Catalytic Enantioselective Cross-Nucleophile Coupling via Valence Tautomerism

Valence tautomerism, traditionally underexplored in asymmetric catalysis compared to the more familiar two-electron prototropic tautomerism like keto-enol, presents a promising avenue for novel chemical transformations. In this study, we harness one-electron valence tautomerism through a dual photoredox/nickel-catalyzed system to facilitate oxidant-free, enantioselective cross-nucleophile coupling (CNC). This method efficiently couples a diverse range of β-keto esters and amides with silyl enol ethers and allyl silanes, producing coupling products that feature a quaternary stereocenter with high stereocontrol. The reaction demonstrates broad tolerance for different functional groups and molecular architectures. Mechanistic investigations, including Stern-Volmer quenching, cyclic voltammetry, electron paramagnetic resonance (EPR), radical trapping, and density functional theory (DFT) calculations, corroborate a radical mechanism involving valence tautomerism. We anticipate that this mechanistic insight will inspire the discovery of new chemical transformations and provide a framework for describing key steps in future catalytic reactions.