Selective Anomeric Acetylation of Unprotected Sugars with Acetic Anhydride in Water

Abstract

Unprotected sugars are selectively acetylated simply by stirring in aqueous solution in the presence of acetic anhydride and a weak base such as sodium carbonate. The reaction is selective for acetylation of the anomeric hydroxyl group of mannose, 2-acetamido, and 2-deoxy sugars and can be performed on a large scale. Competitive intramolecular migration of the 1-<i>O</i>-acetate to the 2-hydroxyl group when these two substituents are <i>cis</i> causes over-reaction and the formation of product mixtures.