A Direct Method for β-Selective Glycosylation with an N-Acetylglucosamine Donor Armed by a 4-O-TBDMS Protecting Group.

A new direct method for β-selective glycosylation with an N-acetylglucosamine (GlcNAc) donor was developed. This substrate, which can be readily prepared from commercially available GlcNAc in two steps, contains a 4-O-tert-butyldimethylsilyl (TBDMS) protecting group as a key component. We found that this functionality could have a favorable effect on the reactivity of the GlcNAc donor. Glycosylation with the armed donor using primary alcohols in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf) in 1,2-dichloroethane smoothly gave the desired coupling products in good yields with complete β-selectivity, while sterically hindered acceptors were less efficient.