Photoredox-catalyzed generation of α-carbonyl carbocations: general access to α-tertiary amino acid derivatives†

Abstract

α-Carbonyl carbocations, serving as the umpolung forms of synthetically fundamental α-carbonyl carbanions, are highly reactive species. The controlled generation and subsequent strategic employment of these reactive intermediates remain challenging. Herein, we report a photoredox-catalyzed approach for generating α-carbonyl carbocations from the corresponding α-carbonyl radicals through a single electron transfer (SET) oxidation process. These α-carbonyl radicals are readily accessible through radical addition to various α,β-unsaturated carbonyl compounds, including α,β-unsaturated esters, acid, amides and ketones. Furthermore, the Ritter reaction can be initiated by addition of nitriles to α-carbonyl carbocations, enabling the general synthesis of α-tertiary amino acid derivatives. This method features mild conditions, does not require strong acids and terminal oxidants, utilizes visible light, operates without pre-functionalization, offers a broad substrate scope and good group tolerance, etc. Moreover, further extension to the late-stage modification of natural products through this photoredox-catalyzed generation and utilization of α-carbonyl carbocations is also demonstrated.