Regiochemistry of cyclocondensation reactions in the synthesis of polyazaheterocycles.

The syntheses of several polyazaheterocycles are demonstrated. The cyclocondensation reactions between β-enaminodiketones [CClC(O)C(=CNMe)C(O)-COEt] and aromatic amidines resulted in glyoxalate-substituted pyrido[1,2-]pyrimidinone, thiazolo[3,2-]pyrimidinone and pyrimido[1,2-]benzimidazole. Pyrazinones and quinoxalinones were obtained through the reaction of these glyoxalates with ethylenediamine and 1,2-phenylenediamine derivatives. On the other hand, the reaction of glyoxalates with amidines did not lead to the formation of imidazolones, but rather -acylated products were obtained. All the products were isolated in good yields. DFT-B3LYP calculations provided HOMO/LUMO coefficients, charge densities, and the stability energies of the intermediates, and from these data it was possible to explain the regiochemistry of the products obtained. Additionally, the data were a useful tool for elucidating the reaction mechanisms.