ABSTRACT
The reaction of (S)-alpha-(1-hydroxyalkyl)vinyl sulfoxides (S)-5 with alkyl radicals and tributyltin hydride gave the addition-hydrogenation products with high diastereoselectivity, whereas the reaction with (R)-alpha-(1-hydroxyalkyl)vinyl sulfoxides (R)-5 resulted in complete recovery of the starting sulfoxides. Stereoselective intramolecular hydrogen bonding between the hydroxy group and the diastereotopic sulfonyl oxygen led to high diastereoselectivity in the radical reaction of alpha-(1-hydroxyethyl)vinyl sulfone 12. An important role of intramolecular hydrogen bonding on the diastereoselectivity as well as the reactivity toward alkyl radicals is discussed.
ABSTRACT
Reactions of alpha-sulfinyl carbanions, derived from p-tolyl sulfoxides bearing various alkyl groups, with various electrophiles were examined. The reaction of alpha-sulfinyl carbanions, derived from the beta-silylethyl sulfoxides, with ketones or trimethyl phosphate, gave the syn products with high stereoselectivity. Interaction between the silicon in the trialkylsilyl group and the carbonyl oxygen in nucleophiles was postulated to stabilize the transition state, leading preferably to the syn diastereisomers. This novel silicon-oxygen interaction was supported by an MO calculation study using the MOPAC 93/PM3 and the Gaussian 94 Beche3LYP/3-21+G methods.
