Revisiting Glycosylations Using Glycosyl Fluoride by BF 3 ·Et 2 O: Activation of Disarmed Glycosyl Fluorides with High Catalytic Turnover.

Catalytic glycosylations with glycosyl fluorides using BF 3 ·Et 2 O are presented. Glycosylations with both armed and disarmed donors were efficiently catalyzed by 1 mol% of BF 3 ·Et 2 O in a nitrogen-filled glovebox without the use of dehydrating agents. Our finding is in sharp contrast with conventional BF 3 ·Et 2 O-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.