Catalytic Activation\nof Thioglycosides with Copper-Carbenes\nfor Stereoselective 1,2-<i>Cis</i>-Furanosylations

Thioglycoside activation, crucial for oligosaccharide\nsynthesis,\nfaces challenges with the need for stoichiometric promoters, additives,\nand cryogenic conditions, particularly in stereoselective 1,2-<i>cis</i>-linkage formation. This study introduces a carbene-based\ncatalytic method using Cu(OTf)<sub>2</sub> for thioglycoside activation,\nenabling efficient 1,2-<i>cis</i>-furanosylation in ribose\nand arabinose. The method is orthogonal to conventional thioglycoside\nand alkyne donors, accommodates sterically demanding acceptors, and\nachieves stereoselectivity independent of the donor anomeric configuration\nand C2-protecting groups, with copper chelation playing a key role.