Dimethylformamide: an unusual glycosylation modulator.

However, most of these methods require additional steps forthe installation of a specific functionality and are thereforeless convenient for routine synthesis. Herein, we report asimple and general a-glycosylation method in which N,N-dimethylformamide (DMF) is used as a modulating moleculeto direct the stereochemical course of glycosylation. Furtherelaboration of this approach led to a practical a-selectiveprocedure based on preactivation that is useful for theglycosylaton of both O-glycoside and thioglycoside acceptors.In a previous study of the chlorination of glycosylhemiacetals, we observed that residual DMF in the glyco-sylation mixture promoted the formation of 1,2-cis a-glyco-sidic bonds.