A chitosan-based magnetic nanocomposite was synthesized by an eco-friendly and simple procedure, and was characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. It was then used for the efficient synthesis of tetrahydrobenzoxanthen-11-one derivatives via a one-pot three-component condensation of 2-naphthol, various aldehydes and dimedone in ethanol. The catalyst was recovered easily and reused several times without significant loss of catalytic activity.

A practical and green approach for the one-pot multicomponent synthesis of tetraheterocyclic benzimidazolo[2,3-b]quinazolinones has been described via the condensation of 2-aminobenzimidazole or 2-aminobenzothiazole, dimedone, and various aldehydes using Fe3O4@chitosan as an environmentally benign and reusable nanocomposite catalyst in good to excellent yields.

New hybrid magnetic composite nanostructure are prepared via ultrasonic treatment by glass-ceramic method, characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), energy-dispersive X-ray (EDX), element distribution image (EDX mapping), thermal gravimetric analysis (TGA)/differential thermal analysis (DTA) and N adsorption-desorption by Brunauer-Emmett-Teller (BET) analyses. Then, the catalytic activity of the prepared CoFeO@BO-SiO nanoparticles was tested in the synthesis of 2-substituted-3-(phenylamino)-dihydroquinazolin-4(1H)-ones in deep eutectic solvent (DES) based on choline chloride as an eco-friendly and recyclable media. This novel protocol offers several advantages such as high yields (70-93%), short reaction times (10-20min), environmentally-friendly reaction media, easily isolation of the products, simple preparation and recoverability of the nanocatalysts (at least 5 times), recyclability of the solvents from the reaction mixture without use of hazardous volatile organic solvent. The catalyst was readily recycled by the use of an external magnetic field and could be reused several times without significant loss of activity or mass. The saturation magnetization of CoFeO@BO-SiO nanoparticles was 8.97emug. Their average size distribution was about 12.5nm. DES was a mixture of choline chloride and urea that was recovered from the filtrate by evaporating the water under vacuum.

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A practical and green approach for the ultrasound-enhanced one-pot multicomponent synthesis of tetraheterocyclic imidazo(thiazolo)pyrimidines is described via the condensation of an 2-aminobenzimidazole or 2-aminobenzothiazole, dimedone and various aldehydes in the presence of FeO@clay as an environmentally benign and reusable core/shell nanocomposite catalyst in relatively quantitative yields. This novel eco-friendly protocol includes several advantages such as avoiding hazardous solvents, reusability of the catalyst, easy work-up, short reaction times, room temperature and mild reaction conditions. Furthermore, ultrasonic irradiation and synergistic catalyst showed considerable superiority vs. traditional heating or stirring conditions.

1,4-Dihydropyridines are synthesized from various aromatic aldehyde, dimedone or 1,3-cyclohexandione, ethyl acetoacetate or methyl acetoacetate and ammonium acetate catalyzed by magnetite/chitosan at room temperature under mild reaction conditions. This process offers an easy and efficient synthesis of 1,4-dihydropyridine derivatives in high yields. The benefits of this protocol are simplicity, nontoxicity, low cost, simple workup, and an environmentally benign nature. The catalyst is recovered by filtration and reused at least five times without significant loss in catalytic activity.

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