Metal oxide nanoparticles as reusable heterogeneous catalysts in the synthesis of 1,4-dihydropyridine derivatives via solvent-free Hantzsch reaction: A comparative study

The catalytic effect of three nano-sized metal oxides including Al2O3, Fe3O4, and TiO2 nanoparticles, in the synthesis of 1,4-Dihydropyridines by one-pot three-component reaction of aliphatic aromatic aldehydes, ammonium acetate, and ethyl acetoacetate, has been investigated. Different reaction conditions were studied in the presence of Al2O3, Fe3O4, and TiO2 nanoparticles as catalysts. The results showed that nano TiO2 acts as more effective heterogeneous catalyst than others and the reaction proceeded more easily and gave the highest yields of the products in shorter reaction times under thermal solvent-free conditions. Short reaction times, simple isolation of the products, and usage of eco-friendly catalysts are some features of this procedure. In addition, the catalysts were easily recovered and used in multiple catalytic cycles.