Electrochemical reduction of (5-etoxycarbonylmethylidene-4-oxothiazolidine-2-ylidene)-N-phenylethanone in aprotic medium: A spectroelectrochemical approach

Electrochemical reduction of (5-etoxycarbonylmethylidene-4-oxothiazolidine-2-ylidene)-N-phenylethanone has been studied in dimethylsulfoxide (DMSO) by cyclic and linear voltammetry with both, stationary and rotating electrode coupled with UV–Vis and EPR spectroelectrochemistry in order to identify the intermediates and to elucidate the reaction mechanism. The results point out an ECE mechanism, with deprotonation of the substrate by the electrogenerated base (EGB) anion radical (self-protonation) as the chemical step following the first electron transfer. The proposed reduction mechanism is supported by DigiSim simulations. The EPR spectrum recorded during the electrochemical reduction in DMSO at the potential of the second redox couple is well resolved, confirming the reduction of (5-etoxycarbonylmethylidene-4-oxothiazolidine-2-ylidene)-N-phenylethanone to its corresponding dianion radical. Solvent dependent semiempirical PM3-MO calculations allow a rationalization of the experimental results in terms of the electronic structure and reactivity of the intermediate species.