Inorganic-organic hybrid silica based tin complex as a novel, highly efficient and recyclable heterogeneous catalyst for the one-pot preparation of spirooxindoles in water.

In the present study, a tin complex immobilized on silica gel as a novel, green, highly efficient and heterogeneous reusable catalyst was synthesized by grafting 2-amino benzamide onto the silica gel surface as a result of the reaction between isatoic anhydride and 3-aminopropyl-functionalized silica gel, followed by complexing with tin chloride. The resulting organic-inorganic hybrid material was evaluated in the one-pot three-component synthesis of spiro[indoline-pyrazolo[4',3':5,6]pyrido[2,3-d]pyrimidine]trione derivatives in water via the condensation reaction of isatins, barbituric acids, and 1H-pyrazol-5-amines. All the reactions were completed in short reaction times and all the products were obtained in high to excellent yields with high purity. In addition, the synthesized novel catalyst could be separated from the reaction mixture by simple filtration and can be reused up to seven runs without significant loss in activity.