Modular enantioselective photocatalysts from privileged pybox scaffolds

Modern organic synthesis relies upon the availability of chiral catalysts to control the stereochemistry of bond-forming reactions. Several families of chiral catalysts have become recognized as "privileged" structures because of their notable generality for diverse transformations with different reaction mechanisms. However, examples of highly enantioselective photocatalyst structures remain scarce. We have designed a family of enantioselective photocatalysts by modifying the structures of privileged pyridine bis(oxazoline) complexes with electron-donating carbazole units. The chiral ligands are accessible through a three-step synthetic sequence starting from commercially available chiral pool materials, and their charge-transfer photochemistry can be rationally tuned to optimize photocatalytic activity. We demonstrate the generality of these new chiral photocatalyst structures in a series of three model asymmetric reactions, which includes both photoredox and excited-state photoreactions.