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

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-xylopyranosyl bromide ( 1), using a sacrificial zinc anode gave an α,β anomeric mixture of [4-(4-cyanobenzoylphenyl)] 2,3,4-tri- O-acetyl-1,5-dithio- d-xylopyranoside ( 6) in 40–70% yield, according to the experimental conditions used (nature of solvent, electrolyte salt, and temperature). High selectivity favouring the α anomer of 6 is observed starting from the α anomer of 1. Mechanistic aspects are discussed. Graphic