Mechanistic aspect of ring transformations in the reaction of 5-nitro-4-pyrimidinone with acetophenone derivatives and cycloalkanones depending on the electron density/ring size of the ketone

3-Methyl-5-nitro-4-pyrimidinone undergoes two kinds of nucleophilic type ring transformations upon treatment with cycloalkanones in the presence of ammonium acetate, which affords 4,5-disubstituted pyrimidines and 5,6-disubstituted 3-nitro-2-pyridones. In order to improve the synthetic utility of this reaction, it is necessary to control the regioselectivity of these ring transformations. In the present work, we performed DFT calculation to realize the selectivity of two ring transformation products. In cases of adduct intermediates derived from cyclohexanone and cyclooctanone, the 2-attack proceeds preferably to give condensed pyrimidines. On the other hand, the adduct intermediate derived from cycloheptanone undergoes the 4-attack predominantly to afford condensed nitropyridone.