Control of Site-Selectivity in Hydrogen Atom Transfer by Electrostatic Interaction: Proximal-Selective C(sp³)-H Alkylation of 2-Methylanilinium Salts Using a Decatungstate Photocatalyst

Site-selective C(sp3)-H alkylation of 2-methylanilinium salts via radical intermediates was developed. The anionic decatungstate photocatalyst ([W10O32]4-) interacts with the ammonium group of the substrate through electrostatic interaction and selectively abstracts a hydrogen atom from the proximal benzylic carbon atom under UV irradiation. A variety of 2-methylanilinium salts reacted with electron-deficient alkenes. The alkylated product was successfully converted into an aryl iodide via cleavage of the C-N bond and a tetrahydrobenzoazepinone derivative by intramolecular cyclization. Mechanistic studies clearly show the existence of the interactions between [W10O32]4- and the ammonium group.