Electrochemical synthesis of CN-substituted imidazo[1,5-a]pyridines via a cascade process using NH4SCN as both an electrolyte and a non-trivial cyanating agent

Abstract

[CN] species were generated in the course of electrochemical oxidation of SCN anions and used in the three-component electrosynthesis of 1-cyano-imidazo[1,5-a]pyridines from pyridine-2-carboxaldehydes, amines, and NH₄SCN. In contrast to previously known electrochemical methods, NH₄SCN acts as a CN source rather than a SCN source. A variety of 1-cyano-imidazo[1,5-a]pyridines were obtained in good yields under constant current conditions in an undivided electrochemical cell. The electrosynthesis presumably involves the generation of a cyanating reagent, its addition to the CN bond of the imine, formed from pyridine-2-carboxaldehyde and amine, followed by a cascade of DMSO-mediated or Shono-type anodic oxidation and cyclization. The leading 1-cyano-imidazo[1,5-a]pyridines exhibit better antifungal activity against Venturia inaequalis, Rhizoctonia solani, and Bipolaris sorokiniana than the commercial fungicide triadimefon.