Application N-aminophthalimide for effective and efficient synthesis of new 1,4- dihydropyridine derivatives and electronic properties analyses, vibrational frequencies, NMR chemical shift analysis: A DFT study

Abstract

A straightforward and effective approach to synthesize novel 1,4-dihydropyridine derivatives was demonstrated through the Hantzsch four-component condensation involving aromatic aldehydes, DEAD (diethyl acetylenedicarboxylate), malononitrile, and N-aminophthalimide, using a minimal amount of triethylamine as a catalyst, conducted at ambient temperature in ethanol. The synthesized molecules were characterized by IR, NMR, mass spectrometry, and elemental analysis of C, H, and N. The molecular structures of specific compounds (5a-e) were explored via quantum theoretical studies using the B3LYP method and the 6–311 + G** basis set, leading to the acquisition of geometric parameters from optimized structures which were then corroborated with experimental data. Validation of the compounds' structures was accomplished through IR, ¹H NMR, ¹³C NMR, and elemental analysis. Further theoretical studies provided insights into the IR spectra, ¹H NMR, and ¹³C NMR chemical shifts for the ground state of these new 1,4-dihydropyridine derivatives. To compare this agreement, a correlation graph based on theoretical and experimental data was analyzed, showing a very good correlation. A slight discrepancy was observed between the calculated and experimental vibrational states, which may result from intermolecular hydrogen bonding. Furthermore, the theoretical calculations refer to the gas phase, whereas the experimental data pertain to the solid phase. In addition to analyses of the frontier molecular orbitals (FMOs), the total density of states (DOS), molecular electrostatic potential (MEP), NBO, Mulliken atomic charges, and thermodynamic parameters. A strong concordance between the theoretical predictions and experimental findings was established.