Reaction Rate and Stereoselectivity Enhancement in Glycosidations with O-Glycosyl Trihaloacetimidate Donors due to Catalysis by a Lewis Acid-Nitrile Cooperative Effect.

Activation of -glycosyl trihaloacetimidate glycosyl donors with AuCl as a catalyst and pivalonitrile (BuCN) as a ligand led to excellent glycosidation results in terms of yield and anomeric selectivity. In this way, various β-d-gluco- and β-d-galactopyranosides were obtained conveniently and efficiently. Experimental studies and density functional theory (DFT) calculations, in order to elucidate the reaction course, support formation of the BuCN-AuCl-OR(H) AuCl complex as a decisive intermediate in the glycosidation event.