Lewis Acid Mediated Aminobenzannulation Reactions of δ-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2-a]indoles

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, TiCl4 or GaCl3 for 1 and InCl3 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