Iridium(III)‐Catalyzed Intermolecular C(sp3)−H Insertion Reaction of Quinoid Carbene: A Radical Mechanism

Described herein is an IrIII/porphyrin‐catalyzed intermolecular C(sp3)−H insertion reaction of a quinoid carbene (QC). The reaction was designed by harnessing the hydrogen‐atom transfer (HAT) reactivity of a metal‐QC species with aliphatic substrates followed by a radical rebound process to afford C−H arylation products. This methodology is efficient for the arylation of activated hydrocarbons such as 1,4‐cyclohexadienes (down to 40 min reaction time, up to 99 % yield, up to 1.0 g scale). It features unique regioselectivity, which is mainly governed by steric effects, as the insertion into primary C−H bonds is favored over secondary and/or tertiary C−H bonds in the substituted cyclohexene substrates. Mechanistic studies revealed a radical mechanism for the reaction. On the rebound: Direct intermolecular C(sp3)−H arylation is achieved by an IrIII/porphyrin‐catalyzed formal quinoid carbene (QC) insertion reaction through a stepwise radical mechanism. This reaction is enabled by the hydrogen‐atom transfer (HAT) reactivity of the metal‐QC intermediate, and the subsequent radical rebound step is facilitated by an electrophilic IrIII center that preserves the radical character of the QC ligand.