Reaction of Alkynes and Azides: Not Triazoles Through Copper–Acetylides but Oxazoles Through Copper–Nitrene Intermediates |
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| Authors: | Dr Estela Haldón Dr Maria Besora Dr Israel Cano Dr Xacobe C Cambeiro Prof Miquel A Pericàs Prof Feliu Maseras Prof M Carmen Nicasio Prof Pedro J Pérez |
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| Institution: | 1. 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;2. Institute of Chemical Research of Catalonia (ICIQ), Av. Pa?sos Catalans 16, 43007 Tarragona (Spain);3. Departament de Química Orgànica, Universitat de Barcelona, Martí i Franquès 1‐11, 08028 Barcelona (Spain);4. Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra (Spain);5. Departamento de Química Inorgánica, Universidad de Sevilla, Aptdo 1203, 41071 Sevilla (Spain) |
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| Abstract: | Well‐defined copper(I) complexes of composition Tpm*,BrCu(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. |
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| Keywords: | alkynes click chemistry copper nitrenes oxazoles reactive intermediates |
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