Transition Metal‐Catalyzed C(sp 3 )H Bond Functionalization Adjacent to Heterocycles

Abstract Within the last two decades, transition metal‐catalyzed CH bond functionalization of organic substrates has become a powerful tool to access relatively complex frameworks of general synthetic interest. However, significant challenges remain in developing a catalyst system that efficiently functionalizes a specific CH bond in the presence of other chemically equivalent CH bonds. Among various genre of CH bonds, those adjacent to a heteroaromatic system are distinctly special in terms of their reactivity, which is influenced by not only coordinating the heteroatom to a transition metal catalyst but also the electronic impacts of the ring during the CH bond cleavage event. This article depicts an up‐to‐date account on the functionalization reactions of methyl and/or methylene CH bonds adjacent to a heteroaromatic ring by various late and earth‐abundant transition metals, in which the heterocyclic nucleus takes part actively or passively to accelerate the required functionalization process. Of note, this article does not cover examples, wherein transition metals serve as a Lewis acid catalyst in promoting the nucleophilic attack of a methyl/methylene‐CH bond of alkylheteroarenes to an electrophilic coupling partner.