HCl-Promoted Indole Ring Opening toward 3-Aminoaryl-2-methylquinolines: A Divergent Route to Azepino[4,5- b ]quinolones

Abstract

A concise stepwise strategy for the synthesis of tetrahydrobenzazepinoquinoline derivatives from 2-methylindole substrates is described. C3-alkylation followed by acid-mediated intramolecular cyclization furnishes 3-aminoaryl 2-methylquinoline derivatives. Subsequent treatment with aromatic aldehydes under the same conditions enables a Pictet–Spengler-type annulation, providing access to diverse tetrahydrobenzazepinoquinoline frameworks. The method proceeds under metal-free conditions and enables rapid assembly of structurally complex fused nitrogen-containing heterocycles. The practicality of the protocol is demonstrated through scale-up synthesis, and all compounds were characterized by NMR and Mass spectroscopic analysis.