Recyclable synthesis of mesityl iodonium(III) salts

Sustainable and scalable one-pot synthesis of diaryliodonium salts

Two one-pot routes from iodoarenes to diaryliodonium triflates have been developed in the sustainable solvent ethyl acetate. The first method yields the recently reported aryl(dimethylisoxazolyl)iodonium triflates, circumventing the need for stepwise synthesis of this chemoselective arylating reagent. The second method gives other types of diaryliodonium salts, and the scalability of the protocols was exhibited with two >45 mmol scale-ups with impressively low E-factors.

Iodoarene Activation: Take a Leap Forward toward Green and Sustainable Transformations

Constructing chemical bonds under green sustainable conditions has drawn attention from environmental and economic perspectives. The dissociation of (hetero)aryl-halide bonds is a crucial step of most arylations affording (hetero)arene derivatives. Herein, we summarize the (hetero)aryl halides activation enabling the direct (hetero)arylation of trapping reagents and construction of highly functionalized (hetero)arenes under benign conditions. The strategies for the activation of aryl iodides are classified into (a) hypervalent iodoarene activation followed by functionalization under thermal/photochemical conditions, (b) aryl-I bond dissociation in the presence of bases with/without organic catalysts and promoters, (c) photoinduced aryl-I bond dissociation in the presence/absence of organophotocatalysts, (d) electrochemical activation of aryl iodides by direct/indirect electrolysis mediated by organocatalysts and mediators acting as electron shuttles, and (e) electrophotochemical activation of aryl iodides mediated by redox-active organocatalysts. These activation modes result in aryl iodides exhibiting diverse reactivity as formal aryl cations/radicals/anions and aryne precursors. The coupling of these reactive intermediates with trapping reagents leads to the facile and selective formation of C-C and C-heteroatom bonds. These ecofriendly, inexpensive, and functional group-tolerant activation strategies offer green alternatives to transition metal-based catalysis.

Access to arynes from arenes via net dehydrogenation: scope, synthetic applications and mechanistic analysis

Arynes undergo a wide range of chemical transformations making them versatile reactive intermediates for organic synthesis. Access to arynes has long been dominated by pre-functionalised reagents, e.g., the venerable o-trimethylsilylaryl triflates. However, a move toward developing methods to access arynes that are both mild and efficient has prompted research into aryl "onium" aryne precursors. Here, we leverage aryl "onium" species as in situ or isolated intermediates in a net dehydrogenation of simple arenes as a novel and efficient way to access arynes. We describe a unified strategy in which two different tactics are employed to access diversely substituted arynes from simple arenes. (1) We developed a one-pot method that converts simple arenes into aryl thianthrenium salts and uses them in situ to generate arynes. (2) We developed a two-step process to convert arenes into aryl(Mes)iodonium salts and ultimately trapped arynes to expand the scope of compatible arenes. The net transformations from arenes to trapped arynes are complete with 2-4 hours. Mechanistic analysis through competition experiments, deuterium kinetic isotope effects (DKIE) and Density Functional Theory (DFT) provide key comparisons of the two approaches described in this work and yield a user's guide for selecting the appropriate "onium" leaving group based on the arene.

Synthesis of Heterocyclic Sulfonium Triflates by Cu-catalyzed Selective S-arylation with Aryl(mesityl)iodonium Salts

BACKGROUND

An efficient method for synthesizing cyclic arylsulfonium salts has been developed by selective aryl transfer to the sulfur atom from aryl(mesityl)iodonium triflates, a recyclable series of diaryliodonium salts.

METHODS

The utilization of sulfonium salts as valuable intermediates is well-established, as they exhibit high reactivity under conditions of heating or UV irradiation. However, their synthesis typically involves the reaction of diarysulfoxide with acid anhydride, which requires the oxidation of sulfur(II) to sulfoxide(IV) and thus limits the scope of synthesis. Hence, in this study, we employed recyclable mesityliodonium(III) salts and copper catalysis.

RESULTS

The method was used to synthesize cyclic arylsulfonium salts without the need for preoxidation of the sulfur atom, resulting in a facile and high-yield synthesis.

CONCLUSION

The desired cyclic arylsulfonium salts were synthesized through selective transfer of the aryl group from mesityliodonium salts, demonstrating the effectiveness of the new approach.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Auxiliary strategy for the general and practical synthesis of diaryliodonium(III) salts with diverse organocarboxylate counterions

Diaryliodonium(III) salts are versatile reagents that exhibit a range of reactions, both in the presence and absence of metal catalysts. In this study, we developed efficient synthetic methods for the preparation of aryl(TMP)iodonium(III) carboxylates, by reaction of (diacetoxyiodo)arenes or iodosoarenes with 1,3,5-trimethoxybenzene in the presence of a diverse range of organocarboxylic acids. These reactions were conducted under mild conditions using the trimethoxyphenyl (TMP) group as an auxiliary, without the need for additives, excess reagents, or counterion exchange in further steps. These protocols are compatible with a wide range of substituents on (hetero)aryl iodine(III) compounds, including electron-rich, electron-poor, sterically congested, and acid-labile groups, as well as a broad range of aliphatic and aromatic carboxylic acids for the synthesis of diverse aryl(TMP)iodonium(III) carboxylates in high yields. This method allows for the hybridization of complex bioactive and fluorescent-labeled carboxylic acids with diaryliodonium(III) salts.

An efficient and chemoselective method to generate arynes

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.

Oxidative Cycloaddition Reactions of Arylboron Reagents via a One-pot Formal Dehydroboration Sequence

Arylboron compounds are widely available and synthetically useful reagents in which the boron group is typically substituted. Herein, we show that the boron group and ortho-hydrogen atom are substituted in a formal cycloaddition reaction. This transformation is enabled by a one-pot sequence involving diaryliodonium and aryne intermediates. The scope of arylboron reagents and arynophiles is demonstrated, and the method is applied to the formal synthesis of an investigational drug candidate.

Regiodivergent and Stereoselective Synthesis of Highly Substituted 1,3-Dienes via Arylative Acyloxy Migration of Propargyl Esters

We report the first catalyst-controlled regiodivergent method that enables the synthesis of structurally diverse 1,2,3,4-tetrasubstituted conjugated dienes with excellent regio- and stereochemical outcomes from the same set of readily available propargyl esters and diaryliodonium salts. In this diene chemistry, the in situ generated, highly electrophilic aryl-CuIII complex serves not only as a π-Lewis acid catalyst for alkyne activation/acyloxy migration but also as an aryl electrophile equivalent. The competitive arylative 1,2- and 1,3-acyloxy migration patterns are exquisitely dictated by Cu and Au/Cu relay catalyses, respectively, providing a modular and attractive approach to traditionally inaccessible tetrasubstituted 1,3-dienes in a regiodivergent manner. Finally, the synthetic utility of this method is demonstrated by further synthetic derivatization of 1,3-dienes into an array of useful compounds.

Synthesis of Arynes via Formal Dehydrogenation of Arenes

Arynes offer immense potential for diversification of benzenoid rings, which occur in pharmaceuticals, agrochemicals, and liquid crystals. However, accessing these high-energy intermediates requires synthetic precursors, which involve either harsh conditions or multistep syntheses. The development of alternative methods to access arynes using simpler substrates and milder conditions is necessary for a more streamlined approach. Here, we describe a two-step formal dehydrogenation of simple arenes to generate arynes at a remote position relative to traditionally reactive groups, e.g., halides. This approach is enabled by regioselective installation and ejection of an "onium" leaving group, and we demonstrate the compatibility of simple arenes (20 examples) and arynophiles (8 examples). Moreover, through direct comparison, we show that our formal dehydrogenation method is both more functional group tolerant and efficient in generating arynes than the current state-of-the-art aryne precursors. Finally, we show that aryne intermediates offer opportunities for regioselective C-H amination that are distinct from other methods.

Recyclable Hypervalent Iodine Reagents in Modern Organic Synthesis

Hypervalent iodine (HVI) reagents have gained much attention as versatile oxidants because of their low toxicity, mild reactivity, easy handling, and availability. Despite their unique reactivity and other advantageous properties, stoichiometric HVI reagents are associated with the disadvantage of generating non-recyclable iodoarenes as waste/co-products. To overcome these drawbacks, the syntheses and utilization of various recyclable hypervalent iodine reagents have been established in recent years. This review summarizes the development of various recyclable non-polymeric, polymer-supported, ionic-liquid-supported, and metal–organic framework (MOF)-hybridized HVI reagents.

1 Introduction

2 Polymer-Supported Hypervalent Iodine Reagents

2.1 Polymer-Supported Hypervalent Iodine(III) Reagents

2.2 Polymer-Supported Hypervalent Iodine(V) Reagents

3 Non-Polymeric Recyclable Hypervalent Iodine Reagents

3.1 Non-Polymeric Recyclable Hypervalent Iodine(III) Reagents

3.2 Recyclable Non-Polymeric Hypervalent Iodine(V) Reagents

3.3 Fluorous Hypervalent Iodine Reagents

4 Ionic-Liquid/Ion-Supported Hypervalent Iodine Reagents

5 Metal–Organic Framework (MOF)-Hybridized Hypervalent Iodine Reagents

6 Conclusion

Copper-Catalyzed Chemo-, Regio-, and Stereoselective Multicomponent 1,2,3-Trifunctionalization of Internal Alkynes

Herein, we report the first diaryliodonium salts promoted multicomponent 1,2,3-trifunctionalization of alkynes, where both the acetylenic bond and the adjacent nonactivated propargylic C(sp³)-H bond were functionalized synergistically to generate α-arylated enones with high chemo-, regio-, and stereoselectivity. A broad spectrum of diaryliodonium salts and internal alkynes could be utilized in this protocol, and a diverse collection of highly substituted and stereochemically defined linear and cyclic complex structures could be elaborated from the enone products.

Refining boron-iodane exchange to access versatile arylation reagents

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-λ³-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_EAr.

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...

Recent Advances in Transition-Metal-Free Late-Stage C-H and N-H Arylation of Heteroarenes Using Diaryliodonium Salts

Transition-metal-free direct arylation of C-H or N-H bonds is one of the key emerging methodologies that is currently attracting tremendous attention. Diaryliodonium salts serve as a stepping stone on the way to alternative environmentally friendly and straightforward pathways for the construction of C-C and C-heteroatom bonds. In this review, we emphasize the recent synthetic advances of late-stage C(sp2)-N and C(sp2)-C(sp2) bond-forming reactions under metal-free conditions using diaryliodonium salts as arylating reagent and its applications to the synthesis of new arylated bioactive heterocyclic compounds.

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.

Iodolopyrazolium Salts: Synthesis, Derivatizations, and Applications

The synthesis of iodolopyrazolium triflates via an oxidative cyclization of 3-(2-iodophenyl)-1H-pyrazoles is described. The reaction is characterized by a broad substrate scope, and various applications of these novel cyclic iodolium salts acting as useful synthetic intermediates are demonstrated, in particular in site-selective ring openings. This was finally applied to generate derivatives of the anti-inflammatory drug celecoxib. Their application as highly active halogen-bond donors is shown as well.

Site-selective aromatic C-H λ3-iodanation with a cyclic iodine(iii) electrophile in solution and solid phases

An efficient and site-selective aromatic C-H λ³-iodanation reaction is achieved using benziodoxole triflate (BXT) as an electrophile under room temperature conditions. The reaction tolerates a variety of electron-rich arenes and heteroarenes to afford the corresponding arylbenziodoxoles in moderate to good yields. The reaction can also be performed mechanochemically by grinding a mixture of solid arenes and BXT under solvent-free conditions. The arylbenziodoxoles can be used for various C-C and C-heteroatom bond formations, and are also amenable to further modification by electrophilic halogenation. DFT calculations suggested that the present reaction proceeds via a concerted λ³-iodanation-deprotonation transition state, where the triflate anion acts as an internal base.

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.