Transmetallation versus β-hydride elimination: The role of 1,4-benzoquinone in chelation-controlled arylation reactions with arylboronic acids

Abstract

The formation of an atypical, saturated, diarylated, Heck/Suzuki, domino product produced under oxidative Heck reaction conditions, employing arylboronic acids and a chelating vinyl ether, has been investigated by DFT calculations. The calculations highlight the crucial role of 1,4-benzoquinone (BQ) in the reaction. In addition to its role as an oxidant of palladium, which is necessary to complete the catalytic cycle, this electron-deficient alkene opens up a low-energy reaction pathway from the post-insertion Ï-alkyl complex. The association of BQ lowers the free-energy barrier for transmetallation of the Ï-alkyl complex to create a pathway that is energetically lower than the oxidative Heck reaction pathway. Furthermore, the calculations showed that the reaction is made viable by BQ-mediated reductive elimination and leads to the saturated diarylated product. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.