Enantioconvergent photoredox radical-radical coupling catalyzed by a chiral-at-rhodium complex

Abstract

Racemic α-chloro imidazol-2-yl-ketones undergo an enantioconvergent photoactivated C–C bond formation with N-aryl glycines catalyzed by a single bis-cyclometalated chiral-at-rhodium catalyst in yields of up to 80% and up to 98% enantiomeric excess (ee). Control experiments support a mechanism which is initiated by a single electron transfer from N-aryl glycinate to the photochemically excited rhodium-bound α-chloro imidazol-2-yl-ketone, followed by chloride fragmentation of the α-chloroketone, decarboxylation of the glycinate, and a subsequent highly stereocontrolled radical-radical coupling. This work showcases the ability of the chiral rhodium catalyst to serve a dual function as chiral Lewis acid and at the same time as the photoredox active species upon substrate binding.