Oxidant‐ and Base‐Free Oxidative Lactonization of 2‐Arylbenzoic Acids in Two‐Molecule Photoredox System

The photoinduced oxidative lactonization of 2‐arylbenzoic acids without an oxidant or base was achieved in a two‐molecule photoredox system using biphenyl and 9,10‐dicyanoanthracene under an Ar atmosphere. The intramolecular radical addition of photogenerated carboxyl radicals to benzene rings leads to the corresponding benzo‐3,4‐coumarins, found in the core structural unit of medicinal materials, through oxidation by the protonated radical anion of 9,10‐dicyanoanthracene. This is a unique photochemical oxidative reaction pathway observed in photoredox systems.