Borane-Catalyzed Transfer Hydrogenations of Pyridines with Ammonia Borane

With the use of ammonia borane as a hydrogen source, a borane catalyzed metal-free transfer hydrogenation of pyridines was successfully realized for the first time to furnish a variety of piperidines in 44–88% yields with moderate to excellent cis-selectivities. The ease in handling without requiring high pressure H₂ makes this transfer hydrogenation practical and useful.