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