Intramolecular N-acyliminium ion versus Friedel-Crafts cyclization onto 3-indoles: synthesis of the novel rings pyrrolizino[2,1-b]indole and homologues |
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Authors: | Raffaella Cincinelli Sabrina Dallavalle Lucio Merlini Raffaella Nannei Leonardo Scaglioni |
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Affiliation: | Dipartimento di Scienze Molecolari Agroalimentari, Università di Milano, Via Celoria 2, 20133 Milano, Italy |
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Abstract: | Acid treatment of indole-2-carboxylic acid β- and γ-oxoamides causes Friedel-Crafts intramolecular cyclization to β-carbolinones and dihydro-2H-azepino[3,4-b]indol-1-ones, in contrast to secondary δ-,?-, and ζ-oxoamides, which cyclize to the novel heterocyclic rings pyrrolizino[2,1-b]indole, indolizino[2,1-b]indole, and 9a,11-diaza-indeno[1,2-a]azulene, via an intermediate N-acyliminium ion. Tertiary amides lead only the Friedel-Crafts ring closure, thus allowing the synthesis of larger fused rings. |
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Keywords: | Friedel-Crafts Acyliminium ion Indole-fused heterocycles Synthesis |
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