Photocatalytic Fluoro Sulfoximidations of Styrenes

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.

Photocatalytic Synthesis and Functionalization of Sulfones, Sulfonamides and Sulfoximines

Sulfur(VI)-based functional groups are popular scaffolds in a wide variety of research fields including synthetic and medicinal chemistry, as well as chemical biology. The growing interest in sulfur(VI)-containing molecules has motivated the scientific community to explore new methods to synthesize and modify them. Here, photocatalysis plays a key role granting access to new types of reactivity under mild reaction conditions. In this Perspective, we present a selection of works reported in the last six years focused on the photocatalytic assembly and reactivity of sulfones, sulfonamides, and sulfoximines. We addressed the key synthetic intermediates for each transformation, while discussing limitations and strength points of the protocols. Future directions of the field are finally presented.

A Catalytic Three-Component Aminofluorination of Unactivated Alkenes with Electron-Rich Amino Sources

We present herein a copper-catalyzed three-component aminofluorination of unactivated alkenes with N-bromodialkylamines and readily available nucleophilic fluoride under the assistance of a bidentate auxiliary. This protocol exhibits excellent functional group tolerance toward a wide range of unactivated alkenes and N-bromodialkylamines to furnish the corresponding β-fluoroalkylamines in a highly regio- and diastereoselective manner. The appropriate choice of nucleophilic fluoro source is essential to make this reaction a reality. Further DFT calculations show that the exothermic ion exchange between external fluoride ion and Cu(II) intermediate provides additional driving force to the irreversible migratory insertion, which offsets the unfavorable reaction energetics associated with the subsequent C(sp3)-F reductive elimination. This finding offers a new avenue to catalytic intermolecular aminofluorination of unactivated alkenes with electron-rich amino sources via a remarkable reductive elimination of Cu(III) species to forge the C(sp3)-F bonds.

Base-Promoted Synthesis of S-Arylisothiazolones via Intramolecular Dehydrative Cyclization of α-Keto-N-acylsulfoximines

A base (Et3N)-promoted synthesis of 1,4-diarylisothiazolones from α-keto-N-acylsulfoximines has been achieved. The reaction proceeds via α-hydrogen abstraction from sulfoximine, followed by an intramolecular nucleophilic attack at the keto carbonyl to form a tert-hydroxy isothiazolone intermediate. The 1,4-substituted isothiazolone is obtained after dehydration via an E1cB path. This one-pot synthesis of isothiazolinones has a broad substrate scope, has a high atom economy, and provides products with good yields. The ΔELUMO-HOMO is calculated using Gaussian 16 at the B3LYP/6-31G(d,p) level of theory.

Electrochemical N-Aroylation of Sulfoximines by Using Benzoyl Hydrazines with H2 Generation

Developed here is a robust electrochemical cross-coupling reaction between aroyl hydrazine and NH-sulfoximine via concomitant cleavage and formation of C(sp2 )-N bonds with the evolution of H2 and N2 as innocuous by-products. This sustainable protocol avoids the use of toxic reagents and occurs at room temperature. The reaction proceeds via the generation of an aroyl and a sulfoximidoyl radical via anodic oxidation under constant current electrolysis (CCE), affording N-aroylated sulfoximine. The strategy is applied to late-stage sulfoximidation of L-menthol, (-)-borneol, D-glucose, vitamin-E derivatives, and marketed drugs such as probenecid, ibuprofen, flurbiprofen, ciprofibrate, and sulindac. In addition, the present methodology is mild, high functional group tolerance with broad substrate scope and scalable.

Palladium-Catalyzed Fluorinative Bifunctionalization of Aziridines and Azetidines with gem-Difluorocyclopropanes

An unprecedented Pd-catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C-C and C-F bond cleavage of gem-difluorocyclopropanes, leading to various β,β'-bisfluorinated amines and β,γ-bisfluorinated amines. This reaction was achieved by incorporating a 2-fluorinated allyl group and a fluorine atom scissored from gem-difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2-fluorinated allyl palladium complex to generate η2 -coordinated N-allyl aziridine followed by fluoride ligand transfer affording the final β- and γ-fluorinated amines.

Iodine(III)-Mediated Migratory gem-Difluorinations: Synthesis of β Transformable Functionality Substituted gem-Difluoroalkanes

Geminal-difluoroalkanes featuring intriguing steric and electronic properties are of great significance in medicinal chemistry, and great progresses have been achieved for their synthesis. In recent years, iodine(III) reagent-mediated migratory gem-difluorination of alkenes has proved to be an efficient and powerful strategy to access to diverse gem-difluoroalkanes, especially those bearing a readily transformable functionality (TF), which are important for rapid assembly of complex gem-difluorinated molecules in a modular and diverse manner. In this review, we systematically summarize the recent development of iodine(III)-mediated migratory gem-difluorination reactions for the synthesis of gem-difluoroalkanes bearing a synthetically versatile TF at the β position. The reaction mechanism and the utilities of the products are also discussed. This review is presented and grouped basically according to the types of transformable functionalities within the products.

NIS-initiated photo-induced oxidative decarboxylative sulfoximidation of cinnamic acids

N-Iodosuccinimide catalyzed, visible-light-induced oxidative decarboxylative cross-coupling between cinnamic acids and NH-sulfoximines is presented. This strategy results in the formation of α-keto-N-acyl sulfoximines via the construction of two new CO bonds and one C-N bond. The in situ-generated N-iodosulfoximine serves as the light-absorbing species in the absence of any external photosensitizer. The keto carbonyl and amidic carbonyl oxygen in the resulting product originate from dioxygen and water respectively.

Visible-Light-Induced Difluoroalkylation of Alkenes and Alkynes with Fluoro-Containing Hypervalent Iodane (III) Reagents Under Photo-Catalyst-Free Conditions

A visible-light-induced difluoroalkylation of unactivated alkenes by fluoro-containing hypervalent iodine-based difluoroalkylation reagent was achieved for the first time under photo-catalyst-free conditions. Moreover, the same reaction conditions were applicable to the difluoroalkylation of alkynes to give the hydrodifluoroalkylation products in moderate to excellent yields. The readily available reagent, broad substrate scope, and photo-catalyst-free conditions make this protocol an efficient and environmental friendly method for the hydrodifluoroalkylation of alkenes and alkynes.

Superbase-Mediated gem-Difluoroalkenylations of Sulfoximines

At ambient temperature, deprotonated sulfoximines react with 1-trifluoromethylalkenes to provide either N- or C-gem-difluoroalkenylated products. The reaction site depends upon the N substituent of the starting material. The optimal conditions involve the use of a superbasic system NaOH in dimethyl sulfoxide. The reactions are characterized by a broad substrate scope and medium to high yields. Scale-up experiments of both the N- and C-gem-difluoroalkenylations proceeded well. Treatment of a N-difluoroallyl sulfoximine with an aryl thiol under dioxygen afforded the corresponding oxygenated addition product.

Synthesis of β-Arylseleno Sulfoximines: A Metal-Free Three-Component Reaction Mediated by Tetrabutylammonium Tribromide

A tetrabutylammonium tribromide-mediated three-component reaction of alkenes, diselenides, and sulfoximines has been established herein, providing direct and metal-free access to diverse β-arylseleno sulfoximine derivatives. This regioselective sulfoximido-selenization protocol proceeds efficiently under mild and ambient conditions with generally good yields. This strategy is featured by step and atom economy, practicability, a broad substrate scope, and gram-scale synthesis.

Photo-catalyzed acetoxysulfoximination of styrene with sulfoximidoyl thianthrenium salt

We report the design and synthesis of a redox-active thianthrenium-containing sulfoximination reagent. Photo-catalyzed acetoxysulfoximination of styrene with various functional groups is described. Preliminary mechanistic studies indicated that the sulfoximination reagent (2aa) received a single electron transfer (SET) from the photo-excited Ir(ppy)₃ catalyst to produce a sulfoximidoyl radical as a key intermediate in this transformation.

Recent advances in visible light-induced C(sp3)–N bond formation

Synthetic chemists have long focused on selective C(sp ³)-N bond-forming approaches in response to the high value of this motif in natural products, pharmaceutical agents and functional materials. In recent years, visible light-induced protocols have become an important synthetic platform to promote this transformation under mild reaction conditions. These photo-driven methods rely on converting visible light into chemical energy to generate reactive but controllable radical species. This Review highlights recent advances in this area, mostly after 2014, with an emphasis placed on C(sp ³)-H bond activations, including amination of olefins and carbonyl compounds, and cross-coupling reactions.

Photoinduced Three-Component Difluoroalkylation of Quinoxalinones with Alkenes via Difluoroiodane(III) Reagents

An environmentally friendly strategy for the photocatalyzed three-component reaction between quinoxalinones, alkenes, and hypervalent iodine(III) reagents is disclosed. The new designed difluoroiodane(III) reagent shows excellent reactivity, providing a wide range of difluoroalkyl-substituted quinoxaline-2(1H)-ones in moderate to excellent yields under mild conditions. Experimental studies demonstrated that a difluoroalkyl radical intermediate was involved in this reaction.

Oxidative Fluoroarylation of Benzylidenecyclopropanes with HF·Py and Aryl Iodides via Iodonio-[3,3]-Rearrangement

Reported herein is an in situ-generated hypervalent iodine-incorporating fluoroarylation of benzylidenecyclopropanes using commercially available HF·Py and aryl iodides as fluorine and aryl sources, respectively. The reaction proceeds via regioselective 1,2-fluoroiodination of a double bond followed by an iodonio-[3,3]-rearrangement of the formed cyclopropyl-I^(III) species. The protocol offers facile access to valuable monofluorinated 1,1-bis-benzyl-alkenes with mild reaction conditions and moderate to good yields. The synthetic utility of the products was demonstrated by further transformations. Preliminary mechanistic studies were conducted.

Introduction of Lipophilic Side Chains to NH-Sulfoximines by Palladium Catalysis Under Blue Light Irradiation

Palladium catalysis under blue (LED) light irradiation allows conversion of NH-sulfoximines into products with long lipophilic side chains attached to the S═N moiety. The three-component reactions involve both radicals and organometallic intermediates stemming from alkyl bromides and butadienes. The substrate scope is broad, and the products are formed in moderate to good yields.

Visible-Light-Mediated α-Ketoacylations of NH-Sulfoximines with gem-Difluoroalkenes

A photochemical approach for the preparation of α-keto-N-acyl sulfoximines from NH sulfoximines and gem-difluoroalkenes has been developed. In the presence of NBS, the reactions proceed in air without the need of a photocatalyst or additional oxidant. Results of mechanistic studies suggest that the two oxygens in the products stem from water and dioxygen.

Synthesis and Transformations of NH-Sulfoximines

Recent years have seen a marked increase in the occurrence of sulfoximines in the chemical sciences, often presented as valuable motifs for medicinal chemistry. This has been prompted by both pioneering works taking sulfoximine containing compounds into clinical trials and the concurrent development of powerful synthetic methods. This review covers recent developments in the synthesis of sulfoximines concentrating on developments since 2015. This includes extensive developments in both S-N and S-C bond formations. Flow chemistry processes for sulfoximine synthesis are also covered. Finally, subsequent transformations of sulfoximines, particularly in N-functionalization are reviewed, including N-S, N-P, N-C bond forming processes and cyclization reactions.

Visible light-induced C-C bond cleavage in a multicomponent reaction cascade allowing acylations of sulfoximines with ketones

Visible light induces C-C-bond cleavage reactions of ketones, which can be utilized for N-acylations of sulfoximines. No (photo)catalyst is required, and the reactions occur at ambient temperature in air. The substrate scope is broad for both ketones and sulfoximines. For converting NH-sulfoximines, the presence of NBS is essential.

Photocatalytic Synthesis of Difluoroacetoxy-containing Sulfoximines

[Bis(difluoroacetoxy)iodo]benzene and NH-sulfoximines react to give new hypervalent iodine(III) reagents, which under photocatalysis transfer difluoroacetoxy and sulfoximidoyl groups to styrenes with high regioselectivity. The results of mechanistic investigations suggest the intermediacy of radicals and reveal the importance of the difluoroacetoxy group on the iodine reagent.

Visible-Light-Driven Photoredox-Catalyzed Three-Component Radical Cyanoalkylfluorination of Alkenes with Oxime Esters and a Fluoride Ion

A metal-free, photoredox-catalyzed three-component cyanoalkylfluorination of alkenes under mild and redox-neutral conditions is reported. This protocol features use of readily available alkenes, oxime esters, and cost-effective nucleophilic fluoride reagents, giving diverse cyanoalkylfluorinated products with generally good yields. Excellent functional group tolerance and mild reaction conditions also render this protocol suitable for cyanoalkylfluorination of pharmaceutically relevant molecule-derived alkene.

Three-Component Carbosilylation of Alkenes by Merging Iron and Visible-Light Photocatalysis

A mild, efficient, and one-pot protocol for three-component carbosilylation of alkenes with imidazoheterocycle and silanes has been developed by merging iron(II) and visible-light photocatalysis. This C-C and C-Si bond-forming method provides functionalized organosilicon derivatives having imidazoheterocycles moieties in good yields. The reaction possibly proceeds through a radical pathway.

Cobalt-Catalyzed Divergent Aminofluorination and Diamination of Styrenes with N-Fluorosulfonamides

A cobalt-catalyzed aminofluorination reaction of styrenes with N-fluorosulfonamides serving as both the amination and fluorination agents has been developed. The switch of selectivity in this catalytic reaction from aminofluorination to diamination could be easily achieved by the addition of 1.0 equiv of PPh₃. Both transformations tolerated a wide array of substrates under mild reaction conditions.

Iodine(III)-Mediated Fluorination/Semipinacol Rearrangement Cascade of 2-Alkylidenecyclobutanol Derivatives: Access to β-Monofluorinated Cyclopropanecarbaldehydes

A hypervalent iodine(III)-mediated ring-contractive fluorination reaction of 2-alkylidenecyclobutanol derivatives is presented. The protocol allows the facile synthesis of β-monofluorinated cyclopropanecarbaldehydes via a fluorination/semipinacol rearrangement cascade using nucleophilic Py·HF as the fluorine source. For challenging electron-rich arene substrates, the installation of a protecting group on the free alcohol is pivotal for maintaining the reaction efficiency. The synthetic utility was demonstrated by the scalability of this reaction and further transformations of the products.

One-Pot Synthesis of N-Iodo Sulfoximines from Sulfides

This is the first report on the synthesis and characterization of N-iodo sulfoximines. The synthesis was designed as a room temperature one-pot cascade reaction from readily available sulfides as starting compounds, converted into sulfoximines by reaction with ammonium carbonate and (diacetoxyiodo)benzene, followed by iodination with N-iodosuccinimide or iodine in situ, in up to 90% isolated yields, also at a multigram scale. Iodination of aryls with N-iodo sulfoximines, oxidation, and conversion to N-SCF₃ congeners have been demonstrated.

5-(Diarylimino)- and 5-(sulfoximido)dibenzothiophenium triflates: syntheses and applications as electrophilic aminating reagents

The one-pot synthesis of well-defined 5-(diarylimino) and 5-(sulfoximido)dibenzothiophenium triflates, respectively from diarylimines or sulfoximines, is reported and the structures of a series of these compounds are elucidated by X-ray crystallography. In analogy to their hypervalent I(iii) analogues, the iminoyl and sulfoximidoyl groups of these compounds can be selectively transferred to organic substrates. Specifically, the uncatalyzed imination of thiols or sulfinates proceeds with good yields, while under the mild reaction conditions offered by visible light photoredox catalysis, the radical amination of hydrazones or the sulfoximidation of benzylic, allylic and propargylic C-H bonds takes place satisfactorily.

Visible light-promoted NH-halogenation of sulfoximines with dichloromethane or dibromomethane

In the presence of a hypervalent iodine reagent, N-halo sulfoximines are obtained by catalyst-free visible light-promoted halogenations of their NH-counterparts with dichloro- or dibromomethane as halogen source.

A Unified Strategy for Arylsulfur(VI) Fluorides from Aryl Halides: Access to Ar-SOF3 Compounds

A convenient protocol to selectively access various arylsulfur(VI) fluorides from commercially available aryl halides in a divergent fashion is presented. Firstly, a novel sulfenylation reaction with the electrophilic N-(chlorothio)phthalimide (Cl-S-Phth) and arylzinc reagents afforded the corresponding Ar-S-Phth compounds. Subsequently, the S(II) atom was selectively oxidized to distinct fluorinated sulfur(VI) compounds under mild conditions. Slight modifications on the oxidation protocol permit the chemoselective installation of 1, 3, or 4 fluorine atoms at the S(VI) center, affording the corresponding Ar-SO2 F, Ar-SOF3 , and Ar-SF4 Cl. Of notice, this strategy enables the effective introduction of the rare and underexplored -SOF3 moiety into various (hetero)aryl groups. Reactivity studies demonstrate that such elusive Ar-SOF3 can be utilized as a linchpin for the synthesis of highly coveted aryl sulfonimidoyl fluorides (Ar-SO(NR)F).

Photocatalytic Fluoro Sulfoximidations of Styrenes

Reactions of difluoroiodotoluene with NH‐sulfoximines provide new hypervalent iodine(III) reagents, which photocatalytically transfer a fluoro and a sulfoximidoyl group onto styrenes with high regioselectivity. The substrate scope is broad with respect to both sulfoximines and olefins. Following an operationally simple protocol, a large library of fluorine‐containing N‐functionalized sulfoximines can be accessed. Results from mechanistic investigations revealed the importance of radical intermediates.