Electroreductive heterocyclization of ortho-piperidino substituted nitro(het)arenes

Electrochemical reduction of ortho-piperidino substituted nitro(het)arenes in an undivided cell on a lead cathode in 8% HCl gave either 1,2,3,4-tetrahydropyrido[1,2-a]-benzimidazoles or 6,7,8,9-tetrahydropyrido[3′,2′:4,5]- imidazo[1,2-a]pyridines. The reductive heterocyclization mechanism involves the initial formation of a nitroso derivative followed by the formation of an imidazole ring.