title: Reaction of alkynes and azides: not triazoles through copper-acetylides but oxazoles through copper-nitrene intermediates.
abstract: Well-defined copper(I) complexes of composition [Tpm*(,Br) Cu(NCMe)]BF4 (Tpm*(,Br) =tris(3,5-dimethyl-4-bromo-pyrazolyl)methane) or [Tpa(*) Cu]PF6 (Tpa(*) =tris(3,5-dimethyl-pyrazolylmethyl)amine) catalyze the formation of 2,5-disubstituted oxazoles from carbonyl azides and terminal alkynes in a direct manner. This process represents a novel procedure for the synthesis of this valuable heterocycle from readily available starting materials, leading exclusively to the 2,5-isomer, attesting to a completely regioselective transformation. Experimental evidence and computational studies have allowed the proposal of a reaction mechanism based on the initial formation of a copper-acyl nitrene species, in contrast to the well-known mechanism for the copper-catalyzed alkyne and azide cycloaddition reactions (CuAAC) that is triggered by the formation of a copper-acetylide complex.
authors.affiliation: Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, CIQSO-Centro de Investigación en Química Sostenible and Departamento de Química y Ciencias de los Materiales, Campus de El Carmen s/n, Universidad de Huelva, 21007 Huelva (Spain), Fax: (+34) 959219942.
authors.forename: Estela
authors.initials: E
authors.lastname: Haldón
authors.forename: Maria
authors.initials: M
authors.lastname: Besora
authors.forename: Israel
authors.initials: I
authors.lastname: Cano
authors.forename: Xacobe C
authors.initials: XC
authors.lastname: Cambeiro
authors.forename: Miquel A
authors.initials: MA
authors.lastname: Pericàs
authors.forename: Feliu
authors.initials: F
authors.lastname: Maseras
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Nicasio
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Pérez
keywords: alkynes; click chemistry; copper; nitrenes; oxazoles; reactive intermediates