Synthesis, regioselectivity, and DFT analysis of new antioxidant pyrazolo[4,3-c]quinoline-3,4-diones

The condensation of hydrazine, N-methylhydrazine, and N-phenylhydrazine with ethyl 4-chloro-2-oxo- 1,2-dihydroquinoline-3-carboxylate derivatives has been investigated. As a result, 12 new antioxidant pyrazolo[4,3- c]quinolin-3,4-diones were obtained with good to high yields. When two cross-products could be possible, only one isomer bearing the methyl or the phenyl group at the N1 position is isolated and unequivocally characterized using 1D and 2D NMR techniques, FT-IR, and combustion analyses. DFT analysis of the reaction mechanism was carried out in the Pearson’s hard soft acid base framework, confirming the assigned structure to the observed pyrazolo[4,3-c]quinolin-3,4-diones. These calculations indicate a favored kinetic control for the synthesized pyrazolo[4,3- c]quinolin-3,4-diones compared to its possible regioisomer.The authors thank the Regional University Hospital of Besanc¸on for support (France). Financial support from Regional Council of Franche-Comté (Besanc¸on, France) is also acknowledged. Computations have been performed on the supercomputer facilities of the Me´socentre de calcul de Franche-Comté (Besanc¸on, France)Peer Reviewe