S-Acetyl migration in synthesis of sulfur-containing glycosides

Unexpected products are often found in the synthesis of sulfur-containing glycosides where the sulfur-containing group is acquired through substitution of a leaving group by a thioacetate reagent. Thus low yields have to be born. The reason has been disclosed to originate from the basicity and nucleophilicity of sulfur atom leading to a thioacetyl group migration in this study. The migration may occur through a five or six-membered ring tetrahedral intermediate, followed by cleavage of CS bond of this intermediate to form a sulfhydryl anion and subsequently another acetyl group migration from the thioacetate reagent to the sulfhydryl anion, leading to an unexpected product with an acetylated neighboring hydroxyl group. The occurrence of the migration may depend on the concentration of thioacetate reagent and the steric and stereoelectronic effects of the substrate itself. Based on these results, the yields for synthesis of sulfur-containing glycosides can be highly improved.