Formal Glycosylation of Quinones with <i>exo</i>-Glycals Enabled by Iron-Mediated Oxidative Radical–Polar Crossover
Haijuan Liu, Adrien G. Laporte, Damien Tardieu, Damien Hazelard, Philippe Compain
Abstract
The intermolecular C–O coupling reaction of 1,4-quinones with exo-glycals under iron hydride hydrogen atom transfer (HAT) conditions is described. This method provides a direct and regioselective access to a wide range of phenolic O-ketosides related to biologically relevant natural products in diastereomeric ratios up to >98:2 in the furanose and pyranose series. No trace of the corresponding C-glycosylated products that might have resulted from the radical alkylation of 1,4-quinones was observed. The results of mechanistic experiments suggest that the key C–O bond-forming event proceeds through an oxidative radical–polar crossover process involving a single-electron transfer between the HAT-generated glycosyl radical and the electron-acceptor quinone.