Issue 24, 1992

A regioselective and stereospecific synthesis of allylsilanes from secondary allylic alcohol derivatives

Abstract

Primary and secondary allylic acetates and benzoates react with the dimethyl (phenyl)silyl-cuprate reagent to give allylsilanes, provided that the THF in which the cuprate is prepared is diluted with ether before addition of the allylic ester. The reaction is reasonably regioselective in some cases: (i) when the allylic system is more-substituted at one end than the other, as in the reactions 45 and 910; (ii) when the steric hindrance at one end is neopentyl-like, as in the reactions 1516; and (iii) when the disubstituted double bond has the Z configuration, as in the reactions Z-19E-21 or, better, because the silyl group is becoming attached to the less-sterically hindered end of the allylic system, Z-20E-22. The regioselectivity is better if a phenyl carbamate is used in place of the ester, and a three-step protocol assembling the mixed cuprate on the leaving group is used, as in the reactions 2324 and E- or Z-29E-21, or, best of all, because the silyl group is again becoming attached to the less-sterically hindered end of the allylic system, E- or Z-30E-22. This sequence works well to move the silyl group onto the more substituted end of an allyl system, but only when the move is from a secondary allylic carbamate to a tertiary allylsilane, as in the reaction 3839. Allyl(trimethyl)silanes can be made using alkyl- or aryl-cuprates on trimethylsilyl-containing allylic esters and carbamates, as in the reactions 4041, and 4344. The reaction of the silyl-cuprate with allylic esters and the three-step sequence with the allylic carbamates are stereo-chemically complementary, the former being stereospecifically anti and the latter stereospecifically syn. Homochiral allylsilanes can be made by these methods with high levels of stereospecificity, as shown by the synthesis of the allylsilanes 54, 58 and 59.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 1, 1992, 3331-3349

A regioselective and stereospecific synthesis of allylsilanes from secondary allylic alcohol derivatives

I. Fleming, D. Higgins, N. J. Lawrence and A. P. Thomas, J. Chem. Soc., Perkin Trans. 1, 1992, 3331 DOI: 10.1039/P19920003331

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