Formation of Imidazo[1,5-a]pyridine Derivatives Due to the Action of Fe on Dynamic Libraries of Imines.

An imidazo[1,5-a]pyridine derivative was unexpectedly obtained through the action of Fe on a dynamic library of imines generated in situ via condensation of benzaldehyde and 2-picolylamine. The reaction product was easily isolated as the only nitrogen-containing product eluted from the chromatographic column. A reaction mechanism is proposed, in which combined kinetic and thermodynamic effects exerted by Fe on the various steps of the complex reaction sequence are discussed. The Fe nature of the added metal cation was found to be pivotal for the achievement of the imidazo[1,5-a]pyridine derivative as well as its amount in the reaction mixture. When the electronic effects were evaluated, gratifying yields were obtained only in the presence of moderately electron-releasing or moderately electron-withdrawing groups on the aldehyde reactant. No traces of imidazo[1,5-a]pyridine derivatives were obtained for p-OCH and p-NO benzaldehyde.