Glycosyl Radical-Based C–H Glycosylation of Coumarins Enabled by Photocatalysis

We report the photocatalytic C-H glycosylation of coumarins with glycosyl radicals. This transformation employs an organic photosensitizer and proceeds under mild conditions in the presence of a weak acid. The reaction exhibits α-selectivity with pyranohexose-derived donors and β-selectivity with pyranopentose-derived ones. It has been successfully applied to modify eight natural coumarins and scaled up to gram quantities under continuous-flow conditions.