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.

Graphic abstract

中文翻译：

---

纳米磁催化（Fe 3 O 4 @ S–TiO 2）：一种新型的磁性纳米催化剂，用于在无溶剂条件下合成新的高度取代的四氢吡啶衍生物

通过水热法制备了一种新型的纳米磁性催化剂（Fe ₃ O ₄ @ S–TiO ₂）。首先，Fe ₃ O ₄合成纳米粒子，然后将氧化铁纳米粒子（IONPs）分散在乙醇溶液中，然后添加异丙氧基钛和硫脲以修饰IONPs。合成的磁性绿色催化剂已通过多种方法（TEM，SEM，EDS，XRD，VSM和FTIR）进行了表征。这些技术证实了将硫掺杂的二氧化钛壳放置在磁铁矿芯的表面上是正确的。该纳米催化剂的催化活性已在100°C和无溶剂条件下非对映选择性合成新的高度取代的四氢吡啶衍生物中进行了研究。已证实，与未掺杂的Fe ₃ O ₄ @TiO ₂相比，该纳米催化剂可以提高反应速率。并且还会导致高反应产率。在五次成功运行后，该催化剂可以轻松回收和再利用，而不会损失活性。此外，我们证明乙酰丙酮可以高产率地合成四氢吡啶，是一种可接受且有效的β-二酮。

图形摘要