N−H and C−H Functionalization of Sulfoximine: Recent Advancement and Prospects

Iodine-Promoted Sulfoximidation of Cinnamic Acids via Oxidative C═C Bond Cleavage

An iodine-promoted C═C bond cleavage with concomitant decarboxylation and cross-coupling between cinnamic acids and NH-sulfoximines has been developed. This reaction proceeds via selective C═C bond cleavage, followed by decarboxylation and oxidative sulfoximidation. This metal- and base-free protocol involves dioxygen as the source of oxygen, which is facilitated by tert-butyl hydroperoxide (TBHP) as the oxidant affording N-aroylated sulfoximines with good functional group tolerance and good yields.

Synthesis of N-Sulfinyl Sulfoximines from 5-(Sulfoximido)dibenzothiophenium Triflates and Sodium Sulfinates

A transition-metal-free and efficient S-O/S-N bond interconversion reaction has been developed. The protocol facilitates an efficient synthesis of N-sulfinyl sulfoximines by reacting sulfoximido-substituted sulfonium salts with a wide range of sodium sulfinates, featuring broad substrate scope, including a plethora of heterocyclic and fluoroalkyl substrates, high functional group tolerance, and mild conditions.

Syntheses of Sulfilimines by Iron-Catalyzed Iminations of Sulfides with 2,2,2-Trichloroethyl Sulfamate

N-protected sulfilimines are prepared by imination of sulfides with a combination of 2,2,2-trichloroethyl sulfamate (H2NTces), (diacetoxyiodo)benzene (PIDA), and a catalytic amount of iron triflate. The reaction proceeds at room temperature, and after only 3 h a wide range of acyclic and cyclic NTces-sulfilimines with various functional groups and (hetero)aryl substituents can be obtained. By subsequent oxidation followed by deprotection, the products are converted into NH-sulfoximines.

Synthesis of Benzo[e][1,4,3]oxathiazin-3-one 1-Oxides from NH-S-(2-Hydroxyaryl)sulfoximines

Cyclizations of NH-S-(2-hydroxyaryl)sulfoximines with 1,1'-carbonyldiimidazol (CDI) give unprecedented benzo[e][1,4,3]oxathiazin-3-one 1-oxides in good yields. The standard synthetic protocol involves the use of DCE at an increased temperature for 16 h. Under mechanochemical conditions, a representative product was obtained without a solvent at ambient temperature in only 60 min. X-ray single-crystal structure analysis confirmed the molecular scaffold representing a three-dimensional heterocycle.

Electrochemically Enable N-Sulfenylation/Phosphinylation of Sulfoximines via Oxidative Dehydrocoupling Reaction

An electrochemical oxidative cross-coupling strategy for the synthesis of N-sulfenylsulfoximines from sulfoximines and thiols was accomplished, giving diverse N-sulfenylsulfoximines in moderate to good yields. Moreover, this strategy can be extended to construct the N-P bond of N-phosphinylated sulfoximines. With electrons as reagents, the oxidative dehydrogenation cross-coupling reaction proceeds smoothly in the absence of traditional redox reagents.

PIDA/I2-mediated photo-induced aerobic N-acylation of sulfoximines with methylarenes

A visible-light-promoted, PIDA/I2-mediated acylation of NH-sulfoximines with methylarenes as an acyl source has been achieved. This transition metal and photosensitizer-free approach provides easy access to N-acylsulfoximines via oxidative coupling of sulfoximines with easily available methylarenes without using any peroxide source. Mechanistic investigations suggest the intermediacy of radicals and the importance of molecular oxygen.

Synthesis of Pyrazolesulfoximines Using α-Diazosulfoximines with Alkynes

Sulfoximines and pyrazoles are both important motifs in medicinal compounds. Here we report the synthesis and reactivity of sulfoximine diazo compounds as new reagents for the incorporation of sulfoximines. The use of N-silyl sulfoximines enabled formation of monosubstituted diazo compounds. Their application is demonstrated in a [3 + 2] cycloaddition with alkynes to form pyrazole sulfoximines in a new combination of these important chemotypes. Further derivatization of the pyrazole sulfoximines is demonstrated, including silyl deprotection to form unprotected pyrazolesulfoximines.

Organoboron/Palladium Cocatalytic Allylation of NH-Sulfoximines Using Allylic Alcohols

Synergistic organoboron/palladium cocatalysis enables dehydrative couplings of NH-sulfoximines with allylic alcohols, furnishing the corresponding N-allylated products. The reactions proceed in the absence of a Brønsted base and are tolerant of diverse sulfoximine partners, including functionalized variants. Experimental and computational studies suggest that the sulfoximine reagent is activated by complexation to the boronic acid cocatalyst.

Fluoroalkyl Sulfoximines for Versatile Photocatalytic Radical Fluoroalkylations

Fluoroalkyl sulfoximines, which serve as electron-accepting fluoroalkyl radical sources, are easy-to-handle, solid, and bench-stable chemicals. Fluoroalkyl radicals can be generated from sulfoximine reagents using strong one-electron injectors, such as a highly reducing photoredox catalyst in the excited state. Our group has developed photocatalytic radical di- and mono-fluoromethylation and α-monofluoroalkylation of olefins with the corresponding fluoroalkyl sulfoximines. In this personal account, appropriate combinations of fluoroalkyl sulfoximines and photoredox catalysts, leading to successful radical fluoroalkylation, have been discussed.

Sulfoximine Assisted C-H Activation and Annulation via Vinylene Transfer: Access to Unsubstituted Benzothiazines

In this study, we report the synthesis of unsubstituted 1,2-benzothiazines through a redox-neutral Rh(III)-catalyzed C-H activation and [4+2]-annulation of S-aryl sulfoximines with vinylene carbonate. Notably, the introduction of an N-protected amino acid ligand significantly enhances the reaction rate. The key aspect of this redox-neutral process is the utilization of vinylene carbonate as an oxidizing acetylene surrogate and an efficient vinylene transfer agent. This vinylene carbonate enables the cyclization with the sulfoximine motifs, successfully forming a diverse array of 1,2-benzothiazine derivatives in moderate to good yields. Importantly, this study highlights the potential of Rh(III)-catalyzed C-H activation and [4+2]-annulation reactions for the synthesis of optically pure 1,2-benzothiazines with high enantiomeric purity.

A Copper-Catalyzed Interrupted Domino Reaction for the Synthesis of Fused Triazolyl Benzothiadiazine-1-oxides

Copper(I)-catalyzed domino reactions of 2-azido sulfoximines with 1-iodoalkynes yield fused triazolyl-containing benzothiadiazine-1-oxides. The protocol features the synthesis of two fused heterocyclic rings in one step with good to excellent yields and a broad functional group tolerance. Detailed mechanistic investigations indicate that a copper π-complex initiates a cycloaddition and oxidative C-N coupling reaction sequence. The results suggest an interrupted domino process involving an iodinated triazole as a key intermediate.

Dehydrogenative Imination of Low-Valent Sulfur Compounds-Fast and Scalable Synthesis of Sulfilimines, Sulfinamidines, and Sulfinimidate Esters

Herein, we describe an electrochemical pathway for the synthesis of sulfilimines, sulfoximines, sulfinamidines, and sulfinimidate esters from readily available low-valent sulfur compounds and primary amides or their analogues. The combination of solvents and supporting electrolytes together act both as an electrolyte as well as a mediator, leading to efficient use of reactants. Both can be easily recovered, enabling an atom-efficient and sustainable process. A broad scope of sulfilimines, sulfinamidines, and sulfinimidate esters with N-EWGs is accessed in up to excellent yields with broad functional group tolerance. This fast synthesis can be easily scaled up to multigram quantities with high robustness for fluctuation of current densities of up to 3 orders of magnitude. The sulfilimines are converted into the corresponding sulfoximines in an ex-cell process in high to excellent yields using electro-generated peroxodicarbonate as a green oxidizer. Thereby, preparatively valuable NH sulfoximines are accessible.

Recent Advances in the Synthesis of Cyclic Sulfoximines via C-H Bond Activation

Sulfoximines, a ubiquitous class of structural motifs, are widely present in bioactive molecules and functional materials that have received considerable attention from modern organic chemistry, pharmaceutical industries, and materials science. Sulfoximines have proved to be an effective directing group for C-H functionalization which was widely investigated for the synthesis of cyclic sulfoximines. Within the last decade, great progress has been achieved in the synthesis of cyclic sulfoximines. Thus, this review highlights the recent advances in the synthesis of cyclic sulfoximines via the C-H activation strategy and is classified based on the substrate types.

Electro-mechanochemical approach towards the chloro sulfoximidations of allenes under solvent-free conditions in a ball mill

An electro-mechanochemical protocol for the synthesis of vinylic sulfoximines has been developed. Utilising mechanochemically strained BaTiO₃ nanoparticles, the catalytic active system is generated in situ by the reduction of copper(II) chloride. Various combinations of electron-donating and -withdrawing groups are tolerated, and the approach leads to products with difunctionalised double bonds in good to excellent yields. Attempts to add a sulfoximidoyl chloride to an alkyne proved difficult. Additions of a sulfonyl iodide to allenes and alkynes proceeded smoothly in the presence of silica gel without the need for activation by a piezoelectric material.

Cu(II)-Catalyzed, Site Selective Sulfoximination to Indole and Indolines via Dual C-H/N-H Activation

A copper-catalyzed protocol furnishing N-arylated sulfoximines has been developed via dual N-H/C-H activation. Arylalkyl- and less reactive diarylsulfoximines were efficiently coupled with privileged scaffolds like indolines, indoles, and N-Ar-7-azaindoles. Sulfoximines based on medicinally relevant scaffolds (phenothiazine, dibenzothiophene, thioxanthenone) were also well tolerated. Detailed mechanistic studies indicate that the deprotometalation and protodemetalation step is the reversible step.

The Preparation of Diaryl Sulfoxinium Triflates and Their Application in Palladium-Catalyzed Cross-Coupling Reactions

Treatment of N-methyl-S,S-diaryl sulfoximines with methyl trifluoromethanesulfonate provides bench-stable sulfoxinium salts in excellent yields. Applying them in Sonogashira-, Heck- and Suzuki-type cross-coupling reactions leads to the corresponding products by sequential C-S bond cleavage and C-C bond formation. Electronic factors induced by substituents on the S-aryl groups govern the coupling efficiency.

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.

Iron(II)-Catalyzed Nitrene Transfer Reaction of Sulfoxides with N-Acyloxyamides

An iron(II)-catalyzed nitrene transfer reaction of sulfoxides with N-acyloxyamides has been developed, leading to the efficient construction of N-acyl sulfoximines with high functional-group compatibility. The current catalytic transformation was carried out under an air atmosphere at ambient temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. Application of the methodology was demonstrated by facile C-H acetoxylation and olefination using the N-acyl sulfoximine as the directing group.

Cobalt(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective Synthesis of Benzothiadiazine-1-oxides via C-H Activation

Among sulfoximine derivatives containing a chiral sulfur center, benzothiadiazine-1-oxides are important for applications in medicinal chemistry. Here, we report that the combination of an achiral cobalt(III) catalyst and a pseudo-C₂ -symmetric H₈ -binaphthyl chiral carboxylic acid enables the asymmetric synthesis of benzothiadiazine-1-oxides from sulfoximines and dioxazolones via enantioselective C-H bond cleavage. With the optimized protocol, benzothiadiazine-1-oxides with several functional groups can be accessed with high enantioselectivity.

Rh(III)-catalysed C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes: facile access to [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazines

Reported herein is rhodium-catalysed oxidative C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes via a chelation-assisted strategy, which provides an efficient approach for the construction of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazine skeletons from easily available substrates. This protocol exhibits a good compatibility with halogen substituents, thus paving the way for further transformation to prepare various organic functional molecules. The resulting benzothiazine derivative shows a deep blue emission with Commission Internationale de 'Eclairage (CIE) coordinates of (0.15, 0.04), a high quantum yield, and a delayed fluorescence lifetime.

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-Promoted Synthesis of β-Keto Sulfoximines from N-Tosyl-Protected Sulfoximidoyl Chlorides

Under visible light, N-tosyl-protected sulfoximidoyl chlorides react with aryl alkynes to give β-keto sulfoximines. The reaction is characterized by a high functional group tolerance and good yields. It can be improved by the presence of a ruthenium photocatalyst. Air is the source of the ketonic oxygen in the products.

Leveraging the Domino Skeletal Expansion of Thia-/Selenazolidinones via Nitrogen-Atom Transfer in Hexafluoroisopropanol: Room Temperature Access to Six-Membered S/Se,N-Heterocycles

Herein, a highly regioselective domino skeletal-expansion process that transforms 2-aminothiazolidinone into six-membered S,N-heterocycle is developed with the aid of TMS-azide in hexafluoroisopropanol (HFIP) at ambient temperature. Functioning of the C2 tertiary amine as latent reactive group on thiazolidinone moiety was the key to this development, which allowed relay substitution with azide and imparted subsequent ring-expansion under metal/acid free-conditions. The reaction also underscored an intermolecular nitrogen-atom transfer process from TMS-azide leading to final products, where any intermediary azidothiazolidinone was absent. The strategy was extendable to analogous synthesis of Se,N-heterocycles, and furthermore, late-stage drug-modification and follow-up transformations were also performed. Density functional theory calculations and control experiments provided important mechanistic insights and highlighted potential roles of HFIP in the transformation.

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.

Rhodium-catalyzed C-H activation/cyclization of aryl sulfoximines with iodonium ylides towards polycyclic 1,2-benzothiazines

The synthesis of 1,2-benzothiazine derivatives through rhodium-catalyzed C-H activation/cyclization of S-aryl sulfoximines with iodonium ylides was developed for the first time. In this report, C-H and N-H bond functionalization was realized towards a series of tricyclic and tetracyclic sulfoximine derivatives with moderate to excellent yields under simple reaction conditions.

Three-Dimensional Heterocycles by 5-exo-dig Cyclizations of S-Methyl-N-ynonylsulfoximines

Upon treatment with Cs₂CO₃, S-methyl-N-ynonylsulfoximines undergo 5-exo-dig cyclizations to give three-dimensional heterocycles. The reactions proceed at ambient temperature with a wide range of substrates affording the corresponding products in good to excellent yields.

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.

A metal-free Petasis reaction towards the synthesis of N-(α-substituted)alkyl sulfoximines/sulfonimidamides

Herein, we disclose a metal-free novel approach for the synthesis of N-(α-substituted)alkyl sulfoximines/sulfonimidamides via one-pot multicomponent Petasis reactions of aryl boronic acids, ortho-hydroxyarylaldehydes and sulfoximines/sulfonimidamides in moderate to very good yields. The presence of two chiral centres provides a mixture of diastereomers almost in a 1 : 1 ratio, which are separated successfully in most of the cases. The -OH functionality of Petasis products is further utilized to derive heterocycles via O-allylation, followed by intramolecular Heck cyclization, proving the synthetic utility of the products.

Photochemistry of N-Phenyl Dibenzothiophene Sulfoximine†

Sulfoximines are popular scaffolds in drug discovery due to their hydrogen bonding properties and chemical stability. In recent years, the role of reactive intermediates such as nitrenes has been studied in the synthesis and degradation of sulfoximines. In this work, the photochemistry of N-phenyl dibenzothiophene sulfoximine [5-(phenylimino)-5H-5λ⁴ -dibenzo[b,d]thiophene S-oxide] was analyzed. The structure resembles a combination of N-phenyl iminodibenzothiophene and dibenzothiophene S-oxide, which generate nitrene and O(³ P) upon UV-A irradiation, respectively. The photochemistry of N-phenyl dibenzothiophene sulfoximine was explored by monitoring the formation of azobenzene, a photoproduct of triplet nitrene, using direct irradiation and sensitized experiments. The reactivity profile was further studied through direct irradiation experiments in the presence of diethylamine (DEA) as a nucleophile. The studies demonstrated that N-phenyl dibenzothiophene sulfoximine underwent S-N photocleavage to release singlet phenyl nitrene which formed a mixture of azepines in the presence of DEA and generated moderate amounts of azobenzene in the absence of DEA to indicate formation of triplet phenyl nitrene.

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.

Synthesis of Benzothiadiazine-1-oxides by Rhodium-Catalyzed C-H Amidation/Cyclization

A rhodium-catalyzed C-H amidation/cyclization sequence provides benzothiadiazine-1-oxides from sulfoximines and 1,4,2-dioxazol-5-ones in good yields. The reaction is characterized by a high functional group tolerance and, in contrast to most previous transformations of this type, is well-suited for S-alkyl-S-aryl-substituted sulfoximines.

N-(2,3,5,6-Tetrafluoropyridyl)sulfoximines: synthesis, X-ray crystallography, and halogen bonding

N-(Tetrafluoropyridyl)sulfoximines are obtained from NH-sulfoximines and pentafluoropyridine under solution-based or mechanochemical conditions, and the solid-state structures of 26 products have been determined by X-ray diffraction analysis.