A regiocontrolled and stereocontrolled synthesis of allylsilanes from β-silyl enolates

Abstract

The α-lithiated diphenylphosphine oxides 3 react with methyl iodide to give the phosphine oxides 4 and 5 in a ratio of 3–4 : 1. The corresponding reaction with aldehydes gives all four diastereoisomeric alcohols 7–10, which are not suitable for the synthesis of allylsilanes by a Wittig–Horner reaction. The β-dimethyl(phenyl)silyl enolates 13–15 and 25–28 react with aldehydes to give aldol products with high diastereoselectivity. The benzyl and allyl ester groups can be cleaved from these aldols to give the acids 16–18 and 29–32. The acids, in turn, can be induced to undergo decarboxylative elimination stereospecifically either in a syn or an anti sense to give the allylsilanes 19, 20, 23, 24, 33, 34 and 39–41. A similar series of reactions can be carried out with the β-trimethylsilyl enolates 45 and 46 giving the allylsilanes 49, 50, 53 and 54.