Electrochemical Oxidation of 1,3‐Cyclohexadiene

Abstract

The electroinitiated cation radical Diels‐Alder reaction was attempted for 1,3‐cyclohexadiene in methylene chloride with tetrabutylammonium tetrafluoroborate as the supporting electrolyte. The expected endo/exo adducts (4:1) were formed in very low yields. The major product was characterized by 1H and 13C NMR as polycyclohexadiene with mainly 1,4‐addition mode segments. Different voltages, supporting electrolytes, electrode materials, and concentrations were used in an effort to optimize reaction results. Polymerization was still a major competing reaction, but the use of tetrabutylammonium hexafluorophosphate as supporting electrolyte and of graphite electrodes instead of platinum, improved the Diels‐Alder adduct yield. Cation radical polymerization of 1.3‐cyclohexadiene with tris(p‐bromophenyl) aminium hexachloroantimonate gave a mixture of products that contained the expected Diels‐Alder polymer as well as the product of cationic polymerization.