Advances in Synthetic Applications of Hypervalent Iodine Compounds

Synthesis of Dioxo-Azabicyclo[3.2.1]octanes via Hypervalent Iodine-Mediated Domino Reaction

Bicyclo[3.2.1]octane (BCO) skeleton widely exists in natural products and biologically active molecules, whereas the development of convenient approaches to construct this structure remains a challenge. Herein, we describe a cascade reaction to synthesize 6,8-dioxa-3-azabicycle[3.2.1]octane derivatives from β-keto allylamines via an oxidation-cyclization reaction. A series of dioxo-azabicyclo[3.2.1]octanes bearing a quaternary carbon center were obtained in good yields under mild reaction conditions. Moreover, the mechanistic rationale for this novel domino reaction is supported by control experiments.

Identification of O-arylated huperzinines as novel cholinergic anti-inflammatory pathway agonists against gout arthritis

Lycodine alkaloids are important natural products with diverse biological effects. In this manuscript, we set out the first structural optimization of the 2-pyridone moiety of Lycodine alkaloid via selective O-arylation under metal-free conditions and obtained a series of potent bioactive molecules against monosodium urate (MSU)-induced IL-1β production. Further investigations demonstrated that these natural product derivatives could activate the neuro-immunomodulatory cholinergic anti-inflammatory pathway (CAP) to block the initial phase of NLRP3 inflammasome activation. Compared with the clinical drugs hydrocortisone and indomethacin, as well as commercially available CAP agonists GTS-21 and pnu282987, 3k and 3q possessed greater potency against MSU-induced IL-1β production. Meanwhile, these molecules possessed less cytotoxicity against promonocytic THP-1 macrophages when compared with colchicine. This work reports a concise strategy for direct modification of 2-pyridone moiety from natural Lycodine alkaloids, and provides novel frameworks for discovering CAP activators and drugs for gout arthritis.

Radical 6-Endo Addition Enables Pyridine Synthesis under Metal-Free Conditions

Metal-free synthesis of heterocycles is highly sought after in the pharmaceutical industry and has garnered widespread attention due to eliminating the need to remove trace metal catalysts from the reaction. We report a radical 6-endo addition method for pyridine synthesis from cyclopropylamides and alkynes under metal-free conditions. Various terminal and substituted alkynes are inserted as C2 units into cyclopropylamides to synthesize versatile pyridines with 57 examples. Mechanistic investigations and computational studies indicate the unprecedented 6-endo-trig addition of vinyl radicals to the imine nitrogen atom rather than the conventional 5-exo-trig addition to the imine carbon atom, in which the hypervalent iodine(III) plays a critical role. This reaction easily scales up with excellent functional group compatibility and suits the late-stage pyridine installation on complex molecules.

Building Catalytic Reactions One Electron at a Time

ConspectusClassical education in organic chemistry and catalysis, not the least my own, has centered on two-electron transformations, from nucleophilic attack to oxidative addition. The focus on two-electron chemistry is well-founded, as this brand of chemistry has enabled incredible feats of synthesis, from the development of life-saving pharmaceuticals to the production of ubiquitous commodity chemicals. With that said, this approach is in many ways complementary to the approach of nature, where enzymes frequently make use of single-electron "radical" steps to achieve challenging reactions with exceptional selectivity, including light detection and C-H hydroxylation. While the power of radical elementary steps is undeniable, the fundamental understanding of─and ability to apply─these in catalysis remains underdeveloped, constraining the palette with which chemists can make new reactions.Motivation to remedy this traditional underemphasis on radical catalysis has been intensified by the runaway success of outer-sphere photoredox catalysis, not only confirming the versatility of radicals in anthropogenic catalysis but also teaching the value of robust and well-understood catalytic cycles for reaction design. Indeed, I would argue the success of outer-sphere photoredox catalysis has been fueled by strong fundamental understanding of its underlying radical elementary steps, with consideration of single-electron transfer (SET) energetics allowing new reactions to be designed de novo with enviable confidence. However, outer-sphere photoredox catalysis is an outlier in this regard, with other mechanistic approaches remaining underexplored.Our research group is part of a growing movement to expand the vocabulary of synthetic radical catalysis beyond the traditional outer-sphere photoredox SET manifold, assembling new cycles comprised of hydrogen atom transfer (HAT), light-induced homolysis (LIH), and radical ligand transfer (RLT) steps in new combinations to achieve challenging transformations. These efforts have been made possible by the ever-growing understanding of these radical elementary steps and discovery of catalyst systems with significant mechanistic flexibility, most recently iron/thiol (Fe/S) cocatalysis.In this Account, I will focus on our efforts applying HAT and LIH steps in Fe/S cocatalysis, sharing broad guidelines we have found helpful for using these steps and demonstrating how they can be combined to make new reactions using three case studies: radical hydrogenation (HAT + HAT), decarboxylative protonation (LIH + HAT), and alkene hydrofluoroalkylation (LIH + HAT, with an intervening radical alkene addition). These efforts have highlighted the importance of several key parameters, including bond dissociation energy (BDE) and radical polarity, and I hope our findings similarly provide a valuable framework to others designing new radical catalytic reactions.

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.

Skeletal Editing by Hypervalent Iodine Mediated Nitrogen Insertion

Hypervalent iodine reagents are versatile and readily accessible reagents that have been extensively applied in contemporary synthesis in modern organic chemistry. Among them, iodonitrene (ArI=NR), is a powerful reactive species, widely used for a single-nitrogen-atom insertion reaction, and skeletal editing to construct N-heterocycles. Skeletal editing with reactive iodonitrene components has recently emerged as an exciting approach in modern chemical transformation. These reagents have been extensively used to produce biologically relevant heterocycles and functionalized molecular architectures. Recently, the insertion of a nitrogen-atom into hydrocarbons to generate N-heterocyclic compounds using hypervalent iodine reagents has been a significant focus in the field of molecular editing reactions. In this review, we discuss the rapidly emerging field of nitrene insertion, including skeletal editing and nitrogen insertion, using hypervalent iodine reagents to access nitrogen-containing heterocycles, and the current mechanistic understanding of these processes.

Photocatalyst-free regioselective sulfonamidation of N-(2-hydroxyaryl)amides in visible-light

In this work, we report a regioselective sulfonamidation of N-(2-hydroxyaryl)amides with iminoiodinanes and iodine in visible light at room temperature. The method does not require a strong oxidant, metal or photocatalyst and enables direct functionalization of a C-H bond to a C-N bond. Mechanistic investigations suggest in situ generation of an N-centered radical from N,N-diiodo-sulfonamide by homolytic N-I bond cleavage followed by its site-specific addition to N-(2-hydroxyaryl)amides to furnish para-sulfonamide derivatives.

Low-Cost, Safe, and Anion-Flexible Method for the Electrosynthesis of Diaryliodonium Salts

An electrochemical approach toward the synthesis of diaryliodonium salts based on anodic C-I coupling between aryl iodides and arenes is presented. In contrast to previous protocols, our method requires no chemical oxidants, strong acids, or fluorinated solvents. A further advantage is that by use of the appropriate supporting electrolyte, the counterion of choice can be introduced, which is time- and cost-saving as compared to postsynthesis ion exchange. This "anion-flexibility" is particularly interesting when considering the pronounced effect of the counterion on the reactivity of diaryliodonium species in aryl transfer reactions. The scope of our method comprises 24 examples with isolated yields of up to 99%. Scalability was demonstrated by the synthesis on a gram scale. Furthermore, it was shown that the diaryliodonium-containing post-electrolysis solution can be used without further workup as a reactive medium for O-arylation reactions. Finally, a series of para-substituted diaryliodonium compounds was studied using linear sweep voltammetry on a microelectrode and analyzed with respect to the influence of the electronic structure on the redox behavior.

Transition-metal-catalyzed enantioselective C-N cross-coupling

Chiral amine scaffolds are among the most important building blocks in natural products, drug molecules, and functional materials, which have prompted chemists to focus more on their synthesis. Among the accomplishments in chiral amine synthesis, transition-metal-catalyzed enantioselective C-N cross-coupling is considered one of the most efficient protocols. This approach combines traditional C(sp2)-N cross-coupling methods (such as the Buchwald-Hartwig reaction Ullmann-type reaction, and Chan-Evans-Lam reaction), aryliodonium salt chemistry and radical chemistry, providing an attractive pathway to a wide range of structurally diverse chiral amines with high enantioselectivity. This review summarizes the established protocols and offers a comprehensive outlook on the promising enantioselective C-N cross-coupling reaction.

Hypervalent iodine-mediated cyclization of bishomoallylamides to prolinols

A change in mechanism was observed in the hypervalent iodine-mediated cyclization of N-alkenylamides when the carbon chain between the alkene and the amide increased from two to three atoms. In the latter case, cyclization at the amide nitrogen to form the pyrrolidine ring was favored over cyclization at the amide oxygen. A DFT study was undertaken to rationalize the change in mechanism of this cyclization process. In addition, reaction conditions were developed, and the scope of this cyclization studied.

Easy Access to α-Ketothioamides via Oxidative Amidation of Bunte Salts Using Electrolysis or Hypervalent Iodine

Two new protocols leveraging electrochemical and hypervalent iodine-mediated synthesis of α-ketothioamides have been developed by using easily accessible and cost-effective Bunte salts and secondary amines. The methods are efficient, simple, and straightforward, and showcase the formation of C-N bonds across diverse substrates under ambient conditions.

Iodine/DMSO-catalyzed oxidative deprotection of N-tosylhydrazone for benzoic acid synthesis

An oxidative deprotection of tosylhyrdazones has been demonstrated to afford benzoic acids using iodine and DMSO system. This efficient oxidative deprotection protocol offers exceptional functional group toleration under mild reaction conditions without any initiators or bases. Notably, the tosylhydrazone with the heteroaryl ring or with the aryl ring having base-sensitive hydroxyl and ester functional groups smoothly afforded the corresponding benzoic acid analogues under developed conditions. Moreover, this method features short reaction times, high product yields and easy purification by avoiding column-chromatographic purification.

Metal-free site-selective functionalization with cyclic diaryl λ3-chloranes: suppression of benzyne formation for ligand-coupling reactions

While hypervalent halogens are versatile reagents enabling diverse reactions in organic synthesis, the utility of hypervalent chlorine compounds, particularly cyclic λ3-chloranes, remains underdeveloped despite their unique electronic properties and innate enhanced reactivity. Herein, we illustrate the elusive ligand coupling reaction of cyclic λ3-chloranes that suppresses the more facile competing reaction modality involving benzyne intermediates. The methodology can be performed in three-component as well as two-component fashions, offering direct access to a wide range of unsymmetrically substituted biaryl molecules in very high yields and excellent ortho-regioselectivity. The reactions were scalable, and the versatility was demonstrated by constructing different types of C-S and C-N bonds under mild conditions. The reaction outcomes were also compared with those of corresponding λ3-iodanes and λ3-bromanes, demonstrating the superiority of cyclic λ3-chloranes in ligand-coupling reactions under metal-free conditions.

Hydrogen-bond activation enables aziridination of unactivated olefins with simple iminoiodinanes

Iminoiodinanes comprise a class of hypervalent iodine reagents that is often encountered in nitrogen-group transfer (NGT) catalysis. In general, transition metal catalysts are required to effect efficient NGT to unactivated olefins because iminoiodinanes are insufficiently electrophilic to engage in direct aziridination chemistry. Here, we demonstrate that 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) activates N-arylsulfonamide-derived iminoiodinanes for the metal-free aziridination of unactivated olefins. 1H NMR and cyclic voltammetry (CV) studies indicate that hydrogen-bonding between HFIP and the iminoiodinane generates an oxidant capable of direct NGT to unactivated olefins. Stereochemical scrambling during aziridination of 1,2-disubstituted olefins is observed and interpreted as evidence that aziridination proceeds via a carbocation intermediate that subsequently cyclizes. These results demonstrate a simple method for activating iminoiodinane reagents, provide analysis of the extent of activation achieved by H-bonding, and indicate the potential for chemical non-innocence of fluorinated alcohol solvents in NGT catalysis.

Energetic Hypervalent Organoiodine Electrochemistry for Aqueous Zinc Batteries

Hypervalent organoiodine compounds have been extensively utilized in organic synthesis, yet their electrochemical properties remain unexplored despite their theoretically high redox potential compared with inorganic iodine, which primarily relies on the I-/I0 redox couple in battery applications. Here, the fundamental redox mechanism of hypervalent organoiodine in a ZnCl2 aqueous electrolyte is established for the first time using the simplest iodobenzene (PhI) as a model compound. We validated that the PhI to PhICl2 transition is a single-step and reversible reaction, enabling two-electron transfer of I+/I3+ redox chemistry (1.9 V vs Zn2+/Zn) with high capacity (422 mAh giodine-1, and 262.6 mAh g-1 based on PhI) and high theoretical energy density (801.8 Wh kg-1). It was also elucidated that such organoiodine electrochemistry exhibits rich tunability in terms of the global reactivity of various PhI derivatives, including multiple iodine-substituted isomers and functional substituents. Additionally, the stabilizing anion ligands affect the reversibility and stability of trivalent organoiodine compounds. By limiting side reactions and improving the stability of trivalent organoiodine at low temperatures, the zinc-PhI battery demonstrated the feasibility of I+/I3+ conversion and sustained stable performance over 400 cycles. This work bridges the gap between hypervalent organoiodine chemistry and battery technology, highlighting the potential for future high-performance battery applications.

Hypervalent Iodine (III)-Based Complexation for Chiroptical Supramolecular Glass, Deep Eutectic Solvent and Luminescent Switch

Hypervalent iodine(III) have widely been utilized for organic synthetic reagents. They are also recognized as positive charge-assisted, exceptionally robust biaxial halogen bond donors, while their potential in supramolecular materials is barely explored. This work reports a cyclic diaryliodonium ion as biaxial halogen bonding donor that displays remarkable binding affinity toward phenanthroline or acridine acceptors with chiral pendants. Biaxial halogen bonding enables chiroptical evolution in solution, allowing for rational control over supramolecular chirality. Leveraging their strong binding affinity, the halogen bonding complexes manifested amorphous properties and deep eutectic behavior in the solid state. Capitalizing on these attributes, this work achieves the successful preparation of supramolecular glasses and deep eutectic solvents. Additionally, halogen bonding appended light irradiation-triggered luminescence through a hydrogen atom transfer process, showing applications in anti-counterfeit and display.

Iodine-promoted sequential C(sp3)-H oxidation and cyclization of aryl methyl ketones with 2-(2-aminophenyl)quinazolin-4(3H)-ones

An I2-promoted, metal-free protocol has been developed for the one-pot synthesis of 6-aroyl-5,6-dihydro-8H-quinazolino[4,3-b]quinazolin-8-ones from readily accessible substrates. This reaction involves the in situ sp3 C-H oxidation of aryl methyl ketones to phenylglyoxal, followed by imine formation and intramolecular nucleophilic addition, resulting in the formation of two new C-N bonds. Furthermore, the method is applicable to a wide range of aryl methyl ketones, including heterocycles and drug-derived substrates, yielding the desired products with yields ranging from 62% to 93%. Additionally, the practical utility of this approach was demonstrated through gram-scale synthesis.

Photochemical tandem reaction of nitrogen containing heterocycles, bicyclo[1.1.1]pentane, and difluoroiodane(III) reagents

A visible light-induced difluoroalkylation/heteroarylation of [1.1.1]propellane with nitrogen containing heterocycles and difluoroiodane(III) reagents was achieved. Various heteroarenes and difluoroiodane(III) reagents exhibited good compatibility, yielding the desired products in moderate to good yields. The accessibility of the reagents and the mild reaction conditions establish this method as an alternative and practical strategy for accessing diverse 1-difluoroalkyl-3-heteroaryl bicyclo[1.1.1]pentanes (BCPs).

Overriding Cage Effect in Electron Donor-Acceptor Photoactivation of Diaryliodonium Reagents: Synthesis of Chalcogenides

In recent times, diaryliodonium reagents (DAIRs) have witnessed a resurgence as arylating reagents, especially under photoinduced conditions. However, reactions proceeding through electron donor-acceptor (EDA) complex formation with DAIRs are restricted to electron-rich reacting partners serving as donors due to the well-known cage effect. We discovered a practical and high-yielding visible-light-induced EDA platform to generate aryl radicals from the corresponding DAIRs and use them to synthesize key chalcogenides. In this process, an array of DAIRs and dichalcogenides react in the presence of 1,4 diazabicyclo[2.2.2]octane (DABCO) as a cheap and readily available donor, furnishing a variety of di(hetero)aryl and aryl/alkyl chalcogenides in good yields. The method is scalable, features a broad scope with good yields, and operates under open-to-air conditions. The photoinduced chalcogenation technology is suitable for late-stage functionalizations and disulfide bioconjugations and facilitates access to biologically relevant thioesters, dithiocarbamates, sulfoximines, and sulfones. Moreover, the method applies to synthesizing diverse pharmaceuticals, such as vortioxetine, promazine, mequitazine, and dapsone, under amenable conditions.

Transition-Metal-Free C-Diarylations to Reach All-Carbon Quaternary Centers

Herein, we disclose a convenient protocol for the α-diarylation of carbon nucleophiles to yield heavily functionalized quaternary products. Diaryliodonium salts are utilized to transfer both aryl groups under transition-metal-free conditions, which enables an atom-efficient and high-yielding method with broad functional group tolerance. The methodology is amenable to a wide variety of carbon nucleophiles and can be utilized in late-stage functionalization of complex arenes. Furthermore, it is compatible with a new class of zwitterionic iodonium reagents, which gives access to phenols with an ortho-quaternary center. The diarylated products bear an ortho-iodo substituent that can be utilized in further transformations, including the formation of novel, functionalized six-membered cyclic iodonium salts.

Synthesis and characterization of mesoporous silica supported metallosalphen-azobenzene complexes: efficient photochromic heterogeneous catalysts for the oxidation of cyclohexane to produce KA oil

The oxidation of cyclohexane to produce KA oil (cyclohexanone and cyclohexanol) is important industrially but faces challenges such as low cyclohexane conversion at high KA oil selectivity, and difficult catalyst recyclability. This work reports the synthesis and evaluation of new heterogeneous catalysts consisting of Co(ii), Mn(ii), Ni(ii) and Cu(ii) salphen-azobenzene complexes [ML1] immobilized on amino-functionalized mesoporous silica (SBA-15, MCM-41, MCM-48) through coordination bonding. In the first step, the salphen-azobenzene ligand was synthesized and complexed with Co, Mn, Ni and Cu metal ions. In the second step, aminopropyltriethoxysilane (APTES) was grafted onto the surface of different types of commercial mesoporous silica. The immobilization of [ML1] onto the mesoporous silica surface and the thermal stability of the obtained materials were confirmed using different characterization techniques such as FT-IR, powder XRD, SEM, TEM, BET, and TGA. The obtained results revealed high dispersion of [ML1] through the silica surface. The catalytic activity of the prepared materials Silica-N-ML1 was evaluated on the cyclohexane oxidation to produce KA oil using various oxidants. The cis-trans isomerization of the azobenzene upon UV irradiation was found to affect the catalytic performance of Silica-N-ML1. The cis isomer of SBA-15-N-CoL1 exhibited the highest cyclohexane conversion (93%) and KA selectivity (92%) under mild conditions (60 °C, 6 h) using m-CPBA as oxidant. Moreover, The SBA-15-N-CoL1 showed high stability during four successive cycles.

Modular Synthesis of Tripeptide Analogs with an Aminobitriazole Skeleton Using Diynyl Benziodoxolone as a Trivalent Platform

A new synthesis method of tripeptide analogs with an aminobitriazole skeleton was proposed. The method involves assembling three amino acid-derived modules at the amino group site and onto a triisopropylsilyl diynyl benziodoxolone by copper-catalyzed electrophilic diynylation of amino acid-derived sulfonamides, chemoselective azide-alkyne cycloadditions with amino acid-derived azides, and deprotection. Various complex aminobitriazoles substituted with pyrene, nucleoside, and N-acetylglucosamine were also synthesized. The produced aminobitriazoles have three sp3 chiral centers and a C-N axial chirality.

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

Hypervalent Iodine Amino Acid Building Blocks for Bioorthogonal Peptide Macrocyclization

Ethynylbenziodoxol(on)es (EB(X)xs) reagents have emerged as useful reagents for peptide/protein modification due to their versatile reactivity and high selectivity. Herein, we report the successful introduction of ethynylbenziodoxoles (EBxs) on different amino acid building blocks (Lys/Orn/Dap), and show their compatibility with both solid phase peptide synthesis (SPPS) and solution phase peptide synthesis (SPS). The selective incorporation of the EBx core into peptide sequences enable efficient macrocyclizations under mild conditions for the synthesis of topologically unique cyclic and bicyclic peptides.

Manganese-Mediated Electrochemical Oxidation of Thioethers to Sulfoxides Using Water as the Source of Oxygen Atoms

Oxygen-atom transfer reactions are a prominent class of synthetic redox reactions that often use high-energy oxygen-atom donor reagents. Electrochemical methods can bypass these reagents by using water as the source of oxygen atoms through pathways involving direct or indirect (mediated) electrolysis. Here, manganese porphyrins and related mediators are shown to be effective molecular electrocatalysts for selective oxidation of thioethers to sulfoxides, without overoxidation to the sulfone. The reactions proceed by proton-coupled oxidation of a MnIII-OH2 species to generate a MnIV-OH and MnV═O species. This methodology is compared to direct electrolysis methods initiated by single-electron oxidation of the thioether, and chloride-mediated electrochemical oxidation of thioethers. The Mn-mediated reactions operate at lower applied potential and exhibit improved substrate scope and functional group compatibility relative to direct electrolysis, and the tunability of the Mn-based mediators allows for improved performance relative to chloride-mediated electrolysis. An electrochemical parallel screening platform is developed and applied to a library of pharmaceutically relevant thioethers.

Photocatalyst-Free Visible Light-Induced C(sp2)-H Arylation of Quinoxalin-2(1H)-ones and Coumarins

Herein, we describe a visible light-induced C(sp2)-H arylation method for quinoxalin-2(1H)-ones and coumarins using iodonium ylides without the need for external photocatalysts. The protocol demonstrates a broad substrate scope, enabling the arylation of diverse heterocycles through a simple and mild procedure. Furthermore, the photochemical reaction showcases its applicability in the efficient synthesis of biologically active molecules. Computational investigations at the CASPT2//CASSCF/PCM level of theory revealed that the excited state of quinoxalin-2(1H)-one facilitates electron transfer from its π bond to the antibonding orbital of the C-I bond in the iodonium ylide, ultimately leading to the formation of an aryl radical, which subsequently participates in the C-H arylation process. In addition, our calculations reveal that during the single-electron transfer (SET) process, the C-I bond cleavage in iodonium ylide and new C-C bond formation between resultant aryl radical and cationic quinoxaline species take place in a concerned manner. This enables the arylation reaction to efficiently proceed along an energy-efficient route.

Advancing carbohydrate functionality: The role of hypervalent iodine

Hypervalent iodine reagents have undergone significant development and widespread application in the functionalization of carbohydrates. This is primarily attributed to their exceptional properties, including mildness, ease of handling, high selectivity, environmental friendliness, and stability. This review aims to emphasize the utilization of hypervalent iodine compounds in the functionalization of carbohydrates. The present article covers various aspects, including glycal functionalization, C-H or N-H insertion reactions, O-arylations, C-2 deoxy-2-iodo glycoconjugates, iminosugars, and C3-oxo-glycals, achieved through the use of hypervalent iodine reagents/catalysts. Additionally, it explores hypervalent iodine-mediated bioactive 1,3,5-trioxocane synthesis followed by rare sugars synthesis.

Electrocatalytic continuous flow chlorinations with iodine(I/III) mediators

Electrochemistry offers tunable, cost effective and environmentally friendly alternatives to carry out redox reactions with electrons as traceless reagents. The use of organoiodine compounds as electrocatalysts is largely underdeveloped, despite their widespread application as powerful and versatile reagents. Mechanistic data reveal that the hexafluoroisopropanol assisted iodoarene oxidation is followed by a stepwise chloride ligand exchange for the catalytic generation of the dichloroiodoarene mediator. Here, we report an environmentally benign iodine(I/III) electrocatalytic platform for the in situ generation of dichloroiodoarenes for different reactions such as mono- and dichlorinations as well as chlorocyclisations within a continuous flow setup.

Palladium-Catalyzed Tsuji-Trost-Type Reaction of 3-Indolylmethylacetates with O, and S Soft Nucleophiles

The chemical valorization of widespread molecules in renewable sources is a field of research widely investigated in the last decades. In this context, we envisaged that indole-3-carbinol, present in different Cruciferae plants, could be a readily available building block for the synthesis of various classes of indoles through a palladium-catalyzed Tsuji-Trost-type reaction with O and S soft nucleophiles. The regiochemical outcome of this high-yielding functionalization shows that the nucleophilic substitution occurs only at the benzylic position. Interestingly, with this protocol, the sulfonyl unit could be appended to the indole nucleus, providing convenient access to new classes of molecules with potential bioactivity.

Intermolecular α-Functionalization of Benzylamides with N-Nucleophiles via Oxidative Umpolung: Synthesis of Tetrasubstituted 3,3'-Oxindoles

A hypervalent iodine-mediated intermolecular α-umpolung reaction between α-aryl- or alkyl-substituted amides and benzotriazoles or purine derivatives as N-centered nucleophiles has been established. The reaction involves sequential intra/intermolecular oxidative C-N couplings in a controlled manner, affording tetrasubstituted 3,3'-oxindoles in moderate to good yields. This approach efficiently addresses the challenges in constructing tetrasubstituted carbon centers via α-umpolung functionalizations of carbonyl compounds and serves as a new strategy for synthesizing biologically important 3,3'-disubstituted oxindoles.

Oxidation of benzylic alcohols to carbonyls using N-heterocyclic stabilized λ3-iodanes

We present N-heterocycle-stabilized iodanes (NHIs) as suitable reagents for the mild oxidation of activated alcohols. Two different protocols, both involving activation by chloride additives, were used to synthesize benzylic ketones and aldehydes without overoxidation in up to 97% yield. Based on MS experiments an activated hydroxy(chloro)iodane is proposed as the reactive intermediate.

Hypervalent Iodine Promoted Selective [2 + 2 + 1] Cycloaddition of Aromatic Ketones and Methylamines: A One-Pot Access to 1-Pyrrolines

Herein, a versatile highly regioselective three-component annulation of simple aromatic ketones and methylamines using a hypervalent iodine reagent for polyarylated 1-pyrrolines has been described in good to excellent yields. Meanwhile, unsymmetrical 1-pyrroline isomers could be realized and synthesized. Such an intriguing one-pot two-step tandem assembly strategy with green conditions and high regioselectivity shows predictable inspiration in related annulation reactions.

Divergent role of PIDA and PIFA in the AlX3 (X = Cl, Br) halogenation of 2-naphthol: a mechanistic study

The reaction mechanism for the chlorination and bromination of 2-naphthol with PIDA or PIFA and AlX3 (X = Cl, Br), previously reported by our group, was elucidated via quantum chemical calculations using density functional theory. The chlorination mechanism using PIFA and AlCl3 demonstrated a better experimental and theoretical yield compared to using PIDA. Additionally, the lowest-energy chlorinating species was characterized by an equilibrium of Cl-I(Ph)-OTFA-AlCl3 and [Cl-I(Ph)][OTFA-AlCl3], rather than PhICl2 being the active species. On the other hand, bromination using PIDA and AlBr3 was more efficient, wherein the intermediate Br-I(Ph)-OAc-AlBr3 was formed as active brominating species. Similarly, PhIBr2 was higher in energy than our proposed species. The reaction mechanisms are described in detail in this work and were found to be in excellent agreement with the experimental yield. These initial results confirmed that our proposed mechanism was energetically favored and therefore more plausible compared to halogenation via PhIX2.

Decennary Update on Oxidative-Rearrangement Involving 1,2-Aryl C-C Migration Around Alkenes: Synthetic and Mechanistic Insights

In recent years, numerous methodologies on oxidative rearrangements of alkenes have been investigated, that produce multipurpose synthons and heterocyclic scaffolds of potential applications. The present review focused on recently established methodologies for oxidative transformation via 1,2-aryl migration in alkenes (2013-2023). Special emphasis has been placed on mechanistic pathways to understand the reactivity pattern of different substrates, challenges to enhance selectivity, the key role of different reagents, and effect of different substituents, and how they affect the rearrangement process. Moreover, synthetic limitations and future direction also have been discussed. We believe, this review offers new synthetic and mechanistic insight to develop elegant precursors and approaches to explore the utilization of alkene-based compounds for natural product synthesis and functional materials.

Preparation of a benziodazole-type iodine(III) compound and its application as a nitrating reagent for synthesis of furazans via a copper-catalyzed cascade process

The existing hypervalent I(III) reagents bearing ONO2 group are limited in types and their applications primarily focused on the nitrooxylation reactions featuring a fully-exo fashion. Herein, a benziodazole-type O2NO-I(III) compound was prepared and its reaction with β-monosubstituted enamines in the presence of CuI could trigger a radical nitration/cyclization/dehydration cascade to provide a series of less explored but biologically interesting furazan heterocycles. Mechanistically, the benziodazole-type O2NO-I(III) compound acts as a nitrating reagent and incorporates its NO moiety into the final furazan product in a fully-endo model, a process of which was proposed to involve nitration, cyclization and dehydration.

PhI(OAc)2-Promoted 1,2-Transfer Reaction between 1,1-Disubstituted Allylic Alcohols and Thiophenols

The PhI(OAc)2-promoted 1,2-transfer reaction between allylic alcohols and thiophenols, conducted in an argon atmosphere, has proven to be effective in producing β-carbonyl sulfides from 1,1-disubstituted allylic alcohols in high yields. This method offers a fast and efficient way to synthesize β-carbonyl sulfides, which are valuable intermediates in organic synthesis. This discussion focuses on the effects of the oxidizer, temperature, and solvent on the reaction. A proposed tentative mechanism for this reaction is also discussed.

Hypervalent Iodine-Catalyzed Fluorination of Diene-Containing Compounds: A Computational Study

Studies have shown that the incorporation of fluorine into materials can improve their properties, but C-F bonds are not readily formed in nature. Although some researchers have studied the reaction of fluorinating alkenes catalyzed by hypervalent iodine, far too little attention has been paid to its reaction mechanism. This study aimed to explore the mechanism of the hypervalent iodine-catalyzed 1,4-difluorination of dienes. We found that the catalyst is favorable for the activation of C1=C2 double bonds through halogen bonds, and then two HFs interact with one F atom in the catalyst via hydrogen bonds, resulting in the cleavage of I-F bonds and the formation of [F-H∙∙∙F]-. Subsequently, the catalyst interacts with C1, and the roaming [F-H···F]- attacks C4 from the opposite side of the catalyst. After the fluorination step is completed, the nucleophile F- substitutes the catalyst via the SN2 mechanism. Our calculations demonstrated that the interaction between HF and F- is favorable for the stabilization of the transition state within the fluorination process for which the presence of two HFs in the reaction is the best. We also observed that [F-H∙∙∙F]- attacking C4 from the opposite side of the catalyst is more advantageous than attacking from the same side. This study therefore offers a novel perspective on the mechanism of the hypervalent iodine-catalyzed fluoridation of dienes.

Predicting bond dissociation energies of cyclic hypervalent halogen reagents using DFT calculations and graph attention network model

Although hypervalent iodine(III) reagents have become staples in organic chemistry, the exploration of their isoelectronic counterparts, namely hypervalent bromine(III) and chlorine(III) reagents, has been relatively limited, partly due to challenges in synthesizing and stabilizing these compounds. In this study, we conduct a thorough examination of both homolytic and heterolytic bond dissociation energies (BDEs) critical for assessing the chemical stability and functional group transfer capability of cyclic hypervalent halogen compounds using density functional theory (DFT) analysis. A moderate linear correlation was observed between the homolytic BDEs across different halogen centers, while a strong linear correlation was noted among the heterolytic BDEs across these centers. Furthermore, we developed a predictive model for both homolytic and heterolytic BDEs of cyclic hypervalent halogen compounds using machine learning algorithms. The results of this study could aid in estimating the chemical stability and functional group transfer capabilities of hypervalent bromine(III) and chlorine(III) reagents, thereby facilitating their development.

Rh(III)-catalyzed atroposelective C-H alkynylation of 1-aryl isoquinolines with hypervalent iodine-alkyne reagents

An efficient Rh(III)-catalyzed enantioselective C-H alkynylation of isoquinolines is disclosed. The C-H alkynylation of 1-aryl isoquinolines with hypervalent iodine-alkyne reagents proceeded in DMA at room temperature in the presence of 2.5 mol% chiral SCpRh(III) complex along with 20 mol% AgSbF6, providing axially chiral alkynylated 1-aryl isoquinolines in excellent yields (up to 93%) and enantioselectivity (up to 95% ee). The diverse transformations of the product further enhance the potential utility of this reaction.

Hypervalent iodine-catalyzed amide and alkene coupling enabled by lithium salt activation

Hypervalent iodine catalysis has been widely utilized in olefin functionalization reactions. Intermolecularly, the regioselective addition of two distinct nucleophiles across the olefin is a challenging process in hypervalent iodine catalysis. We introduce here a unique strategy using simple lithium salts for hypervalent iodine catalyst activation. The activated hypervalent iodine catalyst allows the intermolecular coupling of soft nucleophiles such as amides onto electronically activated olefins with high regioselectivity.

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.

Visible Light-Induced Reactions of Diazo Compounds and Their Precursors

In recent years, visible light-induced reactions of diazo compounds have attracted increasing attention in organic synthesis, leading to improvement of existing reactions, as well as to the discovery of unprecedented transformations. Thus, photochemical or photocatalytic generation of both carbenes and radicals provide milder tools toward these key intermediates for many valuable transformations. However, the vast majority of the transformations represent new reactivity modes of diazo compounds, which are achieved by the photochemical decomposition of diazo compounds and photoredox catalysis. In particular, the use of a redox-active photocatalysts opens the avenue to a plethora of radical reactions. The application of these methods to diazo compounds led to discovery of transformations inaccessible by the classical reactivity associated with carbenes and metal carbenes. In most cases, diazo compounds act as radical sources but can also serve as radical acceptors. Importantly, the described processes operate under mild, practical conditions. This Review describes this subfield of diazo compound chemistry, particularly focusing on recent advancements.

Oxidative hydrolysis of aliphatic bromoalkenes: scope study and reactivity insights

We have developed an operationally simple method for the synthesis of dialkyl α-bromoketones from bromoalkenes by utilizing a hypervalent iodine-catalyzed oxidative hydrolysis reaction. This catalytic process provides both symmetrical and unsymmetrical dialkyl bromoketones with moderate yields across a broad range of bromoalkene substrates. Our studies also reveal the formation of Ritter-type side products by an alternative reaction pathway.

Accessing elusive σ-type cyclopropenium cation equivalents through redox gold catalysis

Cyclopropenes are the smallest unsaturated carbocycles. Removing one substituent from cyclopropenes leads to cyclopropenium cations (C3+ systems, CPCs). Stable aromatic π-type CPCs were discovered by Breslow in 1957 by removing a substituent on the aliphatic position. In contrast, σ-type CPCs-formally accessed by removing one substituent on the alkene-are unstable and relatively unexplored. Here we introduce electrophilic cyclopropenyl-gold(III) species as equivalents of σ-type CPCs, which can then react with terminal alkynes and vinylboronic acids. With catalyst loadings as low as 2 mol%, the synthesis of highly functionalized alkynyl- or alkenyl-cyclopropenes proceeded under mild conditions. A class of hypervalent iodine reagents-the cyclopropenyl benziodoxoles (CpBXs)-enabled the direct oxidation of gold(I) to gold(III) with concomitant transfer of a cyclopropenyl group. This protocol was general, tolerant to numerous functional groups and could be used for the late-stage modification of complex natural products, bioactive molecules and pharmaceuticals.

Rh-Catalyzed α-Arylation of Cyclic 1,3-Dicarbonyls with Benzocyclobutenols Enabled by a Cyclic Iodonium Ylide Strategy

To date, the general and catalytic α-arylation of cyclic 1,3-dicarbonyls remains elusive. We now report the first Rh-catalyzed α-arylation of cyclic 1,3-dicarbonyls with benzocyclobutenols through a cyclic iodonium ylide strategy. Our strategy represents a good solution for the previously challenging α-arylation of cyclic 1,3-dicarbonyls with sterically demanding aryl partners, which is especially appropriate for structurally unique heteroaromatic 1,3-dicarbonyls. Our approach features mild conditions, readily available starting materials, high yields, excellent functional group-tolerance, and simple operation, providing expedient access toward medically important 2-aryl (hetero)cyclic 1,3-dicarbonyls. The practicality of this approach is demonstrated by the gram-scale synthesis, one-pot synthesis, and numerous downstream transformations.

Silver-Catalyzed Coupling of Ethynylbenziodoxolones with CO2 and Amines to Afford O-β-Oxoalkyl Carbamates

A novel three-component coupling reaction of ethynylbenziodoxolones (EBXs) with CO2 and amines has been achieved via silver catalysis, thereby providing an efficient method for the construction of a range of structurally diverse and valuable O-β-oxoalkyl carbamates. The transformation proceeds under mild reaction conditions and exhibits a wide substrate scope and good functional group compatibility. In addition, this strategy could be extended to the synthesis of α-acyloxyketones using carboxylic acids as the nucleophiles to react with EBXs.

Amino- and Alkoxybenziodoxoles: Facile Preparation and Use as Arynophiles

We report here on the facile synthesis of amino- and alkoxy-λ3-iodanes supported by a benziodoxole (BX) template and their use as arynophiles. The amino- and alkoxy-BX derivatives can be readily synthesized by reacting the respective amines or alcohols with chlorobenziodoxole in the presence of a suitable base. Unlike previously known nitrogen- and oxygen-bound iodane compounds, which have primarily been employed as electrophilic group transfer agents or oxidants, the present amino- and alkoxy-BX reagents manifest themselves as nucleophilic amino and alkoxy transfer agents toward arynes. This reactivity leads to the aryne insertion into the N-I(III) or O-I(III) bond to afford ortho-amino- and ortho-alkoxy-arylbenziodoxoles, iodane compounds nontrivial to procure by existing methods. The BX group in these insertion products exhibits excellent leaving group ability, enabling diverse downstream transformations.

Visible-Light-Triggered Synthesis of N-α-Ketoacylated Sulfoximines by Denitrogenative and Oxidative Functionalization of Vinyl Azides

We have introduced a sulfoximidation reaction initiated by visible light between α-phenyl vinyl azides and NH-sulfoximines. The cost-effective and readily accessible hypervalent iodine reagent (PIDA) easily promoted the oxidative sulfoximidation process to afford N-α-ketoacylated sulfoximines in good to high yields, involving the formation of two new C-O bonds and one C-N bond. Additionally, the protocol offers noteworthy advantages, including its metal-free and photocatalyst-free reaction and its broad substrate compatibility.

Assembly and Disassembly of Supramolecular Hypervalent Iodine Macrocycles via Anion Coordination

This study explores the dynamic self-assembly and disassembly of hypervalent iodine-based macrocycles (HIMs) guided by secondary bonding interactions. The reversible disassembly and reassembly of HIMs are facilitated through anion binding via the addition of tetrabutylammonium (TBA) salts or removal of the anion by the addition of silver nitrate. The association constants for HIM monomers with TBA(Cl) and TBA(Br) are calculated and show a correlation with the strength of the iodine-anion bond. A unique tetracoordinate hypervalent iodine-based compound was identified as the disassembled monomer. Last, the study reveals the dynamic bonding nature of these macrocycles in solution, allowing for rearrangement and participation in dynamic bonding chemistry.

Alkoxy Diazomethylation of Alkenes by Photoredox-Catalyzed Oxidative Radical-Polar Crossover

Herein, we present the discovery and development of the first photoredox-catalyzed alkoxy diazomethylation of alkenes with hypervalent iodine reagents and alcohols. This multicomponent process represents a new disconnection approach to diazo compounds and is featured by a broad scope, mild reaction conditions, and excellent selectivity. Key to the process was the generation of diazomethyl radicals, which engaged alkenes and alcohols in an inter- and intramolecular fashion by a photoredox-catalyzed oxidative radical-polar crossover leading to unexplored β-alkoxydiazo compounds. The synthetic utility of such diazo compounds was demonstrated with a series of transformations involving C-H, N-H, and O-H insertions as well as in the construction of complex sp3-rich heterocycles.