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Lewis Acid Mediated Aminobenzannulation Reactions of δ‐Ketoalkynes: Synthesis of 1‐Aminocarbazoles and 9‐Aminopyrido[1,2‐ a ]indoles
Author(s) -
Facoetti Diego,
Abbiati Giorgio,
Rossi Elisabetta
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900039
Subject(s) - chemistry , lewis acids and bases , regioselectivity , enamine , nucleophile , intramolecular force , moiety , nucleophilic addition , medicinal chemistry , lewis acid catalysis , aldol reaction , pyrrolidine , stereochemistry , catalysis , organic chemistry
2‐Acyl‐ N ‐propargylindoles 1 and 2‐acyl‐3‐propargylindoles 5 undergo aminobenzannulation reactions with pyrrolidine in the presence of an appropriate Lewis acid to give 9‐aminopyrido[1,2‐ a ]indoles 6 and 1‐aminocarbazoles 7 , respectively. The selection of the appropriate Lewis acid, TiCl 4 or GaCl 3 for 1 and InCl 3 for 5 , allows the domino process involving the initial formation of an enamine intermediate, followed by a regioselective 6‐ exo ‐ dig intramolecular nucleophilic attack of the nucleophilic terminus of the unsaturated system (the β‐carbon of the enamino moiety) to the carbon–carbon triple bond. Moreover, several features concerning the reaction mechanism and the role of both catalysts, in connection with the electronic properties of the reacting alkynes, are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)