Magnetic copper-loaded aminouracil Schiff base nanoclay for synthesizing 2-amino-4H-pyrans, benzimidazoles, and benzoxazoles

In the present work, a novel magnetically recoverable heterogeneous nanocatalyst, designated as M-Clay-APTES-AU-Schiff base@Cu, was prepared through a four-step post-synthetic modification of Cloisite 30B nanoclay. The synthesis commenced with co-precipitation of Fe₃O₄ on the clay surface to impart magnetic recoverability, followed by covalent grafting of 3-aminopropyltriethoxysilane (APTES). Imine-condensation of the surface amine with terephthalaldehyde and 6-aminouracil (AU), in a one-pot reaction, installed a bifunctional Schiff base ligand bearing pendant uracil N, O-donor sites, onto which Cu species (introduced as Cu(II) acetate) were subsequently incorporated; the oxidation state of the surface copper was not independently confirmed. The composition, structure, thermal behavior, surface area, and magnetic response of the resulting material were characterized by FT-IR, XRD, TGA, FE-SEM/EDS, BET, VSM, CHN, and ICP-OES analyses. The catalyst was evaluated in the one-pot synthesis of 2-amino-4 H -pyran derivatives (via three-component condensation of aldehydes, malononitrile, and dimedone) and of benzimidazole and benzoxazole derivatives (via condensation of aromatic aldehydes with o-phenylenediamine or 2-aminophenol, respectively). Under optimized conditions in refluxing ethanol, 2-amino-4 H -pyrans were obtained in 89–98% isolated yield within 5 min over a diverse range of aldehyde substrates, and benzazoles were produced in 70–97% yield within 30 min. The catalyst was readily recovered by an external magnet and reused across five consecutive cycles with only a modest decline in activity (isolated yield: 95→86% and 97→91% for the two reaction families, respectively). A hot-filtration test and post-use ICP-OES analysis (residual Cu content 1.94 mmol g⁻¹, < 3.5% loss) confirmed the heterogeneous nature of the catalytic process.