Expanding the scope of stereoselective α-galactosylation using glycosyl chlorides

Recently, we reported that silver(I) oxide mediated Koenigs-Knorr  glycosylation  reaction can be dramatically accelerated in the presence of catalytic acid additives. We have also investigated how well this reaction works in application to differentially protected  galactosyl  bromides. Reported herein is the  stereoselective synthesis  of α-galactosides with galactosyl chlorides as  glycosyl  donors. Chlorides are easily accessible, stable, and can be efficiently activated for glycosylation. In this application, the most favorable reactions conditions comprised cooperative Ag 2 SO 4  and Bi(OTf) 3  promoter system.