Synergistic dual catalysis has emerged as a new and powerful strategy in chemical synthesis.1 In this dual catalytic process, each catalyst could selectively activate the substrates to enable the chemical transformations that are not possible with either one of the catalysts.1 The main challenge for the development of synergistic catalysis is ensuring catalyst cross-compatibility, balancing kinetics for substrate activation and avoiding catalyst deactivation. Here we present a novel synergistic Rh(II)/Pd(0) dual catalysis strategy that promotes the denitrogenative cross-coupling of 1-sulfonyl-1,2,3-triazoles 1 with allyl carboxylates, which does not occur when using a Rh(II) or Pd(0) catalyst alone. In this dual catalysis process, Rh(II) and Pd(0) catalysts activate 1-sulfonyl-1,2,3-triazoles and allyl carboxylates in a substrate-selective manner with balanced-kinetics to generate an ?-imino Rh(II)-carbene and a ?-allyl Pd(II)-complex. Coordination of the pendant ?-imine of the Rh(II)-carbene with the Lewis acidic Pd-complex plays a key role in not only placing the activated species in proximity but also in reversing electronic nature of the Pd-complex, which may facilitate the nucleophilic transfer of the carboxylate onto the electrophilic carbenic carbon. This effectively accomplishes the formal 1,3-insertion of ?-imino Rh(II)-carbenes into the sp3 C?O bond of allyl carboxylates to yield N-allylated (Z)-amino vinyl carboxylates (Scheme 1).2
(1) Allen, A. EMacMillan, .; D. W. C. Chem. Sci. 2012, 3, 633-658.
(2) Chen, Z.-S.; Jeon, H. J.; Chen, S.-W.; Xuan, Z.; Lee, S.-g. 2015, manuscript submitted.