Nitrosonium Ion Catalyzed Oxidative Bromination of Arenes

A nitrosonium catalyzed bromination of electron-rich arenes has been developed, using bromide salts as bromine sources, oxygen gas as a terminal oxidant and Brønsted acids (sulfuric acid, TFA or HBr). This arene bromination process is free of transition metals, proceeding in acetic acid and under mild temperatures (25–50 °C) to give brominated arenes with good to excellent yields. Our mechanistic studies indicated that this oxidative bromination of arenes reaction is catalyzed by nitrosnium ion (NO⁺), without the involvement of Br₂ or Br⁺. The kinetic isotope effect of this reaction was measured using pentadeuteriophenyl phenyl ether (k_H/k_D=1.1).