Expedient Synthesis of Superarmed Glycosyl Donors via Oxidative Thioglycosidation of Glycals.

Superarmed glycosyl donors have higher reactivity compared to their perbenzylated armed counterparts. Generally, the 2-- benzoyl-3,4,6-tri--benzyl protecting group pattern gives rise to increased reactivity due to an O-2/O-5 cooperative effect. Despite having a high reactivity profile and applicability in many expeditious strategies for glycan synthesis, regioselective introduction of the superarming protecting group pattern is tedious for most sugar series. Reported herein is a streamlined synthetic route to yield superarmed glycosyl donors of the d-gluco and d-galacto series equipped with an ethylthio, phenylthio, -tolylthio, benzoxazol-2-ylthio, -allyl, or -pentenyl anomeric leaving group. This streamlined approach was made possible due to the refinement of the oxidative thioglycosylation reaction of the respective glucal and galactal precursors. The applicability of this approach to the direct formation of disaccharides is also showcased.