The reaction of (2S,S-S)-alpha-(1-hydroxyethyl)vinyl sulfoxide with alkyl radicals and tributyltin hydride gave the addilion-hydrogenation products with high diastereoselectivity, whereas (2R,S-S)-alpha-(-1-hydroxyethyl)vinyl sulfoxide gave no products under similar conditions. An important role of intramolecular hydrogen bonding for the diastereoselectivity as well as the reactivity toward alkyl radicals is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.