Exploration of thioglycosides in photoinduced desulfurative cross-coupling reactions

Thioglycosides have been a mainstay of O-glycosylation chemistry. Here we demonstrate that under mild photochemical conditions, readily synthesized bench-stable electron poor thioglycosides are also useful C-glycoside precursors, undergoing desulfurative glycosyl radical generation. Two complementary classes thioglycosides are described. The glycosyl dithioimidocarbonates, undergo radical coupling in the presence of 4CzIPN, a weak acid and Hantzsch ester, under blue light illumination. Alternatively, 4-cyanotetrafluorophenyl or 4-tetrafluropyridyl thioglycosides can be used to generate glycosyl radicals in the presence of a base and Hantzsch ester under blue light irradiation in a catalyst-free approach. These radicals perform well in Geise-like reactions to yield C-glycosides with high stereoselectivity. Furthermore, related thioethers bearing 4-cyanotetrafluorophenyl groups are also potent radical precursors.