Iron‐Catalyzed C–H Activation/Aza‐Annulation with 2‐Butyne for Accessing Methylated Aza‐Arenes

Abstract The incorporation of methyl groups into aza‐arene frameworks not only often improves their biological activity as the “magic methyl” effect, but also notably affects their solid‐state electronic properties by modulating π‐π stackings, which makes them promising candidates for developing organic electronic materials. This study focuses on the iron‐catalyzed C−H annulation of ketones with 2‐butyne via their oxime ethers, offering an efficient pathway to synthesizing methylated π‐extended aza‐arenes. The reactions utilize isobutyl aluminum(III) catecholate as a base and Triphos (bis(2‐diphenylphosphinoethyl)phenylphosphine) as a ligand. Reported C−H activation methods using rhodium catalysis proved less effective with π‐conjugated substrates. Regioselective C−H aza‐annulation with 1‐(trimethylsilyl)propyne following desilylation provides also mono‐methylated azaarenes. The reactions also generate tetra‐methylated aza‐arene products by two‐fold C−H aza‐annulation on chromeno[3,2‐ a ]xanthene‐13,14‐dione and quinacridone. These methylated aza‐arenes exhibit strong π‐π stacking, a narrow emission band, and tunable photophysical properties, indicating their potential applications as electronic materials.