More Like this

1. Carbodicarbene‐Stibenium Ion‐Mediated Functionalization of C(sp ³ )−H and C(sp)−H Bonds

   https://doi.org/10.1002/anie.202415070  

   Warring, Levi; Westendorff, Karl_S; Bennett, Marc_T; Nam, Kijeong; Stewart, Brennan_M; Dickie, Diane_A; Paolucci, Christopher; Gunnoe, T_Brent; Gilliard, Jr., Robert_J (November 2024, Angewandte Chemie International Edition)

   Abstract Main‐group element‐mediated C−H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(^pyCDC)Sb][NTf₂]₃(1) (^pyCDC=bis‐pyridyl carbodicarbene; NTf₂=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6‐di‐tert‐butylpyridine to enable C(sp³)−H bond breaking to generate the stiba‐methylene nitrile complex [(^pyCDC)Sb(CH₂CN)][NTf₂]₂(2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction. Computational studies suggest that C−H activation proceeds via a mechanism in which acetonitrile first coordinates to the Sb center through the nitrogen atom in a κ¹fashion, thereby weakening the C−H bond which can then be deprotonated by base in solution. Further, we show that1reacts with terminal alkynes in the presence of 2,6‐di‐tert‐butylpyridine to enable C(sp)−H bond breaking to form stiba‐alkynyl adducts of the type [(^pyCDC)Sb(CCR)][NTf₂]₂(3 a–f). Compound1shows excellent specificity for the activation of the terminal C(sp)−H bond even across alkynes with diverse functionality. The resulting stiba‐methylene nitrile and stiba‐alkynyl adducts react with elemental iodine (I₂) to produce iodoacetonitrile and iodoalkynes, while regenerating an Sb trication. 

   more » « less
2. Copper Catalyzed Benzylic sp ³ C-H Alkenylation

   https://doi.org/10.1039/D4SC03430A  

   Chen, Ting-An; Staples, Richard J; Warren, Timothy H (September 2024, Chemical Science)

   The prenyl group is present in numerous biologically active small molecule drugs and natural products. We introduce benzylic C-H alkenylation of substrates Ar-CH3 with alkenylboronic esters (CH2)3O2B-CH=CMe2 as a pathway to form prenyl functionalized arenes Ar-CH2CH=CMe2. Mechanistic studies of this radical relay catalytic protocol reveal diverse reactivity pathways exhibited by the copper(II) vinyl intermediate [CuII]-CH=CMe2 that involve radical capture, bimolecular C-C bond formation, and hydrogen atom transfer (HAT). 

   more » « less
3. Phosphine-Directed sp ³ C–H, C–O, and C–N Borylation

   https://doi.org/10.1021/acs.joc.0c01706  

   Morris, Kelsey C.; Wright, Shawn E.; Meyer, Gillian F.; Clark, Timothy B. (November 2020, The Journal of Organic Chemistry)

   null (Ed.)
4. Transition-metal-free C(sp ³ )–H/C(sp ³ )–H dehydrogenative coupling of saturated heterocycles with N -benzyl imines

   https://doi.org/10.1039/D0SC00031K  

   Liu, Zhengfen; Li, Minyan; Deng, Guogang; Wei, Wanshi; Feng, Ping; Zi, Quanxing; Li, Tiantian; Zhang, Hongbin; Yang, Xiaodong; Walsh, Patrick J. (January 2020, Chemical Science)

   A unique C(sp 3 )–H/C(sp 3 )–H dehydrocoupling of N -benzylimines with saturated heterocycles is described. Using super electron donor (SED) 2-azaallyl anions and aryl iodides as electron acceptors, single-electron-transfer (SET) generates an aryl radical. Hydrogen atom transfer (HAT) from saturated heterocycles or toluenes to the aryl radical generates alkyl radicals or benzylic radicals, respectively. The newly formed alkyl radicals and benzylic radicals couple with the 2-azaallyl radicals with formation of new C–C bonds. Experimental evidence supports the key hydrogen-abstraction by the aryl radical, which determines the chemoselectivity of the radical–radical coupling reaction. It is noteworthy that this procedure avoids the use of traditional strong oxidants and transition metals. 

   more » « less
5. Intermolecular C(sp ³ )−H Amination of Complex Molecules

   https://doi.org/10.1002/anie.201713225  

   Chiappini, Nicholas D.; Mack, James B. C.; Du Bois, J. (March 2018, Angewandte Chemie International Edition)

   Abstract A general and operationally convenient method for intermolecular amination of C(sp³)−H bonds is described. This technology allows for efficient functionalization of complex molecules, including numerous pharmaceutical targets. The combination of pivalonitrile as a solvent, Al₂O₃as an additive, and phenyl sulfamate as a nitrogen source affords differential reaction performance and substrate scope. Mechanistic data strongly implicate a pathway for catalyst decomposition that initiates with solvent oxidation, thus providing rationale for the marked influence of pivalonitrile on this reaction process. 

   more » « less