Phenothiazinium as Metal‐Free CH Arylation Reagent for Unactivated Arenes

The construction of (hetero)biaryls plays a crucial role in chemical science, with applications in pharmaceuticals, agrochemicals, natural products, and organic materials. While aryl sulfonium salts (aryl thianthrenium‐salts and aryl DBT‐salts) have provided access to (hetero)biaryls, these methods typically require photocatalysts or transition metals to activate the reagents. Herein, a mild, visible light‐mediated, transition metal‐free, and catalyst‐free arylation of arenes using aryl phenothiazinium salts as dual functional reagents is reported. A variety of biaryls and heterobiaryls are obtained in moderate to high yields.