Revisiting Glycosylations Using Glycosyl Fluoride by BF3·Et2O: Activation of Disarmed Glycosyl Fluorides with High Catalytic Turnover.

Catalytic glycosylations with glycosyl fluorides using BF3·Et2O are presented. Glycosylations with both armed and disarmed donors were efficiently catalyzed by 1 mol% of BF3·Et2O in a nitrogen-filled glovebox without the use of dehydrating agents. Our finding is in sharp contrast with conventional BF3·Et2O-mediated glycosylations, where excess Lewis acid and additives are required. Mechanistic studies indicated that the chemical species formed by the reaction of in situ generated HF and glass vessels are involved in the catalytic cycle.