5 Aliphatic Compounds Part (i) Hydrocarbons By L. HILL and S. E. THOMAS Department of Chemistry University of Warwick Coventry CV4 7AL 1 Alkanes Functionalization of alkanes continues to attract the attention of many research groups. It has been demonstrated for example that asymmetric hydroxylation of ethylbenzene by iodosylbenzene occurs in the presence of catalytic amounts of a homochiral binaphthyl iron porphyrin to give a 40% yield of 1-phenylethanol of 41% e.e.' New methods for inserting an oxygen atom into carbon-hy,drogen bonds include the use of a novel dioxirane species methyl(trifluoromethyl)dioxirane,* catalytic oxidation with RuO generated in situ from RuC13 and Na10,,3 and the use of the oxidizing solution formed when fluorine is passed through wet a~etonitrile.~ All these methods work efficiently and exhibit good regioselectivity for tertiary carbon-hydrogen bonds.It has been reported that in the presence of SbF5 excess dichloromethane or dibromomethane will chlorinate or brominate respectively saturated hydrocarbon^,^ and caesium fluoroxysulphate has been used to fluorinate saturated hydrocarbons.6 2 Alkenes Synthesis.-The Wittig reaction and related processes have once again been the subject of numerous reports. A review covering developments in the area since 1978 has been published.' a$-Unsaturated esters and ketones have been synthesized in good yield and with high E-stereoselectivity by a reaction which is heralded as the first example of a catalytic Wittig-type reaction.8 The products were generated by adding various aldehydes to methyl bromoacetate or a-bromoacetophenone at room temperature in the presence of triphenyl phosphite potassium carbonate and catalytic amounts of tri-n-butylarsine (Scheme 1).The tri-n-butylarsine is thought to be regenerated by reduction of the tri-n-butylarsine oxide by the triphenyl phosphite. Stoichiometric amounts of tri-n-butylarsine and zinc powder have also ' J. T. Groves and P. Viski 1. Am. Chem. Soc. 1989 111 8537. R. Mello M. Fiorentino C. Fusco and R. Curci J. Am. Chem. SOC.,1989 111 6749. A. Tenaglia E. Terranova and B. Waegell Tetrahedron Lett. 1989 30,5271. S. Rozen M. Brand and M. Kol. J. Am. Chem. SOC.,1989 111 8325. G. A. Olah A.-H. Wu and 0. Farooq J. Org. Chem. 1989 54 1463.S. Stavber and M. Zupan Tetrahedron 1989 45 2737. ' B. E. Maryanoff and A. B. Riitz Chem. Rev. 1989 89 863. * L. Shi W. Wang Y. Wang and Y.-Z. Huang J. Org. Chem. 1989 54 2027. 87 L. Hill and S. E. Thomas + P(OPh) A R + OP(OPh), R+O + BrnX -x R = alkyl aryl 61-87'/0 X = COzMe COPh Reagents i cat. BuiAs K,CO been shown to mediate the conversion of aldehydes and methyl bromoacetate into a,P-unsaturated esters.' Use of the base sodium hexamethyldisilazane to generate iodomethylenetriphenylphosphoranefrom the phosphonium iodide (1) facilitated the development of a high-yielding stereoselective procedure for the synthesis of (Z)-l-iodoalk-l-enes.'o~'' (Ph,PCH,I) I-The reductive dimerization of aldehydes and ketones by low-valent titanium species to give alkenes is the subject of two reviews published this ear.'^,'^ An optimized procedure for this reaction has also been reported in an attempt to reduce the confusion which has arisen as a result of the numerous reducing systems used for the tran~formation.'~ TiCI3 is converted into the crystalline complex TiC13(dimethoxyethane)l.5, which is then used as the titanium source in the coupling reaction.The results are reproducible even when aged batches of TiC13 are used and the complex is by far the most effective titanium source employed to date. For example coupling of diisopropyl ketone to produce tetraisopropylethene proceeds to give 12% yield using TiC13/LiA1H4 37% yield using TiC13/Zn-Cu and 87% yield with TiC13(dimethoxyethane)l,5/Zn-Cu.It has been discovered that 3-hydroxycarboxylic acids readily undergo an oxidative decarboxylation-deoxygenation process on heating with oxophilic vanadium com- plexes (Scheme 2).15 It is of note that the reactivity provides a direct link between 'aldol-type' products and alkenes. Conversion of acyclic ketone enamines into either a 2-or an E-alkene may be determined by choice of reagents for a hydroboration-elimination sequence.I6 For R OH R R R = alkyl aryl Reagents i CI,V=O or CI,V=NTol A Scheme 2 Y. Shen B. Yang and G. Yuan J. Chem. SOC.,Chem. Commun. 1989 144. 10 G. Stork and K. Zhao Tetrahedron Lett. 1989 30,2173. H. J. Bestmann H. C. Rippel and R. Dostalek Tetrahedron Lett. 1989 30 5261. 12 J. E. McMurry Chem.Rev. 1989 89 1513. D. Lenoir Synthesis 1989 883. 14 J. E. McMurry T. Lectka and J. G. Rico J. Org Chem. 1989 54 3748. l5 I. K. Meier and J. Schwartz J. Am. Chem. SOC.,1989 111 3069. I6 B. Singaram C. T. Goralski M. V. Rangaishenvi and H. C. Brown J. Am. Chem. SOC.,1989 111 384. Aliphatic Compounds- Part (i) Hydrocarbons example hydroboration of (E)-1-morpholino-1-phenylprop-1-ene by 9-BBN fol-lowed by methanolysis affords an 80% yield of (2)-1-phenylprop-1-ene whereas hydroboration by borane-methyl sulphide followed by methanolysis and oxidation with alkaline hydrogen peroxide gives a 50% yield of (E)-1-phenylprop-1-ene -(Scheme 3). . .. m 80% Ph ...... Ph>-\ I 111 II IV ~ 50% Ph Reagents i 9-BBN; ii MeOH; iii H3B SMe,; iv alkaline H202 Scheme 3 Reviews of synthetic and theoretical aspects of pyramidalized alkenes17 and bridgehead alkenes" have been published.Reactions.-Further uses of the reagent N-acetoxyaminoquinazolonein aziridination reactions have been reported. Vinylsilanes and vinylstannanes have been aziridi- nated19 and the vinylsilane derivatives converted into azirines (Scheme 4). In contrast to peracid epoxidation of cyclohex-3-en-1-01 which occurs with poor stereoselec- tivity aziridination of cyclohex-3-en- 1-01 occurs with high stereoselectivity to give the cis derivative (2) in 70% isolated yield.20 Q %Me3 I =( 2&SiMe3 -Ph Ph Ph = Q-NHOAc; ii CsF I NHOAc Scheme 4 Linked bis-tartrate esters (3) have been used as ligands in the Sharpless epoxidation reaction in order to gain information about the structure of the active catalytic species.21 The conclusions drawn from results obtained with these ligands are in agreement with conclusions from kinetic studies and support the hypothesis that the substrate is epoxidized by a C2-symmetric dimer and not by a monomeric species W.T. Borden Chem. Rev. 1989 89 1095. 18 P. M. Warner Chem. Rev. 1989 89 1067. 19 R. S. Atkinson and B. J. Kelly J. Chem. Soc. Chem. Commun. 1989 836. 20 R. S. Atkinson B. J. Kelly and C. McNicolas J. Chem. Soc. Chem. Commun. 1989 562. P. R. Carlier and K. B. Sharpless J. Org. Chem. 1989 54 4016. L. Hill and S. E. Thomas present even in a small equilibrium amount. Transition-metal-catalysed epoxidations have been reviewed.22 Asymmetric dihydroxylation of alkenes has been intensely studied this year.Further examination of the osmium-catalysed process in which Cinchona alkaloid derivatives are used as chiral ligands revealed that two diol-generating catalytic cycles are involved (Scheme 5).23 The first cycle turns over faster and produces diol ‘A HO OH Scheme5 in high enantiomeric excess whereas the second cycle turns over more slowly and exhibits low/opposite enantiofacial selectivity. Thus slow addition of the alkene to the reaction mixture minimizes production of diol by the second cycle and increases the enantiomeric excess of the product. Under ‘slow addition’ conditions the scope of this asymmetric dihydroxylation process is much increased and includes simple hydrocarbon alkenes aromatic alkenes allylic alcohols a$-unsaturated esters etc.22 K. A. Jorgensen Chem. Rev. 1989 89 431. 23 J. S. M. Wai I. Marko J. S. Svendsen M. G. Finn E. N. Jacobsen and K. B. Sharpless J. Am. Chem. SOC.,1989 111 1123. Aliphatic Compounds- Part ( i) Hydrocarbons Chemical yields for these reactions are 80-95% and enantiomeric excesses are 50-89Y0.~~ The homochiral diamine (4)25 and the homochiral bipyrrolidine ( 5)26 both give high yields and enantiomeric excesses in stoichiornetric osmium tetroxide dihydroxylations (8 1-95% chemical yield 92-98% e.e. and 79-97% chemical yield 82-97% e.e. respectively). Optically active 1 -arylalkanols have been generated by asymmetric hydroboration of styrenes under cationic rhodium catalysis (Scheme 6).27The observed Markov- nikov selectivity is ascribed to q3-benzylrhodium intermediates formed by addition of a cationic rhodium hydride species to the styrenes.Investigations into the stereochemical outcome of hydroboration-oxidation of chiral allylic alcohol deriva- tives28 and allylic amine derivative^^^ using either 9-BBN or a catechol-borane/ rhodium catalyst system for the hydroboration step reinforce previous observations that the two methods may give complementary stereochemical results. An efficient procedure for the conversion of terminal alkenes into one-carbon homologated primary alkanenitriles has been developed (Scheme 7).30 **,/ + HB’*n ‘0 OH Yield 7698% e.e.76-96% Reagents i cat. [Rh(COD),ICBF, cat. (+)-BINAP; ii H202 NaOH Scheme 6 R = alkyl H 72-98% Reagents i (cyclohexyl)2 BH; ii CuCN; iii Cu(OAc),. H20 Cu(acac) Scheme 7 24 B. B. Lohray T. H. Kalantar B. M. Kim C. Y. Park T. Shibata J. S. M. Wai and K. B. Sharpless Tetrahedron Lett. 1989 30 2041. 25 E. J. Corey P. D. Jardine S. Virgil P.-W. Yuen and R. D. Connell J. Am. Chem. Soc. 1989 111 9243. 26 T. Oishi and M. Hirama J. Org. Chem. 1989 54 5834. 21 T. Hayashi Y. Matsumoto and Y. Ito J. Am. Chern. Sac. 1989 111 3426. 28 K. Burgess and M. J. Ohlmeyer Tetrahedron Lett. 1989 30,395. 29 K. Burgess and M. J. Ohlmeyer Tetrahedron Lett. 1989 30 5857. 30 Y. Masuda M. Hoshi and A. Arase J. Chem. SOC.,Chem. Commun. 1989 266. L.Hill and S. E. Thomas Interesting results have been obtained using an electroreductive intermolecular coupling of alkenes and ketones.31 For example coupling of ketone (6) with 4-methylpenta-l,3-diene using a carbon fibre cathode in DMF gave bisabolol (7) in 80% yield. The reaction of butan-2-one with hexa- 1,Sdiene could be controlled to give either the 1 :1 adduct (8) or the 2 1 adduct (9) by altering the amount of electricity used. HO Me HO Me (8) Synthetic routes to the R-and S-enantiomers of the sulphonimidamide (10) have been published. Both enantiomers were converted into reagents thought to be the corresponding chiral selenium diimide reagents (1 1) which were then used in allylic amination reactions of alkene~.~~ The diastereoisomeric excesses generated were modest [amination of methylenecyclohexane with (1 1) gave allylic amide (12) in 42% d.e.1 but significant.n (1 1) [derived from (R)-(lo)] 3 Polyenes Synthesis.-It has been demonstrated that the [2,3] Wittig rearrangement may be used for the synthesis of chiral allenes of high optical purity and predictable absolute c~nfiguration.~~ For example conversion of the propargylic alcohol (13) (prepared in 93% e.e. by reduction of the corresponding ketone with Darvon alcohol/LiAlH,) into the stannylmethyl ether (14) followed by treatment with Bu"Li at -78 "C gave allene (15) of 93% e.e. in 62% yield based on (13). The results provide evidence in support of a non-dissociative pathway for this type of rearrangement.31 T. Shono S. Kashimura Y. Mori T. Hayashi T. Soejima and Y. Yamaguchi J. Org. Chem. 1989 54 6001. 32 S. Tsushima T. Yamada T. Onami K. Oshima M. 0. Chaney N. D. Jones and J. K. Swartzendruber Bull. Chem. SOC.Jpn. 1989 62 1167. 33 J. A. Marshall E. D. Robinson and A. Zapata J. Org. Chem.. 1989 54 5854. Aliphatic Compounds- Part (i) Hydrocarbons 93 H <OH H / Bu-= Me \ Me Bu)c=c=c.Me A review of the chemistry of cyclic allenes (ten-membered to five-membered rings and bicyclic systems) and cyclic butatrienes (ten-membered to five-membered rings) has been published this year.34 Once again numerous syntheses of substituted buta-l,3-dienes have been reported. Substituted 2,5-dihydrothiophene S,S-dioxides which are stable precursors of the corresponding buta-l,3-dienes have been prepared uia reactions of 3-methylene-2,3-dihydrothiophene S,S-dioxide with electrophiles and nu~leophiles.~~ The method was applied to the synthesis of (*)-ipsenol (Scheme 8).New approaches to sulphur-substituted buta-1,3-dienes (16) (17),36(18),37 and ( 19)38 have been published. ji-/1-ry i ii-iv o//S\\ S“o (*)-ipsenol 50% 0 50% Reagents i Me2CHCH,CH,N02 1,1,3,3-tetramethylguanidine; ii H202/ K2CO3;iii NaBH,; iv A Scheme 8 SPh R = alkyl aryl vinyl R = alkyl aryl vinyl (16) (17) S02Tol + R R = H,SO,Ph R = alkyl CH=CHMe OAc C1 (18) (19) Intermolecular coupling of two alkynes to give buta- 1,3-dienes has been achieved.39 Hydrozirconation of one alkyne with Schwartz’s reagent [(qS-CSH5)2ZrHC1] yields a chlorovinylzirconocene which is converted into a methylvinylzirconocene using either methyllithium or methylmagnesium bromide.Loss of methane occurs at room 34 R. P. Johnson Chem. Rev. 1989,89,1111. 35 T.Nomoto and H. Takayama J. Chem. SOC.,Chem. Commun. 1989 295. 36 W.H. Pearson K.-C. Lin and Y.-F. Poon J. Org. Chem. 1989,54 5814. 37 A. Padwa B. Harrison S. S. Murphee and P. E. Yeske J. Org. Chem. 1989,54 4232. 38 T.G.Back E. K. Y. Lai and K. R. Muralidharan Tetrahedron Left. 1989,30 6481. 39 S.L. Buchwald and R. B. Nielsen J. Am. Chem. SOC., 1989.111 2870. L. Hill and S. E. Thomas R1 R' 11 ... &R2 .. 111 ___ CP& 'c1 Me CH4 R2 R3 U R' R' J/ \\R4 45-74% cp2zr$R2 2 R3 53-87% Reagents i Cp,ZrHCl; ii MeMgBr or MeLi; iii TMSCI; iv R3-E-R4; v H30+; vi I2 Scheme 9 temperature to give an alkyne complex which couples with a second alkyne to form a metallacyclopentadiene.The metallacycle is converted into a diene on treatment with aqueous acid or a 1,4-diiododiene on treatment with iodine (Scheme 9). In most cases the sequence can be carried out as a one-pot procedure and in many cases only a single regioisomer is observed. Insect pheromones containing an E,Z or Z,Econjugated diene have been synthe- sized by adding (2)-dialkenylcuprates to phenylthioacetylene and then cross-coup- ling the resulting alkadienyl sulphides with Grignard reagents in the ,presence of a nickel(11) cataly~t.~' the pheromone of For example (557E)-dodeca-5,7-dien-l-ol the forest tent caterpillar Malacosoma disstria was synthesized in 57% yield and 98% isomeric purity from phenylthioacetylene (Scheme 10).--SPh 2EEO-SPh 74% .. ... 11. 111 \ HO EE = ethoxyethyl Yield 77% -5Z,7 E 98% Reagents i EEO-),CuLi; ii -MgBr NiC12(dppe); iii p-TsOH Scheme 10 Symmetrically functionalized 1,3-dienes have been efficiently generated using a palladium(I1)-catalysed homocoupling of 1-alkenyl~tannanes.~~ 40 V. Fiandanese G. Marchese F. Naso L. Ronzini and D. Rotunno Tetrahedron Lett. 1989 30,243. 41 G. A. Tolstikov M. S. Miftakhov N. A. Danilova Y. L. Vel'der and L. V. Spirikhin Synthesis 1989,633. Aliphatic Compounds- Part ( i) Hydrocarbons Nickel( 0)-catalysed couplings of Grignard reagents with 5-alkyl-2,3-dihydrofurans have been elegantly exploited in a stereoselective iterative approach to isoprenoid chains.42 Each cycle involves alkylation of 5-lithio-2,3-dihydrofuranwith a homoally- -lic iodide nickel(o)-catalysed coupling with methylmagnesium bromide and conver- sion of the alcohol thus produced to the corresponding iodide (Scheme 11).The dihydropyran Wenkert reaction has been applied to the synthesis of (2)-undec-Cen-1-01 (20) an intermediate in syntheses of the insect pheromones heptacosa-7,ll- diene nonacosa-7,ll -diene and pentacosa-7,l 1-diene.43 y1i_ 97% .. . 11-IV 1 84% 98% .. . I 11-IV 81% 90% 11 I Reagents i ; ii MeMgBr Ni'; iii MeS02CI; iv NaI Li Scheme 11 Reactions.-Efficient addition of a propynylic moiety to the P position of an a,P-unsaturated carbonyl compound using metal derivatives is difficult as the reaction tends to give a mixture of 1,2- and 3,4-addition pxoducts and a mixture of propynylic and allenic products.It has been reported however that triphenylstan- nylallenes (21) may be regarded as effective propynylic anion equivalents as they 42 P. Kocienski S. Wadman and K. Cooper J. Org. Chem. 1989 54 1215. 43 T. L. Davis and D. A. Carlson Synthesis 1989 936. L. Hill and S. E. Thomas RC H =C =C H SnPh R R = H Me R = H Me (211 (22) add to cyclic and acyclic a$-unsaturated ketones in the presence of titanium tetrachloride to give P-prop-2-ynylic ketones (22) in good yield (59-8~4.~~ The silver( 1)-catalysed cyclization of a series of optically active allenic amines (23) has been examined.45 The product 2-substituted pyrrolidines (24) were formed in up to 80% diastereoisomeric excess (X = CONHMe and CH,NHMe) and the degree of asymmetric induction observed appeared to reflect the ability of the stereocentre to co-ordinate silver( I) ions.c\\c,\ NH PhAx Ph4 X = Me CO,Me CH,OH CONHMe CH,NHMe (23) (24) A double asymmetric hydrogenation of a conjugated diene has been Thus hydrogenation of buta- 1,3-diene-2,3-dicarboxylic acid (25) in the presence of catalytic quantities of Ru2Cl4{( R)-binap},NEt gave (S,S)-2,3-dimethylsuccinic acid (26) in 98% d.e. 96% e.e. and 77% yield. Reduction of anhydrous magnesium chloride with lithium in tetrahydrofuran using naphthalene as an electron carrier gives highly reactive magnesium.Addition of 1,3-dienes to this reagent produces substituted but-2-ene-l,4-diylmagnesiumcom-pounds e.g. (27) which react with electrophiles to give either 1,2- 1,4-,or 2,l-addition products depending on the substrate/electrophile employed.47 Two transition-metal-assisted reactions which lead to 1,4-functionalization of 1,3-dienes have been reported. Reduction of the bis[tricarbonylchromium(~)]com-44 J.-I. Haruta K. Nishi S. Matsuda Y. Tamura and Y. Kita J. Chern. SOC.,Chern. Cornrnun. 1989 1065. 45 D. N. A. Fox D. Lathbury M. F. Mahon K. C. Molloy andT. Gallagher J. Chern. Soc. Chern. Cornrnun. 1989 1073. 46 H.Murarnatsu H. Kawano Y. Ishii M. Saburi and Y. Uchida J. Chern. Soc, Chern. Cornrnun. 1989,769. 47 H. Xiong and R. D. Rieke J. Org. Chern. 1989 54 3247. 97 Aliphatic Compounds- Part ( i) Hydrocarbons plex (28) with lithium naphthalenide followed by reaction of the resulting dianion with alkyl halides and finally oxidative cleavage of the tricarbonylchromium( 0) groups gives rise to substituted 1,4-diphenylbut-2-enes (29) in 49-89'/0 yield.48 Stirring iodomethane with 1,3-dienes in the presence of Bu,NFe(CO),NO followed by addition of carbon nucleophiles leads to 1,4-acylation/alkylationand the produc- tion of alkenes (30) in 35-60% yield.49 &Nu 0 R = H,alkyl \/ Nu = CH(CO,Me), CH(COMe)CO,Me R = alkyl ally1 CMe( CO,Et) (29) (30) Examination of zirconium-mediated cyclizations of 1,6- and 1,7-dienes has revealed some very interesting results.Treatment of hepta-l,6-diene with ( q5-C5H5)2ZrC12 and butyllithium followed by bromination gave trans-1,2-bis(bromomethy1)cyclopentane. However treatment of the same diene with ( 7'-C5Me5)ZrC1 and sodium amalgam followed by bromination gave the isomeric cis-dibromide (Scheme 12).50 This contrast in stereochemical outcome was also observed with substituted hepta-l,6-dienes but application of the ( T~-C~H,),Z~C~,-,-: mediated reaction to octa-1 ,7-diene prod~cts.~~*~'- gave predominantly cis disubstituted Q:r 97%88% trans \ iii ii Q:r 78% 99% cis Reagents i (V~-C~H~)~Z~CI~, BuLi; ii Br,; iii ( ~15-CSMe,)ZrC1, Na/Hg Scheme 12 4n R.D. Rieke K. P. Daruwala and M. W. Forkner J. Org. Chem. 1989 54 21. 49 K. Itoh S. Nakanishi and Y. Otsuji Chem. Lett. 1989 615. 50 W. A. Nugent and D. F. Taber J. Am. Chem. SOC.,1989 111 6435. 51 C. J. Rousset D. R. Swanson F. Lamaty and E.-I. Negishi Tetrahedron Lett. 1989 30,5105. L. Hill and S. E. Thomas The reaction of tetraarylhexapentaenes (3 1) with catalytic quantities of Nio has been investigated and found to give the novel [4]radialene system (32) in 40-64% yield.52 Ar Ar Ar Ar Ar )=c=c=c=c< Ar Ar (31) Several successful palladium-catalysed cyclizations of trienyl triflates have been reported. For example heating trienyl triflates (33) in the presence of catalytic quantities of palladium gave the spirotricyclic dienones (34) in 72% (n = 1) and 70% (n = 2) yield re~pectively.~~ 4 Alkynes Synthesis.-Hydroxyalkynes or ynols are tautomers of ketenes and triple bond analogues of enols.The first direct observation of an ynol was made in 1986 when ethynol was generated in the gas phase and characterized by its mass spectrum. Ethynol (35) has been prepared again this year by irradiation of 3-hydroxy- cyclobuten- 1,2-dione (semisquaric acid) in an argon matrix and its infrared spectrum recorded.54 The synthetic approach to ethynol was then adapted to generate and observe ynols in solution for the first time.55 Phenylynol was generated by flash photolysis of phenylhydroxycyclopropenone (36) (or its methyl ether) and mesity- 52 M. Iyoda Y.Kuwatani and M. Oda J. Am. Chem. SOC.,1989 111 3761. 53 N. E. Carpenter D. J. Kucera and L. E. Overman J. Org. Chem. 1989 54 5846. 54 R. Hochstrasser and J. Win Angew. Chem. Int. Ed. Engl. 1989 28 181. 55 Y. Chiang A. J. Kresge R. Hochstrasser and J. Win J. Am. Chem. Soc. 1989 111 2355. Aliphatic Compounds- Part (i) Hydrocarbons lynol was obtained from mesitylhydroxycyclopropenone (or its methyl ether) in an analogous manner. Alkynyl phosphate esters (37) have been prepared by decomposi- tion of readily available alkynyl(pheny1)iodonium phosphates (38)? 0 II 0 II OR2 R',R2 = alkyl + R'-1Ph *\'O0' R2 0R2 Optically active 3-hydroxyalkynes have been synthesized from allyl alcohol precur- sors. Treatment of optically active CU,~ -epoxy alcohols obtained from allyl alcohols by the Sharpless epoxidation with triphenylphosphine and carbon tetrachloride gave a,P -epoxy chlorides which on exposure to butyllithium were transformed into 3-hydroxyalkynes without loss of stereochemical integrity (Scheme 13).57 - HO R'&\ LR1&\ R1-&= R2 OH R2 c1 R2 67-91% Yield 7694% e.e.71-96% Reagents i PPh, CCI,; ii BuLi Scheme 13 Ketones activated by P-carbonyl or phenyl groups have been efficiently dehydrated to alkynes using (Ph3P+),0 20Tf and trieth~lamine,~~ and a convenient method for preparing 1-iodoalk- 1 -ynes which involves treating terminal alkynes with bis(trimethylsily1) peroxide and zinc iodide in the presence of butyllithium has been reported.59 Cycloalkynes such as cycloheptyne cyclohexyne benzyne and cyclopentyne which are transient molecules in the free state are stabilized by co-ordination either to mononuclear electron-rich transition metal fragments or by formation of dinuclear or polynuclear metal complexes.The chemistry of these complexes has been reviewed.60 The enediyne (39) has been synthesized by coupling the dibromide (40) with trimethylsilylethyne and alkyne (41),61 and syntheses of enediynes (42) and (43) have been reported.62 A three-component synthesis of 1,5-dien-3-ynes has been designed.63 The process utilizes a palladium-catalysed coupling of an alkenyl iodide with the carbon-tin 56 P. J. Stang T. Kitamura M. Boehshar and H. Wingert J. Am. Chem. SOC.,1989 111 2225.57 S. Takano K. Samizu T. Sugihara and K. Ogasawara J. Chem. SOC.,Chem. Commun. 1989 1344. 58 J. B. Hendrickson and M. S. Hussoin Synthesis 1989 217. 59 A. Ricci M. Taddei P. Dembech A. Guerrini and G. Seconi Synthesis 1989 461. 60 M. A. Bennett and H. P. Schwemlein Angew. Chem. Int. Ed. EngL 1989 28 1296. 6' A. G. Myers M. M. Alauddin M. A. M. Fuhry P. S. Dragovich N. S. Finney and P. M. Harrington Tetrahedron Letr. 1989 30,6997. 62 R. Gleiter and R. Merger Tetrahedron Lett. 1989 30,7183. 63 Y. Hatanaka K. Matsui and T. Hiyama Terrahedron Left. 1989 30. 2403. L. Hill and S. E. Thomas TBDMSO ? \ TMS EtO,Cs YOMe )=\ OMe Br Br (39) n = 1,2 n = 1,2 (42) (431 bond of trimethylstannyl( trimethylsily1)ethyne followed by a second coupling reac- tion between the resulting intermediate and a second alkenyl iodide.The reaction proceeds with retention of the double bond geometry of the alkenyl iodides and has been used to synthesize several conjugated (E,E)-,(E,Z)-,and (2,Z)-1,5-dien-3-ynes including a naturally occurring polyenyne isolated from Grindelia humilis Hook (Scheme 14). -58% Reagents i Ac0-l cat. Pd(PPh,),; ii I (Et2N)$+ Me,SiF; (TASF) Scheme 14 Reactions.-A convenient chemoselective method for semihydrogenation of alkynes has been reported.64 A combination of acetic acid and the silicon hydride tetramethyl- dihydrodisiloxane in the presence of a palladium( 0)catalyst results in rapid reduction of alkynes to alkenes. Although the &-selectivity observed with some substrates is not universal it is of note that the chemoselectivity is such that the method may be used in the presence of conjugated alkenes and nitro groups.A ‘heterogenized homogeneous’ catalyst consisting of a palladium complex anchored in montmoril- lonite clay has also been reported to be useful for semihydrogenation of alkyne~.~~ Alkynes have been efficiently silylformylated using dimethylphenylsilane and carbon monoxide in the presence of catalytic quantities of €UI,(CO),~(Scheme 15).66 It was observed that the terminal carbon of alk-1-ynes is silylated specifically and that bulky substituents on the alkyne inhibit the silylformylation process. 64 B. M. Trost and R. Braslau Tetrahedron Lett. 1989 30 4657.65 G. V. M. Sharma B. M. Choudary M. R. Sarma and K. K. Rao J. Org. Chem. 1989 54 2997. 66 I. Matsuda A. Ogiso S. Sato and Y. Izumi J. Am. Chem. Soc. 1989 111 2332. Aliphatic Compounds- Part ( i) Hydrocarbons R’ R2 R1-E-RZ + Me,PhSiH >=( OHC’ ‘SiMe2Ph R’ = H alkyl SiMe, Ph 43-99% R2= H Me Ph CO,R Reagents i CO (30kg cm-’) cat. Rh,(CO),2 Et3N Scheme 15 Alkyl radicals and perfluoroalkyl radicals have been generated from alkyl iodides and perfluoroalkyl iodides respectively by reaction with triethylborane and then added to alkynes to give either alkenyl iodides or fluorinated alkenyl iodide^.^',^^ NbC13( dimethoxyethane) reacts with alkynes to give complexes which on hydroly- sis yield cis-alkenes. Thus the complexes may be regarded as 1,2-alkene dianion equivalents.This relationship has been exploited in a regioselective synthesis of 2,3-disubstituted-l-naphthols which involves coupling alkynes with 1,2-aryldial- dehydes in the presence of NbCl,(DME) (Scheme 16).69 R’ = alkyl aryi R2 = alkyl aryl SiR 53-87% Reagents i NbC13(DME); ii KOH Scheme 16 Several interesting transition-metal-promoted cyclizations of 1 n-diynes have been reported this year. 1,6- 1,7- and 1,8-Diynes with alkyl aryl or trimethylsilyl terminal substituents have been shown to undergo cyclization with 2,6-dimethylphenyl isocyanide in the presence of a stoichiometric amount of bis(cyc1o-octadiene)nickel(o) to form bicyclic iminocyclopentadienes (44).70 A nickel(0)-catalyzed synthesis of bicyclic pyrones (45) from 1,6- and 1,7-diynes and carbon dioxide which was previously only effective with dialkyl-substituted diynes has been extended to unsubstituted diynes by changing the phosphine incorporated into the catalyst.71 A successful nickel(o)-catalysed hydrosilylation of 1,7-diynes to give 1,2-dialkylidenecyclohexaneswith a (2)-vinylsilane moiety (46) has been reported,72 @N*r (yJ0 KSi(0EtL R’ R R’= Et Ph SiMe (44) (45) (46) 67 Y.Ichinose %-I. Matsunaga K. Fugami K. Oshima and K. Utimoto Tetrahedron Lett. 1989 30,3155. 68 Y. Takeyama Y. Ichinose K. Oshima and K. Utimoto Tetrahedron Lett. 1989 30 3159. 69 J. B. Hartung and S. F. Pedersen J. Am. Chem. Soc. 1989 111 5468. 70 K. Tamao K. Kobayashi and Y. Ito J. Org. Chem.1989 54 3517. 7‘ T. Tsuda S. Morikawa and T. Saegusa J. Chem. Soc. Chem. Commun. 1989 9. 72 K. Tamao K. Kobayashi and Y. Ito J. Am. Chem. Soc, 1989 111. 6478. L. Hill and S. E. Thomas and 1 ,n-diynes have been cyclized to macrocyclic enynes under palladium catalysis.73 For example diyne (47) was cyclized to the 26-membered lactone (48) in 70% yield. The S,S-acetal (49) has been cyclized to the tetracyclic product (50).74Removal of the chiral auxiliary gave material of 90% e.e. 0 *do** f-7-C02 E COZEt 0 (47) C <SiMe3 It 73 B. M. Trost S. Matsubara and J. J. Caringi J. Am. Chem. Soc. 1989,111 8745. 74 D. Guay W. S. Johnson and U. Schubert J. Org. Chem. 1989,54 4731.