Utilisation d'ylides du phosphore en chimie des sucres. XI. Synthèse des quatre didésoxy-3, 5-méthyl-3-pentoses parl'intermédiaire de sucres insaturés ramifiés

Treated with methylthiomethylenetriphenylphosphorane, 5-deoxy-1,2-O-iso-propylidene-β-D -threo- and -α-D -erythro-furanos-3-uloses led with good yields to a mixture of the cis-trans isomers of the corresponding methylthiovinylidenic sugars. There was no inversion of configuration at C(4) with the thero-furanosulose and a small one (7%) with its erythro isomer. These unsaturated branched-chain thio-sugars are useful synthetic intermediates. For examples, the desulfurization-hydrogenation (Raney Nickel) of each of these alkenes afforded in good yield two 3-deoxy-3-C-methyl-pentoses epimeric at C(3) and having the same configuration at C(4) as the starting alkenes. In all cases the isomer formed by attack from the less hindered face of the double bond was the preponderant one.