Melamine trisulfonic acid as a highly efficient catalyst for the synthesis of polyhydroquinolines under solventfree conditions

A highly efficient, simple and clean solvent-free protocol for the synthesis of polyhydroquinolines is described. The one-pot multi-component condensation reaction between arylaldehydes, dimedone (5,5-dimethylcyclohexane-1,3-dione), β-ketoesters and ammonium acetate in the presence of 2.5 mol% of melamine trisulfonic acid (MTSA) at 60 °C affords the title compounds in high yields (83-98%) and short reaction times (3-30 min).