (47) Et Et \ /Et H' \ /Et /c=c\ +-/c=c\ H HH Na mixture containing 85-90 of the trans-isomer (46). Polarographic measure- ments do not support the intervention of dianions in the reduction of acetylenes with sodium in liquid ammonia or HMPA. 25 A. J. de Jong L. Brandsma and J. F. Arens Rec. Trav. chim. 1974 93 15. 26 H. 0.House and G. F. Kinloch J.Org. Chem. 1974 39 747. 256 R. S. Atkinson The I3C n.m.r. spectra of several polyynes showz7 that the chemical shifts of all the acetylenic 3C-atoms differ so that even in the pentayne (48),assignments of all the signals is possible. 2 Allenes Reviews have appeared on transition-metal-allene complexes2* and the synthesis of allenes from acetylenes using hydr~boration.~~ A series of papers has examined homoallenic participation in tosylate solv~lyses.~~ The racemic allenecarboxylic acid (49) is reduced with hydrogen gas and the micro-organism Clostridium kluyveri to give equal amounts of (50) and (51). From the absolute configurations of (50) and (51) which are probably both R a trans-addition of hydrogen to both enantiomers of (49)is o~curring.~' Et Et I I Ph Et Ph c L CO,H k0,H + /c=' C0,H H H P11 H Metal-halogen exchange of a-bromovinyltriphenylsilanewith butyl-lithium gives the vinylcarbanion (52) which reacts with both aldehydes and ketones forming isolable silanols (Scheme 6).The latter are converted into allenes by Ph,Si R' R' SiPh R' SiPh, \ II II c-=CH + \c=o + R~-C-C=CH -+ R~-C-C=CH, / I I RZ OH c1 \ /C=C=CH2 R2 Scheme 6 27 R. Zeisberg and F. Bohlmann Chem. Ber. 1974 107 3800. 2a B. L. Shaw and A. J. Stringer Inorg. Chim. Acta Rev. 1973 7 1. 29 G. Zweifel Intra-Sci. Chem. Reports 1973 7 181 ; see also T. Leung and G. Zweifel J. Amer. Chem. Soc. 1974 96,5620. 'O M. Santelli and M. Bertrand Tetrahedron 1974 30 227 235 243 251 257. B.Rambeck and H. Simon Angew. Chem. Internat. Edn. 1974 13 609. A lip hatic Compounds-Purt (i) Hydro carbons treatment with thionyl chloride followed by tetraethylammonium fluoride in DMS0.32 A new route to allenic alcohols (53) involves the copper (I) halide catalysed ring-opening of acetylenic epoxides with Grignard reagents.33 R2 R' R2 I R'MgBr-Cul \ / ---+ R'CGC-C \7 hydrolysis /c=c=c \ 0 R3 CH,OH (53) Addition of the carbenoid precursor (54)to the sulphide (55)yielded the allenic thio-ether (56) as the major product by 2,3-sigmatropic rearrangement of the intermediate ~lide.~~ Hydrolysis of (56) in the presence of mercury(I1) chloride gave artemisia ketone (57) in quantitative yield. Acetylenic sulphonium ylides (55) 1 such as (58) undergo 2,3-sigmatropic rearrangements providing a route3' to terminal and internal allenes.R I Ill SPh :C(CO,Me) + PhSCH,C-CR (Me02C),C ) -+ -+ S,I ~~~~~ C Ph (58) R = Et 71% R = Ph80% 32 T. H. Chan and W. Mychajlowskij Tetrahedron Letters 1974 171. 33 P. Vermeer J. Meijer C. de Graaf and H. Schreurs Rec. Trav. chim. 1974 93 46. 34 D. Michelot G. Linstrumelle and S. Julia J.C.S. Chem. Comm. 1974 10. 35 P. A. Grieco M. Meyers and.R. S. Finkelhor J. Org. Chem. 1974 39 119. 258 R. S. Atkinson Reaction of butynylenedisulphonium salts (59) with alkoxides at -40 "C gives colourless solutions of butatrienylsulphonium salts (60) which undergo cycloaddition with dienes such as cyclopentadiene affording stable propadienyl- sulphonium salts.3h + + + NaOMe,MeOH R,SCH,CrCCH,SR 5R,SCH=C=C=CH (59) (60) CH lc/ I I H +SRz A synthesis of (+)-isocaryophyllene (61) is based3' on the addition of dimethyl- ketene to the R-(+)-allene (62)giving (63) with an R configuration at position 1.Y c +c ____ D-~-D+lay I1 0 0' H CHI (62) (63) (61) The reaction of allenes with ground-state oxygen atoms has been examined3' and INDO-MO calculations have been made upon a large number of distorted geometries of singlet and triplet allenes as models for medium and small cyclic allene~.~~ 3 Olefins Recent reviews involving olefins include olefin synthesis with organic phosphonate car bani on^,^' sensitized photo-oxygenation of olefins," regio- and stereo-specificity in the cyclization of medium ring 1,5-diene~?~ allylic ~ulphoxides,4~ the role of high-pressure kinetics in studies of the transition states of Diels-Alder reactions,44 rotational isomerism in the simplest molecules with conjugated 36 H.Braun and G. Strobl Angew. Chem. Internat. Edn. 1974,13,470; H. Braun G. Strobl and H. Gotzler ibid. p. 469. 37 M. Bertrand and J. L. Gras Tetrahedron 1974 30 793. 38 J. J. Havel J. Amer. Chem. SOC.,1974 % 530. jg P. W. Dillon and G. R. Underwood J. Amer. Chem. SOC.,1974 96,779. 40 J. Boutagy and R. Thomas Chem. Rev. 1974 74 87. 4' R. W. Denny and A. Nickon Org. React. 1973 20 133. 42 J. K. Sutherland Tetrahedron 1974,30 1651. 43 D. A. Evans and G. C. Andrews Accounts Chem. Res. 1974 7 147.44 J. R. McCabe and C. A. Eckert Accounts Chem. Res. 1974 7 251. Aliphatic Compounds-Part (i) Hydrocarbons double bonds,45 the reactivity of allylic organometallic compounds of Li Na Mg Zn Cd and Al,46 1,3-anionic cycloadditions of organolithium compounds to olefins per- and poly-fluorinated olefins and dienes,' the synthesis of olefins 1,3-dienes and enynes from alkynes uia hydr~boration,~ and cyclobutanes from photochemical metal-catalysed and cation-radical-induced dimerization of m~no-olefins.~~ I R (64) R = H (67) R = D P-Pinene (64)is a reactive olefin in ene reactions and with maleic anhydride yields (65) and (66). Using stereospecifically labelled P-pinene (67) results in exclusive transfer of the deuterium suggesting a preference in the ene reaction for a transition state (68) where the p-orbital which is generated as the C-H bond is broken is parallel to the existing 7r-orbitals involved.48 The major diastereo- isomer (66) was shown to have the R configuration at C-2 by correlation with S-( +)-3-methylpentanoic acid and hence this product is formed uia the endo-orientation (69).Double thermal cyclization of dienones has been as a route to poly- cyclic compounds; the enol form of the ketone undergoes an intramolecular ene reaction (Scheme 7). The two spiro-fused diones (70) and (71) were distinguish- ed by the equivalence of the methyl groups in the n.m.r. spectrum of (71) and their non-equivalence in the case of (70). '' V. I. Tyulin Sovrem. Probl. Fir.Khim. 1973 I 333. 46 G. Courtois and L. Miginiac J. Organometallic Chem. 1974 69 1. 47 L. J. Kricka and A. Ledwith Synthesis 1974 539. *' R. K. Hill J. W. Morgan R. V. Shetty and M. E. SynerhoIm J. Amer. Chem. Soc. 1974 96 4201 ;see also V. Garsky D. F. Foster and R. T. Arnold ibid. p. 4207. 49 F. Leyendecker J. Drouin and J. M. Conia Tetrahedron Letters 1974 2931. R.S. Atkinson A -+ d -gH 50 % 0 (71) Scheme 7 Diels-Alder reactions are often catalysed by Lewis acids. A similar catalysis has been found in the ene reaction between P-pinene and methyl vinyl ketone which react at room temperature in the presence of aluminium chloride. In the absence of the latter the ene reaction of P-pinene with acrylonitrile requires 6 h at 230 OC50 3,6-Dihydro-1,2-oxathiin-2-oxides (72)fragment rapidly and stereospecifically to sulphur dioxide and 1,3-dienes via retro-Diels-Alder reactions reaction of the cis-hydroxymethylsulphoxide(73) with N-chlorosuccinimide leads to 0 CI (73) d (72) immediate SOz evolution.By contrast,52 formation of the same products from the isomeric 2,5-dihydrothiophen 1,l-dioxides requires temperatures of ca. 120"C. The benzo-analogues (74) were isolable and isomerized to (75) on heating in benzene. o-Quinodimethane (76) an intermediate in this reaction was trapped by carrying out the pyrolysis in the presence of maleic anh~dride.~ B. B. Snider J. Org. Chem. 1974 39 255. '' F. Jung M. Molin R. Van Den Elzen and T. Durst J. Amer. Chem. SOC.,1974 96 935.Aliphatic Compounds-Part (i) Hydrocarbons 261 a0 H HO (74) Addition of the cis-divinylcuprate (77) to enone (78) proceeds in higher yield than addition of the corresponding trans-divinylcuprate. The product formed with a high degree of stereoselectivity is (79) which however has the 13-cis-15p-configuration compared with the 13-trans-15a (80)of the natural prostaglandins. A method for the simultaneous change of configuration of both double bond and chiral centre in (79) into those of the natural material involves a reaction with toluene-p-sulphenyl chloride rapid 2,3-sigmatropic rearrangement of the inter- mediate sulphenate ester to sulphoxide (81)occurs. In the presence of the thio- philic trimethylphosphite (81) is converted into + In the addition of tetramethylketenimmonium ion (82) to dienes the C=N< reacts as a dienophile with the cisoid conformation and the C=C reacts in a 52 J.M. McIntosh H. B. Goodbrand and G. M. Masse J. Org. Chem. 1974 39 202; J. M. McIntosh and R. S. Steevensz Canad. J. Chem. 1974,52 1934. 53 J. G. Miller W.Kurz K. G. Untch and G. Stork J. Amer. Chern. Suc. 1974 96,6774. R. S. Atkinson Me Me Me\ + AgBF -+ \ +/ BF,-(ZnCl,-) Me /c=c\ /C=C=N \ NMe (ZnC1,) Me Me Me Reagents i )-f ; ii )-(; iii H,O Scheme 8 [2 + 21 cycloaddition with the transoid conformation (Scheme 8).54 Ketenim-monium salts such as (82) can be prepared from the corresponding cr-chloroen- amine by using zinc chloride instead of the more expensive AgBF4.55 Cycloaddition of the zwitterion (83) to dienes follows predictions based on frontier molecular orbital calculations.Thus unlike the bulk of heterocyclic zwitterions (83)is (4n) electro~elective.~~ Thio-Claisen rearrangement of ally1 phenyl sulphides differs in several respects from the more familiar oxygen analogue. o-Allylthiophenol has been identified as an intermediate in the reaction forming thiochroman (84)and thiocoumaran \ [dj (85) 54 J. Marchand-Brynaert and L. Ghosez Tetrahedron Letters 1974 377. 55 A. Sidani J. Marchand-Brynaert and L. Ghosez Angew. Chem. Znternar. Edn. 1974 13 267. 56 K.-L. Mok and M. J. Nye J.C.S. Chem. Comm. 1974 608. A liphat ic Compounds- Part (i) Hydrocarbons 263 (85) with great facility.In contrast to the oxy-Claisen rearrangement which is catalysed by electrophiles the thio-Claisen rearrangement is accelerated by nucleophiles. It is suggested that the rate-determining pericyclic transition state of the reaction is lowered by nucleophilic assistance to C-S bond breaking.57 A short route58 to patchouli alcohol the major component of patchouli oil an important raw material in perfumery uses an intramolecular Diels-Alder reaction as the key step (Scheme 9). KOBu' A. 30 % I Scheme 9 Allylic trichloroacetamidates (86) are obtained in high yield from trichloro- acetonitrile and alcohols. They undergo thermal 3,3-sigmatropic rearrangement in refluxing xylene to yield trichloroacetamides (87). The reaction is catalysed to a startling degree by mercuric salts the rearrangement being observable even at -78 "C.A two-step mechanism involving iminomercurationdeoxymercura-tion is proposed (Scheme CCI, I CCI CCI CCl Scheme 10 5' H. Kwart and J. L. Schwartz J. Org. Chern. 1974 39 1575. 58 F. Naf and G. Ohloff Helv. Chim. Acta 1974 57 1868. 59 L. E. Overman J. Amer. Chem. SOC.,1974 96 597. 264 R.S. Atkinson Further progress in the construction of cyclopentanes by cycloaddition reac- tions with olefins has been made using the ally1 anion (88). A concerted reaction is favoured over the alternative stepwise Michael addition because of the high stereospecificity of the reaction and the absence of any non-cyclized product.60 This method should allow for the fusion of five-membered rings on to other cyclic ketones.Thermolysis of the homoallyl ether (89) leads to fragmentation products through an unusual eight-membered transition state. The corresponding acetylenic analogue behaves similarly with the formation of allene.' CH,=CH 0 H II I Ph /CH /CH2 Ph ' CH,=CH (89) CH,=CH 0-H 0 \ H A synthetic equivalent of the acyl anion is a-methoxyvinyl-lithium (90). Its reactions with electrophiles yield vinyl ethers which are easily converted into the 6o J. P. Marino and W. B. Mesbergen J. Amer. Chem. SOC.,1974 96,4050. A. Viola S. Madhavan R. J. Proverb B. L. Yates and J. Larrahondo J.C.S. Chem. Comm.. 1914.842. Aliphatic Compounds-Part (i) Hydrocarbons Reagents i THF -65 "C;ii 0 ;iii H +;iv PhCN ;v HCl-MeOH ;vi vii NH,Cl Scheme 11 corresponding carbonyl compounds with dilute acid (Scheme 11).Exclusive 1,Zaddition is observed when ap-unsaturated carbonyl compounds are used.62 ~r-(2-Methoxyallyl)nickel bromide (91)has been prepared :it reacts with halides aldehydes and ketones introducing the acetonyl functional group (Scheme 12).63 Br . MeO</ +Ni(CO) -MeO<:Nil ,Ni,;>OMe CH,Br Br (91) / H H \c=c/H+(91)-DMF \c=c/H 84 % Hi /\ Ph /\ Br Ph CH,COMe Scheme 12 Tungsten and molybdenum atoms generated by resistive heating of their respective wires react with butadiene on co-condensation at liquid nitrogen temperatures. Trisfbutadienyl) tungsten is obtained as a white crystalline material which is fairly stable in air ;the corresponding molybdenum compound is yellow.Tungsten(0) and molybdenum(0) complexes are difficult to obtain with ligands other than C0.64 62 J. G. Baldwin G. A. Hofle and 0.w. Lever J. Amer. Chem. SOC.,1974 96,7125. 63 L. S. Hegedus and R. K. Stiverson J. Amer. Chem. SOC.,1974 96 3250. 64 P. S. Skell E. M. Van Dam and M. P. Silvon J. Amer. Chem. SOC.,1974 96 626. 266 R.S. Atkinson 2-Phenyl-1,3-oxathiolans[e.g. (92)] fragment to olefins and lithium thioben- zoate on treatment with strong bases. As a result of the higher acidity of the C-2 proton this reaction seems to be more widely applicable than the correspond- ing fragmentation of 2-phenyl-l,3-dio~olans.~~ A simple in situ method of hydroboration of olefins uses sodium borohydride in THF-acetic acid.The stereospecificity and yields in the reaction are com- parable with those obtained using gaseous diborane.66 Borane-methyl sulphide is a stable liquid BH complex which is now commercially available. It has several advantages over borane-THF for the hydroboration-oxidation of olefins including its greater solubility in a wide variety of ~olvents.~' Deu teriated terminal olefins have been prepared from carbonyl compounds. ['HJmethylene iodide and magnesium amalgam. In contrast to the Wittig reaction no scrambling of the label occurred in the products.68 A study has been made of butadienes which have bulky substituents hindering attainment of cisoid and transoid conformations and hence giving rise to atro- pisomers as in the case of hindered biphenyls.Thus the butadienes (93)and (94) CO,H O CO H HOCH,C-CC=CCH,OH @OCH,C~CC~CCH~O -"Q; \ CO H Y/ ,Br c=c Br HOCH /\/ \ /Br ... . I1I.IV Br .C=C. ,Br 1 /c=c\ Br /\/ Br' CH,O,C Br /c=c\ CH,OH (93) Reagents i. phthalic anhydride; ii 2Br,; iii resolve; iv NaOH Scheme 13 65 M. Jones P. Temple E. J. Thomas and G. H. Whitham J.C.S. Perkin I 1974 433. 66 V. Hach Synthesis 1974 340. 67 C. F. Lane H. L. Myatt J. Daniells and H. B. Hopps J. Org. Chem. 1974 39 3052; C. F. Lane ibid. p. 1437. 68 D. Hasselmann Chem. Ber. 1974 107 3486. A lip hat ic Compounds-Par t (i) Hydrocarbons 267 have been partially resolved (Scheme 13). Both (-)-(93) and (-)-(94) are optically stable in the solid state however they gradually racemize in solution at room temperat~re.~~ Allylic bromination with N-bromosuccinimide has been considered to be a radical-chain mechanism involving free bromine as a result of the similarity in substitution pattern by the two reagents at allylic positions of substituted alkenes.Further support for this mechanism has come from the use of NBS under con- ditions where the succinimidyl radical is the chain carrier (Scheme 14).70This Br Scheme 14 involves increasing the concentration of NBS by changing the solvent to aceto- nitrile and carrying out the bromination in the presence of ethylene which scavenges both Bra and Br . The succinimidyl radical reveals itself as a species of low discrimination in hydrogen abstractions.It appears that the success of the Ziegler bromination using NBS in CCl is directly attributable to the low solubility of NBS in this solvent. [>-CH=CH % wHCH,Br wHBrCH,Br + BrCH,CH,CH=CHCH,Br (1) 0 b(0PO Et2)= CH p(OPO,Et,)Me -+ FMe (3) -FYIH2 -+ I1 [>-CH=CH ArSCl wHClCH,SAr (4) S 'Ar The effect of a cyclopropyl group upon the rates of electrophilic addition to alkenes has been ~tudied.~' Acceleration by large factors (ca. lo3)occurs for cyclopropyl relative to phenyl when the transition state for addition leads to a 69 M. Rosner and G. KiSbrich Angew. Chem. Internat. Edn. 1974 13 741. 'O J. C. Day M. J. Lindstrom and P. S. Skell J. Amer. Chem. SOC.,1974 96,5616. D. G. Garratt A.Modro K. Oyama G. H. Schmid T. T. Tidwell and K. Yates J. Amer. Chem. SOC.,1974 % 5295. R.S. Atkinson relatively open positive charge on the adjacent carbon [reactions (1) and (2)]. However small rate differences occur (factors between 1and 4)when the substrate contains another strongly stabilizing substituent [reaction (3)] or when a bridged intermediate is formed [reaction (4)]which precludes resonance stabilization. Hence the magnitude of the acceleration gives an indication of the transition state structure.

ISSN:0069-3030    

DOI:10.1039/OC9747100247

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

10 Aliphatic Compounds Part (ii) Other Aliphatic Compounds By E. W. COLVIN Chemistry Department University of Glasgow Glasgow G 12 800 The major areas of activity over the past year include the following :continuing detailed studies of the tetrahedral intermediate involved in carbonyl substitution reactions and the not unrelated topic of the protonation site of amides; the proof and spatial definition of front octants for ketones (see chapter 2 p. 37); amplification of the exciton chirality method for configuration determination ; and more structural studies on P-halogeno-alkyl radicals. 1 Carboxylic Acids From measurements of gas-phase equilibria the intrinsic acidities of a- p- and y-chloro-substituted aliphatic acids have been evaluated ;’ the effects of the chloro-substituent parallel those in solution but they are much larger the attenuation in solution is attributed to weaker H-bonding of the chloro-stabilized acid anions to water molecules.Related studies have been carried out on substi- tuent effects on the intrinsic acidities of benzoic acids,’ and on the intrinsic acidities of carbon acids.3 Some of the techniques and results of gas-phase acidity and basicity determinations have been re~iewed.~ 2 Peracids The preparations of a number of new peracids have been described and their epoxidizing abilities have been delineated. 0-Benzylmonoperoxycarbonic acid (1) is quite stable in the cold and shows’ reactivity intermediate between those of m-chloroperbenzoic acid and perbenzoic acid the last having now been prepared on a polymer support.6 The peroxycarbamic acids (2) and (3) have been generated in situ (3) having been isolated and crystallized ;’both efficiently convert olefins into epoxides with concurrent production of innocuous by- products.‘ R. Yamdagni and P. Kebarle Canad. J. Chem. 1974,52 861. R. Yamdagni T. B. McMahon and P. Kebarle J. Amer. Chem. Soc. 1974,96 4035. T. B. McMahon and P. Kebarle J. Amer. Chem. Sac. 1974,96,5940. C. Agami Bull. SOC.chim. France 1974 869. R. M. Coates and J. W. Williams J. Org. Chem. 1974 39 3054. C. R.Harrison and P. Hodge J.C.S. Chem. Comm. 1974 1009. ’ J. Rebek S. F. Wolf and A. B. Mossman J.C.S. Chem. Comm. 1974 71 1. 269 270 E. W. Colvin Evidence has been presented* for the intervention of the 1,4-biradical l-oxa- tetramethylene (4) in the thermodecarboxylation of y-peroxy-lactones.0 3 Carboxylic Acid Anhydrides A dynamic n.m.r. spectroscopic investigationg of formic anhydride has revealed the EZ-configuration (5) in solution in accord with gas-phase electron-diffraction data; the low barrier (18$_1 kJmol-') for topomerization is taken as further evidence for the diminished importance of resonance in anhydrides in comparison to esters and imides. The conformations of some gem-dimethyl-substituted cyclic anhydrides have been determined." 4 Lactones While the n-+ T* Cotton effect of A2-butenolides is easily influenced by asym- metry external to the lactone ring the chirality at the y-carbon of the butenolide is the sole sign-determining factor in the 71 +T* c.d.spectrum ;the latter absorp- tion is therefore recommended' for the determination of absolute configuration of A2-butenolides. If X is greater than Y in polarizability then lactone (6) will show a negative effect and uice oersa. Equilibration studiesI2 on a number of 2,4-disubstituted y-butyrolactones have indicated that the cis-stereoisomer is the thermodynamically more stable in all cases. Detailed kinetic and mechanistic studiesI3 of the alkaline hydrolysis of a variety of lactone ring sizes have been reported in detail. W. Adam and L. M. Szendrey J. Amer. Chem. SOC.,1974,96,7135 ;see also W. Adam Angew. Chem. Internat. Edn. 1974 13 619. E. A. Noe and M. Raban J.C.S. Chem. Comm. 1974,479. ' G.Borgen Acta Chem. Scand. 1974 B28 13. I. Uchida and K. Kuriyama Tetrahedron Letters 1974 3761. S. A. M. T. Hussain W. D. Ollis C. Smith and J. F. Stoddart J.C.S. Chem. Comm. 1974,873. l3 G. M. Blackburn and H. L. H. Dodds J.C.S. Perkin If 1974 377; see also M. Balak-rishnan G. V. Rao and N. Venkatasubramanian ibid. p. 1093. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds 271 A number of naturally occurring lactones and tetronic acids have been synthe- sized or have had their syntheses improved. These include tetronic acid14 itself and some 5-carboxymethyltetronic acids,' including (S)-carlosic acid' (7). Pestalotin'7.'8 (€9,a synergist of gibberellins and ~trigol'~-~' (9) a germination stimulant of witchweed seeds have both yielded to elegant total syntheses.OH OH 5 a-Amino-acids Information regarding the rotamer populations of amino-acids can be obtained by considering the '3C-C-C-H coupling constant22 between the or-CO,-and the p-protons. A second chlorine-containing natural (L)-amino-acid (10) has \mco2-CI NH been isolated :2 optically pure vinylglycine has been synthe~ized.~~ 14 J. V. Greenhill and T. Tomassini Tetrahedron Letters 1974 2683. 15 A. Svendsen and P. M. Boll Tetrahedron Letters 1974 2821. 16 J. L. Bloomer and F. E. Kappler J. Org. Chem. 1974 39 I 13. 17 R. M. Carlson and A. R. Oyler Tetrahedron Letters 1974 2615. 18 D. Seebach and H. Meyer Angew. Chem. Internat. Edn. 1974 13,77. 19 J. B. Heather R. S. D. Mittal and C. J. Sih J. Amer. Chem.SOC.,1974,% 1976. 20 G. A. MacAlpine R. A. Raphael A. Shaw A. W. Taylor and H.-J. Wild J.C.S. Chem. Comm. 1974,834. 21 See also J. M. Cassady and G. A. Howie J.C.S. Chem. Comm. 1974 512. 22 J. Feeney P. E. Hansen and G. C. K. Roberts J.C.S. Chem. Comm. 1974 465. 23 S.-I. Hatanaka S. Kaneko Y.Niimura F. Kinoshita and G. Soma Tetrahedron Letters 1974 3931. 24 P. Friis P. .Helboe and P. 0. Larsen Acta Chem. Scand. 1974 B28,317. 272 E. W. Coluin RyCoz-Ac,O ”-,/’. I PY I NH,’ NHAc Scheme 1 Kinetic and mechanistic studies on the Dakin-West reaction (Scheme 1) have convinced Allinger’’ that the oxazolone mechanism alone is in accord with the experimental facts on this transformation. A chiral host molecule capable of achieving the total optical resolution of amino-acid ester salts by specific molecular complexation has been described.26 6 Carboxylic Acid Amides Although there is now considerable evidence for the formation of a tetrahedral intermediate in carbonyl substitution reactions the instability of this inter- mediate and the complicated kinetics of its simultaneous formation and break- down have precluded much detailed analysis.It has now been reported2’ that the reaction of the imidate cation (1 1) with nucleophiles proceeds via the stable tetrahedral species (12) permitting a thorough mechanistic study. An ab initio studyz8 of the reactivity of aminodihydroxymethane has provided theoretical evidence for the operation of marked stereoelectronic effects sub- 25 N.L. Allinger G. L. Wang and B. B. Dewhurst J. Org. Chem. 1974 39 1730; see also J. Lepschy G. Hofle L. Wilschowitz and W. Steglich Annulen 1974 1753. 26 L. R. Sousa D. H. Hoffman L. Kaplan and D. J. Cram J. Amer. Chem. SOC.,1974 96 7100; see also J. M. Timko R. C. Helgeson M. Newcomb G. W. Gokel and D. J. Cram ibid. p. 7097; M. Newcomb R. C. Helgeson and D. J. Cram ibid. p. 7367. 2’ N. Gravitz and W. P. Jencks J. Amer. Chem. SOC.,1974,96 489 499 507. J. M. Lehn and G. Wipff J. Amer. Chem. SOC.,1974,96,4048. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds 273 stantiating Deslongchamps' postulate2' that the direction of cleavage of the tetrahedral intermediate is controlled by lone-pair orbitals being orientated antiperiplanar to the bond being cleaved.The comparison of imidate and amide hydrolysis in concentrated acids may be unwarranted evidence having been presented3' that 0-alkyl cleavage occurs in the imidate case neutral amide H,O -Me '*O + II hi+ -+ H,O-Me + PhCNHMe II C Ph /\ NHMe Scheme 2 being the leaving group (Scheme 2). Other studies of amide3' and thi~amide~~ hydrolysis have been reported. The stereochemistry of open-chain O-methyl- imidates and large-membered cyclic lactim ethers has been revised33 to E. RTo 0 (13) From a careful study of the two sets of amides (13) and (14) using criteria such as ring size electronic effects change in hybridization during reaction and conjugation Kre~ge~~ has discounted N-protonated conjugate acids not only as the principal products of equilibrium protonation of amides in dilute and moderately concentrated aqueous acids but also as essential intermediates in acid-catalysed amide hydrolysis.The predominant protonated form of DMF in aqueous acid is the 0-protonated amide a doublet methyl signal being observed3' by I3Cn.m.r. spectroscopy at all acidities. Further evidence has been presented36 for S-protonation of primary thioamides. Liler3 has published full details of her work on the site of protonation of benzamide and has promised a detailed response to the many critics of N-protonation. 29 P. Deslongchamps P. Atlani D. Frthel and A. Malaval Canad. J. Chem. 1972 50 3405; P.Deslongchamps C. Lebreux and R. Taillefer ibid. 1973 51 1665. 30 R. A.McClelland J. Amer. Chem. SOC.,1974 96 3690. 3' B. C. Challis and S. P. Jones J.C.S. Chem. Comm. 1974 748. 3z A. J. Hall and D. P. N. Satchell Chem. and Ind. 1974 527. 33 C. 0.Meese W. Walter and M. Berger J. Amer. Chem. SOC.,1974,96 2259. 34 A. J. Kresge P. H. Fitzgerald and Y. Chiang J. Amer. Chem. SOC.,1974,96 4698. 35 R. A. McClelland and W. F. Reynolds J.C.S. Chem. Comm. 1974 824. 36 W. Walter M. F. Sieveking and E. Schaumann Tetrahedron Letters 1974 839. 3' M. Liler J.C.S. Perkin ff 1974 71. 274 E. W. Colvin A spectroscopic investigation3* has shown that while bistrimethylsilylform- amide has the amide structure (15) all other bistrimethylsilylamides studied are in the imidate form (16). An ab initio study of hydrogen bonding involving the amide linkage has been rep~rted,~’as has an n.m.r.spectroscopic study4’ of hydrogen exchange in on have amidiurn ions. Hartree-Fock SCF calc~lations~~ amido-radi~als~~ predicted the TI ground state (17) in accord with e.s.r. spectroscopic assignments. 7 Ketones and Aldehydes An ab initio study43of nucleophilic addition to the carbonyl group has pro- duced results in qualitative agreement with those derived from solid-state data. A similar of the protonation of the carbonyl group gave a basicity order of amide > carboxylic acid > acid fluoride ‘Y acetaldehyde > keten > form-aldehyde an order which closely follows the degree of negative charge on oxygen. Gas-phase ionic reactions related to acid-catalysed carbonyl reactions in solution have been studied4’ by ion-cyclotron resonance.Cyclohexanone and acetophenones form complexes with AgBF in dichloro- methane as shown46 by the enhanced solubility of the silver salts. I3C n.m.r. spectroscopic evidence indicated that the carbonyl group is acting as a n-donor ” C. H. Yoder W. C. Copenhafer and B. DuBeshter J.Amer. Chem. SOC.,1974,96,4283. 39 A. Johansson P. Kollman S. Rothenberg and J. McKelvey J. Amer. Chem. SOC. 1974,96 3794. 40 C. L. Perrin J. Amer. Chem. SOC.,1974 96 5629 5631. 41 T. Koenig J. A. Hoobler C. E. Klopfenstein G. Hedden F. Sunderman and B. R. Russell J. Amer. Chem. SOC.,1974 96 4573. 42 J. N. S. Tam R. W. Yip and Y. L. Chow J. Amer. Chem. SOC.,1974,96,4543,4573 O3 H. B. Biirgi J. M. Lehn and G. Wipff J.Amer. Chem. SOC.,1974,96 1956. 44 A. C. Hopkinson and I. G. Csizmadia Cunud.J. Chem. 1974,52,546; see also A. Levi G. Modena and G. Scorrano J. Amer. Chem. SOC.,1974 96 6585; D. G. Lee and M. H. Sadar ibid. p. 2862. 45 J. K. Pau J. K. Kim and M. C. Caserio J.C.S. Chem. Comm. 1974 120 121. 46 D. R.Crist Z.-H. Hsieh G. J. Jordan F. P. Schinco and C. A. Maciorowski J. Amer. Chem. SOC.,1974,96,4932. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds giving a rather weak Ag-0 bond (18); no evidence of syn-anti isomerism could be detected even at low temperatures. (18) The resolution of ketones and the determination of their specific rotation via formation of the corresponding dioxolans with chiral 1,Zdiols have been des- ~ribed.~’3C n.m.r.chemical shifts of carbonyl and thiocarbonyl groups have been ~orrelated.~’ Harris49 has published a welcome review of his work on the synthesis of p-polycarbonyl systems and their cyclization to polyketide metabolites. The 6-tetraketone (19) has been prepared5’ and identified with ‘Harris’s tetraketone’ isolated in 1914 by degradation of caoutchouc. Dioxocarboxylic acids which occur in significant amounts in plant cuticular lipids can be readily obtained5’ by alkylation of acetylacetone dianion with m-bromoalkanoates (Scheme 3). Scheme 3 Acetylacetone forms two isomeric enol acetates (20) and (21) both in the (S)-cis-conformation in approximately equal proportions (Scheme 4);the stability (20) Scheme 4 47 J. Y. Conan A. Natat F. Guinot and G.Lamaty Bull. SOC. chim. France 1974 1400 1405; Tetrahedron Lerters 1974 1667; J. Brugidou H. Christol and R. Sales Bull. Soc. chim. France 1974 2027,2033. 48 H.-0. Kalinowski and H. Kessler Angew. Chem. Internat. Edn. 1974 13 90. 49 T. M. Harris C. M. Harris and K. B. Hindley Fortschr. Chem. org. Nafurstoffe 1974 31 217. B. Franck V. Scharf and M. Schramayer Angew. Chem. Internat. Edn. 1974,13 136. ’’ R. 0.Pendarvis and K. G. Hampton J. Org. Chem. 1974,39,2289. 276 E. W. Coluin of the isomer (20) is attributed5* to some degree of neighbouring-group inter- action a rationale consistent with 'H n.m.r. spectroscopic data. In work based on the conceptually useful analogy between mass spectrometric and anodic chemistry it has been found53 that anodic oxidation of simple ketones in acetonitrile leads to y-hydrogen abstraction with subsequent solvent .z% Hzo* MeCN a,, NHCOMe Scheme 5 capture and/or rearrangement/capture (Scheme 5); no &cleavage is observed.Improved syntheses of m~condialdehyde~~ and t-b~tylmalondialdehyde~ have been described. (S)-(+ )-4-Methylheptan-3-one the principal alarm pheromone of the ant Atta texana has been synthesized in high optical 8 Alcohols Complexing agents such as copper hexafluoroacetylacetonate,are of considerable utility in the determination of absolute configuration of alcohols glycols and related systems by the exciton chirality method,57 which has been demonstrated to be operative5' even at considerable separation of the two interacting chromo- phores ; it has also been applied5' to the chirality determination of conjugated enone ester and lactone benzoates.The absolute configurations of chiral secon- dary alcohols (and amines) can be ascertained6' by a study of the 'H n.m.r. spectra of the derived diastereoisomeric esters (and amides) of or-phenylbutyric and hydratropic acids. Significant preparative-scale resolution of racemic alcohols can be achieved61 via their hippurate esters by selective hydrolysis catalysed by a-chymotry psin. 52 D. V. C. Awang Canad. J. Chem. 1973,51 3752. 53 J. Y. Becker L. R. Byrd and L. L. Miller J. Amer. Chem. Soc. 1974,96,4718. 54 G. Kossmehl and B. Bohn Chem. Ber. 1974 107,710. 55 C. Reichardt and E.-U. Wiirthwein Chem. Ber. 1974,107 3454.56 R. G. Riley and R. M. Silverstein Tetrahedron 1974 30 1171. 57 J. Dillon and K. Nakanishi J. Amer. Chem. SOC.,1974,96,4055 4057,4059. '* S. L. Chen N. Harada and K. Nakanishi J. Amer. Chem. SOC.,1974,96,7352. 59 M. Koreeda N. Harada and K. Nakanishi J. Amer. Chem. Sac. 1974 96,266. 6o G. Helmchen Tetrahedron Letters 1974 1527. 6' Y. Y. Lin D. N. Palmer and J. B. Jones Canad. J. Chem. 1974 52 469. A lip hatic Compo unds-Par t (ii ) 0ther Aliphatic Compounds 277 The average solution conformations of all 18 possible isomers of the six- carbon aliphatic alcohols have been elucidated62 by 'H and 13C n.m.r. spectro- scopic studies. The thermochemistry of some aliphatic alcohols has been studied63 using pulsed ion-cyclotron resonance spectroscopy.The copper-catalysed vapour-phase rearrangement of allylic alcohols to saturated ketones appears64 to proceed by initial dehydrogenation generating a small amount of @-unsaturated ketone. In the rate-limiting step the C-3 hydrogen of the alcohol is transferred to the enone fi-carbon atom (Scheme 6). @-f++-A.(+q/ slow 0 OH 0 OH 0 0 Scheme 6 9 Amines While in most cases correlation of the absolute configurations of chiral amines with results from the Horeau method is valid it has been re~omrnended~~ that such assignments should always be substantiated by direct chemical correlation or by unambiguous c.d. measurements. Bis-2,4-dinitrophenyl derivatives of diamines show66 induced Cotton effects allowing chirality determination ;those with negative C-N chirality show a negative Cotton effect for the longest wave- length band.10 Alkyl Halides Ab initio calculation^^^ on the geometric structure and energy surface of the chloroethyl cation have given results in good agreement with those derived experimentally from super-acid data. Further evidence68 of a bridged transition state in the formation of P-bromoalkyl radicals has been presented. P-Chloro- and /3-bromo-t-butyl radicals (22) and (23) have been generated in a [2H16]adamantane matrix by X-irradiation of isobutyl chloride or bromide at 77 K. E.p.r. spectroscopic studies have shown6' that while radical (22) prefers the same eclipsed conformation (25) as it does in solution radical (23) prefers the staggered conformation (26); radical (23) is much less stable than (22).The analogous /3-fluoro-radical (24) also prefers an eclipsed conformation. 62 K. L. Williamson D. R. Clutter R. Emch M. Alexander A. E. Burroughs C. Chua and M. E. Bogel J. Amer. Chem. SOC.,1974,96 1471. 63 R. T. McIver and J. S. Miller J. Amer. Chem. SOC.,1974 96 4323. 64 G. Eadon and M. Y. Shiekh J. Amer. Chem. Soc. 1974,96 2288. 65 H. E. Smith A. W. Gordon and A. F. Bridges J. Org. Chem. 1974 39 2309. 66 M. Kawai U. Nagai and T. Kobayashi Tetrahedron Letters 1974 1881. 67 W. J. Hehre and P. C. Hibberty J. Amer. Chem. SOC.,1974,96 2665. " E. N. Cain and R. K. Solly J.C.S. Chem. Comm. 1974 148. 6q R. V. Lloyd D. E. Wood and M. T. Rogers J. Amer. Chem. SOC.,1974,96 7130. 278 E. W. Colvin CI Me2CCH2X (22) x = c1 MeH AMe hI@Le (23) X = Br H (24) X = F H (25) (26) N.m.r.spectroscopic studies7' of 2-fluoroethanol have confirmed that the major conformer (95%) is gauche (27); no evidence of intramolecular F-H bonding could be detected. H$? H 11 SulphurCompounds The first example of asymmetric induction promoted by isotopic dissymmetry has been pre~ented.~ Halogenation of the chiral sulphoxide (28) followed by oxidation resulted in optical activity in the a-halogenosulphone (29). CH,Ph PhCD,- S -00 PhCD2S02EHPh IX (28) (29) A further example of the intramolecular transfer of chirality from sulphur to carbon is seen'2 in the Pummerer-type rearrangement of chiral (30) to (31) (Scheme 7). Reagent :i dicyclohexylcarbodi-imide Scheme 7 '* R.C. Griffith and J. D. Roberts Tetrahedron Letters 1974 3499. 'I M. Cinquini and S. Colonna J.C.S. Chem. Comm. 1974 769. '* B. Stridsberg and S. Allenmark Actu Chem. Scand. 1974 BR8 591. Aliphatic Compounds-Part (ii) Other Aliphatic Compounds t-Butyl- and n-butyl-lithium are unsatisfactory bases for the generation of u-sulphinyl carbanions owing to competitive C-S bond cleavage ; the chiral sulphoxide (32) is ra~ernized~~ in a few minutes at -78 "C(Scheme 8). Methyl-lithium or a lithium dialkylamide are much better reagents for such carbanion formation. 0 0 I I Bu'Li + Bu'S*Ar -+ Bu'SAr + Bu'Li (32) Scheme 8 12 Miscellaneous Further detail^'^?^ have been given of the determination of enantiomeric purity by n.m.r.spectroscopy using chiral lanthanide shift reagents. The defensive compound in the frontal-gland secretion of soldier termites has been identified76 as 1-nitro-trans-pentadec-1-ene.The chemistry of hydroxamic acids and N-hydroxy-imide~~~ has been reviewed as has that ofcarbon suboxide:8 C,02 a precursor of inter alia malonic acid derivatives and of halogenovinylene carbonate^.'^ 73 T. Durst M. J. LeBelle R. V. den Elzen and K.-C. Tin Canad. J. Chem. 1974,52,761. 74 M. D. McCrearty D. W. Lewis D. L. Wernick and G. M. Whitesides J. Amer. Chem. SOC.,1974 96 1038. 75 H. L. Goering J. N. Eikenberry G. S. Koermer and C. J. Lattimer J. Amer. Chem. Sac. 1974 96 1493. l6 J. VrkoE and K. Ubik Tetrahedron Letters 1974 1463.77 L. Bauer and 0. Exner Angew. Chem. Internat. Edn. 1974 13 376. 78 T. Kappe and E. Ziegler Angew. Chem. Internat. Edn. 1974 13 491. '' H.-D. Scharf Angew. Chem. Internat. Edn. 1974 13 520.

ISSN:0069-3030    

DOI:10.1039/OC9747100269

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

11 Aromatic Compounds By T. J. TEWSON Department of Chemistry University of Manchester Institute of Science and Technology Sackville Street Manchester 1 General Ah initio and semi-empirical INDO methods have been applied to benzene Dewar benzene benzvalene and prismane and gave values for equilibrium geometries dipole moments and spin-spin coupling constants in good agreement with known values.' A full report of the non-empirical ab initio valence-bond treatment of benzene shows greater contribution from polar wavefunctions than has been shown before and gives good correlation for resonance energy2 which previous valence-bond treatments have failed to do. The vaiue of the diamagnetic ring current as a measure of aromaticity has been q~estioned,~ out-of-plane magnetic susceptibility being dependent on delocaliza- tion but not necessarily on aromaticity thus reviving the whole problem of defining aromaticity.X-Ray crystal analysis of 1,8-(dibromomethy1)naphthaleneshows that the hydrogens and bromine approach closer than the van der Waals radius4 and some strain is relieved by bending substituents out of plane and distorting the nucleus. N.m.r. measurements of rotation in substituted 1,3,5-trineopentyl-benzenes establish AG' and relative sizes of hydrogen fluorine chlorine bromine methyl and i~dine.~ Variations in 'through-space' fluorine-fluorine coupling in substituted 1,8- difluoronaphthalenes have been attributed to variations in distance between fluorines caused by the substituent.6 The synthesis and conformational inversions of a series of hindered unsym- metrically and symmetrically substituted triarylmethanes have been rep~rted.~ ' M.D. Newton J. M. Schulman and M. M. Manus J. Amer. Chcm. SOC..1974,96 17. J. M. Nabeck and G. A. Gallup J. Amer. Chem. SOC.,1974 96,3386. T. G. Schmatz T. D. Gierke P. Beak and W. H. Flygare Terrahedron Letters 1974 2885. J. R. Robert J. S. Sherfinski R. E. Marsh and J. D. Roberts J. Org. Chem. 1974 39 11 52. B. Nilsson P. Marlinson K. Oisson and R. Carter J. Amer. Chem. Soc. 1974 96 3 190. F. B. Mailory C. W. Mallory and M.-C. Fedarko J. Amer. Chem. Soc. 1974,96 3536. P. Finocchiaro D. Gust and K. Mislow J. Amer. Chem. Soc. 1974 96,2165 3198 3205. 281 282 T. J. Tewson Enantiomers invert by a 'two-ring flip' mechanism which is comparatively slow at room temperature (AG = -21.9 kcal mol- for trimesitylmethane) but di- astereoisomers invert by a 'one-ring flip' which is considerably slower.Theoret- ical calculations using full relaxation empirical force field methods' confirm the propeller-like conformations and show that the central carbon+arbon bond is stretched and the central CCC angle expanded to 117.7" to accommodate the strain. The calculations also agreed with the 'two-ring flip' mechanism of in-version. N.m.r. studies of the conformations of o-substituted diphenyl-ethers -sulphides -methanes -ketones -sulphoxides and -sulphones9 have been per- formed and the conformations of p-fluoro o-substituted-acetophenones a-methylstyrenes and am-dimethylbenzyl alcohols studied by the effect of con- jugation on the 19Fchemical shifts." The free energy difference of axial and equatorial benzyl groups has been estimated'' by n.m.r.methods as 1.81 kcal mol-' in favour of the equatorial substituent. Collisional activation energy spectra of C,H,+ ions have been obtained12 and these can be tropylium benzyl o-tolyl m-tolyl p-tolyl and norbornadienyl ions which do not interconvert in the time sequence of the technique s). The same technique applied to carbocations from ethylbenzene showed that a /? and spiro ions (1 )-43) are all stable,' although (2)does rearrange to (3). Benzyl + or spiro-cations formed in strong acids from aromatics containing electron- donating groups show an e.s.r.signal corresponding to ca. 5 :d of cation concen- tration. The signal intensity is reversibly temperature dependent disappears in the presence of oxygen and is suggested to be due to a tri~1et.I~ C6F6+AsF6-has been prepared in tungsten hexafluoride ~olution'~ and is a paramagnetic species presumably a triplet. Photolysis of hexachlorobenzene in the presence of antimony pentafluoride containing chlorine gave C6C16' +,16 which is also a triplet. Protonation of phenols and alkoxybenzenes in superacid shows that 8 J. D. Andose and K. Mislow J. Amer. Chem. SOC.,1974,96 2168. 9 H. Benjamins and W. D. Chandler Canad. J. Chem. 1974,52 597. LO M. G. Belsham A. R. Muir M. Kinns L. Phillips and Li-Ming Twanmoh J.C.S. Perkin 11 1974 119. I1 J. E.Anderson J.C.S. Perkin II 1974 10. 12 F. W. McLafferty and J. Winkler J. Amer. Chem. SOC.,1974 96 5182. 13 N. M. Nibbering T. Nishishita C. C. Van der Sande and F. W. McLafferty J. Amer. Chem. SOC.,1974 96 5668. 14 M. Ya. Zarubin A. M. Kutnevich and A. P. Lukashenko Zhur. org. Khim. 1974 10 400. 15 T. J. Richardson and N. Bartlett J.C.S. Chem. Comm. 1974,427. 16 E. Wasserman R. S. Hutton V. J. Kuck and E. A. Chandross J. Amer. Chem. Soc. 1974 96 1966. Aromatic Compounh 283 oxygen and carbon protonation follow different acidity functions' and both are solvent dependent. The ion (4)is irreversibly transformed into (5) on heating to 40 "C as the charge is stabilized by the methyl group." Homoaromaticity.-Molecular orbital treatment" of tropylium anions and cations with respect to homoaromaticity nonhomoaromaticity antihomoaro- maticity and dihomoaromaticity shows that the opened cyclopropyl ring is favoured in all forms including the dihomotropylium ion (6).Ab initio molecular orbital treatment of circumambulatory degenerate rearrangements of bicyclo- [3,l,O]hexenyl and homotropylium cations shows that the former goes with inversion as has been found experimentally and is antiaromatic and so de-stabilized with respect to the transition state whilst the latter should go with retention but is aromatic and so stabilized with respect to the transition state.20 Homocyclopropenyl cation (7) the simplest homoaromatic system possible has been prepared.21 Benzene Oxides Episulphides and Cyclopropa-Aromatics.-Low-temperature photolysis of benzene oxide naphthalene 1,2-oxide and phenanthrene 9,lO-oxide shows oxygen migration and formation of keto-phenols and ketones.22 syn-Benzene bisepisulphide does not isomerize to the 1On system (8) although this is an allowed process.23 The biphenylene oxide (9) has been ~ynthesized~~ " J.W. Larsen and M. Eckert-Maksic J. Amer. Chem. SOC.,1974 96 431 1. T. V. Chuikova. A. A. Shtark. and V. D. Shteingarts Zhur. org. Khim. 1974 10 132. R.C. Haddon Tetrahedron Letters 1974 2797. *' W. J. Helrre J. Amer. Chem. SOC.,1974 96 5207. G. A. Olah J. Starral and G. Liang J. Amer. Chem. Suc. 1974 96 6233. 22 D. M.Jerima B. Witkop C. L. McIntosh and 0. L. Chapman J. Amer. Chem. SOC. 1974,% 5579. 23 E. Vogel E.Schmidbauer and H.-J. Altenbach Angew. Chem. Internat. Edn. 1974 13 736. 24 G. Jikeli and H. Gunther Angew. Chem. Internat. Edn. 1974 13 277. 284 T.J. Tewson and is quite stable. o-Bromobenzyl methyl ether gives benzocyclopropene on treatment with n-butyl-lithium but attempted Birch reduction of the product gives only ring-opened material.” The structure of the product from p-quinone dibenzenesulphonimide and diphenyldiazomethane has been reassigned*‘ and is (10)rather than a benzene derivative. Two reactions suggest the formation of dibenzobicyclo[4,1,0]heptatriene (11) as an intermediate trapping experiments with dienes2’” and thi01s~’~ giving products derived from the cyclopropene compound. 2 Benzene and its Derivatives The n-complex uersus a-complex or ‘early’ uersus ‘late’ transition-state argument for electrophilic substitution with extremely active electrophiles continues.Competitive rates for boron-trifluoride-catalysed nitration with methyl nitrate in nitromethane show better correlation with n-complex than a-complex mechanism,**“ although neither correlation coefficient is very good. This method has the advantage that the possibility of mixing control is removed. On the other hand nitration with NOz+BF,- and NOz+PF,-gives normal substrate selec- tivities and o :rn :p ratios with deactivated aromatics such as nitrobenzene and nitrotoluene.28h A long study of the additivity principle in bromination and nitration reactions29 concludes that in nitration the toluene to benzene rate ratio should be 79 rather than 20 as is found by direct measurement suggesting that even in ‘normal’ nitration either a n-complex mechanism or diffusion con- trol is involved.Nitration of 1,2,4-trimethylbenzene with sulphuric-nitric acid mixtures shows large variation in the ratio of 5 to 6 substitution with sulphuric acid ~trength.~’ This suggests that ipso-attack and subsequent rearrangement is important and that this rather than a n-complex mechanism can explain the anomalous rate ratios. Tetranitrotitanium(1v) nitrates aromatic hydrocarbons in high yield,31 but competitive reactions show a low toluene to benzene ratio 25 P. Radlick and H. T. Crawford J.C.S. Chem. Comm. 1974 127. 26 A. G. Pinkins and J. Tsuji J. Org. Chem. 1974 39 497. *’ (a) W.E. Billups L. P. Win and W. Y. Chow J. Amer. Chem. SOC.,1974 96 4026; (b)T. T. Coburn and W. M. Jones J. Amer. Chem. SOC.,1974 96 5218. 28 (a) G. A. Olah and H. C. Lin J. Amer. Chem. SOC.,1974 96 2892; (b)G. A. Olah and H. C. Lin ibid. p. 549. 29 R. Daneli A. Ricci H. M. Gilow and J. H. Ridd J.C.S. Perkin If 1974 1477. ’* R. B. Moodie K.Schofield and J. B. Weston J.C.S. Chem. Comm. 1974 382. ’’ R. G. Coombes and L. W. Russell J.C.S. Perkin fI 1974 830. Aromatic Compounds of cu. 4 with normal o:p substitution suggesting that a n-complex is the rate- determining step. Nitrato-complexes of zirconium(1v) and iron(Ir1) give the same o :p ratios for aromatic hydrocarbons but different amounts of 3- and 4-sub- stituted products with pyridine and q~inoline,~~ suggesting that n-complexes are involved.Electrophilic substitution reactions which give cyclohexadiene intermediates have been reviewed33 and the reaction of 26 different phenols in the solid state with gaseous chlorine has been to give high yields of substitution products but often with isolatable cyclohexadienones as intermediates. Anomal- ously high amounts of p-substituted products in the bromination of phenols with N-bromosuccinimide and 2,4,6,6-tetrabromocyclohexadienonehave been shown to be due to electrophilic addition of HBr either in 1,2 or 1,4 fashion.35 The 1,2-addition compound rearranges to give the 1,4-product which then gives p-bromophenol. Nitrations in acetic acid or acetic anhydride of methyl-benzenes often give side-chain substitution.This has been shown to be due to elimination from the 1,4-addition product (12) to give the methylenecyclo- hexadiene( 13) which can react further with the reagents.36 I-Chloro-2,3-dimethyl- benzene gives a similar addition pr~duct,~’ but in strong acid this eliminates CI OAc CH ’’NO (1 <\ acetic acid to give the benzenonium ion (14) which in the presence of mesitylene gives the biphenyl (15). 2,3- and 2,4-Dimethylbenzonitriles also give 1,4-addition in nitric-acetic acid mixtures but in this case strong acid gives phenyl acetates rather than the benzenonium ion.38 Measurement of ionization and appearance potentials of alkyl-substituted benzenes to determine whether the Nathan-Baker order is due to solvation gave inconclusive results but definitely established that bulky groups affect conjugative interaction^.^' Hydrogen exchange on 9,10-dihydro-9,10-(trans-ll-amino-12-32 R.G. Coombes and L. W. Russell J.C.S. Perkin I 1974 1751. 33 P. B. de la Mare Accounts Chem. Res. 1974 7 361. 34 R. Lamarfine and R. Perrin J. Org. Chem. 1974 39 1744. V. Cato L. Lopez G. Pesco C. and P. E. Todesco J.C.S. Perkin ZZ 1974 1 189 I 192. 36 A. J. Fischer and J. N. Ramsay J. Amer. Chem. Soc. 1974 96 1616. 37 A. Fisher and C. C. Greig J.C.S. Chem. Comm. 1974 50. 38 A. Fischer and C. C. Greig Cunud. J. Chem. 1974 52 1231. 3g D. A. Ponomarev V. V. Takhistov M. E. Akopyan and Yu. L. Sergeev Zhur. org. Khim.,1974 10 403. 286 T. J. Tewson methy1ethano)anthracene (16) shows no difference in reactivities of the two rings in spite of the predicted field effect of the protonated nitr~gen.~' Anilinium ions in general showed a marked deviation from the addivity principle in nitration reactions:l owing to independent directing effects not shown in monosubstituted benzenes.Increasing the sulphuric acid concentration in nitric-sulphuric acid nitrating mixtures leads to the rate of nitration of toluene changing from first- to zero-~rder.~~ This is interpreted as establishing that formation of the nitron- ium ion becomes the rate-limiting step but the same result in nitric acid-acetic anhydride mixtures is shown to be a medium effect43 and not due to formation of the electrophile. Friedel-Crafts acylation of bromotoluenes and xylenes has been reported to give anomalous products but careful examination of partial rate factors shows that the unexpected products are in fact as expected !44 Friedelxrafts alkylation of benzene with optically active 2-chloro- 1-phenylpropane at low temperature gives 1,2-diphenylpropane with almost complete retention of optical presumably through the concerted formation of the ion (17).Alkyl chloro- sulphites arenesulphinates chloro- and fluoro-sulphates and sulphones react with aromatic hydrocarbons in the presence of aluminium chloride or antimony pentafluoride to give alkylated rather than sulphonated product~.~~'*~ The reaction is highly selective and toluene-benzene rate ratios in competitive re- actions correlate well with Brown's g+,giving a positive p value.46' However aromatic sulphoxides undergo deoxygenation on treatment with thionyl chloride 40 A.J. Layton J. H. Rees and J. H. Ridd J.C.S. Chem. Comm. 1974 518. 41 R.S. Cook R. Phillips and J. H. Ridd J.C.S. Perkin ZZ 1974 1 166. 42 J. W. Chapman and A. N. Strachan J.C.S. Chem. Comm. 1974,293. 43 N. C. Marziano J. H. Rees and J. H. Ridd J.C.S. Perkin IZ 1974 600. 44 T. A. Elwood W. R. Flack K. J. Inman and P. W. Rabideau Tetrahedron 1974 30 535. 45 S. Masuda T. Nakajima and S. Suga J.C.S. Chem. Comm. 1974 954. 46 (a)G. A. Olah J. Nishimura and Y.Yanada J. Org. Chem. 1974,39,2430; (b)G. A. Olah and J. Nishimura J. Amer. Chem. SOC. 1974 96 2214; (c) G. A. Olah and J. Nishimura J. Org. Chem. 1974 39 1203. Aromatic Compounds 287 and Friedel-Crafts catalysts47 and chlorosulphonylbenzoyl chlorides acylate rather than sulphonate in the presence of aluminium tri~hloride.~' Tetra- chlorocyclopropene reacts with aromatic hydrocarbons in the presence of aluminium chloride to give initially aryltrichlorocyclopropenes,49which react further with the catalyst to give arylcyclopropenium salts.Substituent effects are transmitted across the cyclopropene ring. Substituted 1,2,4,5-tetrafluorobenzene reacts with sulphur sulphur monochloride sulphur dichloride and pentafluoro- phenylsulphenyl chloride to give diary1 sulphides in good yield.50 Reaction of olefins with aromatics using tungsten hexachlorideeethylaluminium dichloride catalyst depends upon the intermediate complex formed with the catalyst.An olefin-aromatic complex gives alkylation whilst a bisolefin complex leads to metathesis of the olefin? The intermediate complexes formed in Friedel- Crafts acylations have been reviewed.'* Nitration studies on p-~ymene~,~ show that ipso-attack at the isopropyl group is the predominant reaction and the intermediate can either rearrange to give nitro-p-cymenes or be substituted with loss of the isopropyl group to give nitrotoluene whilst in compounds (18a-c; n = 2 3 or 4) the amount of ips0 attack increases with ring size.536 1,2-Dihydrobenzocyclobutenereacts with sulphur trioxide complexes to give 2(o-sulphophenyl)ethanol from ips0 @KH21" '\ (18) a;n = 2 b:n=3 c I1 = 4 attack and 3-and 4-sulphonic acids from conventional substit~tion,~~" the ratios depending upon the SO complex and the solvent used.Partial rate factors for sulphonation of alkyl benzenes show that fo decreases with increasing size of the alkyl group owing either to retardation of formation of the o-complex or to its collapse to the sulphonic acid; the isomer distribution for 5-and 6-substitution in the sulphonation of 3-substituted benzenesulphonic acid parallels conjugative electron release over the acid strength 104-1 15% H2S04,54C although the reaction is complicated by formation of sulphonic anhydrides. The discrepancy between p values for chlorination of 2-substituted thiophens and substituted benzenes with chlorine in acetic acid has been shown to be due to the 47 I. Granoth J.C.S.Perkin I 1974 2166. 48 E. C. Dart and G. Holt J.C.S. Perkin I 1974 1403. 49 J. S. Chickos E. Patton and R. West J. Org. Chem. 1974 39 1647. G. C. Yakobson G. C. Furin and T. V. Terent'eva Zhur. org. Khim. 1974 10 799. H. L. Hocks A. J. Hubert and Ph. Teyssie Terrahedron Lerrers 1974 874. s2 B. Chevrier and R. Weiss Angew. Chem. Internat. Edn. 1974 13 1. 53 (a)R. C. Hahn and D. L. Stack J. Amer. Chem. SOC.,1974 % 4335; (b)M. W. Galley and R. C. Hahn. ihid. p. 4337. 54 (a) A. Koeberg-Telder and H. Cerfontain J.C.S. Perkin I/ 1974 1200; (6) H. Cerfontain and Z. R. H. Schaasberg-Nienhus ibid. p. 536; (c) A. Koeberg-Telder C. Ris and H. Cerfontain ibid. p. 98. 288 T. J. Tewson use of incorrect data,55 and the values are in fact the same.Partial rate factors for molecular chlorination of methyl phenyl and diphenyl sulphoxides show the sulphoxide group to be activating whilst for protiodesilylation it is deactivating ; this is explained by interactions of the sulphoxide group with the reagents and solvent.56 Rates of nitration of methyl phenyl sulphoxide show that an equilib- rium of protonated and unprotonated sulphoxides is in~olved.~ ' Alkyl-aromatics adsorbed on silica are cleanly substituted by halogens with isomer distribution suggesting electrophilic sub~titution.~~ Chlorine or t-butyl hypochlorite in carbon tetrachloride chlorinate phenols giving high yields of ortho-products apparently by an ionic me~hanism.'~ Low-temperature chlorina- tion of anisole in the dark produces 1,3,4,5,6-pentachloromethoxycyclohexane via initial formation of 4-chloroani~ole.~~ Electrophilic substitution of aryl gem-dichlorocyclopropanesshows that the dichlorocyclopropyl group is largely para-directing unlike the cyclopropyl group.6 The nitrosyl complex [Ru(bipy),(NO)XI2 nitrosates activated aromatics in + good yield.62 Iodine tris(trifluor0acetate) gives aryl bis(trifluoroacetoxy)iodo- compounds the positional selectivity indicating an electrophilic reaction.63 A series of papers has been published on the preparation of o-substituted amines phenols and thiophenols via intermediates formed on the heteroatoms.Thus N-aryl nitrones give o-chloro-imines on treatment with thionyl chloride or phosgene,6Q and o-hydroxy-amines on treatment with oxalyl followed by hydrolysis ; o-formylation of phenol^^^".^ and arnine~~~'~ is achieved via formation of sulphonium salts (19) ylide formation and a Sommelet-Hauser rearrangement.+/ z-s c'"R (19) Z =NHorO 55 R. N. McDonald and J. M. Richmond J.C.S. Chem. Comm. 1974 333. 56 A. C. Boicelli R. Danieli A. Mangini A. Ricci and G. Pirazzini J.C.S. Perkin II 1974 1343. 57 N. C. Marziano E. Maccarone C. M. Cunino and R. G. Passerini J. Org. Chem. 1974 39 1098. '' C. Yaroslavsky Tetrahedron Letters 1974 3395. 59 W. D. Watson J. Org. Chem. 1974 39 1160. 'O W. D. Watson and J. P. Heeschen Tetrahedron Letters 1974 695. '' 0. M. Nefedov and R. N. Shafran Zhur. org. Khim. 1974 10 477. 62 W. L. Bowden W. F. Little and T.J. Meyer J. Amer. Chem. SOC.,1974 96 5605. 63 I. I. Maletina V.V. Orda and L. M. Yagupol'skii Zhur. org. Khim. 1974 10 296. 64 (a)D. Liotta A. D. Baker S. Goldstein N. L. Goldman F. Wienstein-Lame D. Felsen- Rhengold and R. Engel J. Org. Chem. 1974 39 2718; (6) D. Liotta A. D. Baker N. L. Goldman and R. Engel ibid. p. 1975. 65 (a) P. G. Gassman and D. R. Amick Tetrahedron Letters 1974 3463; (6) P. G. Gassman and D. R. Amick ibid.,p. 889; (c) P. G. Gassman and H. R. Drewes J. Amer. Chem. SOC.,1974,96,3003;(d)P. G. Gassman and G. D. Gruetzmacher ibid. p. 5487; (e)P. G. Gassman G. Gruetzmacher and T. J. Van Bergen ibid. p. 5512. Aromatic Compounds Electrophilic displacement reactions have been used to prepare isomers that would be otherwise inaccessible.Thus treatment of aryltrimethylstannanes with nitrosyl chloride followed by oxidation gives nitro-compounds66 and of aryltrimethylsilanes with thallium trifluoroacetate gives arylthallium bis-(trifluoroacetates).67 Electrophilic displacement of the diazonium cation from o-aryl azophenols has been observed68 and it appears to be a better leaving group than Brt Cl' or NO,+ although the mechanism of the displacement is not clear. Aryl-lead trifluoroacetates on treatment with trifluoroacetic acid give aryl trifluoroacetates ;69 the reaction apparently goes through a radical cation although if an aromatic solvent is used biphenyls are obtained with substitution patterns suggestive of an electrophilic reaction. Hypobromous acid brominates acetophenone in the ring" rather than in the side chain.t-Butyl hypobromite bromination of 1,3,5-tribromobenzene is very slow in the absence of potassium t-butoxide7' but faster than that of 1,3,5-trimethoxybenzene in its presence suggesting (20) as an intermediate. Gas-phase halogenation of aromatics using Br+ and I+ produced by nuclear decay Br using high moderator concentrations shows very low ~electivity~~ and a large amount of substituent replacement. The extent of replacement and increased o-substitution in going from fluoro- to iodo-benzene suggests that aryldihalo genonium ions are formed. Pyrolysis of methanesulphonyl azide produces a nitrene and in aromatic solvents the singlet inserts but the triplet behaves as an ele~trophile.~~"~~ Rate studies of the reactions between dimethylamine and 4-flUOrO- or 4-chloro-nitrobenzenes show that the former reaction but not the latter has a large salt effect which is interpreted as electrophilic catalysis of the breakdown of the intermediate.74 Arrhenius parameters for nucleophilic displacement on picryl chloride by 3-and 3,hubstituted anilines show that the disubstituted bh C.Eaborn I. D. Jenkins and D. R. M. Walton J.C.S. Perkin I 1974 870. 67 H. C. Bell J. R. Kalman J. T. Pinhey and S. S. Sternhell Tetrahedron Letters 1974 3391. 68 N. J. Bunce J.C.S. Perkin I 1974 942. 69 H. C. Bell J. R. Kalman J. T. Pinhey and S. S. Sternhell Tetrahedron Letrers 1974 853 857. 70 T. L. Broxton L. W. Deady J. D. McCormack L. C. Kaun and S. H. Toh J.C.S. Perkin I 1974 1769.71 M. H. Mach and J. F. Bunnett J. Amer. Chem. SOC.,1974 96,936. 12 E. J. Knust A. Halpern. and G. Stocklin J. Amer. Chem. SOC.,1974 96 3733. 73 (a)R. A. Abramovitch T. D. Bailey T. Takaya and V. Una J. Org. Chem. 1974 39 340; (6)R. A. Abramovitch G. N. Knaus and V. Una ibid. 1974 p. 1101. 74 D. Ayediran T. 0.Bamkole and J. Hirst J.C.S. Perkin 11 1974 1013. 290 T.J. Tewson compounds follow an isokinetic relationship and that the rates are governed by a -I effect but that relative rates for the monosubstituted compound are temperature dependent.75 Rates of ionization of aromatic hydrocarbons as measured by detritiation with ethoxide ion vary considerably from the equilib- rium a~idities.'~ Nitrobenzene undergoes reversible hydrogen exchange with sodium borohydride as shown by tritium labelling presumably through the nitro-cyclohexadienyl anion (21).Methoxide ion displacement on polyfluoro- benzenes shows that the order of displacement is rn > o >> p which is explained by the inductive effect.77 (21) NO. (22) Enthalpic stabilities of carbanionic a-complexes between acetone or cyclo- pentanone and poly(nitro)aromatics show them to be as stable as the oxygen analogue^.^' The a-complexes between 1,3,5-trinitrobenzene and substituted anilines have been characterized by n.m.r. and visible and it has been confirmed that in the presence of potassium methoxide a a-complex of structure (22) is formed.79b The isopropoxide ion reacts with 2,4,6-trinitrotoluene to give both a a-complex and the anion with proton transfer being the rate-determining step for anion formation."" Sodium and potassium t-butoxide form only the anion although with a fully deuteriated methyl group the o-complex is formed as well.''" Rate' lo and equilibrium constants for the formation of 1 1 a-complexes between cyanide ion and 1,3,5-trinitrobenzene in alcoholic solvents and equilibrium constants for the cyanide complexes with 2,4,6-trinitrotoluene and 2,4,6-trinitro- anisole'l' have been determined.The rate and equilibrium constants for the formation of the a-complexes between methoxide and picryl chloride' have also been determined. The 2,4,6-trinitrophenyl ether of catechol with sodium meth- oxide gave'* a Meisenheimer complex (23) and the Meisenheimer complex 75 S.I. Ette and J. Hirst J.C.S. Perkin 11 1974 76. '' A. Albagli J. R. Jones and R. Stewart Canad. J. Chem. 1974 52 1059. 77 R. D. Chambers W. K. R. Musgrave J. S. Waterhouse D. Lyn H. Williams J. Burden W. B. Hollyhead and J. C. Tatlow J.C.S. Chem. Comm. 1974 240. 78 R. M. Murphy C. A. Wulf and M. J. Straus J. Amer. Chem. SOC.,1974 96 2678. 79 (a)E. Buncel and J. G. K. Webb Canad. J. Chem. 1974 52 630; (b) E. Buncel H. Jarrell H. W. Leung and J. G. K. Webb J. Org. Chem. 1974 39 272. (a) E. Buncel A. R. Norris K. E. Russell P. Sheridan and H. Wilson Canad. J. Chem. 1974 52 1750; (b) E. Buncel A. R. Norris K. E. Russell P. Sheridan and H. Wilson ibid. p. 2306. (a)L. H. Gan and A. R. Norris Canad. J. Chem. 1974,52 1; (b)L.H. Gan and A. R. Norris ibid. p. 8; (c)L. H. Gan and A. R. Norris ibid. p. 18. V. N. Drozd V. N. Knyazev and A. A. Klimov Zhur. org. Khim. 1974 10 828. Aromatic Compounds 29 1 n n from l-(fi-hydroxyethoxy)-2,4-dinitrobenzene (24) is more stable than that (25) from N-fi-hydroxyethyl-N-methyl-2,4-dinitrobenzene because of the greater ground-state stability of the latter c~mpound.~2-Picrylthioethane-1-thiol gave a complex (26) on treatment with base but with the n-propyl compound nucleophilic displacement of an o-nitro-group occurred.84 Nucleophilic displacement reactions of benzenediazonium salts in the absence of strong base light or reducing agents proceeds via the phenyl cation formation of which is the rate-determining step.85 The cation reacts with gaseous nitrogen.86 Synthesis of o-substituted benzonitriles has been achieved by nucleophilic dis- placement from o-nitrobenzonitriles,87 and photolysis of 2-allyloxyacetophenone in methanol gave methoxyacetophenone by a nucleophilic displacement reaction and 3-methyl-2-vinylbenzofuranby hydrogen abstraction from the acetophenone Cleavage of aryl-substituent bonds with potassium in liquid ammonia has been studied in the presence of acetone thus permitting distinction between ionic and radical cleavage.Electronegative substituents (F C1 Br I 0,and S) undergo radical cleavage whilst if the substituent is phosphorus arsenic antimony or bismuth anionic cleavage occurs ; aryl-selenium bonds are cleaved uia both routes.89 Reductive dehalogenation of aryl bromides with lithium di-n-propyl- amide has been studied in the presence of a large excess of the amine to suppress aryne formation and showng0 to involve the transition state (27).For iodo- anisoles however reductive dehalogenation probably proceeds by amide ion u3 C. F. Bernasconi and H. S. Cross J. Org. Chem. 1974,39 1054. 84 E. Farina C. A. Veracini and F. Pietra J.C.S. Chem. Comm. 1974 672. 85 K. G. Harbison R. J. Rogers C. G. Swan J. E. Sheals and D. G. Gorenstein Tetra-hedron Letters 1974 2913. 86 R. G. Bergstrom G. H. Wahl jun. and H. Zollinger Tetrahedron Letters 1974 2974. 87 J. R. Beck R. L. Sobczak R. G.Suhr and J. A. Yahner J. Org. Chem. 1974,39,1839. 88 F. R. Sullivan and L. B. Jones J.C.S. Chem. Comm.1974 312. 89 R. A. Rossi and J. F. Bunnett J. Amer. Chem. SOC.,1974,% 112. 90 E. R. Biehl S. Lapis and P. C. Reeves J. Org. Chem. 1974 39 1900. 292 T. J. Tewson attack at the halogen to give the carbanion. Metal-ammonia reduction of bi- phenyls and of methoxybiphenyls in the absence of a proton source forms dianions which give 1,6dihydrobiphenyls on work-up; in the presence of a proton source reduction goes further to give isomeric phenylcycl~hexenes.~ o- m-,and p-Dibenzoylbenzenes all gave radical anions with alkali metals in liquid ammonia; the o-isomer gave (28) with two equivalents of potassium whereas two equivalents of lithium gave (29).92 Hydrogen abstraction from phenols has been correlated with quantum mechan- ical indices which shows that over a wide range of reactivities the relationship is far more complex than a simple Hammett relati~nship.~~ Partial rate factors for amination with ammonium radical cations establish that the reaction shows the same selectivities as electrophilic substitution and is sensitive to steric and polar but not conjugative effects.94 The authors suggest that the inductive order for electrophilic substitution is due to reactions involving electron transfer and that the Nathan-Baker order is followed by reactions involving the Wheland intermediate.E.s.r. studies of 1,l-di-t-butylbenzyl radical (30) in which the radical is at 90" to the aromatic ring show that the ~-a delocalization is much smaller than expected.95" Other e.s.r. studies confirm that the 2,4,6-tri-t-butylphenyl radical is a o-radi~al.~~' 2-Hydroxy- and 2-methoxy-phenyl radicals generated by photo- lysis of the related iodo-compounds at low temperature are a-radicals which rearrange to phenoxy radicals on further photolysis or warming.96 Rates of 91 A.J. Birch and G. Nadamuni J.C.S. Perkin I 1974 545. 92 J. A. Campbell R. W. Koch J. V. Hay M. A. Ogliaruso and J. F. Wolfe J. Org. Chem. 1974 39 146. 93 I. Luskovits J. Kardos and M. Simonyi Tetrahedron Letters 1974 2085. 94 A. Clerici F. Minisci and 0.Porta J.C.S. Perkin I 1974 416. 95 (a) K. Schreiner and A. Bernelt Angew. Chem. Internat. Edn. 1974 144; (6)L. R. C. Barclay D. Griller and K. V. Ingold J. Amer. Chem. SOC.,1974 96 3011. Q6 P. H. Kasai and D. McLeod jun.J. Amer. Chem. SOC.,1974 96 2338. Aromatic Compounds 293 aromatic cyclohexylation by cyclohexyl radicals show a marked dependence on the polarity of the medium; an initial reversible n-complex which rearranges to a a-complex and then collapses to the product is ~uggested.~' The reactions of cyclopropyl radicals with aromatics for both substitution and hydrogen- abstraction processes show that the radicals have very little polar character.98 Phenyl radicals react with p-xylene to give 2,5-dimethylbiphenyl and 4,4-di- methylbibenzyl; the proportion of the latter compound increases with tem- perature which is taken to indicate reversible formation of the o-complex (31).99 Pyrolysis of phenyl acetate to phenol and keten has been established as a radical not a concerted reaction ;other products are also formed.'oo"*b Dimerization of benzyl radicals containing methyl ethyl and isopropyl groups gave'" significant amounts of o-and p-semibenzene dimers e.g.(32). Ph IH CR'R' C R( 'R' (32) (34) Decomposition of benzoyl peroxide in the presence of nitrogen dioxide has been examined quantitatively and the proposed mechanism confirmed."' Pentafluorobenzoyl peroxide and hexafluorobenzene at 200 "C give a mixture from which (33) can be isolated in poor yield but defluorination of the mixture gave (34) in good yield suggesting a mixture of isomeric cyclohexadiene structures formed by migration of o-radical~."~ The phenol (35) gives (36) on oxidation Bu' D..I OMe J5U' y -OMe OH (35) 97 J.R. Shelton and A. L. Lipman jun. J. Org. Chem. 1974,39 2386. 98 T. Shono and I. Nishiguchi Tetrahedron 1974 30 2183. 99 R. Henriquez A. R. Morgan P. Mulholland D. C. Nonhebel and G. G. Smith J.C.S. Chem. Comm. 1974,987. 100 (a)A. C. Barefoot and F. A. Carroll J.C.S. Chem. Comm. 1974,357; (b) C. E. Kahnus and D. M. Hercules J. Amer. Chem. SOC.,1974 % 449. I01 K. J. Skinner H. S. Hochster. and J. M. McBride J. Amer. Chem. SOC.,1974,% 4301. 102 Y.Rees and G. H. Williams J.C.S. Perkin I 1974 2266. 103 L. V. Vlasova L. S. Korbrina and G. C. Yakobson Zhur. org. Khim. 1974 10 787. 294 T. J. Tewson with one-electron oxidants presumably uia a secondary radical formation on the methoxyl carbon.lo4 The formation of aromatic a-radicals postulated in the electrochemical reduction of aryl halides has been confirmed by the electro- chemical reduction of (37),where the second aromatic ring acts as an internal radical trap.' O5 Electrochemical reduction of aryltrimethyl-silanes and -germanes produces silyl- and germyl-substituted cyclohexa- 1,4-dienes with the products being the same as predicted from a Birch reduction.lo6 Perchlorobenzyl- and perchlorophenyl-aminyl radicals are extremely stable and in solution the former exists in equilibrium with its dimer.lo' Tetraphenylethylene radical cations cyclize to 9,lO-diphenylphenanthrenevia disproportionation to the dication and tetraphenylethylene cyclization and not disproportionation being the rate-determining step.'08 Analysis of the e.s.r.and CIDNP spectra obtained from a study of the decomposition of benzenediazonium salts suggests that the azo-benzene radical cation is responsible for the spectra but that this is not a major reaction path~ay.'~' y-Irradiation of bromobenzene and p-bromophenols gives hydrogen radical addition to the carbon bearing bromine and no sign of a n-complex radical is detectable by e.s.r. spectroscopy. ' The y-induced radical chain reduction of aryl diazonium salts shows two classes of kinetics one which is proportional to the hydrogen source but independent of dose rate and another which is indepen- dent of the hydrogen source but dependent on the dose. A mechanism is proposed' ' to explain this. Theoretical studies using semi-empirical INDO methods of phenylcarbene cycloheptatrienylidene and cycloheptatetraene and the benzo-annelated analogues show that the allene isomer should be more stable than the carbene in the parent compounds but not in benzo-analogues,' l2and to' support this view the carbene (38) the dimerization of which was reported in last year's Annual I04 R.C. Eckert Hou-Ming Chang and W. P. Tucker J. Org. Chem. 1974 39 718. 105 J. Grimshaw and J. Trocha-Grimshaw Tetrahedron Letters 1974 993. 106 C. Eaborn R. Jackson and R. Pearce J.C.S. Perkin I 1974 2055. I07 (a)S. Olivetta M. Ballester and J. Castafier Tetrahedron Letters 1974 587 615. 108 U. Svanholm A. Roulan and V. D. Parker J. Amer. Chem. Soc. 1974,96 5108. 109 J. Bargon and K.-G. Seifert Tetrahedron Letters 1974 2265.I10 J. Edwards D. J. Hills S. P. Mistra and M. C. R. Symons J.C.S. Chem. Comm. 1974 556. Ill J. E. Packer R. K. Richardson P. J. Spoole and D. R. Webster J.C.S. Perkin 11 1974 1472. 112 R. L. Tyner W. M. Jones Y. Ohm and J. R. Sabin J. Amer. Chem. SOC.,1974 96 3765. Aromatic Compounds Reports (p. 422) was generated from a chiral precursor which gave only one of the two dimers obtained previously suggesting that a stereospecific cyclo- addition from the allene form is responsible for the formation of the dimers. ' ' 3a Photolysis of phenol in chloroform effects a photo-Reimer-Tiemann reaction giving the same products as in the base-catalysed reaction. Such photoreactions can be performed on dihydroxybenzenes and anilines for which the base- catalysed reaction does not work ;it is presumed that the reaction goes through an aromatic radical or radical cation.' 3b Photochemical addition of olefins to benzene gives 1,Zaddition if the olefin has donor or acceptor properties but 1,3-addition if it has neither; with donors the addition is specifically endo but with acceptors it is exo.' 13' These results parallel the behaviour of liquid mixtures of olefins with benzene as shown by n.m.r. where the average orientation of the olefin is endo to the aromatic nucleus when it is a donor and exo when it is an acceptor.' '3d Furan undergoes photo- (39) H-(40) chemical 2,5- 1',4'-cycloaddition with benzene to give (39) which isomerizes further to (40)on further irradiation or heating.' l4 Molecular Rearrangements.-The allyl ether (41 ; R = H) prepared from phloroacetophenone and propargyl bromide followed by reduction gave deoxyhumulones (42 ;R = H) on thermal rearrangement but the attempted synthesis of the natural product (41 ; R = Me) gave only products of C-alkyla-tion.' '' The y-chloro-y-methylallyl ether (43) under either thermal or catalytic forcing conditions gave the m-substituted phenol (44)by an intermolecular process.' l6 Rates of Claisen rearrangement of allyl aryl ethers in trifluoroacetic 'I3 (a)R.A. LaBar and W. M. Jones J. Amer. Chem. SOC.,1974 96 3646; (b) K. Hirao M. Ikegame and 0. Yonemitsu Tetrahedron 1974 30 2301; (c) D. Bryce-Smith A. Gilbert B. Orger and H. M. Tyrrell J.C.S. Chem. Comm. 1974 334; (d)D. Bryce-Smith A.Gilbert and H. M. Tyrrell ibid. p. 699. "* J. Berridge D. Bryce-Smith and A. Gilbert J.C.S. Chem. Comm. 1974 964. E. Collins and P. Shannon J.C.S. Perkin I 1974 944. E. K. Aleksandrova L. I. Bunina-Krwornkova Kh. V. Bal'yan and V. M. Feoktishov Zhur. org. Khim.,1974 10 825. 296 T. J. Tewson R H OH R*R acid show good correlation with (ap+ om)/2 indicating a polar transition state. Large salt and isotope effects confirm a polar mechanism and indicate that proton transfer is involved in the rate-determining step.' ' Rearrangement of cin- namylphenyl ether gives both 0-and p-substituted products. The ratio is depen- dent on the acidity of the solvents used and there is no abrupt change of rate in liquid-crystal solvents on going from the nematic to isotropic phase all contrary to previous reports establishing that alignment of the molecule in the liquid crystal is not important in the formation of transition states.' '' Base-catalysed rearrangement of catechol monoallyl ethers gives different products from the thermal reaction and involves successive sigmatropic rearrangements of the anion.' l9 Claisen rearrangement of the allylic amine (45)proceeds without migration of the double bond suggesting that the reaction is unlikely to be con- cer ted.''' Pure o-ally1 thiophenol has been isolated and shown to undergo the Claisen- type rearrangement which is catalysed by nucleophiles. It is suggested that nucleophilic attack at the allylic carbon triggers a concerted process ;I2 ' 2-methylallyl phenyl sulphide when passed over y-alumina at 300 "C gives 2,2-dimethyl-2,3-dihydrobenzothiophenin a Claisen-type rearrangement.22 3-Phenylprop-2-ynyl ally1 ethers (46) isomerize to the allene on treatment with base and this undergoes [,4 + ,2] cycloaddition to give dihydronaphthalenes (47).' 2-Methoxyallyl bromide gives bicyclo[3,2,2]nona-4,7-dien-3-one(48) ' * U. Svanholm and V. D. Parker J.C.S. Perkin 11 1974 169. M. J. S. Dewar and B. Nahlovsky J. Amer. Chem. SOC.,1974 96,460. W. D. Ollis R. Somanathan and I. 0. Sutherland J.c.S. Chem. Comm. 1974 494. lZo G. de Saqui-Sannes M. Riviere and A. Lattes Tetrahedron Letters 1974 2073. "' H. Kwart and J. L. Schwartz J. Amer. Chem. SOC.,1974 % 1575. G. Dzhamatova T. A. Dunilova and E. A. Viktorova Zhur.org. Khim. 1974,10 76. A. J. Bartlett T. Laird and W. D. Ollis J.C.S. Chem. Comm. 1974 496. Aromatic Compounds in low yield on treatment with silver salts the absence of dihydroindanones suggesting that a concerted cycloaddition is involved. 24 The benzidine rearrangement is implicated in the photolysis of 1,4-diethyl- 1,4-diphenyl-2-tetrazene as NN-diethylaminobenzene-N-ethylaniline (49)is obtained from the rea~ti0n.I~’ The phenylhydrazones from a-substituted acetones rearrange in acidic conditions to give p-substituted anilines (50),also apparently (48) (49) through the benzidine rearrangement. ’ The photo-Fries rearrangement of aryl benzoates is shown to be a singlet reaction both by CIDNP and the in- effectivenessof naphthalene on altering the path of the rea~ti0n.I~’ The Wallach rearrangement of phenylnaphthyl and naphthylnaphthyl azoxybenzenes gives the product with the hydroxy-group on the naphthyl ring regardless of the initial position of the oxygen of the azoxy-group.12* A mechanism has been proposed for the rearrangement and denitrosation of N-methyl-N-nitrosoaniline in hydro- chloric acid (Scheme l).’29 o-Substituted nitrosobenzenes in very dilute solution H H k I PhN-NO Ph-7!JkNO-PhNCH, I I CH CH + p2 NOCl P-NOC~H~NHCH 3 Scheme 1 in concentrated sulphuric acid give quinone oximes presumably by way of the nitroso cation rather than the self-condensation products which are obtained in more concentrated solutions.’ 30 124 H.M. R. Hoffman and A.E. Hill Angew. Chem. Internat. Edn. 1974 13 136. 12’ J.-D. Cheng and H. J. Shine J. Org. Chem. 1974 39 336. 126 F. Sparatoge V. Boido and G. Pirisiono Tetrahedron Letters 1974 2371. 12’ W. Adam J.C.S. Chem. Comm. 1974,289. 12* A. Dolenko and E. Buncel Canad. J. Chem. 1974 52,623. D. Lyn H. Williams and J. A. Wilson J.C.S. Perkin II 1974 13. I3O E. Yu. Balyaev L. M. Gornosfaev M. S. Tabis and E. L. Borina Zhur. obshchei Khim. 1974 44 633. 298 T.J. Tewson Solvolysis of 3,3-diaryltricyclo[3,2,1,1,2*4]oct-8-yl tosylates (51) to the bicyclo- octenes (52) shows anchimeric participation of the aryl group but the low p-value of -1.68 points to the rearrangement being concerted.' 31 The photo-induced rearrangement of 1,1,5,5-tetraphenyl-3,3-dimethylpenta-1,4-diene yields a cyclo- propane product.This may involve either a di-n-methane rearrangement or a [,2 + ,2,](or [,2 + n2s])process. If the latter mechanism is correct then irradiation of 1,1,5,5-tetrapheny1-3,3-dimethylpen t-1 -ene should give a cyclo- propane derivative. This does not occur and 1,4,5,5-tetraphenyl-3,3-dimethyl-pent-1-ene is formed via a novel 1,Qphenyl migration.'32 Photolysis of triptycene is shown by trapping experiments to proceed through the carbene (53) rather than by the di-n-methane rearrangement as had been previously proposed. ' Arynes.-MIND0/3 calculations on bisdehydrobenzenes (54a-c) show that the o-and p-isomers should have a singlet ground state but the result with the rn-isomer is not clear.Also the rn-isomer should have a ground-state energy similar to the o-isomer although no accounts of its attempted preparation have yet appeared.'34 Ene addition of benzyne to cyclic olefins is shown to be a concerted reaction rather than a radical one,'35 but the [2 + 21 and [2 + 2 + 21 reactions of tetrachlorobenzene and norbornadiene are very little affected by high pressure and the authors conclude that pressure studies on concerted re- actions are only meaningful when a great deal is known about the transition states of the alternative reaction modes.' 36 Cycloaddition of benzyne to +unsaturated 131 J. W. Wilt T. P. Mallory P. K. Mookerjee and D. R. Sullivan. J. Org. Chem. 1974 39 1327. 13' H. E. Zimmerman and R. D. Little J. Amer. Chem. SOC.,1974 96,5143.H. Iwamura and K. Yoshimura J. Amer. Chem. SOC.,1974 % 2654. 134 M. J. S. Dewar and W.-K. Li J. Amer. Chem. SOC., 1974 96 5569. 135 G. Mehta and B. Palsingh Tetrahedron 1974 30,2409. I 36 W. J. Le Noble and R. Mukhtar J. Amer. Chem. SOC.,1974 96,6191. Aromatic Compounds carbonyl compounds gives 1,Zaddition to both the carbon-oxygen and carbon- carbon double bonds the ratio of which depends upon the reactivity of the car- bony1 group and not upon the formation of intermediate radicals.' 37 The formation of benzyne- from N-nitrosoacetanilide and benzenediazonium acetate has been studied by isotope labelling. It was shown that a 'pre-equilib- rium' Elcb mechanism is not involved but a reversible Elcb mechanism cannot be distinguished by this method from a concerted E2 mechanism.'38 Benzyne from 1-aminobenzotriazole in carbon disulphide reacts with the solvent to give 39 benzo-1,3-dithiolium carbene (55) initially which can either dimerize or react with other substrates.2-Polychloroarylethanolsdo not react with base to give furans by nucleophilic displacement but lithiation gives an aryl lithio-compound which on reflux eliminates to a benzyne and then reacts with the alcohol to give the furan in good ~ie1d.I~' However the cyclizations of o-halogeno-stilbenes and a-phenylcinnamic acids to phenanthrenes by potassium-liquid ammonia do not go through benzynes but involve radical anions.141 Quinone Methides Dimethides and Related Compounds.-A full report on the formation of o-xylylene by the photolysis of 1,4-dihydrophthalazine has been published together with details of the further photolysis to benzocyclobutane and the preparation of o-xylylene from five other l-Phenyl-1-tolyl on photolysis with maleic anhydride gives products that are suggestive of the formation of o-xylylene intermediates.143 1,8-Naphthoquinodimethide 13' A. T. Browne and R. H. Levin Tetrahedron Letters 1974 2043. 138 J. I. G. Cadogan C. D. Murray and J. T. Sharp J.C.S. Perkin I 1974 1321. '39 J. Tdakayama J.C.S. Chem. Comm. 1974 166. I4O N. J. Foulgar and B. J. Wakefield J.C.S. Perkin I 1974 871 S. V. Kessar S. Narula S. S. Gandhi and U. K. Nadir Tetrahedron Letters 1974 2905. 14' C. R. Flynn and J. Michl J. Amer. Chem. SOC.,1974 96 3281.14' A. C. Pratt J.C.S. Chem. Comm. 1974 183. 300 T. J. Tewson (55b) has been synthesized from (55a) and e.s.r. studies show that the triplet is only 200 cal rnol-' above the singlet and thus is thermally accessible.'44 Non-photochemical formation of o-xylylene apparently occurs when o-xylene di- halides are heated with copper(0)-t-butyl isocyanide as trapping experiments give products suggestive of o-xylylene formation. 145 Photolysis of o-tolualdehyde gives the dimeric hemi-acetal by way of the photo- enol (56),and benzoin from hydrogen abstraction by the tri~1et.l~~" The same enol has been trapped with dienophiles and the stereochemistry confirmed as being the (E)-isomer none of the (2)-isomer being formed; ring-closure to cyclobutenols occurs in dilute solution.146b Thermolysis of benzocyclobutenols gives the same enol ;146c vinyl and phenyl substituents assist the reaction.'46d Photolysis of l-(o-tolyl)propane-l,2-dioneproduces a similar enol (57) as was shown by trapping experiment^,'^^" but ring-closure was not reported for this compound. Annelated benzocyclobutenols (58) are reversibly photolysed to the cyclic ketones (59),the forward reaction requiring 2537 8,light and the backward 3000 8,;the reaction was presumed to go through an o-xylyleqe photo-en01 of the same type. 146 Thermolysis of vinylbenzocyclobutenes gives the o-xylylenes (60) which either undergo 1,7-hydrogen shifts to o-tolylbutadienes or ring-closure to 1,2-dihydronaphthalenes depending on the nature of R' and R2.14' (58) (59) 44 R.M. Pagni C. R. Watson jun. and J. E. Boor J. Amer. Chem. SOC.,1974 % 4064. 145 Y. Ito K. Yonezawa andT. Saegusa J. Org. Chem. 1974 39 2769. 146 (a)D. M. Findlay and M. F. Tehir J.C.S. Chem. Comm. 1974 514; (b)B. J. Arnold S. M. Mellows P. G. Sammes and T. W. Wallace J.C.S. Perkin I 1974 401 ; (c) B. J. Arnold P. G. Sammes and T. Wallace ibid. p. 409; (d)B. J. Arnold P. G. Sammes and T. Wallace ibid. p. 405; (e) Y. Ogata and K. Takagi J. Org. Chem. 1974 39 1385; (f)M. L. Viriot-Villaume C. Carre and P. Caubere Tetrahedron Letters 1974 3301. 14' M. R. Camp R. H. Levin and M. Jones jun. Tetrahedron Letters 1974 3575. Aromatic Compounds 301 80"C ___* (62) (63) 1-Methoxymethyl-2-naphthol in glacial acetic acid gives the quinone methide (61) which dimerizes to (62) the product of kinetic control; above 80°C this isomerizes to (63).14* In the equilibria of aryl azo-1-and 2-naphthols (64) and (65) the 1-naphthol exists as a 1 1 mixture of the phenol and quinone imine Ar Ar N//N ,N-H N Ar Ar I I N N' 'H whilst the 2-naphthol derivative is almost entirely in the phenol form presumably stabilized by more favourable hydrogen bonding.149 Quinones.-A molecular orbital study of 36 quinones by self-consistent-field methods gave good general correlations with observed physical data except for the carbonyl stretching frequencies. l5 Oxidation of 1,4-diphenylnaphthalene-2,3-diols with lead tetra-acetate gave trimers from 1;4-diphenyl-2,3-naph-thaqinone (66) and low-temperature oxidation with trapping reagents also gave products from the quinone f~rmation.'~ p-Alkylphenols gave good yields of lJ8 G.Catteral J.C.S. Chem. Comm. 1974 41. 14' S. Millefori F. Zuccarrello A. Millefori and F. Guerrera Teetrahedron 1974 30 735. G. J. Gleicher D. F. Church and J. C. Arnold J. Amer. Chem. SOC.,1974 96 2403. '" D.W. Jones and R. L. Wife J.C.S. Perkin I 1974 1. 302 T.J. Tewson Ph Ph (66) p-quinols on oxidation with thallium triperchlorate.' 52 Oxidation of phenol by peracetic acid has shown that 0-and p-hydroxylation first occur with the o-dihydroxybenzene then being oxidized to hexa-2,4-dienoic acid whilst the p- compound is oxidized to p-quinone. 2-Azido-3-vinyl-l,4-quinonesgive indole quinones on heating 54a photolysis of 2-azido-1,4-quinones with dienes gives 2-alkenyl-2,3-dihydroindole-4,7-diones,' 54b and the condensation of hydro-quinones with halogenated maleic anhydrides gives polyhydroxylated naph- thoquinones in excellent yield.1s5 Cyclophanes.~6lParacyclophane (67) has been prepared the aromatic ring apparently being bent 20" out of the plane as measured from the U.V.spectrum although the n.m.r. spectrum still shows a ring current.' 56 3-Carboxy[7]para-cyclophane has been prepared and its U.V. spectrum shows a general red shift as expected. One proton is forced into the n-electron cloud giving a very low-field signal in the n.m.r. and a limited accuracy X-ray analysis shows the para-carbons are 17" and the benzylic carbons 24" out of the plane.lS7 (67) Force-field calculations of the conformations of [n]paracyclophanes have been performed and the results are in good agreement with experimental data in so far as these are known.ls8 The conformation and geometry of the aromatic rings in [2,2]metacyclophanes are affected by substituents in the bridges.' 59 (S)-4-Deuterio[2,2]paracyclophanehas been prepared'60" and its c.d.spectrum obtained and successfully described theoretically. 160b Flipping of [2,2]meta- paracyclophane (68) requires that the 1-proton of the meta aromatic ring has to 152 Y. Yamada K. Hosaka H. Sanjoh and M. Suzuki J.C.S. Chem. Comm. 1974,661. ' 53 R. A. G. Marshall and R. Naylor J.C.S. Perkin II 1974 1242. '54 (a) P. Germeraad and H. W. Moore J. Org.Chem. 1974 39 774; (b)P. Germeraad and H. W. Moore ibid. p. 781. R. Huot and P. Brassard Cunad.J. Chem. 1974,52 838. 156 V. V. Kane A. D. Wolf and M. Jones jun. J. Amet. Chem. SOC.,1974 96 2643. Is' N. L. Allinger T. J. Waller and M. G. Newton J. Amer. Chem. SOC.,1974 96 4588. 58 N. L. Allinger J. T. Sprague and T. Liljefors J. Amer. Chem. SOC., 1974 96 5100. 15' E. Langer and H. Lehner Tetrahedron Letters. 1974 1357. 16' (a)P. H. Hoffman E. C. Ong 0.E. Weigang,jun. and M. J. Nugent J. Amer. Chem. SOC.,1974 96,2620; (b)M. A. Hassloch M. J. Nugent and 0.E. Weigang jun. ibidl p. 2619. Aromatic Compounds (68) X = H or D (69) X = H F or CN pass through the n-cloud of the other ring and the rate of inversion as measured by the n.m.r. spectrum is affected by deuterium substitution with KdK = 1.20 +_ 0.04 Substitution at the 4-position also affects the rate of inversion but correlation with Hammett values gives curves rather than a straight line; this is attributed to bond-length changes caused by substitution.'6'" The diene (69) can flip more easily than the saturated compound if X = H but fluorine or cyanide substitution completely stops the inversion below 140 "C.161b [2,2]-(2,6)-Pyridinoparacyclophane-1,g-diene(70)and the related saturated compound have been prepared; the saturated compound flips on the n.m.r.time-scale but the diene does not and an X-ray crystal structure of the diene shows the pyridine ring to be at right angles to the benzene ring. The authors speculate that in the boron trifluoride complex (71) bonding occurs .through the benzene ring as flipping does not take place on the n.m.r.time-scale.'62'*b Coupling of 2,6-dibromomethyltoluene with 2,6-dimethylthiotoluene gives both syn-and anti- dithiametacyclophanes. Stevens rearrangement on the anti-compound followed by Hofmann elimination gives the anti-[2,2]dimethylmetacyclophane-lg-diene (72) which is in equilibrium both thermal and photolytic with the pyrene (73) but the syn-isomer gives only the pyrene (74) which is not in equilibrium with the cyclophane.' Three-and four-layered [2,2,2]metacyclophanes have been 16' (a)S. A. Sherrad R. L. Costa. R. A. Barnes and V. A. Bockelheide J. Amer. Chem. SOC. 1974 96 1565; (b) V. Bockelheide P. H. Anderson and T. A. Hylton ibid.p. 1558. 16' (a)V. Bockelheide K. Galuszko and K. S. Szeto J. Amer. Chem. SOC.,1974 96 1578; (6) V. Bockelheide K. Galuszko K. S. Szeto L. H. Weaver and B. W. Mathews ibid. p. 1585. '63 R. H. Mitchell and V. Bockelheide J. Amer. Chem. Soc. 1974,96 1547. 304 T.J. Tewson (74) (75) n U (82) X = Br or OTs prepared and form both syn- and anti-isomers the anti-compounds being con- verted into the syn-isomers on heating (75) +(76).'64 [2,2]-(2,5)-( 1,4)-Furano- and thiopheno-naphthophanes have been synthesized and the naphthothio- phenophanes isolated in both syn- and anti- forms (77) and (78).16' Synthesis of both chiral and achiral [2,2]-( 1,5)-naphthalenophanes has been achieved'66 and [9]metacyclophane with a hydroxy-group in position 16has been synthesized ; the bridge lies on one side of the ring and cannot invert and Reimer-Tiemann reaction gives the appropriate troponecyclophane in good yield.' 67 Syntheses of [2,6]para~yclophane-1,6-diene'~~ (79) l-phenyl-12-oxo[ 131- paracyclophan- 1-en-1 3-one [8]-(3,6)-pyridazinophane(8l) and its mono- N-~xide'~' have been described.Neither em-nor endo-[10]-(2,4)-quinoline-cyclophane 1-bromide or tosylate (82) undergoes bimolecular nucleophilic or '64 T. Umenoto T. Otsuko and S. Misumi Tetrahedron Letters 1974 1523. 16' S. Mizogami N. Osaka T. Otsubo Y. Sakata and S. Misumi Tetrahedron Letters 1974 799. M. W. Haenel Tetrahedron Letters 1974 3053. 16' T. Hiyama Y.Ozaki and H. H. Nozaki Tetrahedron 1974 30 2661.L. G. Kaufman and D. T. Longone Tetrahedron Letters 1974 3229. 16' D. Bichan and M. Winnik Tetrahedron Letters 1974 3857. T. Hiyama S. Hirano and H. Nozaki J. Amer. Chem. SOC.,1974 96 5287. Aromatic Compounds (84) (85) X = 0 or CH ionization reactions establishing the rigidity of bridging hydrocarbon chains. Photochemical reaction of [10]-(9,1O)-anthracenopha-4,6-diyne(83) in benzene gives the dimer (84) and in the presence of furan or cyclopentadiene gives the addition product (85).17 Birch reduction of [2,2]paracyclophane gives a tetra- hydro-(dl) compound in agreement with CNDO calculations on the likely inter- mediate~,'~~ and substitution of [2,2]metacyclophanes in positions 4 and 8 occurs using radical cation conditions whereas normal electrophilic conditions cause transannular reactions.' 74 3 Non-benzene System! Dissolution of l,l-dichloro-2,5-diphenylcyclopropabenzene(86) in fluorosul-phonic acid gives the stable cation (87) an aromatic system as shown by its n.m.r.spectrum,' but the 2,2,5,5-tetramethylbicyclo[4,1 ,O]hepta- 1(6)-en-6-one (88) is unstable toward both acid and base. 0 Ph Ph w W. E. Parham P E. Olson K. R. Reddy and K. B. Sloan J. Org. Chem. 1974 39 172. 17' T. Inoue T. Kaneda and S. Misumi Tetrahedron Letters 1974 2969. 173 J. L. Marshall and B.-H. Song J. Org. Chem. 1974 39 1342. K. Nishiyama K. Hata and T. Sato J.C.S. Perkin Zi 1974 577. 175 B. Halton A. D. Woolhouse H. M. Hugel and D. P. Kelly J.C.S. Chem. Comm. 1974 247. 306 T.J.Tewson Cyclobutadiene chemistry has been reviewed' 76 and two further stable cycls- butadienes (89) and (90) have been synthesized. Compound (89) is stable in the solid state below 80°C'77and (90) does not react with either dienophiles or dienes but does undergo addition with bromine and hydrogen.178 The synthesis of and X-ray studies on 172-dithiosquaric acid (91) show it to be a stable flat com- pound. 79 Preparation of the cyclobutadiene iron tricarbonyl complex (92) containing an intramolecular trap has been reported. Photolylic generation of the cyclobutadiene gives the Dewar benzene derivative (93) which then re- arranges to (94).'8o CH,-0-CH,-CrCMe N.m.r. studies of the reaction of 2-chlorotropone with methoxide ion show that the 7-methoxy-compound (95)is first formed; this rearranges rapidly to the geminal methoxy compound (96).' 81 Ethanethiolate reacts with tropone to give the mono-addition product at C-7 and the gem-adduct is not formed.'82 OMe (95) (96) Annulenes as aromatic compounds have been reviewed.183 A crystal structure analysis of bis(potassium dig1yme)- 1,3,5,7-tetramethylcyclo-octatetraeneshowed G. Maier Angew. Chem. Internat. Edn. 1974 13 425. I" H. Straub Angew. Chem. Internat. Edn. 1974 13 405. 17' M. P. Cava H. Fironzabadi and M. K. Kreiger J. Org. Chem. 1974 39 40. 179 D. Coucouvanis F. J. Hollander R. West and D. Eggerding J. Amer. Chem. Suc. 1974 96 3006. lE0R. H. Grubbs T. A. Pancoast and R. A. Grey Tetrahedron Letters 1974 2425. "' F. Pietra J.C.S.Chem. Cumm. 1974 544. ''' C. A. Veracini and F. Pietra J.C.S. Chem. Cumm. 1974 623. F. Sondheimer Chimiu (Switz.) 1974 28 163. Aromatic Compounds 307 it to be flat with equal bond lengths and definitely an aromatic systern.lg4 sym-Dibenzo-1,5-cyclo-octadiene-3,5-diyne(97) and sym-dibenzo-1,3,5-cyclo-octad-ien-7-yne (98) show paramagnetic ring currents and are easily reduced to 10n systems.lS5 Bicyclo[3,3,2]decatrienyl dianion (99) is the longicyclic homologue of the cyclo-octatetraene dianion and as such is a stable 1k system.186 The cis-benzocyclononatetraenyl dianion isomerizes to the trans-compound on standing at room ternperature.lg7 Analysis of the crystal structure of 1,6-methano[l0]annulen-ll-oneshows it to be virtually the same as those of the other 1,6-rnethano[lO]annulenes,with no interactions between the carbonyl group and the aromatic system.188 Various derivatives of 1,6-methano[ lolannulene can be prepared from lH-3,8-methano- cyclopropa[ lolannulene (100) by opening the cyclopropane ring with nucleo- philes ;' 89 the bridged annulenes are generally photo-oxidized initially to 1,4-endoperoxides which rearrange to diepoxides.190 Two reports of the synthesis and structure of 8b,8c-diazocyclopent[f,gl-acenaphthylene (101) establish that it is a planar 1277 antiaromatic compound with no tendency to form the 107c monocyclic system,191a*b and comparison of its molecular diamagnetic susceptibility with the proton magnetic resonance of (102) shows that it is a 4n system with a paramagnetic ring current.The prepara- I 84 S. Z. Goldberg K. N. Raymond C. A. Harmon and D. H. Templeton J. Amer. Chem. SOC.,1974 % 1348. Ia5 H. W. C.Wong P. J. Gcrratt and F. Sondheimer J. Amer. Chem. SOC.,1974 % 5604. IB6 M. J. Goldstein S. Tomada and G. Whittaker J. Amer. Chem. SOC.,1974 % 3676. la7 A. G. Anastassiou and E. Reichmans Angew. Chem. Internat. Edn. 1974,13. 728. lS8 S. It6 and Y. Fukazawa Tetrahedron Letters 1974 1045. E. Vogel and J. Sombreck Tetrahedron Letters 1974 1627. lg0 E. Vogel A. Alscher and K. Wihus Angew. Chem. Internat. Edn. 1974,13 398. lgl (a) J. L. Alwood D. C. Hrucir C. Wong and W. W. Pandler J. Amer. Chem. SOC. 1974 96 6132; (6)W. Flitsch and H. Lerner Tetrahedron Letters 1974 1677. 308 T.J.Tewson tion and n.m.r. tudies of 1,7-methano[l2]annulene (103) and 1,6-methano[ 121- annulene (104) show both 10 be paratropic; both are easily reduced to 14n dianions and (103) but not (104) reveals rapid degenerate n-bond shift in the low-temperaturcs 3C n.m.r. lH-Aza[l3]annulene and its N-acylated derivatsves have been prepared none of which are particularly stable but the parent compound shows a diamagnetic ring current whilst the N-sub- stituted compounds do not.192d Ill I1 C C (106) (107) The three didehydro[ 14lannulenes (105H107)have been synthesized and although the diamagnetic ring current increases with conjugation the stability decreases.Ig3 The two furano[l4]annulenes (108) and (109) and the benzo[ 141- *''(a) E. Vogel H. Konigshofen K.Mullen and J. M. F. Oth Angew. Chem. Internat. Edn. 1974 13 281; (b) E. Vogel M. Mann Y.Sakata K. Miillen and J. M. F. Oth ibid. p. 283; (c) J. M. F. Oth K. Mulien H. Konigshofen M. Mann Y. Sakata and E. Vogel ibid. p. 284; (d) A. G. Anastassiou and R. L. Elliott J. Amer. Chem. Soc. 1974 96,5257. M. Iyoda M. Morigaki and M. Nakagawa Tetrahedron Letters 1974 1817 3677. Aromatic Compounds 309 (1 14) (115) (118) a; X = N-H b; X = N-1R = H Me,or Et c;x=o d;X = S,R = HorEt \ e; X = S=O R = H or Et \\/ CrC-C~C \/ No (116) X = 0 f;X= S ,R=HorEt (117) X = H / \o annulenes (110) and (111) all show a diamagnetic ring current although this is decreased in the benzo cases and the furano-compounds react with dimethyl acetylenedicarboxylate to give conformationally mobile ad cts.194 The [15]annulenone 4,7 :10,lZdioxides (1 12H115)have been prepared all of which give stable 14z systems with acid particularly (1 13).Ig5 The [15]annulenone (116) and [15]annuIene (1 17) also form stable 14n systems (1 16dd~ith trifluoro- acetic acid and (1 17) with trityl tetrafluoroborate.196 The didehydrohetero[l7]- annulenes (118a-f) have all been synthesized ;the nitrogen oxygen and uulphur 194 P. J. Beeby R. T. Weavers and F. Sondheirner Agnew. Chrm. Internat. Edn.. 1974. 13. 138; R. T. Weavers and F. Sondheimer ibid. pp. 139 141. lY5H. Oagawa N. Shimojo H. Kato and H. Saikachi Terrahrdron 1974 30 1033. ‘96 H. Ogawa H. Kato N. Ibii T. M. Cresp and M. V. Sargent Tetrahedron Letters 1974 3889.310 T. J. Tewson C C c C Ill Ill 111 111 C C Po c C C C Ill 111 Ill 111 mo0u compounds are all diatropic but the syn-ethyl sulphoxide and the sulphone are paratropic whilst the anti-ethyl sulphoxide is atropic.’ 97 The authors speculate that the axial oxygen has a 2p overlap that allows an 18n Mobius configuration; the syn-compound cannot do this and so is paratropic. MIND0/3 and MIND0/2’ studies of [18]annulene give an alternating bond structure and the authors suggest that the X-ray crystal structure which gives an equal bond length structure is due to a non-centrosymmetric structure with an equal proportion of the two alternating forms present in the cry~ta1.I~~ The tetradehydro[ 18lannulones (1 19)-(122) all undergo electrochemical reduction to the phenolic compounds and (121) and (122) require a lower potential than ben~oquin0ne.I~~ Triepoxyr 19Jannulenone (123) and triepoxy[2l]annulenone (124) have been prepared ;(123) shows a diamagnetic ring current but (124) shows 19’ P.J. Beeby J. M. Brown P. J. Garratt and F. Sondheimer Tetrahedron Letters 1974 599; J. M. Brown and F. Sondheimer Angew. Chem. Internat. Edn. 1974 13 339 377. 19* M. J. S. Dewar R. C. Haddon and P. J. Student J.C.S. Chem. Comm. 1974 569. N. Darby K. Yamamoto and F. Sondheimer J. Amer. Chem. SOC.,1974 96 248. Aromatic Compounds 31 1 0 0 (123) no ring current and is not paratropic suggesting that in this series Hiickel's (4n + 2) rule breaks down when n = 5.200,201 4 Condensed Systems Local aromatic properties of polycyclic benzenoid hydrocarbons have been assessed by a numerically simple extension of Clar's valence formula using the number of complete aromatic sextets that each n-electron can participate in which gives good results in predicting reactivities and structures.202 The second triplet state of naphthalene has been prepared by intermolecular energy transfer and its lifetime measured as -1.5 x 10-s which is an order of magnitude less than that for anthra~ene.~'~ An attempt to prepare the 2,3- dideh ydronaphthalene (1 25) by pyrolysis of 2,3-diazidonaphthalene gave trans- 1,2-dicyano- 1 ,Zdih ydro benzocyclobutene in~tead.~ 1,2-Dihydroxy- 1,2-di h yd- O4 ro- and 1,4-dihydroxy- 1,4-dihydro-naphthaleneshave been synthesized.20s The disproportionation of 1,2-dihydro- and 1,4-dihydro-naphthaleneshas also been studied ; the 1,2-compound undergoes a thermal concerted reaction to naph- thalene and tetralin but the 1,4-compound rearranges and disproportionates in a reaction that is catalysed by the walls of the reaction Synthetic studies of polynitro-1,5- and -1,8-dimethylnaphthaleneshave been reported.207 Oxidation of 'k-region' dihydropolycyclic aromatics with sodium dichromate gives 'k-region' o-quinones which on reduction and treatment with dimethyl 2oo T.M. Crespand M. V. Sargent J.C.S. Chem. Comm. 1974 101. 201 T. M. Cresp and M. V. Sargent J.C.S. Perkin I 1974 2145. 202 M. Randic Tetrahedron 1974 30 2067. '03 C. C. Ladwig and R.S. H. Liu J. Amer. Chem. SOC.,1974,96 6210. '04 M. E. Peeks C. W. Rees and R. C. Storr J.C.S. Perkin I 1974 1260. '05 A. M. Jeffrey H. J. C. Yeh and D. M. Jerina J. Org. Chem. 1974 39 1405. '06 G. B. Gill S. Hawkins and P. H. Gore J.C.S. Chem. Comm. 1974 742. *07 S. R. Robinson B. C. Webb and C. H. J. Wells J.C.S. Pcrkin I 1974 2239. 312 T. J. Tewson acetal give 'k-region' arene oxides in good yield.208 Anthracene ancl phenanth- rene are fluorinated over potassium tetrafluorocobaltate followed by defluorina- tion to give the perfluoroaromatic compounds in a yield which is modest but none the less a considerable improvement over previous achicd ement~.~'~ Substituted anthracenes can be prepared in high yield by sodiLdn bdrohydride reduction of the appropriate anthraquinones,2 lo and 9,lO-dihydroanthracenes are synthesized by reduction of anthraquinones with phosphorus iodine and hydrogen iodide.2 9-Methyl- and 9,lO-dimethyl-anthracene are sulphonated on the methyl groups by reaction with the sulphur trioxide-dioxan The cis-and trans-isomers of 9,1O-dihydro-9,1O-diphenylphenanthrene have been reassigned on the basis of the ex.spectra of the appropriate radical anions.21 Thioanthracene radical cation perchlorates undergo substitution reactions in excellent yields.214 The kinetics of addition of the trichoromethyl radical to 9-substituted anthracenes correlate well with Brown's oP+substituent parameters with a pt = -0.83.2l5 1-Methoxyanthraquinones undergo photo- chemical nucleophilic substitution with replacement of the methoxy-group.2 l6 Photocycloaddition of olefins to 9-cyanophenanthrene proceeds either through a singlet exciplex or a triplet state depending upon the olefin,2 7a and the exciplex involved in the photoaddition of or-methylstyrene and 9-cyanophenanthrene has been An attempt to repeat the synthesis of (126) gave instead the photolysis product (127) when the reaction was performed in daylight.However when light was excluded work-up gave (126). The authors who worked in Colorado suggest that the ambient light in Oxford where the reaction was originally performed was too dim to effect the transformation !218 '08 H. Cho and R. G. Harvey Tetrahedron Leffers 1974 1491. 209 J. Burdon J. R. Knights I. W. Parsons and J.C. Tatlow Tetrahedron 1974,30 3499. 210 T. R. Criswell and B. Klanderman J. Org. Chem. 1974 39 70. 2' I R. N. Renaud and J. C. Stephens Cunud. J. Chem. 1974,52 1229. 212 A.-K. Telder and H. Cerfontain Tetrahedron Letters 1974 3535. 'I3 N. L. Bauld and .I.D. Young Tetrahedron Letters 1974 3143. 2'4 K. Kim V. J. Hull and H. J. Shine J. Org. Chem. 1974 39 2534. 'I5 J. C. Arnold G. J. Gleicher and J. D. Unruh J. Amer. Chem. SOC.,1974 96 787. 'I6 J. Griffiths and C. Hawkins J.C.S. Perkin I 1974 2283. 'I' (a)K. Mizimo C. Pac and H. Sakurai J. Amer. Chem. Soc. 1974 96 2993; (6) R. Caldwell and L. Smith ibid. p. 2994. 'I8 S. J. Cristol and J. S. Perry Tetrahedron Letters 1974 1921. Aromatic Compounds The odd-alternant hydrocarbon benzo[cd]pyrenyl anion (128) has been prepared and its n.m.r.spectrum shows that the charge is carried on alternate carbon atoms.2 l9 (128) The kinetics of protiodetritiation of hexahelicene benzo[c]phenanthrene in all six positions correlate well with Huckel localization energies with no evidence that puckering in the chain is localized in one position.220 However synthesis of several dimethylhexahelicenes shows that as the steric interactions increase the torsional strain in the molecule becomes more uniformly distributed over the molecule.221 Two double helicenes diphenanthro[4,3-a ; 3’,4’-o]picene(1 29) and benzo[s]diphenanthro[4,3-a ; 3’,4’-olpicene ( 1301 have been synthesized ; (129) (130) was isolated as exclusively d1,222a but the optically active forms racemize at 220 “C with t+= 20 min which is very similar to the behaviour of the hexaheli- cenes ; the meso-form is not involved in the racemization.222b ’19 I.Murata K. Yamamoto and 0.Hara Trirrihedron Letters 1974. 2047. ’lo J. Le Guen and R. Taylor J.C.S. Perkin II 1974 1274. 22 W. H. Laarhoven and Th. J. M. Cupper Tetrahedron 1974 30 1101. ”’ (a) R. H. Martin Ch. Eyndels and N. Defay Tetrahedron 1974 30 3339; (6) W. H. Laarhoven Th. J. M. Cupper and R. J. F. Nivard ibid. p. 3343. 314 T. J. Tewson (131) Photo-dehydrocyclization of 8-phenyl-di-p-naphthylethylenegives 42 yd ben-zocorene (131) as well as the expected products 1-phenylpentahelicene and 10-phenyl[ 1,2-a]anthracene the corene being a photo-oxidation product of the anthra~ene,~~~‘ and the same reaction on 4,5-diphenyltriphenyleneand 43- diphenylphenanthrene gives 1 ,Zphenyl shifts rather than cyclization although some benzo[e]naphtho[ 1,2,3,4-ghi]perylene was also isolated in the case of the triphenylene.223b Photolysis of trans-5,5’-dimethoxy-2,2’,4,4’-tetramethylstilbene gave 4,7-di- methoxy-1,3,6-trimethylphenanthreneby loss of a methyl group as well as the expected product 4,7-dimetho~y-l,3,6,8-tetramethylphenanthrene.~~“ al-An ternative synthesis for polycyclic aromatics has been reported :dibenzyl aromatics can give quinonoid-type compounds which can undergo Diels-Alder reactions with maleic anhydride to give more condensed compounds.Thus 3,8-diphenyl- pyrene was synthesized from 1,5-dibenzylnaphthalene ; 1,6-diphenylcoronene was also synthesized.225 Azulene and methylazulene react with strong nucleophilic bases to give either nucleophilic addition or methylene-azulenate anions,226 and 2-chloroazulene- 1,3-dicarboxylate reacts with alkali-metal acetylides to give 4-and 6-substituted azulene-1,3-dicarboxylates, presumably by addition and elimination.227 Polaro- graphic reduction potentials of (132)-(136) show considerable deviation from (133) (134) R = H (135) R = Me 223 (a) A.H. Tinnemans and W. H. Laarhoven J. Amer. Chem. Soc. 1974 96 4611; (b) A. H. Tinnemans and W. H. Laarhoven ibid. p. 4617. M. S. Newman and H. M. Chung J. Org. Chem. 1974,39 1036. 224 225 E. Clar M. M. Lovat and W. Simpson Tetrahedron 1974 30 3293.226 R. N. McDonald H. E. Petty N. L. Wolfe and J. V. Pankstehs J. Org. Chem. 1974 39 1877. 227 T. Fujita T. Morita and K. Takase Tetrahedron Letters 1974 2585. Aromatic Compounds the energy of the lowest HMO orbital unlike benzenoid compounds. This may be caused by the radical anion forming a 6x-electron system in the five-membered ring228 (137). Synthesis of indeno[2,1-a]azulene (138) and of indeno[ 1,2-a]-azulene (139) has been achieved by an extremely elegant route.229 Synthesis of 6-hydroxy-7H-naphth[3,2,1-cd]azulene-7-one(140) and the study of its tauto- merism have been reported.230 A new convenient synthesis of heptalene (141)has been reported and its 13C n.m.r. spectrum shows that it undergoes a rapid r-bond shift with AE of -3.5 kcalmol-' in a similar fashion to the [12]annulene (103).23* An elegant study of the photochemical conversion of 6b,l2~-dihydrocyclobuta[ 1,241:3,4-a']-bisacenaphthylene (142) into dinaphth[de- 1,2,3 :d'e'-5,6,7]azulene (143) shows 228 A.G. Anderson jun. and G. M. Masda J. Org. Chem. 1974,39 512. 229 A. Chen M. Yasunami and K. Takase Tetrahedron Letters 1974 2581. 230 N. Abe T. Morita and K. Takase Tetrahedron Letters 1974 3621. 23' E. Vogel H. Konigshofen J. Wassen K. Miillen and J. M. Oth Angew. Chem. Internat. Edn. 1974 13 732. 316 T. J. Tewson H 0aa. I 6 OH that light of A = 277 nm is required to achieve the singlet -triplet conversion of the starting material and that light of A = 360 nm converts triplet (142) into the product (143).Light of A = 214nm can effect the conversions of (142) into (143) and (144) into (144a) in one step although in the case of (144) the con- version cannot be accomplished with two photons.232 Synthesis of the 1,2-dihydroxybenzocycloheptenes(145) and (146) has been reported but they are stable only in solution.233 However synthesis of cyclo-hepta[cd]phenalen-6-one (147) and the cyclohepta[cd]phenalenium cation (148) ”‘ J. M. Labrum J. Kolc and J. Michl J. Amer. Chem. SOC.,1974 96 2636. 233 P. D. Carpenter D. J. Humphreys and G. R. Proctor J.C.S. PerkinI 1974 1527. Aromatic Compounds shows them both to be stable the cation being the weakest base of this type ye^ dis~overed.~~" The syntheses of bisbenzo[4,5]cyclohepta[ 1,2-a:2' 1'-albenzene-5.7-dione (149) and bisbenzo[4,5]cyclohepta[ 1,2-a:1',2'-d]benzene-5,7-dione (150) have also been reported.235 234 1.Murata K. Yamamoto and Y. Kayane Angew. Chem. Intrrnat. Edn. 1974 13 807 808. 23J I. Agranat and D. Avnir J.C.S. Perkin I 1974 1155.

ISSN:0069-3030    

DOI:10.1039/OC9747100281

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

12 HeterocycI ic Chemistry By 0. METH-COHN and R. K. SMALLEY The Ramage 1aboratories Department of Chemistry and Applied Chemistry University of Salford Salford M5 4WT 1 Three-membered Ring Compounds 2H-Azirines continue to be widely used in syntheses. 2-(fi-Naphthyl)-2H-azirine is highly photolabile and adds via its nitrile ylide in high yield to electron- deficient dipolarophiles to give 2-(P-naphthyl)-A1-pyrrolines.'However with electron-rich acyclic or alicyclic alkenes only dimer (1 ; Ar = B-naphthyl) is obtained. On the basis of fluorescence emission data it is concluded that azirine ring-opening to give a nitrile-ylide is a fast process and that the dipolar inter- mediate derives most probably from an excited singlet state azirine rather than from a triplet species.A detailed study of the thermochemistry of carbene and nitrene rearrangements shows the azepinylidene moiety (2)to be a viable alterna- tive to azirine (3) in many nitrene reactiom2 Oxazoles isoxazoles imidazoles pyrazoles and pyrroles are available by intramolecular 1,3-dipolar cycloadditions of 2H-azirines bearing unsaturated side- (see also p. 328) For example photolysis of 3-formyl-2-phenylazirine (4;X = 0)affords 2-phenyloxazole (6 ;X = 0)by way of nitrile ylide (5). Similar reactions yield imidazole (6;X = NPh) and pyrroles (6 ;X = CHCN CHCHO and CHC0,Me). On thermolysis however the 2H-azirines ring-open to the vinyl-nitrene intermediate (7) and heterocycles (8) isomeric with the photo- products are formed (Scheme 1). An interesting extension of these reactions involves the P-styryl-2H-azirine (4;X = CHPh) which as either the E-or 2-isomer undergoes photolytic ' A.Padwa and S. I. Wetmore J. Org. Chem. 1974 39 1396. ' C. Wentrup Tetrahedron 1974 30 1301. ' (a) A. Padwa J. Smolanoff and A. Tremper Tetrahedron Letters 1974 29; (b) A. Padwa and J. Smolanoff ibid. p. 33. 319 3 20 0.Meth-Cohn and R.K. Smalley Scheme 1 ring-opening to nitrile ylide (5:X = CHPh) and then intramolecular cyclization followed by a [1,5]-hydrogen shift to give benzazepine (9).3b The room temperature [4 + 21 cycloaddition of 2,3-diphenyl-2H-azirine with thiobenzoyl isocyanate is regiospecific and yields azirino-thiadiazinone (10) (85 73."At 80 "C (10) undergoes ring-expansion to the thiadiazepinone (1 l) which on prolonged heating extrudes sulphur to form the triphenylpyrimi- done (12).Ph Ph PhF'y Ph (9) A full report on the reaction between 2H-azirines and cyclopentadienones to give 3H-azepines via 2H-azepine intermediates noted last year,5 has now appeared.6 Apparently use of 1,3-diphenylinden-2-one (13) and phencyclone (14) permits isolation of compounds (15) and (16) examples of the hitherto elusive 2H-azepine system. In compound (15) [1,5]-hydrogen shift to give the 3H-azepine involves disruption of the benzene ring and cannot be induced. The V. Nair and K. H. Kim Tetrahedron Letters 1974 1487. Ann. Reports (B) 1973 70 471. A. Hassner and D. J. Anderson J. Org. Chem. 1974 39 3070. Heterocyclic Chemistry 32 1 phenanthro-azepine (16) however with strong base or on heating to cu.200 "C isomerizes to the 3H-ijjomer (17). (16) (17) A mixture of N-bromusuccinimide and sodium azide in aqueous dimethoxy- ethane has been reported to be a superior reagent for the stereospecific synthesis of aziridines from alkenes particularly for regioselective and stereospecific synthesis of polyenes bearing a terminal aziridine group.' More work on the stereoselective formation of aziridines by the action of Grignard reagents on oximes has been reported,*O and use of an excess of isobutyl-magnesium bromide in toluene is advocated for the synthesis of cis-2,3-di- substituted aziridines from ketoximes.8b Formyl aziridines are now available by the gentle acid hydrolysis of the anils [e.g.(18)] formed from ap-dibromo- aldehydes uia the Cromwell aziridine synthesis,' and a new variation on the Wenker synthesis ofaziridines has appeared which involves treating N-substituted /3-amino-alcohols with triphenylphosphine and trimethylamine in carbon tetrachloride. lo The action of chlorocarbenes on azomethine linkages is not usually a good preparative method for aziridines. However imidoyl dichlorides (19) react with dichlorocarbene generated by pyrolysis of (bromodichloromethy1)phenyl-mercury in benzene at 80°C to give tetrachloroaziridines e.g. (20; R2 = CI) in 30-50 % yield. In one case (20;R2 = F) a 74 % yield was achieved." A detailed account of the l-azaspiro[2,2]pentanes reported last year l2 has been published.I-Aryldiaziridines are available in reasonable yield by photo- lytic decomposition of 1-aryltetrazolines (21).14 ' D. van Ende and A. Krief Angew. Chem. Internat. Edn. 1974 13 279. (a)R. Bartnik and A. Laurent Compr. rend. 1974,279 C 289; (b) Y. Diab. A. Laurent and P. Mison Tetrahedron Letters 1974 1605. L. Wartski and A. Sierra Escudero Compt. rend. 1974 279,C 149. lo R. Appel and R. Kleinstuck Chem. Ber. 1974 107,5. " D. Seyferth W. Tronich and Houng-min Shih J. Org. Chem. 1974 39,158. Ann. Reports (B) 1973 70,474. l3 J. K. Crandall and W. W. Conover J. Org. Chem. 1974 39,63. l4 T.Akiyama T. Kitamura T. Isida and M. Kawanisi Chem. Letters 1974 185. 0.Meth-Cohn and R.K. Smalley Diaziridines react with phthaloyl chloride to give diazirino[ 1,241phthalazin- 3,8-diones (22) which in boiling toluene ring-open to yield 2-(alken- 1-yl)-4-hydroxyphthalazinones (23).5a With enamines and ynamines (22) reacts via (24) to give pyrazolo[ 1,241- and indazolo[ 1,2-b]phthalazindiones respec- tively. In the presence of nitrones the tricyclic system (25) is obtained in what may be regarded as a rare example of the cycloaddition of two different 1,3-dipolar species (Scheme 2). 0 0 (25) Scheme 2 Stereospecific syntheses of cis-and trans-1-phenyl-2-vinyloxirans have been described'6" and their configurations established. 16' The 2-conformers undergo electrocyclic reaction to dihydrofurans when heated in a sealed tube with chloro- benzene at 210-250 0C.16cThe oxirano[2,3-b]indole (26) apparently the last surviving unchallenged example of this elusive system has been shown to be a mixture of parent indole and 2-acetyl-5-nitroacetanilide.The chemistry and biochemistry of arene oxides is of current interest and of note is an investigation of the stereochemical course of ring-opening of arene (a)H. W. Heine R. Henrie L. Heitz and S. R. Kovvali J. Org. Chem. 1974 39 3187; (b)H. W. Heine and L. Heitz ibid. p. 3192. l6 (a)J.-C. Paladini and J. Churche Buff.Sac. chim. France 1974 187; (b)J.-C. Paladini and J. Churche ibid. p. 192; (c)J.-C. Paladini and J. Churche ibid. p. 197. " D. M. Harrison J.C.S. Perkin I 1974 2609. Heterocyclic Chemistry 323 0 AcZO - L EtOAc 0 oxides by nucleophiles. * A useful regiospecific isomerization of epoxides to allylic alcohols may be achieved using the new reagent diethylaluminium 2,2,6,6- tetramet hylpiperidide.The antibiotic (27) the first reported natural product containing a benzene dioxide unit is interconvertible with its valence isomer the 1,6dioxocine (28) and readily rearranges to either 2-(rn-hydroxyphenyl)-y-pyroneor 2-(3'-furano)- y-pyrone depending on reaction conditions.20 SAC "o'-oso (1 KOH-MeOH i p-TsCI py ______) --L 7 ii. MeCOSH py CHZCI, -2O'C TsO-' s ,-S SAC (29) (30) Scheme 3 The first synthesis of an arene bis-episulphide (29)has been described (Scheme 3).21 The structure is thermolabile and slowly reverts to sulphur and benzene with tt = 30min in chloroform at 20°C. This instability and failure of the episulphide to yield its valence tautomer the dithiocin (30) supports an earlier prediction that this hitherto unprepared l0n-electron system is non-aromatic.Scheme 4 Benzothiirans (31) rather than the thioketocarbenes (32; X = S) are thought to be intermediates in the production of dibenzodithians by pyrolysis of o-bromothiophenoxides (Scheme 4).22 In contrast o-bromophenoxides appears A. M. Jeffrey H. J. C. Yeh D. M. Jerina R. M. de Marinis C. H. Foster D. E. Piccolo and G. A. Berchtold J. Amer. Chem. SOC.,1974 96 6929. l9 A. Yasuda S. Tanaka K. Oshima H. Yamamoto and H. Nozaki J. Amer. Chem. SOC. 1974 96 6513. 'O D. B. Bordens and J. E. Lancaster J. Org. Chem. 1974,39,435. 21 E. Vogel E. Schmidbauer and H.-J. Altenbach Angew.Chem. Internat. Edn. 1974 13 736. 22 J. I. G. Cadogan J. T. Sharp and M. J. Trattles J.C.S. Chem. Comm. 1974 900. 0.Meth-Cohn and R. K. Smalley to decompose via a ketocarbene (32; X = 0)since only one dibenzodioxan corresponding to (33 ;0 in place of S) is formed. The first thiaziridine 1,l-dioxide (34) has been prepared.23 2 Four-membered Ring Compounds Sodium naphthalenide in diglyme is heralded as an improved reagent for de-tosylating N-tosylazetidine and azetidine may be obtained in 70 % yield.24 The first example of a cyclic four-membered nitrone (36) has been synthe~ized.~~ Apparently cyclization of oxime (35)is only successful using "'-tetramethyl- 1,8-diaminonaphthalene as the base. A detailed account of the acid chloride- induced interconversion of aziridine carboxylates and azetidinones via the strained bicyclic intermediate (37) has appeared.26 Bu' (35) [2 + 21 Cycloadditions continue to be a rich source of azetidinones.A useful general method involves treating chloro-enamines conveniently prepared in situ from tertiary amides and phosgene with Schiff bases.*' The reaction of imines and thioimidates with phenylmalonyl chloride constitutes a stereoselective method of preparing azetidinones e.g. (38) in high yield.28 1,3-Dimetallation of /?-lactams using n-butyl-lithium in THF at 0°C has been described and provides a convenient method for introducing substituents directly at the 3-position of the azetidinone ring.29 Indene in the presence of 'Rose Bengal' sensitizer and radiation of 2 < 450 nm suffers singlet oxygen addition to give dioxetan (39) in 55% yield.30 Diketen 23 H.Quast and F. Kees Angew. Chem. Internat. Edn. 1974 13 742. 24 J. White and G. McGillivray J. Org. Chem. 1974,39 1973. 25 D. St. C. Black R. F. C. Brown B. T. Dunstan and S. Sternhell Tetrahedron Letters 1974 4283. 26 J. A. Deyrup and S. C. Clough J. Org. Chem. 1974 39 902. 27 M. de Poortere J. Marchand-Brynaert and L. Ghosez Angew. Chem. Internat. Edn. 1974 13 267. 2B A. K. Bose J. C. Kapur B. Dayal and M. S. Manhas J. Urg. Chem. 1974 39,312. 29 T. Durst R. Van Den Elizen and R. Legault Canad. J. Chem. 1974,52 3206. 30 P. A. Burns and C. S. Foote J. Amer. Chem. Soc. 1974 96 4340. Heterocyclic Chemistry 325 COCl aph-pph-B: Ar,y,flo AI--?~ 0 (38) .Ph (39) -0 Ph /N Ar (40) Ar -N (41) 0 has been treated with azo-compounds for the first time and under photolytic conditions yields the pyridazine-3,5-dione (41) possibly by way of the photolabile spiro-adduct (40).3 Examples of photocycloadditions of alkenes to thiones are of current interest.0-Alkylthiobenzoates react uia the nn* triplet state with variaus alkenes to give isomeric mixtures of thietan~.~~ Cyclo-octatetraene under light of R 2 340 nm undergoes 1,4-cycloaddition with thiobenzophenone to yield adduct (42)(58 %).33 By contrast a much less efficient 1,2-addition is observed with fulvenes and ace- naphthalene and norbornadiene fails to react. Further details and examples of reactions between thiocarbonate (43)34 and various alkenes have been pub- li~hed,~ and similar reactions are observed with 00-diphenyl thiocarbonate and the thioparabanate (44).35b Cycloadditions with (44)to give spirothietans e.g.(45) appear to involve an nn* excited state and proceed only with light of wavelength >400 nm. R' R' Ph (42) (44) (451 Similar cycloadditions between thiouridines and alkenes may be the key to explaining the light-induced cross-linking of 4-thiouridine with cytidine in E. coli. RNA,36" in which thietanes have been proposed as inter'mediate~.~~ Thiouridine and thiothymidine derivatives are found to undergo photoaddition with acrylonitriles the products being formed presumably by way of an inter- mediary thietan. 6b Cycloadditions of sulphenes and enamines are useful sources of thietan 1,l-dioxides.The reactions are stereoselective but the cis :trans isomer ratio varies with the nature of the substituent groups.38 Whether these cycloadditions are 31 T. Kato M. Sato and K. Tabei J. Org. Chem. 1974 39 3205. 32 A. Ohno T. Koizumi and Y. Akasaki Bull. Chem. SOC.Japan 1974,47 319. 33 T. Cantrell J. Org. Chem. 1974 39 853. 34 Ann. Reports (B) 1973 70 481. 35 (a) H. Gotthardt and M. Listl Chem. Ber. 1974 107 2552; (b)H. Gotthardt and S. Nieberl Tetrahedron Letters 1974 3397. 36 (a) J. L. Fourrey P. Jouin and J. Moron Tetrahedron Letters 1974 3005; (b) C. Fombert J. L. Fourrey P. Jouin and J. Moron ibid. p. 3007. 37 D. E. Bergstrom and N. J. Leonard Biochemistry 1972 1 I 1.38 W. E. Truce and J. F. Rach J. Org. Chern. 1974 39 1109. 0.Meth-Cohn and R. K. Smalley concerted (n2s + z2s) or stepwise processes remains to be resolved. Naphtho[l,8- bclthiete (47)can be prepared in 97 % yield by photolysing (Pyrex filter) a benzene solution of dithiolononaphthalene dioxide (46) under nitrogen.39 S-mono- and SS-di-oxide derivatives are also reported. (46) (47) A new synthesis of 1,3-dithietans has been achieved by treating active methyl- ene compounds with two equivalents of sulphur di~hloride.~' Isolable thietes e.g. (48) are intermediate in the formation of thianaphthalenes from P-mercapto- ethyl alkyl or aryl ketones4' Treatment of (48)with sodium hydride has been reported to yield the remarkably stable green thiacyclobutadienes (49) which are perhaps best represented as ylides (50).Ph Ph The first N-thioacetylketimines have been prepared by irradiating thioketones in acetonitriIe solution. A thiazete intermediate is presumably involved (Scheme 5).42 Scheme 5 Significantly and in contrast with other light-induced thione cycloadditions already mentioned no reaction is observed with light of 2 > 470 nm from which it follows that n-+ z* transitions are not involved. The mechanistic details of these reactions are not as yet clear. 39 J. Meinwald and S. Knapp J. Amer. Chem. Soc. 1974 96 6533. 40 S. K. Gupta J. Org. Chem. 1974 39 1944. 41 R. S. Devdar V. N. Gogte and B. D. Tilak Tetrahedron Letters 1974 391 I. 42 D. S. L. Blackwell P.D. Mayo and R. Suau Tetrahedron Letters 1974 91. Heterocyclic Chemistry 3 Five-memberedRing Compounds On the basis of seven different criteria the ground-state aromaticity of benzene compared with some heterocycles was found to follow the order; benzene > thiophen > selenophen > tellurophen > f~ran.~~ The relative reactivity and aromaticity of five-membered heterocycles have been evaluated on the basis of acid-catalysed proton exchange reactions indicating decreasing aromaticity in the series isoxazole pyrazole is~thiazole.~~ Also the partial rate factors for some positions in N-methylpyrrole furan thiophen isoxazole isothiazole and N-methylpyrazole were computed with reference to benzene.44 The oPvalues of azoles have been determined by a study of the i.r.and n.m.r. spectra of N-(p-aminophenyl)azoles.4’ The use of variable temperature I3Cn.m.r. spectroscopy is often better than ‘H n.m r. to elucidate the syn-anti equilibria of 2-acyl heterocycles since larger chemical shift differences are observed.46 The NOE of the peri-protons (or substituents) in carbazole carbolines or dibenzothiophens etc. assist in assign- ing the structure of substitution reaction The study of tautomerism in the azoles by I3Cn.m.r. analysis of chemical shifts48 and more effectively of C-H coupling data has been reported.49 A perturbation treatment of 1,3-dipolar cycloaddition reactions allows the qualitative prediction of the regioselectivity. The effectiveness of the method is shown by numerous example^.^' A similar approach based on favourable secondary overlap of orbitals in the transition state with particular application to nitrone cycloadditions has also been published.’ ’ Q NO2 (51) The first isolable Meisenheimer (51) complex of a pyrrole has been reported the reaction being conducted in an n.m.r.tube.’2 A new simple one-pot synthesis 43 F. Fringuelli G. Marino A. Taticchi and G. Grandolini J.C.S. Perkin II 1974 332. 44 S. Clementi P. P. Forsythe C. D. Johnson A. R. Katritzky and B. Terem J.C.S. Perkin II 1974 399. ” P. Bouchet C. Coquelet and J. Elguero J.C.S. Perkin II 1974 449. 46 D. J. Chadwick G. D. Meakins and E. E. Richards Tetrahedron Letters 1974 3183. 4’ B. P. Roques S. Combrisson R. Oberlin and J.Barbet Tetrahedron Letters 1974 1641. 4M J. Elguero C. Marzin and J. D. Roberts J. Org. Chem. 1974 39 357. 49 M. Begtrup J.C.S. Chem. Comm. 1974 702. J. Bastide and 0.Henri-Rousseau Bull. SOC.chim. France 1974 1037. R. Gree F. Tonnard and R. Carrie Tetrahedron Letters 1974 135. ” F. de Santis and F. Stegel Tetrahedron Letters 1974 1079. 0.Meth-Cohn and A. K. SmaUey of L-proline has been reported which commences with readily available chiral pyroglutamic acid and involves no racemization.’ Numerous examples of the use of cycloaddition in the synthesis of simple and condensed pyrroles have been described (see also p. 319). Thus vynyl triphenyl- phosphonium bromide reac& as a dipolarophile with the ylide derived photo- chemically from azirine (52) (Scheme 6).54” The same ylide may be trapped by diethyl azodicarboxylate yielding triazole~~~’ and by acid chlorides to yield oxaz01es.~ 4c f’ Ph, Ph R (52) + I H Scheme 6 Enamines react readily with cyclopropen-ones and -thiones to give novel fused pyrrolocyclopropane betaines in a stepwise cycloaddition reaction (e.g.Scheme 7).’5”,b The thiones behave analogously with some anilssSc while two (53)X = 0or S Scheme 7 moles of phenylcyclopropenone react with the above enamines to give the spiro- lactone (54) probably by way of the betaine (53).55d By use of functionalized dipoles a general synthesis of 5-5,5-6,5-5-5 and 6-5-6fused heterocycle has been elab~rated.~~ Thus the aziridine (55)yields the tricyclic pyrrole (56)by sequential treatment with trans-dibenzoylethylene and an amine (Scheme 8).The supposed N-arylpyrroline (57)’’ has been shown by two groups of workers to be8 msxture of 2-isomers of the dimer (58) probably formed by cycloaddition as shown (Scheme 9).580-c 53 H. J. Monteiro Synthesis 1974 137. 54 ( ) N. Gakis H. Heimgartner and H. Schmid Hefo. Chim. Actu 1974 57 1403; (b) P. Gilgen H. Heimgartner and H. Schmid ibid. p. 1382; (c) U. Schmid P. Gilgen H. Heimgartner H. J. Hansen and H. Schmid ibid. p. 1393. 55 (a)T. Eicher and S. Bohm Chem. Ber. 1974 107,2186; (6)T. Eicher and S. Bohm igid. p. 2238; (c) T. Eicher and J. L. Weber Tetrahedron Letters 1974 3409; (d)T. Eicher and S. Bohm Chem. Ber. 1974 107 2215. 56 J. W. Lown and B.E. Landberg Canad. J. Chem. 1974,52 798. j7 G. Wittig and H. Sommer Annulen 1955 594 1. 58 (a)G. A. Swan and J. D. Wilcock J.C.S. Perkin I 1974 885; (6)G. D. Khandelwal G. A. Swan. and R. B. Roy ibid. p. 891 ; (c) G. H. Kerr O.,Meth-Cohn E. B. Mullock and H. Suschitzky ibid. p. 1614. Heterocyclic Chemistry phCvophjCoph PhCO COPh PhCO-dH CHCOPh PhCO , %.-*7 NI NI PhCO CH,Ph CH,Ph CH,Ph (55) (2 trans isomers) R-N Ph I Ph CH,Ph Scheme 8 (56) N ii) -+ -HX I Ar R (57) R (58) Scheme 9 Indole syntheses continue unabated. Further examples of Gassman's excellent procedures9 using N-chloroanilines and dialkylsulphides have been de-lineated,60a-c while a high-yield vapour-phase one-step synthesis by copper- catalysed thermolysis of o-nitrophenylethanol has also been reported.61 Tryptamines are obtained from the half-ester of readily available 3-chloro- propylmalonic acid after a AppKlingermann reaction and subsequent cycliza- tion (Scheme Both of the diazonium nitrogens are incorpomted into the b H H Scheme 10 59 Ann.Reports (B) 1973 70 486. 6o (a) P. G. Gassman T. J. van Bergen D. P. Gilbert and B. W. Cue jun. J. Amer. Gem. SOC.,1974 96 5495; (6)P. G. Gassman D. P. Gilbert and T. J. van Bergen J.C.S. Chem. Comm. 1974 210; (c) P. G. Gassman and T. J. van Bergen J. Amer. J. Bakke H. Heikman and E. B. Hellgren Acra Chem. Scand. (B),1974 28 393. C. Szantary L. Szabo and G. Kalaus Synthesis 1974 354. Chem. SOC.,1974,% 5508.62 330 0.Meth-Cohn and R. K. Smalley product. o-Methoxyphenylhydrazones of ethyl pyruvate give the expected indoles under Fischer conditions together with 2-ethoxycarbonyl-4-amino indoles derived by loss of the methoxy-group as methanol.63 The previously unreported 2-alkyl-isatogens are formed by treatment of 2-alkylindolines with m-chloroperbenzoic Reduction of indoles to 2,3-dihydroindoles is easily accomplished with borane and triethylamine cis-addition being ~bserved.~' A versatile use of N-ally1 carbazoles for the synthesis of P-alkylated aldehydes and ketones has been announced (Scheme 11) involving metallation alkylation and subsequent enamine hydrolysis.66 * y, BuLi/TMEDA "' RX _____) 4 ether -IS "C 2f Li R R Scheme 11 I Diazocyclopentadiene (59) reacts readily with mono- or di-substituted acetyl- enes to give the spiro-pyrazoles (60) which can undergo 1,5-sigmatropic re- arrangements to pyrazolopyridines (61) or indazoles (62) depending upon the nature of the substit~ents.~~~~ The interaction of hexafluoroacetone azine and -RZ h RZ I ONz + 111 -+ (61) R' R' (59) R' k2 (62) isobutene reported to give a pyridazine derivative (63)68has been shown by X-ray analysis to yield the novel dipolar pyra~ole~~".~ (64) (Scheme 12).This 63 H. Ishii Y. Murakami H. Takeda and T. Furnse Chem. and Pharm. Bull. (Japan) 1974 22 1981. 64 T. H. C. Bristow H. E. Foster and M. Hooper J.C.S. Chem. Comm. 1974 677. '' J. G. Berger Synthesis 1974 508.66 M. Julia A. Schonteeten and M. Baillarge Tetrahedron Letters 1974 3433. '' (a) H. Durr and R. Sergio Chem. Ber. 1974 107 2027; (b) H. Durr and R. Sergio ibid. p. 2037; (c) H. Durr and W. Schmidt Annalen 1974 1140. 6a S. E. Armstrong and A. E. Tipping J. Fluorine Chem. 1973 3 119. 69 (a) K. Burger W. Thenn and A. Gieren Angew. Chem. Internat. Edn. 1974 13 474; (b) A. Gieren P. Narayanau K. Burger and W. Thenn ibid. p. 475; (c) K. Burger W. Thenn M. Schickaneder and H. Peuker ibid. p. 476; (4K. Burger W. Thenn R. Rauh and M. Schickaneder ibid. p. 477. Heterocyclic Chemistry (CF3)2C=N-N=C(CF3)2 + Me A-Me Scheme 12 azomethinimine dipole reacts with nucleophiles such as methanol69c and with dipolarophiles e.g.acetylene dicarb~xylates.~'~ The mesoionic 4-diazo-3,5-dimethylpyrazole(65) easily made by the action of nitrous acid on 3,5-dimethylpyrazole is a versatile intermediate. With acetic acid the pyrazolopyrazole (66)is obtained7O" while with Grignard reagents the 4-azopyrazoles are Coupling with phenols and enols is hs expected70b and the Gomberg reaction is effective for arylation in the 4-po~ition.~" Finally the reagent is a useful oxidant converting secondary alcohols into ketones in the presence of hydr~quinone!~'~ Triethyl phosphite best known for its ability to deoxygenate nitro- and nitroso-compounds has been shown similarly to convert o-carbonyl azobenzenes into indazole derivatives. The reaction is believed to involve a concerted process rather than a carbene.Novel condensed sym-triazole N-oxides (68) have been elaborated from 2-aminopyridines and pyrimidines by way of the sulphimides (67) (Scheme 13)72 (see also p 348). The pyrimidinotriazoles are reversible valence tautomers as shown by variable 'O (a) G. Fukata Y. Kawazoe and T. Yaguchi J. Pharm. SOC.Japan 1974 94 17; (b)G. Fukata Y. Kawazoe and T. Yaguchi ibid. p. 23; (c) G. Fukata Y. Kawazoe and T. Yaguchi ibid. p. 31 ;(d)G. Fukata Y. Kawazoe and T. Yaguchi ibid. p. 36. " J. H. Lee A. Matsumoto M. Yoshida and 0.Simamura Chem. Letters 1974 951. T. L. Gilchrist C. J. Harris C. J. Moody and C. W. Rees J.C.S. Chem. Comm. 1974 486. 0.Meth-Cohn and R. K. Sinalley I (67) X=CHorN Scheme 13 temperature n.m.r.spectroscopy. Similar tautomerism was noted for the 1,2,3- triazolo[ l,ia]pyrimidines at elevated temperature^.'^ Another novel and remarkably stable mesoionic heterocycle (69) is reported as being unaffected by boiling 65 % sulphuric acid and only susceptible to nitration or bromination in the su bst ituent rings. ' Arl-N,X N-Ar * Ar2 (69) The ketone (70) undergoes acyl rearrangement at ambient temperature by way ofa carbinolamine (Scheme 14). The mixture of products finally quanti- tatively yields the N-acetylbenzimidazole (71).75 While 1-methjl-2-methylthio- imidazole reacts with two molecules of dimethyl acetylenedicarboxylate (DMAD) I COPh AC (71) Scheme 14 to give successively the fused imidazoles (72) and (73) the corresponding 2-amino analogue (74) reacts both as an amidine to give the expected product (79 and 73 G.Tennant and R. J. S. Vevers. J.C.S. Chem. Comm. 1974 671. '* A. Matsumoto J. H. Lee M. Yoshida and 0. Simamura Bull. Chem. SOC.Japan 1974 47 946. l5 Y. Akasaki and A. Ohno J. Amer. Chem. SOC.,1974,96 1957. Heterocyciic Chernistry 333 an enamine to give ultimately the diazepine (76).76 Both (73) and (76) undergo interesting rearrangements to pyridines with et hylamine. E MeS E E%c+yqE N E ill N SMe ';" SMe I I Me Me E Me (72) E = C0,Me (73) 0 New approaches to oxazoles include the action of TsCH,NC on ketones in the presence of thallous ethoxide (giving oxazolines that are useful sources of a-hydroxyaldehydes) ;77 the reaction of a-diazoketones with nitriles catalysed by tungsten hexachloride (possibly involving a carbene complex);78 the treatment of ethanolamines and carbon disulphide under basic conditions giving oxazolidine- 2-thiones ;79 and the stereospecific ring-opening of isomerically pure aziridines with anhydrous hydrogen chloride in ether followed by treatment of the derived PhCO PhCoN~Ncoph COPh Ph A o%N>Ph N 1,2-chloroamine salts with sodium carbonate.80 Specific pure isomers of 2-oxazolidinones are thereby obtained in high yield.The structure (78) of benzoyl- cyanide trimer first prepared in 18958' and given the problematical structure (77) by Diels and Stein,82 has been ingeniously solved by means of I3Clabelling '' F. Troxler H.P. Weber A.Jaunin and H. R. Loosli Helv. Chim. Acra 1974 750. " (a)0. H. Oldenziel and A. M. van Leusen Tetrahedron Letters 1974 163 (6) 0. H. Oldenziel and A. M. van Leusen ibid. p. 167. i8 K. Kitakani T. Hiyama and H.Nozaki Tetrahedron Letters 1974 1531. l9 M. Chanon F. Chanon and J. Metzger J.C.S. Chem. Comm. 1974,425. A. Hassner and S. S. Burke Tetrahedron 1974 30,2613. *' J. W. Nef Annalen 1895 287 303. 0.Meth-Cohn and R.K. Sinalley and n.m.r. spectro~copy.~~ The further use of oxazolines for the synthesis of chiral alkanoic acid derivatives has been reported. Thus 2-chlor0-,~~~ 2-meth~xy-,~",~ and 2-and 3-hydro~y-~~~ 2-meth~l-,~~' derivatives are easily made. Also a new chiral hydride reducing agent (79) readily made and regenerated has been The role of isoxazoles as masked polyketides has been ex- ploited by use of e.g.the bis-isoxazole (80) for the synthesis of phenols (Scheme 15) under very mild conditions. 4-and 5-Halogenobenzofurazans undergo (55-80 %) Scheme 15 nucleophilic substitution by two mechanisms. While fluoro- and chloro- derivatives follow an addition-elimination process the iodo analogues undergo cine-substitution viaan aryne and the bromo-compounds give a mixed pathway.86 The photo-isomerization of 4-substituted benzofuroxans appears to proceed without the intermediacy of o-dinitrosobenzenes and when the 4-nitro-derivatives isomerize they do not involve a Boulton-Katritzky type rearrangement." Flash photolysis studies suggest that any proposed intermediate must have a very short lifetime (< s at -40°C).82 0.Diels and H. Stein Ber. 1907 40 1655. g3 G. Hofle Tetrahedron Letters 1974 347. 84 (a) A. I. Meyers G. Knauss and P. M. Kendall Tetrahedron Letters 1974 3495; (6) A. I. Meyers and G. Knauss ibid. p. 1333; (c) A. 1. Meyers G. Knauss and K. Kamata J. Amer. Chem. SOC.,1974 96,268; (6)A. I. Meyers and P. M. Kendall Tetrahedron Letters 1974 1337. 85 S. Anricchio. S. Morocchi and A. Ricca Tetrahedron Letters 1974 2793. 86 L. Di Nunno S. Florio and P. E. Todesca J.C.S. Perkin II 1974 1 17 1. 87 G. Calzaferri R. Gleiter K.-H. Knauer H.-D. Martin and E. Schmidt Angew. Chem. Internat. Edn. 1974 13 86. Heterocyclic Chemistry 335 Mesoionic systems fall into two classes; those in which the elements that contribute two electrons each to the aromatic sextet are adjacent or non-adjacent.Many examples of the latter class are known and numerous new examples of isomeric pairs have been reported (Scheme 16) ;8806 interpretation X = 0,Y= S or NR' X = S,Y = NR' X = NR' Y= NR2 Scheme 16 of their mass spectra has been shown to be an efficient method of distinction.88e Very few examples of the former class are known although several new examples e.g. (81) and (82) some unstable have been devised.89 Me Me I NR -NTs (81) (82) X = 0or S Some novel SN-heterocycles have come to light including a missing benzo- isothiazole (83),90 the dipolar thiadiazole dioxides (84),91 and 6a-thia-1,6- diazapentalene (85) which despite an unsymmetrical crystal structure (X-ray RR \/ N-S-N \ Me crystallography) appears to show CZvsymmetry in solution down to -70 "C (n.m~.).~~ 1,2,4-Thiadiazoles are conveniently available by heating 1,3,4-oxathiazol-2-ones in the presence of nit rile^.^^ 8n (a)A.R. McCarthy W. D. Ollis and C. A. Ramsden J.C.S. Perkin I 1974 627; (b) W. D. Ollis and C. A. Ramsden ibid. p. 633; (c) W. D. Ollis and C. A. Ramsden ibid. p. 638; (4W. D. Ollis and C. A. Ramsden ibid. p. 642; (e)W. D. Ollis and C. A. Ramsden ihid.,p. 645. 89 G. V. Boyd and T. Norris J.C.S. Perkin I 1974 1028. 90 P. K. Klaus P. Hofbauer and W. Rieder Tetrahedron Letters 1974 3319. J. Martin 0. Meth-Cohn and H. Suschitzky J.C.S. Perkin I 1974 2451. 92 A. S. Ingram D. H. Reid and J. D.Symon J.C.S. Perkin I 1974 242. 93 R. K. Howe and J. E. Franz J. Org. Chem. 1974 39 962. 0.Meth-Cohn and R.K. Smalley An interesting rearrangement of the mesoionic system (86)has been observed (Scheme 17).94 Desulphurization of the systems (87) offers a useful route to the Scheme 17 heterocumulenes (88).95 Thermal extrusion of SO2 from condensed 1,2,5-thiadiazole dioxides gives dinitriles in good yields.96 R Ph,P RKZ=C=Y X = Y = S,Z = N S X X = NR’ Y = NR’,Z = CR3 or N (88) (87) Diels-Alder reactions of the tetrahydrobenzothiazole (89) with singlet oxygen give a mixture of thiolactams (90) and (91),9’ while similar interaction of the diene (92)with DMAD followed by sulphur extrusion gives the nove spirobenzo-thiazoles (93).98 The rates of N-methylation of the heterocycles (94) are not much diminished in the corresponding benzo- series and suggests the following order of reactivity Se > NMe > S > 0.99 94 0.Buchardt J.Domanus N. Harrit A. Holm G. Isaksson and J. Sandstrom J.C.S. Chem. Comm. 1974 376. 95 J. Goerdeler J. Haag C. Lindner and R. Losch Chem. Ber. 1974 107 502. 96 G. Ege and E. Beisiegel Synthesis 1974 22. ” H. H. Wasserman and G. R. Lenz Tetrahedron Letters 1974 3947. 98 G. Kobayashi Y. Matsuda Y. Tominaga and K. Mizuyama Heterocycles 1974 2 309. 99 M. Davis L. W. Deady and E. Holmfeld Austral. J. Chem. 1974 27 1917. Heterocyclic Chemistry o;+-S SMe R R (92) 1 MeO,C ,CO,Me RI SMe (94) X = NMe 0,S or Se (93) Furans and pyrroles are derived from the singlet oxygen adducts of dienes in high yield (Scheme 18).loo Novel asymmetric Birch reduction of 2-and 3-furoic R2 R3 A$Rl R2 base R3 +R3dR1 0-0 0 OH -Y2 R2 I R4 Scheme 18 acid with isopropylidene-cr-D-glucofuranoseas the proton source gave chiral 2,3-dihydro-3-furoic acid and 2,5-dihydro-2-furoic acid, respectively."' Two examples of [4 + 41 photocycloaddition of furan to benzene and anthracene have been reported.'02",b loo K.Kondo and M. Matsumoto Chem. Letters 1974 701. lo' T. Kinoshita and T. Miwa J.C.S. Chem. Comm. 1974 181. lo* (a)J. Berridge D. Bryce-Smith and A. Gilbert J.C.S. Chem. Comm. 1974 964; (b)K. Mizuno C. Pac and H. Sakura J.C.S. Perkin I 1974 2360. 0.Meth-Cohn and R.K.Smalley Ethylene iminocarbonate (95) has been prepared for the first time but rapidly trimerizes at room temperature. 1,4-Dioxa-2,3-benzofulvene (96),the dimer derived from 6-diazocyclohexa-2,4-dienone, shows considerable dipolar character as indicated by 13C n.m.r. and dipole-moment measurement attributable to aromatic delocalization. Other related hetero-analogues have also been reported. O4 Two new approaches to thieno[c]cyclobutenes have been ~utlined.''~ 1-Phenyl-4-(2'-thienyl)-buta-1,3-dienecyclizes under U.V. irradiation to give only 4-phenylbenzo[b]thiophen and no thienylnaphthalene indicating the greater 'double-bond character' of the thiophen bond.lo6 The synthesis of 3,4-unsubsti- tuted 2,5-dihydrothiophens1 07' and by thermolysis of the derived sulphones of specific butadienes,' 07b involves treatment of a-mercaptoaldehydes with vinylphosphonium salts.o-Claisen rearrangement of 2-chloroallyl ethers from phenols and thiophenols followed by cyclization with loss of HCl offers a novel entry to benzofurans and benzothiophens. lo* Similarly aryl prop-2-ynyl sulphoxides undergo consecutive [2,3] and [3,3] sigmatropic rearrangements leading ultimately to condensed thiophens (e.g.Scheme 19).lo9 The 'cross-bred' Hofmann elimination approach to paracyclophanes has been used to synthesize the stable isomers (97) and (98)"'' and related 1,4- and 9,lO-fused anthracene derivatives. Multi-layered analogues have similarly been devised the thiophen series showing restricted rotation."9b Although the isomers gave the same mass spectra they were not thermally interconvertible and both showed considerable diamagnetic shielding from n-n interactions in their n.m.r.spectra. Further extended helicenes with alternately fused benzene and thiophen rings involving five seven nine and eleven members have been constructed." Io3 C. R. Flynn and J. Michl J. Org. Chem. 1974 39 3442. Io4 R. Clinging F. M. Dean and G. H. Mitchell Tetrahedron 1974,30,4065. lo5 (a)H. Hauptmann Tetrahedron Letters 1974 3589; (b)M. P. Cava M. V. Lakshini-kantham and M. Behforouz J. Org. Chem. 1974 39 206. Io6 C. C. Leznoff W. Lilie and C. Manning Canad. J. Chem. 1974 52 132. lo' (a)J. M. McIntosh H. B. Goodbrand and G. M. Masse J. Org. Chem. 1974,39 202; (b)J.M. McIntosh and R. S. Steevensz Canad. J. Chem. 1974,52 1934. Io8 W. K. Anderson and E. J. LaVoie J.C.S. Chem. Comm. 1974 174. Io9 Y. Makisumi and S. Takada J.C.S. Chem. Comm. 1974 848. 'lo (a)S. Mizogami N. Osaka T. Otsubo Y. Sakata and S. Misumi Tetrahedron Letters 1974 799; (b) S. Mizogami N. Osaka T. Otsubo Y. Sakata and S. Misumi Chem. Letters 1974 515. Heterocyclic Chemistry -0 R R I R / PhSH 5h \/ Scheme 19 anti (97) The relatively stable 1-alkyl thiophenium hexafluorophosphates can now be made in high yield by the action of alkyl fluorosulphonates or methyl iodide and silver borofluoride on suitable thiophens followed by anion exchange with sodium hexafluorophosphate. They do not undergo Diels-Alder reactions.2,3,5-Tri- and tetra-methylthiophens couple with 2,4-dinitrobenzenediazonium chloride exclusively on an a-methyl-group while 2,5-dimethylthiophen reacts both in the ring and at the ~ide-chain."~ A convenient one-pot method for 2-substitution of benzothiophens and other condensed thiophens lies in the ozono- lysis followed by reaction of the intermediate with an active methylene group (Scheme 20).'14 The intermediate o-formyl disulphide (99) may be prepared by an alternative route and similarly employed. 'I1 P. G. Lehman and H. Wynberg Austral. J. Chem. 1974 27 315. R. F. Heldeweg and H. Hogeveen Tetrahedron Letters 1974 75. S. T. Gore R. K. Mackie and J. M. Tedder J.C.S. Chem. Comm. 1974 272. 'I4 K. J. Brown and 0. Meth-Cohn Tetrahedron Letters 1974 4069.0.Meth-Cohn and R. K. Smalley 2 R = NO2 CN C02H NHCOR' or Ar Scheme 20 2 2 Benzyne (from 1-aminobenaotriazole) reacts with carbon disulphidt to give the highly nucleophilic carbene (loo),which undergoes interesting reactions with protic solvents; for example with acetic acid it gives (101) and (102).1'5 The same carbene is obtained by the action of base on the corresponding benzo- 1.3-dithiolium salts.'16 q5x50' ' ss I +*>:-Highly conducting 1 :1 charge-transfer complexes some with almost metallic behaviour have been reported (Scheme 2l)."' The selenium analogues show (103)X = S or Se Scheme 21 the highest conductivity yet reported for an organic system. Similar stable compounds existing as cation radical/anion radical complexes with 1 :1 2 1 and 1 :2 stoicheiometries derive from the heterocycle (103) and DDQ.'' ' Is J.Nakayama J.C.S. Chem. Comm. 1974 166. G. Scherowsky and J. Weiland Annalen 1974 403. ' E. M. Engler and V. V. Patel J. Amer. Chem. Soc. 1974 96 7376. 'I8 Y. Ueno and M. Okawara Chem. Letters 1974 1135. 342 0.Meth-Cohn and R. K. Smalley ynamines or enamines suffer [4 + 21 cycloaddition followed by loss of carbon dioxide to give substituted pyridines in high yield. 124a Alternatively 2,4,6-trialkylpyridines may be obtained by self-addition of the oxazinone at 300 "C and loss of appropriate fragments (Scheme 23).' 24b Similar products are obtained by loss of hydrogen cyanide or cyanoformate from the Diels-Alder adduct (106; R = CO,Me X = -CH=N-) formed by treating pyrimidine mono- or di-carboxylates with ynamines.'25 Ring expansion of cyclopentadiene with chloroamine provides a new route to pyridine ;a similar reaction with indene yields isoquinoline.' 26 2-Pyridones are available by treating keto-phenyl hydrazones with methyl acrylate in the presence of aluminium ~hloride,'~' and have also been isolated from the reaction of tetracyclones with sulphonyl azides.' 28 The search for simple direct ways of substituting the pyridine ring still attracts attention and this year has seen some advance in the old problem of directly nitrating pyridine in that tetranitratotitanium(1v) reacts with pyridine at room temperature to give a &lo% yield of 3-nitropyridine ;Iz9 in contrast tetra- nitratozirconium(rv) yields mainly the 4-nitro-isomer.Quinoline yields the 3-nitro- and surprisingly the 7-nitro- (90%) derivatives with the two reagents respectively. 3-Nitroquinoline N-oxide is formed in high yield (6@-80 %) by treating the N-oxide with sodium nitrite and toluene-p-sulphonyl chloride in DMF. 30 A useful method OF selectively formylating 2-aminopyridines at the 3-position has been reported,' 31 and a general synthesis of pyridine aldehydes from bromopyridines is worthy of mention.'32 One-step treatment of 3-aminopyridine with cuprous halide halogen acid water and sodium nitrite is claimed as a superior method of synthesis for 3- chloro- and 3-br0mo-pyridine.'~~ The rare 2,Sdihydropyridines have been isolated from the reaction of t-butyl-lithium with ~yridine,'~~ whereas regio- specific substitution of pyridine useful for the preparation of 4-vinyl-1,4-dihydro- and ultimately 4-vinylpyridines occurs when pyridine is treated with trialkyl- alkynylborates in the presence of acetyl chloride.' 35 Direct 2-acylamination of pyridine results on treating pyridine N-oxide with imidoyl Side-chain arylation of a-picoline and quinaldine results (a) W.Steglich E. Buschmann and 0.Hollitzer Angew. Che'm. Znternaf. Edn. 1974 13 533; (6)E. Buschmann and W. Steglich ibid. p. 484. 125 H. Neunhoffer and G. Werner Annalen 1974 1190. E. Schmitz U. Bicker and K. P. Dietz 2. Chem. 1974 14 230. 12' J. Barluenga V. Gotor and F. Palacios Synthesis 1974 717. 128 R. A. Abramovitch and G.N. Knaus J.C.S. Chem. Comm. 1974 238. R. G. Coombes and L. W. Russell J.C.S. Perkin I 1974 1751. I3O M. Hamana and M. Yatabe J. Pharm. SOC.Japan 1974,94 566. 131 P. G. Gassman and C. T. Huang J.C.S. Chem. Comm. 1974,685. G. R. Newkome J. M. Robinson and J. D. Sauer J.C.S. Chem. Comm. 1974 410. 133 T. Talik Z. Talik and H. Ban-Oganowska Synthesis 1974 293. 134 R. F. Francis W. Davis and J. T. Wisener J. Org. Chem. 1974 39 59. A. Pelter and K. J. Gould J.C.S. Chem. Comm. 1974 347. 136 (a) R. A. Abramovitch and G. M. Singer J. Org. Chem. 1974 39 1795; (b) R. A. Abramovitch and R. B. Rogers ibid. p. 1795. Heterocyclic Chemistry on heating their N-oxides with bromobenzene in KNH2-liquid ammonia,' 37 while 3-arylation of pyridines is conveniently brought about by treating pyridine N-oxides with benzyne;'38 if the 3-position is blocked (Scheme 24; R = Me) the 2-isomer is obtained.A related reaction occurs between 3,5-dibromo- pyridine N-oxide and phenyl isocyanate (Scheme 24) :'39 quinoline N-oxides behave similarly. '40 PhNCO + 5.8% 2-isomer R = Br DMF 110°C N-Ph '0 Ph Ph Scheme 24 The product from treating pyridine N-oxide with sodium acetylide in dimethyl sulphoxide has been shown to be the ring-opened oximinoacetylene (107)rather than 2-ethynylpyridine N-oxide as reported earlier. '41 Pyridine ring cleavage is also observed on treating pyridine with thiophosgene and barium carbonate in wet dichloromethane at room temperat~re.'~~ In this case thiocyanato- aldehydes (108) and (1W),the former being the kinetically controlled product are obtained.There has been further exploitation of the 1,3-dipolar character of 3-oxido- pyridinium c~rnpounds,~~~~*~ additions taking place across the 2,6-positions. 13' T. Kato and T. Niitsuma J. Pharm. SOC. Japan 1974 94 766. 13' R. A. Abramovitch and I. Shinkai J. Amer. Chem. SOC. 1974 96,5265. 139 T. Hisano T. Matsuoka and M. Ichikawa Heterocycles 1974 2 163. 140 M. Hamana H. Noda and M. Hoyana Heterocycles 1974 2 167. I4l U. Fritzsche and S. Hunig Annalen 1974 1407. 14* F. T. Boyle and R. Hull J.C.S. Perkin I 1974 1541. I4j (a)N. Dennis A. R. Katritzky T. Matsuo S. K. Parton and Y. Takeuchi J.C.S. Perkin I 1974 746; (6) N. Dennis A. R. Katritzky and S.K. Parton. ibid.,p. 750. 0.Meth-Cohn and R.K. Smalley moHmMe ___) Et,N \ A/ MhM' \ N Me I '.-I Me Me Scheme 25 Many examples of [4+ 21 cycloaddition of heterocyclic zwitterions to enes are known whereas examples of 1,4-addition to dienes (4n systems) do not appear to be documented. Orbital symmetry predictions for this process are favourable and an example has recently been recorded (Scheme 25).144 (1 10) (1 11) The first Reissert-like compound (1 10)derived from pyridine is claimed from the reaction of pyridine with ethyl chloroformate and potassium cyanide in dichloromethane.' 45 Action of Grignard reagents on 2-acylated pyridine-2- thiols constitutes a new ketone synthesis ;cyclic intermediate (1 11) is inv01ved.l~~ Perkin reaction between pyridine-2-aldehyde and vinyl ketones or acetic anhydride constitutes a useful one-step synthesis of pyrroloindolizines e.g.(l12),'47"9b and this ring-system is also available by [4+ 21 cycloaddition of acetylene dicarboxylates with indolizines. 148 Vapour-phase pyrolysis of (1 13) as a pathway to 2,7-diazabiphenylene (114) has been de~cribed,'~~ and its non-identity with a diazabiphenylene reported previously' 50 indicates that the latter compound is the 2,6-diaza analogue. 144 K.-L. Mok and M. J. Nye J.C.S. Chem. Comm. 1974 608. 145 R. H. Reuss N. G. Smith and L. J. Winters J. Org. Chem. 1974 39,2027. 146 M.Araki S. Sakata H. Takei and T. Mukaiyama Bull. Chem. SOC.Japan 1974 47 1777. 14' (a) E. Pohjala Acra Chem. Scand.(B) 1974 28 582; (b) E. Pohjala Heterocycles 1974 2 585. *" C. Maseda M. Sone Y. Tominaga R. Natsuki Y. Matsuda and G. Kobayashi, J. Pharm. SOC.Japan 1974 94,839. '49 J. A. H. MacBride J.C.S. Chem. Comm. 1974 359. I5O J. M. Kramer and R. S. Berry J. Amer. Chem. Soc. 1971 93,1303. Heterocyclic Chemistry 345 Addition of perfluoro-2-methylpent-2-ene to primary aromatic amines in THF at 20 "C provides a facile low-temperature route to 2,3-disubstituted-4- arylaminoquinolines e.g. (1 1 5).'" Phenyl isocyanate and ethyl cyanoacetate react to form 3-cyano-4-hydroxy-2-quinolone,' and not as reported pre-52 viously,' 3-cyano-4-hydroxy- 1-phenylazetinone. 2-Quinolones are also avail- able by a new synthesis which involves heating aryl isocyanates with alkynes in the presence of aluminium chloride.'54 NHAr (Trifluoromethy1)quinoline N-oxides on photolysis in benzene ring-expand to give almost quantitative yields of benzoxazepines (1 16)which with methanol and hydrochloric acid undergo ring-contraction to give (trifluoromethyl) sub- stituted indoles in practicable yields.'55",b Sulphuryl chloride is a useful reagent for the perchlorination of q~inoline,'~~ and a method for the selective reduction of the carbocyclic ring in quinoline and isoquinoiine has been de~cribed."~ Of interest is the synthesis of the aza-adamantane analogue of quinine,ls8 and the formation of substituted isoquinolines by regiospecific cycloaddition of benzocyclobutanes and Schiff bases.'59 Similar intramolecular [4+ 21 cycloadditions provide a neat method of synthesis of benzoisoquinolines (Scheme 26).l6O H H X or Y = 0 78 "/ cis X = Y = H 62% trans Scheme 26 'l W. T. Flowers R. N. Haszeldine C. R. Owen and A. Thomas J.C.S. Chem. Comm. 1974 134. ' R. F. Abdulla and P. L. Unger Tetrahedron Letters 1974 178 1. lS3 Ann. Reports (B) 1973 70,477. G. Merault P. Bourgeois and N. Duffaut Bull. SOC.chim. France 1974 1949. 15' (a) Y. Kobayashi I. Kumadaki Y. Hirose and Y. Hanzawa J. Org. Chem. 1974 39 1836; (6) C. Kaneko S. Hayashi and Y. Kobayashi Gem. and Pharm. Bull. (Japan) 1974 22 2147. C. Ciudaru S. Catuna R. Chira and V. Denes Synthesis 1974 356. F. W. Vierhapper and E. L. Eliel J. Amer. Chem. SOC.,1974 96 2256. 'li8 W. N. Speckamp and J. Dijkink Heterocycles 1974 2 291.'59 T. Kametani T. Takahashi K. Ogasawara and K. Fukumoto Tetrahedron 1974 30,1047. 160 W. Oppolzer Tetrahedron Letters 1974 1001. 0.Meth-Cohn and R.K. Smalley Intramolecular nitrene cyclizations have been utilized to prepare thieno- quinolines,' 610 and benzoacridanes,' 61b while phenanthridines are accessible from o-substituted arene diazonium salts and nitriles. '62 A modification of the classical Pomeranz-Fritsch isoquinoline synthesis has appeared and has found ready use in alkaloid synthese~,'~~~*~ while further evidence for the intermediacy of A2-oxazolines in the Pictet-Gams reaction has been presented. 3-Isoquinolones are available in good yield by U.V. irradiation of N-chloro- acetylbenzylamines in aqueous acetonitrile and again the method has found use in alkaloid chemi~try.'~' l-Amino-3-(o-tolyl)isoquinolineand not (1 1 7)'66 is the product obtained by treating o-toluonitrile with sodium in THF.16? Dications (1 18) and related species as anticipated undergo covalent hydration at the azomethine bonds [positions 1 and 2 in (118)] and the non-aromatic products previously reported'68 from the reactions are err0ne0us.l~~ New 2-l7' and 4-pyrimidone' "syntheses have appeared and the electrophilic fluorinating agent CF,OF has been used to prepare a series of 5-fluoro-5,6-dihydrouracils.'72 A high-yield synthesis of 5-cyanopyrimidines starting from alkyl N-cyano- imidates and malononitrile has been reported which is also adaptable for the synthesis of 5-cyanouracils.' 73 A new method of functionalizing the C-5 position of pyrimidine has been published which involves reacting 6-amino- or 6-hydrazino-pyrimidines with diethyl azodicarboxylate.' 74 Yields of the resulting 5-hydrazinopyrimidine (1 19) are good (60-90 %).16 1 (a)G. R. Cliff G. Jones and J. McK. Woolland J.C.S. Perkin I 1974 2072; (6)R. N. Carde and G. Jones ibid. p. 2066. 162 R. C. Petterson J. T. Bennett D. C. Lankin G. W. Lin J. P. Mykytka and T. G. Troendle J. Org. Chem. 1974 39 1841. 163 (a) A. J. Birch A. H. Jackson and P. V. R. Shannon J.C.S. Perkin I 1974 2185; (b) A. J. Birch A. H. Jackson and P. V. R. Shannon ibid. p. 2190. 164 A. 0. Fitton and J. R. Frost J.C.S. Perkin I 1974 1153. 165 M. Ikeda K. Hirao Y. Okuno and 0.Yonemitsu Tetrahedron Letters 1974 1181. 166 K. Yamada S. Ishihara and H. Iida Synthetic Comm. 1973 3 181. 167 V. Dave and E. W. Warnhoff Synthetic Comm. 1974 4 17. 168 J. E. Dickeson I. F. Eckhard R. Fielden and L. A. Summers J.C.S. Perkin I 1973 2885. 169 J. W. Bunting J.C.S. Perkin I 1974 1833. 170 0.S. Tee and M. Endo J. Heterocyclic Chem. 1974 11 441. 171 V. D. Adams and R. C. Anderson Synthesis 1974 286. 172 D. H. R. Barton W. A. Bubb R. H. Hesse and M. M. Pechet J.C.S. Perkin I 1974 2095. 173 H. Kristinsson J.C.S. Chem. Comm. 1974 350. 174 E. C. Taylor and F. Sowinski J. Org. Chem. 1974,39,907. Heterocyclic Chemistry 347 Details of an earlier preliminary report on the mild (cold water) cleavage of pyrimidines have now appeared and mechanistic details are discussed.' 75 More examples of thermally induced perfluoroalkylpyridazine rearrangements have been reported,' 76 and 4,5-dehydropyridazines are proposed as intermediates in the amination of 4-halogenopyridazines with KNH2 in liquid ammonia.' 77 ANRORC reactions continue to hold interest and several new examples have been firmly established' 78a-d and others have been hinted at.'79a*b The versatility of diazines and their N-oxides or quaternary salts in this type of reaction is borne out by the many and varied ring-contractions which they can be made to undergo with hydroxylamine,'80a KNH in liquid ammonia,' 'ObVe and carbanions'"f (Scheme 27)."5 c1 Me R' (b) KNH N-" Meq2a 42 'N -75 "C I Ph (a) R' = R2 = Me (60%I 0- (b) R' = Ph; R2 = NH2 (62%) R' I I Me H I H H 67 % when 60 % when R' = Br R2 = H R' = R2 = C1 or Br Scheme 27 175 J.Clark M. Curphey and I. W. Southon J.C.S. Perkin I 1974 161 1. 176 R. D. Chambers M. Clark J. R.Maslakiewicz W. K. R.Musgrave andP. G. Urban J.C.S. Perkin I 1974 1513. I77 D. E. Klinge H.C. van der Plas and A. Koudjis Rec. Trau. chim. 1974 93 201. 178 (a) A. P. Kroon and H. C. van der Plas Rec. Trao. chim. 1974 93 11 1 ; (b) E. A. Oostreen H. C. van der Plas and H. Jongejan ibid. p. 114; (c) G. M. Sanders M. van Dijk and H. J. den Hertog ibid. p. 198; (d)A. P. Kroon and H. C. van der Plas ibid. p. 227. 179 (a) K. Kasuga M. Hirobe and T. Okamoto J. Pharrn. SOC.Japan 1974 94 945; (b)W.Czuba and H. Poradowska Roczniki Chem. 1974 48 1233. 180 (a) H.C. van der Plas M. C. Vollering H. Jongejan and B. Zuurdeeg Rec. Trav. chim. 1974,93,225; (b)D. E. Klinge H. C. van der Plas G. Geurtsen and A. Koudjis ibid. p. 236; (c) R.Peereboom H. C. van der Plas and A. Koudjis ibid. p. 58; (4R. Peereboom and H. C. van der Plas ibid. p. 277; (e)R.Peereboom and H. C. van der Plas ibid. p. 284; (f)E. A. Oostreen and H. C. van der Plas ibid. p. 233. 0.Meth-Cohn and R. K. Smalley Particular mention may also be made of the remarkably high yield (86%) of phenanthrene obtained by treating benzo[h]quinoline N-oxide with sodium hydride in DMSO. The reaction foIlows an ANRORC pathway.I8' Further studies on the cycloadditions of N-arylbenzaminides derived from benzocinnolines have been published,I8 and pyridazine N-imides while not behaving as their benzocinnoline counterparts prove to be simple effective precursors of the pyrazolo[2,3-b]pyridazinesystem (120).' 82c R ( 120) Examples of the somewhat rare bimolecular [2 + 21 cycloaddition to an azomethine bond are observed in the high-yield acetone-photosensitized cycloadditions of 1,3-dimethyl-6-azauracil and 1,3-dimethyl-6-azathymine to various unsaturated linkages.' 83 Reactions of sulphimides with 1,3-dip0les~*~" and with diphenylcyclopro- penone and its thio-analogue,'84b provide a novel synthetic route to a variety of heterocycles (see also p.331) one of which (121) converts readily into the stable radical (122) during work-up (Scheme 28).I I Ph Ph (121) (122) Scheme 28 Dihydro-1,3-oxazine chemistry continues to flourish. 185a,b 3,5-Dialkyl-2,4,6-trioxo-1,3,5-perhydro-oxazines (123) formed in high yield by the low-temperature reaction of isocyanates with carbon dioxide and tributylphosphine in an inert solvent undergo ring-cleavage with a variety of nucleophiles and provide a useful synthesis of 2,4-dialkylallophanates thioallophanates and 1,3,5-trialkyl- biurets.'86 A similar ring system (124) is available by [4 + 21 cycloaddition of Y. Hamada and i. Takeuchi Tetrahedron Letters 1974 495. Is' (a) M. J. Rance C. W. Rees P. Spagnolo and R. C. Storr J.C.S. Chem. Comm. 1974 658; (6) J. J. Barr R. C. Storr and J. Rimmer ibid. p. 657; (c) C. W.Rees R. W. Stephenson and R. C. Storr ibid. p. 941. J. S. Swenton and J. A. Hyatt J. Amer. Chem. SOC.,1974 96 4879. Is' (a)T. L. Gilchrist J. Harris and C. W. Rees J.C.S. Chem. Comm. 1974,485;(b)T. L. Gilchrist J. Harris and C. W. Rees ibid. p. 487. Is' (a)T. A. Narwid and A. I. Meyers J. Org. Chem. 1974,39,2572; (6)R. E. Ireland and A. I(.Willard ibid. p. 421. A. Etienne and B. Bonte Bull. SOC.chim. France 1974 1497. Heterocyclic Chemistry thiocarbonyl isocyanates with ketones. "'The thiadiazine dioxide (125)appears to have chemistry analogous to 2-pyrimidone ;for example electrophilic substi- tution proceeds solely at the 4-positi0n.'~~ New syntheses for 2,3-dihydro-4-pyrones1 *' have appeared and 4-thia- pyrones e.g. (1 26) are available from the reaction of diphenylcyclopropen-one or -thione with the meso-ionic dithiole system ( 127).l9O Diketen shows variation in its reaction with quir~oline"~" and acridine N-oxides.'91 In the former case the y-pyrone (1 28) is obtained while in the latter instance a bridged intermediate (129) is held responsible for the 4-acetonyl- acridine produced.3-Substituted chromylium salts hitherto accessible only with difficulty are now obtainable from salicylaldehydes in high yield. 192 Chromone-3-aldehydes may be prepared by facile one-step Vilsmeier-Haack reaction on o-hydroxyacetophenones. 93a Equally ready is the formation of 3-chlorochromone by treating 3-formylchromone with sodium hypochlorite in acetic Diborane is involved in a new synthesis of chromanones (Scheme 29) which are readily dehydrogenated to chromones using palladium charcoal.' 94 A.Schulze and J. Goerdeler Tetrahedron Letters 1974 221. G. A. Pagani J.C.S. Perkin I 1974 2050. R. Garry L. Nyffenegger and R. Vessiere Bull. Soc. chim. France 1974 933 H. Matsukubo and H. Kato J.C.S. Chem. Comm. 1974,412. 191 (a) T. Kato H. Yamanaka R. Sakamoto and T. Shiraishi Chem. and Pharm. Bull. (Japan) 1974 22 1206; (b) T. Kato T. Chiba and M. Daneshtalab Heterocycles 1974 2 315. P. Bouvier J. Andrieux and D. Molho Tetrahedron Letters 1974 1033. (a) A. Nohara T. Umetani and Y.Sanno Tetrahedron 1974,30,3553; (b)A. Nohara K. Ukawa and Y. Sanno ibid. p. 3563. *94 B. S. Kirkiacharian G. H. Elia and G. Mahuzier Compt. rend.1974 279 C 151. 0.Meth-Cohn and R. K. Smalley i. B2H ii NaOH-H,O ~ i.B,H &Me Cr>dMe t- 11. Na,Cr,O,/H' \ AcO H R 0' R = H or OH Scheme 29 Enol ethers of p-dicarbonyl compounds when treated with sulphonium ylides prove to be a useful source of thiabenzene oxides (130),195 and trithiocarbamate SS-dioxides (131) a new system appear to have potential in the syntheses of novel sulphur heterocycles e.g. the air-sensitive 2H-thiapyran (1 32). 19' The supposed thiabenzenes and thianaphthalews isolated from the reaction of phenyl-lithium with thiopyrylium salts have now been shown to be oligomers of undetermined structure.'97 An interesting example of diene formation by retro-Diels-Alder reaction has been recorded (Scheme 30).Ig8 The dihydro-1,2-oxathiin oxide (133) is isolable but cannot be prepared by the reverse [4+ 21 cycloaddition since the alternative chelitropic process to give 2,5-dihydrothiophen 1,l -dioxide is favoured (Scheme 30).Scheme 30 New routes to 3-arylphosphabenzenes (134),199phosphinolines (1 35),200a benzazaphosphocines (1 36),200band phosphoindoles ( 137)200" have been de- veloped. 95 C. M. Harris J. J. Cleary and T. M. Harris J. Org. Chem. 1974 39 72. 196 J. A. Boerma N. H. Nilsson and A. Senning Tetrahedron 1974 30,2735. '97 G. H. Senkler jun. J. Stackhouse B. E. Maryanoff and K. Mislow J. Amer. Chem. SOC.,1974 96 5649. 198 F. Jung M. Molin R. Van Den Elzen and T. Durst J. Amer. Chem. SOC. 1974 96 935. D. Mark1 and D. Matthes Tetrahedron Letters 1974 4381.(a) L. E. Rowley and J. M. Swan Austral. J. Chem. 1974 27 801; (6)D. J. Collins L. E. Rowley and J. M. Swan ibid. p. 815; (c) D. J. Collins L.. E. Rowley and J. M. Swan ibid. p. 83 1. Heterocyclic Chemistry I (135) Ar m x YZ w od ‘OR (138) (139) (137) The first arsabenzenes (138) bearing a functional group have been synthe- sized,201u,band preliminary experiments indicate that arsabenzaldehyde ( 138; R = CHO) exhibits normal aldehyde reactivity. Conformational and configurational studies of six-membered heterocycles are still attracting considerable attention and studies this year include oxazolo- [3,4-~]pyridines,’ O’ silacyclohexanes,2 hexah ydrotetrazines,’ O4 2,2-disu bsti- tuted-1,3-dio~ans,’~~ and substituted piperidines.206u,b Paramagnetic shifts in the n.m.r.spectra have confirmed the equatorial preference for the NH group in piperidine. 2o N.m.r. spectroscopy has also been successfully employed in showing the existence of boat-shaped conformers in the hetero-analogues of bicyclo[3,3,l]nonane (139; X = Z = S Y = 0),which usually exist in the double-chair conformation.208 The findings have been confirmed by X-ray analysis. 5 Seven-membered Ring Compounds and Macrocycles Thiotropone reacts probably in a stepwise rather than a concerted manner with dichloroketen to give the pseudoaromatic system (140) (Scheme 3 l).209 [@j5&@ CI c1 (===-Js +Cl,C=C=O + ( 140) Scheme 31 ’01 (a)G. Markl and F. Kneidl Angew.Chem. Inrernar. Edn. 1974 13,668; (b)G. Markl and F. Kneidl ibid. p. 667. ‘02 Y. Takeuchi P. J. Chivers and T. A. Crabb J.C.S. Chem. Comm. 1974 13 210. ’03 R. J. Ouelette J. Amer. Chem. SOC.,1974 96 2421. ’04 R. A. Y. Jones A. R. Katritzky A. R.Martin D. L. Ostercamp A. C. Richards and J. M. Sullivan J. Amer. Chem. SOC.,1974 96 576. ’05 W. F. Bailey and E. L. Eliel J. Amer. Chem. SOC.,1974 96 1798. ’06 (a)V. J. Baker I. D. Blackburne and A. R. Katritzky J.C.S. Perkin II 1974 1557; (b) V. J. Baker I. D. Blackburne A. R.Katritzky R. A. Kolinski and Y. Takeuchi ibid. p. 1563. ’07 I. D. Blackburne A. R.Katritzky and Y. Takeuchi J. Amer. Chem. SOC.,1974 96 682. ’08 N. S. Zefirov E. N. Kurkutova and A. V. Goncharov Zhur. org. Khim. 1974,10 1124.2 09 R. Cabrino G. Biggi and F. Pietra Synthesis 1974 276. 0.Meth-Cohn and R. K. Smalley Scheme 32 The use of ring expansion to synthesize otherwise difficultly accessible systems has been thoroughly exploited. Thus o-ethoxycarbonylphenyl azides give good yields of 2-alkoxy-3-ethoxycarbonyI-3H-azepinesunder U.V. irradiation.2 The formation of azepinothiophens (Scheme 32) represents the first example of the photo-expansion of a fused bicyclic aromatic system and leads to (141) one of the rare 2H-azepines. 3H-Azepines are well documented but the anti- aromatic 1 H-analogues remain elusive despite attempts to isomerize such likely Ph c:: COPh Me . Ph ( 142) precursors as (142).2’2 Nevertheless the 1H-azepines appear to mediate several reaction pathways peculiar to azepines.Novel approaches to 1,2-diazepines have been elaborated from 2,4,6-triarylthiopyrylium salts and hydrazines. 21 CH,=C(OMe) i Ht ____) ____, hv ii NaBH Ph .. /\ .. Me Me Me Me Me ‘Me I Scheme 33 210 R. K. Smalley W. A. Strachan and H. Suschitzky Synthesis 1974 503. ’‘ ’ B. Iddon M. W. Pickering and H. Suschitzky J.C.S. Chem. Comm. 1974 759. ”’ D. J. Anderson A. Hassner and D. Y.Tang J. Org. Chem. 1974 39 3076. *13 D. J. Harris G. Y.-P. Kan V. Snieckus and E. Klingsberg Cunud. J. Chem. 1974. 52. 2798. 14' to thiepins,' approach Heterocyclic Chemistry 353 Full details of Reinhoudt's benzothiepins,' 14b and ben~oxepins,~~~' (cf ref. 215) have appeared and a similar approach has been used for the first monocyclic silepin synthesis (Scheme 33).216 Thermolysis of the silepin gives o-terphenyl via a novel silanocaradiene.Cycloaddition of aziridines to sym-tetrazines with concomitant nitrogen extrusion offers a high-yield route to 1,2.4-triazepines (Scheme 34) which decompose to give pyrazoles or pyrimidines R3 R3 1 Scheme 34 on heating.21 The first report of the synthesis of 6,7-benzo-lH- 1,2,4-triazepines has also been reported.218 Carbon monoxide extrusion is observed during the photo-action of phenylacetylene on 2,6-diphenylthiopyran-4-one 1,l -dioxide yielding the thiepin dioxide (143).2'9 Mono- and poly-olefins can react in a thermally allowed cycloaddition manner with fragments derived from molecular sulphur.220 Thus cycloheptatriene on heating with sulphur gives the novel nine-membered heterocycle (144) which we interpret as a (R6s+ R4s) cyclo- addition.221 The benzothiepin valence tautomer (145) reported last year222 Ph i, I,a..as)f7J-j5m S S o/'"o S (144) (145) (146) (143) has now been successfully converted into the anti-aromatic benzothiepin (146) by treatment with a rhodium complex at 0°C and work-up below -10°C.223 Mild warming of (146) gave naphthalene and sulphur. 214 (a)D. N. Reinhoudt and C. G. Kouwenhoven Terrahedron 1974 30 2093; (6) D. N. Reinhoudt and C. G. Kouwenhoven ibid. p. 2431 ; (c) D. N. Reinhoudt and C. G. Kouwenhoven Rec. Trav. chim. 1974 93 129. '' Ann. Reports (B) 1972 69 459. ' T. J. Barton R. C. Kippenhan and A.J. Nelson J. Arner. Chem. SOC.,1974,96 2272. D. J. Anderson and A. Hassner J.C.S. Chem. Comm. 1974 45. S. Conde C. Corral and R. Madronero Tetrahedron 1974 30 195. 2'9 N. Ishibe K. Hashimoto and M. Sunami J. Org. Chem. 1974 39 103. *'O E.g. T. C. Shields and A. N. Kurtz J. Amer. Chem. Soc. 1969 91 5415. 221 H. Fritz and C. D. Weis Tetrahedron Letters 1974 1659. 222 Ann. Reports (B) 1973 70 519. 223 I. Murata T. Tatsuoka and Y. Sugihara Angew. Chem. Internat. Edn. 1974 13 142. 0.Meth-Cohn and R. K. Smajley Photolysis or thermolysis (with or without silver catalysis) of (145) causes ring-contraction to yield the fused cyclobutene (147).224 1 -Ethoxycarbonyl- 1,2-diazepine reacts with singlet oxygen to give a reasonably stable endo-peroxide (148) which undergoes ring-opening and fragmentation N’ (147) reactions under further phot~lysis.~~’ lH-Benzo-1,2-diazepines may be converted into the less accessible 3H-analogues by successive reduction and oxidation steps (Scheme 35).226 N-CO Scheme 35 1,2-Dihydropyridines prefer to react as enamines with dimethyl acetylene- dicarboxylates yielding interesting azocines (Scheme 36).227 Tetrathieno-cyclo-octatetraene (149) may be prepared by the dimerization of the dilithio- C0,Me Scheme 36 2,2’-or -3,3’-dithienyl (Scheme 37) and exists in a ‘saddle’ conformation.228 N-Chloroacetyl-/3-(m-methoxyphenyl)ethylamine undergoes a surprising photo- chemical cyclization either at the ring or on the methoxy-group depending on solvent polarity and viscosity the latter process involving solvent-caged z24 I.Murata T. Tatsuoka and Y.Sugihara Tetrahedron Letters 1974 199. 225 T. Tsuchiya H. Arai H. Hasegawa and H. Igeta Tetrahedron Letters 1974 4103. 226 J. Kurita and T. Tsuchiya J.C.S. Chem. Comm. 1974 936. 227 R. M. Acheson G. Paglietti and P. A. Tasker J.C.S. Perkin I 1974 2496. 228 L. Weber and G. Schmid Angew. Chem. Internat. Edn. 1974 13 467. Heterocyclic Chemistry radicals (Scheme 38).229 3-Acetylcoumarin (150) reacts with an excess of diazo-ethane causing ring-expansion to the oxonin (1 5 l) some intermediates being isolable.23* Li Li Li Li ( 149) Scheme 37 co ~2 ~~~c) OMe ~ \ THF OMe 0 Scheme 38 (152) R = Ac H or -229 Y. Okuno and 0.Yonemitsu Tetrahedron Letters 1974 1169.230 R. Clinging F. M. Dean and L. E. Houghton,J.C.S. Perkin I 1974 66. 0.Meth-Cohn and R. K. Smalley Novel annulenes continue to proliferate including the atropic benzazonins (152)231 and dithiocin (153),232 the paratropic [12]diazapyracylenes (154),233 diatropic aza[13]ann~lene~~~,~~ and a and its anion,235 aza[l7]ann~lene,~~~ series of 18n[17]heteroannulenes (155).236"*b*' The [19]- and [21]-annulenones (156a and b)237",b the former being diatropic but the latter potentially paratropic showed only normal olefinic character. as did other related [2l]annulenones. 0 (156) a;m = n = 1 h;m=l,n=O The strategy for the synthesis of a 'trefoil-knotted' compound (157) has been outlined and suitable model precursors synthesi~ed.~~' Large numbers of new variants of the crown polyethers have been made including numerous polyether ~ulphides,~~~ and new simpler routes to particularly useful systems (dibenzo-18- 231 A.G. Anastassiou and E. Reichmanis Angew. Chem. Internat. Edn. 1974 13 404. 232 H. J. Eggelte and F. Bickelhaupt Angew. Chem. Internat. Edn. 1974 13 345. 233 W. Flitsch and H. Lerner Tetrahedron Letters 1974 1677. 234 A. G. Anastassiou and R. L. Elliott J. Amer. Chem. Soc. 1974 96 5257. 235 G. Schroder G. Frank H. Rottele and J. F. M. Oth Angew. Chem. Internat. Edn. 1974 13 205. 236 (a)J. M. Brown and F. Sondheimer Angew. Chem. Internat. Edn. 1974 13 337; (b)J. M. Brown and F. Sondheimer ibid. p. 339; (c) P. J. Beeby J.M. Brown P. J. Garratt and F. Sondheimer Tetrahedron Letters 1974 599. 237 (a)T. M. Cresp and M. V. Sargent J.C.S. Chem. Comm. 1974 101; (6) T. M. Cresp and M. V. Sargent J.C.S. Perkin I 1974 2145. 238 G. Schill R. Henschel and J. Boeckmann Annalen 1974 709. 239 J. J. Christensen J. Heterocyclic Chem. 1974 11 45. 357 Heterocyclic Chemistry (158) n = 14 ~rown-6,~~~ 12-crown-4 and 15-cro~n-5~~~) 18-cr0wn-6,~~’ including a novel purification approach using the acetonitrile complex have been announced.241 Some useful pyridine-based analogues (158) have been prepared.243 Thus (158; n = 2 or 3) solubilize NaMnO (but not KMnO,) in benzene. Nitrogen analogues of the crown ethers have been made with 3-7 nitrogen atoms.244 The tetra-am-compound reacts with ethyl orthocarbonate followed by alkali to give the unusual degenerate heterocycle (159).245 6 Reviews Reviews of the chemistry of non-benzenoid aromatic and heteroaromatic p-lactam antibiotics,247 benzofuran~,~~~ annulene~,~,~ benzimida~oles,~~~ oxa~oles,~ ” 53 50 1,2,3-tria~oles,~1-,2- and 3-benza~epines,~ diben~azepines,~ and 1,5-benzodiazepine~,~~~ 2,3-dihydr0-1,4-diazepines~~~ pyridine~,~~~ crown nitrogen-bridged six-membered ring systems,25 dibenzothiophen~,~~~ ethers sulphides et~.,~~’ polyfluoroheteroaromatics,260 and the homolytic “O J.Ashby R. Hull M. J. Cooper and E. M. Ramage Synthetic Comm. 1974 4 1 13. G. W. Gokel D. J. Cram C. L. Liotta H. P. Harris and F. L. Cook J. Org. Chem. 1974 39 2445. 242 F.L. Cook T. C. Carnsb M.P. Bvrne C. W. Bowers D. H. Speck and C. L. Liotta Tetrahedron Letters 1974 4029. 243 F. Vogtle and E. Weber Angew. Chem. Internat. Edn. 1974 13 149. 244 J. E. Richman and T. J. Alkins J. Amer. Chem. SOC. 1974,96 2269. 245 J. E. Richman and H. E. Simmons Tetrahedron 1974 30 1769. ’06 F. Sondheimer Chimia (Switt.) 1974 28 163. 24’ J. W. F. K. Barnick Chem. Tech. (Amsterdam) 1974 29 189. 14’ A. Mustafa ‘Benzofurans’ in ‘The Chemistry of Heterocyclic Compounds’ Wiley New York 1974 Vol. 29. 249 P. N. Preston Chem. Rev. 1974 74 279. 150 R. Lakhan and B. Ternai Adv. Heterocyclic Chem. 1974 17. 15’ T. L. Gilchrist and G. E. Gymer Adv. Heterocyclic Chem. 1974 16 33. 252 S. Kasparek Ado. Heterocyclic Chem. 1974 17. 253 L. J. Kricka and A.Ledwith Chem. Rev. 1974 74 101. 254 D. Lloyd H. P. Cleghorn and D. R. Marshall Adv. Heterocyclic Chem. 1974 17 1. 255 D. Lloyd and H. P. Cleghorn Adv. Heterocyclic Chem. 1974 17 27. * 56 ‘Pyridine and its Derivatives’ in ‘The Chemistry of Heterocyclic Compounds’ ed. ed. R. A. Abramovitch Wiley New York 1974 Vol. 14 supplement Part 2 and Part 3. 257 L. J. Kricka and J. M. Vernon Ado. Heterocyclic Chem. 1974 16 87. 258 J. Ashby and C. C. Cook Adv. Heterocyclic Chem. 1974 16 181. 259 J. J. Christensen D. J. Eatough and R. M. Izatt Chem. Rev. 1974 74 351. 260 G. G. Yakobson T. D. Petrova and L. S. Kobrina Fluorine Chem. Rev. 1974,7 115. 358 0.Meth-Cohn and R.K. Smalley substitution of heteroaromatic compounds26' have appeared. Heteroaromatic N-imines have been surveyed,262 and syntheses of cyclohexane- 1,3-dione-based heterocycles examined.The synthesis of heterocycles using primary nitro-comp~unds~~~ (mainly 1,3-oxazines -silazines -borazines and pyrimidines) thiaz~lines,~'~ cyclic peroxides,266 tervalent phosphorus diketeq2@ oxidative coupling of organo-copper derivatives,269 halovinylene carbonate^,^ 70 and carbon sub- oxide27' and the synthesis of penta~ocine,~~~ indoles etc. benzodiaz~cines,~~~ from asymmetric ketones274 and uia nitrene~,~~~ and newer synthetic approaches to N-hetero~ycles~~~ have been appraised. Cycloaddition 'reactions of acyl is~cyanates,~~ cationic dipole^,^ 78 organolithium (anionic) and azolium ylides with dialkyl arylphosphonates280 have been evaluated.An account of heterocycles as synthetic intermediates has appeared.281 The concept of merostabilization has been introduced to account for the stability of radicals particularly heterocyclic derivatives,282 and reviews on base- catalysed proton exchange in heterocyclic systems283 and the mass spectra of in dole^^*^ have been published. The stereochemistry of four-membered hetero- cycle~~~~ and the conformation of sulphur-containing heterocycles,286 chair- chair interconver~ion~~ and non-chair structures288 involving six-membered rings has been covered. A general review on the aromaticity of heterocycles has appeared.289 26' F. Minisci and 0. Porta Adv. Heterocyclic Chem. 1974 16 123. 262 H.-J. Timpe Ado. Heterocyclic Chem.1974 17. 263 A. Y. Strakov E. Gudriniece and D. Zicane Khim. geterotsikl. Soedinenii 1974 1011. 264 T. Urbanski Synthesis 1974 613. 265 K. Hirai and Y. Kishida Heterocycles 1974 2 185. 266 W. Adam Angew. Chem. Internat. Edn. 1974 13 619. 267 J. I. G. Cadogan and R. K. Mackie Chem. SOC. Rev. 1974,3 87. 268 T. Kato Accounts Chem. Res. 1974 7 265. 269 T. Kauffmann Angew. Chem. Internat. Edn. 1974 13 291. 270 H.-D. Scharf Angew. Chem. Internat. Edn. 1974 13 520. "' T. Kappe and E. Ziegler Angew. Chem. Internat. Edn. 1974 13 491. 272 T. Kametani K. Kigasawa M. Hiiragi and N. Wagatsuma Heterocycles 1974 2 79. 273 T. Kametani,-K. Kigasawa M. Hiiragi and K. Wakisaka Heterocycles 1974 2 349. 274 I. I. Grandberg and V. I. Sorokin Russ. Chem. Rev. 1974 43 115.275 T. Kametani F. F. Ebetino T. Yamanaka and K. Nyu Heterocycles 1974 2 209. 276 A. N. Kost Khim. geterosikl. Soedinenii 1974 277. 277 B. A. Arbuzov and N. N. Zobova Synthesis 1974,461. 278 C. K. Bradsher Adv. Heterocyclic Chem. 1974 16 289. '19 T. Kauffmann Angew. Chem. Internat. Edn. 1974 13 627. A. Takamizawa H. Harada H. Sat0 and Y. Hamashima Heterocycles 1974 2 521. 281 A. I. Meyers 'Heterocycles in Organic Synthesis' Wiley New York 1974. 282 R. W. Baldcock P. Hudson A. R. Katritzky and F. Soti J.C.S. Perkin I 1974 1422; A. R. Katritzky and F. Soti ibid. p. 1427. 283 J. A. Elvidge J. R. Jones C. O'Brien E. -A. Evans and H. C. Sheppard Ado. Hetero- cyclic Chem. 1974 16 1. 284 R. A. Khmel'nitskii Khim. geterotsikl. Soedinenii 1974 291.285 R. M. Moriarty Topics Stereochem. 1974,8 271. 286 N. S. Zefirov and I. V. Kazimirchik Uspekhi Khim. 1974 43 252. 287 J. E. Anderson Topics Current Chem. 1974 45 139. 288 G. M. Kellie and F. G. Riddell Topics Stereochem. 1974 8 225. 289 M. J. Cook A. R.Katritzky and P. Linda Ado. Heterocyclic Chem. 1974 17.

ISSN:0069-3030    

DOI:10.1039/OC9747100319

出版商:RSC    

年代:1974

数据来源: RSC