Melamine trisulfonic acid as a highly efficient catalyst for the synthesis of polyhydroquinolines under solvent-free 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 catalytic amount of (2.5 mol%) melamine trisulfonic acid (MTSA) as a recyclable, green and attractive sulfonic acid-containing catalyst at 60 °C affords the title compounds in high yields (83-98%) and short reaction times (3-30 min). The advantages of this method are efficiency, generality, high yield, short reaction time, cleaner reaction profile, simplicity, recyclability of the catalyst, ease of product isolation, and good compliance with the green chemistry protocols.