Electron-deficient pyridinium salts/thiourea cooperative catalyzed <i>O</i>-glycosylation via activation of <i>O</i>-glycosyl trichloroacetimidate donors

Abstract

The glycosylation of O -glycosyl trichloroacetimidate donors using a synergistic catalytic system of electron-deficient pyridinium salts/aryl thiourea derivatives at room temperature is demonstrated. The acidity of the adduct formed by the 1,2-addition of alcohol to the electron-deficient pyridinium salt is increased in the presence of an aryl thiourea derivative as an hydrogen-bonding cocatalyst. This transformation occurs under mild reaction conditions with a wide range of O -glycosyl trichloroacetimidate donors and glycosyl acceptors to afford the corresponding O -glycosides in moderate to good yields with predictable selectivity. In addition, the optimized method is also utilized for the regioselective O -glycosylation by using a partially protected acceptor.