Hypervalent Iodine Research Articles

Chemoenzymatic Cyclization by Vanadium Chloroperoxidase for Synthesis of 4-Hydroxyisochroman-1-Ones.

4-Hydroxyisochroman-1-ones belong to the class of the secondary metabolite 3,4-dihydroisocoumarins. They exhibit a wide range of biological activities. These compounds can be synthesized through halocyclization using hypervalent iodine species or N-bromosuccinimide, followed by hydrolysis. Nonetheless, the reactions required specific conditions and generated toxic byproducts. In this study, Curvularia inaequalis vanadium chloroperoxidase (CiVCPO) catalyzed the chemoenzymatic cyclization of 2-vinylbenzoic acids with different electron-donating groups (1 a-1 e) to produce good yields of 4-hydroxyisochroman-1-ones (3 a-3 e) by adding KBr and H2O2 in citrate buffer (pH 5). The reaction mixture contained 30 % DMSO to improve substrate solubility without enzyme activity loss. The condition is more environmentally friendly than chemical methods. Therefore, it offers an alternative approach for synthesizing 4-hydroxyisochroman-1-ones.

Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts.

Diaryliodonium salts have become widely recognized as arylating agents in the last two decades. Both, symmetrical and unsymmetrical forms of these salts serve as effective electrophilic arylating reagents in various organic syntheses. The use of diaryliodoniums in C-C and carbon-heteroatom bond formations, particularly under metal-free conditions, has further enhanced the popularity of these reagents. In this review, we concentrate on various arylation reactions involving carbon and other heteroatoms, encompassing rearrangement reactions in the absence of any metal catalyst, and summarize advancements made in the last five years.

Hypervalent Iodine Catalyzed Cascade C−H Functionalization: An Atom‐Economical Strategy to Access Diverse 2‐Substituted Benzothiazoles

AbstractA metal‐free 4,5‐difluoro‐2‐iodobenzoic acid catalyzed C−H functionalization strategy has been developed for the synthesis of 2‐(hetero)aryl benzothiazoles from aryl isothiocyanates and unfunctionalized arenes/thiophenes/furans at room temperature. The procedure entails one‐pot cascade carbon−carbon and carbon−sulfur bond formation facilitated by triflic acid, which serves as both a Brønsted acid and a ligand source at the in situ generated I(III) center. This process is atom‐economical and offers benefits over existing protocols for synthesizing benzothiazoles in terms of ease of use, eco‐friendliness, and not requiring the typical use of aryl aldehyde/carboxylic acid precursors. Mechanistic studies were carried out, and the synthetic utility of the protocol was demonstrated for the synthesis of the benzothiazole‐based antitumor drug GW‐610.

Nitrogenation of Alkynes with Nitrones to Prepare Functionalized [1,4]Oxazinones through Csp-Csp2 Bond Cleavage.

Herein, we report a novel strategy of hypervalent iodine(III) compound-mediated selective Csp-Csp2 bond cleavage of alkynes and C═N/N-O bond cleavage of nitrones and recombination of C-C/C-O/C-N multiple bonds to access various functionalized [1,4]oxazinones bearing a vicinal carbon stereocenter in good yields and high diastereoselectivity. Mechanistic studies revealed that the reaction undergoes a domino [4 + 3] cycloaddition, 1,3-rearrangement of N-O bond, intramolecular cyclization, dearomatization, and rearomatization over four steps in a single flask. The present method features good functional group tolerance, broad substrate scope, and C-C/C═N/N-O multiple bonds cleavage and recombination.

Recent Applications of Sulfonium Salts in Synthesis and Catalysis.

The use of sulfonium salts in organic synthesis has experienced a dramatic increase during the last years that can arguably be attributed to three main factors; the development of more direct and efficient synthetic methods that make easily available sulfonium reagents of a wide structural variety, their intrinsic thermal stability, which facilitates their structural modification, handling and purification even on large scale, and the recognition that their reactivity resembles that of hypervalent iodine compounds and therefore, they can be used as replacement of such reagents for most of their uses. This renewed interest has led to the improvement of already existing reactions, as well as to the discovery of unprecedented transformations; in particular, by the implementation of photocatalytic protocols. This review aims to summarize the most recent advancements on the area focusing on the work published during and after 2020. The scope of the methods developed will be highlighted and their limitations critically evaluated.

Enantioselective Synthesis of Azatricycles via Post-Ugi Cyclizations.

We report a new method to create enantioenriched azatricycles using chiral α-amino acids in a two-step process after an Ugi reaction. Amino acids are great building blocks for making pure chiral molecules. Using chiral natural molecules in multicomponent reactions (MCRs) helps increase their variety by adding new chiral centers. The Ugi reaction, discovered by Ivar Karl Ugi in 1959, is a versatile MCR that helps create complex molecular structures and natural products through additional transformations called post-Ugi modifications. Designing these modifications requires selecting the right amine, acid, aldehyde/ketone, and isocyanide. Amino acids, with their primary amine and carboxylic acid groups and a pre-existing chiral center, are ideal for making diverse and selective post-Ugi modifications. Our method uses ipso-cyclization and aza-Michael cyclization with hypervalent iodine to create various azaspirotricyclic structures with high stereocontrol. This approach works well with different substrates and shows promise for further development in drug discovery.

Metal‐Free Generation of Acyl Fluorides via Activation of Cyclopropyl Esters using a Hypervalent Iodine(III) Species and Selectfluor

AbstractAn efficient method for the activation of non‐activated cyclopropyl esters is developed using a hypervalent iodine(III) species and Selectfluor for the generation of acyl fluoride intermediates. The reactive acyl fluoride intermediate is smoothly transformed into various functional groups such as amides, esters, thioesters, and ketones depending on the nucleophile used in the in‐situ transformation. Utilizing the oxidation process of an iodoarene by Selectfluor, the activation is improved from a stoichiometric to catalytic protocol. Furthermore, the activation is employed in the chemoselective activation of target cyclopropyl ester in the presence of other ester moieties.

Merging the Reactivity of (Pseudo)cyclic Hypervalent Iodine Reagents and Carbenes or Carbenoids

AbstractIn this short review, we present applications merging the reactivity of cyclic hypervalent iodine reagents with carbenes and carbenoids developed in the period 2014–2024. The use of more stable cyclic hypervalent iodine reagents has led to major advances in this area. The combination of iodine(III) chemistry with carbenes or carbenoids enables new disconnections that are not possible using classical reactivity. Both the use of hypervalent iodine compounds as partners in reactions with metal carbenes and as reagents combining the reactivity of iodine(III) and carbenes in a single molecule to give carbyne equivalents are discussed in this review.1 Introduction2 Transfer of Fluorinated Groups (F, CF3)3 Oxy- and Aminoalkyn(en)ylation3.1 Oxy- and Aminoalkynylation with Acceptor-Substituted Diazo Compounds3.2 Oxyalkenylation with Acceptor-Substituted Diazo Compounds3.3 Oxyalkynylation with Acceptor-Acceptor-Substituted Diazo Compounds4 Carbyne Equivalents4.1 Diazo-Based Reagents4.2 Sulfur Ylide Based Reagents5 Conclusion

Hypervalent Iodine‐Mediated Regioselective Dearomatization of Non‐Activated Arenes

AbstractThe dearomatizations of non‐activated arenes, particularly those under mild reaction conditions, are highly desired transformations in organic synthesis due to their power in converting flat aromatic rings into three‐dimensional frameworks. Although hypervalent iodine (HVI)‐mediated dearomatization of phenol derivatives has developed rapidly, HVI‐mediated dearomatization of non‐activated arenes remains an urgent and challenging task. To fulfil this task, in this work, we established an HVI‐mediated oxidative dearomatization of non‐activated arenes by using biphenylureas and N‐ or O‐nucleophiles as reactants. This electrophilic dearomatization (DEAr) process is highly regioselective, which enabled different N‐ and O‐nucleophiles to react at the distal C4‐position of the phenyl ring, thus generating dearomative spiro‐products in a single step under mild conditions with wide substrate scope (43 examples, 22%–76% yield). This approach not only provides a successful example for dearomatization of non‐activated arenes under mild reaction conditions, but also has overcome the challenges in HVI‐mediated dearomatization of non‐activated arenes, which will enrich the chemistry of dearomatization.

Arylation of Secondary Phosphines with Diaryliodonium Salts under Metal‐Free and Non‐Photochemical Conditions

A new, efficient, as well as metal‐ and irradiation‐free approach for the direct arylation of secondary phosphines has been developed. The reaction employs diaryliodonium salts as electrophilic aryl‐transfer reagents, effecting the P–Ar bond‐formation in a single step, under mild conditions, using t‐BuOK as a base and DMSO as a solvent, at room temperature. The protocol furnishes expedient access to diverse unsymmetrical triarylphosphines and, upon a one‐pot oxidation, the corresponding triarylphosphine oxides. Experimental and computational studies support the inner sphere aryl‐transfer mechanism through a reductive coupling at the hypervalent iodine center. The calculations also point to a key role played by potassium ions, providing extra stabilization to the P–C bond‐forming transition state by binding the reactants via cation‐π interactions.

Density functional theory investigation of hypervalent iodine KICl2 passivation at PbI2 vacancy sites on the MAPbI3 surface

This study explores the impact of hypervalent KICl2 passivation on the electronic properties and stability of MAPbI3 perovskite slabs with PbI2 vacancies using density functional theory (DFT). Adsorption energy calculations reveal that KICl2 exhibits stronger binding energy (−4.73 eV) compared to O2 (−3.32 eV) and H2O (−3.28 eV), indicating higher stability on the MAPbI3 surface. However, due to the potential for KICl2 to dissociate into KCl and ICl in solution, these compounds were also evaluated as alternative passivation agents. The surface free energy of the KICl2-passivated slab is the lowest among the configurations studied, further confirming its enhanced surface stability. The projected density of states (PDOS) and band structure analyses show that KICl2 passivation introduces defect states near the conduction band minimum (CBM), reducing the bandgap from 1.89 eV (clean surface) to 1.81 eV. These defect states, contributed by Cl-3p and I-5p orbitals, enhance charge separation, potentially improving carrier collection. In contrast, the KCl-ICl passivated surface exhibits flat states near valence band edge, which could increase hole density and reduce hole mobility. Optical absorption calculations indicate that the KICl2-passivated surface shows stronger absorption in the 3–7 eV range. These findings suggest that KICl2 passivation improves both the electronic properties and surface stability of MAPbI3, offering a promising strategy for enhancing perovskite solar cell efficiency.

Taming Tethered Nitreniums for Alkene Functionalization Reactions.

We present the first examples of amino-trifluoroacetoxylations of alkenes using N-alkoxy carbamate tethers. Hypervalent iodine oxidants mediate this transformation, providing a "green" alternative to existing intramolecular amino-hydroxylation protocols which use toxic metals such as osmium. In all cases examined, the reaction is regioselective and stereospecific, with the geometry of the starting alkene controlling the diastereomeric outcome. By analogy to prior art and from our own observations, we posit that a transient nitrenium species serves as a key intermediate.

Oxidative Remote Aryl Rearrangement of N-Cinnamyl-N-alkoxybenzyl Sulfonamides Using Hypervalent Iodine(III).

An oxidative remote aryl rearrangement of N-cinnamyl-N-alkoxybenzyl sulfonamides with a hypervalent iodine(III) compound was developed to furnish 5,6-disubstituted 1,3-oxazinanes in high yields. This reaction proceeded through the dearomatization of the alkoxybenzene ring on the benzyl group, which acts as a good aryl donor, inducing the regioselective installation of the aryl group and the oxygen atom via cascade transformation. An enantioselective oxidative remote aryl rearrangement using C2-symmetrical chiral iodoarene gave enantioenriched products with high enantioselectivity.

Umpolung Phosphorylation of Tyrosine via 1,2-Phospha-Brook Rearrangement.

Phosphorylated tyrosine is a fundamental building block of bioactive peptides and proteins. However, the chemoselective phosphorylation of tyrosine over other nucleophilic amino acid residues in unprotected peptides remains a significant challenge. Here we report an umpolung strategy that converts the C-terminal tyrosine into an electrophilic spirolactone cyclohexadienone motif through hypervalent iodine oxidation, followed by a 1,2-phospha-Brook rearrangement using phosphite diesters as nucleophilic phosphoryl donors. This reaction proceeds chemoselectively at the tyrosine phenol and is applicable to a wide range of peptide substrates containing various nucleophilic amino acid residues, including serine and threonine.

Synthesis, Material Properties, and Organocatalytic Performance of Hypervalent Iodine(III)-Oxidants in Core–Shell-Structured Magnetic Nanoparticles

Magnetic nanoparticles (MNPs) based on magnetite (Fe3O4) are attractive catalyst supports due to their high surface area, easy preparation, and facile separation, but they lack stability in acidic reaction media. The search for MNPs stable in oxidative acidic reaction media is a necessity if one wants to combine the advantages of MNPs as catalyst supports with those of iodine(III) reagents being environmentally benign oxidizers. In this work, immobilized iodophenyl organocatalysts on magnetite support (IMNPs) were obtained by crossed-linking polymerization of 4-iodostyrene with 1,4-divinylbenzene in the presence of MNPs. The obtained IMNPs were characterized by TGA, IR, SEM, STEM, and HAADF to gain information on catalyst morphology, average particle size (80–100 nm), and their core–shell structure. IMNP-catalysts tested in (i) the α-tosyloxylation of propiophenone 1 with meta-chloroperbenzoic acid (m-CPBA) and (ii) in the oxidation of 9,10-dimethoxyanthracene 3 with Oxone® as the side-oxidant showed a similar performance as reactions using stoichiometric amounts of iodophenyl. The developed IMNPs withstand strong acidic conditions and serve as reusable organocatalysts. They are recyclable up to four times for repeated organocatalytic oxidations with rates of recovery of 80–92%. This is the first example of a—(4-iodophenyl)polystyrene shell—magnetite core-structured organocatalyst withstanding strong acidic reaction conditions.

Practical Synthesis of N-Anilinylphenothiazines Using a Cyclic Hypervalent Iodine Coupling Reagent

AbstractAn improved protocol for the synthesis of N-anilinylphenothiazines based on the coupling reaction of anilines with phenothiazines using cyclic iodine(III) reagent is presented. In the improved method, the product can be isolated and purified without using column chromatography, and the cyclic hypervalent iodine reagent can be quantitatively recovered by aliquot manipulation. The workup procedure presented here is simpler compared to previously reported ones, facilitating large-scale synthesis. The para-selective phenothiazination of nitrogen-containing heterocycles such as hydroquinoline, which is important in pharmacology, was also successfully performed.

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.

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

AbstractMetal‐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.

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.

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.