Montmorillonite clay-catalyzed [4+2] cycloaddition reactions: a facile synthesis of pyrano- and furanoquinolines

Aryl amines react smoothly with cyclic enol ethers such as 3,4-dihydro-2H-pyran (DHP) and 2,3-dihydrofuran (DHF) on the surface of montmorillonite KSF under mild reaction conditions to afford the corresponding pyrano- and furano[3,2-c]quinolines in high yields with high diastereoselectivity.