Synthesis, NMR analysis, and DFT calculation studies on 2H-quinolizine derivative under solvent-free conditions

Computational studies have been carried out at DFT-B3LYP/6-31G and 6-31++G** level of theory on the structural and spectroscopic properties of 2H-quinolizines. 2H-quinolizines obtain from four-component reaction of the zwitterion generated from pyridine and dialkylcarbodiimide with electron-deficient dialkyl acetylenedicarboxylat. The optimized geometry of these compounds and their bonding characteristics, and NMR Spectra as well as charge have been calculated and analyzed. The influence of the bulk solvent was investigated at the B3LYP/ 6-31++G** level using polarizable continume model. The results of this study show that the 4d is more stable than the 11 in the gas and solvent phase, due to intra molecular hydrogen bonding. Also, natural bond orbital (NBO) analysis shows that there is long π-electron delocalization in compound 4d in comparison to compound 11, which leads to the stabilization of the compound 4d inrelative to compound 11. There is a good agreement between the experimental and calculated chemical shifts in 13C and 1H-NMR.