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1. Copper Catalyzed sp3 C-H a-Acetylation

   https://doi.org/10.26434/chemrxiv.11407116  

   Okoromoba, O; Jang, E.S.; McMullin, C.; Cundari, T. R.; Warren, T. H. (December 2019, ChemRxiv)

   null (Ed.)

   α-substituted ketones are important chemical targets as synthetic intermediates as well as functionalities in in natural products and pharmaceuticals. We report the sp3 C-H α-acetylation of sp3 C-H substrates R-H with arylmethyl ketones ArC(O)Me to provide α-alkylated ketones ArC(O)CH2R at RT with tBuOOtBu as oxidant via copper(I) β-diketiminato catalysts. Proceeding via alkyl radicals R•, this method enables α-substitution with bulky substituents without competing elimination that occurs in more traditional alkylation reactions between enolates and alkyl electrophiles. DFT studies suggest the intermediacy of copper(II) enolates [CuII](CH2C(O)Ar) that capture alkyl radicals R• to give R-CH2C(O)Ar under competing dimerization of the copper(II) enolate to give the 1,4-diketone ArC(O)CH2CH2C(O)Ar. 

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2. Copper( ii ) ketimides in sp ³ C–H amination

   https://doi.org/10.1039/D1SC01990B  

   Jayasooriya, Isuri U.; Bakhoda, Abolghasem; Palmer, Rachel; Ng, Kristi; Khachemoune, Nour L.; Bertke, Jeffery A.; Warren, Timothy H. (December 2021, Chemical Science)

   Commercially available benzophenone imine (HNCPh 2 ) reacts with β-diketiminato copper( ii ) tert -butoxide complexes [Cu II ]–O t Bu to form isolable copper( ii ) ketimides [Cu II ]–NCPh 2 . Structural characterization of the three coordinate copper( ii ) ketimide [Me 3 NN]Cu–NCPh 2 reveals a short Cu-N ketimide distance (1.700(2) Å) with a nearly linear Cu–N–C linkage (178.9(2)°). Copper( ii ) ketimides [Cu II ]–NCPh 2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R–NCPh 2 products in a process that competes with N–N coupling of copper( ii ) ketimides [Cu II ]–NCPh 2 to form the azine Ph 2 CN–NCPh 2 . Copper( ii ) ketimides [Cu II ]–NCAr 2 serve as intermediates in catalytic sp 3 C–H amination of substrates R–H with ketimines HNCAr 2 and t BuOO t Bu as oxidant to form N -alkyl ketimines R–NCAr 2 . This protocol enables the use of unactivated sp 3 C–H bonds to give R–NCAr 2 products easily converted to primary amines R–NH 2 via simple acidic deprotection. 

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3. Copper‐Catalyzed C(sp ³ )−H Amidation: Sterically Driven Primary and Secondary C−H Site‐Selectivity

   https://doi.org/10.1002/anie.201810556  

   Bakhoda, Abolghasem; Jiang, Quan; Badiei, Yosra M.; Bertke, Jeffery A.; Cundari, Thomas R.; Warren, Timothy H. (February 2019, Angewandte Chemie International Edition)

   Abstract Undirected C(sp³)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N₃. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ²‐N,O‐NC(O)Ar) to provide carbon‐based radicals R^.and copper(II)amide intermediates [Cu^II]‐NHC(O)Ar that subsequently capture radicals R^.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups. 

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4. Cobalt‐Catalyzed Aerobic Oxidative Cleavage of Alkyl Aldehydes: Synthesis of Ketones, Esters, Amides, and α‐Ketoamides

   https://doi.org/10.1002/chem.202101035  

   Li, Tingting; Hammond, Gerald_B; Xu, Bo (May 2021, Chemistry – A European Journal)

   Abstract A widely applicable approach was developed to synthesize ketones, esters, amides via the oxidative C−C bond cleavage of readily available alkyl aldehydes. Green and abundant molecular oxygen (O₂) was used as the oxidant, and base metals (cobalt and copper) were used as the catalysts. This strategy can be extended to the one‐pot synthesis of ketones from primary alcohols and α‐ketoamides from aldehydes. 

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5. Ynamide and Azaalleneyl. Acid‐Base Promoted Chelotropic and Spin‐State Rearrangements in a Versatile Heterocumulene [(Ad)NCC( ^t Bu)] ⁻

   https://doi.org/10.1002/anie.202401433  

   Russell, John_B; Jafari, Mehrafshan_G; Kim, Jun‐Hyeong; Pudasaini, Bimal; Ozarowski, Andrew; Telser, Joshua; Baik, Mu‐Hyun; Mindiola, Daniel_J (April 2024, Angewandte Chemie International Edition)

   Abstract We introduce the heterocumulene ligand [(Ad)NCC(^tBu)]⁻(Ad=1‐adamantyl (C₁₀H₁₅),^tBu=tert‐butyl, (C₄H₉)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid‐base chemistry, which promotes an unprecedented spin‐state change of the [V^III] ion. These unique scaffolds are prepared via addition of 1‐adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡C^tBu(OTf)] (A) (BDI⁻=ArNC(CH₃)CHC(CH₃)NAr), Ar=2,6‐ⁱPr₂C₆H₃) and [(dBDI)V≡C^tBu(OEt₂)] (B) (dBDI²⁻=ArNC(CH₃)CHC(CH₂)NAr). ComplexAreacts with C≡NAd, to generate the high‐spin [V^III] complex with a κ¹‐N‐ynamide ligand, [(BDI)V{κ¹‐N‐(Ad)NCC(^tBu)}(OTf)] (1). Conversely,Breacts with C≡NAd to generate a low‐spin [V^III] diamagnetic complex having a chelated κ²‐C,N‐azaalleneyl ligand, [(dBDI)V{κ²‐N,C‐(Ad)NCC(^tBu)}] (2). Theoretical studies have been applied to better understand the mechanism of formation of2and the electronic reconfiguration upon structural rearrangement by the alteration of ligand denticity between1and2. 

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