An environmentally benign and clean biopolymer-based heterogeneous nanocatalyst was prepared and its properties and morphology were characterized using scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Then, its catalytic activity was investigated in two important organic reactions. In these reactions, efficient and selective syntheses of 1,2-disubstituted benzimidazole and 1,5-benzodiazepine derivatives were carried out using 1,2-diamines and aldehydes or ketones in the presence of a catalytic amount of magnetically recoverable chitosansupported iron oxide nanoparticles (Fe 3 O 4 /chitosan), as a biodegradable nanocomposite, in ethanol at ambient temperature in high yields. The Fe 3 O 4 /chitosan nanocatalyst can be recovered easily and reused without any significant loss of the catalytic activity.
The development of simple, practical and inexpensive catalysis systems using natural materials is one of the main goals of pharmaceutical chemistry as well as green chemistry. Owing to the ability of easy separation of nanocatalyst, those goals could be approached by applying heterogeneous bionanocatalyst in combination with magnetic nanoparticles. Starch is one of the most abundant natural polymers; therefore, preparing bionanocatalyst from starch is very valuable as starch is largely available and inexpensive. An ecologically benign and efficacious heterogeneous nanocatalyst was prepared based on a biopolymer, and its attributes and morphology were specified by using Fourier transform infrared spectra, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermal analysis and vibrating sample magnetometer measurements; followed by studying catalytic behaviour of bionanocomposite in a multicomponent reaction to synthesize of 4H-pyran derivatives. 4H-pyran is extremely valuable in pharmaceutical chemistry, and the development of methods for synthesis of different derivatives of 4H-pyran is momentous. Revealing environmentally benign nature, mild condition, easy work-up, low cost and non-toxicity are some of the advantages of this protocol. Besides, the bionanocomposite was recovered using an external magnetic bar and could be re-used at least six times with no further decrease in its catalytic activity.
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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