High-efficient synthesis of 2-imino-2H-chromenes and dihydropyrano[c]chromenes using novel and green catalyst (CaO@SiO2@AIL)

Abstract

In this work, 1,3,5,7-tetraazaadamantan-1-ium chloride (AIL) functionalized silica-coated calcium oxide hybrid nanocatalyst (CaO@SiO2@AIL) as a novel, efficient, green and recyclable heterogeneous ionic liquid catalyst was synthesized. Catalytic activity of the CaO@SiO2@AIL hybrid nanoparticles was investigated for synthesis of the pharmaceutically valuable 2-imino-2H-chromene and dihydropyrano[c]chromene derivatives. A wide range of amines and aromatic aldehydes containing either electron-withdrawing or electron-donating substituent were examined using optimized conditions to produce the desired products. 2-Imino-2H-chromenes were synthesized under solvent-free condition, and dihydropyrano[c]chromenes were prepared in aqueous medium as green conditions within short reaction times, high yields and using easy workup procedures. Structure confirmation and surface properties of the core/shell hybrid nanoparticles were considered via Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy, WDS map scan, thermogravimetric and elemental analyses. This IL-supported heterogeneous nanocatalyst can be reused at least six times without considerable loss of its performance.