α,β-Unsaturated Acyl Azoliums from N-Heterocyclic Carbene Catalyzed Reactions: Observation and Mechanistic Investigation

Authors

  • Jessada Mahatthananchai,

    1. Laboratory for Organic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH) Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich (Switzerland), Fax: (+41) 44-633-1235 http://www.bodegroup.org
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  • Dr. Pinguan Zheng,

    1. Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, PA 19104 (USA)
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  • Prof. Dr. Jeffrey W. Bode

    Corresponding author
    1. Laboratory for Organic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH) Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich (Switzerland), Fax: (+41) 44-633-1235 http://www.bodegroup.org
    • Laboratory for Organic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH) Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich (Switzerland), Fax: (+41) 44-633-1235 http://www.bodegroup.org
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  • We are grateful to NIGMS (National Institutes of Health, GM-079339), the National Science Foundation (CHE-0449587), Bristol Myers Squibb, and ETH Zurich for support of this research. We thank Darko Santrac for a preliminary study, and NMR and MS services (ETHZ) for spectroscopic data.

Abstract

original image

Caught in the act: Acyl azoliums have long been thought to be key reactive intermediates in N-heterocyclic carbene catalysis, but they have never been observed under catalytic conditions. Now, this has been successfully achieved by the characterization of α,β-unsaturated acyl azoliums (see scheme) using different spectroscopic techniques. Kinetic studies revealed the origin of their unexpected chemoselectivity in acylation and annulation reactions.

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