Silica-supported ZnCl2 -: A highly active and reusable heterogeneous catalyst for the one-pot synthesis of dihydropyrimidinones-thiones

A novel silica-supported zinc chloride catalyst was prepared and investigated for the Biginelli reaction. The key features of the catalyst include rapid reaction with 100% conversion of aldehyde, good catalyst recyclability, and high stability under the reaction conditions (passes hot filtration test successfully). A low catalyst loading (12 mol% of ZnCl2) was required to achieve a quantitative reaction. Other catalysts such as SiO2-AlCl2, SiO2-AlCl2-ZnCl2 were also prepared and their activity was compared with SiO2-ZnCl2 for the Biginelli reaction.