Synthesis, characterization and density functional theory study of di-acylation of n-aminoquinazolin-4(3H)-one derivatives

We have synthesized N-Acetyl-N-(2-ethyl-4-oxo-4H-quinazolin-3-yl)-acetamide, N-Acetyl-N-(2-isopropyl-4-oxo-4H-quinazolin-3-yl)-acetamide, N-Acetyl-N-(2-ethyl-4-oxo-4H-quinazolin-3-yl)-benzamide and N-Acetyl-N-(2-benzhydryl-4-oxo-4H-quinazolin-3-yl)-acetamide then characterized by IR and NMR techniques. The molecular geometries and vibrational frequencies of DAQ derivatives at the ground state have been calculated using density functional theory at B3LYP/6-31G* level of theory. The optimized bond lengths and bond angles showed better agreement with the experimental values. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. According to the DFT calculation, the quinazolinone and imide planes, linked by the N-N bond, are as expected approximately orthogonal and the imide carbonyl groups are present as mixtures of exo-endo and endo-exo conformations. The N-N rotation barrier has been explained on the basis of DFT theory. (author)