Photobromination of carbohydrate derivatives. VI. Functionalization at C6 of 2,3,4-Tri-O-acetyl-1,6-anhydro-β-D-glucopyranose

Abstract

Photobromination of 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-glucopyranose gives the syrupy 6S (exo) bromide in high yield; further reaction leads to secondary bromination at this position. The monobromide reacts with methanol and thiophenol under conditions of kinetic control to give mainly the endo-methoxy and -phenylthio derivatives formed by direct nucleophilic displacement, and from the latter the exo-methoxy acetal was obtained by a second nucleophilic substitution. Acetolysis of these compounds can lead to the corresponding exo-6-acetoxy ester or monocyclic products formed by opening of the five-membered rings.