Synthesis, Crystal Structure and DFT Studies of 1,3-Dimethyl-5-propionylpyrimidine- 2,4,6(1H,3H,5H)-trione

Novel 1,3-Dimethyl-5-propionylpyrimidine-2,4,6(1H,3H,5H)-trione was synthesized and recrystallized from ethanol. The compound was characterized by 1H NMR, 13C NMR in CDCl3, DMSO-d6 and acetone-d6, elemental analysis and X-ray diffraction. The NMR data observed that the title compound exists in the enol tautomer rather than keto, and it stabilized by strong H-bond as observed form the NMR data at different temperatures. Theoretical calculations (DFT) were carried out using Gaussian09 program package and B3LYP correlation function. Full geometry optimization of the keto and enol forms were carried out using 6-311G++(d,p) basis set. The structure and energy of the transition state between these two tautomers were calculated. The frontier orbital energy and atomic net atomic charges of the tautomers were presented. The experimental results of the title compound have been compared with the theoretical results and it was found that the experimental data are in a good agreement with the calculated values. The transition state calculations also support the stability of enol form compared to keto form at room temperature.