Mechanism of Benzoquinone-Promoted Palladium-Catalyzed Oxidative Cross-Coupling Reactions

(Chemical Equation Presented) This communication describes mechanistic studies of the Pd-catalyzed oxidative cross-coupling of benzo[h]quinoline with simple arenes. Through a series of experiments, including determination of the order of the reaction in various reagents, H/D exchange studies, kinetic isotope effect investigations, and the evaluation of electronic effects, we propose a detailed mechanism for these reactions. Importantly, this mechanism explains the key role of benzoquinone in these transformations; in addition, it provides insights that allow the rational tuning of reaction conditions to control the chemoselectivity of Ar-Ar′ coupling. © 2009 American Chemical Society.