Targeted glycosyl donor delivery for site-selective glycosylation

[GRAPHICS] n-Pentenyl ortho esters (NPOEs) and n-pentenyl glycosides (NPGs) are interconvertible glycosyl donors which are activated by reaction with halonium ions. In a series of cyclic syn-1,3-diols, NPOEs have been found to specifically glycosylate the equatorial-OH while the NPG glycosylates predominantly, but not exclusively, the axial-OR. When the cyclic diol acceptor is presented with equivalent amounts of an NPOE and an NPG in a three component reaction, a single, double-glycosylation product is obtained, which conforms to the foregoing preferences, presenting evidence for site-selective glycosylation.