5 Aliphatic Compounds Part (i)Hydrocarbons By B. V. SMITH Department of Chemistry King's College London (KQC) Kensington Campus Campden Hill Road London W8 7AH 1 Alkanes The synthesis of very long chain alkanes has been reported; chains of greater than 150 carbons undergo folding to the crystalline state. Methods for the synthesis of long chain alkanes with lateral side chains have also been developed. Throughout this work great emphasis was placed on the elimination from the reactants of minor constituents that would lead to unwanted by-products in the process of molecular doubling used to construct such systems.'-3 An interesting report of direct aliphatic fluorination has appeared! Careful fluorination at low temperature led to direct replacement of tertiary hydrogens; thus 3-methylnonane in 1 :1 CFCI3-CHCl3 at -78 "C afforded 3-fluoro-3-methylnonane (65% ).Protected alcohols of suitable structure e.g. p-nitrobenzoates also gave replacement products. Some selectivity was observed in the fluorination since the p-nitrobenzoate of 3,7-dimethyloctan-3-01 showed reactivity at the C- H remote from the ester function. A modified zeolite catalyst has been used in a study of alkane oxidation. Zeolite 5Acontaining either Fe" or Pd" acts as an inorganic mimic of the enzyme alkane-w- hydroxylase; for linear alkanes the primary :secondary oxidation ratio for the first three carbons is ca. 0.6.5 A further report of the Gif system for functionalization of saturated hydrocarbons has appeared with special reference to a cyclic system.6 The partial oxidation of methane (02-Si02) to form CH20 was contrasted with the complete oxidation achieved by N20.7 Regioselective photocatalysed formation of alk- l-enes from alkanes was noted when RhCI(CO)(PMe3)2 in an atmosphere of CO was used.8 Photolysis of bis- E.Igner 0.I. Paynter D. J. Simmonds and M. C. Whiting J. Chem. Soc. Perkin Trans. 1 1987. 2447. 'I. Bidd D. W. Holdup and M. C. Whiting J. Chem. SOC.,Perkin Trans. 1 1987 2455. E. A. Adegoke H. Ephraim Bassey D. J. Kelly and M. C. Whiting J. Chem. SOC.,Perkin Trans. I 1987 2465. 'S. Rozen and C. Gal 1.Org. Chem. 1987 52 4928. N. Herron and C. A. Tolman J. Am. Chem. SOC.,1987 109 2837. D. H. R. Barton J. C. Beloeil A. Billion J. Boivin J.-Y. Lallemand and S.Mergui Helu. Chim. Acta 1987 70 273. ' S. Kasztelan and J. B. Moffat 1.Chem. SOC.,Chem. Commun. 1987 1663. T. Sakakura T. Hayashi and M. Tanaka Chem. Lett. 1987 859. 93 94 B. K Smith diphosphine complexes of iron in the presence of e.g. pentane led to a mixture of pent-1 -ene and a bis-diphosphinepentenyl iron hydride.' Electrophilic conversions of methane have been reviewed." 2 Alkenes Synthesis.-Dehydration of 1-( p-alkoxyphenyl)-l,2-diphenylbutan-l-ols by CS and base is a stereoselective process in contrast to the acid-catalysed reaction. Thus (1) gave alkene with 2 E ratios of 21 1and 2 1 respectively. This selection was applied in the synthesis of 2-(2), Tamoxifen an anti-cancer drug whose activity is isorner- dependent.l1 Stereospecific deoxygenation of 1,2-diols via the 2-dimethylamino-l,3- dioxolane (3) and triflic anhydride in the presence of di-isopropylethylamine in toluene is an efficient process.12 No isomerization was detected during reaction; meso-dihydrobenzoin gave cis-stilbene in 85% yield and the (*)-isomer gave only the trans-alkene (94%).(11 (2) (3) Isotope labelling showed that the acid-catalysed isomerization of the 4-methyl group of 1,1,1,2,3,3-hexadeuterobutan-2-01between positions 1 and 4 occurs faster than dehydration to but-2-ene. l3 The results require that this isomerization occurs by hydride transfer as well as by hydration of the formed but-2-ene. Epoxides with iodine -Ph3P in moist MeCN form alkenes in good yields (>70%);the intermediate is presumed to be the i~dohydrin.'~ A simple efficient dehydrohalogenation of uic-dihalogenoalkanes was observed with silica gel and CCI4 in the dark; thus Ph,C(Br)CH2Br gave (lh) Ph,C=CHBr (96%).15 A general route to E-alkenes employs the sequence shown in Scheme 1.The method gave high yields and >99% isomer purity.16 A related route to E-1,2- R2 \ RI-CGC-X -i R1-x 2R1 B-OMe R' iiiuH n n n H BR H R2 H R2 X = Br or I Reagents i R$BH; ii NaOMe; iii H+(R3C02H) Scheme 1 M. V. Baker and L. D. Field J. Am. Chem. SOC. 1987 109 2825. 10 G. A. Olah. Acc. Chem. Rex 1987 20 422. " R. McCague J. Chem. SOC.,Perkin Trans. I 1987 1011. l2 J. L.King B. A. Posner K. T. Mak and N. C. Yang Tetrahedron Lett. 1987 28 3919. l3 P. E. Dietze and W.P. Jencks J. Am. Chem. SOC.,1987 109 2057. l4 L. Garlaschelli and G. Vidari Gazz. Chim. Ital. 1987 117 251. A. R. Suarez and M. R. Mazzieri J. Org. Chem. 1987 52 1145. l6 H. C. Brown D. Basavaiah S. U. Kulkarni H. D. Lee E. Negishi and J.-J. Katz J. Org. Chem. 1986 51 5270. Aliphatic Compounds -Part (i Hydrocarbons BBr2 R' Ri Reagents i R'ZnCI Pd'; ii R'X then base Scheme 2 disubstituted alkenes (Scheme 2) utilizes E-2-(bromoethenyl)dibromoborane(4) as an efficient prec~rsor.'~ By extension of the method synthesis of dienes and enynes was also realized with excellent isomer purities. There is still considerable interest in the Wittig and cognate reactions. Stereoselec- tion is one clear goal but modifications in method will be considered also.Stereo- control in the Horner-Wittig process has been usefully applied to the synthesis of specific en-01s." The known propensity of threo-(5) to form E-alkene by elimination of Ph2POS by action of base was exploited to prepare pure E-non-6-en-1-01 and E-dec-5-en- 1-01 which are pheromones. The Z-isomer of the latter compound was prepared from the erythro-precursor. Both these routes showed complete stereo- specificity. Extension of this approach was used as a route to E-/Z-trisubstituted alkenes and to Z-a-bisabolene (6) a perfume component. An extension of earlier work by Vedejs on the Wittig reaction of stabilized ylides has provided evidence against reversibility.'' The reactions studied provide evidence for kinetic control in reactions of aliphatic aldehydes and stabilized ylides.Addition of LiCH(PPh,)CO,Et to cyclohexanecarbo-aldehyde gave phosphines (7) and (8) (ca. 3 1); methylation of (7) (methyl triflate) and elimination of MePh,PO [using NaN(SiMe,),] gave the Z-alkene as major product. By using the labelled salt (9) it was concluded that deuterium-labelled Z-alkene (1 1) had been formed exclusively from an intermediate (10) by deprotonation at oxygen. The mixture of Z-and E-(11) which contained no deuterium was therefore considered to arise by a pathway FO2Et CO2Et ph2pYH Ph2p?H HOA HO+R k H H " S. Hyuga Y. Chiba N. Yamashima S. Hara and A. Suzuki Chem. Lett. 1987 1757. A. D. Buss N. Greeves R. Mason and S. Warren J. Chem. SOC.,Perkin Trans. 1 1987 2569.E. Vedejs T. Fleck and S. Hara J. Org. Chem. 1987 52 4637. B. V. Smith Me Me \ \ qO2Et Ph2PYD phzprD -O+H R involving dedeuteriation at the a-carbon. In no case was E-alkene containing a-D formed from (9). Therefore 'Wittig-reversal' is ruled out in this system and no other form of equilibration is occurring. It was surmized that an ylide such as Ph,P=CHCO,Et behaves in the same way as Ph,P(Me)=CHCO,Et which shows E-selectivity (95 :5) with C6H,,CH0 under kinetic control. Phosphorus ylides based on the dibenzophosphole ring system convert aldehydes into truns-disu bs t it u t e d ox a p h osp h e tan e s with good-to-excell en t se1e c tivity. Decomposition (70-1 10 "C) gave alkenes with E-/Z-ratios between 6 :1 and 100 :1 (see Scheme 3).,' A one-pot olefination of aldehydes utilizes an ylide derived from an allylic nitro-compound (12) and PBu,; addition of RCHO in the presence of base (BuLi) gave the product.21 R2 R ,R2 __* DBP -!+ DBP-Ph -!!+ DBP-Li DBP-0 DBP-0 Me VI VI 4 4 R' R' RZ DBP= opn% w \ / R2 Reagents i Ph4P+Br- LiNEt2; ii Li-THF; iii NaNH, 2eq.Et1 THF; iv R'CHO -78°C; v A 70°C (5-10 h) Scheme 3 Replacement of Ph3P by Ph2P(CH2)2C02H has been found to increase E-selec- tivity and produces a water soluble phosphine oxide Ph,P(O)(CH,),CO; in Wittig reactions.22 The use of solid-liquid systems for Wittig and Wittig-Horner (and Knoevenagel) reactions has shown that DMSO/MgO or HMPT/ZnO systems are effective catalysts for the Whig reactions and that MCl (M = Hg Cd) or ZnO are better for the Knoevenagel reaction.The E-/Z-ratio was however variable.23 20 E. Vedejs and C. Marth Tetrahedron Lett. 1987 28 3445. 21 R. Tamura M. Kato K. Saegusa M. Kakihana and D. Oda J. Org. Chem. 1987 52 4121. 22 H. Daniel and M. Le Corre Tetrahedron Lett. 1987 28 1165. 23 H. Moison F. Texier-Boullet and A. Foucaud Tetrahedron 1987 43 537. Aliphatic Compounds -Part ( i) Hydrocarbons The boron analogue of the Wittig reaction has shown interesting selectivity. Thus as shown in Scheme 4,appropriate choice of conditions can be used for production of E-or Z-isomers. An additional use of the intermediate (13) is as a precursor of erythro-1,2-di0ls.~~ Ar' iii Ar R u A HH I Ar H u n HR -f Reagents i ArCHO -78 "C THF; ii TFAA -1 10 "C;iii -110 "C 20 "C; iv Me,SiCI -78 "C; v aq.HF MeCN r.t.Scheme 4 A further attempt has been made to prepare tetra-t-butylethylene; reaction between (14) and an excess of Me2TiC12 gave only the bicyclic product (15).25 High E-/Z-ratios were reported for the olefination of aldehydes using a chromium reagent from a gem-di-iodoalkane and Cr"C12; thus C5H,,CH0 and MeCHI gave 94% of oct-2-ene (E/Z = 96 :4).26The modification of Peterson methylenation by using Ce"' helps to overcome the high basicity and lack of selectivity of the reagent Me3SiCH2Li and affords a useful route to methylene alkene~.~~ 24 A. Pelter D. Buss and E. Colclough J. Chem. Soc. Chem. Commun. 1987 297. 25 J.Dannheim W. Grahn H. Hopf and C. Parrodi Chem. Ber. 1987 120 871. 26 T. Okazoe K. Takai and K. Utimoto J. Am. Chem. Soc. 1987 109 951. 27 C. R. Johnson and B. D. Tait J. Org. Chem. 1987 52 281. B. V. Smith Regio-and stereo-selective coupling of 1,l-dichloroalk- 1 -enes with organo-magnesium or -zinc reagents may be achieved with catalysis by a palladium diphos- phine system. Coupling may be sequential; thus PhCH=CC12 affords first PhCH=C(Ph)Cl and then PhCH=CPh,.28 Other methods and products reported are decomposition of diazines in the presence of diazo-compounds leading to unsymmetrical hal~genoalkenes;~~ elimina-tion from glycolate and thioglycolate complexes of rhenium leading to simple alkene~;~' the palladium-mediated coupling of an aryl bromide and CH2=CHSnBu3 to form ArCH=CH2 31 (this method also allows use of functionalized aryl bromides); and the formation of 1-halogenoalk-1-enyl trimethyl~ilanes,~~ via use of LiNPr; Me3SiC1 and vinyl halides.The influence of hydrogen donor and temperature on the stereoselection of radical reactions has been considered. For the species (16) from PhC=CH and C6Hll the Z/E ratio reflects the difference in activation energy of hydrogen transfer; the 2-isomer is formed more easily.33 Me (Bu ')SiMS i(Bu ') Me2 The 'silicon alkene' R,Si=SiR has been prepared at low temperature. Oxidation (0,)gave an epoxide analogue and water added across the system.34 The hindered 2-1,2-bis-(t-butyldimethylsilyl)-1,2-bis(trimethylsilyl)ethylene ( 17) has been obtained.The central C=C bond length was measured as 1.369 A.An attempt to isomerize the double bond (24 E) was frustrated by decomposition of the material.35 Reactions.-Catalytic hydrogenation of olefins in biphasic water-liquid systems has been examined. A water-soluble catalyst derived from RhC13 and a tris-sulphonic acid based on triphenylphosphine allows reduction to take place at ordinary temperature and pressure.36 Ultrasound treatment of nickel powder generates a highly active hydrogenation catalyst capable of effecting reduction at atmospheric pressure. The increase in activity (estimated as a factor of lo5)was shown to arise from profound changes in surface structure rather than from an increase in surface area.37 A review of directed homogeneous hydrogenations has appeared.38 Enan- 28 A.Minato K. Suzuki and K. Tamao J. Am. Chem. Soc. 1987 109 1257. 29 M. P. Doyle A. H. Devia K. E. Bassett J. W. Terpstra and S. N. Mahapatro J. Org. Chem. 1987 52 1619. 30 W. A. Herrmann D. Marz E. Herdtweck A. Schafer W. Wagner and H.-J. Kneuper. Angew. Chem. Int. Edn. Engl. 1987 26 462. 31 D. R. McKean G. Parrinello A. F. Renaldo and J. K. Stille J. Org. Chem. 1987 52 422. 32 N. Shimizu F. Shibata and Y. Tsuno Bull. Chem. Soc. Jpn. 1987 60,777. 33 B. Giese J. A. Cionzilez-Gomez S. Lachheim and J. 0. Metzger Angew. Chem. Int. Edn. Engl. 1987 26 479. 34 S. Masamune Y. Eriyama and T. Kawase Angew. Chem. Znt. Edn. Engl. 1987 26 584. 35 H. Sakurai K. Ebata C. Kabuta and Y. Nakadaira Chem.Lett. 1987 301. 36 C. Larpent R. Dabard and H. Patin Tetrahedron Lett. 1987 28 2507. 37 K. S. Suslich and D. J. Casadonte J. Am. Chem. Soc. 1987 109 3459. 38 J. M. Brown Angew. Chem. Int. Edn. Engl. 1987 26 190. Aliphatic Compounds -Part (i) Hydrocarbons tioselective hydrogenation of allylic and homoallylic alcohols has been reported to occur in excellent yield and with high optical purities in the presence of the chiral catalyst (18).39 Thus geraniol gave citronellol in 97-100% yield (optical purity 96-98'/0). Use of (R) and (S) forms of the catalyst gave products of opposite enantioselectivity. Reduction of unsaturated (and cycloalkenyl) alcohols by LiAlH4 was studied as a function of solvent concentration and temperat~re.~' A number of papers have been published under the general heading of modelling chemical rea~tivity.~' They cover the regio- and stereo-chemistry of electrophilic addition to double bonds (especially in allylic systems) facial selectivity in Diels- Alder reactions and reactivity and stereoselectivity of chiral allylic alcohols and ethers and alkenes in electrophilic addition.The role of surfaces in the addition of HC1 to a simple alkene42 and in the production of alkyl iodides and vinyl iodides (from 12-alumina)43 has been stressed. Supported reagents enter into a facile selective two-phase addition to alkenes in which supported MX (M = Na K; X = SCN N3 OAc) and 12-CHC13 give high yields of adduct at room temperature; typically PhCH=CH2 gave PhCH(SCN)CH,I (79%).44 Evidence has been presented supporting the occurrence of a reversible step in electrophilic br~mination.~~ Reaction of erythro- and threo-2-bromo- 1,Z-diphenyl-ethanol with gaseous HBr (in C1CH2CH2Cl and CHC1,) gave intermediates which collapsed to form rneso-l,2-dibromo-l,2-diphenylethane; some release of bromine led to the production of trans-stilbene.cis-Stilbene was not produced in this way. Thus as shown in Scheme 5 the erythro-isomer (19) has a favourable arrangement of anti-phenyl groups such that protonation and bromine-induced loss of water can occur easily to generate (20). With the threo-isomer an unfavourable conformation would have to be achieved for such a process and hence cis-stilbene is not produced. Significantly the addition of bromine to both olefins was shown not to be stereo- specific and isomerization of cis-stilbene at incomplete conversion was confirmed.Detailed examination of product distributions of dibromides formed from the bromohydrins and from direct addition showed that the ratios of formed dibromides 39 H. Takaya T. Ohta N. Sayo H. Kumobayashi S. Akutagawa S. Inoue 1. Kasahara and R. Noyori J. Am. Chem. SOC.,1987 109 1596. 40 M. Vincens R. Fadel and M. Vidal Bull. SOC.Chim. Fr. 1987 462. 41 W. J. Hehre et al. J. Am. Chem. SOC., 1987 109 650 663 666 672. 42 J. Tierney F. Costello and D. R. Dalton J. Org. Chem. 1986 51 5191. 43 L. J. Stewart D. Gray R. M. Pagni and G. W. Kabalka Tetrahedron Lett. 1987 28 4497. 44 T. Ando J.H. Clark D. G. Cork M. Fujita and T. Kimura J. Chem. SOC.,Chem. Commun. 1987 1301. 45 G. Bellucci C. Chiappe and F. Marioni J. Am. Chem. SOC.,1987 109 515. 100 B. V. Smith I Br H Ph Conditions i H+,-H,O;ii -Br2; iii collapse of ion pair; iv +Br (unless removed) Scheme 5 were different; this is contrary to the expectation based on a common bridged intermediate. However the complete suppression of formation of (*)-dibromide in reaction of (19) with HBr argues that the reverse reactions of the trans-bromonium bromide ion-pair in Scheme 5 proceeds to a higher extent than might be inferred on the basis of recovered olefin. The isomerization (cis + trans) was rationalized in a similar way. Caesium fluoroxysulphate has been advocated for simple fluorination of alkene~.~~ Although some specificity (syn-addition) was noted for E-alkenes the 2-isomers gave non-stereospecific reaction.A convenient method for conversion of (cyc1o)alkenes into trans-fluoroiodo-derivatives uses the reagent I+( collidine),BFi ; the process is regio- and stereo-~pecific.~' Alkenes form vicinal fluoroiodides with polymer-supported HF in the presence of N-iodosuccinimide. The reaction exhibits Markovnikov-type regioselectivity and anti-stereospecificity and good yields are obtained; addition to alkynes is also In the presence of Mn"' acetate and chloride ions formation of either dichloro-adducts or monochloro(rep1acement) products occurs with a$ -unsaturated esters.49 The peroxide-mediated addition of a-bromoacids to alkenes leads to 4-alkanolides probably via a free-radical route.50 Synthetically valuable allylic sulphones have been prepared by iodosulphonylation of alkenes followed by treatment of the adduct with base.5' Hydration of terminal alkenes with Cl,AlH 02,and a catalytic quantity of PhB(OH) gives good yields of primary alcohols; e.g.,dodec-1-ene afforded dodecan- 1-01 (75%).52 There is still considerable interest in epoxidation reactions.Two papers explore the theoretical aspects; the first concentrates on the role of 0x0-iron p~rphyrins~~ and the second analyses the electronic and steric factors which determine the course of the asymmetric (Sharpless) epoxidation of allylic alcohols.54 46 S. Stavber and M. Zupan J. Org. Chem. 1987 52 919 47 R.D. Evans and J. H. Schauble Synfhesis 1987 551. da A. GregorCiC and M. Zupan Bull. Chem. SOC.Jpn. 1987 60,3083. 49 H. Yonemura H. Nishino and K. Kurosawa Bull. Chem. SOC.Jpn. 1987 60,809. 50 T. Nakano M. Kayarna and Y. Nagai Bull. Chem. SOC.Jpn. 1987 60 1049. 51 K. Inomata S. Sasaoka T. Kobayashi Y. Tanaka S. Igarashi T. Ohtani H. Kinoshita and H. Kotake Bull. Chem. SOC.Jpn. 1987 60 1767. 52 K. Maruoka H. Sano K. Shimoda and H. Yamarnoto Chem. Lerr. 1987 73. 53 K. A. J~rgensen,J. Am. Chem. SOC.,1987 109 698. 54 K. A. Jergensen R. A. Wheeler and R. Hoffrnann J. Am. Chem. Soc. 1987. 109 3240. Aliphatic Compounds -Part (i) Hydrocarbons 101 Incorporation of 3A or 4A molecular sieves into the methodology increases the scope of the asymmetric epoxidation of primary allylic alcohols.55 High conversion (>95%) and high e.e.(90-95%) was realised. In some cases cumene hydroperoxide was substituted for the usual t-BuOOH. Sharpless has explored the idea of in situ derivatization of low molecular weight water-soluble products of such reactions. Epoxidation of alkenes with dimethyl dioxirane shows sensitivity to steric factors; cis-alkenes are generally more reactive (8-10 times) than their trans-anal~gues.~~ Among other methods reported the cobalt-catalysed reaction of t-BuOOH and iodo~ylbenzene,~~ and the haemin-catalysed process (with some rearrar~gement),~~ the manganese porphyrin-t-BuOOH system59 may be mentioned. Inter-and intra-molecular epoxidation has been accomplished using silyl- protected peroxyesters and a copper salt.60 Thus oct-2-ene gave 83% of epoxide; all trans-farnesol gave a mixture of epoxides (82%; 6,7 10,ll = 1:4.5) but by changing conditions the amount of 6,7-epoxide was increased markedly.Sodium hypochlorite in the presence of alumina or montmorillonite smoothly epoxidizes alkenes which carry two electron-withdrawing groups.6' Cation radical-catalysed oxygenation of alkylated olefins (and dienes) has been reviewed.62 Conversion of an alkene into a primary amine is efficiently performed using a hydroboration (Me,BH)-amination (NH20S03H) sequence.63 Tosylisocyanate serves as a convenient equivalent for hydr~xyamination.~~ Sulphonation of oct-1-ene has been shown to furnish a p-sultone with one molar equivalent of SO,; with an excess of SO, a carbyl sulphate is produced.65 Similar work provided evidence for formation of these species as judged by n.m.r.evidence.66 Hydrocyanation in an anti-Markovnikov sense has been noted for an organozir- conium-mediated process as shown in Scheme 6.67Hydroformylation of phosphine- bearing terminal alkenes can lead to a reversal of regioselectivity (with respect to simple alkenes) in the presence of a rhodium catalyst.68 Synthesis of simple acids (and esters) from coupling of alkenes and COz brought about by zerovalent metal catalysts has been explored.69 Erythro-selective addition of PhSeH to E-nitroalkenes gave an intermediate which by elimination of benzeneselenic acid afforded the Z-i~omer.~~ Intramolecular palladium-catalysed cyclization of terminally unsaturated esters has been used as a route to large-ring lac tone^.^^ 5s Y.Gao R. M. Hanson J. M. Klunder S. Y. KO H. Masamune and K. B. Sharpless J. Am. Chem. SOC.,1987 109 5765. 56 A. L. Baumstark and C. J. McCloskey Tetrahedron Lett. 1987 28 3311. 57 J. D. Koola and J. K. Kochi J. Org. Chem. 1987 52 4545. 58 T. G. Taylor and A. R. Miksztal J. Am. Chem. SOC.,1987 109 2770. 59 P. N. Balasubramian A. Sinha and T. C. Bruice J. Am. Chem. SOC.,1987 109 1456. 60 1. Saito T. Mano R. Nagata and T. Matsuura Tetrahedron Lerr. 1987 28 1909. 61 A. Foucaud and M. Bakouetila Synthesis 1987 854. 62 S. F. Nelsen Acc. Chem. Res. 1987 20 269. 63 H. C. Brown K.-W. Kim M. Srebenik and B.Singaram Tetrahedron 1987 43 4071. 64 B. M. Trost and A. R. Sudhakar J. Am. Chem. Soc. 1987 109 3792. 65 B. H. Bakker and H. Cerfontain Tetrahedron Lett. 1987 28 1699 1703. 66 D. W. Roberts P. S. Jackson C. D. Saul and C. J. Clemett Tetrahedron Lett. 1987 28 3383. 67 S. L. Buchwald and S. J. La Maire Tetrahedron Lett. 1987 28 295. 68 W. R. Jackson P. Perlmutter and G.-H. Suh J. Chem. SOC.,Chem. Commun. 1987 724. 69 H. Hoberg K. Jenni K. Angermund and C. Kriiger Angew. Chem. Int. Edn. Engl 1987 26 153. 70 N. Ono A. Kamimura T. Kawai and A. Kaji J. Chem. SOC.,Chem. Commun. 1987 1550. 71 J. K. Stille and M. Tanaka J. Am. Chem. SOC.,1987 109 3785. 102 B. V. Smith R3 R' ii Cp,Zr(H)Cl Cp,Zr(Cl)/\r -RZ Cp2Zr Reagents i CH,=CR'R'; ii R3NrC; iii I2 Scheme 6 Donor-acceptor interactions as probed by olefins have been reviewed.72 It has been inferred that the similar rates of hydroboration and oxymercuration of alkenes point to similar steric requirements in the transition states of reaction.73 3 Polyenes Synthesis.-A stereocontrolled chemoselective synthesis of diene (and enyne) sys- tems relies on the palladium-catalysed coupling reaction between an alkenyl iodide and an alkynyl ~tannane.~~ High yields of conjugated enynes were obtained which furnished dienes in high isomer purity.By this route the pheromones 52,7E-dodeca- 5,7-dien-l-ol and the 5E,7Z-isomer were prepared in a high state of purity as shown in Scheme 7. A very general method for all possible geometric isomers of a 1,3-diene is the palladium-catalysed cross coupling of an E-or 2-vinyl halide with an E-or 2-vinylstannane; the geometry of each partner is reproduced in the product diene.75 The reaction is tolerant of functional groups in either partner and constitutes an extremely versatile and valuable method.By this methodology 2-l-iodohex-l-en-6-01 and E-1-trimethylstannylhex-1-enegave the 52,7E-isomer of the above named pheromone directly in 73% yield. A synthesis of dienes shown in Scheme 8 has I J Bu-E-SnMe3 + 1 1(cH2)40THP -../i-'i\ (CH2)rOH Reagents i (MeCN),PdCI, THF 22 "C; ii (Sia),BH; iii AcOH; iv NaOH H202; v Hf Scheme 7 '' Z. V. Todres Tetrahedron 1987 43 3839. 73 D. J. Nelson P. J. Cooper and J. M. Coerver Tetrahedron Lett.1987 28 943. 74 J. K. Stille and J. H. Simpson J. Am. Chem. Soc. 1987 109 2138. 75 J. K. Stille and B. L. Groh J. Am. Chem. Soc. 1987 109 813. 103 Aliphatic Compounds -Part ( i) Hydrocarbons Reagents i CH,=C(Me)MgBr THF 0°C; ii CrO, CSHsN; iii Me2C(SePh), BuLi THF -78°C; iv S0Cl2 2eq. Et,N CH2C12 r.t. Scheme 8 been published.76 Stereo-defined synthesis of conjugated dienes (and arylated alkenes) rests upon the Pd- or Ni-catalysed coupling of an alkenyl or aryl iodide with an alkenyl metal (M = Al Zr Zn).77 The palladium catalyst gave very high stereospecificity; with nickel partial scrambling was observed. Thus for E -C,H,,CH=CHAIBu; and 2-C,H9CH=CHI the formed diene showed isomer purity >98%. The [3-(diphenylphosphino)allyl]titanium reagent formed as shown in Scheme 9 reacted with aldehydes regio- and stereo-specifically to give 1,3-diene~.~~ OTiL, Reagents i Bu'Li; ii Ti(OPr'),; iii RCHO; iv Me1 Scheme 9 The intermediate invoked to explain such selectivity is chair-like (21); by changing reagent to that derived from Ph,P(O)CH(Me)CH=CH a higher yield of diene with greater E-selectivity was obtained compared to that from Ph2P(0)CH2CH=CH2.It was inferred that (22) was responsible for such selection. These methods taken together thus form useful additions to synthetic routes in the diene field. Extension of this approach as a route to a 1,4-dialkyl-1,3-diene was also described. WMe) &-PPh2 LnTi-'C-R H I 0-b L ,i.i.+6-R IH (21 1 (22) An interesting silicon-directed diene synthesis is shown in Scheme Another approach to 2,E-conjugated dienes uses a stepwise process in which an a#-unsaturated aldehyde is generated from [Ph,AsCH2CHO]+Br-and RCHO in good- to-excellent yield; a Wittig reaction with BuLi in HMPA-THF led to the desired diene.80 This route also gave an entry into the dienols and derivatives which are 76 R.V. Bonnert and P. R. Jenkins J. Chem. SOC.,Chem. Commun. 1987 1540. 77 E. Negishi T. Takahashi S. Baba D. E. Van Horn and N. Okukado J. Am. Chem. SOC.,1987,109,2393. 78 Y. Ikeda J. Ukai N. Ikeda and H. Yamamoto Tetrahedron 1987 43 723 731. 79 P. A. Brown R. V. Bonnert P. R. Jenkins and M. R. Selim Tetrahedron Lett. 1987 28 693. 80 Y.-Z. Huang L. Shi J. Yang and Z. Cai J. Org. Chem.1987 52 3558; cf Tetrahedron Lett. 1985 26 6447. 104 B. V. Smith Reagents i Me,SiCH,MgCl; ii PCC; iii &MgBr; iv AcOH AcONa Scheme 10 pheromones. Facile stereoselective synthesis of conjugated E,E-dienes including those carrying amine silane and stannane groups has also been reported as another variation of the theme.81 Self-coupling of an alkenyl stannane (23) [Pd(OAc), Bu'OOH-C,H,] led to a 1,3-diene whereas cross-coupling with an ally1 stannane (24) led to a 'methylene- interrupted' (non-conjugated) diene (25).82 R' R' --SIlR Successive treatment of a hindered alkene with BH,-THF (to form R,BH) followed by reaction with 1,4-dichlorobut-2-yne and alkyl-lithium gave 2-alkylbuta-l,3-dienes (see Scheme ll).83 R' CICH2CECCH2CI + c1 1iii L9 R'R2B R' H Reagents i RiBH; ii R'Li; iii -LiCI Scheme 11 Efficient and stereospecific syntheses of various dienyl alcohols have been presen- ted.A Wittig sequence involving an E-oxidoallylic phosphorane and an aldehyde R2CH0 led to dienol (26) as major product.84 In a related process a zirconium- mediated Wittig rearrangement followed by Peterson elimination was exploited to produce 2E,4Z-dienols (see Scheme 12).85 1-Oxygenated E,E-dienes have been T. Ishii N. Kawamura S. Matsubara K. Utimoto S. Kozima and T. Hitomi J. Org. Chem. 1987 52 4416. " S. Kanemoto S. Matsubara K. Oshima K. Utimoto and H. Nozaki Chem. Lett. 1987 5. 83 A. Arase and M. Hoshi J. Chem. SOC.,Chem. Commun. 1987 531. 84 A. Hosoda T. Taguchi and Y.Kobayashi Tetrahedron Lett. 1987 28 65. 85 S. Kuroda T. Katsuki and M. Yamaguchi Tetrahedron Lett. 1987 28 803. Aliphatic Compounds -Part (i) Hydrocarbons R$i 0 ii iii *yOH 2R:Siq OH __* R:Si R2 R2 A R2 1iv v vi OH OTHP Reagents i Redal; ii BrCH2C02H;iii Me,CHI; iv LDA-THF; v Cp2ZrC12;vi DHP PTSA; vii LAH then H+; viii NaH Scheme 12 CO2Et OLi OLi 0~3 R15 i __* I - + R2 R' ii R,< iii Rl( R* R2 R2 [R3= SiMe or Ac] Reagents i LiCHBrz THF/TMP Bu"Li -78 "C + r.t.; ii LiH THF A; iii Me,SiCI or Ac,O Scheme 13 prepared stereospecifically from cqP-unsaturated esters in a one-pot reaction (see Scheme 13).86The reaction of 2,5-dihydroxythiophen S,S-dioxides and a carbonyl compound may lead to a-hydroxydienes such as (27) (X = Ph) or 28 (X = Me) after ring cleavage of the first-formed add~ct.~' The phenyl group (27) and the methyl group (28) were situated at C-3 in the ring.By this approach the naturally occurring E-tagetone (29) was prepared in a three-step process. x 86 C. J. Kowalski and G. S. Lal Tetrahedron Lert. 1987 28 2463. 87 S. Yamada H. Suzuki H. Naito T. Nomoto and H. Takayama J. Chem. SOC.,Chem. Cornmun. 1987 332. 106 B. V. Smith Synthesis of 2-alkylthiobuta- 1,3-dienes has been reported.88 1-Phenylthioalka-l,3- dienes (and 1,3,5-trienes) were obtained by cross-coupling either E-or 2-2-bromo-l- phenylthioalk-1-enes with alk-1-enyl or alka-1,3-dienyl-1,3,2-benzodioxaboroles in the presence of Pd(PPh3)4; excellent yields were obtained e.g.96% for (30).89 1,3-Dienes containing an allylic sulphone moiety have been characterized." Butadienes carrying a 1-dirnethylamino-gro~p~~ and captodative substituents9* have been prepared. A stereocontrolled approach to olefins and methylene-interrupted dienes relies upon the mediation of allylcerium corn pound^.^^ Several examples were given of this method which has the advantage of working smoothly with systems containing cis-double bonds. Thus (31) (whose acetate is found in certain algae) was synthesized in acceptable yield. Molybdenum hexacarbonyl has been shown to couple allylic acetates to produce 1,5-dienes; 2,2'-bipyridyl accelerated the rate of reaction.94 In such a process 3-acetoxyoct-1-ene gave hexadeca-6,lO-diene (48%) and 9-vinyl- tetradec-6-ene (52%) in 54% overall yield.Several examples have been given of nitrone cycloaddition and deamination sequences which led to E,E-1,5 -diene~.~~ 1,2-Dienes are formed in the palladium-catalysed hydrogenolysis of 3-methoxycar- bonyloxyalk-1-ynes (32) with ammonium formate in DMF.96 Allenyl silanes were produced from an N-phenylcarbamate e.g. (33),by sequential treatment with MeLi CuI and PhMe,SiLi to form (34).97 Elimination of Bu3Sn and OH from p-hydroxyvinylstannanes (35) by CF3S03H-THF gave the trimethylsilyldienes (36) in excellent (>go%) yields. The products (36) could be converted into 1,3-dienes with further acid treatment.98 Routes to cross-conjugated mono- and di-allenes have been explored.99 R2 R'X°Co2Me,@ KONHPh n8 M.Hoshi Y. Masuda and A. Arase J. Chem. SOC.,Chern. Commun. 1987 1629. 89 T. Ishiyama N. Miyaura and A. Suzuki Chem. Lett. 1987 25. 90 K. Hayakawa M. Takewaki I. Fujimoto and K. Kanematsu J. Org. Chem. 1986 51 5100. 9' B. Potthoff and E. Breitmaier Chem. Ber. 1987 120 255. 92 N. StCvenart-De Mesmaeker R. MerCnyi and H.G. Viehe Tetrahedron Lett. 1987 28 2591 93 €3.-S.Guo W. Doubleday and T. Cohen J. Am. Chem. SOC.,1987 109 4710. 94 Y. Masuyama H. Hirai Y. Kurusu and K. Segawa Bull. Chem. SOC.Jpn. 1987 60,1525. 9s J. J. Tufariello and A. S. Milowsky Tetrahedron Lett. 1987 28 263. 96 J. Tsuji T. Suguira and I. Minami Synthesis 1987 603. 97 I. Fleming K. Takaki and A. P. Thomas J. Chem. Soc. Perkin Trans. 1 1987 2269. 98 C.Nativi A. Ricci and M. Taddei Tetrahedron Lett. 1987 28 2751. 99 F. Lehrich and H. Hopf Tetrahedron Lett. 1987 28. 2697. Aliphatic Compounds -Part ( i) Hydrocarbons A stereoselective (98.2% ) route to 3 E,SZ-undeca-l,3,5-trienehas been realized via palladium-catalysed coupling of hept-1-ynyl zinc chloride and E-or 2-1,2-dibromoethene to form (37) in the first instance; (37) was then elaborated into (38) by sequential coupling with CH,=CHZnCl hydroboration of the product and generation of (38).'0° A related method for undeca-l,3,5-trienes relies on a sequence of coupling reactions mediated by Pdo-Cu' and Nio respectively."' Wittig coupling of oxiranylprop-2-enal (39) and RCH=PPh3 gave (40); (40) uia the episulphide and elimination formed triene (41) and by this approach fucoserratene [(41) R' = Et] was synthesized.Treatment of (40) with NaIO gave a dienal (42).'02 (37) (38) A number of methods were used in an assault on the synthesis of polyene pheromones of lepid~ptera."~ Reactions.-Addition of trifluoroacetyl nitrate to 1,3-dienes afforded a mixture of 1,2- and 1,4-nitrotrifluoroa~etates.~~~ Treatment of these adducts (KOAc or NaH) formed 1-nitro- 1,3-dienes which in turn underwent nucleophilic addition with PhNH2or PhSH-Et,N in ether. From l-nitrobuta-1,3-diene the major product from the latter example is (43). Functionalization of 2-(phenylsulphonyl)-1,3-dienesgives via Michael addition allylic sulphones which can enter irlto further nucleophilic addition catalysed by palladium or promoted by c~prates;"~ a range of compounds was prepared from those versatile starting materials.Sterically hindered manganese-containing porphyrins act as shape-selective catalysts for epoxidation of a range of dienes;Io6 analysis of product ratios suggests that there may be two pathways in such a process. An unusual reaction is the addition of a P-ketoacid to the monoepoxide of a 1,3-diene with decarboxylation; thus the monoepoxide of buta-l,3-diene and 3-oxopentan-l,5-dioic acid gave (44) (73% ; E/Z = 5 :2).'07 Ozonolysis of 2-chloro-3-methylbuta-l,3-diene gave (45) preferentially (>90% ).lo8 I00 B. P. Andreini M. Benetti A. Carpita and B. Rossi Terrahedron 1987 43 4591; cJ Tetrahedron Lett. 1986 27 4351. 101 V. Ratovelomanana and G.Linstrumelle Bull. SOC.Chim. Fr. 1987 174. I02 M. Goldback E. Jakel and M. P. Schneider J. Chem. Soc. Chem. Commun. 1987 1434. 103 H. J. Bestmann K. Roth K. Michaelis 0.Vostrowsky H. J. Schafer and R. Michaelis Liebigs Ann. Chem. 1987 417. 104 A. J. Bloom and J. M. Mellor J. Chem. Soc. Perkin Trans. 1 1987 2737. 105 J.-E. Backvall and S. K. Juntunen J. Am. Chem. SOC.,1987 109 6396. 106 K. S. Suslick and B. R. Cook J. Chem. SOC.,Chem. Commun. 1987 200. 107 T. Tsuda M. Tokai T. Ishida and T. Saegusa J. Org. Chem. 1986 51 5216. 108 K. Griesbaum and M. Meister Chem. Ber. 1987 120 1573. 108 B. V. Smith C1 R -No2 SPh Dimethyl(2,3-dimethylene)butane-l,4-dioatereadily takes part in a Diels-Alder reaction with an inverse electron demand.'" Addition of acryloylferrocene to 1- phenylbuta-l,3-diene is promoted by montmorillonites in which a certain amount of ionic replacement has occurred."' The role of metal reagents in stereo- and regio-selective functionalization of conjugated dienes has been reviewed.' '' Alkyl dichloro- and trichloro-acetates add to buta-l,3-diene under the influence of copper complexes e.g.with 1,lO-phenanthro- line.Trichloroacetates gave 1 :1 adducts (derived from 1,2-and 1,4-addition); generally the reactivity was higher for trichloro-substitution but was diminished by increasing length of the alkyl chain in the ester.'12 4-Bromo-2-sulpholenes serve as butadienyl cation equivalents and permit reaction with cup rate^."^ Thus (46) with Ph,CuLi then Et3N gave (47) in excellent yield and thereby 2-phenylbuta- 1,3-diene as the sole product.The following observations were published in 1987. Selective reduction of non- conjugated dienes uses H2-Pd-PhCH,CHO; virtually no saturated product was formed.' l4 The thermal rearrangement of 3-fluoro-hexa-1,5-diene shows no dramatic effect due to the fluorine atom.' l5 Acetoxybromodienes with remote double bonds are smoothly cyclized by Pdo- RiSnAlR; (to vinylcycloalkenes).' l6 A remarkable double diastereoselection was observed in iodolactonization of the hepta- 1,6-dien-4- oic acid derivative (48)."' The major product (49) was formed with group and face selectivity. 3-Alkyl- and 3,3-dialkyl-l-bromo-1,2-dienes react with organocuprates to yield either a terminal alkyne or an allene."* To some extent this depends on the cuprate used and refutes an earlier claim by Landor that only allene was formed.When R(CN)CuLi or RCuBr.MgLiX was used alkyne was obtained if R was a straight chain group; a tertiary group on the other hand favoured formation of allene in excellent yields. Although use of Ph(CN)CuLi gave allenes (70-80%) the use of 109 C. Grundke and H. M. R. Hoffmann Chem. Ber. 1987 120 1461. 110 S. Toma P. EleEko J. Gaiova and E. SolEaniovL Collect. Czech. Chem. Commun. 1987 52 391. 111 J.-E. Backvai Bull. Chem. SOC.Fr. 1987 665. 112 Z. Vit and M. Hajek Collect. Czech. Chem. Commun. 1985 52 1280. 113 T. Chou S. C. Hung and H.-H. Tso 1. Org. Chem. 1987 52 3394. 114 S.Nishimura M. Ishibashi H. Takamiya N. Koike and T. Matsunaga Chem. Lett. 1987 167. 115 W. R. Dolbier Jr. A. C. Alty and 0. Phanstiel IV J. Am. Chem. SOC.,1987 109 3046. 116 B. M. Trost and R. Walchli J. Am. Chem. Soc. 1987 109 3487. 117 M. J. Kurth and E. G. Brown J. Am. Chem. Soc. 1987 109 6844. 118 A. M. Caporusso C. Polizzi and L. Lardicci Tetrahedron Leu. 1987 28 6073. Aliphatic Compounds -Part (i) Hydrocarbons Ph( CuBr)MgBrLiBr gave excellent yields of phenyl-substituted alkynes. The stereochemistries of both processes were also examined. The nature of the di-lithium allenide from 1,1,3,3-tetraphenylallenehas been investigated and there is some evidence for the existence of two equilibrating structure^."^ Intramolecular addition of the OH group of a hemiacetal to an allene has been observed.'20 Allenic carboxylates and lactones undergo thermally induced 1,3 hydrogen shifts in the presence of CO~(CO)~ .121 Thus Ph2C=C=C(Me)C02R' (R' = Me or Et) gave initially Ph2C=CH-C(C0,R')=CH2 which subsequently entered into Diels- Alder cycloaddition.Lipase-mediated resolution of allenic alcohols generally gave low yields but in some cases the optical purity was high.'22 The reaction with acid R'C02H was carried out in hexane as 'solvent' with a lipase preparation obtained from a microbiological source (Candida cylindracea). This interesting reaction worked best for hindered alcohols; thus whilst (50a) R2 = Me R3 = Et R" = R5 = H) gave recovered alcohol of very low optical purity (<5%) the related (50b) (R2 = H R3 = R4 = R5 = Me) gave optical purity in the recovered alcohol of 70% albeit in low yield (12%).Allenes with an aldehyde RCHO enter into a photoreaction in the presence of Fe(C0)5to form trimethylenemethane tricarbonyl iron c~mplexes.'~~ Allenic nitriles with a diamine or aminoalcohol enter into Michael addition; the product eliminates MeCN at 300 "C forming a pyrimidine or oxazine deri~ative.'~~ Methylene ketenes R'R2C=C=C=0 have been obtained by treating R'R2C=C(Br)COCl with Mn(C0); at -78 "C; dimerization (by cycloaddition) was observed.'25 Two unusual trimers of diketene were prepared by interaction with Me,SiI .l 26 The spontaneous cyclodimerization of the butatriene (51)leads to the cyclobutane (52).'27 RZ Oxidation of 3,6-di-t-butyl-2,2,7,7-tetramethylocta-3,4,5-triene with MCPBA gave a methylenecyclopropanone as principal product.'28 An analogous methylene- cyclopropanone with P2S5 in pyridine gave a mixture containing some butatriene episulphide together with the triene Bu\C=C=C=CBu\ .129 I19 A.Rajca and L. M. Tolbert J. Am. Chem. SOC. 1987 109 1782. I20 N. 0. Nilsen L. Skattebd and Y. Stenstram Acta Chem. Scand. Ser. B 1987 40 459. I21 L. S. Trifonov A. S. Orahovats and H. Heimgartner Helu. Chim. Acta 1987 70 1070. 122 G. Gil E. Ferre A. Meou J. Le Petit and C. Triantyphylides Tetrahedron Lett. 1987 28 1647. 123 R. Aumann H.-D. Melchers and H.-J. Weidenhaupt Chem. Ber. 1987 120 17. I24 T. Z. Fozum A. Johnson S. R. Landor P.D. Landor J. T. Mbafor and A. E. Nkeng-fack J. Chem. Res.(S) 1987 188. 12s A. P. Masters T. S. Sorensen and P. M. Tran Can. J. Chem. 1987 65 1499. I26 I. Ernst H. Fritz and G. Rihs Helu. Chim. Acta 1987 70 203. I27 M. Kaftory I. Agmon M. Ladika and P. J. Stang J. Am. Chem. Soc. 1987 109 782. 128 J. K. Crandall G. E. Salazar and R. J. Watkins J. Am. Chem. Soc. 1987 109 4338. 129 W. Ando H. Hayakawa and N. Tokitoh Tetrahedron Lett. 1987 28 1803. 110 B. V. Smith 4 Alkynes Synthesis.-An efficient synthesis of 1-t-butoxyethyne relies on sequential addition of K0Bu'-Bu'OH and then Br to C2H2; elimination of HBr from BrCH,CH(Br)OBu' gave the desired pr~duct.'~' Sodium acetylides and I+(py),BF react smoothly to give good-to-excellent yields of l-i~doalkynes.'~' Chiral (S)-1-alkynyl-p- tolylsulph- oxides (53)have been prepared in high yields from an alkynyl magnesium bromide and (S)-(-)-menthyl-p-t~luenesulphinate.'~~ Stereoselective reduction of the alkyne furnished either an E-alk-1-enyl-( R)-sulphoxide (LAH-THF) or the 2-(R)-isomer [RhCl( PPh3)3-C6H6-H2].These are useful materials in synthesis. The preparation and characterization of the sulphonates R'CECOR' (R2 = S02Ar or S0,Me) has been rep01-ted.l~~ The synthesis of 1-nitro-2-(trialkylsilyl)alkyneshas been effected via nitronium salt nitration of suitable alkyne These compounds not surprisingly enter into Diels- Alder reactions e.g. with cyclopentadiene. Gentle thermolysis of 2,5-dialkynyl-3,6-diazido-1,4-benzoquinonesleads to an alkynylcyanketene (RC=C-C(CN)=C=O) which is reactive in cycloaddition and towards an alcohol (generating a cyanoallene ester).'35 A metal-mediated approach to enynes employs a palladium catalyst in the presence of a sterically hindered phosphine tris(2,6-dimethoxyphenyl)-phosphine.This method was used for coupling PhCECH and MeC=CCO2Me to form (54)and gave an excellent yield (92%); the role of the phosphine and the probable mechanism were disc~ssed.'~~ 0 (53) (54) Stannylation of 1-trimethylsilyl- 1,3-diynes has been developed for the synthesis of enynes (and dienes and alkene~).'~' Treatment of the diyne with 2.5eq. of (trimethylstanny1)copper in THF gave E-l-trimethylsilyl-3,4-bis(trimethyl-stannyl)alk-3-en-l-ynes.Transmetallation (MeLi) then produced enynyl lithium reagents which with electrophiles produced stereo-defined tri- and tetra-substituted enynes containing the reactive Me3Si group.Equally valuable was the transforma- tion via hydroalumination into 1-trimethylsilylbuta-1,3-dienes and the hydrobor- ation-oxidation sequence affording unsaturated acids. A one-pot synthesis of fluoroenynes has been reported in which an 'eliminative nucleophilic addition' forms a key step.'38 The lithioalkyne R'CECLi is added to 130 M. A. Pericas F. Serratosa and E. Valenti Tetrahedron 1987 43 2311. 131 J. Barluenga J. M. Gonzalez M. A. Rodriguez P. J. Campos and G. Asensio Synthesis 1987 661. 132 H. Kosugi M. Kitaoka K. Tagami A. Takahashi and H. Uda J. Org. Chem. 1987 52 1078. 133 P.J. Stang B. W. Surber Z.-C. Chen K. A. Roberts and A. G. Anderson J. Am. Chem. SOC.,1987 109 228. 134 R. J. Schmitt J. C. Bottaro R. Malhotra and C. D. Bedford J. Org. Chem. 1987 52 2294. 135 N. V. Nguyen K. Chow and H. W. Moore J. Org. Chem. 1987 52 1315. 136 B. M. Trost. C. Chan and G. Ruhter J. Am. Chem. SOC.,1987 109. 3486. I37 G. Zweifel and W. Leong J. Am. Chem. SOC.,1987 109 6409. 138 Y. Shen and W. Qiu J. Chem. SOC.,Chem. Cornmun. 1987 703. Aliphatic Compounds -Part (i) Hydrocarbons 111 the ketophosphonium compound Ph3PC( R2R3)CORf and with elimination of Ph,PO the enyne R2R3C=C(Rf)C=CR' is formed; with R' = R2 = Ph R3 = Me Rf = C2F5,44% of enyne (E/Z = 98/2) was produced. Symmetrically substituted 1,3-diynes (and dienes) were obtained in the copper( 11) nitrate-mediated coupling of organotins in THF.'39 By extension of this method symmetrical biaryls were synthesized.Finally the preparation of five naturally occurring polyacetylenes have been de~cribed.'~' Reactions.-The absolute configuration of (+)-But( Me)C(OH)C=CH. has been reassigned as (S) on the basis of chemical correlation with (S)-Bu'CH(OH)C_CH by applying an organocopper( I) reaction of known anti-stereochemistry." The value of chiral acetylenes as synthetic intermediates has been shown in the prepar- ation of chiral isoxazoles and pyrazole~.'~~ A copper( 1) hydride species prepared in situ from NaBH,-MgBr2-Et3N-CuC1 or NaH-MgBr,-CuC1 converts terminal alkynes cleanly into E,E-1,3-diene~;'~~ from C,H,,CECH there was formed 77% of the 1,3-diene.A hydroformylation protocol for alkynes which leads to an a$-unsaturated aldehyde is shown in Scheme 14.14 Reagents i HCN Ni[POPh314; ii DIBAH PhMe -78 "C Scheme 14 Some enhancement of the hydrogenation activity of Lindlar's catalyst was realized by treatment with lead acetate; sodium acetate was without Epitaxial palladium on a tungsten film has been shown to have enhanced semi-hydrogenation capability together with cis-selectivity for reduction of a1k~nes.l~~ This latter catalyst was claimed to be superior to Lindlar's catalyst. Propargylic esters enter into a Claisen rearrangement to form an ester of an allenyl acetic acid; the free acid on thermolysis (250 "C) forms a b~ta-1,3-diene.'~~ Yields in both steps are high; thus MeC_C-CH,OCOMe gave CH,=C=C(Me)CH( Me)C02H (70%) and finally MeCH=C(Me)CH=CH (100% from the immediate precursor).Alkynes R'C=CR2 with MeOH-PhI(0H)OTs form methyl phenylalkanoate~.'~~ Dichloroketene (Cl,C=C=O from Cl3CCOC1-Zn/Cu) and alkynes form dichlorocyclobutenones which are easily dechlorinated by zinc in acetic acid- I39 s.Ghosal G. P. Luke and K. s. Kyler J. Org. Chem. 1987 52 4296. 140 A. Carpita D. Neri and R. Rossi Gazz. Chim. Ital. 1987 117 481. 141 C. J. Elsevier and H. M. Mooiweer J. Org. Chem. 1987 52 1536. 142 M. Falorni L. Lardicci and G. Giacomelli Gazz. Chim. Ital. 1987 117 7. 143 S. A. Rao and M. Periasamy J. Chem. SOC.,Chem. Commun. 1987 495. 144 E. Campi N. J. Fitzmaurice W.R. Jackson P. Perlmutter and A. J. Smallridge Synthesis 1987 1032. 145 J. G. Ulan E. Kuo W. F. Maier R. S. Rai and G. Thomas J. Org. Chem. 1987 52 3126. 146 J. G. Ulan W. F. Maier and D. Smith J. Org. Chem. 1987 52 3132. 147 J. E. Baldwin P. A. R. Bennett and A. K. Forrest J. Chem. Soc. Chem. Commun. 1987 250. R. M. Moriarty. R. K. Vaid M. P. Duncan and B. K. Vaid Tetrahedron Lett. 1987 28 2845. 14' 112 B. V; Smith ~yridine.'~~ Addition of t-butylcyanketene Me,CC(CN)=C=O to a stannylethynyl ether (R'OCrCSnR:) leads to (stannyloxyviny1)yne ether.'50 Ethers of the type ClCH20R' (R' = Me or Et) were shown to add to alkynes carrying a phenyl group or to but-2-yne.15' The expected addition product was formed i.e. R'OCH,C( R2)=C(C1)R3 together with that resulting from replacement of the vinylic ether by C1.The process was inferred to proceed via a stepwise electrophilic mechanism (vinyl cations were implicated); the secondary product ClCH2C( R2)=C( C1)R3 was thought to arise from an allylic cation. The silver-assisted heterocyclization of acetylenic alcohols or acids affords an easy route to a-methylene oxygenated heterocycles. lS2 The alkyne complexes of early transition metals have been reviewed; diene alkene and alkyl complexes were also in~luded."~ Pyrolysis of acetylene serves as a thermal source of ~iny1idene.l~~ The effect of structure on the zirconium-promoted bicyclization of enynes has been examined.'55 Reductive cyclization of 1,6-and 1,7-enynes [by R,SiH-L2Pd( H)X catalyst] has been probed mechanistically and stereochemically.'56 The products (exocyclic alkenes) were formed in very good yields; in one case the reaction gave complete stereospecificity since (55) afforded (56) as a single diastereoisomer.Diynes cyclized smoothly to E,E-exocyclic diems with Ti or Zr reagents e.g. MeC=C(CH2),C~CMe gave (57) after cyclization followed by treatment with OMe acid.'57 Sodium methoxide was used to convert 5-chloro-5-methylhexa- 1,3-diyne into dimethylpentatetraenylidene (58) which further gave (59) and (60).15*It was presumed that (60) arose from internal return and (59) from solvent addition to (61). Finally 2-quinolone derivatives have been obtained by the cycloaddition of aryl isocyanates to amin~butadiynes.'~~ 149 A.Ammann M. Rey and A. S. Dreiding Helv. Chim. Acta 1987 70 321. G. Himbert and L. Henn Liebigs Ann. Chem. 1987 771. 151 F. Marcuzzi G. Melloni and M. V. Zucca Gazz. Chim. Ital. 1987 117 219. I52 P. Pale and J. Chuche Tetrahedron Lett. 1987 28 6447. 153 H. Yasuda and A. Nakamura Angew. Chem. In?. Edn. Engl 1987 26 723. I54 R. P. Duran V. T. Amorebieta and A. J. Colussi J. Am. Chem. SOC. 1987 109 3154. '55 E. Negishi D. R. Swanson F. E. Cederbaum and T. Takahashi Tetrahedron Lett. 1987 28 917. 156 B. M. Trost and F. Rise J. Am. Chem. SOC. 1987 109 3161. 157 W. A. Nugent D. L. Thorn and R. L. Harlow J. Am. Chem. Soc. 1987 109 2788. 158 S. Basak S. Srivastava and W. J. le Noble J. Org. Chem. 1987 52 5095. 159 M. Ban M. Fenstel G.Himbert and G. Maas Liebigs Ann. Chem. 1987 221.