Efficient, Single-Step Access to Imidazo[1,5-a]pyridine N-Heterocyclic Carbene Precursors

The three-component coupling reaction of substituted picolinaldehydes, amines, and formaldehyde to produce imidazo[1,5-a]pyridinium ions is reported, providing an efficient method for the preparation of N-heterocyclic carbenes (NHCs). Reactions proceed in high yields under mild conditions, allowing the incorporation of diverse functionality and chiral substituents. Higher order condensations are also described that provide access to multidentate NHC ligands useful for a variety of applications.