Iron role in the electrochemical cyclopropanation reaction of activated olefins and halogenated compounds

The electrochemical procedure for cyclopropanation reaction between benzal chloride (BC) and dimethyl itaconate (DMI), using Cu(I) salt, iron rod as sacrificial anode, and low temperature (−10 °C < T < −5 °C), was investigated by cyclic voltammetry and electrolysis. The variation of the experimental parameters of electrolyses, such as the absence or the presence of CuBr during the pre-electrolysis step, or its substitution by an initial amount of iron salt (FeCl2, FeBr2 or FeI2), and pyridine addition to the reaction medium showed that the presence of dissociated Fe(II) is essential to the cyclopropanation process. The Cu(I) salt is deposited on the cathode surface during the pre-electrolysis, providing the accumulation of Fe(II) in solution, which does not act as catalyst in the electrochemical process. The best cyclopropanation yield (81%) was reached in DMF/pyridine (9:1) in the presence of FeI2 salt. A cyclopropanation mechanism involving two possible pathways was suggested, implying both an anionic and a radical BC intermediates.

Graphical abstract.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• Electrochemical method for cyclopropanation of activated olefins. • Cyclopropanation mechanism between olefins and halogenated compounds. • Iron role in the cyclopropanation of olefins through electrochemical process. • Organic electrochemistry reaction mechanism. • Cyclopropanation electrochemical reaction in DMF and iron sacrificial anode.