Diastereoselective electrochemical coupling of beta-nitrostyrenes using constant-current conditions

The electrochemical coupling reactions of beta-nitrostyrene and 4-chloro-beta-nitrostyrene were reported. This is the first report on the electrochemical hydrodimerization of beta-nitrostyrenes. Moreover, the electrochemical processes were performed using the simplest conditions: constant-current (simpler than constant potential), simple and undivided electrochemical cell, employing non-expensive graphite and still electrodes, using green solvent (ethanol), and performing at room temperature. Using various cyclic voltammetry experiments, the effects of potential scan rate and pH on the electrochemical behavior of the reactant were investigated. Moreover, different reaction conditions such as pH, solvent, type of electrodes, and current density were optimized by examining the yield of the product. The optimized conditions were pH = 6, ethanol solvent, steel sheets as a cathode, graphite rod as an anode, and current density = 0.97 mA/cm² (30 mA current). Moreover, using coulometry analysis, the number of exchanged electrons in this process was calculated to help find the possible mechanism. After the completion of the reactions, the structures of the products were confirmed using mass spectrometry, FT-IR, and NMR methods. It was found that only more thermodynamically stable meso configurations were produced, which makes the reaction diastereoselective. The plausible mechanism, which is obeyed from the EC electrochemical mechanism, was proposed for the two-electron transfer reaction.