A Green and Efficient Method for the Synthesis of 3,4- Dihydropyrano[c]chromene using Phosphate Fertilizers (MAP, DAP and TSP) as Heterogeneous Catalysts

This article presents a simple and practical method for the synthesis of 3,4-dihydropyrano[c]chromene, which are heterocyclic compounds possessing a wide range of biological properties. They have been obtained by the condensation of an aromatic aldehyde, malononitrile and 4-hydroxycoumarin in presence of phosphate fertilizers (MAP, DAP and TSP) as heterogeneous catalyst and ethanol as an ecological solvent that makes this procedure environmentally friendly. The aim of this study is the investigation of their catalytic activities through the determination of the optimum conditions, which are the reaction time, the mass of the catalyst used, the nature of the solvent and its appropriate volume. These optimum conditions are the mean ones in the catalytic efficiency and they permit to obtain better yields with shorter reaction times. The developed method herein presents a green strategy which is characterized by mild reaction conditions, high to excellent yields, short reaction times and easy catalyst recovery. In addition, the experiment shows that these catalysts can be reused successfully several times without significant loss of their catalytic activity.