Selective Debromination and alpha-Hydroxylation of alpha-Bromo Ketones Using Hantzsch Esters as Photoreductants

Abstract

Two transformations initiated by photoinduced one-electron transfer to a-bromo ketones have been demonstrated. Hantzsch esters donate one electron to alpha-bromo ketones under photoirradiation, promoting reductive debromination. Subsequent reactions of the resulting radical species of the ketones with molecular oxygen and Hantzsch esters lead to alpha-hydroxylation or debromination, respectively. The relative dominance of the two pathways depends profoundly on the reaction conditions, including solvent, O-2 levels, and the concentration of the Hantzsch esters. The synthetic protocols feature advantages because they require the environmentally benign sources, molecular oxygen and visible light.