Aerobic Heterogeneous Palladium-Catalyzed Oxidative Allenic C−H Arylation : Benzoquinone as a Direct Redox Mediator between O2 and Pd

Transition metal-catalyzed aerobic oxidative reactions using molecular oxygen as the terminal oxidant play a significant role in organic synthesis. Benzoquinone (BQ) has been widely used as an electron-transfer mediator (ETM) in biomimetic palladium-catalyzed aerobic oxidative reactions, but always together with an ETM between O2 and BQ, such as a macrocyclic metal complex. Herein, we report on a heterogeneous palladium-catalyzed allenic C(sp3)–H arylation with only catalytic amounts of BQ under air without the need of an additional ETM. A range of multisubstituted 1,3-dienes were synthesized under mild reaction conditions. Mechanistic studies reveal the bifunctional role of BQ as a ligand for reductive elimination and as an ETM between Pd(0) and O2. This new regime of oxidation has important implications for further development of other transition metal-catalyzed aerobic oxidative reactions.