A novel nanomagnetic catalyst (Fe3O4@S–TiO2) was prepared by the hydrothermal method. At the first, Fe3O4 nanoparticles were synthesized, then iron oxide nanoparticles (IONPs) were dispersed in ethanol solution, followed by the addition of titanium isopropoxide and thiourea to modify IONPs. The synthesized magnetically green catalyst has been characterized by various methods (TEM, SEM, EDS, XRD, VSM and FTIR). These techniques approved that the sulfur–doped titanium dioxide shell was well placed on the surface of the magnetite core. The catalytic activity of this nanocatalyst has been studied in the diastereoselective synthesis of new highly substituted tetrahydropyridine derivatives at 100 °C and under solvent-free conditions. It was confirmed that this nanocatalyst can multiply the rate of the reaction compared to the undoped Fe3O4@TiO2 and can also lead to high reaction yields. This catalyst could be easily recovered and reused without significant loss of activity over five successful runs. Besides, we proved that acetylacetone can be an acceptable and effective β-diketone in the synthesis of tetrahydropyridines in high yields.

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