Acid-Catalyzed Protocol for the Synthesis of Novel 6-Substituted Tetrahydroquinolines by Highly Regioselective C6-Functionalization of Tetrahydroquinolines with Chromene Hemiacetals or β-Nitrostyrenes

A simple and novel method has been developed for the C6-functionalization of unprotected tetrahydroquinoline with chromenes or beta-nitrostyrenes in aqueous medium to afford novel 6-substituted tetrahydroquinolines. This method is simple and convenient, and has low costs and mild reaction conditions. Regioselectively C6-alkylated products were obtained exclusively from tetrahydroquinoline, without the formation of C5-, C7-, C8-, or N-alkylated products.