Mild Activation of 2-Pyridyl 1-Thioglycosides as Stable Donors for α-Stereoselective Glycosylation

The stereoselective α-glycosylation of d-galactosides, d-mannosides, and l-fucosides was accomplished using 2-pyridyl 1-thioglycosides (SPy) as stable donors, which were activated by copper triflate. High α-stereoselectivities were observed with glycan acceptors, while most aglycon acceptors exhibited low selectivity. Orthogonal activation of SPy glycosides in the presence of thioglycosides was effectively demonstrated in the synthesis of oligosaccharides.