Switchable diversification of quaternary ammonium salts using photocatalysis

Abstract

Over the past few decades, significant advances have been made in the radical chemistry of amine molecules. However, the radical reactions of related quaternary ammonium salts remain comparatively underexplored. If radicals could be generated from ammonium salts in a controlled manner, this could lead to a method for producing distonic radical cations, offering valuable synthetic applications for quaternary ammonium salts and their tertiary amine derivatives. In this study, we developed a photoredox-catalyzed method for derivatizing quaternary ammonium salts by reacting α-haloalkylammonium salts with olefins. The key to success is the photocatalytic generation of distonic α-ammonio radicals under both oxidative and reductive quenching conditions. This chemistry enables selective and switchable alkylations and alkenylations, affording structurally new quaternary ammonium salts. The utility of this procedure is showcased in the divergent synthesis and derivatization of bioactive quaternary ammonium salts, a deuterated tertiary amine, and the identification of salinity-tolerance-conferring molecules.