title: Aryl-copper(III)-acetylides as key intermediates in Csp2-Csp model couplings under mild conditions.
abstract: 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 (1ClO4) with p-R-phenylacetylenes (R = NO2, CF3, H) is reported and it is found that facile reductive elimination from a putative aryl-Cu(III)-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 (P NO2, P CF3, 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 Caryl-Csp coupling in these model systems provide important insights for developing milder copper-catalysed Caryl-Csp coupling reactions with standard substrates in the future.
authors.affiliation: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, E17071 Girona (Catalonia, Spain).
authors.forename: Mireia
authors.initials: M
authors.lastname: Rovira
authors.forename: Marc
authors.initials: M
authors.lastname: Font
authors.forename: Ferran
authors.initials: F
authors.lastname: Acuña-Parés
authors.forename: Teodor
authors.initials: T
authors.lastname: Parella
authors.forename: Josep M
authors.initials: JM
authors.lastname: Luis
authors.forename: Julio
authors.initials: J
authors.lastname: Lloret-Fillol
authors.forename: Xavi
authors.initials: X
authors.lastname: Ribas
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D054833:Isoindoles / Q000138:chemical synthesis*; D007546:Isoquinolines / Q000138:chemical synthesis*; D008958:Models, Molecular; D010084:Oxidation-Reduction
chemical_list: D000480:Alkynes; D001555:Benzene Derivatives; C109853:G 1617; D054833:Isoindoles; D007546:Isoquinolines; D003300:Copper
keywords: CarylCsp cross coupling; Pd-free Sonogashira; copper(III); density functional calculations; reaction mechanisms