Selective Oxidative Homo- and Cross-Coupling of Phenols with Aerobic Catalysts

ABSTRACT: Simple catalysts that use atom-economical oxygen as the terminal oxidant to accomplish selective ortho−ortho, ortho−para, or para−para homo-couplings of phenols are described. In addition, chromium salen catalysts have been discovered as uniquely effective in the cross-coupling of different phenols with high chemo-and regioselectivity. Since the groundbreaking work by Barton and Erdtmannthat phenol oxidation is a key step in the biosynthesis of several natural product classes,1 chemists have been inspired to develop laboratory analogues of these important processes.2 Numerous natural products can be constructed via different oxidative phenol couplings including homo-coupling at the same site, homo-coupling at different sites, and cross-coupling of different phenols (Chart 1).2c−f Due to the vast array of useful biological activities associated with these compounds