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.