Utilisation d'ylides du phosphore en chimie des sucres XXIII Eliminations accompagnant certaines réactions de Wittig†

Some reactions of 3-O-alkyl-6-deoxy-1,2-O-isopropylidene-α-D-xylo-hexofuranos-5-uloses (1 and 2) with Wittig reagents are described. These ketosugars react with methylenetriphenylphosphorane and benzylidenetriphenylphosphorane to give the expected unsaturated branched-chain sugars and dienes formed by elimination of H–C(4) and the 3-alkyloxy group. Structural studies on all these compounds have been effected using NMR. spectroscopy and particularly, when necessary, nuclear Overhauser Effect. One important by-product of these reactions is an unsaturated ketone 3,6-dideoxy-1,2-O-isopropylidene-α-D-glycero-hex-3-enofuranos-5-ulose (6). Compounds 1 and 2 do not react with cyanomethylenetriphenylphosphorane.