Ni-Catalyzed Deoxygenative Borylation of Phenols Via O-Phenyl-uronium Activation
Xiaojie Liu, Biping Xu, Weiping Su
Abstract
Herein, we report an efficient method for the Ni-catalyzed deoxygenative borylation of unprotected phenols and also demonstrate that this Ni-catalyzed phenolic C(sp2)-O transformation is applicable to the Suzuki–Miyaura-type and Heck-type cross-couplings of phenols. Investigations on the reaction intermediate have revealed that the achievement of general, mild deoxygenative cross-coupling reactions of phenols is ascribed to the conversion of phenols into the unusual O-phenyl-uroniums that feature active phenolic C(sp2)-O bonds. The Ni-complex intermediate resulting from an oxidative addition of a phenolic C(sp2)-O bond to monophosphine-supported Ni(0) catalyst was characterized and confirmed to be (PCy3)2Ni(Ar)(F) complex, offering experimental evidence for the generally proposed C(sp2)-O oxidative addition step.