Synthesis, characterization and theoretical studies of hexahydroquinoline derivatives using nanopyrophosphate as an effective renewable catalyst

This study aims to optimize the conditions and yield of the quinoline synthesis using an environmentally friendly, heterogeneous, non-toxic, and recyclable catalytic system for the preparation of hexahydroquinolines through a one-pot multi-component reaction. Initially, the nanostructured diphosphate Na2CaP2O7 was prepared by a dry method. Then, the synthesized diphosphate was identified by various techniques, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nano-Na2CaP2O7 was used as an effective and renewable catalyst for the one-step synthesis of hexahydroquinoline derivatives 5(a-l) using aryl aldehydes, malononitrile or ethyl cyanoacetate, 5,5-dimethyl-1,3-cyclohexanedione (dimedone) and ammonium acetate in the presence of catalytic amount of nanodiphosphate Na2CaP2O7. The reaction was carried out at 80°C in ethanol as solvent and was completed within 10minutes, giving impressive yields ranging from 62 to 97%. The synthesized products were characterized by FT-IR, 1H NMR, and 13C NMR. This new process offers several advantages, such as the efficiency of the experiment, a high product yield and the reusability of the catalyst. Finally, density functional theory (DFT) calculations were performed at the B3LYP/6-31G (d,p) level. The frontier molecular orbitals, dipole moment, quantum chemical parameters and molecular electrostatic potential (MEP) were calculated to shed light on the reactive sites for electrophilic and nucleophilic attack. The results suggest that our compounds can be used as reagents in different reactions for pharmaceutical purposes.