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1. Palladium-Catalyzed β-C(sp3)–H Bond Arylation of Tertiary Aldehydes Facilitated by 2-Pyridone Ligands

   https://doi.org/10.3390/molecules29010259  

   Xu, Ziting; Li, Zhi; Liu, Chong; Yang, Ke; Ge, Haibo (January 2024, Molecules)

   2-Pyridone ligand-facilitated palladium-catalyzed direct C–H bond functionalization via the transient directing group strategy has become an attractive topic. Here, we report a Pd-catalyzed direct β-C(sp3)–H arylation reaction of tertiary aliphatic aldehydes by using an α-amino acid as a transient directing group in combination with a 2-pyridone ligand. 

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2. Ligand-promoted palladium-catalyzed β-methylene C–H arylation of primary aldehydes

   https://doi.org/10.1039/D2SC01677J  

   Yang, Ke; Li, Zhi; Liu, Chong; Li, Yunjian; Hu, Qingyue; Elsaid, Mazen; Li, Bijin; Das, Jayabrata; Dang, Yanfeng; Maiti, Debabrata; et al (May 2022, Chemical Science)

   The transient directing group (TDG) strategy allowed long awaited access to the direct β-C(sp 3 )–H functionalization of unmasked aliphatic aldehydes via palladium catalysis. However, the current techniques are restricted to terminal methyl functionalization, limiting their structural scopes and applicability. Herein, we report the development of a direct Pd-catalyzed methylene β-C–H arylation of linear unmasked aldehydes by using 3-amino-3-methylbutanoic acid as a TDG and 2-pyridone as an external ligand. Density functional theory calculations provided insights into the reaction mechanism and shed light on the roles of the external and transient directing ligands in the catalytic transformation. 

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3. Total synthesis of (−)-cylindrocyclophane A facilitated by C−H functionalization

   https://doi.org/10.1126/science.adp2425  

   Bosse, Aaron T; Hunt, Liam R; Suarez, Camila A; Casselman, Tyler D; Goldstein, Elizabeth L; Wright, Austin C; Park, Hojoon; Virgil, Scott C; Yu, Jin-Quan; Stoltz, Brian M; et al (November 2024, Science)

   (−)-Cylindrocyclophane A is a 22-membered C₂-symmetric [7.7]paracyclophane that bears bis-resorcinol functionality and six stereocenters. We report a synthetic strategy for (−)-cylindrocyclophane A that uses 10 C−H functionalization reactions, resulting in a streamlined route with high enantioselectivity and efficiency (17 steps). The use of chiral dirhodium tetracarboxylate catalysis enabled the C–H functionalization of primary and secondary positions, which was complemented by palladium-catalyzed C(sp²)–C(sp²) cross-couplings, resulting in the rapid formation of the macrocyclic core and all stereocenters with high regio-, diastereo-, and enantioselectivity. The use of a late-stage palladium-catalyzed fourfold C(sp²)–H acetoxylation installed the bis-resorcinol moieties. This research exemplifies how multilaboratory collaborations can produce substantial modernizations of complex total synthesis endeavors. 

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4. Ligand‐Controlled Direct γ‐C−H Arylation of Aldehydes

   https://doi.org/10.1002/anie.201913126  

   Li, Bijin; Lawrence, Brianna; Li, Guigen; Ge, Haibo (January 2020, Angewandte Chemie International Edition)

   Abstract The first example of Pd^II‐catalyzed γ‐C(sp³)−H functionalization of aliphatic and benzoheteroaryl aldehydes has been developed using a transient ligand and an external ligand, concurrently. A wide array of γ‐arylated aldehydes were readily accessed without preinstalling internal directing groups. The catalytic mechanism was studied by performing deuterium‐labelling experiments, which indicated that the γ‐C(sp³)−H bond cleavage is the rate‐limiting step during the reaction process. This reaction could be performed on a gram scale, and also demonstrated its potential application in the synthesis of new mechanofluorochromic materials with blue‐shifted mechanochromic properties. 

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5. Visible Light Induced Brønsted Acid Assisted Pd‐Catalyzed Alkyl Heck Reaction of Diazo Compounds and N ‐Tosylhydrazones

   https://doi.org/10.1002/anie.202110924  

   Zhang, Ziyan; Kvasovs, Nikita; Dubrovina, Anastasiia; Gevorgyan, Vladimir (November 2021, Angewandte Chemie International Edition)

   Abstract A mild visible light‐induced palladium‐catalyzed alkyl Heck reaction of diazo compounds andN‐tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acid‐assisted generation of hybrid palladium C(sp³)‐centered radical intermediate, which allowed for new selective C−H functionalization protocol. 

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