Facile synthesis of pyranopyrazoles and 3,4-dihydropyrimidin-2(1H)-ones by a Ti-grafted polyamidoamine dendritic silica hybrid catalyst via a dual activation route

Abstract

A simple, highly efficient and ecofriendly approach for the preparation of biologically potent pyranopyrazoles and 3,4-dihydropyrimidin-2(1H)-ones are described here. A Ti-grafted polyamidoamine dendritic silica hybrid catalyst was successfully synthesized, and its catalytic performance was studied in two important multicomponent reactions such as Biginelli reaction and pyranopyrazole synthesis. Studies demonstrate that the crystalline pore wall structure of the dendritic silica hybrid catalyst makes adsorption of reactants easy. Combining the Lewis acidic and Lewis basic properties of the silica surface facilitates and accelerates the synthesis of the desired products in high yields. The key advantages of the present method are the excellent yield of the products, low catalyst loading, shorter reaction times, facile work-up, and purification of the products by non-chromatographic methods and the reusability of the catalyst.