An efficient protocol for the liquid-phase synthesis of furanoquinolines and pyranoquinolines

A three-step liquid-phase protocol for the synthesis of furanoquinolines and pyranoquinolines is described. The one-pot three-component aza-Diels-Alder reaction of PEG-supported benzaldehyde, anilines and 2,3-dihydrofuran or dihydropyran under TFA gave PEG-supported tetrahydroquinolines, which was assuredly oxidized by DDQ and then cleaved from the support to afford the corresponding furanoquinolines and pyranoquinolines with reasonable yields and purity.