New efficient electrochemical synthesis of 1,5-dithioxylopyranosides in the presence of a sacrificial anode

摘要

Electroreduction of the disulfide derivative RSSR (5, R = - C_6H_4-CO-C_6H_4-CN) on a mercury pool or a carbon gauze electrode in the presence of 2,3,4-tri-O-acetyl-5-thio-D-xylpyranosyl bromide (1), using a sacrificial zinc anode gave an alpha,beta-anomeric mixture of [4-(4-cyanobenzoylphenyl)] 2,3,4-tri-O-acetyl-1,5-dithio-D-xylopyranoside (60 in 40-70% yield, according to the experimental conditions used (nature of solvent, electrolyte salt, and temperature). High selectivity favouring the alpha anomer of 6 is observed starting from the alpha anomer of 1. Mechanistic aspects are discussed.