Synthesis and electrochemical oxidation of hybrid compounds:dihydropyridine-fused coumarins

Abstract

tIn this paper, a series of six dihydropyridine-fused coumarins were synthesized and electrochemicallycharacterized in dimethylformamide (DMF).Dihydropyridine ring oxidation on glassy carbon electrode (GCE) for condensed heterocyclic com-pounds revealed a single anodic peak. Oxidation potential values correlated fairly well with substituenteffects at 9-position. The overall oxidation mechanism involved 2-electrons and 2-protons as determinedby chronoamperometry.Controlled-potential electrolysis followed by UV-Visible spectroscopy proves that dihydropyridine-fused coumarins are electrochemically oxidized in DMF giving rise to the aromatic pyridine derivative.ESR experimental spectra show a triplet, due to the C-centered dihydropyridyl radical trapped withN-tert-butylamine- -phenylnitrone (PBN). Hyperfine coupling constant values (aN) of dihydropyridine-fused coumarins were higher than corresponding values for non-fused ones. These results could be dueto the effect of the coupling of the dihydropyridine moiety with the coumarin ring over the splittingconstant.