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1. Cobalt−NHC Catalyzed C(sp 2 )−C(sp 3 ) and C(sp 2 )−C(sp 2 ) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl and Aryl Grignard Reagents

   https://doi.org/10.1002/cctc.202001347  

   Piontek, Aleksandra ; Ochędzan‐Siodłak, Wioletta ; Bisz, Elwira ; Szostak, Michal ( November 2020 , ChemCatChem)

   The first cobalt‐catalyzed cross‐coupling of aryl tosylates with alkyl and aryl Grignard reagents is reported. The catalytic system uses CoF₃and NHCs (NHC=N‐heterocyclic carbene) as ancillary ligands. The reaction proceeds via highly selective C−O bond functionalization, leading to the corresponding products in up to 98 % yield. The employment of alkyl Grignard reagents allows to achieve a rare C(sp²)−C(sp³) cross‐coupling of C−O electrophiles, circumventing isomerization and β‐hydride elimination problems. The use of aryl Grignards leads to the formation of biaryls. The C−O cross‐coupling sets the stage for a sequential cross‐coupling by exploiting the orthogonal selectivity of the catalytic system.

    

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2. Unusual C–H Bond Activation and C(sp 3 )–C(sp 3 ) Bond Formation at an Fe(II) Bis(amide) Carbene Complex

   https://doi.org/10.1021/acs.organomet.9b00674  

   Wong, Anthony ; Guevara, Kevin ; Wu, Guang ; Ménard, Gabriel ( January 2020 , Organometallics)
3. 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. 

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4. Redox Inversion: A Radical Analogue of Umpolung Reactivity for Base- and Metal-Free Catalytic C(sp 3 )–C(sp 3 ) Coupling

   https://doi.org/10.1021/acs.joc.2c02877  

   Seong, Chris M. ; Ansel, Annabel Q. ; Roberts, Courtney C. ( March 2023 , The Journal of Organic Chemistry)
5. N -Butylpyrrolidone (NBP) as a non-toxic substitute for NMP in iron-catalyzed C(sp 2 )–C(sp 3 ) cross-coupling of aryl chlorides

   https://doi.org/10.1039/D1GC02377B  

   Bisz, Elwira ; Koston, Martina ; Szostak, Michal ( October 2021 , Green Chemistry)

   Although iron catalyzed cross-coupling reactions show extraordinary promise in reducing the environmental impact of more toxic and scarce transition metals, one of the main challenges is the use of reprotoxic NMP (NMP = N -methylpyrrolidone) as the key ligand to iron in the most successful protocols in this reactivity platform. Herein, we report that non-toxic and sustainable N -butylpyrrolidone (NBP) serves as a highly effective substitute for NMP in iron-catalyzed C(sp 2 )–C(sp 3 ) cross-coupling of aryl chlorides with alkyl Grignard reagents. This challenging alkylation proceeds with organometallics bearing β-hydrogens with efficiency superseding or matching that of NMP with ample scope and broad functional group tolerance. Appealing applications are demonstrated in the cross-coupling in the presence of sensitive functional groups and the synthesis of several pharmaceutical intermediates, including a dual NK1/serotonin inhibitor, a fibrinolysis inhibitor and an antifungal agent. Considering that the iron/NMP system has emerged as one of the most powerful iron cross-coupling technologies available in both academic and industrial research, we anticipate that this method will be of broad interest. 

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