New approach to electrochemical iodination of arenes exemplified by the synthesis of 4-iodopyrazoles of different structures

The two-stage electrosynthesis of 4-iodosubstituted pyrazole derivatives was performed. At the first stage, KIO₃ was obtained at the Ni anode under the undivided galvanostatic conditions of electrolysis of an aqueous alkaline solution of KI (or I₂) at the Ni anode. At the second stage, pyrazole and its derivatives were iodinated in the heterophase (H₂O-CHCl₃ (CCl₄)) medium by the KIO₃-KI (or KIO₃-I₂) system in the presence of H₂SO₄. The yields of iodopyrazoles were 74–92%. The electrochemical iodination of anisole, 2-methylpyrazole, and thiophene was carried out to form 4-iodoanisole (88% yield), 4,5-diiodo-2-methylimidazole (54% yield), and a mixture of 2-iodothiophene (60% yield) and 2,5-diiodothiophene (4% yield).