Electrosynthesis of N‑Methylisatin

Isatin in a solution of dry N,N-dimethylformamide/NaClO₄ is electroreduced in the presence of CH₃I. N-methylisatin (NMI) is obtained in quantitative molar yield and high current efficiency by controlled potential electrolysis (CPE). NMI and N-methylisatoic anhydride are the reaction products when CPE is performed in the absence of CH₃I, but adding it once the CPE was completed. The water effect on the identity and yield of the reaction product(s) is investigated. Reaction pathways are proposed.