Copper-catalyzed O-arylation of phenols with diazonium salts

It is well known that diazonium salts (ArN2+) react with phenols (Ar ' OH) to give aryl diazoethers or diazo compounds, but their cross-coupling to exclusively access diaryl ethers is challenging. Herein we disclose the Cu-catalyzed etherification of phenols with aryl diazonium salts at room temperature, yielding diaryl ethers in moderate to excellent yields. The advantages of this protocol are mild reaction conditions, availability of reactants, operational simplicity, high tolerance of other functional groups and easy work-up. Its application to the synthesis of complex biological molecules is demonstrated. The reaction proceeds through single-electron transfer, extrusion of nitrogen, oxidative addition, and reductive elimination to give diaryl ether products.