Visible-light promoted arene C-H/C-X lactonization via carboxylic radical aromatic substitution

We report herein a photocatalytic arene lactonization via carboxylic radical aromatic substitution. This procedure is characterized by its ability to cleave inert C-X bonds (X = H, F, Cl, Br, O, S) under mild and oxidant-free conditions, thus furnishing a general and operationally simple synthetic protocol for diverse substituted coumarins.