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1. SET activation of nitroarenes by 2-azaallyl anions as a straightforward access to 2,5-dihydro-1,2,4-oxadiazoles

   https://doi.org/10.1038/s41467-021-26767-x  

   Zou, Dong; Gan, Lishe; Yang, Fan; Wang, Huan; Pu, Youge; Li, Jie; Walsh, Patrick J. (December 2021, Nature Communications)

   Abstract The use of nitroarenes as amino sources in synthesis is challenging. Herein is reported an unusual, straightforward, and transition metal-free method for the net [3 + 2]-cycloaddition reaction of 2-azaallyl anions with nitroarenes. The products of this reaction are diverse 2,5-dihydro-1,2,4-oxadiazoles (>40 examples, up to 95% yield). This method does not require an external reductant to reduce nitroarenes, nor does it employ nitrosoarenes, which are often used in N–O cycloadditions. Instead, it is proposed that the 2-azaallyl anions, which behave as super electron donors (SEDs), deliver an electron to the nitroarene to generate a nitroarene radical anion. A downstream 2-azaallyl radical coupling with a newly formed nitrosoarene is followed by ring closure to afford the observed products. This proposed reaction pathway is supported by computational studies and experimental evidence. Overall, this method uses readily available materials, is green, and exhibits a broad scope. 

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2. Efficient construction of functionalized pyrroloindolines through cascade radical cyclization/intermolecular coupling

   https://doi.org/10.1039/D3SC05210A  

   Jiang, Yonggang; Liu, Dongxiang; Zhang, Lening; Qin, Cuirong; Li, Hui; Yang, Haitao; Walsh, Patrick J; Yang, Xiaodong (February 2024, Chemical Science)

   A novel tandem radical cyclization/intermolecular coupling between 2-azaallyl anions and indole N-aryloxy acetamides is developed, which enables the synthesis of C3a-substituted pyrroloindolines under mild conditions. 

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3. Synthesis of an elusive, stable 2-azaallyl radical guided by electrochemical and reactivity studies of 2-azaallyl anions

   https://doi.org/10.1039/d0sc04822d  

   Panetti, Grace B.; Carroll, Patrick J.; Gau, Michael R.; Manor, Brian C.; Schelter, Eric J.; Walsh, Patrick J. (April 2021, Chemical Science)

   null (Ed.)

   The super electron donor (SED) ability of 2-azaallyl anions has recently been discovered and applied to diverse reactivity, including transition metal-free cross-coupling and dehydrogenative cross-coupling processes. Surprisingly, the redox properties of 2-azaallyl anions and radicals have been rarely studied. Understanding the chemistry of elusive species is the key to further development. Electrochemical analysis of phenyl substituted 2-azaallyl anions revealed an oxidation wave at E 1/2 or E pa = −1.6 V versus Fc/Fc + , which is ∼800 mV less than the reduction potential predicted ( E pa = −2.4 V vs. Fc/Fc + ) based on reactivity studies. Investigation of the kinetics of electron transfer revealed reorganization energies an order of magnitude lower than commonly employed SEDs. The electrochemical study enabled the synthetic design of the first stable, acyclic 2-azaallyl radical. These results indicate that the reorganization energy should be an important design consideration for the development of more potent organic reductants. 

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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. 

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5. Poly (Vinyl Alcohol) Assisted Synthesis and Anti-Solvent Precipitation of Gold Nanoparticles

   https://doi.org/10.3390/nano10122359  

   Liu, Zhen; Lanier, Olivia L.; Chauhan, Anuj (December 2020, Nanomaterials)

   null (Ed.)

   Gold nanoparticles (GNPs) are commonly synthesized using the Turkevich method, but there are limitations on the maximum concentration of gold nanoparticles that can be achieved using this method (often < 1 mM (=0.34 mg/mL) gold precursor loading). Here, we report an inverse Turkevich method which significantly increases the concentration of gold nanoparticles (up to 5-fold) in the aqueous phase by introducing poly (vinyl alcohol) (PVA) to the synthesis system for stabilization. The aim of this study is to understand the effect of PVA and other synthesis parameters, such as trisodium citrate and tetrachloroauric acid concentration, with the goal of maximizing concentration while maintaining gold nanoparticle morphology, stability, and narrow size distribution. The size distribution of GNPs is investigated for a range of parameters by dynamic light scattering and electron microscopy, and ultraviolet-visible (UV–vis) spectroscopy is also utilized to explore the localized surface plasmon resonance (LSPR). Further, the interaction between GNPs and PVA is investigated by Fourier-transform infrared spectroscopy. In addition to increasing the gold loading by varying synthesis parameters, we also develop a novel anti-solvent precipitation method for the PVA-coated GNPs, which enables continuous condensation and purification of GNPs by forming a gold/PVA nanocomposite. 

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