Photocatalytic Phenol–Arene C–C and C–O Cross-Dehydrogenative Coupling

Abstract

Phenol-containing nonsymmetrical biaryls play an important role in natural-product synthesis, as ligands in metal catalysis, and in organic functional materials. Their synthesis through cross-coupling reactions by two-fold direct C–H activation are important and challenging transformations. In the last decade, a variety of useful oxidative methods have been developed. The key to efficiency and selectivity typically is the application of highly fluorinated solvent systems. Herein, we describe the visible-light-mediated C–C and C–O cross-coupling of electron-rich phenols and arenes by using [Ru(bpz)3](PF6)2] as photocatalyst and ammonium persulfate as terminal oxidant. The method requires no leaving group functionalities, which allows the use of simple activated arenes as starting materials. Furthermore, the approach features good chemo- and regioselectivity as well as functional group tolerance, even upon the replacement of fluoro alcohols by acetonitrile. The selectivity for the formation of nonsymmetrical biaryls is rationalized on the basis of the nucleophilicity N values and the oxidation potentials Eox of the electron-rich substrates.