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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)

   Abstract 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. Nickel‐Catalyzed C( sp ² )−C( sp ³ ) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl Grignard Reagents

   https://doi.org/10.1002/adsc.201801586  

   Piontek, Aleksandra; Ochędzan‐Siodłak, Wioletta; Bisz, Elwira; Szostak, Michal (April 2019, Advanced Synthesis & Catalysis)

   Abstract Aryl tosylates are an attractive class of electrophiles for cross‐coupling reactions due to ease of synthesis, low price, and the employment of C−O electrophiles, however, the reactivity of aryl tosylates is low. Herein, we report the Ni‐catalyzed C(sp²)−C(sp³) Kumada cross‐coupling of aryl tosylates with primary and secondary alkyl Grignard reagents. The method delivers valuable alkyl arenes by cross‐coupling with challenging alkyl organometallics possessing β‐hydrogens that are prone to β‐hydride elimination and homo‐coupling. The reaction is catalyzed by an air‐ and moisture stable‐Ni(II) precatalyst. A broad range of electronically‐varied aryl tosylates, including bis‐tosylates, underwent this transformation, and many examples are suitable at mild room temperature conditions. The combination of Ar−X cross‐coupling with the facile Ar−OH activation/cross‐coupling strategy permits for orthogonal cross‐coupling with challenging alkyl organometallics. Furthermore, we demonstrate that the method operates with TON reaching 2000, which is one of the highest turnovers observed to date in Ni‐catalyzed cross‐couplings. magnified image 

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3. Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp ² )–C(sp ³ ) Coupling

   https://doi.org/10.1021/jacs.2c10778  

   Milbauer, Michael W.; Kampf, Jeff W.; Sanford, Melanie S. (November 2022, Journal of the American Chemical Society)
4. Iron-catalyzed C(sp ² )–C(sp ³ ) cross-coupling at low catalyst loading

   https://doi.org/10.1039/C8CY02374C  

   Bisz, Elwira; Kardela, Marlena; Piontek, Aleksandra; Szostak, Michal (March 2019, Catalysis Science & Technology)

   The iron-catalyzed C(sp 2 )–C(sp 3 ) cross-coupling provides a highly economical route to exceedingly valuable alkylated arenes that are widespread in medicinal chemistry and materials science. Herein, we report an operationally-simple protocol for the selective C(sp 2 )–C(sp 3 ) iron-catalyzed cross-coupling of aryl chlorides with Grignard reagents at low catalyst loading. A broad range of electronically-varied aryl and heteroaryl chlorides underwent the cross-coupling using challenging alkyl organometallics possessing β-hydrogens with high efficiency up to 2000 TON. A notable feature of the protocol is the use of environmentally-friendly cyclic urea ligands. A series of guidelines to predict cross-coupling reactivity of aryl electrophiles is provided. 

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5. Complexity-Building Photoinduced Cascade Involving C _sp² –C _sp³ Coupling of Aromatic Amides via [2 + 2] Reactivity of ESIPT-Generated o- Azaxylylenes

   https://doi.org/10.1021/acs.orglett.3c00092  

   Reddy, D. Sai; Novitskiy, Ivan M.; Kutateladze, Andrei G. (February 2023, Organic Letters)