Enzyme-inspired single-molecule photocatalyst enables singlet-oxygen-driven asymmetric epoxidation and sulfoximination.

Abstract

The development of catalytic systems for the enantioselective epoxidation of sterically hindered trisubstituted alkenes using molecular oxygen (O₂) as the terminal oxidant remains a formidable challenge. Here, we report a biomimetic bifunctional photocatalyst that integrates a chiral manganese center and a covalently tethered anthraquinone photosensitizer within a single molecular scaffold. This unified design emulates the enzymatic principle of spatially coupled oxygen activation and chiral induction. Under visible light and ambient O₂, the catalyst enables the asymmetric epoxidation of challenging trisubstituted alkenes, including cyclic sulfones and linear α,β-unsaturated carbonyls, in up to 99% enantiomeric excess (ee), and also facilitates the efficient conversion of sulfilimines to (chiral) sulfoximines. Mechanistic studies reveal a cascade involving singlet-oxygen-mediated oxidation, oxidative decarboxylation, and acid-assisted O-O bond heterolysis to generate a high-valent Mn⁴⁺=O species as the key active intermediate. By unifying light harvesting, O₂ activation, and asymmetric catalysis in a precious-metal-free platform, this work establishes a versatile, sustainable strategy for the selective oxidation of traditionally recalcitrant substrates.