Acridinium Betaine as a Single-Electron-Transfer Catalyst: Design and Application to Dimerization of Oxindoles

An intramolecular ion-pairing acridinium phenoxide possessing a redox-active component and a basic site within a single molecular framework is developed. The potential of the acridinium betaine as a chemical redox catalyst is demonstrated by its application to the homodimerization of 3-aryl oxindoles, which proceeds through proton-coupled electron-transfer pathway. Analysis of the kinetic profile has provided important clues to understand the reaction mechanism.