Iodine(III) Reagents in Radical Chemistry

Visible-Light-Enabled Oxidative Coupling of Alkenes with Dialkylformamides To Access Unsaturated Amides

A practical and direct method for oxidative cross-coupling of alkenes with dialkylformamides is established employing visible-light-enabled photoredox catalysis. This strategy allows efficient access to diverse unsaturated amides under mild reaction conditions. The application of an appropriate diaryliodonium salt was demonstrated to be critical to the success of this process. This catalyst system is well tolerant of a variety of useful functional groups.

Copper-Catalyzed Amino-oxymethylation of Ynamides with N,O-Acetals

A copper-catalyzed 1,2-difunctionalization of ynamides has been developed by using readily available N,O-acetals as the bifunctional reagents. Importantly, contrary to the initially expected 1,2-oxy-aminomethylation reaction, an unprecedented 1,2-amino-oxymethylation has been observed. This reaction is atom-economical and tolerates a broad substrate scope, affording the difunctionalization products in good yield with unique Z configuration.

Unified and practical access to ɤ-alkynylated carbonyl derivatives via streamlined assembly at room temperature

The development of a unified and straightforward method for the synthesis of ɤ-alkynylated ketones, esters, and amides is an unmet challenge. Here we report a general and practical protocol to access ɤ-alkynylated esters, ketones, and amides with diverse substitution patterns enabled by dual-catalyzed spontaneous formation of Csp3–sp3 and Csp3–sp bond from alkenes at room temperature. This directing-group-free strategy is operationally simple, and allows for the straightforward introduction of an alkynyl group onto ɤ-position of carbonyl group along with the streamlined skeleton assembly, providing a unified protocol to synthesize various ɤ-alkynylated esters, acids, amides, ketones, and aldehydes, from readily available starting materials with excellent functional group compatibility.

Alkene Synthesis by Photocatalytic Chemoenzymatically Compatible Dehydrodecarboxylation of Carboxylic Acids and Biomass

Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridine-catalyzed O-H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C-H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase-acridine-cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.

Cu-Mediated arylselenylation of aryl halides with trifluoromethyl aryl selenonium ylides

An unprecedented arylselenylation of aryl halides with trifluoromethyl aryl selenonium ylides in the presence of copper is described. The reaction proceeded at 100-140 °C under ligand- and additive-free conditions for 3-20 h to form a variety of unsymmetrical diaryl selenides in good to high yields. Arylselenylation is easy to operate, has good functional group tolerance, and demonstrates the different reaction profiles of trifluoromethyl aryl selenonium ylides from the homologous trifluoromethyl aryl sulfonium ylides.

Practical, metal-free remote heteroarylation of amides via unactivated C(sp3)-H bond functionalization

Development of practical methods for the production of multi-functionalized amides is one of the most important topics in both synthetic chemistry and drug discovery. Disclosed herein is a new, efficient, site-selective heteroarylation of amides via C(sp3)-H bond functionalization. Amidyl radicals are directly generated from the amide N-H bonds under mild conditions, which trigger the subsequent 1,5-HAT process. A wide scope of aliphatic amides including carboxamides, sulfonamides, and phosphoramides are readily modified at remote C(sp3)-H bonds by installing diverse heteroaryl groups. Borne out of pragmatic consideration, this protocol can be used for the late-stage functionalization of amides.

A Tunable Trifluoromethyliodonium Reagent

Four complexes of MCl₄ (M=Ti, Zr, Hf) with the hypervalent trifluoromethyl iodine reagent trifluoromethyl-1,3-dihydro-3,3-dimethyl-1,2-benziodoxole (1,=L) are described. With TiCl₄ , an I-O bond cleavage occurs, leading to the formation of the trifluoromethyliodonium alcoholate complexes [Ti₂ Cl₆ (L)₄ ]Cl₂ (2 a) and Ti₂ Cl₈ (L) (2 b). Reactions with ZrCl₄ and HfCl₄ form the complexes ZrCl₄ (L)₂ (3) and HfCl₄ (L)₂ (4), respectively, wherein the original I-O bond is retained and elongated compared to that in free 1. Therefore, the reactivity of 1 can be easily and practically fine-tuned by addition of different metal chlorides, following the order ZrCl₄ /HfCl₄ <TiCl₄ <2 TiCl₄ . Complexes 2 a, 3, and 4 are remarkably bench-stable forms of activated reagent 1, while 2 b is readily accessible in situ. 2 a and 2 b represent the first "real" trifluoromethyliodonium reagents derived from iodanes, that is, with the I-O bond being completely cleaved. The new complexes were shown to be useful for the trifluoromethylation of para-toluenesulfonate under aprotic conditions.

Direct Intermolecular Anti-Markovnikov Hydroazidation of Unactivated Olefins

We herein report a direct intermolecular anti-Markovnikov hydroazidation method for unactivated olefins, which is promoted by a catalytic amount of bench-stable benziodoxole at ambient temperature. This method facilitates previously difficult, direct addition of hydrazoic acid across a wide variety of unactivated olefins in both complex molecules and unfunctionalized commodity chemicals. It conveniently fills a synthetic chemistry gap of existing olefin hydroazidation procedures, and thereby provides a valuable tool for azido-group labeling in organic synthesis and chemical biology studies.

Hypercoordinate iodine for catalytic asymmetric diamination of styrene: insights into the mechanism, role of solvent, and stereoinduction

Stereoselectivity in the asymmetric diamination of styrene catalyzed by chiral hypercoordinate iodine originates from the prochiral face recognition when the substrate binds to the catalyst.

Hypercoordinate iodine has evolved as an impressive class of catalysts for various organic transformations. Extension of this idea to asymmetric applications, such as in the asymmetric difunctionalization of styrene or its derivatives, constitutes an important reaction. In this study, the mechanism and origin of stereoinduction in styrene diamination, with a sulfonimide (HNMs₂) as the diaminating agent and iodoresorcinol (((iPr)₂N(CO)-CH(Me)-O)₂Ar–I) based chiral hypercoordinate iodine as the catalyst, are investigated using density functional theory calculations. The energetically preferred catalytic pathway has been found to involve, among other steps, two very important mechanistic events: (a) the formation of a catalyst–substrate complex by the action of styrene on the catalyst ArI(NMs₂)₂, resulting in the displacement of one of the imidates (NMs₂^–); and (b) a rebound of the departed imidate on the iodine-bound styrene to form an iodonium ion intermediate with a N–C bond. Explicit interaction of the imidate ion with hexafluoroisopropanol (HFIP), used as a solvent additive, lowers the barrier for the formation of the iodonium ion. The P helical fold of the chiral arms of the iodoresorcinol catalyst is found to offer a chiral environment for the reactants. Coordination of the iodine catalyst to the styrene double bond is found to make the benzylic carbon more electrophilic and hence makes it the preferred site for the nucleophilic addition. In the chiral environment of the catalyst, an enhanced polarization of the styrene double bond is noticed when the double bond coordinates through the si prochiral face than the re face. Nucleophilic addition on the re face of the catalyst–substrate complex is associated with a lower activation barrier leading to the experimentally observed S enantiomeric product. The stereoselective model developed in this study can be employed to related asymmetric styrene difunctionalizations using similar hypercoordinate iodine catalysts.

Copper-catalyzed three-component reaction of N-heteroaryl aldehydes, nitriles, and water

An efficient and straightforward method for the synthesis of N-heteroaroyl imides has been successfully developed involving a copper-catalyzed radical-triggered three-component reaction of N-heteroaryl aldehydes, nitriles, and water. Mechanistic studies indicate that the reaction may undergo a radical-triggered Ritter-type reaction in which water serves as the oxygen source for the formation of the C-O bond. The reaction has advantages such as a broad substrate scope for the N-heteroaryl aldehydes, atom economy, and simple operation.

Stereocontrolled Synthesis of Halovinylbenziodoxoles by Hydro- and Iodochlorination of Ethynylbenziodoxoles

We report herein the synthesis of highly substituted and stereochemically well-defined vinylbenziodoxole (VBX) derivatives through hydrochlorination and iodochlorination of ethynylbenziodoxoles. The hydrochlorination is achieved using pyridine hydrochloride as an HCl source in an anti-fashion under mild, open-air conditions to afford a 2-chlorinated VBX product, which serves as a useful building block for the stereoselective synthesis of trisubstituted alkenes. Meanwhile, iodochlorination with iodine monochloride proceeds in an unusual syn-pathway, stereoselectively affording a tetrasubstituted VBX derivative.

Iodine-promoted Intermolecular Dehydrogenation Diamination: Synthesis of Unsymmetrical α,β-Diamido Ketones

Iodine-promoted direct diamination of α,β-unsaturated ketone to form two C-N bonds has been developed starting from chalcone and secondary amine. This reaction was performed in THF at 50 °C in the presence of I₂ and K₂ CO_3. The protocol is metal-free, operationally simple and carried out under mild conditions, providing an effective new way for directing diamination reactions.

On the activation of hypercoordinate iodine(iii) compounds for reactions of current interest

Central to the reactivity of hypercoordinate iodine as a continually emerging compound for organic transformation is its activation by various additives. We wish to present the current understanding on bonding and activation modes under different reaction conditions involving hypercoordinate iodine(iii) compounds.

Electrophilic chloro(ω-alkoxy)lation of alkenes employing 1-chloro-1,2-benziodoxol-3-one: facile synthesis of β-chloroethers

A four-component reaction for electrophilic chloro(ω-alkoxy)lation of alkenes has been described. The stable chloro-iodine(iii) reagent and SOCl2 were used as electrophilic and nucleophilic chlorine sources, respectively. This approach provides a straightforward way to synthesize various useful β-chloro ω-chloroalkyl ethers from a wide range of alkenes, including electron-deficient, aromatic and unactivated alkenes. The synthetic applications of this approach were also explored in some useful transformations.

Access to 2-substituted-2H-indazoles via a copper-catalyzed regioselective cross-coupling reaction

A CuCl catalyzed C-N cross-coupling reaction using commercially available 1H-indazoles with diaryliodonium salts is described. The methodology features ample structural versatility, affording 2-substituted-2H-indazole in good yields and complete N(2)-regiocontrol. Furthermore, the utility of the reaction was demonstrated in the synthesis of a known estrogen receptor β agonist. Mechanistic studies using density functional theory calculations suggested that the complete regioselectivity can be attributed to the only weak base TfO^- in our system which could not deprotonate indazoles, and the catalyst oxidation process would be the rate-determining step.

Synthesis of 4-Iodoisoquinolin-1(2 H)-ones by a Dirhodium(II)-Catalyzed 1,4-Bisfunctionalization of Isoquinolinium Iodide Salts

An efficient Rh₂(II,II)-catalyzed reaction has been developed under mild conditions. This synthetic method proceeds through iodination/oxidation of readily available isoquinolinium iodide salts under aerobic conditions with good to excellent yields. 4-Iodoisoquinolin-1(2 H)-ones are important building blocks for biologically and medicinally important compounds. The developed methodology was applied to the gram-scale synthesis of a key intermediate in the synthesis of the CRTH2 antagonist CRA-680.

Iodine-catalyzed sulfonylation of sulfonyl hydrazides with tert-amines: a green and efficient protocol for the synthesis of sulfonamides

This study provides a direct, sustainable and eco-friendly method for the synthesis of various sulfonamides via the sulfonylation of sulfonyl hydrazides with tert-amines. The method utilizes sulfonyl hydrazides to oxidize and couple with tertiary amines through selective cleavage of C–N bonds. In this reaction, molecular iodine was used as the catalyst and t-butyl hydroperoxide was used as the oxidant.

Sustainable and eco-friendly method for the synthesis of various sulfonamides.

Hypervalent iodine reactions utilized in carbon–carbon bond formations

This review covers recent developments of hypervalent iodine chemistry in dearomatizations, radicals, hypervalent iodine-guided electrophilic substitution, arylations, photoredox, and more.

Solvent-tuned chemoselective carboazidation and diazidation of alkenes via iron catalysis

A solvent-tuned chemoselective carboazidation and diazidation of alkenes with CH₂Cl₂ and TMSN₃ through iron catalysis has been described.

Four-component radical-dual-difunctionalization (RDD) and decarbonylative alkylative peroxidation of two different alkenes with aliphatic aldehydes and TBHP

From difunctionalization of a single alkene to radical-dual-difunctionalization of two different alkenes! A alkylative peroxidation and cross-coupling of two alkenes was established with the aliphatic aldehydes as the alkyl radical source.

Visible-light promoted aerobic difunctionalization of alkenes with sulfonyl hydrazides for the synthesis of β-keto/hydroxyl sulfones

A practical method has been developed for the conversion of alkenes to β-keto/hydroxyl sulfones by their reaction with sulfonyl hydrazides under metal-free conditions. This reaction proceeds through the oxidative addition of alkenes by sulfonyl radicals that are generated by visible-light induced oxidation of sulfonyl hydrazides. Notaly the reaction uses O2 as the terminal oxidant, instead of metal catalysts or oxidants like TBHP, leading to H2O and N2 as the clean by-products. The key features of this reaction include readily available reagents, mild reaction conditions and broad substrate scope.