Single-Electron-Transfer (SET)-Induced Oxidative Biaryl Coupling by Polyalkoxybenzene-Derived Diaryliodonium(III) Salts

Highly chemoselective oxidative dimerization of indolosesquiterpene alkaloids: a biomimetic approach to dixiamycin

Dimeric indolosesquiterpene alkaloids, typically N-N- and C-N-linked xiamycin dimers, feature a pentacyclic framework with four contiguous stereogenic centers at the periphery of a trans-decalin scaffold to which a carbazole unit is attached. In comparison with actual biosynthetic dixiamycin derivatives, we designed C-C-linked xiamycin dimers, aiming to use them as a powerful tool to create unique scaffolds as drug candidates. In this work, we disclose the first synthetic route to access a C-C dimeric indolosesquiterpene skeleton, featuring a hypervalent iodine (PIFA)-catalyzed oxidative dimerization reaction in a single-step operation with overwhelming control over the chemoselectivity and regioselectivity. This strategy has been successfully applied to the synthesis of a C-C dimer of xiamycin A (3) and xiamycin A methyl ester (15) that demonstrates a new synthetic pathway for dimeric indolosesquiterpene alkaloids.

Metal-free and atom-efficient protocol for diarylation of selenocyanate by diaryliodonium salts

We developed an atom- and reaction mass efficient strategy for the preparation of diarylselenides using iodonium salts as reactants. The developed approach allows the obtaining of diarylselenides from the corresponding trimethoxyphenyl-substituted iodonium salts via a two-step one-pot reaction sequence. The proposed metal-free methodology is based on the involvement of both iodonium aryl groups for diarylation.

The C3-H Bond Functionalization of Quinoxalin-2(1H)-Ones With Hypervalent Iodine(III) Reagents

The modification of quinoxalin-2(1H)-ones via direct C-H bond functionalization has begun to receive widespread attention, due to quinoxalin-2(1H)-one derivatives' various biological activities and pharmaceutical properties. This mini review concentrates on the accomplishments of arylation, trifluoromethylation, alkylation, and alkoxylation of quinoxalin-2(1H)-ones with hypervalent iodine(III) reagents as reaction partners or oxidants. The reaction conditions and mechanisms are compared and discussed in detail.

Wet carbonate-promoted radical arylation of vinyl pinacolboronates with diaryliodonium salts yields substituted olefins

Since the landmark work of Heck, Negishi and Suzuki on Pd-catalyzed crossing coupling reactions, innovative discovery of new reactions forming C-C bonds and constructing functional olefins via nonmetal catalysts remains an imperative area in organic chemistry. Herein, we report a transition-metal-free arylation method of vinyl pinacolboronates with diaryliodonium salts to form C(sp²)-C(sp²) bond and provide trans-arylvinylboronates. The resulting vinylboronates can further react with the remaining aryl iodides (generated from diaryliodonium salts) via Suzuki coupling to afford functional olefins, offering an efficient use of aryliodonium salts. Computational mechanistic studies suggest radical-pair pathway of the diaryliodonium salts promoted by the multi-functional wet carbonate.

Can Plasmon Change Reaction Path? Decomposition of Unsymmetrical Iodonium Salts as an Organic Probe

Plasmon-assisted transformations of organic compounds represent a novel opportunity for conversion of light to chemical energy at room temperature. However, the mechanistic insights of interaction between plasmon energy and organic molecules is still under debate. Herein, we proposed a comprehensive study of the plasmon-assisted reaction mechanism using unsymmetric iodonium salts (ISs) as an organic probe. The experimental and theoretical analysis allow us to exclude the possible thermal effect or hot electron transfer. We found that plasmon interaction with unsymmetrical ISs led to the intramolecular excitation of electron followed by the regioselective cleavage of C-I bond with the formation of electron-rich radical species, which cannot be explained by the hot electron excitation or thermal effects. The high regioselectivity is explained by the direct excitation of electron to LUMO with the formation of a dissociative excited state according to quantum-chemical modeling, which provides novel opportunities for the fine control of reactivity using plasmon energy.

Recent progress in (hetero)arene cation radical-based heteroarene modification

The transformation of (hetero)arene cation radicals has become a powerful tool for the construction of highly functionalized (hetero)arenes. These (hetero)arene cation radicals could be generated under electrochemical, photochemical or chemical oxidation systems. The in situ generated (hetero)arene cation radicals can be attacked by various nucleophiles, such as (hetero)aromatics and anions, yielding structurally diverse molecules. Recently, a large number of impressive heteroarene modifications have been designed by this strategy. This review summarizes the advances in heteroarene modification via reactions of in situ formed (hetero)arene cation radicals, ranging from 2010 to 2020.

Exploiting single-electron transfer in Lewis pairs for catalytic bond-forming reactions

A single-electron transfer (SET) between tris(pentafluorophenyl)borane (B(C₆F₅)₃) and N,N-dialkylanilines is reported, which is operative via the formation of an electron donor–acceptor (EDA) complex involving π-orbital interactions as a key intermediate under dark conditions or visible-light irradiation depending on the structure of the aniline derivatives. This inherent SET in the Lewis pairs initiates the generation of the corresponding α-aminoalkyl radicals and their additions to electron-deficient olefins, revealing the ability of B(C₆F₅)₃ to act as an effective one-electron redox catalyst.

Radical–ion pair generation from common Lewis pairs and its application to catalytic carbon–carbon bond formation.

Nucleophilic Arylation of Halopurines Facilitated by Brønsted Acid in Fluoroalcohol

Various aryl-substituted purine derivatives were synthesized through the direct arylation of halopurines with aromatic compounds, facilitated by the combination of triflic acid and fluoroalcohol. This metal-free method is complementary to conventional coupling reactions using metal catalysts and reagents for the syntheses of aryl-substituted purine analogues.

Dataset on synthesis and crystallographic structure of phenyl(TMP)iodonium(III) acetate

The data in this article are related to research article ‘‘Efficient N-arylation of azole compounds utilizing selective aryl-transfer TMP-iodonium (III) reagents (Koseki et al., 2019). For the title compound, phenyl(2,4,6-trimethoxyphenyl)iodonium(III) acetate (Ph(TMP)IOAc), the single-crystal X-ray diffraction measurement together with NMR analysis, like also the method of synthesis and crystallization are presented. The X-ray structure analysis has revealed that the two types of geometries regarding the acetate anion attached to phenyl (TMP)iodonium (III) cation are found in the crystal states.

Aryl Transfer Selectivity in Metal-Free Reactions of Unsymmetrical Diaryliodonium Salts

Aromatic rings are found in a wide variety of products, including pharmaceuticals, agrochemicals, and functional materials. Diaryliodonium salts are new reagents used to transfer aryl groups under both metal-free and metal-catalyzed reactions and thereby synthesize arene-containing compounds. This minireview focuses on recent studies in selective aryl transfer reactions from unsymmetrical diaryliodonium salts under metal-free conditions. Reactions reported from 2007 to 2017, which represents a period of significant growth in diaryliodonium salt chemistry, are presented and organized by the type of reactive intermediate formed in the reaction. Specifically, reactions involving λ³ -iodane, λ³ -iodane radical anions, aryl radicals, and arynes are discussed. Chemoselectivity trends in aryl transfer are compared and contrasted across reaction intermediates and translation to potential auxiliaries are posited.

Transition-Metal-Free Direct C-H Arylation of Quinoxalin-2(1H)-ones with Diaryliodonium Salts at Room Temperature

A method of synthesizing 3-arylquinoxalin-2(1H)-ones using diaryliodonium tetrafluoroborates under mild conditions is described. This protocol has a wide substrate scope and enables direct C-H functionalization. The synthetic potential of this coupling was explored using a range of readily accessible diaryliodonium salts and quinoxalin-2(1H)-ones.

Efficient photolytic C-H bond functionalization of alkylbenzene with hypervalent iodine(iii) reagent

A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.

Unsymmetrical Aryl(2,4,6-trimethoxyphenyl)iodonium Salts: One-Pot Synthesis, Scope, Stability, and Synthetic Studies

Diaryliodonium salts have recently attracted significant attention as metal-free-arylation reagents in organic synthesis, and efficient access to these salts is critical for advancement of their use in reaction discovery and development. The trimethoxybenzene-derived auxiliary is a promising component of unsymmetrical variants, yet access remains limited. Here, a one-pot synthesis of aryl(2,4,6-trimethoxyphenyl)iodonium salts from aryl iodides, m-CPBA, p-toluenesulfonic acid, and trimethoxybenzene is described. Optimization of the reaction conditions for this one-pot synthesis was enabled by the method of multivariate analysis. The reaction is fast (<1 h), provides a high yield of product (>85% average), and has broad substrate scope (>25 examples) including elaborate aryl iodides. The utility of these reagents is demonstrated in moderate to high yielding arylation reactions with C-, N-, O-, and S-nucleophiles including the synthesis of a liquid crystal molecule.

C-H arylation of triphenylene, naphthalene and related arenes using Pd/C

A highly selective arylation of a number of polyaromatic hydrocarbons (PAHs) with aryliodonium salts and Pd/C as the only reagent is reported. The first C-H functionalization of triphenylene is explored, and proceeds at the most sterically hindered position. This non-chelate assisted C-H functionalization extends the reactivity profile of Pd/C and provides controlled access to π-extended PAHs, an important aspect of work towards the preparation of nanographenes. Mechanistic studies suggest in situ formation of catalytically active insoluble nanoparticles, and that the reaction likely proceeds via a Pd(0)/Pd(ii) type reaction manifold.

Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides

The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.

Base promoted direct C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts

A metal-free approach for the C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts was developed.

Metal-free one-pot sequential direct diarylation of pyrazolin-5-ones with diaryliodonium salts

A novel and efficient one-pot sequential C4-diarylation of pyrazolin-5-ones with diaryliodonium salts at room temperature in the absence of a metal catalyst was reported.