Synthesis of hexahydroquinolines using the new ionic liquid sulfonic acid functionalized pyridinium chloride as a catalyst

Sulfonic acid functionalized pyridinium chloride [pyridine-SO3H]Cl has been synthesized as a novel Brönsted acidic ionic liquid and characterized on the basis of its FT-IR, 1H and 13C NMR, MS, thermogravimetry, and derivative thermogravimetry data. The material has also been used as a highly efficient, homogeneous, and reusable catalyst for the preparation of hexahydroquinolines according to the one-pot multi-component condensation of arylaldehydes, dimedone (5,5-dimethylcyclohexane-1,3-dione), β-ketoesters, and ammonium acetate under solvent-free conditions. Sulfonic acid functionalized pyridinium chloride [pyridine-SO3H]Cl has been prepared as a novel Brönsted acidic ionic liquid and characterized using a range of analytical techniques. This compound efficiently catalyzed the synthesis of hexahydroquinolines at 50 °C under solvent-free conditions.