Aqueous Media Preparation of Pyrido[d]pyrimidines Over Calcined TiO2-SiO2 Nanocomposite as an Efficient Catalyst at Ambient Temperature

Pyridopyrimidines represent a highly important class of compounds which exhibit a wide spectrum of biological properties. Nanoscale metal oxide catalysts have been extensively studied for their application in organic reactions owing to their special features such as high surface area and pore sizes as supports. Titanium dioxide nanoparticles (TiO2 NPs) are an attractive candidate for readily available cheap nanocatalysts, due to their unique properties such as being non-toxic, moisture stable and reusable catalyst. 7-amino-2,4-dioxo-5-aryl-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidine-6-carbonitriles were synthesized through the reaction of 4(6)-aminouracil, aromatic aldehydes, and malononitrile using calcined TiO2-SiO2 nanocomposite as a reusable catalyst in water at ambient temperature. All the synthesized compounds were well characterized by their elemental analyses, IR, 1H and 13C NMR spectroscopy. The synthesized catalyst was fully characterized by the powder X-ray diffraction (XRD), the scanning electron microcopy (SEM), the transmission electron microscopy (TEM), and the x-ray fluorescence (XRF) techniques. The reaction proceeded through calcined TiO2-SiO2 nanocomposite catalyzed three-component reaction affording twelve target compounds in high yields. This method introduced a novel protocol to provide 7-amino-2,4-dioxo-5-aryl-1,2,3,4-tetrahydropyrido[2,3- d]pyrimidine-6-carbonitrile derivatives and offer several advantages like very simple operation, using inexpensive, recyclable and non-toxic catalyst, mild reaction conditions, high yields of products (92- 98%), short reaction times (2.5-4 h), and green aspects by avoiding toxic catalysts and hazardous solvents.