Robust Cobalt Catalyst for Nitrile/Alkyne [2+2+2] Cycloaddition: Synthesis of Polyarylpyridines and Their Mechanochemical Cyclodehydrogenation to Nitrogen‐Containing Polyaromatics

The transition‐metal‐catalyzed [2+2+2] cycloaddition of nitriles and alkynes is an established synthetic approach to pyridines; however, these cycloadditions often rely on the use of tethered diynes or cyanoalkynes as one of the reactants. Thus, examples of efficient, fully intermolecular catalytic [2+2+2] pyridine synthesis, especially those employing unactivated nitriles and internal alkynes leading to pentasubstituted pyridines, remain scarce. Herein, we report on simple and inexpensive catalytic systems based on cobalt(II) iodide, 1,3‐bis(diphenylphosphino)propane, and Zn that promote [2+2+2] cycloaddition of various nitriles and diarylacetylenes for the synthesis of a broad range of polyarylated pyridines. DFT studies support a reaction pathway involving oxidative coupling of two alkynes, insertion of the nitrile into a cobaltacyclopentadiene, and C‐N reductive elimination. The resulting tetra‐ and pentaarylpyridines serve as precursors to hitherto unprecedented nitrogen‐containing polycyclic aromatic hydrocarbons via mechanochemically assisted multifold reductive cyclodehydrogenation. Simple, inexpensive, and robust cobalt‐based systems catalyze the [2+2+2] cycloaddition between unactivated nitriles and diarylacetylenes, including aryl and alkyl nitriles and cyanamides as well as di(hetero)arylacetylenes. The resulting tetra‐ and pentaarylpyridines undergo mechanochemistry‐enabled multifold cyclodehydrogenation to furnish nitrogen‐containing polycyclic aromatic compounds with unprecedented skeletons.