Glycosylidene-carbene-mediated homologation of boronic esters for the synthesis of boro-ketosides

C-glycosides are widely present in natural products and artificially designed therapeutic agents. The synthesis of C-glycosides has attracted considerable attention, and strategies based on the transformation of oxocarbenium ions, glycosyl anions, glycosyl radicals, or transition metal complexes have been extensively studied. Glycosylation based on the chemistry of glycosylidene carbenes, by contrast, is far less explored, and the generation of glycosylidene carbenes is a long-standing challenge. Herein, we report a practical method for the generation of glycosylidene carbenes by copper-catalyzed oxidation of bench-stable glycosylidene diaziridines with oxygen at room temperature. Capturing the glycosylidene carbenes with boronic esters afforded boro-ketosides, which were conveniently converted to structurally diversified C-glycosides via vinylation, deuteration, and oxidation reactions. This procedure offers a powerful platform for exploring the chemistry of glycosylidene carbenes and developing innovative glycosylation strategies.