Silver-Catalyzed Imination of Sulfoxides and Sulfides

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 Sulfilimines via Multicomponent Reaction of Arynes, Sulfamides, and Thiosulfonates

In this work, a facile and efficient method for the synthesis of sulfilimines through multicomponent reaction of arynes, sulfamides, and thiosulfonates was developed. A variety of structurally diverse substrates and functional groups were very compatible in the reaction, giving the corresponding sulfilimines in good to high yields. This protocol could be conducted on a gram scale, and the product was easily converted to sulfide and sulfoximine. Mechanism studies revealed that sulfenamide generated in situ is the key intermediate for the reaction.

Base-Promoted S-Arylation of Sulfenamides for the Synthesis of Sulfilimines

Sulfilimines are key intermediates to common motifs in medicines and agrochemicals. Typically, this class of compounds are prepared by imidation of thioethers, transition-metal-catalyzed or base-promoted sulfur alkylation and transition-metal-catalyzed sulfur arylation. Here, we report a practical and efficient base-mediated sulfur arylation reaction for the preparation of sulfilimines. A wide range of N-acyl and N-aryl sulfenamides react with various diaryliodonium salts smoothly to afford the sulfilimines in high yields with excellent chemoselectivities.

Synthesis of Sulfilimines via Selective S-C Bond Formation in Water

Sulfilimines are valuable compounds both in organic synthesis and in pharmaceuticals. Here we developed a mild and simplified method for preparation of sulfilimines via selective S-C bond formation rather than traditional S-N bond formation. The method is both attractive and useful for the following reasons: it uses a readily available alkylation reagent such alkyl bromide or alkyl iodide, it uses water as solvent, it is easy to perform, and it is convenient for late-stage diversification of drugs.

Synthesis of Chiral Sulfoximines via Iridium-Catalyzed Regio- and Enantioselective C-H Borylation: A Remarkable Sidearm Effect of Ligand

Transition metal-catalyzed enantioselective C-H activation of prochiral sulfoximines for non-annulated products remains a formidable challenge. We herein report iridium-catalyzed enantioselective C-H borylation of N-silyl diaryl sulfoximines using a well-designed chiral bidentate boryl ligand with a bulky side arm. This method is capable of accommodating a broad range of substrates under mild reaction conditions, affording a vast array of chiral sulfoximines with high enantioselectivities. We also demonstrated the synthetic utility on a preparative-scale C-H borylation for diverse downstream transformations, including the synthesis of chiral version of bioactive molecules. Computational studies showed that the bulky side arm of the ligand confers high regio- and enantioselectivity through steric effect.

Synthesis of Sulfoximines and Sulfonimidamides Using Hypervalent Iodine Mediated NH Transfer

The development of NH transfer reactions using hypervalent iodine and simple sources of ammonia has facilitated the synthesis of sulfoximines and sulfonimidamides for applications across the chemical sciences. Perhaps most notably, the methods have been widely applied in medicinal chemistry and in the preparation of biologically active compounds, including in the large-scale preparation of an API intermediate. This review provides an overview of the development of these synthetic methods involving an intermediate iodonitrene since our initial report in 2016 on the conversion of sulfoxides into sulfoximines. This review covers the NH transfer to sulfoxides and sulfinamides, and the simultaneous NH/O transfer to sulfides and sulfenamides to form sulfoximines and sulfonimidamides, respectively. The mechanism of the reactions and the identification of key intermediates are discussed. Developments in the choice of reagents, and in the reaction conditions and setups used are described.

Synthesis of Sulfoximine Propargyl Carbamates under Improved Conditions for Rhodium Catalyzed Carbamate Transfer to Sulfoxides

Sulfoximines provide aza-analogues of sulfones, with potentially improved properties for medicinal chemistry. The sulfoximine nitrogen also provides an additional vector for the inclusion of other functionality. Here, we report improved conditions for rhodium catalyzed synthesis of sulfoximine (and sulfilimine) carbamates, especially for previously low-yielding carbamates containing π-functionality. Notably we report the preparation of propargyl sulfoximine carbamates to provide an alkyne as a potential click handle. Using Rh₂(esp)₂ as catalyst and a DOE optimization approach provided considerably increased yields.

Rhodium(III)-catalyzed cascade C-H functionalization/annulation of sulfoximines with iodonium ylides for the synthesis of cyclohexanone-1,2-benzothiazines

A highly efficient Rh(III)-catalyzed cascade C-H activation/annulation of sulfoximines with iodonium ylides under metal-oxidant-free conditions has been reported. The fused cyclohexanone-1,2-benzothiazine scaffold is readily achieved with a one-pot process in this reaction. This protocol exhibits good functional group tolerance and moderate to excellent yields. Additionally, the olefination of the target product illustrates the promising usefulness of this strategy.

Practical Asymmetric Synthesis of Chiral Sulfoximines via Sulfur-Selective Alkylation

Chiral sulfoximines have recently been considered as promising bioisosteres in medicinal chemistry. However, methods for preparing chiral sulfoximines in a stereoselective manner are underdeveloped. Herein, we demonstrate an asymmetric synthesis of chiral sulfoximines through a stereospecific S-alkylation of readily accessible chiral sulfinamides under practical conditions. A key to establishing the practical conditions was the identification of the intermediate structure in our previously reported S-alkylation by X-ray crystallographic analysis.

Accessing Perfluoroaryl Sulfonimidamides and Sulfoximines via Photogenerated Perfluoroaryl Nitrenes: Synthesis and Application as a Chiral Auxiliary

Sulfonimidamides (SIAs) and sulfoximines (SOIs) have attracted attention due to their potential in agriculture and in medicinal chemistry as bioisosteres of biologically active compounds, and new synthetic methods are needed to access and explore these compounds. Herein, we present a light-promoted generation of perfluorinated aromatic nitrenes, from perfluorinated azides, that subsequently are allowed to react with sulfinamides and sulfoxides, generating achiral and chiral SIAs and SOIs. One of the enantiopure SIAs was evaluated as a novel chiral auxiliary in Grignard additions to the imines yielding the product in up to 96:4 diastereomeric ratio.

Dinuclear Silver Complexes in Catalysis

Over the past two decades, there has been a substantial increase in the number of synthetically useful transformations catalyzed by silver. Across the range of silver-catalyzed reactions that have been reported, dinuclear species often emerge as a common feature, either as the (pre-)catalysts themselves or as intermediates during catalysis. This Minireview explores the role of dinuclear silver complexes in homogeneous catalysis, which we hope will aid in the development of improved design principles for silver catalysts.

Silver-Catalyzed Enantioselective Sulfimidation Mediated by Hydrogen Bonding Interactions

An enantioselective sulfimidation of 3-thiosubstituted 2-quinolones and 2-pyridones was achieved with a stoichiometric nitrene source (PhI=NNs) and a silver-based catalyst system. Key to the success of the reaction is the use of a chiral phenanthroline ligand with a hydrogen bonding site. The enantioselectivity does not depend on the size of the two substituents at the sulfur atom but only on the binding properties of the heterocyclic lactams. A total of 21 chiral sulfimides were obtained in high yields (44-99 %) and with significant enantiomeric excess (70-99 % ee). The sulfimidation proceeds with high site-selectivity and can also be employed for the kinetic resolution of chiral sulfoxides. Mechanistic evidence suggests the intermediacy of a heteroleptic silver complex, in which the silver atom is bound to one molecule of the chiral ligand and one molecule of an achiral 1,10-phenanthroline. Support for the suggested reaction course was obtained by ESI mass spectrometry, DFT calculations, and a Hammett analysis.

Catalytic Chemoselective Sulfimidation with an Electrophilic [CoIII (TAML)]- -Nitrene Radical Complex*

The cobalt species PPh4 [CoIII (TAMLred )] is a competent and stable catalyst for the sulfimidation of (aryl)(alkyl)-substituted sulfides with iminoiodinanes, reaching turnover numbers up to 900 and turnover frequencies of 640 min-1 under mild and aerobic conditions. The sulfimidation proceeds in a highly chemoselective manner, even in the presence of alkenes or weak C-H bonds, as supported by inter- and intramolecular competition experiments. Functionalization of the sulfide substituent with various electron-donating and electron-withdrawing arenes and several alkyl, benzyl and vinyl fragments is tolerated, with up to quantitative product yields. Sulfimidation of phenyl allyl sulfide led to [2,3]-sigmatropic rearrangement of the initially formed sulfimide species to afford the corresponding N-allyl-S-phenyl-thiohydroxylamines as attractive products. Mechanistic studies suggest that the actual nitrene transfer to the sulfide proceeds via (previously characterized) electrophilic nitrene radical intermediates that afford the sulfimide products via electronically asynchronous transition states, in which SET from the sulfide to the nitrene radical complex precedes N-S bond formation in a single concerted process.

An efficient imidation of thioethers with nitrene in water

The first imidation of thioethers with free nitrene in water was realized. N-Cbz sulfilimines are formed via imidation of thioethers with free nitrene generated from α elimination of nosyloxycarbamates. In this work, water is successfully applied as solvent for free nitrene, and transition metal catalyst is not needed.

Sulfoximines-Assisted Rh(III)-Catalyzed C-H Activation and Intramolecular Annulation for the Synthesis of Fused Isochromeno-1,2-Benzothiazines Scaffolds under Room Temperature

A mild and facile Cp*Rh(III)-catalyzed C–H activation and intramolecular cascade annulation protocol has been proposed for the furnishing of highly fused isochromeno-1,2-benzothiazines scaffolds using S-phenylsulfoximides and 4-diazoisochroman-3-imine as substrates under room temperature. This method features diverse substituents and functional groups tolerance and relatively mild reaction conditions with moderate to excellent yields. Additionally, retentive configuration of sulfoximides in the conversion has been verified.

Synthesis of ortho-Phenolic Sulfilimines via an Intermolecular Sulfur Atom Transfer Cascade Reaction

To expand the toolbox for the synthesis of ortho-phenolic sulfilimines, sigmatropic rearrangements were introduced to the field of sulfilimine chemistry. Herein we report a N-H sulfenylation/[2,3]-sigmatropic rearrangement cascade reaction. This mild reaction enables commercially available thiols to serve as the sulfenylation reagent and generates water as the sole byproduct. Moreover, the reaction has a wide substrate scope and can be conducted on a gram scale with excellent reaction efficiency.

Synthesis of NH-Sulfoximines by Using Recyclable Hypervalent Iodine(III) Reagents under Aqueous Micellar Conditions

The synthesis of NH-sulfoximines from sulfides has been first developed under mild conditions in an aqueous solution with surfactant TPGS-750-M as the catalyst at room temperature. In this newly developed process, a simple and convenient recycling strategy to regenerate the indispensable hypervalent iodine(III) is used. The resulting 1,2,3-trifluoro-5-iodobezene can be recovered almost quantitively from the mixture by liquid-liquid extraction and then oxidized to give the corresponding iodine(III) species. This optimized procedure is compatible with a broad range of functional groups and can be easily performed on a gram scale, providing a green protocol for the synthesis of sulfoximines.

Batch and Continuous-Flow Iron(II)-Catalyzed Synthesis of Sulfilimines and Sulfoximines using N-Mesyloxycarbamates

The synthesis of sulfilimines and sulfoximines with N-mesyloxycarbamates in presence of catalytic iron(II) chloride hydrate is described. The use of 1-butylimidazole as a base proved instrumental in enabling a homogeneous reaction mixture compatible with continuous flow processes. The amination is applicable to a wide range of substrates, and affords the desired product in good to excellent yields within 1 to 60 minutes.

Ligand-Free, Quinoline N-Assisted Copper-Catalyzed Nitrene Transfer Reaction To Synthesize 8-Quinolylsulfimides

An efficient copper-catalyzed, quinolyl N-directed nitrene transfer reaction to 8-quinolylsulfides was described. A variety of 8-quinolylsulfimides with different functional groups were synthesized in moderate to high yields. The obtained 8-quinolylsulfimides were proved to be promising novel type of bidentate ligands in Pd(II)-catalyzed allylic alkylation.

An in-tether sulfilimine chiral center induces helicity in short peptides

A precisely positioned sulfilimine chiral center in the tether of a stabilized peptide would determine the peptide's secondary structure. Peptide sulfilimines could be prepared by a facile chloramine T oxidation and the two resulting peptide diastereomers showed significant differences in their secondary structures, which were supported by circular dichroism spectroscopy and NMR.

Synthesis of fully-substituted 1,2,3-triazoles via copper(i)-catalyzed three-component coupling of sulfoximines, alkynes and azides

A copper(i)-catalyzed three-component reaction of sulfoximines, alkynes and azides is described, affording a variety of 1,2,3-triazolyl-5-sulfoximines in moderate to good yields.

Access to N-cyanosulfoximines by transition metal-free iminations of sulfoxides

Sulfoxides are stereospecifically converted to N-cyanosulfoximines using N-chlorosuccinimide (NCS) as oxidising agent and cyanamide as nucleophilic amine source.

Sulfur imidations: access to sulfimides and sulfoximines

The overview describes sulfur imidation methods providing a practical “tool box” for synthetic chemists and discusses the advantages and disadvantages associated with the use of the various imidating agents.

Rhodium-catalyzed direct synthesis of unprotected NH-sulfoximines from sulfoxides

A novel rhodium–catalyzed imination of sulfoxides using O-(2,4-dinitrophenyl)hydroxylamine is developed under mild conditions with good functional group tolerance.