Clean and Catalyst-Less Electrosynthesis of Benzofurans viap-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.

Electrochemically Induced Michael Addition Reaction: An Overview

“…Electrochemical oxidation of p ‐phenylenediamine 243 has been achieved using barbituric acid 245a and thiobarbituric acid 245b as nucleophiles in a mixture of phosphate buffer solution and EtOH. Remarkably, electrochemically produced cyclohexa‐2, 5‐diene‐1, 4‐diimine was applied in a 1, 4‐Michael‐type addition reaction with barbituric acids through an ECEC mechanism to form benzofurans 250a , b (Scheme ) …”

“…Remarkably, electrochemically produced cyclohexa-2, 5-diene-1, 4-diimine was applied in a 1, 4-Michael-type addition reaction with barbituric acids through an ECEC mechanism to form benzofurans 250a, b (Scheme 75). [86] Electrochemical oxidation of 4-aminodiphenylamine in aqueous solution using various aryl sulfinic acids 253 as nucleophiles has been performed in 2015 by Salahifar and coworkers. [87] A one-pot and eco-friendly electrochemical method was described for the formation of 4-amino-3-(phenyl sulfonyl)diphenylamines 255 through the Michael type addition reaction of anodically provided N-phenylquinone diimine with aryl sulfinic acids, at a carbon electrode, without toxic solvents and reagents (Scheme 76).…”