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Molecules 2018, 23(4), 838; doi:10.3390/molecules23040838

Indium-Catalyzed Annulation of o-Acylanilines with Alkoxyheteroarenes: Synthesis of Heteroaryl[b]quinolines and Subsequent Transformation to Cryptolepine Derivatives

Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki 214-8571, Japan
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Author to whom correspondence should be addressed.
Academic Editor: Akio Baba
Received: 9 March 2018 / Revised: 25 March 2018 / Accepted: 31 March 2018 / Published: 5 April 2018
(This article belongs to the Special Issue Indium in Organic Synthesis)
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Abstract

We disclose herein the first synthetic method that is capable of offering heteroaryl[b]quinolines (HA[b]Qs) with structural diversity, which include tricyclic and tetracyclic structures with (benzo)thienyl, (benzo)furanyl, and indolyl rings. The target HA[b]Q is addressed by the annulation of o-acylanilines and MeO–heteroarenes with the aid of an indium Lewis acid that effectively works to make two different types of the N–C and C–C bonds in one batch. A series of indolo[3,2-b]quinolines prepared here can be subsequently transformed to structurally unprecedented cryptolepine derivatives. Mechanistic studies showed that the N–C bond formation is followed by the C–C bond formation. The indium-catalyzed annulation reaction thus starts with the nucleophilic attack of the NH2 group of o-acylanilines to the MeO-connected carbon atom of the heteroaryl ring in an SNAr fashion, and thereby the N–C bond is formed. The resulting intermediate then cyclizes to make the C–C bond through the nucleophilic attack of the heteroaryl-ring-based carbon atom to the carbonyl carbon atom, providing the HA[b]Q after aromatizing dehydration. View Full-Text
Keywords: anti-cancer activity; anti-malarial activity; heteroarenes; indium; Lewis acids; pyridine; one-pot; quindolines; tandem reaction anti-cancer activity; anti-malarial activity; heteroarenes; indium; Lewis acids; pyridine; one-pot; quindolines; tandem reaction
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Yonekura, K.; Shinoda, M.; Yonekura, Y.; Tsuchimoto, T. Indium-Catalyzed Annulation of o-Acylanilines with Alkoxyheteroarenes: Synthesis of Heteroaryl[b]quinolines and Subsequent Transformation to Cryptolepine Derivatives. Molecules 2018, 23, 838.

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