Electrochemical Bromination of Arenes in a 200% Cell

Herein, we describe the investigation of electrochemical bromination of electron-rich arenes in a 200% cell. For this application, at first, the influence of an excess of supporting electrolyte (Bu4NBr) on chemical bromination was investigated. The application of >4.0 equiv of Bu4NBr proved to enhance the regioselectivity of the bromination process for O- and N-substituted arenes considerably. The linear paired electrolysis was then optimized upon these insights, and a number of electron-rich arenes could be brominated in high yields with excellent regioselectivity. The use of O-2 as a sacrificial starting material in combination with 2-ethylanthraquinone as a catalyst leads to the enhanced formation of H2O2 at the cathode, resulting in current efficiencies >150% for a considerable number of examples.