Cu(II)-Catalyzed ortho-Selective Aminomethylation of Phenols

A Cu(II)-catalyzed ortho-selective functionalization of free phenols with trifluoroborates to afford C_sp2-C_sp3 coupling products under mild conditions has been developed. A variety of functional groups on the phenol and the potassium aminomethyltrifluoroborate substrates were found compatible, furnishing the corresponding products in moderate to excellent yields. A single-electron transfer radical coupling mechanism involving a six-membered transition state is proposed to rationalize the high levels of ortho-selectivity in the reaction. This protocol provides straightforward access to ortho-aminomethyl-substituted phenols, unnatural amino acids and other bioactive small molecules.