Cyclopentannulation of 3-alkylindoles: a synthesis of a tetracyclic subunit of the kopsane alkaloids.
Indoles which bear an alkyl substituent in the 3-position undergo a [3 + 2] annulation reaction when treated with 1,1-cyclopropane diesters in the presence of Yb(OTf)(3) resulting in 2,3-cyclopentanoindolines. Typically, the reactions are performed at elevated temperatures or at ultrahigh pressures. In cases where steric crowding is an issue, ultrahigh pressures are required. In reactions involving substituted cyclopropanes, significant regio- and diastereocontrol was observed. When the substituent was aromatic or olefinic, the reactions took place at ambient temperature and pressure. The applicability of this methodology to the preparation of a key tetracyclic subunit of the kopsane alkaloids was demonstrated.
England
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DB
Department of Chemistry, The University of Western Ontario, London, Ontario, Canada, N6A 5B7.
Kuss
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TD
Keddy
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RG
Kerr
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MA
D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D000473:Alkanes / Q000737:chemistry*; D003517:Cyclopentanes / Q000138:chemical synthesis* / Q000737:chemistry; D003521:Cyclopropanes / Q000737:chemistry; D007211:Indoles / Q000737:chemistry
D000470:Alkaloids; D000473:Alkanes; D003517:Cyclopentanes; D003521:Cyclopropanes; D007211:Indoles