N-nitrosamine directed stereoselective O-glycosylation reactions of 2-amino thioglycosides with NIS-TfOH.

We described here the stereoselective synthesis of O-glycosides from 2-amino thioglycosides using N-nitrosamine as the directing group. The reaction was activated by using the NIS/TfOH system in dichloromethane at -10 °C. Various sugar and non-sugar acceptors were successfully glycosylated with 2-amino 1-thioglucoside and 2-amino 1-thiogalactoside under mild reaction conditions. These reactions provided β-glycosides in good to excellent yields.