Electrochemical reduction of N-(2-nitro-4-R-phenyl)pyridinium salts using redox-mediators

Electrochemical reduction of N -(2-nitroaryl)pyridinium chlorides was accomplished in acidic aqueous alcoholic medium in the galvanostatic mode using tin, titanium, vanadium, and iron chlorides as redox-mediators. The use of SnCl 2 as a mediator catalyst made it possible to shorten the electrosynthesis time as compared to the direct electroreduction on an electrode and prepare the intramolecular cyclization products, viz ., substituted pyrido[1,2- a ]benzimidazoles, in high yield. The influence of the mediator nature and its amount, current density, temperature, cathode material, medium acidity, and the substrate structure on the efficiency of reductive heterocyclization of N -(2-nitroaryl)pyridinium salts was studied.