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A picolinaldehyde–melamine copper complex was loaded on a magnetic Fe3O4 core, so that it contained 0.33 mmol of Cu per gram, and was used as an efficient catalyst. The as‐synthesized catalyst was characterized using various techniques, including Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and thermogravimetric analysis. The catalyst was used to activate the raw materials in the synthesis of hexahydroquinoline derivatives in one‐pot four‐component reactions. Low reaction time (minutes versus half an hour), solvent‐free condition and magnetically separable catalyst are some salient features of the developed catalyst. Also, the optimum amount of catalyst and temperature were determined as 0.07 g and 87.6 °C, respectively, which were obtained using response surface methodology and optimization techniques.

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The tannic acid–based iron nanoparticle (TAN-Fe-NP) was prepared by a redox reaction between tannic acid and FeCl3 in water and characterized by the Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, energy dispersive X-ray analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Then, a TAN-Fe-NP nanocatalyst was used as an efficient catalyst for the synthesis of polyhydroquinolines from the reaction of ethyl acetoacetate, benzaldehydes, dimedone, and ammonium acetate in ethanol at 60 °C in high yields and low reaction times. Since this catalyst is made of natural materials, it has a great advantage compared with the other catalysts and is cheap, available, natural, safe, nontoxic, and eco-friendly as well.