Visible light-induced aerobic oxidation of an alkene catalyzed by thiobenzoic acid in water†

A metal-free, visible-light-catalyzed oxidative cleavage of the CC bond of an alkene by thiobenzoic acid in water under an O₂ atmosphere has been developed. This protocol features low catalyst loading, green solvent, good functional group tolerance, easy scale-up and further transformation. Meanwhile, our methodology was compatible with various complex structures, such as pharmaceutical drugs ketoprofen methyl ester and fenofibrate. Electron paramagnetic resonance studies, together with control experiments, showed that the superoxide radical anion (O₂˙⁻) is the reactive oxidant. Based on the electrochemical and photophysical characteristics of thiobenzoic acid, its excited state was sufficient to transform molecular oxygen into its reduced activated superoxide radical.