A REGIOCONTROLLED AND STEREOCONTROLLED SYNTHESIS OF ALLYLSILANES FROM BETA-SILYL ENOLATES

The alpha-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 beta-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 beta-trimethylsilyl enolates 45 and 46 giving the allylsilanes 49, 50, 53 and 54.