Theoretical studies on the rotamers and dynamic behaviors of ethyl-5-acetyl-4-(3′,4′-dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3-carboxylate

The potential energy surfaces of ethyl-5-acetyl-4-(3',4'-dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3-carboxylate have been explored by density functional theory B3LYP with 6-31G* basis set method. All minima and maxima points have a flat boat conformation and the aryl ring lies above the 1,4-dihydropyridine ring. Therefore, the rotation of aryl, acetyl, and carboethoxy groups do not cause a major conformational change in this compound. However, the orientations of carbonyl groups and the distortion from planarity of dihydropyridine ring have been changed. Intramolecular H-contacts involving CH-groups as proton donors have also been investigated. Comparative analysis of the results indicates that the barrier to rotation for aryl group is smaller than that of the carbonyl groups. In addition, the barriers to rotation for the carbonyl and aryl groups of the corresponding pyridine, i.e., ethyl-5-acetyl-4-(3',4'-dimethoxyphenyl)-2,6-dimethyl-pyridine-3-carboxylate, have also been computed by a similar basis set to investigate the effect of aromaticity of the dihydropyridine ring on the these parameters.