Green synthesis of benzimidazoloquinazolines and 1,4-dihydropyridines using magnetic cyanoguanidine-modified chitosan as an efficient heterogeneous nanocatalyst under various conditions

In the present study, we demonstrated the synthesis of magnetic cyanoguanidine-modified chitosan (MCGC) as an efficient and green retrievable heterogeneous nanocatalyst for one-pot three-component synthesis of benzimidazoloquinazolines (from 2-aminobenzimidazole, aromatic aldehydes, and dimedone) and 1,4-dihydropyridines (via Hantzsch-type condensation of ethyl acetoacetate, aromatic aldehydes, and ammonium acetate) under the ultrasonic irradiation and reflux conditions. The structure of the catalyst was fully confirmed using Fourier transform infrared spectroscopy, vibrating sample magnetometer, field emission scanning electron microscopy, energy dispersive spectroscopy, and thermogravimetric analysis. Increased amount of amino groups that are generated by modifying the surface of chitosan with cyanoguanidine as well as presence of hydroxyl groups determined the catalytic activity of MCGC. Furthermore, as experimental results confirmed, the ultrasonic-promoted reactions gave the better results in terms of reaction time, yield, and purity of isolated products. Cost effectiveness, mild conditions, low catalyst loading, convenient work-up, and ecofriendly solvent are some of the remarkable advantages of this protocol. Graphic abstract: