Catalytic Activation of Thioglycosides with Copper-Carbenes for Stereoselective 1,2--Furanosylations.

Thioglycoside activation, crucial for oligosaccharide synthesis, faces challenges with the need for stoichiometric promoters, additives, and cryogenic conditions, particularly in stereoselective 1,2--linkage formation. This study introduces a carbene-based catalytic method using Cu(OTf) for thioglycoside activation, enabling efficient 1,2--furanosylation in ribose and arabinose. The method is orthogonal to conventional thioglycoside and alkyne donors, accommodates sterically demanding acceptors, and achieves stereoselectivity independent of the donor anomeric configuration and C2-protecting groups, with copper chelation playing a key role.