BROMINOLYSIS REACTION OF STANNYLENE DERIVATIVES - REGIOSPECIFIC SYNTHESIS OF CARBOHYDRATE-DERIVED HYDROXY-KETONES

The oxidation of six partially protected derivatives of glucose and galactose with two free hydroxy-groups, by treatment with bromine of their O-dibutylstannylene derivatives, dissolved in benzene, in the presence of a hydrogen bromide or proton scavenger, was found to be regiospecific, giving in good yield only one of the two possible hydroxy-ketones. For instance, benzyl 4,6-O-benzylidene-β-D-arabino-hexopyranos-3-uloside (34) was prepared in 72% yield from benzyl 4,6-O-benzylidene-β-D-galactopyranoside. The benzoylation of these dibutylstannylenes in benzene solution without added base was often regiospecific. Possible correlations between the preferred sites of oxidation and benzoylation in these conditions are discussed.