Directed ortho ‐C(sp ² )─H Functionalization of N/O ‐Containing Heterocycles: Catalytic and Mechanistic Insights

C─H activation has revolutionized synthetic organic chemistry by enabling site‐selective functionalization of unactivated C─H bonds, offering superior atom and step economy compared to conventional existing methodologies. This review highlights the recent advances in directing group (DG)‐assisted, transition metal‐catalyzed ortho ‐C(sp 2 )–H functionalization of pharmacologically relevant N/O ‐containing heterocycles that include benzoxazinones, quinoxalin‐2(1 H )‐ones, and 2‐arylquinazolin‐4(3 H )‐ones. The key transformations include Pd‐/Ru‐/Rh‐catalyzed ortho ‐acyloxylation, halogenation, amidation, alkenylation, alkylation, and annulation using diverse coupling partners such as sulfonyl azides, N‐ halosuccinimides (NXS), dioxo acids, alkenes, and azo‐compounds. Emerging sustainable approaches, including microwave‐assisted synthesis, electrochemical C─H activation, heterogeneous catalysis, and photoredox‐mediated transformations, are also discussed. Mechanistic insights reveal common pathways involving cyclometallation, oxidative addition/reductive elimination (Pd(II)/Pd(IV), Rh(III)), and migratory insertion, with DGs playing a crucial role in the regioselectivity. Overall, this review provides a comprehensive overview of recent progress in transition metal‐catalyzed C─H functionalization in a regioselective manner, emphasizing synthetic utility, mechanistic understanding, and applications in drug discovery and advanced organic synthesis.