FeCl3‐Catalyzed Multifunctional LMCT & HAT for Synthesis of Benzo[c]coumarins from 2‐Methyl‐1,1’‐Biaryls at Ambient Temperature

Benzo[c]coumarins demonstrate superior optical properties and biological activities. In recent years, many synthetic methods have been developed for more concise synthetic routes by different starting materials, including aryl carboxylic acids, 2‐arylbenzaldehydes, 2‐arylphenols, and methyl‐1,1’‐biaryls, etc. The major methods consist of using aryl carboxylic acids via transition metal‐catalyzed aryl C–H hydroxylation, using aryl carboxylic acids or 2‐arylbenzaldehydes via aryl carboxyl radical induced lactonization, using 2‐arylphenols via aryl C–H carbonylation/carboxylation and cyclization, and using 2‐methyl‐1,1’‐biaryls via multiple C–H functionalization and lactonization. Herein, we report FeCl3‐catalyzed multifunctional ligand‐to‐metal charge transfer (LMCT) & hydrogen atom transfer (HAT) for the synthesis of benzo[c]coumarins from 2‐methyl‐1,1’‐biaryls. This catalytic system is straightforward, only using FeCl3·6H2O as the catalyst and air as the oxidant under visible‐light irradiation at ambient temperature. Mechanistic studies indicate that multifunctional LMCT & HAT processes generate chlorine radicals and aryl carboxyl radicals, which are key active species that facilitate the smooth transformation.