Photo-bromination of carbohydrate derivatives. Part 3. C-5 bromination of penta-O-benzoyl-α- and -β-D-glucopyranose; a route to D-xylo-hexos-5-ulose derivatives and α-L-idopyranosides

Abstract

Photo-bromination of penta-O-benzoyl-β-D-glucopyranose with bromine gives good yields of the 5-bromoderivative; the α-anomer reacts less well but also gives a crystalline 5-bromide. Hydrolysis gives D-xylo-hexos-5-ulose tetrabenzoate, which exists as the cyclic hydrate and reacts readily with alcohols and thiols to give tetra-O-benzoyl-5-hydroxy-β-D-glucopyranosides and 1-thin-analogues. These 5-hydroxy products can be methylated and the ‘diglycosides’ react with hydrogen chloride to afford 5-chloroglycoside esters from which α-D-idopyranosides are obtainable by reduction. Acetylation of a 5-hydroxyglycoside gives an acyclic product; a 5-hydroxythioglycoside gives some cyclic and some acyclic products.