5 Aliphatic Compounds Part (i) Hydrocarbons By S. E. THOMAS Department of Chemistry University of Warwick Coventry CV4 7AL 1 Alkanes The alkanes are an attractive starting point for the application of molecular modelling techniques because not only do many of their properties vary in a regular manner with molecular mass but also problems associated with more polar compounds do not arise. A modelling study has been carried out on eight physical properties of seventy-four normal and branched alkanes.’ It proved possible to model most of the properties accurately with the exception of melting points which could not be modelled precisely by any of the available indices. The effect of solvent on the conformation of hydrocarbon chains has been probed using the Karplus-like response of ,.Icc to the relative disposition of two 13Catoms about a central carbon-carbon bond.* Results obtained in solvents of widely differing polarity suggest that chain conformation is remarkably insensitive to changes in solvent.The development of systems which effect selective catalytic functionalization of alkanes continues to be an area of intense research activity. Modifications to photochemical polyoxometallate methods3 and photocatalytic RhCl(CO)( PR,) for dehydrogenation of alkanes to alkenes have been reported whilst studies on alkane oxidation include a comparison of the Gif system (iron catalyst oxygen zinc carboxylic acid) with its electrochemical equivalent (the Gif-Orsay system),6 and the use of ruthenium complexes containing polypyridyl ligands to catalyse the oxidation of alkanes by alkyl hydro peroxide^.^ Photochlorination of n-alkanes adsorbed on pentasil zeolites monochlorinates terminal methyl groups more selectively than the corresponding homogeneous reaction and so provides a novel method for synthesizing terminally functionalized linear alkanes.* ’ D.E. Needham I.-C. Wei and P. G. Seybold J. Am. Chem. SOC.,1988 110 4186. * F. M. Menger and L. L. D’Angelo J. Am. Chem. SOC., 1988 110 8241. R. F. Renneke and C. L. Hill Angew. Chem. Inr. Ed. Engl 1988 27 1526. T. Sakakura T. Sodeyama Y. Tokunaga and M. Tanaka Chem. Lett 1988 263. K. Nomura and Y. Saito J. Chem. Soc. Chem. Commun. 1988 161. G. Balavoine D. H. R. Barton J. Boivin A. Gref P. Le Coupanec N.Ozbalik J. A. K. Pestana and H. Rivihre Tetrahedron 1988 44 1091. ’ T.-C. Lau C.-M. Che W.-0. Lee and C.-K. Poon J. Chem. SOC.,Chem. Commun. 1988 1406. N. J. Turro J. R. Fehlner D. P. Hessler K. M. Welsh W. Ruderman D. Firnberg and A. M. Braun J. Org. Chem. 1988 53 3731. 85 S. E. Thomas Two new methods for the reduction of alcohols to alkanes have been reported. Bu;SnH-Et3B reduces dithiocarbonates or thiocarbonates derived from secondary alcohols to the corresponding hydrocarbons under mild conditions' and acetates derived from primary secondary and tertiary alcohols are deoxygenated to hydrocarbons in high yield by p-bis( diphenylhydrosily1)benzene under homolytic conditions." 2 Alkenes Synthesis.-Di-and triquaternary alkenes have been synthesized by dehydration of secondary and tertiary neopentyl alcohols without any rearrangement occurring." For example the triquaternary alkene (1) was synthesized by addition of Bu'Li to nitrile (2) followed by hydrolysis addition of a second equivalent of Bu'Li and dehydration of the resulting alcohol.Lithium tetraalkylcerates prepared by the addition of four equivalents of alkyl-lithium to cerium trichloride add to epoxides to give alkylated alkenes. The utility of this method has been demonstrated in a short synthesis of the sesquiterpene dehydro-a-curcumene (Scheme 1).l2 43% Reagents i dirnethoxyethane-diethyl ether (2 l) -93 +-50 "C,16h Scheme 1 A mild but slow enzyme-assisted procedure for the regio- and stereo-controlled addition of perfluoroalkyl groups to alkynes has been rep~rted.'~ Thus reaction of alkynes with perfluoroalkyl iodides in the presence of several enzyme systems leads to perfluoroalkylated alkenes and perfluoroalkanoic acids (Scheme 2).An E-alkene with a chiral substituent has been synthesized in high optical purity by reaction of an alkyne with a borane bearing the required optically active sub- stituent (Scheme 3).14 K. Nozaki K. Oshirna and K. Utimoto Tetrahedron Lett. 1988,29 6125. 10 H. Sano T.Takeda and T. Migita Chem. Lett. 1988 119. C. A.Drake N. Rabjohn M.S. Tempesta and R. B. Taylor J. Org. Chem. 1988,53 4555. 12 Y. Ukaji and T. Fujisawa Tetrahedron Lett. 1988,29 5165. l3 T. Kitazurne and T. Ikeya J. Org. Chem. 1988,53 2350.14 H. C. Brown R. K. Bakshi and B. Singaram J. Am. Chem. Soc. 1988,110,1529. Aliphatic Compounds -Part (i) Hydrocarbons 87 R R = F CF, CP,. CSF,, C,F,S 24-66% 33-75% R R' = H alkyl aryl Reagents i urease/ Ni porphin or lipoxygenase/Fe porphin or catalase/ Fe protohaem H,O 9-36 days Scheme 2 72% yield 99% e.e. Reagents i NaOMe; ii Pr'C0,H Scheme 3 Addition of Grignard reagents to 5-alkyl-2,3-dihydrofurans in the presence of Ni(o) catalysts produces homoallylic alcohols (Wenkert reaction). This reactivity has been extended to 6-a1kyl-3,4-dihydro-2H-pyrans.l5 The reaction gives trisub- stituted alkenes with retention of configuration and has been applied to the synthesis of (E)-3-acetoxy-7-methylnon-6-ene, the aggregation pheromone of the square- necked grain beetle Cathartus quadricollis (Scheme 4).OAc I Reagents i EtMgBr; ii TsOH pyridine; iii MeMgBr; iv Ac20 Scheme 4 A new method for regiospecific carbon-carbon coupling of terminal alkenes based on a sulphonylation-alkylation-desulphinylationprocess has been described and applied to the conversion of (+)-limonene (3) into (E)-and (2)-a-bisabolenes (4).16This direct extension of a terminal alkene promises to be of further value in natural product synthesis. l5 P. Kocienski N. J. Dixon and S. Wadman Tetrahedron Lett. 1988 29 2353. J. E. Baldwin R. M. Adlington Y. Ichikawa and C. J. Kneale J. Chem. SOC.,Chem. Commwn. 1988,702. S. E. Thomas A review covering the conversion of enol triflates into a wide variety of alkenes by their reaction with organocopper reagents or other nucleophiles in the presence of palladium catalysts has been p~blished.’~ The Wittig reaction and related processes continue to attract a lot of attention.Further mechanistic studies have been and stereoselectivity studies have focused on Wittig reactions of allylic ylides,2’ semi-stabilized ylides,22 and ylide anions derived from semi-stabilized phosphonium ylide~.~~ Higher yielding procedures for the Wittig reaction between trifluoromethylketones and non-stabilized phosphorus ylide~,~~ and the Horner synthesis of didehydroamino acid derivatives from aldehydes and N-acyl-2-(diethoxyphosphory1)glycine esters2’ have been reported. Wittig reactions of esters thiol esters amides anhydrides and imides have been reviewed.26 To date preparation of labelled alkenes by Wittig and related reactions has been limited by scrambling and exchange processes.It has now been shown that Wittig- Horner reactions between aldehydes RCHO and phosphonates (EtO),POCH,R’ performed in 6M K2C03/ D20 give specifically deuterated alkenes RCH=CDR’ (D > 95%) in high yield.27 An ylide bearing a masked formyl group has been generated (Scheme 5).28 It cleanly reacts with aldehydes to give predominantly or exclusively (E)-vinylthiazoles which may be converted into two-carbon homologues of the original aldehydes. Two effective ketone-methylenating agents CH,(AlClMe)2 and CH2(A1ClEt) have been prepared.29 As dietherates with Et20 or THF they smoothly convert aliphatic and aromatic ketones into the corresponding alkenes with little or no concomitant alkylation or reduction.17 W. J. Scott and J. E. McMurry Acc. Chem. Rex 1988 21 47. 18 E. Vedejs C. F. Marth and R. Ruggeri J. Am. Chem. SOC.,1988 110 3940. 19 E. Vedejs and C. F. Marth J. Am. Chem. SOC.,1988 110 3948. 20 H. Yamataka K. Nagareda Y. Takai M. Sawada and T. Hanafusa 1.Org. Chem. 1988 53 3877 21 R. Tamura K. Saegusa M. Kakihana and D. Oda J. Org. Chem. 1988 53 2723. 22 A. Mylona J. Nikkokavouras and I. M. Takakis J. Org. Chem. 1988 53 3838. 23 E. G. McKenna and B. J. Walker Tetrahedron Lett. 1988 29 485. 24 F. Camps F.-J. Sanchez and A. Messeguer Synthesis 1988 823. 2s P. G. Ciattini E. Morera and G. Ortar Synthesis 1988 140.26 P. J. Murphy and J. Brennan Chem. SOC.Rev. 1988 17 1. 27 P. Seguineau and J. Villieras Tetrahedron Lett. 1988 29 477. 28 A. Dondoni G. Fantin M. Fogagnolo A Medici and P. Pedrini Tetrahedron 1988,44 2021. 29 A. M. Piotrwski D. B. Malpass M. P. Boleslawski and J. J. Eisch J. Org. Chem. 1988 53 2829. Aliphatic Compounds -Part (i) Hydrocarbons Reagents i Bu'OK; ii Mel; iii NaBH,; iv Hg2+/H20 Scheme 5 While there are many non-chiroptical methods for the assay of chiral amines alcohols and acids there are very few reliable techniques for measuring the enan- tiomeric purity of chiral alkenes. It is of note therefore that the enantiomers of alkenes (5)-( 8) are cleanly separated by capillary gas chromatography using hep- takis-(2,3,6-tri-O-n-pentyl)-P-cyclodextrin as the stationary phase,30 and that a full account of the use of optically active platinum and palladium complexes as chiral derivatizing agents for alkenes has been p~blished.~~ Reactions.-The potential energy profile for the full catalytic cycle of alkene hydroge- nation using Wilkinson's catalyst has been studied using ab initio MO methods; results indicate that the profile is smooth without any excessively high barriers or very stable intermediate^.^^ It is of note that this is the first ab initio study of the potential energy profile of a full catalytic cycle.Chiral allylic secondary alcohols have been resolved efficiently by homogeneous hydrogenation catalysed by (R)-or (S)-BINAP-Ru diacetate complexes.33 The combined effects of both intra- and intermolecular asymmetric induction give up to 76 :1 differentiation between the enantiomeric substrates.Decomposition of formic acid to hydrogen and carbon dioxide in the presence of catalytic amounts of optically active rhodium complexes has been shown to be a simple and effective alternative source of hydrogen for enantioselective hydrogenation of a$-unsaturated carboxylic Ab initio MO calculations designed to determine the transition state geometries of the reactions between halogens and ethene have been perf~rmed.~' These suggest that the transition state structure for the fluorination of ethene is four-centred whilst the transition state geometry for chlorination and bromination can be regarded as 30 J.Ehlers W. A. Konig S. Lutz G. Wenz and H. tom Diek Angew. Chem. Int. Ed. Engl. 1988 27 1556. 3' D. Parker and R. J. Taylor Tetrahedron 1988 44 2241. 32 C. Daniel N. Koga J. Han X. Y. Fu and K. Morokuma J. Am. Chem. SOC.,1988 110 3773. 33 M. Kitamura 1. Kasahara K. Manabe R. Noyori and H. Takaya J. Org. Chem. 1988 53 708. 34 H. Brunner and W. Leitner Angew. Chern. Int. Ed. Engl. 1988 27 1180. 35 S. Yamabe T. Minato and S. Inagaki J. Chem. SOC.,Chem. Commun. 1988 532. 90 S. E. Thomas a cyclic chloronium (bromonium) ion plus a chloride (bromide) ion. The calculated transition state structures agree with the observed syn-selective fluorination and anti-selective chlorination and bromination of ethene. A new catalytic process for asymmetric cis-dihydroxylation of alkenes has been reported (Scheme 6).36It is of note that unlike asymmetric epoxidations and most asymmetric hydrogenations this process does not require a directing functional group and that very small quantities of the osmium catalyst are required.dihydroquinidine esters “Ho I OH” R3 OH OH 80-95% yield “HO ’ OH” 20-88’/0 e.e. dihydroquinine esters Reagents i 0.2-0.4% OsO, acetone HzO o/ +\N’ w ‘o-Scheme 6 New methods for converting alkenes into epoxides include a sodium perbor- ate/ acetic anhydride system,37 hydrogen peroxide oxidation catalysed by a new class of quaternary ammonium tetrakis( diperoxotungsto) phosphate catalyst,38 and Bu‘OOH oxidation catalysed by a novel polystyrene-supported peptide-linked molybdenum catalyst.39 An interesting approach to the problem of preparing enan- tiomerically pure simple chiral epoxides has been reported.Thus Sharpless epoxida- tion of the alkenyl silanol (9) in the presence of (+)-diethy1 tartrate followed by protodesilylation gives (S)-styrene oxide in 85-95% enantiomeric excess.4o Ph *SiMe20H A simple direct synthesis of thiiranes from alkenes has been developed!’ Treat-ment of bis(trimethylsily1) sulphide with bromine at -78°C forms trimethylsilylsul- phenyl bromide which reacts with 1,2-disubstituted alkenes to give the correspond- ing thiiranes in moderate yield. The regioselectivity and stereoselectivity of the aziridinating agent N-acetoxyaminoquinazolone(10) has been examined.42 Aziridi- 36 E.N. Jacobsen I. Marko W. S. Mungall G. Schroder and K. B. Sharpless J. Am. Chem. SOC.,1988 110 1968. 37 G. Xie L. Xu J. Hu S. Ma W. Hou and F. Tao Tetrahedron Lett. 1988 29 2967. 38 C. Venture110 and R. D’Aloisio J. Org. Chem. 1988 53 1553. 39 Y. Okamoto and W. C. Still Tetrahedron Lett. 1988 29 971. 40 T. H. Chan L. M. Chen and D. Wang J. Chem. SOC.,Chem. Commun. 1988 1280. 41 F. Capozzi G. Capozzi and S. Menchetti Tetrahedron Lett. 1988 29 4177. 42 R. S. Atkinson and B. J. Kelly J. Chem. SOC.,Chem. Commun. 1988. 624. Aliphatic Compounds -Part (i) Hydrocarbons nation of cyclohex-2-en- 1-01 gives predominantly (95 :5) the syn-stereoisomer and aziridination of geraniol is highly selective (11 :1) for the allylic alcohol double bond.The selectivities observed are higher than those seen in corresponding reactions with peracids. This is attributed to stronger hydrogen bonding between (10) and the hydroxy group in the aziridination transition state than occurs between the peracid and the hydroxy group in the epoxidation transition state. Caesium fluoroxysulphate adds to alkenes under mild conditions to give previously unknown vicinal fluoroalkyl ~ulphates.~~ Chlorotrimethylsilane/sodium iodide in the presence of water may be used to convert alkenes into alkyl iodides under mild conditions.44 The procedure has also been used to synthesize deuterated alkyl iodides by replacing the water with D20. Benzenetellurinyl trifluoroacetate reacts with alkenes in acetonitrile in the presence of BF3 -OEt to give 2-oxazolines in good yield via amidotellurinylation of the alkene~.~~ The overall transformation of alkenes into oxazolines proceeds with Markovnikov regioselectivity and cis-stereoselectivity.Samarium diiodide has been shown to be an effective initiator for the addition of fluoroalkyl iodides to alkene~.~~ Convenient procedures for overall anti-Markovnikov hydr~iodination:~ hydro- bromination:* and hydro~hlorination~~ of alkenes have been reported. Hydrobor- ation of alkenes followed by treatment of the resulting boranes with either iodine/sodium methoxide or bramine/sodium methoxide or nitrogen trichloride gives anti-Markovnikov alkyl iodides bromides or chlorides in good yield. It has been demonstrated that rhodium( I)-catalysed and non-catalysed hydroborations may have complementary stereochemical consequence^.^^ For example hydrobor- ation of acyclic 1,l-disubstituted allylic alcohols using 9-BBN occurs with high anti-selectivity whilst Rh(PPh,),Cl-catalysed hydroboration with catecholborane takes place with high syn-selectivity (Scheme 7).Enantioselective hydroboration is mediated by homochiral rhodium( 1)-phosphine c~mplexes.~~ Whilst the reported enantiomeric excesses are moderate this new approach to asymmetric hydroboration appears to be of considerable promise. 43 N.S. Zefirov V. V. Zhdankin A. S. Koz’min A. A. Fainzilberg A. A. Gakh B. I. Ugrak and S. V. Romaniko Tetrahedron 1988 44 6505. 44 S. Irifune T. Kibayashi Y. Ishii and M. Ogawa Synthesis 1988 366.45 N. X. Hu Y. Aso T. Otsubo and F. Ogura Tetrahedron Lett. 1988 29 1049. 46 X. Lu S. Ma and J. Zhu Tetrahedron Lett. 1988 29 5129. 47 H. C. Brown M. W. Rathke M. M. Rogic and N. R. de Lue Tetrahedron 1988 44 2751. 48 H. C. Brown and C. F. Lane Tetrahedron 1988,44 2763. 49 H. C. Brown and N. R. de Lue Tetrahedron 1988,44 2785. D. A. Evans G. C. Fu and A. H. Hoveyda J. Am. Chem. SOC.,1988 110,6917. K. Burgess and M. J. Ohlmeyer J. Org. Chem. 1988 53 5178. S. E. Thomas . ... I 111 1' BunL O H 80-94% Bu nq Me J ii iii + Bunq0H 77-96% Me R = H SiBu'Me, SiBu'Ph Reagents i 9-BBN THF 25 "C;ii catecholborane cat. Rh(PPh,),Cl 25 "C; iii NaOOH Scheme 7 A chloride-free Wacker-type oxidation of terminal alkenes to methyl ketones has been de~eloped.~~ This oxidation proceeds via multi-component catalysis (Scheme 8) but the absence of cupric chloride from the oxidation relay prevents the formation of the chlorinated side products often observed in the Wacker process itself.0 II Fe(Pc) x H20 OH Fe(Pc) 402 0 Fe( Pc) = iron phthalocyanine Scheme 8 3 Polyenes Synthesis.-Thermolysis of 3,4-disubstituted 3-sulpholenes (prepared from 3-substituted 4-bromo-2-sulpholenes by nucleophilic substitution followed by isomerization) has been used to synthesize 2,3-disubstituted buta-l,3-dienes bearing chloro bromo azido trimethylsilyl phenylthio phenylsulphinyl or phenylsul- phony1 Similarly 3-cyano-3-sulpholene a stable crystalline compound has been synthesized and shown to be a good source of the unstable diene 2- cyanobuta- 1 ,3-diene.54 52 J.-E.Backvall and R. B. Hopkins Tetrahedron Lett. 1988 29 2885. 53 T.-S. Chou S.-J. Lee M.-L. Peng D.-J. Sun and S.4. P. Chou J. Org. Chem. 1988 53 3027. 54 P. G. Baraldi A. Barco S. Benetti S. Manfrdini G. P. Pollini D. Simoni and V. Zanirato Tetrahedron 1988.44 6451. Aliphatic Compounds -Part (i) Hydrocarbons Treatment of several a-allenic alcohols with methyllithium and copper iodide followed by N,N-methylphenylaminotributylphosphoniumiodide and a second organolithium reagent (Murahashi conditions) leads to 2-substituted 1,3-dienes in which the substituent is derived from the second organolithium reagent.55 2-(Phenylsulphonyl)-l,3-dienesare versatile synthons which have previously been prepared from 1,3-dienes by a 1,2-sulphonylmercuration-eliminationsequence.To avoid the use of mercury derivatives a new one-pot procedure for the transformation of 1,3-dienes into 2-(phenylsulphony1)- 1,3-dienes has now been de~eloped.~~ The reaction involves 1,2-selenosulphonation by PhS0,SePh in the presence of BF3 followed by MCPBA oxidation and gives good to excellent yields. Several palladium-mediated syntheses of 1,3-dienes have been published in 1988. It had been reported earlier that treatment of allylic acetates with triphenylphosphine and a catalytic amount of palladium acetate led to E,Z-mixtures of 1,3-dienes. Although various allylic acetates had been examined none of the substrates had a substitution pattern that would lead to 1,3-disubstituted 1,3-dienes.Examination of such substrates (11) revealed that they gave rise to stereochemically pure (E)-l,3- dialkyl- 1,3-diene~.~~ Thus the 2-alkyl substituent on the vinyl moiety appears to control the stereochemical outcome of the reaction; the nature of this control is as yet unclear. Cleavage of the .rr-allyl-palladium complex (12) to give 2,3-bis( bromomethy1)buta- 1,3-diene is more efficient with bromine than with copper( 11) bromide the reagent previously employed for this transformation. Palladium( 11) bromide used in the synthesis of (12) from allene is recovered in almost quantitative yield from the reaction.58 Allenes combine with silylated vinyl bromides in the presence of palladium(o) catalysts to give 7r-allyl-palladium complexes which can be trapped by nucleophiles to generate functionalized silylated dienes (Scheme 9).59 R2 I Br 50-75% R' = H n-heptyl R2 = H SiMe, CH,SiMe R3= H,SiMe Nu = CH(CO,Me) ,CH(C02Me)(COMe) Reagents i NaNu cat.Pdo THF or DMSO 65 "C 24 h Scheme 9 55 C. Fan and B. Cazes Tetrahedron Lett. 1988 29 1701. 56 J.-E. Backvall C. Najera and M. Yus,Tetrahedron Lett. 1988 29 1445. 57 F. M. Hauser R. Tommasi P.Hewawawam and Y.S. Rho J. Org. Chem. 1988 53 4886. 58 S. M. Ali S. Tnimoto and T. Okamoto J. Org. Chem. 1988 53 3639. 59 B. Cazes V. Colovray and J. Gore Tetrahedron Lett. 1988 29 627. S. E. Thomas Palladium-catalysed cross-coupling of (E)-1-alkenylalanes with (E)-2-bromo-vinyltrimethylsilane (performed in the presence of the 2-isomer) gives (1E,3E)-1-trimethylsilyl-1,3-dienes of high stereoisomeric purity (>99% ) (Scheme R = n-C,H, ,Bu' Reagents i cat.Pd(PPh,), THF 40 "C 16 h Scheme 10 Mono-and disubstituted penta-1,4-dienes have been synthesized from substituted (2-[ (trimethylsilyl)methyl]cyclopropyl}carbinols (13) by either treatment of the car-binol with acid or its conversion into the corresponding mesylate.61 The high trans-stereoselectivity for the alkene derived from the carbinol terminus has been exploited in a synthesis of a constituent of the pheromone emitted by the melon fly Dacus curcurbitae Coquillett. Me3Si OMe R&- - SiMe3 R R 0 R R = H,al kyl R = H,alkyl H alkyl aryl (13) (14) (15) 2-(Allyloxy)benzothiazoles react with allylic Grignard reagents in the presence of copper(1) bromide to give 1,5-dienes formed by head-to-tail coupling.If however the copper(I) bromide is complexed with the 2-(allyloxy)benzothiazoles prior to Grignard reagent addition then head-to-head coupled 1,Sdienes are generated.62 Allenic ketones give Diels-Alder adducts (14) with furan; modification of the adducts followed by regeneration of the allene moiety by thermofragmentation leads to a wide range of a-functionalized allene~.~~ Pyrolysis of propargylic derivatives (15) results in the extrusion of formaldehyde and the production of trimethylsilylal-lenes in excellent yield.64Several optically active allenes have been prepared includ-ing the enantiomers of (16) synthesized from (+)-and (-)-~amphene,~~ and (17) formed in modest optical purity (e.e.18%) by elimination of the silicon and trifluoroacetate groups from the optically active vinylsilane (18) using tris(dimethyl-amino)sulphur trimethylsilicon difluoride.66 60 B. P. Andreini A. Carpita and R. Rossi Tetrahedron Lett. 1988 29 2239. 61 S. R. Wilson and P. A. Zucker J. Org. Chern. 1988 53 4682. 62 V. Calo L. Lopez and G. Pesce J. Chem. SOC.,Perkin Trans. I 1988 1301. 63 J. L. Gras B. S. Galledou and M. Bertrand Bull. SOC.Chim. Fr. 1988 757. 64 H. Hopf and E. Naujoks Tetrahedron Lett. 1988 29 609. 65 J. MaHay M. Conrads and J. Runsink Synthesis 1988 595. 66 E.Torres G. L. Larson and G. J. McGarvey Tetrahedron Left. 1988 29 1355. Aliphatic Compounds -Part (i) Hydrocarbons 95 h It has been reported that conjugated trienes may be synthesized readily and stereoselectively by coupling 2-trialkylstannyl-3-sulpholenes(19) with vinyl iodides under palladium(0) catalysis followed by de~ulphonylation.~~ Conjugated trienes have also been prepared by a palladium-catalysed reaction between alkenes and either fumaryl chloride or (E)-5-phenylpenta-2,4-dienoyl chloride.68 Interestingly the tosylate of tropone oxime (20)undergoes a ring-opening reaction with secondary amines alkoxides and Grignard reagents to give 6-substituted (1Z,3Z,5Z) -hexa-1,3,5-trienecarbonitriles(21)in high yield.69 The Z,Z,Z-isomers are thermodynami- cally unstable and can be readily converted into more stable isomers.,OTs N II R = H,Me Tetrakis(trimethylsily1)butatriene (22) has been prepared in 41'/o yield from hexakis(trimethylsilyl)but-2-yneby flash vacuum pyrolysis at 650 0C.70 Several approaches to conjugated polyene chains have been investigated. Catalysts of the type M(CHBu')(NAr)(OBu')2 (M = Mo or W) have been shown to catalyse ring-opening metathesis polymerization of (23)in a controlled manner to give (24).7' SiMe3 .+-,- (ArN)(BU'O)~MKBul Me3Si SiMe3 F3C (22) (23) x = 3-7 (24) Treatment of (24)with pivalaldehyde gives a metal-free oligomer which on heating yields a mixture of polyenes containing 7-1 5 double bonds. These can be separated by chromatography at -40°C under a nitrogen atmosphere.Similarly ring-opening H. Takayama and T. Suzuki J. Chem. SOC., 67 Chem. Commun. 1988 1044. 68 A. Kasahara T. Izumi and N. Kudou Synthesis 1988 704. 69 T. Machiguchi T. Hasegawa M. Ohno Y. Kitahara M. Funamizu and T. Nozoe J. Chem. Soc. Chem. Commun. 1988 838. 70 H. Sakurai M. Kudo K. Sakarnoto Y. Nakadaira M. Kira and A. Sekiguchi Chem. Lett. 1988 1441. 71 K. Knoll S. A. Krouse and R. R. Schrock J. Am. Chem. SOC.,1988 110 4424. S. E. Thomas metathesis polymerization of benzvalene (25) with W(CHBu')( NAr)( OBU')~ gives polybenzvalene (26),72 which can be isomerized to conjugated polyene chains under transition metal catalysis. Addition of tungsten metathesis catalysts to 'neat' cyclo- octa-1,3,5,7-tetraene has been shown to lead to high-quality p~lyacetylene.'~ Reactions.-Treatment of buta-l,3-diene with I(py),BF in the presence of benzene or acetonitrile leads exclusively to 1,4-adducts (Scheme ll).74 It is of note that Reagents i CH,CI, C6H6 5 "C 4 h; ii CH2C12 MeCN H,O -5 "C 15 min Scheme 11 earlier reports show that treatment of buta-1,3-diene with I(py),BF in the presence of stronger nucleophiles gives 1,2-adducts.A mild method for stereo- and regioselec- tive 1,4-dialkoxylation of conjugated dienes has been de~eloped.~' The reaction is catalysed by palladium( II) uses p-benzoquinone as the oxidant and requires catalytic amounts of a strong acid. It has been demonstrated that the simple trifluorodiene (27) prepared from commercially available 4-bromo- 1,1,2- trifluorobut-1-ene can be regarded as a C4 synthon in which the fluorine at C2 is retained during the course of various electrophilic and nucleophilic transforma- tion~.~~ Ozonolysis of the sterically hindered buta-1,3-diene (28) has been studied in solution and on solid support^:'^ a range of products including (29)-(33) were obtained.1,4-Dienes cyclize to 2-methylcyclopentanones under an atmosphere of carbon monoxide and hydrogen in the presence of transition metal catalysts. The effects of altering the catalyst and varying the reaction conditions on the regio-and stereochemical outcome of this reaction have been in~estigated.'~ Electrophilic 72 T. M. Swager D. A. Dougherty and R. H. Grubbs J. Am. Chem.Soc. 1988 110 2973. 73 F. L. Klavetter and R. H. Grubbs J. Am. Chem. Soc. 1988 110 7807. 74 J. Barluenga J. M. Gonzalez P. J. Campos and G. Asensio Tetrahedron Lett. 1988 29 6497. 75 J.-E. Backvall and J. 0.Vagberg J. Org. Chem. 1988 53 5695. 76 N. Matsuo and A. S. Kende J. Org. Chem. 1988 53 2304. 77 K. Griesbaum and W. Volpp Chem. Ber. 1988 121 1795. 78 P. Eilbracht M. Acker and I. Hadrich Chem. Ber. 1988 121 579. Aliphatic Compounds -Part (i) Hydrocarbons cyclization of substituted 1,5-dienes has been re~iewed.'~ Reactions are subdivided into those catalysed by Lewis acids and those promoted by either bromonium mercurinium or phenylselenonium ions. Carboxylic acids react readily with cis-1,2-divinylcyclohexane under palladium catalysis and in the presence of oxidizing agents to give exo-cis-hydrindanes (Scheme 12).It has now been reported that the use of chiral acids in this reaction leads to modest asymmetric induction.*' H 70% Reagents i MnO, benzoquinone cat. Pd(OAc)* AcOH r.t. 42 h Scheme 12 Allene oxidation has been the subject of several reports. Addition of dimethyl-dioxirane to simple allenes gives 1,4-dioxaspiro[2.2]pentanes (34) in good yield and intermolecular nucleophilic attack proceeds regioselectively to generate a-hydroxy ketones (35).g' Similarly dimethyldioxirane oxidation of allenic alcohols (36) yields (34) (35) n = 1,2 (36) tetrahydrofuran and tetrahydropyran derivatives (37) via intramolecular nucleophilic addition to the intermediate allene diepoxide.82 Oxidation of vinyl allenes (38) with Bu'OOH and VO(acac) gives cyclopentenones (39) in 40-70% 79 N.Grionlonfoun Bull. SOC.Chim. Fr. 1988 862. 80 A. Heumann and C. Moberg J. Chem. Soc. Chem. Commun. 1988 1516. 8' J. K. Crandall and D. J. Batal J. Org. Chem. 1988 53 1338. 82 J. K. Crandall and D. J. Batal Tetrahedron Left. 1988 29 4791. S. E. Thomas n = 1,2 n = 1,2 (37) (38) (39) yield.83 This stereoselective annulation is rationalized by invoking initial hydroxy- directed allene oxide formation subsequent isomerization of the allene oxide to an oxapentadienyl cation or a vinyl cyclopropanone and finally antarafacial pericyclic ring closure. It has been reported that addition of triphenylstannane or triphenylgermane to allenes in the presence of catalytic amounts of Pd(PPh3)4 gives allylic stannanes or allylic germanes in good yield.84 Silyl-cupration of allene using (PhMe,Si),CuLi followed by treatment with iodine anomalously yields the vinyl iodide (40).85 Lithiation of (40) generates a silylated C,-nucleophile which reacts cleanly with a range of electrophiles.The utility of dimethyl allene-l,3-dicarboxylatein heterocyclic synthesis has been further demonstrated.86 It has been converted into pyridones condensed pyridones thiazopyrones thiazinones thiochromanones and thienopyridones by reaction with appropriate nucleophiles. The reactions of 1,1,4,4-tetraarylbuta-l,2,3-trieneswith elemental sulphur and selenium have been e~amined.~' Sulphurization yields novel 1,2,3,4,5-pentathiepanes (41) and selenation generates 1,2,5-triselenepanes (42).R = Ar R = Ar (41) (42) 4 Alkynes Synthesis.-A method for synthesizing the optically active acetylenic alcohol (43) has been reported;88 lithium amide-induced elimination from (44) readily prepared from L-(+)-tartaric acid gave (43) in 90% yield. 1-Alkoxyalk-1-ynes and l-alkoxyalk- 1 -yn-3-ols have been prepared from chloroacetaldehyde dialkyl a~etals.~~ The reac- tion is initiated by sodium amide and the acetylide anion produced reacts readily 83 S. J. Kim and J. K. Cha Tetrahedron Lett. 1988 29 5613. 84 Y. Ichinose K. Oshima and K. Utimoto Bull. Chem. Soc. Jpn. 1988 61 2693. 85 P. Cuadrado A. M. Gonzalez F. J. Pulido and I. Fleming Tetrahedron Lett.1988 29 1825. 86 G. J. S. Doad D. 1. Okor F. Scheinmann P. A. Bates and M. B. Hursthouse J. Chem. Soc. Perkin Trans. 1 1988 2993. 87 N. Tokitoh H. Hayakawa M. Goto and W. Ando Tetrahedron Lett. 1988 29 1935. 88 J. S. Yadav M. C. Chander and B. V. Joshi Tetrahedron Lett. 1988 29 2737. 89 W. M. Stalick R. N. Hazlett and R. E. Morris Synthesis 1988 287. Aliphatic Compounds -Part (i) Hydrocarbons with a range of alkyl halides and carbonyl compounds to give the alkyne derivatives in good yield. Dehydrobromination of (2)-2-bromovinyl silyl ethers using LDA gives trialkylsil~xyalkynes.~~ This approach provides access to the parent trialkylsily- loxyethynes for the first time. A number of acetylenic ketones have been prepared by reacting lithium acetylides with acetic anhydride N,N-dimethylacetamide or N,N-dimethylben~amide.~' Addition of alkynylzinc chlorides to acyl halides is also a practical approach to acetylenic ketones.It has been demonstrated that formyltrimethylsilane generated from (trimethylsily1)methanol by Swern oxidation reacts with lithium acetylides to give alcohols which can be oxidized readily to acetylenic acylsilanes (45).92 The first synthesis of acetylenic carboxylates has been reported.93 Reaction of PhI(OCOR)* with lithium acetylides or anion exchange of alkynylphenyliodonium tosylates gives alkynylphenyliodonium carboxylates (46) which decompose to acetylenic carboxylates and iodobenzene. 1-1odoalk-1-ynes have been synthesized by treating terminal alkynes with a sol- ution of iodine in DMF in the presence of sodium or potassium carbonate Bu",NCl and a catalytic amount of copper(1) iodide.94 A simple one-pot procedure for the preparation of primary 2-alkynamides (47) from 1-alkynyltrimethylsilanesand chlorosulphonyl isocyanate has been reported." Acetylenedicarbaldehyde has pre- viously only been isolated in the presence of formic acid.A procedure has now been reported for its isolation in pure form which involves acidolysis of the monoacetal (48) with an excess of formic acid followed by dehydration of residual formic acid with PzOs.96 0 + 0 0 Y-i OEt R-G-f R-CGCIPh R-+f SiMe3 -0COR NH2 H OEt (45) (46) (47) (48) Several approaches to enynes have been investigated. Palladium-catalysed dimerization of ethynyl-substituted mono-and disilanes produces head-to-head coupled enynes (49),97 regioselective halide substitution reactions of butatrienes (50) yield halogenoenynes (51),98 and methylation of 2-enynyl bromides (52) with MeMgI and Fe(acac) catalyst gives 2-alkyl-1-en-3-ynes (53)with net inversion of the double bond ge~metry.~' 90 R.L. Danheiser A. Nishida S. Savariar and M. P. Trova Tetrahedron Lett. 1988 29 4917. 91 H. D. Verkruijsse Y. A. Heus-Kloos and L. Brandsma J. Organomet. Chem. 1988 338 289. 92 R. J. Linderman and Y. Suhr J. Org. Chem. 1988,53 1569. 93 P. J. Stang M. Boehshar H. Wingert and T. Kitamura J. Am. Chem. SOC.,1988 110 3272. 94 T. Jeffery J. Chem. SOC.,Chem. Commun. 1988,909. 95 P. C. Bulman Page S. Rosenthal and R.V. Williams Synthesis 1988 621. 96 D. Stephan A. Gorgues A. Belyasmine and A. Le Coq J. Chem. SOC.,Chem. Commun. 1988 263. 97 M. Ishikawa J. Ohshita Y. Ito and A. Minato J. Orgnomet. Chem. 1988 346 C58. 98 C. B. Ziegler Tetrahedron Left. 1988 29 411. 99 J. A. Miller W. Leong and G. Zweifel 1. Org. Chem. 1988 53 1839. 100 S. E. Thomas R = Me,SiSi(Ph)Me, Me2PhSi MePh,Si (50) R' X = Cl,Br,I (49) (51) An enantioselective total synthesis of the enyne (54) a possible biogenetic precur- sor of a wide variety of halogenated cyclic ethers isolated from marine sources has been reported."' Asymmetry is introduced into the synthesis by the use of a Sharpless epoxidation step. A mild synthesis of 1,3-diynes from terminal alkynes which is compatible with a wide range of functional groups has been developed."' The first step of the synthesis involves a palladium(0)-catalysed coupling of terminal alkynes with cis- 1,2- dichloroethene to yield cis-chloroenynes (55); subsequent treatment of (55) with Bu,"NF provides a range of 1,3-diynes in good overall yield.Terminal arylbutadiynes (56) derived in situ from 6-arylhexa-3,5-diyn-2-01~ and base can be coupled with aryl halides under palladium catalysis to give unsymmetrical diarylbutadiynes (57).'02 R-=-? AT'-=-=-Arl -=-= -A r2 -c1 (55) (56) (57) Syntheses and properties of the medium sized carbocyclic dialkynes (58) and (59)103~104and analogues containing heteroatoms (60) and (61)'05 have been reported. Reactions.-Formation of HCN by photochemical dissociation of ammonia in the presence of ethyne has been observed.lo6 The possible role of this reaction and related photochemical processes in the formation of HCN on Jupiter is discussed.100 J. M. Palazon and V. S. Martin Tetrahedron Lett. 1988 29 681. 101 A. S. Kende and C. A. Smith J. Org. Chem. 1988 53 2655. 102 S. Adams Nye and K. T. Potts Synthesis 1988 375. 103 R. Gleiter D. Kratz and V. Schehlmann Tetrahedron Lett. 1988 29 2813. 104 R. Gleiter M. Karcher R. Jahn and H. Irngartinger Chem. Ber. 1988 121 735. 105 R. Gleiter and S. Rittinger Tetrahedron Lett. 1988 29 4529. 106 J. P. Ferris and Y. Ishikawa J. Am. Chem. Soc. 1988 110 4306. Aliphatic Compounds -Part (i) Hydrocarbons Iodine adds stereospecifically anti to alkynes on alumina to give E-dii~doalkenes."~ The reaction which is not observed in the absence of alumina is thought to occur by an ionic mechanism in contrast to the iodination of alkynes in solution where the addition is believed to occur by a free radical mechanism.The stereochemical outcome of acetoxymercuration of diphenylacetylene has been rein- vestigated and on the basis of I3C and 199Hg n.m.r. and X-ray data the product of the reaction being assigned as the trans-adduct (62).'08 This result contrasts with earlier reports on the reaction but is in agreement with the stereochemical outcome of acetoxymercuration reactions of alkylphenylalkynes and dialkylalkynes. It has been reported that P-keto sulphides (63) may be conveniently prepared by a BF3-promoted reaction of ArNHSPh with alkynes in either acetonitrile or acetic acid followed by hydrolysis of the resulting P-acetamidino- or P-acetoxy-vinyl phenyl sulphide~.'~~ Several metal-catalysed additions to alkynes have been reported.Addition of methanol to terminal alkynes under mercury( 11) chloride catalysis gives 2-methoxyalk-l-enes."o The reaction is performed in the presence of triethylamine to prevent acid-catalysed addition of methanol to the product. A full report of pal- ladium- and nickel-catalysed additions of trimethylsilyl cyanide to alkynes has been published,"' and it has been demonstrated that propyne may be added regioselec- tively to N-protected amino acids in the presence of catalytic amounts of arene- ruthenium-phosphine complexes to give isopropenyl esters in good yield."2 Photolysis of diphenyl or dimesityl diselenide with either dimethyl acetylenedicar- boxylate or methyl propiolate gave the first examples of free radical addition of diselenides to alkyne~."~ The products of the reaction between Bu"Li and di- phenylacetylene have been examined by 2D n.m.r.spectroscopy (COSY C-H shift correlation COLOC)."4 In THF the trans product (64) is obtained exclusively whilst in hexane/TMEDA (64) is accompanied by the dilithio product (65). 107 I08 109 110 111 112 113 114 S. Larson T. Lindhardt G. W. Kabalka and R. M. Pagni Tetrahedron Lett. 1988 29 35. Y. K. Grishin D. V. Bazhenov Y. A. Ustynyuk and N. S. Zefirov Tetrahedron Lett.1988 29 4631. L. Benati P. C. Montevecchi and P. Spagnolo Tetrahedron Lett. 1988 29 2381. J. Barluenga F. Aznar and M. Bayod Synthesis 1988 144. N. Chatani T. Takeyasu N. Horiuchi and T. Hanafusa J. Org. Chem. 1988 53 3539. C. Ruppin P. H. Dixneuf and S. Lecolier Tetrahedron Lett. 1988 29 5365. T. G. Back and M. V. Krishna J. Org. Chem. 1988 53 2533. W.Bauer M. Feigel G. Muller and P. von R. Schleyer J. Am. Chem. Soc. 1988 110 6033. 102 S. E. Thomas A number of reports on the oxidation of alkynes to 1,2-dicarbonyl compounds have been published. Ru04 generated by the action of NaI04 on Ru02 mediates the oxidation of disubstituted alkynes to 1,2-diketones in moderate to excellent yield. The compatibility of various functional groups with this oxidizing agent has been inve~tigated."~ Terminal alkynes may be oxidized to ketoaldehydes by the use of dilute hydrogen peroxide Na2M04 salts (M = MeV' or W"') and H~(OAC)~."~ The oxo( salen)chromium(v) complex (66) a proposed intermediate in catalytic oxygen transfer reactions has been shown to react with diphenylacetylene to give benzil."' A method for a-oxidation of alkynes to conjugated ynones using Bu'OOH in the presence of catalytic amounts of Cr03 and TsOH has been reported."' The reactions of alkynes with metal-carbene complexes continue to attract atten- tion.Cyclopentenones are obtained from the reaction between alkynes and a cyclo- propyl-methoxy chromium carbene complex (Scheme 13),* l9 and cyclopentafurans R = H alkyl aryl C0,Et 42-19% Reagents i dioxane 100 "C 4-6 h Scheme 13 are produced when alkynes are added to furan-methoxy chromium carbene com- plexes (Scheme 14).120 72% Reagents i DMF 120"C 5 h Scheme 14 115 R.Zibuck and D. Seebach Helv. Chim. Acta 1988 71 237. 116 F. P. Ballistreri S. Failla and G. A. Tomaselli J. Org. Chem. 1988 53 830. 117 B. Rihter and J. Masnovi J. Chem. SOC.,Chem. Commun. 1988 35. 118 J. Muzart and 0. Piva Tetrahedron Lett. 1988 29 2321. I19 J. W. Herndon S. U. Turner and W. F. K. Schnatter J. Am. Chem. SOC.,1988 110 3334. A. Yamashita A. Toy W. Watt and C. R. Muchmore Tetrahedron Lett. 1988 29 3403. Aliphatic Compounds -Part (i) Hydrocarbons It has been demonstrated that (Ph3P)3RhCl catalyses [2 + 2 + 21 cycloadditions between 1,6-diynes and alkynes to give polysubstituted benzene derivatives.'21 Intramolecular [2 + 2 + 21 cycloadditions are also catalysed by (Ph3P)&C1 and this reactivity has been exploited in a synthesis of calomelanolactone (Scheme 15).'22 0 Calomelanolactone Reagents i cat.(Ph,P),RhCl EtOH 25 "C 12 h Scheme 15 Chemo- and regioselective hydroboration of 2-methoxyenynes (67) with disiamyl- borane followed by oxidation of the intermediate organoborane with aqueous sodium acetate/ hydrogen peroxide produces synthetically useful methoxyenones (68) in good yield.'23 It has been shown that 1,6-enynes may be cyclized regiospecifically to methylene cyclohex-2-enes under (Ph3P)3RhCl ~atalysis.'~~ Terminal substitution on either the alkene or alkyne inhibits this reaction.Enynes and isonitriles cyciize in the presence of Ni(cod) and Bu;P to form 1-iminocyclopent-2-enes (69) which may be hydrolysed to the corresponding cyclopentenone~.'~~ 1,6- and 1,7-enynes have been used as substrates for the cyclization. 121 R. Grigg R. Scott and P. Stevenson J. Chem. Soc. Perkin Trans. 1 1988 1357. I22 S. J. Neeson and P. J. Stevenson Tetrahedron Lett. 1988 29 813. 123 G. Zweifel M. R. Najafi and S. Rajagopalan Tetrahedron Lett. 1988 29 1895. 124 R. Grigg P. Stevenson and T. Worakun Tetrahedron 1988 44 4967. I25 K. Tamao K. Kobayashi and Y. Ito J. Am. Chem. Soc. 1988 110 1286.