Abstract
Four β-keto ester derivatives containing 1,2,4-triazole (A7 and A8) or 1,3,4-oxadiazole (A13 and A14) thioether units were synthesized by S-alkylation of the corresponding thiol/thione precursors with ethyl 4-chloro-3-oxobutanoate in ethanol using sodium acetate as a stoichiometric basic additive. The proposed structures are supported by FT-IR, 1H NMR, and 13C NMR data, including disappearance of the precursor S–H resonances and appearance of signals attributable to the β-keto ester fragment. Solvent-dependent keto–enol behavior was examined qualitatively by 1H NMR spectroscopy in DMSO-d6 and CDCl3 at 298 K. Only keto-form diagnostic resonances were resolved in DMSO-d6. In CDCl₃, A7 displayed signals of both keto and enol species; A8 and A14 displayed resolved enol-form signals without a resolved keto methylene signal; and A13 retained a resolved keto methylene signal without detectable enol resonances. UV/Vis spectra showed intense absorptions mainly in the ultraviolet region and weaker solvent- and concentration-sensitive features at longer wavelengths. Cyclic voltammetry in DMF containing 0.10 M tetrabutylammonium perchlorate revealed multiple cathodic processes that were predominantly irreversible on the experimental time scale. Because the Ag quasi-reference electrode was not calibrated against an internal ferrocene standard, the electrochemical results are interpreted comparatively within this data set rather than as absolute formal potentials. The combined results demonstrate qualitative relationships among heterocycle identity, methoxy substitution, solvent-dependent tautomeric signatures, and electrochemical response.