The mechanism of copper-mediated Sonogashira couplings (so-called Stephens-Castro and Miura couplings) is not well understood and lacks clear comprehension. In this work, the reactivity of a well-defined aryl-Cu III species (1 ClO 4) with p-R-phenylacetylenes (R=NO2, CF3, H) is reported and it is found that facile reductive elimination from a putative aryl-CuIII-acetylide species occurs at room temperature to afford the Caryl - Csp coupling species (IR), which in turn undergo an intramolecular reorganisation to afford final heterocyclic products containing 2H-isoindole (PNO2, PCF3, PHa) or 1,2-dihydroisoquinoline (PHb) substructures. Density Functional Theory (DFT) studies support the postulated reductive elimination pathway that leads to the formation of C sp2-Csp bonds and provide the clue to understand the divergent intramolecular reorganisation when p-H-phenylacetylene is used. Mechanistic insights and the very mild experimental conditions to effect C aryl-Csp coupling in these model systems provide important insights for developing milder copper-catalysed Caryl - C sp coupling reactions with standard substrates in the future. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
|Journal||Chemistry - A European Journal|
|Publication status||Published - 4 Aug 2014|
- density functional calculations
- Pd-free Sonogashira
- reaction mechanisms