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1. Chemoselective bond activation by unidirectional and asynchronous PCET using ketone photoredox catalysts

   https://doi.org/10.1039/d3sc04362b  

   Sun, Rui ; Ruccolo, Serge ; Nascimento, Daniel L ; Qin, Yangzhong ; Hibbert, Nathaniel ; Nocera, Daniel G ( December 2023 , Chemical Science)

   The triplet excited states of ketones effect selective H-atom abstraction from amide N–H bonds in the presence of weaker C–H bondsviaa proton-coupled electron transfer (PCET) pathway in which the electron and proton transfers are asynchronous.

    

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2. Branched‐Selective Direct α‐Alkylation of Cyclic Ketones with Simple Alkenes

   https://doi.org/10.1002/ange.201900301  

   Xing, Dong ; Qi, Xiaotian ; Marchant, Daniel ; Liu, Peng ; Dong, Guangbin ( February 2019 , Angewandte Chemie)

   Herein, we describe an intermolecular direct branched‐selective α‐alkylation of cyclic ketones with simple alkenes as the alkylation agents. Through an enamine‐transition metal cooperative catalysis mode, the α‐alkylation is realized in an atom‐ and step‐economic manner with excellent branched selectivity for preparing β‐branched ketones. Employment of a pair of bulky Brønsted acid and base as additives is responsible for enhanced efficiency. Promising enantioselectivity (74 % ee) has been obtained. Experimental and computational mechanistic studies suggest that a pathway through alkene migratory insertion into the Ir−C bond followed by C−H reductive elimination is involved for the high branched selectivity.

    

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3. Branched‐Selective Direct α‐Alkylation of Cyclic Ketones with Simple Alkenes

   https://doi.org/10.1002/anie.201900301  

   Xing, Dong ; Qi, Xiaotian ; Marchant, Daniel ; Liu, Peng ; Dong, Guangbin ( February 2019 , Angewandte Chemie International Edition)

   Herein, we describe an intermolecular direct branched‐selective α‐alkylation of cyclic ketones with simple alkenes as the alkylation agents. Through an enamine‐transition metal cooperative catalysis mode, the α‐alkylation is realized in an atom‐ and step‐economic manner with excellent branched selectivity for preparing β‐branched ketones. Employment of a pair of bulky Brønsted acid and base as additives is responsible for enhanced efficiency. Promising enantioselectivity (74 % ee) has been obtained. Experimental and computational mechanistic studies suggest that a pathway through alkene migratory insertion into the Ir−C bond followed by C−H reductive elimination is involved for the high branched selectivity.

    

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4. C–H functionalization reactions enabled by hydrogen atom transfer to carbon-centered radicals

   https://doi.org/10.1039/D0SC04881J  

   Sarkar, Sumon ; Cheung, Kelvin Pak ; Gevorgyan, Vladimir ( December 2020 , Chemical Science)

   null (Ed.)

   Selective functionalization of ubiquitous unactivated C–H bonds is a continuous quest for synthetic organic chemists. In addition to transition metal catalysis, which typically operates under a two-electron manifold, a recent renaissance in the radical approach relying on the hydrogen atom transfer (HAT) process has led to tremendous growth in the area. Despite several challenges, protocols proceeding via HAT are highly sought after as they allow for relatively easy activation of inert C–H bonds under mild conditions leading to a broader scope and higher functional group tolerance and sometimes complementary reactivity over methods relying on traditional transition metal catalysis. A number of methods operating via heteroatom-based HAT have been extensively reported over the past few years, while methods employing more challenging carbon analogues have been less explored. Recent developments of mild methodologies for generation of various carbon-centered radical species enabled their utilization in the HAT process, which, in turn, led to the development of remote C(sp 3 )–H functionalization reactions of alcohols, amines, amides and related compounds. This review covers mostly recent advances in C–H functionalization reactions involving the HAT step to carbon-centered radicals. 

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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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