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1. 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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2. δ C–H (hetero)arylation via Cu-catalyzed radical relay

   https://doi.org/10.1039/c8sc04366c  

   Zhang, Zuxiao; Stateman, Leah M.; Nagib, David A. (January 2019, Chemical Science)

   null (Ed.)

   A Cu-catalyzed strategy has been developed that harnesses a radical relay mechanism to intercept a distal C-centered radical for C–C bond formation. This approach enables selective δ C–H (hetero)arylation of sulfonamides via intramolecular hydrogen atom transfer (HAT) by an N-centered radical. The radical relay is both initiated and terminated by a Cu catalyst, which enables incorporation of arenes and heteroarenes by cross-coupling with boronic acids. The broad scope and utility of this catalytic method for δ C–H arylation is shown, along with mechanistic probes for selectivity of the HAT mechanism. A catalytic, asymmetric variant is also presented, as well as a method for accessing 1,1-diaryl-pyrrolidines via iterative δ C–H functionalizations. 

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3. Catalytic β C–H amination via an imidate radical relay

   https://doi.org/10.1039/c8sc05685d  

   Stateman, Leah M.; Wappes, Ethan A.; Nakafuku, Kohki M.; Edwards, Kara M.; Nagib, David A. (February 2019, Chemical Science)

   null (Ed.)

   The first catalytic strategy to harness imidate radicals for C–H functionalization has been developed. This iodine-catalyzed approach enables β C–H amination of alcohols by an imidate-mediated radical relay. In contrast to our first-generation, (super)stoichiometric protocol, this catalytic method enables faster and more efficient reactivity. Furthermore, lower oxidant concentration affords broader functional group tolerance, including alkenes, alkynes, alcohols, carbonyls, and heteroarenes. Mechanistic experiments interrogating the electronic nature of the key 1,5 H-atom transfer event are included, as well as probes for chemo-, regio-, and stereo-selectivity. 

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4. Radical cascade synthesis of azoles via tandem hydrogen atom transfer

   https://doi.org/10.1039/c9sc06239d  

   Chen, Andrew D.; Herbort, James H.; Wappes, Ethan A.; Nakafuku, Kohki M.; Mustafa, Darsheed N.; Nagib, David A. (March 2020, Chemical Science)

   null (Ed.)

   A radical cascade strategy for the modular synthesis of five-membered heteroarenes ( e.g. oxazoles, imidazoles) from feedstock reagents ( e.g. alcohols, amines, nitriles) has been developed. This double C–H oxidation is enabled by in situ generated imidate and acyloxy radicals, which afford regio- and chemo-selective β C–H bis-functionalization. The broad synthetic utility of this tandem hydrogen atom transfer (HAT) approach to access azoles is included, along with experiments and computations that provide insight into the selectivity and mechanism of both HAT events. 

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5. 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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