Diastereoselectivity in the SE2″ reaction of chiral pentadienylsilanes: a test for the relative importance of steric and electronic effects

The homochiral pentadienylsilanes (3Z,5E)-(hepta-3,5-dien-2-yl)dimethyl(phenyl)silane 9, (3Z,5E)-(hepta-3,5-dien-2-yl)trimethylsilane 13, (4Z,6E)-(2-methylocta-4,6-dien-3-yl)dimethyl(phenyl)silane 14 and (4Z,6E)-(2-methylocata-4,6-dien-3-yl)trimethylsilane 17 undergo Lewis acid catalysed reactions with isobutyraldehyde and its dimethyl acetal stereospecifically anti with surprisingly high levels of stereoselectivity, ca. 90:10. The pentadienylsilanes (3Z)-hexa-3,5-dien-2-yldimethyl(phenyl)silane 20aa, (4Z)-(2-methylhepta-4,6-dien-3-yl)dimethyl(phenyl)silane 20ab, (3Z)-(hexa-3,5-dien-2-yl)-trimethylsilane 20ba and (2Z)-(1-phenylpenta-2,4-dienyl)trimethylsilane 20bc undergo dipolar cycloadditions to 2,2-dimethylpropanenitrile oxide regioselectively at the terminal double bond and stereoselectively anti to the silyl group to a somewhat lower extent, ca. 70:30. The pentadienylsilane (3Z,5E)-(6-cyclohexylhexa-3,5-dien-2-yl)trimethylsilane 25 undergoes deuteriodesilylation stereospecifically anti to a lower extent still, ca. 55:45. The pentadienylsilane (3Z,5E)-(8-methyl-8-methoxyethoxymethoxynona-3,5-dien-2-yl)trimethylsilane 34 undergoes an intramolecular reaction stereospecifically anti again to the extent of about 60:40, whereas the reaction of the corresponding allylsilane (3Z)-(6-methyl-6-methoxyethoxymethoxyhept-3-en-2-yl)trimethylsilane 32 is essentially completely anti. These results show that SE2″ reactions can be highly stereoselective in the anti sense, that the high level is probably best accounted for by the steric effect of the silyl group, and that when the steric effect is minimised, the stereospecificity is low, but still measurable. The pentadienylsilanes were prepared by aldol reactions between β-silyl esters and the appropriate α,β-unsaturated aldehyde, followed by decarboxylative elimination. The products of the SE2″ reactions were identified and their stereochemistry determined by comparison with authentic materials or by degradation and synthesis, using chiral auxiliaries to determine the enantiomeric purity. The products of two of the dipolar cycloadditions were identified by degradation and stereospecific vinylogous Peterson elimination, but the vinylogous Peterson elimination taking place with (1RS,2Z,4SR,6SR)-(4,6-dihydroxy-7,7-dimethyl-1-phenyloct-2-enyl)trimethylsilane 67bc and its (1SR) diastereoisomer 68bc was not stereospecific, giving (5E,7E)-2,2-dimethyl-8-phenylocta-5,7-dien-3-ol 73 from both isomers. The stereochemistries of all the reactions are summarised.

[1]  Randall S. Smith,et al.  Evidence for an Oxocarbenium Ion Intermediate in Lewis Acid Mediated Reactions of Acyclic Acetals , 1994 .

[2]  J. Aizpurua,et al.  Asymmetric 1,4-addition of higher order silylcuprates to Oppolzer's N-enoyl sultams , 1994 .

[3]  I. Fleming,et al.  Accurate determination of the extent to which the SE2' reactions of an allenylsilane are stereospecifically anti , 1993 .

[4]  I. Fleming,et al.  Accurate determination of the extent to which an SE2′ reaction of an allylsilane is anti , 1992 .

[5]  K. Houk,et al.  A force field model for the transition structures of intramolecular nitrile oxide cycloadditions , 1992 .

[6]  R. W. Hoffmann,et al.  Allylic 1,3-strain as a controlling factor in stereoselective transformations , 1989 .

[7]  W. Jencks,et al.  Concerted bimolecular substitution reactions of acetal derivatives of propionaldehyde and benzaldehyde , 1989 .

[8]  E. Zass,et al.  Concerning the Stereochemistry of SE'‐Type Reactions , 1989 .

[9]  A. Shani,et al.  The Wittig reaction: comments on the mechanism and application as a tool in the synthesis of conjugated dienes , 1989 .

[10]  W. Kitching,et al.  Syntheesis and stereochemistry of acidolysis of some cyclohept-2-enylstannames and -silanes , 1988 .

[11]  W. Hehre,et al.  Modeling chemical reactivity. 4. Regiochemistry and stereochemistry of electrophilic additions to allylic double bonds , 1987 .

[12]  A. K. Sarkar,et al.  The stereochemistry of an SE2″ reaction of a chiral dienylmethylsilane☆ , 1987 .

[13]  Michael J. Shapiro,et al.  1,3-Syn diastereoselective reduction of β-hydroxyketones utilizing alkoxydialkylboranes , 1987 .

[14]  W. Oppolzer,et al.  Preparation of Enantiomerically Pure β-Silylcarboxyl Derivatives by Asymmetric 1,4-Addition to N-Enoyl-sultams. Preliminary Communication† , 1986 .

[15]  M. Kumada,et al.  Asymmetric synthesis catalyzed by chiral ferrocenylphosphine-transition metal complexes. 3. Preparation of optically active allylsilanes by palladium-catalyzed asymmetric Grignard cross-coupling , 1986 .

[16]  E. Vedejs,et al.  Hyperconjugative Effects of Allylic Substituents Are Not Important in Osmylations. , 1986 .

[17]  R. A. Whitney,et al.  Factors affecting diastereoselectivity in the protiodemercuration of .alpha.-mercurio carbonyl compounds , 1986 .

[18]  K. Houk,et al.  Steric Models for Stereoselectivity of Nitrile Oxide Cycloadditions to Chiral Alkenes , 1986 .

[19]  Davidr . Evans,et al.  The directed reduction of β-hydroxy ketones employing Me4NHB(OAc)3 , 1986 .

[20]  M. Kumada,et al.  Optically active allylsilanes. 8. Stereochemistry in the reaction of optically active allylsilanes with m-chloroperoxybenzoic acid , 1984 .

[21]  I. Fleming,et al.  The relative stereochemistry of some α-methyl-β-silylcarbonyl compounds produced by the diastereoselective alkylation of β-silylenolates☆ , 1984 .

[22]  P. Stein,et al.  Intramolecular nitrile oxide cycloaddition route to carbocyclics: a formal total synthesis of PGF2α , 1984 .

[23]  K. Houk,et al.  Stereoselective nitrile oxide cycloadditions to chiral allyl ethers and alcohols. The inside alkoxy effect , 1984 .

[24]  R. Heck,et al.  Palladium-catalyzed syntheses of aryl polyenes , 1984 .

[25]  I. Fleming,et al.  Stereospecific syntheses and reactions of allyl- and allenyl-silanes , 1984 .

[26]  K. Narasaka,et al.  Stereoselective reduction of β hydroxyketones to 1,3-diols highly selective 1,3-asymmetric induction via boron chelates , 1984 .

[27]  A. Meyers,et al.  Stereoselectivity in the aldol reaction: the use of chiral and achiral oxazolines as their boron azaenolates , 1984 .

[28]  H. Wetter,et al.  Ein Beitrag zur Stereochemie der S′E‐Reaktion: Die Protonierung eines optisch aktiven 1, 1‐Disilyl‐2‐alkens , 1983 .

[29]  I. Hamachi,et al.  Erythroselectivity in addition of γ-substituted allylsilanes to aldehydes in the presence of titanium chloride , 1983 .

[30]  K. Tamao,et al.  Optically active cyclic allylsilanes: Preparation by asymmetric hydrosilylation and anti stereochemistry in SE' reactions☆ , 1983 .

[31]  P. F. Hudrlik,et al.  Protodesilylation reactions of simple .beta.-hydroxysilanes (and .alpha.-hydroxysilanes). Homo-Brook rearrangements , 1982 .

[32]  M. Kumada,et al.  Optically active allylsilanes. 2. High stereoselectivity in asymmetric reaction with aldehydes producing homoallylic alcohols , 1982 .

[33]  M. Kumada,et al.  OPTICALLY ACTIVE ALLYLSILANES. 1. PREPARATION BY PALLADIUM-CATALYZED ASYMMETRIC GRIGNARD CROSS-COUPLING AND ANTI STEREOCHEMISTRY IN ELECTROPHILIC SUBSTITUTION REACTIONS , 1982 .

[34]  Davidr . Evans,et al.  Asymmetric alkylation reactions of chiral imide enolates. A practical approach to the enantioselective synthesis of .alpha.-substituted carboxylic acid derivatives , 1982 .

[35]  M. Kumada,et al.  Anti stereochemistry in protodesilylation of an optically active allylsilane with trifluoroacetic acid-D , 1982 .

[36]  D. Evans,et al.  Enantioselective aldol condensations. 2. Erythro-selective chiral aldol condensations via boron enolates , 1981 .

[37]  D. Parker,et al.  Determination of optical purity at isotopically chiral sites by 2H NMR , 1981 .

[38]  K. Tomioka,et al.  Convenient preparation of .alpha.,.beta.-unsaturated aldehydes , 1978 .

[39]  A. Ishida,et al.  A New Method for the Preparation of δ-Alkoxy-α,β-unsaturated Aldehydes and Polyenals , 1977 .

[40]  D. Duncan,et al.  Catalytic reduction. 4. Hydrogenation of aldehydes over borohydride reduced nickel and palladium , 1977 .

[41]  J. M. Wilkins,et al.  Chemistry of carbanions. XXVII. Convenient precursor for the generation of lithium organocuprates , 1975 .

[42]  C. R. Watts,et al.  Origin of reactivity, regioselectivity, and periselectivity in 1,3-dipolar cycloadditions , 1973 .

[43]  R. W. Strozier,et al.  Frontier molecular orbitals of 1,3 dipoles and dipolarophiles , 1973 .

[44]  M. Christl,et al.  1,3-Dipolare Cycloadditionen, 73. Relative Dipolarophilen- Aktivitäten bei Cycloadditionen des Benzonitriloxids , 1973 .

[45]  F. Carey,et al.  CNDO-MO [complete neglect of differential overlap-molecular orbital] exploration of concerted and stepwise pathways for the Wittig and Peterson olefination reactions , 1973 .

[46]  J. Baeza,et al.  Stereospecific introduction of double bounds via thermolysis of .beta.-lactones , 1972 .

[47]  D. Dull,et al.  .alpha.-Methoxy-.alpha.-trifluoromethylphenylacetic acid, a versatile reagent for the determination of enantiomeric composition of alcohols and amines , 1969 .

[48]  John D. Roberts,et al.  Methylation of Alcohols with Diazomethane , 1959 .

[49]  P. Bailey.  Adipic Acid by Ozonolysis of Cyclohexene , 1958 .