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Regioselective Inter- and Intramolecular Formal [4+2] Cycloaddition of Cyclobutanones with Indoles and Total Synthesis of (±)-Aspidospermidine

Authors

  • Mizuki Kawano,

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Takaaki Kiuchi,

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Shoko Negishi,

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Hiroyuki Tanaka,

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Takaya Hoshikawa,

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Prof. Dr. Jun-ichi Matsuo,

    Corresponding author
    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
    • School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • Prof. Dr. Hiroyuki Ishibashi

    1. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical, and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan)
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  • We thank Prof. Shuhei Fujinami (Kanazawa University) for X-ray crystallographic analysis and Mio Hashizume for technical assistance. This study was partially supported by the Kurata Memorial Hitachi Science and Technology Foundation and JSPS KAKENHI Grant Number 24590007.

Abstract

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This way and that way: A formal [4+2] cycloaddition between various cyclobutanones and indoles proceeded efficiently under Lewis acid catalysis (see scheme; PG = protecting group). The regioselectivity of the reaction could be controlled in such a way that each of the two possible regioisomers of a cycloaddition product could be synthesized selectively. The usefulness of this reaction for the total synthesis of hydrocarbazole natural products was demonstrated.

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