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1. Recent advances in oxidative allylic C–H functionalization via group IX-metal catalysis

   https://doi.org/10.1039/D0CC05554A  

   Kazerouni, Amaan M.; McKoy, Quincy A.; Blakey, Simon B. (November 2020, Chemical Communications)

   null (Ed.)

   Allylic substitution, pioneered by the work of Tsuji and Trost, has been an invaluable tool in the synthesis of complex molecules for decades. An attractive alternative to allylic substitution is the direct functionalization of allylic C–H bonds of unactivated alkenes, thereby avoiding the need for prefunctionalization. Significant early advances in allylic C–H functionalization were made using palladium catalysis. However, Pd-catalyzed reactions are generally limited to the functionalization of terminal olefins with stabilized nucleophiles. Insights from Li, Cossy, and Tanaka demonstrated the utility of RhCp x catalysts for allylic functionalization. Since these initial reports, a number of key intermolecular Co-, Rh-, and Ir-catalyzed allylic C–H functionalization reactions have been reported, offering significant complementarity to the Pd-catalyzed reactions. Herein, we report a summary of recent advances in intermolecular allylic C–H functionalization via group IX-metal π-allyl complexes. Mechanism-driven development of new catalysts is highlighted, and the potential for future developments is discussed. 

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2. β C–H di-halogenation via iterative hydrogen atom transfer

   https://doi.org/10.1039/C8SC01214H  

   Wappes, Ethan A.; Vanitcha, Avassaya; Nagib, David A. (January 2018, Chemical Science)

   A radical relay strategy for mono- and di-halogenation (iodination, bromination, and chlorination) of sp 3 C–H bonds has been developed. This first example of β C–H di-halogenation is achieved through sequential C–H abstraction by iterative, hydrogen atom transfer (HAT). A double C–H functionalization is enabled by in situ generated imidate radicals, which facilitate selective N˙ to C˙ radical translocation and tunable C–X termination. The versatile, geminal di-iodide products are further elaborated to β ketones and vinyl iodides. Mechanistic experiments explain the unique di-functionalization selectivity of this iterative HAT pathway, wherein the second C–H iodination is twice as fast as the first. 

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3. C–H functionalization reactions enabled by hydrogen atom transfer to carbon-centered radicals

   https://doi.org/10.1039/D0SC04881J  

   Sarkar, Sumon; Cheung, Kelvin Pak; Gevorgyan, Vladimir (December 2020, Chemical Science)

   null (Ed.)

   Selective functionalization of ubiquitous unactivated C–H bonds is a continuous quest for synthetic organic chemists. In addition to transition metal catalysis, which typically operates under a two-electron manifold, a recent renaissance in the radical approach relying on the hydrogen atom transfer (HAT) process has led to tremendous growth in the area. Despite several challenges, protocols proceeding via HAT are highly sought after as they allow for relatively easy activation of inert C–H bonds under mild conditions leading to a broader scope and higher functional group tolerance and sometimes complementary reactivity over methods relying on traditional transition metal catalysis. A number of methods operating via heteroatom-based HAT have been extensively reported over the past few years, while methods employing more challenging carbon analogues have been less explored. Recent developments of mild methodologies for generation of various carbon-centered radical species enabled their utilization in the HAT process, which, in turn, led to the development of remote C(sp 3 )–H functionalization reactions of alcohols, amines, amides and related compounds. This review covers mostly recent advances in C–H functionalization reactions involving the HAT step to carbon-centered radicals. 

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4. Asymmetric intermolecular allylic C–H amination of alkenes with aliphatic amines

   https://doi.org/10.1126/science.abq1274  

   Pak Shing Cheung, Kelvin; Fang, Jian; Mukherjee, Kallol; Mihranyan, Andranik; Gevorgyan, Vladimir (December 2022, Science)

   Aliphatic allylic amines are found in a great variety of complex and biorelevant molecules. The direct allylic C–H amination of alkenes serves as the most straightforward method toward these motifs. However, use of widely available internal alkenes with aliphatic amines in this transformation remains a synthetic challenge. In particular, palladium catalysis faces the twin challenges of inefficient coordination of Pd(II) to internal alkenes but excessively tight and therefore inhibitory coordination of Pd(II) by basic aliphatic amines. We report a general solution to these problems. The developed protocol, in contrast to a classical Pd(II/0) scenario, operates through a blue light–induced Pd(0/I/II) manifold with mild aryl bromide oxidant. This open-shell approach also enables enantio- and diastereoselective allylic C–H amination. 

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5. Carbon–Carbon Bond Formation Mediated by an Iron(0)–Olefin Pincer Complex

   https://doi.org/10.1055/a-2615-1768  

   Lincoln, Zachary S; Hoffbauer, Melissa R; Iluc, Vlad M (July 2025, Synthesis)

   Abstract C–H functionalization is a highly appealing strategy for accessing complex molecular structures. Herein, we show that π-tethered pincer ligands can engage in C–H activation when coordinated to iron. These reactions result in C(sp2)–C(sp2) bond formation through oxidative coupling and β-hydride elimination/reductive elimination pathways with alkynes and isocyanides. 

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