7 Aliphatic Compounds Part (i) Hydrocarbons By D. F. EWING Department of Chemistry University of Hull Hull HU6 7RX 1 Alkanes Ever since the pioneering work of Bouveault and Blanc at the beginning of this century the action of sodium on esters has been of great interest to chemists principally as a means of converting the acid moiety into the corresponding alcohol. However recently attention has turned to investigation of the fate of the original alcohol moiety and the conditions under which it is converted into an alkane. Sodium in hexamethylphosphortriamide will convert' the acetyl derivatives of primary and secondary alcohols into the corresponding alkanes in 40-50% yield and in the case of highly hindered alcohol esters the alkane yield can exceed 95%.The relative proportion of alkane and alcohol shows some dependence on the structure of the esterifying acid.The halogenation of alkanes is usually restricted to reaction with chlorine or bromine by a radical process. In contrast elemental fluorine has been found2 to react as an electrophile with tertiary C-H bonds in cyclic and acyclic hydrocarbons to give the fluoride in reasonable yield e.g. 3-methylnonane is converted into 3-fluoro-3-methylnonane in 60% yield by a 2% stream of F2 in nitrogen at -75 "C. 2 Alkenes Synthesis.-From Alkynes. The reduction of acetylenic derivatives with zinc powder has been thoroughly ~haracterized.~ Two methods of activating the zinc were com- pared. The reagent Zn-C2H4Br2 is highly selective for conjugated diynes isolated triple bonds being unreactive.Only one triple bond is reduced to give the 2-enzyne in at least 70% yield. The presence of a heteroatom in the substrate usually leads to enhanced yields. A more powerful system is Zn-Cu-C2H4Br2 which will reduce both triple bonds in conjugated diynes and will react at isolated triple bonds in some cases. A more interesting catalyst system can be prepared from NaH t-amyl alcohol and palladium( 11) acetate in a 3 :2 :1 molar ratio in tetrahydrof~ran.~ With this catalyst the hydrogenation of acetylenes is cu. 99% selective for conversion into alkenes with a 99% stereoselectivity for the 2-product. Quinoline is required as a H. Deshayes and J.-P. Pete Can. J. Chem. 1984 62 2063. 'C. Go1 and S. Rozen Tetrahedron Lett.1984 25 449. M.H.P. J. Aerssens antl L. Brandsma J. Chem. SOC.,Chem Commun. 1984 735. J.-J. Brunet and P. Caubete J. Org. Chem. 1984 49 4058. 107 108 D. E Ewing modifier but exceptional reproducibility of results can be maintained from batch to batch making this catalyst the most attractive to date for monohydrogenation of alkynes. Calcium in a 1 1 mixture of methylamine and ethylenediamine has been investigated' as an alkyne reducing system. Internal alkynes give the corresponding 2-alkene in 80% yield with small amounts of other isomeric alkenes. By Elimination. The reduction of vicinal dibromides with sodium sulphide facilitated by the use of a phase-transfer reagent was reported on last year. The usefulness of this approach has been confirmed independently by other workers.6 Another useful reducing agent for this type of elimination reaction is the species Cp2TiC1 made from titanocene ( Cp2TiC12) by reduction with zinc.' The reaction is stereoselective for anti-elimination and the yield of olefin ranges from 66 to 95% over twelve examples.a-Silyl esters (1) are known to be vinyl di-cation equivalents at least for the unsubstituted compound (R' = R2 = H) and as such can be alkylated twice at carbon-1 to give an alcohol which in turn undergoes facile elimination to afford an alkene (Scheme 1). This reaction has now been extended to substituted compounds R' IPh,MeSiCCOOEt R2I R'R'IA Ph2MeSiCCOR3 * Ph2MeSiLCR3R40H R2I R2I -+ R' R3 \/C=C R2' \R4 (1) (2) Reagents i R3MgBr; ii R4MgBr or R4Li Scheme 1 to give ultimately tri- and tetra-substituted alkenes (2).8The yields are very variable and as might be expected very sensitive to the cumulative steric effect of R' R2 R3,and R4 in (2).a-Lithiated benzyl phenyl sulphones ArCH2S02Ph undergo elimination to afford E-1,2-diarylethenes only very slowly at ambient temperature. In the presence of elemental tellurium the rate of this reaction is significantly enhanced' but some of the cis form is also obtained. However isomerization to give a pure trans product is simply achieved by refluxing with TeC1,. Alkyl or ally1 sulphones are unreactive even in the presence of tellurium. Other Syntheses. Direct arylation of alkenes can be affected by one equivalent of t-butyl perbenzoate in presence of a catalytic amount of a palladium salt (Scheme 2)." The perester acts as a hydrogen acceptor and this oxidative coupling reaction can be extended to furan with yields in the 50-70% range.The reaction of alkenes with trialkylsilanes usually gives a silylated alkane. However in the presence of high concentrations of rhodium( I) catalysts the reaction is more complex and gives R. A. Benkeser and F. G. Belmonte J. Org. Chorn. 1984,49 1662. D. Landini L. Milesi M. L. Quadri and F. Rolla J. Org. Chern. 1984 49 152. ' S. G. Davies and S. E. Thomas Synthesis 1984 1027. D. Hernandez and G. L. Larson J. Org. Chern. 1984,49 4285. L. Engman J. Org. Chem. 1984 49 3559. J. Tsuji and H.Nagashima Tetrahedron 1984 40,2699. Aliphatic Compounds -Part ( i) Hydrocarbons Y C6H + r-/ 2'Fy R Ph Reagent i PhC03CMe3(100 mol YO),Pd(OCOPh)2 (5 mol Oh) CH,COOH 110 "C Scheme 2 a much increased proportion of silylated alkenes." There is clearly some potential in this reaction but further work is required.Reactions.-There is much interest at present in the oxygenation of alkenes by methods which mimic the action of natural mono-oxygenases such as the cytochrome group. Tetraphenylporphyrin (TPP) complexes of several metals have been investi- gatedt2 using NaOCl as oxygen source. This reagent has the advantage that it can be effective in dilute solution. Epoxidation of styrene with Mn(TPP)OAc can be achieved with 80% conversion but analogous complexes of Co Fe and Cr are decreasingly effective.Selectivity for epoxidation can vary between 60 and 100%. In another studyt3 with iodosylbenzene as oxidant Fe(TPP)Cl shows 100% selec-tivity for epoxidation but other species such as FeC13 and Fe(acac)j are much less selective. The overall yield of oxidized products is also lower. In contrast copper(I1) species with iodosylbenzene catalyse alkene epoxidation efficiently without the mediation of a porphyrin moiety.I4 It is postulated that the active species is [Cu2OIPhI4+ or a derived (p-0xo)dicopper complex. Some interesting mechanistic revelationst5 have come from work with a TPP complex of cobalt with O2as oxidant and BH as reductant. This system leads to regioselective oxidation of styrenes to benzylalcohols in high yield (75-95%). Other arylalkenes are less reactive and the overall results suggest that activation of the alkene is the primary role of the catalyst.This is in clear contrast to the ideas of most other workers who claim that TPP complexes activate 02. A very high selectivity for terminal double bonds is observed for epoxidation with hydrogen peroxide using a hydroxy platinum complex as catalyst.16 This catalyst probably functions as a base providing hydroxide ion by dissociation and generates no oxidation products other than the epoxide. The reagent KHS05 in the presence of a ketone results in epoxidation of unfunctionalized alkenes. The active intermedi- ate is a dioxirane species derived from the ketone and thus if the ketone is chiral the oxidation of prochiral alkenes shows" significant enantioselectivity (enan- tiomeric excess in the range 5 to 12.5%).This is an interesting example of asymmetric induction particularly since the chiral agent is not only catalytic (rather than stoicheiometric) but can be easily recovered. The stereorelationship between the plane of a C=C moiety and the per-acid group -C03H in the transition state of an epoxidization reaction is not easily examined. However some work with the A. Onopchenko E. T. Sabourin and D. L. Beach J. Org. Chem. 1983,48 5101; 1984,49,3389. 12 B. Meunier E. Guilmet M.-E. De Carvalho and R. Poilblanc J. Am. Chem Soc. 1984 106 6668. l3 M. Fontecave and D. Mansuy J. Chem. SOC Chem. Commun. 1984 879. 14 C. C. Franklin R. B. Van Atta A. Fan Tai and J. S. Valentine J. Am. Chem.SOC.,1984 106 814. T. Okamoto and S. Oka J. Org. Chem. 1984 49 1589. 16 G. Strukul and R. A. Michelin J. Chem. SOC.,Chem. Commun. 1984 1538. " R. Curci M. Fiorentino and M. R. Serio J. Chem. Soc. Chem. Commun. 1984 155. 110 D. F. Ewing per-acid (3) (generated in situ from the acid chloride) suggests18 that the C=C is probably co-planar with the -C03H moiety (rather than orthogonal). This inference is based on a selectivity for 1,2-over 1,I-disubstituted alkenes and a cis-selectivity of between 4 and E relative to the trans compound. Catalysis of the oxidation of olefins to ketones by palladium species (variants on the Wacker process) has been reviewed." Emphasis is placed on the synthetic usefulness of this reaction. Alper and co-workers2' have found that PdC1,-CuC1,- HC1-0 is an exceedingly mild catalytic system for the hydrocarboxylation of alkenes with CO and H20 to give the branched acid only i.e.RCH=CH2 to RCH( CH3)COOH. At room temperature and atmospheric pressure terminal alkenes give the corresponding acid in 60-100% yield. A high regioselectivity is also found for alk-2-enes but not for alk-3-enes. Dienes give a monocarboxylic acid. The influence of the structure of the olefin and the nature of the mercury salt and the solvent have been studied in detail for the solvomercuriation-demercuriation reaction.21 Hg(OAc) is effective only in MeOH whereas Hg(02CF3)2 works well in primary secondary or tertiary alcohols. Much poorer selectivity for ether forma- tion is observed with the corresponding nitrate and methanesulphonate salts.A very complex dependence on olefin structure is evident. Two novel mercuriation reactions are shown in Scheme 3. The reaction with a sulphinate salt22 offers a convenient upR1CH=CR2S02Ph R'C H =cHR* jiLA R1CH2CH2NHS02C,H,Me Reagents:i HgCL2-PhS02Na H20 2 days at RT ii 50% NaOH-dioxane; iii TsNH2-Hg(N03), CH2C12; iv NaBH Scheme 3 route to vinylsulphones in 70-80% yield via an arenesulphonomercuric intermedi- ate. Reductive demercuriation of the analogous sulphonamidomercuric derivative provides an entry to N-alkylsulphonamides in 70-100% yield. Starting with a 1,4-or 1,S-diene bis-alkylation at nitrogen can be achieved thus indicating an intriguing route to N-hetero~ycles.~~ An improvement in the stereospecificity of the trans- 18 J.Rebeck L. Marshall R. Wolak and J. McManis J. Am. Chem. SOC.,1984 106 1170. 19 J. Tsuji Synfhesis 1984 369. 20 H. Alper J. B. Woell B. Despeyroux and D. J. H. Smith J. Chem SOC.,Chem. Commun. 1983 1270; B. Despeyroux and H. Alper Ann. N.Y.Acad. Sci 1984,415 148. 21 H. C. Brown J. T. Kurek M.-H. Rei and K. L. Thompson J. Org. Chem. 1984,49 2551. 22 W. Sas J. Chem. SOC.,Chem. Commun. 1984 862. 23 J. Barluenga C. Jimtnez C. Nijera and M. Yus,J. Chem. Soc. Perkin Truns. 1 1984 721. Aliphatic Compounds -Part (i) Hydrocarbons 111 metallation of vinylboranes to vinylmercury compounds has been obtained,24 par- ticularly for longer-chain alkenes such as dec-2-ene (Scheme 4). Catecholborane is the best borane for the first step and Hg(OAc),-NaOAc or HgC12 the best mercuric salt for the second step.With optimization of reaction conditions a trans-selectivity of 99% was possible. H H i \/ ii \/ R'C=CH -R' -R' c=c H/c=c\BR H/\HgOAc Reagents i BRiH; ii Hg(oA~)~-NaoAc Scheme 4 A number of minor studies of alkane hydroboration reactions includes the selection of a primary alkene to react with 9-borobicyclo[3.3.1]nonane followed by reaction with a lithium acetylide. Specific rearrangement of the primary alkyl group of the borate is induced by (Bu)~S~C~.~~ The synthesis of boranes containing the isopinocampheyl (Ipc) group has been improved to give even higher levels of optical purity enantiomeric excess (e.e.) 99.9O/0.~~ Not only does this lead to higher levels of optical induction in alkene adducts but careful recrystallization of the initial adduct boranes allows the Ipc group to exercise a normal diastereoisomeric role resulting in boranes of ca.100% e.e.27 Many optically pure compounds are thus readily accessible from alkenes by this route. Lithium triethylborohydride has been examined as a reducing agent for styrenes and similar conjugated alkenes.28 The reaction is highly regiospecific (Markovnikov) and electron deficient olefins are most reactive as would be expected. A full report has now appeared29 on the activation of alkenes by the presence of esters to hydroboration with LiBH4. The product obtained after suitable hydroly- sis is usually a dialkylborinate thus providing access to compounds such as alcohols ketones or iodides.Either vinyl- or divinyl-borinates are formed from alkynes. The regioselectivity is not very high in some cases styrene being a good example but this is generally a useful reaction. Asbestos fibres (chrysolite) have been developed3' as a novel hydrogenation catalyst for linear and cyclic alkenes. Mild conditions (1 atmosphere at 27 "C) are sufficient. Treatment of the fibres with titanocene increases the rate of H2 addition for n-alkenes but cyclohexene is unreactive suggesting that the treated and untreated fibres have different catalytic sites. Another catalyst [(hexa-1,5-diene)RhI2 is effec- tive for the hydrogenation of alkenes and polyenes in an aqueous-organic two-phase system under ambient condition^.^' In many cases the yields are 100% and carbonyl groups are not reduced.24 R. C. Larock and K. Narayanan 1. Org. Chem 1984,49 3411. 2s K. K. Wang and K.-H. Chu J. Org. Chem. 1984,49 5175. 26 H. C. Brown and B. Singaram J. Org. Chem. 1984 49 945. 27 H. C. Brown and B. Singarem J. Am. Chem Soc. 1984 106 1797. 2s H. C. Brown and S.-C. Kim,J. Org. Chem. 1984,49 1064. 29 H. C. Brown V. Somayaji and S. Narasimhan 1 0%.Chem 1984,49 4822. 30 D. Conk and C. De Blois Can. J. Chem 1984 62 392. 31 K. R. Januszkiewin and H. Alper Can. J. Chem. 1984,62 1031. 112 D. F. Ewing A novel approach to the functionalization of isoprenoids is shown in Scheme 5.32 The adduct (4) from arylsulphenylation can be converted into either the trans-allylic or internal allylic alcohols with full retention of the original stereochemistry.This method is suitable for large-scale production of oxygenated terpenes with excellent site regio- and stereo-control. The sulphenamides PhSNH(CXC,H,) (X = NOz Ii \v (4) lv R>oAc PhS '7PACvi PhS \vii Reagents i PhSCI-CH2C12,0 "C; ii Excess Et3N-DMF 20 h at 60 "C;iii 30% H202-AcOH 20 h at 20 "C; iv (MeO),P-MeOH 48 h at 20 "C; v Heat; vi TsOH 1 h at 0 "C; vii 10% KOH(aq)-EtOH 3 h at 20 "C Scheme 5 C1 Me or OMe) react readily with alkenes at ambient temperature in the presence of 1.5 equivalents of BF3-Et,0.33 High regioselectivity (Markovnikov) and stereoselectivity (trans) suggest the involvement of an episulphonium ion. The substituent effect on yield (lowest for donor substituents) is also in keeping with this electrophilic mechanism.32 Y. Masaki K. Hashimoto K. Sakuma and K. Kaji J. Chern. SOC.,Perkin Trans. 1 1984 1289. 33 L. Benati. P. C. Montevecchj and P. Spagnoko Tetrahedron Left. 1984 25 2039. Aliphatic Compounds -Part ( i) Hydrocarbons 113 Arylselenenylation is known to proceed stereospecifically to give a trans adduct. However reaction of the adduct with further ArSeCl results in formation of RSG(Ar)SeAr. This species will react with chloride sources such as Bu,N+Cl- to give the cis-dichloride in 55-100% yield for terminal and cis- and tr~ns-alkenes.~~ Arylselenenylation followed by treatment with silver nitrate in presence of HgC12 has been investigated3' as a route to nitroselenides R',SiCH(SePh)CHR2N02.This addition-substitution appears to operate with full regio- and stereo-control but yields are variable (3746%). Oxidation in the normal way gives alkenes such as Me3SiCH=CRN02. Some useful extensions to the selenosulphonation of alkenes have been Alkaneselenosulphonates RS02SePh are readily obtained from the reaction between the corresponding sulphinic and seleninic acids. The photochemically promoted reaction of these compounds with alkenes depends upon the nature of R. The addition reaction does not occur if extrusion of SO2 (to give RSePh) is favoured (e.g. for R = benzyl). Bis-sulphonylselenides (ArSO,),Se (Scheme 6) undergo radical addition to cyclohexene to yield the expected product (5) and the corresponding selenide probably formed by photodissociation of (5).Styrene affords the analogous selenide (6) as the sole product.ArS0,H -!+ ArS0,SeS02Ar -!!+ " rrso2Ar 1 iii -SeSO,Ar (5) PhCHCH2S02Ar I Se I PhCHCH2S02Ar (6) Reagents i Se0,-THF 24 h at 20 "C; ii Cyclohexene hv; iii Styrene hv Scheme 6 A comprehensive investigation3' of the addition of hydrazoic acid to 23 alkenes has demonstrated that activated systems (enol ethers) do not require a catalyst but for styrene 1,l-dialkyl- and trialkyl-alkenes TiCl promotes the formation of the azide in 5540% yield. Curiously monosubstituted and 1,2-disubstituted alkenes are unreactive. The mechanism is unclear and further study of this reaction is required.Another synthetically useful reaction recently developed38. is the reaction of styrenes at -70 "C with NOT BF in MeCN-CH2C12 to give the nitroacetamidation products (50-80% yield) with high regioselectivity but variable stereocontrol. Simple alkenes are liable to polymerize under these conditions. The new electrophilic reagent chlorine chlorosulphate (7) is obtained from C12 and SO3 at -78 "C. This reagent leads to more control over the addition reaction 34 A. M. Morella and A. D. Ward Tetrahdron Lett. 1984 25 1197. 35 T. Hayama S. Tomoda Y. Takeuchi and Y. Nomura J. Org. Chem. 1984 49 3235; Tetrahedron Lerr. 1983 24 2795. 36 Y.-H. Kang and J. L. Kice J. Org. Chem. 1984 49 1507. 37 A. Hassner R. Fibiger and D. Andisik J. Org. Chem. 1984 49 4237.38 A. J. Bloom M. Fleischmann and J. M. Mellor 1. Chem. Soc. Perkin Trans. I 1984. 2357. 114 D. F. Ewing 0 rl c1-0-s-c1 II 0 than is the case with the more reactive species C10S02F and C1OSO2CF3 and generally behaves as a good electrophile although the regioselectivity is Activation of such weak electrophiles (in this case C12) by SO3 may have wider application and further interesting results can be expected from this work. Bromina- tion4' of 1-phenylpropenes with tetrabutylammonium dichlorobromate ( i.e. BrC12) shows anti-stereospecificity but little regioselectivity in contrast to addition of bromine chloride. Reactions of alkenes with nucleophiles catalysed by palladium( 11) species have been re~iewed.~' This article also covers certain insertion reactions.Fleming has previously demonstrated that the reagent (PhMe2Si)2CuLi is a versatile source of a nucleophilic silyl group which is reactive towards various alkenic and alkynic substrates. One of the shortcomings of this reagent is the inevitable loss of the second silyl group and this is overcome42 with the mixed cuprate Me(PhMe,Si)CuLi which preferentially transfers the silyl group to an alkene. Another variant is (Me3Si),CuLi-HMPA which has the advantage that the ultimate fate of the silyl group will be a volatile species thus obviating problems of product purification. 3 Polyenes Synthesis.-Recent developments in allene chemistry have been reviewed,43 includ- ing methods of synthesis. A new route4 to terminal allenes involves the transfer of the alkynyl moiety in Ph3SnCH2C-CH to suitable alkyl bromides or iodides (chlorides react poorly).This radical reaction appears to tolerate protected amino or carboxyl functions but yields are only fair (40-60%). Several notable routes to conjugated dienes have been reported recently. The di-anion (8) reacts readily45 with monofunctional electrophiles (alkyl halides) to give the corresponding disubstituted butadienes (9; R = alkyl allyl or benzyl) in variable yield (20-70% ). Dihalides afford cyclic compounds incorporating one or more diene moiety. Extrusion of the heteroatom from simple heterocycles (10) (Scheme 7) by treatment with an aliphatic Grignard reagent produces a diene with a 2,Zgeometry exclusively,& but PhMgBr gives a mixture of Z,Z and E,E dienes.Tellurophene is the most reactive furan the least reactive heterocycle and yields are high (80%) for non-alkylated heterocycles. An E-selective route to 1,3-dienes has been developed4' using the Wittig reagent Ph2( RCH,)P=CH(alkenyl). With 39 N. S. Zefirov A. S. Koz'min and V. D. Sorokin J. Org. Chem. 1984 49 4087. 40 T. Negoro and Y. Ikeda Bull. Chem. SOC.Jpn. 1984 57 2111 2116. 41 L. S. Hegedus Tetrahedron 1984 40 2415. 42 I. Fleming and T. W. Newton J. Chem. SOC.,Perkin Trans. I 1984 1805. 43 D. J. Pasto Tetrahedron 1984 40 2805. 44 J. E. Baldwin R. M. Adlington and A. Basak J. Chem. SOC.,Chem. Commun. 1984 1284. 45 R. B. Bates B. Gordon T. K. Highsmith and J. J. White J. Org. Chem.1981 49 2981. 46 E. Wenkert M. H. Leftin and E. L. Michelotti J. Chem. SOC.,Chem. Commun. 1984 617. 47 E. Vedejs and H. W. Fang J. Org. Chem. 1984.49 210. Aliphatic Compounds -Part (i) Hydrocarbons R3 Reagents i RBr or RCI; ii R3MgBr Ni(PPh3)2C12 Scheme 7 aliphatic aldehydes an E 2 ratio of 15 :1 can be achieved in good cases which compares favourably with that for the analogous triphenyl phosphorus ylide. A similar improvement4* in established synthetic methodology is the dehydrobromination of 1,2-dibromocyclohexane with Li2C03-LiCl at 160 "C in HMPA. The diene distils from the reaction vessel directly in up to 90% yield. This procedure may well be of value in other syntheses. Dimerization of butadiene to octa-1,3,6-triene in 95% selectivity can be achieved49 with a new aminophosphinite nickel(0) complex at ambient temperature.The proton donor need be present only in equimolar amounts and the catalytic activity is very high (TN > 5000). Aprolonged reaction time results in isomerization to an octa-2,4,6- triene in 85% yield. l-substituted 1,6-dienes can be formed" by treatment of an a-chloroester with the bis-Grignard reagent BrMg(CH2),MgBr followed by lithium powder. With shorter-chain bis-Grignards a cyclic alkylidene derivative is formed. A range of polyunsaturated compounds are accessible5' by elimination from p-acetoxy sulphones (Scheme 8). The starting aldehyde can contain a double or triple OAc SO Ph iv ii RIM ,o R,+ iii R' SO Ph Reagents i PhS02CH2R2-BuLi-THF -78 "C; ii Ac,O-pyridine TsOH; iii BU'OK-THF 20 "C; iv PhS02C2Hs-BuLi-THF -78 "C 48 A.Weisz and A. Mandelbaum J. Org. Chem. 1984 49 2648. 49 P. Denis A. Montreux F. Petit G. Buono and G. Peiffer J. Org. Chem 1984 49 5274. so J. Barluenga M. Yus J. M. Concellon P. Bernad and F. Alvarez J. Chem. Res.(S) 1984 122. 51 T. Mandai T. Yanagi K. Araki Y. Morisaki M. Kawada and J. Otera J. Am. Chem. SOC.,1984,106,3670. 116 D. F. Ewing bond thus leading to enyne or diyne structures. With alkylaldehydes the double elimination gives a diene rather than an alkyne. This reaction is clearly a useful entry to complex polyunsaturated compounds of many types. A timely survey of synthetic methods has appeared52 for the class of polyenes known as dendralenes e.g.(1 1). This is a somewhat neglected area which contains many interesting synthetic problems. Reactions.-Two useful papers53 have described the reaction of allenylzinc com- pounds (RC=C=CH)ZnCl with aldehydes to give homopropargylic alcohols with high regioselectivity (98-99% ). Similar results are found with the analogous aluminium compounds but the stereocontrol is much worse in this case. The activity of the system PdCl2-CuCl2-HC1-O2-CO for hydrocarboxylation of alkenes is dis- cussed above.20 With allene this reagent will induce oxidative carbonylation to afford CH2=C(CH20Me)COOMe in 85% yield.s4 There must be some commercial poten- tial in this reaction. Arylpolyenes are of potential interest as organic semiconductors and Pd(0Ac)- (0-tolyl) has been investigateds5 as a catalyst for the arylation of 1,3-dienes and conjugated trienes.Both mono-and di-arylated species are obtained with aryl bromides and iodides but the yield is very variable depending on the structure of both aryl halide and diene. The site-selectivity of 1,3-dienes in the reaction with HgO-HBF has been studieds6 for a range of compounds. Formation of 1,4-diethers is favoured in most cases with high regio- and stereo-selectivity. 1 ,CAddition to dienes mediated by acylcobaltcar- bony1 complexes is a useful route to nitroenones.” Both 1,2- and 1,Caddition is found with PhSeC1 but subsequent reaction with a range of nucleophiles results in exclusive formation of 1,4-isomers.~~ 4 Alkynes Synthesis.-Although most types of unsaturated group have been successfully cross- linked by Pt or Ni catalysis formation of conjugated diynes by this method has proved difficult.This problem has now been resolveds9 using E-2-chloro-iodoethene with a Pd complex as coupling agent (Scheme 9). Possibly this reaction could be used to prepare conjugated poly-ynes. An analogous procedure has been described for the synthesis of Me,SiC_CCH=CHC=CSiMe3 which is likely to be a valuable precursor of poly(diacetylenes) hexatriene or other polyenes. In this case an alkynyl 52 H. Hopf Angew. Chem. Int. Ed. Engl. 1984 23 948. 53 G. Zweifel and G. Hahn J. Org. Chem. 1984 49 4565. 54 H. Alper F. W. Hartstock and B. Despeyroux J. Chem. SOC.,Chem. Commun. 1984,905. 55 T.-A. Mitsudo W.Fischetti and R. F. Heck J. Org. Chem. 1984 49 1640. 56 J. Barluenga J. Pirez-Prieto and G. Asensio J. Chem. SOC.,Perkin Trans. I 1984 629. 57 L. S. Hegedus and R. J. Perry J. Org. Chem 1984,49 2570. 58 R. S. Brown S. C. Eyley and P. J. Parsons J. Chem SOC.,Chem Commun. 1984,438. 59 E.-I. Negishi N. Okukado S. F. Lovich and F.-T. Luo J. Org. Chem. 1984 49 2629. 117 Aliphatic Compounds -Part ( i) Hydrocarbons / H iii Reagents i BuLi; ii Zn CI, ICH=CHCI Pd(PPh,),; iii NaNH,-NH,(liq) 1 h; iv H+; v Me,SiCl; vi R2Cl Scheme 9 Grignard reagent is coupled with dichloroethene.60 Direct coupling of an arylbromide or iodide with propargyl alcohol is best achieved with PhPdI( PPh& Et,N-CUI in an organic solvent.6' The resulting arylynols ArCrCCH20H are easily converted in an overall one-pot process into arylacetylenes with Mn0,-KOH in benzene.In a recent report62 the CuBr-Me2S-mediated coupling of acetylenic Grignard reagents (RCECMgBr) with propargylic tosylate (CH-CCH20Ts) is applied to the synthesis of the diyne moiety RC_CCH2CrCH for subsequent elaboration into an insect pheromone. The isomerization of long-chain aliphatic alkynes is readily promoted by LiNH(CH2)3NH2. In the presence of sodium or potassium alkoxide this reaction is even more efficient,63 and dec-2-yn-1-01 for example is converted into dec-9-yn- 1-01 with 99% selectivity (93% isolated yield) in 15 minutes at room temperature. Another intriguing aspect of this isomerization reagent is the exchange of the NH hydrogen atoms with the alkyne CH2 atoms.64 If C6H,C~C-cH20H is treated with sodium or potassium in D2NCH,CH2CH,ND2 the isomerized alkyne incorporates 86-90% deuterium.The initial position of the triple bond is relatively unimportant. Reactions.-Nitrosochlorination of alkyne carboxylic esters has been achieved6' with NOCl gas at 0°C. Terminal alkynes also give some oxime by rearrangement. The reagent TiCl,-A12Et3Cl gives rise to carbometallation of but-3-yn-1-01.~ Only one ethyl group is incorporated with high regio- and stereo-selectivity to give the resulting enol in 70% yield at -23 "C. At higher temperatures this yield is much reduced and a complex mixture of products is formed. A convenient method of a-deuteriation of terminal alkynes in the presence of other functional groups (such as OR COOR NR,) involves exchange with D20 catalysed by SO,.At 90-95 "C one pass with this reagent gives 60-8O% incorpor-ation of deuterium. A mechanism is postulated for this exchange rea~tion.~' M) J. A. Walker S. P. Bitler and F. Wude J. 0%.Chem 1984 49 4733. 61 N. A. Bumagin A. B. Ponomaryov and 1. P. Beletskaya Synthesis 1984 728. 62 R. Baker M. J. O'Mahony and C. J. Swain J. Chem. Res.(S) 1984 190. 63 S. R. Abrams Can. J. Chem. 1984 62 1333. 64 S. R. Abrams J. Org. Chem. 1984 49 3587. 65 M. M. Siddiqui F. Ahmad and S. M. Osman J. Chem. Res. (S) 1984 186; (M), 1984 1801. 66 F. W. Schultz G. S. Ferguson and D. W. Thompson J. Org. Chem. 1984,49 1736. 67 C.-A. Chang K. G. Cronin D.D. Crotts E. Dunach T. R. Gadek and K. P. C. Vollhardt J. Chem. SOC.,Chem. Commun. 1984. 1545. 118 D. F. Ewing Organocuprates ( i. e. RMgBr-CuBr-Me,S) can react with propargylic ethers and acetates in two competing ways (Scheme The usual alkylation reaction is predominant with acetates using Et,O as solvent but the reverse is true for methyl ethers using THF as solvent. The mechanism which accounts for all the subtleties of these results is likely to be complex and may involve a Cu"' species. The influence of reactant structure on the ratio of allenic to alkynic reduction products suggests that these may arise by different mechanisms. CH,CH,C=CR + CH,CH=C=CHR 3 '..C R =C H3C HC I ox CH3CHCECR + CH,CH=C=CREt I Et X = Me,COMe Reagents i EtMgBr-CuBr-Me,S-THF -30 "C; ii H20 Scheme 10 C.Sahlberg and A. Claesson J. Org. Chem. 1984 49 4120.