Synthesis of bioactive heterocycles using reusable heterogeneous catalyst HClO₄–SiO₂ under solvent-free conditions

We are reporting a simple, efficient and green protocol for the synthesis of chromenes and dihydropyrimidines (products of Knoevenagel and Biginelli reaction, respectively) by the use of silica-supported perchloric acid (HClO₄–SiO₂) as an effective heterogeneous catalyst. Short reaction times, high product yields, simple procedure and reusability of the catalyst are the superior characteristics of this protocol.