Electro-oxidation of phenylamine derivatives (1a and 1b) have been studied in the presence of pyrazolidine-3,5-dione (3) as a nucleophile in phosphate buffer solution mixed with ethanol, using voltammetric and spectroscopic techniques. The obtained results indicated that the oxidized form of phenylamines (2a and 2b) participate in Michael addition type reactions with pyrazolidine-3,5-dione (3) and via ECECCCCC mechanisms convert to the corresponding new polycyclic indoles (12a and 12b). In the present study, new polycyclic indole derivatives were synthesized with good yields and high purity using a facile, one-pot and environmentally friendly electrochemical method, without any chemical catalysts, toxic solvents and hard conditions. (C) 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy Medical Sciences. Published by Elsevier B.V. All rights reserved.