Clean and Catalyst-Less Electrosynthesis of Benzofurans via p-Phenylenediamine Oxidation in the Presence of Barbiturics

Abstract

Electrochemical oxidation of p-phenylenediamine (1a) was studied in the presence of barbituric acid (3a) and thiobarbituric acid (3b) as nucleophiles in a mixture of phosphate buffer solution (pH 6.0, 0.15 M) and ethanol (80:20 v:v) using cyclic voltammetry and controlled-potential coulometric techniques. The results show that electrochemically generated cyclohexa-2, 5-diene-1, 4-diimine (2a) participates in a 1, 4-Michael-type addition reaction with barbituric acid derivatives via an ECEC mechanism to form new benzofurans (6a-b). The electrochemical synthesis of new benzofurans has been successfully performed in good yields and high purity using a facile, one-pot, clean and non-catalyst method by 3 carbon electrodes in an undivided cell, without using any hazardous solvents.