Facile Cu(OTf) 2 -Catalyzed Preparation of Per- O -acetylated Hexopyranoses with Stoichiometric Acetic Anhydride and Sequential One-Pot Anomeric Substitution to Thioglycosides under Solvent-Free Conditions

Solvent-free per-O-acetylation of hexoses with a stoichiometric amount of acetic anhydride employing 0.03 mol % Cu(OTf)2 proceeded in high yields (90-99%) at room temperature to give exclusively pyranosyl products as an anomeric mixture, the alpha/beta ratio of which was dependent on the temperature and amount of catalyst used. Sequential anomeric substitution with p-thiocresol in the presence of BF3.etherate gave the thioglycosides, isolated exclusively or predominantly as one anomer in 66-75% yields.