Quantum chemical study of regioselectivity of reactions of substituted pyrido[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazoles with electrophiles

The geometric, charge, and electronic characteristics of 7-substituted pyrido1,2-a]benzimidazoles and their cations were calculated using the DFT method with the B3LYP functional in the 6-31G** basis set. High regioselectivity of the reactions between the condensed imidazole derivatives and electrophilic agents was explained by the results of quantum chemical simulation. It was concluded that the S _EAr reaction was orbitally controlled. According to Fukuís concept, the reaction center of the electrophilic attack was the C(8) atom of the heterocyclic system, which agreed well with the experimental data.