Visible-Light-Promoted Direct Desulfurization of Glycosyl Thiols to Access of C-Glycosides

Abstract

C-Glycosides are essential for the study of biological processes and the development of carbohydrates-based drugs. Despite tremendous hurdles, glycochemists have often fantasized of the efficient, highly stereoselective synthesis of C-glycosides with the shortest steps under mild conditions. Herein, we report a desulfurative radical protocol to synthesize C-alkyl glycosides and coumarin C-glycosides under visible-light induced conditions without the need of an extra photocatalyst, in which stable and readily available glycosyl thiols that could be obtained in two or three steps from native sugars are activated in situ by pentafluoropyridine. The benefits of this procedure include high stereoselectivity, broad substrates scope, and easily handle. Mechanistic studies indicated that the in situ produced tetrafluoropyridyl S-glycosides formed key EDA complexes with Hantzsch ester (for C-alkyl glycosides) or Et3N (for coumarin C-glycosides), which upon irradiation of visible light, triggered a cascade of glycosyl radical process to access C-glycosides smoothly.