9 Aliphatic Compounds Part (i) Hydrocarbons By D. R. TAYLOR Department of Chemistry University of Manchester Institute of Science and Technology Manchester M60 1QD 1 Acetylenes The catalytic cyclotrimerization of acetylenes has been reviewed with special reference to the co-oligomerization of a,w-diynes with silylacetylenes to produce fused ring systems.’ A new general method for the synthesis of 1,3-enynes which is stereo- and regio-selective involves the reaction of an alkynylzinc chloride with a vinyl halide in the presence of a palladium(0) complex (Scheme l).’ Alkynyl-lithium reagents R’ H R’ H \/A ‘c=c / c=c R2/ \x R2/\CrCR3 Reagents i R3C-CZnCI (R3=H or Bu”) Pd(PPh3)4-THF Scheme 1 are unsuitable for the reaction but are easily converted into the alkynylzinc chlorides which are stable to disproportionation and do not attack functional groups such as esters.Since enynes are themselves readily converted into dienyl- mercurials recently shown to dimerize smoothly in contact with rhodium salts,3 a new route to conjugated tetraenes has been opened up (Scheme 2). Reagents i (cyclo-C6H1 1)2BH; ii Hg(0Ach; iii aq. NaCl; iv [ClRh(COh]2-LiC1-(Me2N)3P0 Scheme 2 K. P. C. Vollhardt Accounts Chem. Res. 1977 10 1. * A. 0.King N. 0.Okukado and E.-i. Negishi J.C.S. Chem. Comm. 1977,683. R. C. Larock and J. C. Bernhardt J. Org. Chem. 1977.42 1680. 175 176 D. R. Taylor Enynes bearing remote functionality [e.g. (l),required for the synthesis of a sex pheromone of the grape-vine moth] can be obtained by an elegant combination of methods discovered by C.A. and H. C. Brown (Scheme 3).4 It features the use of the acetylene 'zipper' [KNH(CH2XNH2] which has also been used to effect the migration of the CEC bond in alkynylborate~.~ iii,iv 1 CzCEt -/ EtCEC H R2B H \/ v vi \/ c=c c=c /\ /\ H (CH2 )6 OAc H (CH2)60Ac (1 1 Reagents i KNH(CH2),NH2; ii Ac20; iii (Pr'MeCHkBH; iv EtCrCLi; v 12; vi H202-NaOAc Scheme 3 The stereospecific syn-addition of organometallic compounds (e-g. RCu) to the CEC bond continues to provide fascinating examples of synthetic value. However treatment of a terminal acetylene (but not C2H2) with lithium dialkylcuprates in THF leads to quantitative metal-hydrogen exchange.This undesirable reaction can be avoided (i) by using diethyl ether as solvent or better (ii) by adding lithium bromide to the reaction mixture in THF when deprotonation is completely suppressed (Scheme 4).6 Organocopper-magnesium halide complexes may also be Reagents 1 R2R3CuLi-Et20 (X =Li) or R2R3CuLi-LiBr-THF (X=Li,LiBr); ii Df(E =D) or BrCN-THF (E =Br) or N-chlorosuccinimide-(Me2N)3P0 (E =CI); (R' =alkyl or aryl R2 R3 =alkyl) Scheme 4 used to prepare vinylcuprates (2; R3=Br or R2 X =MgHal) a reaction which may usefully be followed by copper-halogen exchange using N-halogenosuc~inimide~ or cyanogen bromide or iodide,8 or by copper-nitrile exchange using cyanogen chloride or an arenesulphonyl cyanide.8 If a silylacetylene is used in this type of reaction sequence organocopper addition proceeds with the opposite regioselec- tivity so providing a route to 1-substituted 1 -silylalkenes (Scheme 5).9710 E.4 Negishi and A.Abramovitch Tetrahedron Letters 1977,411. C. A. Brown and E.4. Negishi J.C.S. Chem. Comm. 1977,318. H. Westmijze H. Kleijn and P. Vermeer Tetrahedron LetZers 1977 2023. 'A. B. Levy,P. Talley and J. A. Dunford Tetrahedron ktters 1977 3545. * H. Westmijze and P. Vermeer Synthesis 1977 784. M. Obayashi K. Utimoto and H. Nozaki Tetrahedron Letters 1977 1805. lo H. Westmijze J. Meijer and P. Vermeer Tetrahedron Letters 1977 1823. Aliphatic Compounds-Part (i) Hydrocarbons R13Si H MgY % c=c E'\/ 'R2 Reagents i R2CuMgBr2 (R' = Me R2 = Pr" n-C5HI1 or n-C6H13 X = Y = Br) or R22CuMgY (R' = Ph Y =CI or Br X = R2 = Et Pr' cyclo-C6H1 1.or Bu'); ii H20 (DzO) (E = H or D) or N-halogenosuccinimide (E =halogen) or iodoalkane (E = Me Pr" n-C5HIl or n-C6H13 erc.) Scheme 5 Vinylcoppers may also be obtained from alkyne-hydrozirconation products by transmetallation;" the overall process is both regio- and stereo-specific. Copper(1) arylacetylides react with arylcoppers to yield mixed diarylacetylenes (Ar'CGCAr2) via the formation of well-defined and isolable organo-cluster species Ar',Cu,(C_CAr2),. The highly selective formation of mixed acetylenes was shown to result from the detailed structure of the organo-cluster compounds in which triangular copper faces are occupied exclusively by one Ar' and. two Ar2C?C ligands.12 The synthesis of acetylenes and allenes uia polymetallation usually Iithiation of alkynes continues to receive attention.l3-I5 Perlithiopropyne the structure of which has been determined by ab initio cal~ulation,'~ reacts with iodoethane to afford a low yield of an ene-diyne (3) whereas with trimethyl-silyl or -germyl chloride or with diethyl sulphate it yields allenic and/or acetylenic derivatives by straightforward substitution (Scheme 6).13 But- 1-yne and but-2-yne are converted CH3ECH I* C3Li4% (Me3X)2C=C=C(XMe3)2 Et,CC=CEt +Et2C=C=CEt2 EtCrCCEt=CEtC=CEt (3) Reagents i Bu"Li-hexane; ii Me3XCI (X = Si or Ge); iii EtZSO,; iv EtI Scheme 6 by excess alkyl-lithium into the same trilithiated material but the 2-yne reacts much more slowly.A trilithiated product is also obtained by lithiation of hexa-2,4- diyne; it is a source of some exotic alkylated silylated or germylated allenynes including the hexasilylbisallene (4). l3 (Me3SihC=C=C(SiMe3)C(SiMe3)=C=C(SiMe3)2 (4) Several publications have appeared reporting investigations into the bromination of acetylenes. Solvent effects on the ratet6 and kinetic product distribution" are M. Yoshifuji M. J. Loots and J. Schwartz Tetrahedron Letters 1977 1303. G. van Koten R. W. M. ten Hoedt and J. G. Noltes J. Org. Chem. 1977,42,2705. l3 W. Priester R. West and T. L. Chwang J. Amer. Chem. SOC.,1976 98 8413; W. Priester and R. West ibid. pp. 8421 8426. I4 E. D. Jemmis D. Poppinger P. von R. Schleyer and J. A. Pople J. Amer. Chem. Soc. 1977,99,5796.Is N. M. Libman P. A. Brestkin and S. G. Kuznetsov J. Org. Chem. U.S.S.R., 1976,12 2480. I6 M.-F. Ruasse and J.-E. Dubois J. Org. Chem. 1977 42 2689. G. D. Mel'nikov and S. P. Mel'nikov J. Org. Chem. U.S.S.R. 1977 13 625. 178 D. R. Taylor considered to be compatible with the formation possibly via a fast reversibly formed v-complex of a bromovinyl cation in which the empty p-orbital is con- jugated with the benzene .rr-orbitals and therefore coplanar with the &carbon's a-bonds (5). The last-mentioned structural element implies hyperconjugation an (5) interaction which would explain the greater difference between bromination rates of similarly substituted olefins and acetylene^^^*^'*'^ than are found for rates of acid-catalysed hydration:20 the &bromine atom is more destabilizing in (5) than in the corresponding intermediate bromocation from styrene.The AdEC1 mechanism (a variant of AdE2)is thus confirmed. It should be noted that the nature of any substituents attached to their w-bonds greatly affects the relative bromination rates of correspondingly substituted olefins and acetylenes; indeed some olefinic acids appear to react more slowly than their acetylenic counterparts," though this may be misleading since allowance may have to be made for example for their different acidities which may affect ionic strength. Triethylammonium hydrogen dichloride appears to be the best reagent for achieving the addition of hydrogen chloride to the CGC bond no catalyst is required.The alkynes studied with the exception of phenyl-t-butylacetylene,all reacted stereoselectively to give syn-adducts an observation attributed to the powerfully nucleophilic anion HC12-forcing the adoption of an AdE3mechanism.21 Hydrogen chloride also without catalyst is adequate for hydrochlorination of sulphur-and selenium-substituted acetylenes an addition which proceeds exclusively in an anti-orientation.22 Mixed acetylenes of the type R'SCzCSeR2 react regiospecifically by protonation next to selenium presumably because sulphur is better able to stabilize an adjacent cation. Ph/ \R c1 R (<lo%) + \c=c / a R 'c=c / Ph/ \a (mainly) Reagents i CuCI2-LiCI (40-fold excess) MeCN (R.= H Me Pr" or Ph); ii CuC1,-KI or -I2 (five-fold excess) MeCN (R = H Me Et Pr" or Pr') Scheme 7 S.De Young S. Ehrlich and E. Berliner J. Amer. Chem. SOC.,1977,99 290. l9 G.H. Schmid A. Modro,and K. Yates J. Org. Chem. 1977,42 2021. 2o G. Modena F. Rivetti G.Scorrano and U. Tonellato J. Amer. Chem Soc. 1977,99 3392. 2' J. Cousseau and L. Gouin LCS. Perkin I 1977 1797. 22 S. I. Radchenko and A. A. Petrov J. Org. Gem. U.S.S.R. 1977 13 36. Aliphatic Compounds-Part (i) Hydrocarbons 179 Full details have now appeared of the anti-chlorination of acetylenes using copper(I1) chloride-lithium chloride in large excess in acetonitrile and the tech- nique can also be applied to iodochlorination (using CuCl,-12 or CuC1,-KI) with good regioselectivity (Scheme 7).23 Electrophilic attack upon the C=C bond by both mercurinium and sulphenium cations proceeds almost exclusively to form anti-adducts via bridged vinyl cations; in the latter addition the intermediate episulphonium ions [e.g.(6)] have been isolated as stable antimonates or tetrafluor~borates.~~ Me \c=c /Me \/ S+ SbCl6-I Me (6) New reducing agents termed complex reducing agents (CRA) have been developed by treating sodium hydride with metal salts such as iron(II1) chloride (FeCRA) or nickel(r1) acetate (NiCRA) in the presence of alko~ide.~~,~~ Triple bonds may either be reduced to 2-alkenes or fully reduced to alkanes by a judicious choice of reagents and conditions which are generally mild enough to leave carbonyl groups unaffected.26 Conversions of acetylenes into allenes by substitutions which are accompanied by the well-known propargyl rearrangement are often poorly understood in mechanistic terms.The complexities which can arise are exemplified by the reac- tion of the diphenylbutynol (7;R = Ph2COH) with lithium aluminium deuteride (Scheme 8). Whereas in dialkyl ethers the main product is the allene (8) none of this product appears to be formed when the solvent is only slightly altered to THF.27 Me D LiAID4 -/ I-RCGCMe -Ph,C-C=C + Ph2C-C=CMe I (7) OAID3 OAlD3 [A’D/ -OAID3 1.. I Ph2C=C=CDMe H Me R H R Me (8) \/c=c \/c=c \c=c / /R \D D/ \Me D/ \H [R = Ph,C(OH)] Scheme 8 23 S. Uemura H. Okazaki A. Onoe and M. Okano J.C.S. Perkin I 1977,676. ’* G. Capozzi V. Lucchini G. Modena and P.Scrimin Tetrahedron Letfers 1977,911. ’’ J. J. Brunet L. Mordenti B. Loubinoux and P. Caubere Tetrahedron Letters 1977 1069. ’‘ J. J. Brunet and P.Caubere Tetrahedron Letters 1977 3947. *’ M. P. Hartshorn R. S. Thompson and J. Vaughan Aushal. I.Chem. 1977.30.865. 180 D. R. Taylor Two I3C n.m.r. studies of acetylenic compounds have recently been reported. One establishes correlations for chemical shifts in a@-acetylenic ketones,28 and the other claims to show that chiral recognition is possible across the CEC bond in molecules such as 2,5-di~hlorohex-3-yne.~~ 2 Alkanes A review has appeared dealing with the conformations of hydrocarbon chains.30 The synthe~is,~’ thermal stability,31 and thermodynamic properties3* of some strained alkanes have been reported 13C n.m.r.spectra can be used to study conformational and rotational barriers in such Two new syntheses of alkanes have been developed. The first uses the addition of alkyimercury(I1) halides or acetates to electron-deficient olefins to generate the saturated C-C linkage and is followed by sodium borohydride reduction to cleave the C-Hg bond.34 The second technique is to convert an alcohol into a chloro- formate which may then be conveniently reduced under free-radical conditions by a trial kyl~ilane.~~ Further examples have appeared36 of oxyfunctionalization of alkanes using pro- tonated ozone [see Ann. Reports (B) 1976 73,1721. As an alternative hydrogen R3CH [R3C--+:H l& R3COH + HOR3CCH3 ____+ H OH 3R3CCH20H.+I R R2ii ‘O-CH2R 4 -H20 R2C-CH2R I O+ aR,&H2R -HO +2R2C-CH2~OH2 H’ ‘OH Scheme 9 G.A. Kalabin A. G. Proidakov L. D. Gavrilov and L. 1. Vereshchagin J. Org. Chem. U.S.S.R.,1977. 13,449. ” A. J. Jones and P. J. Stiles Tetrahedron Letters 1977 1965. 30 M. A. Winnik Accounts Chem. Res. 1977 10 173. 31 H.-D. Beckhaus and C. Ruchardt Chem. Ber. 1977,110,878. ’’D. N. J. White and M. J. Bovill J.C.S. Perkin 11 1977 1610. 33 S. Brownstein J. Dunogues D. Lindsay and K. U. Ingold J. Amer. Chem. SOC.,1977,99 2073. 34 B. Giese and J. Meister Chem. Ber. 1977 110 2588. ’’N. C. Billingham R. A. Jackson and F. Malek J.C.S. Chem. Comm. 1977 344. A liphatic Compounds-Part (i ) Hydrocarbons 181 peroxide may be used either in superacid~~~,~~ or in concentrated trifluoroacetic Studies by 'H n.m.r.in superacid suggest that the Ceaction proceeds via electrophilic attack by HO' (or the incipient cation H0.0H2) on the weakest available C-H u-bond followed by nucleophilic attack by hydrogen peroxide upon the carbenium ion and subsequent alkyl migration to oxygen (Scheme 9). Predominantly branched alkanes were studied. Reactions between n-alkanes and hydrogen peroxide in trifluoroacetic acid yield alkan-2-01s and -3-ols with negli- gible amounts of terminal 3 Allenes An exhaustive review of the synthesis and chemical reactions of the interesting phospha-allene ylides has appeared.39 These ylides yield allenes when subjected to the Wittig reaction with carbonyl compounds. An extension of earlier work [see Ann.Reports (B) 1976 73 1731 on the synthesis of allenes via allenylcoppers has been rep~rted.~' Electrophilic attack upon the intermediate (9) by iodine yields optically active iodoallenes if optically active propargyl esters are used as starting materials. However when the elec- trophile is an acid anhydride or chloromethyl methyl ether (Scheme 10) only R1R2C(OAc)C_CH 5 [R'R2C=C=CHCuR32] (9) Kd Li \ R1R2C(COR4)C=H RZ=Y R'R~C(CH~OM~)C=CH R'R~C=C=CHI R'C(COR4)=C=CH2 (10) Reagents i R32CuLi (R3 = alkyl); ii 12 (MeOCH2)2; iii CICH20Me; iv (R4CO)20 (R4= Me n-CSH11 or Ph) Scheme 10 acetylenic products are formed initially although these may isomerize to for example allenones (10). An alternative synthesis of allenes operates upon the same type of starting material [R,C(OAc)CrCH] but generates intermediate allenylborates which can be converted into a wider variety of functionalized allenes by prot~lysis~~ or hydrolysed with a retro-propargyl rearrangement to acetylenes (Scheme 11).Full details have appeared of the syntheses of higher cumulenes by flash-pyroly- tic retro-Diels-Alder and by Skattebgl's method,43 described in last 36 N. Yoneda and G. A. Olah J. Amer. Chem. SOC.1977,99,3113. 37 G. A. Olah N. Yoneda and D. G. Parker J. Amer. Chem. SOC.,1977,99,483. 38 N. C. Deno E. J. Jedziniak L. A. Messer M. D. Meyer S. G. Stroud and E. S. Tomezsko Tetrahedron,1977,33 2503. 39 H. J. Bestmann Angew. Chem. Internat. Edn. 1977 16 349. 4" J.-M. Dollat J.-L. Luche and P.Crabbe J.C.S. Chem. Comm. 1977 761. 41 M. M. Midland J. Org. Chem. 1977 42 2650. 42 J. C. Ripoll and A. "huillier Tetrahedron,1977,33 1333. 43 G. Karich and J. C. Jochims Chem. Ber. 1977 110 2680. 182 D. R. Taylor R'CECCHR2 R'CH=C=CRZ2 Scheme 11 year's Report (pp. 176-177). As the number of cumulated double bonds increases the rotational barrier decreases uniformly and not in an alternating fashion which would have suggested a dependence upon molecular planarity.44 A number of allenes of potential commercial interest have been synthesized this year.4547 These included 2,4,5-trienamides regarded as potential insecticides in which a Wittig reaction was used to introduce the non-allenic C=C bond:' and the synthesis of allenic barbiturates from allenylmalonates.The latter derivatives were prepared by an addition-elimination sequence using malonate and 1-halogeno-allenes (Scheme 12) but the correct choice of base to generate the malonate anion must be made otherwise acetylenic or dienic isomers of the desired allenes may pred~minate.~~ R'R2C=C=CHCR3(C02Eth (11) ii [R'R2C=C=C] % R'R2CCR3(C02Et)2+ (1 1) I C=CH R3=H 1 R'R2C=CHCH=C(C02Et)2 Reagents i NaH-C6H6-R3CH(C02Eth (R3= H or Et); ii NaOEt-EtOH; iii R3CH(C02Eth Scheme 12 Reactions of magnesium or lithium with 1,3-dihalogenopropanes yield cyclo- propanes and not 1,3-propane-dimetaI compounds. Hence the importance of the discovery that hydroboration of propadiene followed by mercuration yields pro- pane- 1,3-dimercury(11) chloride which although it cannot be transmetallated directly may nevertheless be converted into propane- 1,3-dirnagnesium(11) halide in two steps (Scheme 13).48 This interesting bis-Grignard reagent has so far only been used to generate glutaric esters propane- 1,3-distannyl derivatives and more significantly two silacyclobutanes in good yield.Propadiene has also been used as a precursor in propenyl ketone synthesis; the required C-2 acylation was effected with sodio a1 kylironte tracarbonyl .49 K. Bertsch G. Karich and J. C. Jochims,.Chem. Ber. 1977 110 3304. 45 P. D. Landor S. R. Landor and 0.Odyek. J.C.S. Perkin I 1977,93. 46 S. R. Landor P. D. Landor and P. F. Whiter J.C.S. Perkin I 1977 1710. 47 L. A. van Dijck B. Thankwerden and J.G. C. M. Vermeer Rec. Trau. chim. 1977 % 200. 48 L. C. Costa and G. M. Whitesides J. Amer. Chem. Soc.,1977,99 2390. 49 A. Guinot P. Cadiot and J. L. Roustan J. Organometallic Chem. 1977 128 C35. Aliphatic Compounds-Part (i)Hydrocarbons .. CH2=C=CH2 -R1HgCH2CH2CH2HgR’ BrMg(CH,),MgBr // Me02C(CH2)3C02Me Me3Sn(CH2hSnMe3 Reagents i BzH,; ii Hg(0Ach; iii NaCl; iv 2R’Li-THF; v Mg-MgBr2-THF; vi CO,; vii H+-MeOH; viii CH2N2; ix Me3SnC1; x R22SiC12 (R2 = Ph or Me) Scheme 13 Further additions of resonance-stabilized enolates to allenic sulphonium salts have been investigated.” When the addend is a cyano-stabilized enolate a cyano- furan is formed; this and earlier furan syntheses are shown to proceed by a direct substitution mechanism rather than via addition-elimination.Other uni- and bi-dentate nucleophiles were found to yield products of addition-substitution (Scheme 14). When the attacking nucleophile is a malonate anion the isolable allylic adducts [12; Z=R3C(C0,Et)2 R3=H or Me] are converted by alkoxide into ylides which undergo [2,3] sigmatropic shifts.51 Me2kH=C=CH2 I,Me~;2 lii \ Me2SCH2CZ=CH2 + Reagents i R2COCHR’ (R’ = Ac ArSO, C02R3 or CN;R2= Ph); ii HXCH2CH2X- (X = S or SO,); iii Z-(Z= CN or PhS02); iv Z-(-Me2S) Scheme 14 Further examples of ene reactions of alkylallenes have been reported. The acyclic enophile Et02CN=NC02Et reacts with allenes including cyclonona-l,2- diene to produce the expected 2-bicarbamyl- 1,3-dienes in excellent yield,52 whereas the cyclic enophile N-phenyltriazolinedione induces apparent prototropic shifts in some allenes.The ene reactions of such allenes are found to be two to five times faster than those of comparably substituted mono-olefins presumably as a result of lower steric hindrance and developing resonance interactions in the B. S. Ellis G. GrifFiths P. D. Howes C. J. M. Stirling and B. R.Fishwick J.C.S. Perkin I 1977 286. ” G. Griffirhs P. D. Howes and C. J. M. Stirling JCS. Perkin I 1977 912. ’’ C. B. Lee and D. R. Taylor J.CS. Perkin I 1977 1463; J. Chem Res. (S) 1977,136; (M)1601. 184 D. R. Taylor transition state. Ene adducts were not however obtained when cyclonona- 1,2- diene was treated with acetylenic enophiles; the 1 1 adducts obtained were simple [2 + 21 cycloadducts (Scheme 15).R CH2CR2 =C=CR3R4 R 'CH=CR2C=CR3R4 I N(CO2Et)NHC02Et Reagents i Et02CN=NC02Et [R' = H R2-R4 = Me or R1 = R3 = R4 = H R2 = Me or R2 = R3 = H R1R4 = (CH,)5]; ii ECECE [E = CF3 or CO,Et R2 = R3 = H R'R4 = (Cf-I2)=J; iii N=NCONPhCO (R' = H R2-R4 = Me) Scheme 15 Further uses of allenes in synthesis have appeared. Allenic nitriles undergo Michael additions when treated with phenylhydrazine conjugated adducts cyclize thermally to 5-aminopyrazoles whereas unconjugated adducts give 3H-indoles via a [3,3]sigmatropic shift.53 Ketene cycloadducts of cyclohexanylideneallene have also been found useful since their thermal isomerization leads to annelated pro- ducts (Scheme 16).54 & Me,C=C=O s"; + HZ 0 boo "C 0 Scheme 16 4 Olefins and Dienes Advances in the following areas relevant to olefin chemistry have been reviewed recently stepwise [2 + 21 cycloadditions of enol industrial Wittig reac- tion~,~~ the Prins ~eacfion,~' structural effects in acid-catalysed hydrati~n,~' and the 53 S.R. Landor P. D. Landor Z. T. Fornum and G. M. Mpango Tetrahedron Letters 1977 3743. 54 M. Bertrand G. Gil A. Junino and R. Maurin Tetrahedron Letters 1977 1779. " R. Huisgen Accounts Chem. Res. 1977 10 117. '' H. Pommer Angew. Chem. Internat. Edn. 1977 16,423. '' V. J. Nowlan and T. T. Tidwell Accounts Chem. Res. 1977 10 252. 58 D. R. Adam and S. P. Bhatnagar Synthesis 1977 661. Aliphatic Compounds-Part (i) Hydrocarbons 185 synthesis of insect sex pheromone^.^^ The last-mentioned review includes useful discussion of the control of stereochemistry in Wittig and related reactions.Aspects of organometallic olefin chemistry which have also been reviewed include olefin insertions in catalysis6' and the applications of organosilicon compounds6' and organopalladium compounds62 in synthesis. Olefin metathesis reactions continue to receive enthusiastic attention and besides numerous individual research report~,6~~~ the proceedings of a symposium have been p~blished.~' The excellent new olefin synthesis which involves the coupling of two molecules of a carbonyl compound by low oxidation states of titanium7' (TiC13-LiAlH, TiC1,-K or -Li or TiC1,-Zn) has been used successfully in several laboratorie~.~~-'~ It is especially useful for symmetrical tetrasubstituted olefins for which a Wittig reaction would be unsuitable.Since the reaction involves a pinacol-type reductive dimerization as the first step (Scheme 17) it is not obvious that unsymmetrical R'R~C=O -+R'R~C-O s R'R~C-O R'R~C=CR'R~ t 2~ -R R C-0 Scheme 17 olefins (R'R2C=CR3R4) could be prepared from a mixture of two carbonyl compounds. However McMurry's group has now shown that the use of an excess of acetone with for example a cycloalkanone gives synthetically useful yields of isopropylidene-cycloalkanes. With mixtures of acetone and diaryl ketones essen- tially only mixed olefins (Me,C=CAr,) are obtained; since the reduction potentials of diaryl ketones are lower than that of acetone a radical coupling pathway (path a) is deemed less likely than the formation of aryldianions (Ar2c-03 which attack acetone preferentially (path b).75 The procedure is exceptionally useful for the preparation of very hindered olefins such as adamant~lideneadamantane~' and led to another first-time achievement the synthesis and successful resolution by h.p.1.c.59 C. A. Henrick Tetrahedron 1977,33 1845. " G. Henrici-Olivk and S. Olive Topics Current Chem. 1976 67 107. 61 S. S. Washburne J..Organometallic Chem. 1976 123 1. 62 B. M. Trost Tetrahedron 1977,33,2615. 6' E. Verkuijlen F. Kapteijn J. C. Mol and C. Boelhouwer J.C.S. Chem Comm. 1977 198. 64 J.-P. Laval A. Lattes R. Mutin and J. M. Basset J.C.S. Chem. Comm. 1977 502. 65 P. G. Gassman and T. H.Johnson J. Amer. Chem. Soc. 1977,99,622. 66 T.J. Katz and J. McGinnis J. Amer. Chem. SOC. 1977 99 1903. 67 J. L. Bilhou J. M. Basset R. Mutin and W. F. Graydon J. Amer. Chem. SOC. 1977,99,4083. " R. Baker and M. J. Crimmin Tetrahedron Letters 1977,441. 69 T. J. Katz and W. H. Hersh Tetrahedron Letters 1977 585. 70 Proceedings of the International Symposium on Metathesis Noordwijkerhout Sept. 1977 Rec. Trao. chim. 1977,96 ml. 71 J. E. McMurry and M. P. Fleming J. Amer. Chem. SOC. 1974,96,4708; J. Org. Chem. 1976,41 896. 72 B. Feringa and H. Wynberg J. Amer. Chem. Soc.,1977,99,602. 73 D. Lenoir Synthesis 1977 553. 74 G. A. Olah and G. K. S. Prakash J. Org. Chem. 1977,42,580. 75 J. E. McMurry and L. R. Krepski J. Org. Chem 1976,41,3929. 186 D.R.Taylor on alumina-(+)-TAPA [2-(2,4,5,7-tetranitro-9-fluorenylideneamino-oxy)pro-pionic acid] of the (*)-cis-and (*)-trans-bi-hexahydrophenanthrylidenes(13a and b) in which chirality stems solely from torsional di~tortion.~~ (1 3a) (13b) Tetrakis(neopentyl)ethylene synthesized by the Ti" coupling reaction is unaffected by bromine in carbon tetrachloride and is not even protonated in FS03H-S02C1F although the more powerful Magic Acid cleaves the neopentyl groups.74 Another exceptionally unreactive olefin (14) named [ 10,101-betweenane has been reported; it has a doubly trans-cycloalkene 7r-bond and so has no accessible face for attack upon the olefinic Another alternative to the Wittig reaction in this case suitable for preparations of terminal alkenes is the interaction of a Grignard reagent with Eschenmoser's salt (15) (Scheme 18).77The intermediates are amine oxides which decompose at somewhat higher temperatures than the intermediate betaines of the Wittig pro- cedure.CH -he21-2R'R2CHCH2NMe2 '-( 15) ii 1 R'R2C=CH2 2 R'R2CHCH2$Me2 I 0- Reagents 1 R'R2CHMgX or R'R2CHLi; ii H202; iii 150 "C Scheme 18 Further papers on the useful olefin synthesis technique based on diphenyl-phosphinoyl migrations have a~peared.~' The main limitations foreseen for this approach are (i) that the necessary Ph,P(O) migration no longer occurs when an alternative tertiaky migration origin is present and (ii) that aryl groups at the 76 J. A. Marshall and M. Lewellyn J. Amer. Chem Soc. 1977,99 3508.77 J. L. Roberts P. S. Borromeo and C. D. Poulter Tetrahedron Letters 1977 1299. 78 A. H. Davidson I. Fleming J. I. Grayson A. Pearce R. L. Snowden and S. Warren LCS. Perkin I 1977 550; A. H. Davidson C. Earnshaw J. I. Grayson and S. Warren ibid p. 1452. Aliphatic Compounds-Part (i ) Hydrocarbons 187 migration terminus or four- or five-membered alicyclic rings at the migration origin tend to produce substantial amounts of vinyl- rather than allyl- phosphine oxides (Scheme 19). A Wittig-Horner route to vinyl ethers and hence ultimately applicable to ketone synthesis has also appea~ed.’~ R2 I I ,R’ migration Ph (0)-c-c-c +/ R2 R’ 2 ‘ A1 \ R‘ OH P migration R2 \+ I I c-c-c-/I I Ph2P(O) R2 \ I \I I c=c-c-c-c-c-I /I I /Ph21&3) PhJW Scheme 19 Olefin syntheses via vinylsilanes should prove more easy to undertake now that vinysilanes are accessible from ketones by a two-step procedure (Scheme 20).80 0 NNHTs Li SiMe3 TsNHNH~ BuLi Me3SiX I *c/H \ C-q \ Scheme 20 Trisubstituted vinylsilanes produced stereospecifically or with a stereochemistry subsequently determined by for example 13C n.m.r.spectroscopy may be con- verted by a variety of electrophilic reagents into trisubstituted alkenes of known structure (Scheme 21).81 The hydrolysis of vinylsilanes which leads to the replacement of Si by H has been found to occur readily in wet acetonitrile with toluenesulphinic acid as catalyst but in this reaction the geometry about the double bond is not retained.” ’’C.Earnshaw C. J. Wallis and S. Warren J.CS. Chem. Comm. 1977,314. 8o R.T.Taylor C. R. Degenhardt W. P. Melega and L. A. Paquette Temahedron Lefters 1977 159. T. H. Chan P. W. K. Lau and W. Mychajlowskij Tetrahedron Letters 1977 3317; T. H.Chan W. Mychajlowskij and R. Amouroux ibid. p. 1605. G.Buchi and H. Wiiest Tetrahedron Letters 1977,4305. 188 D. R. Taylor R CHzR' RCHO 4RCH(OH)C(SiMe3)=CH2 % \/ C=C I H' \SiMe3 iv. iii 1. Reagents 1 CH2=C(Li)SiMe3 -78 "C;ii Ac20; iii R'&uLi; iv SOC12-Et20 25 "C;v Br2 or I2 or AcCI-AICl or Cl2CHOMe-AICl3 Scheme 21 The alkenylboranes derived by syn-addition of 9-borabicyclononane (9-BBN) to terminal acetylenes have been found to be much more reactive towards carbonyl groups than saturated organoboranes.Their addition to aldehydes followed by oxidative hydrolysis in the usual way provides an ultra-mild pseudo-Grignard synthesis of allylic alcohols of known geometry (Scheme 22).83 Terminal olefins ~~ H' \CHRl I OH Reagents i 9-Borabicyclononane (9-BBN); ii R'CHO-THF; iii NaOH-H202 Scheme 22 have been prepared by a two-carbon homologation procedure commencing with the reaction of vinylmagnesium bromide with a trialkylborane yielding a vinylborate(1 -) which is cleaved with alkali and iodine.84 Borate esters formed quantitatively from a secondary alcohol and boric acid feature in a mild procedure for olefin formation which is effectively a two-step dehydration of the alcohol. The esters are decomposed by boron trifluoride etherate at 100"C,and olefin yields are excellent; isomeric mixtures of compositions similar to those obtained by other dehydration methods are formed.85 Ally1 alcohols can be converted into olefins by replacement of the hydroxy-group by alkyl or aryl residues on treatment with the appropriate alkyl- or aryl-magnesium halide in the presence of nickel(I1) complexes though the formation of 83 P.Jacob and H. C. Brown J. Org. Chem. 1977,42,579. K. Utimoto. K. Uchida M. Yarnaya and H. Nozaki Tetrahedron 1977,33 1945. M. P.Doyle S. B. Williams and C. C. McOsker Synthesis 1977 717. Aliphatic Compounds-Part (i) Hydrocarbons 189 mixtures of isomers indicated that allylic rearrangement accompanied the substitu- tion.86 A more reliable technique for achieving this rather unusual hydroxyl replacement would seem to be that based on the initial conversion of the alcohol into a lithium allyloxyalkylcuprate a source of the allyloxy nucleophile for reaction with the phosphonium iodine (16) (Scheme 23).87 \ II Ill \ II C=C-C-OH -% [ y=C-F-OCuR C=C-C-R / I / I + Reagents i MeLi; ii Cur; iii 3RLI; iv Ph3PNMePh I-(16) -78 to i2.5 “C Scheme 23 Some elegant syntheses of naturally occurring compounds have been reported which are based upon the use of butadiene telomers as starting materials.Exam- ples include the synthesis of cis-civetone88 and queen ~ubstmce.~~ Tidwell and co-workers have previously shown that the rates of acid-catalysed hydration of 1,l -disubstituted alkenes can be satisfactorily correlated with the sum of the up+constants of the l-sub~tituents,~~ according to the equation This correlation also applies to the rates of hydration of 2-substituted buta-1,3- dienes vinyl acetates and vinylphosphates and successfully provides a correlation for literature data on hydration rates of 22 substituted styrene~.’~ This finding is taken to confirm the Ads,2 (rate-determining C-protonation) mechanism.Hydra- tion rates of 1,2-disubstituted olefins require the mathematical model to be slightly m~dified.~’ An alternative procedure for effecting the uic-addition of halogens to olefins which avoids the use of elemental bromine or chlorine has been reported. Positive halogenonium ions are formed from the mixed reagent HX-H202 and the addition of phase-transfer catalyst (PTC) to the two-phase brew minimizes halohydrin formation:92 aq.HX-H,O R’CH=CHR2 AR’CHXCHXR2+ 2H20 ca4-pTc Suitable conditions for vicinal anti-addition of I’ -OH- I+-Cl- and 1’-OCOR-to alkene~~~ and for vicinal alkoxyselenation (addition of RO-SePh) of olefins?’’ have been reported. 86 C. Chuit H. Felkin C. Frajerman G. Roussi and G. Swiernewski J. Organometallic Chem. 1977 127,371. 87 Y. Tanigawa H. Kanamaru A. Sonoda and S.-1. Murahashi J. Amer. Chem. Soc. 1977,99 2361. 88 J. Tsuji and T. Mandai Tetrahedron Letters 1977 3285. 89 J. Tsuji K. Masaoka and T. Takahashi Tetrahedron Letters 1977 2267. 90 W. K. Chwang P. Knittel K. M. Koshy and T. T. Tidwell J. Amer. Chem. SOC.1977,99,3395; S. Y. Attia J. P. Berry K. M..Koshy Y.-K. Leung E. P. Lyznicki V. J. Nowlan K. Oyama and T. T. Tidwell ibid. p. 3401. 91 P. Knittel and T. T. Tidwell J. Amer. Chem Soc. 1977,99 3408. 92 T.-L. Ho B. G. B. Gupta and G. A. Olah Synthesis 1977 676. 93 R.C. Cambie D. Chambers P. S. Rutledge and P. D. Woodgate J.C.S. Perkin I 1977 2231; R. C. Cambie W. I. Noall G. J. Potter P. S. Rutledge and P. D. Woodgate ibid. p. 226. 94 A. Toshirnitsu S. Uernura and M. Okano J.C.S. Chem. Comm. 1977 166. 95 N. Miyoshi S. Murai and N. Sonoda Tetrahedron Letters 1977 851 190 D. R. Taylor There have been two useful advances in olefin hydroboration both stemming from H. C. Brown’s group. Firstly the relatively stable reagent Me,S,BH is commercially available and makes an excellent starting material for generating borane for addition to hindered olefins or for the preparation of ~atechylborane.~~ Secondly it is possible to add 9-BBN selectively to one (usually the less-hindered) double bond of non-conjugated dienes and hence to introduce functionality at the site of carbon-boron bond formation a procedure which should find numerous applications in synthesis (Scheme 24).97 Scheme 24 This year has not been noteworthy for novel developments in olefin cyclo- additions although major papers on the application of the concept of hard and soft acids and bases to the Woodward and Katz model of the Diels-Alder reaction and to [2+2] cycloadditions have appeared.98 The basis for this treatment of the Diels-Alder reaction is that unsymmetrical reagents will unite to form the two new 0-bonds non-synchronously via a non-symmetrical transitiou state hence predic- tion of the orientation of addition may be made by determining which 0-bond should be formed faster.The assumption is made that this bond will be that linking the softest centres i.e. the terminal atoms with greatest overlap stabilization. This leads for electron-deficient (low LUMO) and electron-rich (high HOMO) reac-tants to the rule that atoms with the largest coefficients in these MOs will bond preferentially. Note that all four frontier orbitals must be considered if both reactants have similar electron densities at their terminal atoms. Applications of Diels-Alder reactions to complex synthetic problems continue to impress this Reporter.Examples which should illustrate this are (i) the use of inter-and intra-molecular Diels-Alder additions of cyanodienes formed in situ by elec- trocyclic ring-opening of benzocyclobutenes (Scheme 25)99 and (ii) a sequence which may involve the first known example of a bimolecular pericyclic reaction in natural biosynthesis. loo Ene reactions have proved a more fruitful area for new developments. A series of conjugated dienes which undergo the ene reaction and cycloaddition simul- taneously were treated with a variety of enophiles (maleic anhydride azo-esters 96 H. C. Brown A. K. Mandal and S. U. Kulkarni J. Org. Chem. 1977,42 1392. 97 R. Liotta and H. C. Brown J. Org. chem. 1977,42 2836. 98 0.Eisenstein.J. M. Lefour N. T. Anh and R. F. Hudson Tetrahedron 1977 33 523; C. Minot and N. T. Anh ibid. p. 533. 99 T. Kametani Y. Hirai F. Satoh and K. Fukumoto J.C.S. Chem. Comm. 1977 16. loo R. D. Stipanovic A. A. Bell D. H. O’Brien and M. J. Lukefahr Tetrahedron Letters 1977 567. Aliphatic Compounds-Part (i) Hydrocarbons &,H28 Me0 ' -OEt Reagents i isoprene 180 "C,2h; ii NaNH, liq. NH3; iii 210-215 "C,toluene sealed tube Scheme 25 etc.). The product distributions indicated that steric factors were not of prime importance in the partitioning of a given diene between the two pathways.'" However the relative reactivities of different dienes towards a given eno-phile/dienophile were explicable on a steric basis; for example (17) is ten times more reactive than (18)towards diethyl azodiformate at 25 "C,because its reactive face is less hindered than either face of (18) in spite of the statistical advantage of (18) which has a suitably placed axial hydrogen on both sides of the ring.A concerted ene reaction seems therefore to be occurring a conclusion also reached after a kinetic study of ene reactions between maleic anhydride and a series fbr \ii Reagents i PhSO,N=SO; ii SO,; iii allylic rearrangement; iv retro-ene -SO2 Scheme 26 lo' B. M. Jacobson A. C. Feldstein and J. I. Smallwood I. Org. Chem 1977,42 2849. 192 D. R. Taylor of acyclic mono-olefins. lo' Some novel enophiles have been reported they include N-sulphinylbenzenesulphonamide(PhSOZN=S=0)lo3 and sulphur dioxide,lo4 the latter causing rapid thermal isomerization of thermodynamically unstable olefins such as P-pinene (Scheme 26).Other novel ene reactions were those induced by the acyl cation (from acetyl hexachloroantimonate) in which a carbocation addi- tion-elimination sequence was precluded by the absence of rearrangement pro- duct~,~~~ and the ally1 anion (Scheme ,,).''' -+ products Scheme 27 Catalytic ene reactions of chloral have been the subject of an elegant investiga- tion. Lewis acids which complex with chloral lower the required temperature for ene insertion which becomes a relatively clean reaction though not always free from by-product formation. Subsequent functional group modification may make this a useful technique for attacking the allylic position in synthesis (Scheme 28).1°' Pr"CH2CH=CH2 Pr"CH=CHCH2CH(0H)CCl3 y iv-vi Pr"CH=CHCH=CHC02Et Pr"CH=CHCH2 CH( OH)CH ii'y I Pr"CH2 CH2CH2C02H Reagents i CC13CHO-SnC14 (1-5%) CC14; ii NaH-TsCI; iii NaOEt-EtOH; iv Pd/C-H*; v Cr03; vi aq.NaOH; vii Bun3SnH Scheme 28 With a chiral olefin such as P-pinene choice 0f.a suitable Lewis acid catalyst enables stereochemical control of the reaction to be achieved. An improved technique for allylic oxidation by selenium dioxide uses mainly t-butyl hydroperoxide as the oxidant with only 1-2% SeO, unless the olefin is very unreactive when higher proportions may have to be used."' A detailed study of chromyl chloride oxidation of olefins has shown that all of the three primary products namely expoxide chlorohydrin and vicinal dichloride arise by syn-addition.lo9 These observations necessitate a revision of earlier mechanistic pro- F.R. Benn J. Dwyer and I. Chappell J.CS. Perkin ZZ 1977 533. G. D6l&ris,J. Kowalski J. Dunogues and R. Calas Tetrahedron Letters 1977 4211. '0.1 M. M. RogiC and D. Masilamani J. Amer. Chem. SOC.,1977,99 5219. lo' H. M. R. Hoffmann and T. Tsushima J. Amer. Chem. Sac. 1977,99,6008. 1mJ. H. Edwards and F. J. McQuillan J.CS. Chem. Comm. 1977 838. lo' G. B. Gill and B. Wallace J.C.S. Chem. Comm. 1977,380,382. M. A. Umbreit and K. B. Sharpless J. Amer. Chem. Soc.,1977,99,5526. '09 K. B. Sharpless A. Y. Teranishi and J.-E. Backvall J. Amer. Chem SOC.,1977,99,3120. Aliphatic Compounds-Part (i) Hydrocarbons posals based on the intermediate formation of cations and a scheme involving organochromium(v1) species was advanced (Scheme 29).By contrast evidence that hindered olefins may react with singlet oxygen via a cationic perepoxide pathway was obtained by the detection of substantial amounts of cationic rear- rangement products from camphenylideneadamantane.' '' J J Scheme 29 A new variety of polymer-bound hydrogenation catalyst uses rhodium(II1) chloride or other metal halides complexed to a phosphine which is chemically bonded to silica. ' Photoelectron spectroscopy bas shown that ethylene chemi- sorbed on tungsten has essentially sp3-hydridized carbon atoms with a carbon- carbon bond length stretched to 1.54 a further manifestation of the diverse applications of this recently developed analytical technique.'Io F. McCapra and I. Beheshti J.C.S. Chem. Comm. 1977,517. '" K. Kochloefl W. Liebelt and H. Knozinger J.CS. Chem. Comm 1977,510. T. V. Vorburger B. J. Waclawski and E. W. Plummer Chem. Phys. Letters 1977,46,42.