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.

Synthesis of Cage-Shaped Aluminum Aryloxides: Efficient Lewis Acid Catalyst for Stereoselective Glycosylation Driven by Flexible Shift of Four- to Five-Coordination.

Monomeric cage-shaped aluminum aryl oxides 1Al were synthesized using tripodal triphenolic ligands. The Lewis acidity and catalytic activity of the obtained 1Al·py were investigated. The Lewis acidity of 1Al·py originates from the flexible change in the coordination number of the aluminum center, allowing the catalytic O-glycosylation to occur with a high efficiency and an unusual stereoselectivity.