Solvent-promoted photochemical carbonylation of benzylic C–H bonds under iron catalysis

Abstract

This paper describes the iron-catalyzed photochemical carbonylation of benzylic C–H bonds resulting in the synthesis of various aryl ketones. Using 5 W blue LED irradiation, the reactions proceed smoothly in the presence of 2 mol% of FeBr₃ in MeOH at 35 °C. The catalytic system could be extended for the oxidation of silane, thioether, and phosphine into silenol, sulphoxide, and phosphoxide, respectively. A mechanistic study suggests that a hydrogen bond-stabilized iron-hydroperoxo species is the reactive intermediate. It is shown that the reaction proceeds via a four-electron-transfer pathway, and a benzylic cation seems to be the crucial reactive species. The method is applied for the synthesis of pomalyst, haloperidol, melperone, and lenperone.