Deracemization through Sequential Photoredox-Neutral and Chiral Brønsted Acid Catalysis.

Catalytic deracemization is an ideal synthetic strategy due to its formally perfect atom utilization. Asymmetric photocatalysis has been appreciated as a promising tool to accomplish this attractive reaction pattern in an economical fashion, but it remains underdeveloped. Here, we report a new platform based on photoredox-neutral catalysis, allowing efficient and modular optical enrichment of α-amino esters and other valuable analogues. Two single-electron transfer processes between the photocatalyst and the substrates serve to provide the key prochiral intermediates, and the chiral Brønsted acid catalyst mediates enantioselective protonation to reconstitute a stereogenic C-H bond. The efficiency of deracemization is determined by the enantiofacial differentiation effect during the stereocentre-forming step.