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Gold-Catalyzed Annulations of 2-Alkynyl Benzaldehydes with Vinyl Ethers: Synthesis of Dihydronaphthalene, Isochromene, and Bicyclo[2.2.2]octane Derivatives

Authors

  • Deepika Malhotra,

    1. Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40208 (USA), Fax: (+1) 502-852-3899
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    • These authors contributed equally to this work.

  • Dr. Le-Ping Liu,

    1. Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40208 (USA), Fax: (+1) 502-852-3899
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    • These authors contributed equally to this work.

  • Dr. Mark S. Mashuta,

    1. Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40208 (USA), Fax: (+1) 502-852-3899
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  • Prof. Dr. G. B. Hammond

    Corresponding author
    1. Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40208 (USA), Fax: (+1) 502-852-3899
    • Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40208 (USA), Fax: (+1) 502-852-3899
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Abstract

With the suitable selection of a gold catalyst as well as the appropriate control of the reaction conditions, various new gold-catalyzed cyclizations of 2-alkynyl benzaldehyde with acyclic or cyclic vinyl ethers have been developed. Acetal-tethered dihydronaphthalene and isochromenes were obtained from the reactions of 2-alkynyl benzaldehydes with acyclic vinyl ethers under mild conditions. And, more interestingly, the gold-catalyzed reactions of 2-alkynyl benzaldehyde with a cyclic vinyl ether afforded the bicyclo[2.2.2]octane derivative involving two molecules of cyclic vinyl ethers. These products contain interesting substructures that have been found in many biologically active molecules and natural products. In addition, a gold-catalyzed homo-dimerization of 2-phenylethynyl benzaldehyde 1 a was observed when the reaction was carried out in the absence of vinyl ether, affording a set of separable diastereomeric products. Plausible mechanisms for these transformations are discussed; a gold-containing benzopyrylium was regarded as the crucial intermediate by which a number of these new transformations took place.

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