Visible-Light-Induced Direct Photolysis of Phosphorus Iodide Salts for Difluoroalkylation of C(sp2)-H by an Intramolecular Charge-Transfer Complex.

Abstract

Green, safe, simple, and efficient strategies for generating fluoroalkyls are an ongoing challenge for the synthetic community. Generally, the main form of synthesizing difluoroalkylated heteroaromatic compounds is to use catalysts, oxidants, and a high temperature to generate difluoroalkyl radicals and react with heteroaromatic hydrocarbons. In contrast, the strategy of using intramolecular charge-transfer complexes (ICTCs) to generate difluoroalkylated heteroaromatic compounds remains an unexplored challenge. Here, for the first time, we carried out a difluoromethylation reaction between various difluoroalkyl radicals generated in the form of photoactivated ICTCs and heteroaromatic C(sp2)-H compounds (with high stability and multiple active sites) to obtain various fluorine-containing compounds. This method only depends on the substrate in the reaction, avoiding the need for a metal, exogenous photocatalyst, and oxidant. In addition, this metal-free approach provides controlled synthetic conditions, employs a scalable flow technique with high temporal and spatial efficiency, and demonstrates successful gram-scale applications, thus proving the usefulness and versatility of this new scheme.