Photoelectrochemical Asymmetric Epoxidation of Alkenes with Water as an Oxygen Source in a Biphasic System

Photoelectrochemical (PEC) oxidation of organics to value-added chemicals presents a sustainable alternative to conventional anodic oxygen evolution reactions. While significant progress has been made in PEC organic transformations, asymmetric PEC organic conversions remain underexplored. In this study, we report the chloride-mediated PEC enantioselective epoxidation of alkenes at a mesoporous BiVO₄ photoanode in a CH₂Cl₂/aqueous NaCl biphasic system using water as an oxygen source. The NaCl electrolyte serves as a redox mediator and chlorine precursor, where photo-oxidation generates reactive chlorine species (Cl₂/HClO) that migrate into the organic phase to enable asymmetric catalysis via chiral Mn-salen catalysts. Spectroelectrochemical analysis verified the photogenerated Mn^V═O species as the key intermediate. A key innovation of this study lies in the use of a pendant alkyl chain-modified pyridine N-oxide additive, which uniquely stabilizes the Mn^V═O intermediate through axial coordination while simultaneously acting as a phase-transfer catalyst to facilitate hypochlorous acid migration, dramatically boosting the epoxidation efficiency. This approach achieves high yields (up to 95%) and enantioselectivities (up to 88% enantiomeric excess), even in a challenging artificial seawater/CH₂Cl₂ biphasic system. By utilizing water as a green oxygen source and coupling with solar fuel production, this work presents a practical and efficient route for asymmetric PEC synthesis.