One-pot synthesis of diaryliodonium salts from arenes and aryl iodides with Oxone-sulfuric acid

Key-to-lock halogen bond-based tetragonal pyramidal association of iodonium cations with the lacune rims of beta-octamolybdate

The structure-directing "key-to-lock" interaction of double σ-(IIII)-hole donating iodonium cations with the O-flanked pseudo-lacune rims of [β-Mo8O26]4- gives halogen-bonded iodonium-beta-octamolybate supramolecular associates. In the occurrence of their tetragonal pyramidal motifs, deep and broad σ-(IIII)-holes of a cation recognize the molybdate backbone, which provides an electronic pool localized around the two lacunae. The halogen-bonded I⋯O linkages in the structures were thoroughly studied computationally and classified as two-center, three-center bifurcated, and unconventional "orthogonal" I⋯O halogen bonds. In the latter, the O-atom approaches orthogonally the C-IIII-C plane of an iodonium cation and this geometry diverge from the IUPAC criteria for the identification of the halogen bond.

Exogenous photocatalyst-free aryl radical generation from diaryliodonium salts and use in metal-catalyzed C-H arylation

We demonstrate (1) detectable halogen bonding is not critical for enabling light-driven radical generation from diaryliodonium salts and (2) radicals generated by this route can be captured by transition-metals for C-H arylation reactions. These results are the first step toward developing new metal-catalyzed aryl radical couplings without exogenous photocatalysts.

3-sulfonyloxyaryl(mesityl)iodonium triflates as 1,2-benzdiyne precursors with activation via ortho-deprotonative elimination strategy

Benzyne has long captivated the attention of chemists and has gained numerous synthetic achievements. Among typical benzyne generation methods, removal of two vicinal substituents from 1,2-difunctionalized benzenes, i.e., Kobayashi's protocol, are prevailing, while ortho-deprotonative elimination from mono-substituted benzene lags far behind. Despite the advantages of atom economy and ready achievability of precursors, a bottle neck for ortho-deprotonative elimination strategy resides in the weak acidity of the ortho-hydrogen, which normally demands strong bases as the activating reagents. Here, an efficient aryne generation protocol is developed, where ortho-deprotonative elimination on 3-sulfonyloxyaryl(mesityl)iodonium triflates occurs under mild conditions and the generated 3-sulfonyloxyarynes can serve as efficient 1,2-benzdiyne synthons. This array of 1,2-benzdiyne precursors can be conveniently prepared with high functional group tolerance, and densely substituted scaffolds can be accessed as well. Carbonate and fluoride salts are found to serve as efficient activating reagents, which are the weakest bases used in ortho-deprotonative elimination strategies. Particularly, this scaffold has predictable chemoselective generation of the designated aryne intermediates. The success of this ortho-deprotonative elimination protocol sets up a unique platform with a broad spectrum of synthetic applications.

Halogen Bonding Involving Gold Nucleophiles in Different Oxidation States

A single-crystal X-ray diffraction (XRD) study of diaryliodonium tetrachloroaurates (or, in the recent terminology, tetrachloridoaurates), [(p-XC₆H₄)₂I][AuCl₄] (X = Cl, 1; Br, 2), was performed for 1 (the structure is denoted as 1a to show similarity with the isomorphic structure 2a) and two polymorphs─2a (obtained from MeOH) and 2b (from 1,2-C₂H₄Cl₂). Examination of the XRD data for these three structures revealed 2-center C-X···Au^III (X = Cl and Br) and 3-center bifurcated C-Br···(Cl-Au) halogen bonding (abbreviated as XB) between the p-Cl or p-Br atoms of the diaryliodonium cations and the gold(III) atom of [AuCl₄]^-. The noncovalent nature of Au^III-involving interactions, the nucleophilicity of the gold(III) atoms, and the electrophilic role of p-X atoms of the diaryliodonium cations in the XBs were studied by a set of complementary computational methods. Combined experimental and theoretical studies allowed the recognition of the d-nucleophilicity of the [d⁸Au^III] atom which, regardless of its rather substantial formal 3+ charge, can function as a d-nucleophilic partner of XB. This conclusion was also supported by theoretical calculations performed for the structures' refcodes BINXOM and ICSD 62511; the obtained data verified the nucleophilicity of Au^III toward a K⁺ ions or a σ-(Cl)-hole, respectively. All our results, together with consideration of relevant literature, indicate that gold atoms in the three oxidation states (0, I, and even III) exhibit nucleophilicity in XBs.

Zwitterionic iodonium species afford halogen bond-based porous organic frameworks

Porous architectures characterized by parallel channels arranged in honeycomb or rectangular patterns are identified in two polymorphic crystals of a zwitterionic 4-(aryliodonio)-benzenesulfonate. The channels are filled with disordered water molecules which can be reversibly removed on heating. Consistent with the remarkable strength and directionality of the halogen bonds (XBs) driving the crystal packing formation, the porous structure is stable and fully preserved on almost quantitative removal and readsorption of water. The porous systems described here are the first reported cases of one-component 3D organic frameworks whose assembly is driven by XB only (XOFs). These systems are a proof of concept for the ability of zwitterionic aryliodonium tectons in affording robust one-component 3D XOFs. The high directionality and strength of the XBs formed by these zwitterions and the geometrical constraints resulting from the tendency of their hypervalent iodine atoms to act as bidentate XB donors might be key factors in determining this ability.

Palladium-Catalysed Intermolecular Direct C–H Bond Arylation of Heteroarenes with Reagents Alternative to Aryl Halides: Current State of the Art

Abstract:

Abstract: This unprecedented review with 322 references provides a critical up-to-date picture of the Pd-catalysed intermolecular direct C–H bond arylation of heteroarenes with arylating reagents alternative to aryl halides that include aryl sulfonates (aryl triflates, tosylates, mesylates, and imidazole-1-sulfonates), diaryliodonium salts, [(diacetoxy)iodo]arenes, arenediazonium salts, 1-aryltriazenes, arylhydrazines and N’-arylhydrazides, arenesulfonyl chlorides, sodium arenesulfinates, arenesulfinic acids, and arenesulfonohydrazides. Particular attention has been paid to summarise the preparation of the various arylating reagents and to highlight the practicality, versatility, and limitations of the various developed arylation protocols, also comparing their results with those achieved in analogous Pd-catalysed arylation reactions involving the use of aryl halides as electrophiles. Mechanistic proposals have also been briefly summarised and discussed. However, data concerning Pd-catalysed direct C–H bond arylations involving the C–H bonds of aryl substituents of the examined heteroarene derivatives have not been taken into account.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Preparation and Synthetic Applicability of Imidazole-Containing Cyclic Iodonium Salts

A novel approach to the preparation of imidazole-substituted cyclic iodonium salts has been developed via the oxidative cyclization of 1-phenyl-5-iodoimidazole using a cheap and available Oxone/H₂SO₄ oxidative system. The structure of the new polycyclic heteroarenes has been confirmed by single-crystal X-ray diffractometry, revealing the characteristic structure features for cyclic iodonium salts. The newly produced imidazole-flanked cyclic iodonium compounds were found to readily engage in a heterocyclization reaction with elemental sulfur, affording benzo[5,1-b]imidazothiazoles in good yields.

Scalable electrochemical synthesis of diaryliodonium salts

Cyclic and acyclic diaryliodonium are synthesised by anodic oxidation of iodobiaryls and iodoarene/arene mixtures, respectively, in a simple undivided electrolysis cell in MeCN-HFIP-TfOH without any added electrolyte salts. This atom efficient process does not require chemical oxidants and generates no chemical waste. More than 30 cyclic and acyclic diaryliodonium salts with different substitution patterns were prepared in very good to excellent yields. The reaction was scaled-up to 10 mmol scale giving more than four grams of dibenzo[b,d]iodol-5-ium trifluoromethanesulfonate (>95%) in less than three hours. The solvent mixture of the large-scale experiment was recovered (>97%) and recycled several times without significant reduction in yield.

Copper-Catalyzed C–H Arylation of Fused-Pyrimidinone Derivatives Using Diaryliodonium Salts

Copper-catalyzed Csp2–Csp2 bond forming reactions through C–H activation are still one of the most useful strategies for the diversification of heterocyclic moieties using various coupling partners. A catalytic protocol for the C–H (hetero)arylation of thiazolo[5,4-f]quinazolin-9(8H)-ones and more generally fused-pyrimidinones using catalyst loading of CuI with diaryliodonium triflates as aryl source under microwave irradiation has been disclosed. The selectivity of the transfer of the aryl group was also disclosed in the case of unsymmetrical diaryliodonium salts. Specific phenylation of valuable fused-pyrimidinones including quinazolinone are provided. This strategy enables a rapid access to an array of various (hetero)arylated N-containing polyheteroaromatics as new potential bioactive compounds.

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.

One-Pot Synthesis and Conformational Analysis of Six-Membered Cyclic Iodonium Salts

Two one-pot procedures for the construction of carbon-bridged diaryliodonium triflates and tetrafluoroborates are described. Strong Brønsted acids enable the effective Friedel-Crafts alkylation with diversely substituted o-iodobenzyl alcohol derivatives, providing diphenylmethane scaffolds, which are subsequently oxidized and cyclized to the corresponding dibenzo[b,e]iodininium salts. Based on NMR investigations and density functional theory (DFT) calculations, we could verify the so-far-undescribed existence of two stable isomers in cyclic iodonium salts substituted with aliphatic side chains in the carbon bridge.

Diaryliodoniums Salts as Coupling Partners for Transition-Metal Catalyzed C- and N-Arylation of Heteroarenes

Owing to the pioneering works performed on the metal-catalyzed sp2 C–H arylation of indole and pyrrole by Sanford and Gaunt, N– and C-arylation involving diaryliodonium salts offers an attractive complementary strategy for the late-stage diversification of heteroarenes. The main feature of this expanding methodology is the selective incorporation of structural diversity into complex molecules which usually have several C–H bonds and/or N–H bonds with high tolerance to functional groups and under mild conditions. This review summarizes the main recent achievements reported in transition-metal-catalyzed N– and/or C–H arylation of heteroarenes using acyclic diaryliodonium salts as coupling partners.

Diaryliodonium as a double σ-hole donor: the dichotomy of thiocyanate halogen bonding provides divergent solid state arylation by diaryliodonium cations

The reactivity of [Ar¹Ar²I](SCN) toward the solid-state arylation depends on the preorganization of halogen bond (XB)-bound SCN⁻: N-XB-bound thiocyanates, which, in contrast to N,S-XB-bound, undergoes the extremely rare N-arylation of SCN⁻.