Transition‐Metal‐Mediated/Catalyzed Synthesis of Pyridines, Pyrimidines, and Triazines by [2+2+2] Cycloaddition Reactions

Nitrogen‐containing six‐membered heterocycles such as pyridines, pyrimidines, and triazines are widely used in the synthesis of natural products and pharmaceuticals. Recently, a promising approach to these structures via [2+2+2] cycloadditions of alkynes and nitriles has been developed. Transition‐metal complex catalysts play key roles in the regio‐, chemo‐, or stereo‐selectivity of transformations. Here, we summarize recent advances in metal‐mediated/catalyzed [2+2+2] cycloadditions for synthesizing pyridines and pyrimidines. We also describe progress in triazine synthesis via metal‐mediated/catalyzed nitrile cyclotrimerization.