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1. Bis-arylation of phenylene-bridged bis-azolium salts and tetra-arylation of bis-azoles to access symmetrical and unsymmetrical CCC-aNHC pincer ligand precursors

   https://doi.org/10.1016/j.tet.2025.135045  

   Cecil, AC; Fosu, E; Donnadieu, B; Hollis, TK (January 2026, Tetrahedron)

   Copper-mediated methodologies for the arylation of bis-azolium salts and bis-azoles are efficient pathways to access symmetrical and unsymmetrical N-heterocyclic carbene precursors. The arylation of bis-azolium salts with various aryl halides was achieved in moderate yields to furnish numerous C2-arylated bis-azolium salts. Access of C2-arylated bis-azolium salts from bis-azoles was also achieved in a single pot domino reaction via the use of iodonium salts as embedded electrophiles. The latter methodology utilizes the aryl iodide byproduct from the N-arylation step for the C–H activation step to mitigate waste and the need to recycle. We also demonstrated the use of these azolium salts in metalation and found success in obtaining metal complexes containing abnormal N-heterocyclic carbenes. 

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2. An efficient and chemoselective method to generate arynes

   https://doi.org/10.1039/d3sc05429b  

   Metze, Bryan E; Roberts, Riley A; Nilova, Aleksandra; Stuart, David R (December 2023, Chemical Science)

   Arynes hold immense potential as reactive intermediates in organic synthesis as they engage in a diverse range of mechanistically distinct chemical reactions. However, the poor functional group compatibility of generating arynes or their precursors has stymied their widespread use. Here, we show that generating arynes by deprotonation of an arene and elimination of an “onium” leaving group is mild, efficient and broad in scope. This is achieved by using aryl(TMP)iodonium salts (TMP = 2,4,6-trimethoxyphenyl) as the aryne precursor and potassium phosphate as the base, and a range of arynophiles are compatible. Additionally, we have performed the first quantitative analysis of functional group compatibility for several methods to generate arynes, including the method developed here and the current state of the art. Finally, we show that a range of “sensitive” functional groups such as Lewis and Brønsted acids and electrophiles are compatible under our conditions. 

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3. Preparation and structure of phenolic aryliodonium salts

   https://doi.org/10.1039/c8cc06211k  

   Yoshimura, Akira; Shea, Michael T.; Guselnikova, Olga; Postnikov, Pavel S.; Rohde, Gregory T.; Saito, Akio; Yusubov, Mekhman S.; Nemykin, Victor N.; Zhdankin, Viktor V. (January 2018, Chemical Communications)

   Phenol based aryliodonium salts were prepared by the reaction of [hydroxy(tosyloxy)iodo]arenes with aryl silyl ethers in the presence of trifluoromethanesulfonic acid. Structures of several aryliodonium salts with the hydroxy group in the para -position of the phenyl ring were established by single crystal X-ray crystallography. Under basic conditions, 4-hydroxyphenyl(phenyl)iodonium salts form a dimeric hypervalent iodine( iii ) complex, oxyphenyl(phenyl)iodonium ylidic salt, the solid structure of which was confirmed by X-ray crystallography. Phenolic iodonium salts are potentially useful phenol transfer reagents in reactions with various anionic nucleophiles. 

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4. Regioselective Synthesis of 1,2,3,4‐Tetrasubstituted Arenes by Vicinal Functionalization of Arynes Derived from Aryl(Mes)iodonium Salts**

   https://doi.org/10.1002/chem.202100201  

   Nilova, Aleksandra; Sibbald, Paul_A; Valente, Edward_J; González‐Montiel, Gisela_A; Richardson, H_Camille; Brown, Kevin_S; Cheong, Paul_Ha‐Yeon; Stuart, David_R (March 2021, Chemistry – A European Journal)

   Abstract Herein, the synthesis of 1,2,3,4‐tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described.^[1]In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4‐tetrasubstituted benzenoid rings. Significantly, it was found that halide substituents are compatible under these conditions, enabling post‐synthetic elaboration via palladium‐catalyzed coupling. This concise strategy is predicated on two regioselective events: 1) ortho‐ deprotonation of aryl(Mes)iodonium salts to generate a substituted aryne intermediate, and 2) regioselective trapping of said arynes, thereby improving previously reported reaction conditions to generate arynes at room temperature and in shorter reaction times. Density functional theory (DFT) computations and linear free energy relationship (LFER) analysis suggest the regioselectivity of deprotonation is influenced by both proximal and distal ring substituents on the aryne precursor. A competition experiment further reveals the role of arene substituents on relative reactivity of aryl(Mes)iodoniums as aryne precursors. 

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5. Refining boron–iodane exchange to access versatile arylation reagents

   https://doi.org/10.1039/d1cc06341c  

   Karandikar, Shubhendu S.; Stuart, David R. (January 2022, Chemical Communications)

   Aryl(Mes)iodonium salts, which are multifaceted aryl transfer reagents, are synthesized via boron-iodane exchange. Modification to both the nucleophilic (aryl boron) and electrophilic (mesityl–λ 3 –iodane) reaction components results in improved yield and faster reaction time compared to previous conditions. Mechanistic studies reveal a pathway that is more like transmetallation than S E Ar. 

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