Zwitterions as catalytic electron donor species for visible light-induced photoactivation of oxime esters and direct C3-alkylation of quinoxalin-2(1H)-ones

Abstract

A novel ternary EDA complex catalysis strategy has been developed for the photoactivation of oxime esters. By augmenting the electron-donating properties of zwitterions with a base, a ternary EDA complex is formed, facilitating intermolecular charge transfer under visible light. This process enables the single-electron reduction of γ,δ-unsaturated oxime esters, resulting in the homolytic cleavage of the N–O bond. The resulting iminyl radicals then undergo intramolecular cyclization to generate alkyl radicals, enabling C3-alkylation of quinoxalin-2(1H)-ones in good to excellent yields. Additionally, a novel covalent fluorescent labeling method was established using this mild alkylation method.