Preparation of Core/Shell CaO@SiO2-SO3H as a Novel and Recyclable Nanocatalyst for One-Pot Synthesize of Dihydropyrano[2,3-c]Pyrazoles and Tetrahydrobenzo[b]Pyrans

The core/shell CaO@SiO2-SO3H nanoparticles were prepared by stabilizing of sulfonic acid on the surface of silica-coated CaO nanoparticles. The structure of CaO@SiO2-SO3H was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), wavelength-dispersive X-ray spectroscopy (WDX) and thermal gravimetric analysis (TGA). CaO@SiO2-SO3H was used as a new acidic catalyst for green synthesis of dihydropyrano[2,3-c]pyrazoles and tetrahydrobenzo[b]pyrans via one-pot three-component reactions with good to excellent yields. This catalyst could be recycled and reused for six runs without significant loose of activity.