External Oxidant-Free Dehydrogenative Lactonization of 2-Arylbenzoic Acids via Visible-Light Photocatalysis

An external oxidant-free C–H functionalization/C–O bond formation reaction for constructing benzo-3,4-coumarins accompanied by quantitative H 2 evolution has been developed. High functional group tolerance and excellent reaction efficiency are shown in this transformation. Meanwhile, the substrates containing heterocyclic substituents such as thienyl-, pyridinyl-, and pyrrolylbenzoic acids displayed good performance. Importantly, this reaction can be performed with good efficiency on a gram scale. A cyclic voltammetry study and density functional theory calculations could provide insight into the mechanism of this reaction.