Azacycle-Directed Formal Aromatic C(sp²)–H Insertion with Cr(0) Fischer Carbene Complex via Oxidative Hydrogen Migration

An azacycle-directed intermolecular aromatic C­(sp2)–H functionalization of Cr(0) Fischer carbene complexes under catalyst-free conditions is reported. Arenes with pyridines, pyrimidine, and pyrazole as directing groups reacted with chromium(0) carbene complexes in good yields and excellent regioselectivities. According to the mechanistic studies based on experiments and computations with density functional theory (DFT), the reaction is proposed to follow an unconventional mechanism via oxidative hydrogen migration and reductive elimination, which is different from the classical electrophilic substitution mechanism.