Green, catalyst-free, facile and one pot electrochemical synthesis of new bis-indoles from p- phenylenediamine oxidation in the presence of cyanoacetate derivatives

Abstract

Electrochemical oxidation of p- phenylenediamine has been investigated in the presence of methyl and ethyl cyanoacetate as a nucleophile in phosphate buffer solution mixed with ethanol (10/90 v/v) using cyclic voltammetry and controlled-potential coulometry methods. The results revealed that cyclohexa-2,5-diene-1,4-diimine derived from electro-oxidation of p- phenylenediamine participates in 1,4-Michael addition reactions with cyanoacetate derivatives. The formed adducts convert to the corresponding bis-indole derivatives via ECECCC (Electrochemical, chemical, chemical reactions) mechanism. In the present work, new bis-indoles were synthesized with high purity and good yields using controlled potential electrochemical oxidation at five graphite electrode in an undivided cell under mild conditions.