Catalytic Activation of Thioglycosides with Copper-Carbenes for Stereoselective 1,2-<i>Cis</i>-Furanosylations

Thioglycoside activation, crucial for oligosaccharide synthesis, faces challenges with the need for stoichiometric promoters, additives, and cryogenic conditions, particularly in stereoselective 1,2-<i>cis</i>-linkage formation. This study introduces a carbene-based catalytic method using Cu(OTf)₂ for thioglycoside activation, enabling efficient 1,2-<i>cis</i>-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.