Controllable stereoselective synthesis of cis or trans pyrano and furano tetrahydroquinolines: Polyaniline-p-toluenesulfonate salt catalyzed one-pot aza-Diels–Alder reactions

cis as well as trans pyrano tetrahydroquinolines were synthesized using a polymeric solid acid catalyst, polyaniline-p-toluenesulfonate (PANI–PTSA) salt, by conveniently controlling the reaction conditions. One-pot three component aza-Diels–Alder reactions involving aromatic aldehydes, aniline, and 3,4-dihydro-2H-pyran are effectively catalyzed by PANI–PTSA under solvent free condition at room temperature afford cis pyranoquinolines and the reaction carried out at 80 °C gave trans configuration. Whereas reactions involving 2,3-dihydrofuran instead of 3,4-dihydro-2H-pyran gave major cis furanoquinolines under solvent free conditions and 100% cis configuration with the use of solvents. This process conforms to the principles of ‘green’ chemistry by the usage of solvent free medium, easily handleable, recyclable and eco-friendly nature of the catalyst. In addition, this method provides simple work up procedure, short reaction time and use of easily synthesizable cheaper catalyst.

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► PANI–PTSA serves as reusable catalyst to prepare cis or trans tetrahydroquinolines.
► cis or trans products were obtained by controlling the reaction temperature.
► Tetrahydroquinolines were obtained in a very short time.