Novel insight on aromaticity enhancement of pyridone heterocycles using the anomeric effect-Schleyer hyperconjugation aromaticity: A DFT and NBO study

Considering the value of 2-pyridone and 4-pyridone heterocyclic groups in organic chemistry, in this study, the anomeric effect and Schleyer hyperconjugation aromaticity for the first time have been used to increase the aromaticity of these heterocycles. The anomeric effect in tetrahydropyrans containing 2-pyridone or 4-pyridone ring on the anomeric carbon in axial and equatorial conformers has been investigated using the DFT-B3LYP/ 6-311++G(d,p) calculation method. On the other hand, the aromaticity of 2-pyridone and 4-pyridone in the considered conformers was investigated by nucleus-independent chemical shift indices (NICS) and the harmonic oscillator model of electron delocalization index (HOMED). The results illustrate that placing 2-pyridone and 4pyridone in the axial position increases their aromaticity through the anomeric effect. Furthermore, connecting the ring from the carbon atom to the anomeric position is better than the nitrogen atom for aromaticity increment. Aromaticity indices show that the anomeric effect-Schleyer hyperconjugation interaction is more robust in the presence of nitrogen atoms than oxygen or sulfur atom.