Novel MgO-SnO ₂ solid superbase as a high-efficiency catalyst for one-pot solvent-free synthesis of polyfunctionalized 4H-pyran derivatives

We report for the first time the hydrothermal synthesis of MgO-SnO ₂ solid superbase using P123 as template. The basicity of the materials was determined by two approaches of Hammett indicators method and temperature- programmed desorption using CO ₂ as adsorbate (CO ₂-TPD). It was found that Mg/Sn molar ratio has an effect on MgO-SnO ₂ basicity, and superbasicity was observed only at Mg/Sn molar ratio of 1. With variation of Mg/Sn molar ratio, superbase strength (H-) was in the 26.5-33.0 range, showing superbasic value up to 0.939 mmol/g. The structure and texture of the as-prepared materials were studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 physioadsorption methods. We detected particles of spherical morphology having diameter of ca. 150 nm. N2 adsorption- desorption results suggested that the materials are of mesoporous structure, having specific surface area of 115.2 m2/g and average pore diameter of 6 nm. The superbase was found to exhibit excellent catalytic activity towards the one-pot synthesis of polyfunctionalized 4Hpyrans through the condensation of aldehydes, malononitrile, and an active methylene compound. Its excellent catalytic efficiency is related to its superbasicity of the MgO-SnO ₂. The results provide a new route for the design and preparation of composite oxide superbases. Furthermore, the solid superbases will facilitate a strategy for high-efficiency synthesis of polyfunctionalized 4H-pyrans.