Synthesis of 2-substituted benzimidazole, coumarin, benzo[b][1,4]oxazin and dihydropyrimidinone derivatives using core-shell structured Fe3O4@SiO2-ZnCl2 nanoparticles as an effective catalyst

Abstract

In this paper, a magnetic nanocatalyst of Fe3O4@SiO2-ZnCl2 has been used which enhances the synthesis of benzimidazoles, coumarins, benzoxazines and dihydropyrimidinones. To begin with, 2-substituted benzimidazoles have been synthesized in proper to high yields from 1,2-phenylenediamine with extensive diversity of aromatic aldehydes in the presence of magnetic nanocatalyst. Then, this magnetic nanocatalyst has been used for the synthesis of coumarin derivatives via Pechmann condensation reaction of phenols with ethyl acetoacetate in good yield under solvent-free conditions. Next, the synthesis of benzo[b][1,4]oxazines has been accomplished efficiently by the multi-component condensation of 2-aminophenol, aromatic aldehyde and isocyanide using magnetic nanocatalyst. Lastly, dihydropyrimidinones were synthesized by a one-pot three-component cyclocondensation using β-keto ester, substituted aromatic aldehyde and urea. The benefits of this method are facile, easy work-up, catalyst reusability and leading to good yields. Theoretical assessments allow us to corroborate the reactions mechanism.