Unexpected Orthogonality of <i>S</i>-Benzoxazolyl and <i>S</i>-Thiazolinyl Glycosides: Application to Expeditious Oligosaccharide Assembly

Thorough mechanistic studies of the alkylation pathway for the activation of glycosyl thioimidates have led to the development of the “thioimidate-only orthogonal strategy”. Discrimination among S-thiazolinyl (STaz) and S-benzoxazolyl (SBox) anomeric leaving groups was achieved by fine-tuning of the activation conditions. Preferential glycosidation of a certain thioimidate is not simply determined by the strength of activating reagents; instead, the type of activationdirect vs indirectcomes to the fore and plays the key role.