Iron-Catalyzed Hetero-Cross-Dehydrogenative Coupling Reactions of Sulfoximines with Diarylmethanes: A New Route to N-Alkylated Sulfoximines

Advances in cross-coupling and oxidative coupling reactions of NH-sulfoximines - a review

Due to the special structure and physicochemical properties of sulfoximines, research on sulfoximines has achieved great progress in recent decades, especially in chemical and medicinal fields. This review highlights recent advancements in the N-functionalization of NH-sulfoximines, focusing on classical cross-coupling reactions with electrophilic agents and oxidative coupling reactions with extensive organic compounds, including specific (hetero)arenes, alkenes (1,4-naphthoquinones), alkanes (cyclohexanes), nucleophiles (thiols, disulfides, sulfinates, diarylphosphine oxides), organyl boronic acids, and arylhydrazines. Transition metal-catalyzed, metal-free, electrochemical and radical oxidative coupling reactions are discussed. This review also reports and discusses the mechanistic pathways of some typical reactions.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C-H Functionalization

Radical C-H functionalization represents a useful means of streamlining synthetic routes by avoiding substrate preactivation and allowing access to target molecules in fewer steps. The first-row transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) are Earth-abundant and can be employed to regulate radical C-H functionalization. The use of such metals is desirable because of the diverse interaction modes between first-row transition metal complexes and radical species including radical addition to the metal center, radical addition to the ligand of metal complexes, radical substitution of the metal complexes, single-electron transfer between radicals and metal complexes, hydrogen atom transfer between radicals and metal complexes, and noncovalent interaction between the radicals and metal complexes. Such interactions could improve the reactivity, diversity, and selectivity of radical transformations to allow for more challenging radical C-H functionalization reactions. This review examines the achievements in this promising area over the past decade, with a focus on the state-of-the-art while also discussing existing limitations and the enormous potential of high-value radical C-H functionalization regulated by these metals. The aim is to provide the reader with a detailed account of the strategies and mechanisms associated with such functionalization.

Selective N=S Coupling Reactions of N-Methoxy Arylamides and Sulfoxides Catalyzed by Iron Salt

An iron-catalyzed selective N=S coupling of N-methoxy amides and sulfoxides has been developed and was found to be a highly efficient method for the synthesis of N-acyl sulfoximines. Electron-donating as well as electron-withdrawing groups on the phenyl ring are tolerated, and even sensitive substituents are compatible. The current catalytic transformation was conducted under an air atmosphere and can be easily scaled up to a gram scale with a catalyst loading of only 1 mol %. In this case, both coupling partners are used in their native forms, thus obviating prior functionalization and activation.

InCl3 catalyzed simultaneous reductive sulfoximination and O-silylation: synthesis of silyloxy benzylsulfoximine

This article describes the synthesis of ortho-silyloxy benzylsulfoximine via the reaction of salicylaldehyde and sulfoximine in the presence of silane and InCl3. The steps include simultaneous reductive sulfoximination and an O-silylation process. To the best of our knowledge, this is the first report of this kind of reaction, where both reductive amination (here sulfoximination) and O-silylation occur concurrently.

Facile synthesis of N-(α-furanyl) alkyl sulfoximines via gold catalyzed Michael addition/cyclization of enynones and sulfoximines

Herein, we prepare a new array of N-(α-furanyl) alkyl sulfoximines via a gold catalyzed reaction of enynone with sulfoximine in moderate to very good yields. The reaction involves Michael addition of sulfoximine to enynone, followed by intramolecular cyclization. The presence of two chiral centres led to the formation of a mixture of diastereomers approximately in a 1 : 1 ratio. The salient features of the protocol include broad substrate scope, high efficiency and high yields. The synthetic utility of the protocol is explored using Suzuki-Miyaura cross-coupling and mild, metal-free opening of the furan ring.

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.

A Counterion/Ligand-Tuned Chemo- and Enantioselective Copper-Catalyzed Intermolecular Radical 1,2-Carboamination of Alkenes

The copper-catalyzed enantioselective intermolecular radical 1,2-carboamination of alkenes with readily accessible alkyl halides is an appealing strategy for producing chiral amine scaffolds. The challenge arises from the easily occurring atom transfer radical addition between alkyl halides and alkenes and the issue of enantiocontrol. We herein describe a radical alkene 1,2-carboamination with sulfoximines in a highly chemo- and enantioselective manner. The key to the success of this process is the conceptual design of a counterion/highly sterically demanded ligand coeffect to promote the ligand exchange of copper(I) with sulfoximines and forge chiral C-N bonds between alkyl radicals and the chiral copper(II) complex. The reaction covers alkenes bearing distinct electronic properties, such as aryl-, heteroaryl-, carbonyl-, and aminocarbonyl-substituted ones, and various radical precursors, including alkyl chlorides, bromides, iodides, and the CF₃ source. Facile transformations deliver many chiral amine building blocks of interest in organic synthesis and related areas.

Lewis acid triggered N-alkylation of sulfoximines through nucleophilic ring-opening of donor-acceptor cyclopropanes: synthesis of γ-sulfoximino malonic diesters

Scandium triflate (Sc(OTf)₃) catalyzed, mild, and regioselective ring-opening reaction of donor-acceptor (D-A) cyclopropanes has been developed using sulfoximines for the synthesis of γ-sulfoximino malonic diesters. This protocol allows the synthesis of different N-alkyl sulfoximines in good to excellent yields (up to 94%) with broad functional group tolerance. In this process, N-H and C-C bonds are cleaved to form new C-N and C-H bonds. The feasibility of this method is supported by a gram-scale reaction and synthetic elaboration of the obtained product.

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.

Iron-Catalyzed Oxidative Amination of Benzylic C(sp3)-H Bonds with Anilines

Iron-catalyzed oxidative amination of benzylic C(sp³)-H bonds with anilines bearing electron-withdrawing groups (EWGs) or electron-donating groups (EDGs) is realized based on simple variations of N-substituents on imidazolium cations in novel ionic Fe(III) complexes. The structural modification of the imidazolium cation resulted in regulation of the redox potential and the catalytic performance of the iron metal center. Using DTBP as oxidant, [HItBu][FeBr₄] showed the highest catalytic activity for anilines bearing EWGs, while [HIPym][FeBr₄] was more efficient for EDG-substituted anilines. This work provides alternative access to benzylamines with the advantages of both a wide substrate scope and iron catalysis.

Identification and optimization of biphenyl derivatives as novel tubulin inhibitors targeting colchicine-binding site overcoming multidrug resistance

Microtubule targeting agents (MTAs) are among the most successful chemotherapeutic drugs, but their efficacy is often limited by the development of multidrug resistance (MDR). Therefore, the development of novel MTAs with the ability to overcome MDR is urgently needed. In this contribution, through modification of the unsymmetric biaryl compounds, we discovered a novel compound dxy-1-175 with potent anti-proliferative activity against cancer cells. Mechanistic study revealed that dxy-1-175 inhibited tubulin polymerization by interacting with the colchicine-binding site of tubulin, which caused cell cycle arrest at G₂/M phase. Based on the predicted binding model of dxy-1-175 with tubulin, a series of new 4-benzoylbiphenyl analogues were designed and synthesized. Among them, the hydrochloride compound 12e with improved solubility and good stability in human liver microsome, exhibited the most potent anti-proliferative activity with IC₅₀ value in the low nanomolar range, and markedly inhibited the growth of breast cancer 4T1 xenograft in vivo. Notably, 12e effectively overcame P-gp-mediated MDR and our preliminary data suggested that 12e may not be a substrate of P-glycoprotein (P-gp). Taken together, our study reveals a novel MTA 12e targeting the colchicine-binding site with potent anticancer activity and the ability to circumvent MDR.

Electrochemical Oxidative C(sp3)-H/N-H Coupling of Diarylmethanes with Sulfoximines or Benzophenone Imine

Herein, we report an efficient electrochemical method for the synthesis of N-alkylated sulfoximines by electrochemical oxidative C(sp³)-H/N-H coupling of sulfoximines and diarylmethanes. In addition, we used the same conditions for electrochemical dehydrogenative amination of diarylmethanes with benzophenone imine as an aminating agent. The reactions showed good functional group tolerance and afforded the corresponding products in moderate to good yields without the use of a stoichiometric oxidant, a metal catalyst, or an activating agent.

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.

Metal-Free, Acid-Catalyzed 1,6-Conjugate Addition of NH-Sulfoximines to para-Quinone Methides: Accessing to Diarylmethine Imino Sulfanone

We have reported an efficient and metal-free method for the construction of α-diarylmethine imino sulfanone using acid-catalyzed 1,6-conjugate addition of sulfoximines on para-quinine methides (p-QMs). This method showed broad functional group tolerance and a wide range of substrate scope with good to excellent yield. The excellent protocol exhibits mild reaction conditions with high atom economy. The practicability of the present method was supported by a Gram-scale reaction.

One-pot multi-step cascade protocols toward β-indolyl sulfoximidoyl amides via intermolecular trapping of an α-indolylpalladium complex by CO

Various β-indolyl sulfoximidoyl amides were efficiently prepared from ortho-iodoanilines, propargyl bromides, 1 atm of CO, and substituted NH-sulfoximines, through a palladium-catalyzed indole annulation/carbonyl insertion/C-N bond formation cascade. Mostly good to high yields of the products were obtained through this multi-step, one-pot reaction protocol under very gentle reaction conditions. The obtained β-indolyl sulfoximidoyl amides could be converted into biologically interesting sulfoximine analogues that contain a tryptamine moiety.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Catalytic Direct α-Amination of Arylacetic Acid Synthons with Anilines

A unique α-amination approach using various anilines has been developed for arylacetic acids via adaptation as benzazoles. The reaction proceeds through a single electron transfer mechanism utilizing an iron-based catalyst system to access α-(N-arylamino)acetic acid equivalents. Modification of approved drugs, facile cleavage of the benzazole auxiliary, and tolerance of amide linkage forming conditions constitute the potential applicability of this strategy.

Benzylic Methylene Functionalizations of Diarylmethanes

Diarylmethanes are cardinal scaffolds by virtue of their unique structural feature including the presence of a benzylic CH2 group that can be easily functionalized to generate a variety of fascinating molecules holding immense importance in pharmaceutical, agrochemical, and material sciences. While the originally developed protocols for benzylic C-H functionalization in diarylmethanes employing base-mediated and metal-catalyzed strategies are still actively used, they are joined by a new array of metal-free conditions, offering milder and benign conditions. With the recent surge of interest towards the synthesis of functionalized diarylmethanes, numerous choices are now available for a synthetic organic chemist to transform the benzylic C-H bond to C-C or C-X bond offering the synthesis of any molecule of choice. This review highlights benzylic methylene (CH2 ) functionalizations of diaryl/heteroarylmethanes utilizing various base-mediated, transition-metal-catalyzed, and transition-metal free approaches for the synthesis of structurally diverse important organic molecules, often with a high chemo-, regio- and enantio-selectivity. This review also attempts to provide analysis of the scope and limitations, mechanistic understanding, and sustainability of the transformations.

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.

Synthesis of α-Substituted Primary Benzylamines through Copper-Catalyzed Cross-Dehydrogenative Coupling

A copper-catalyzed route to α-substituted, primary benzylamines by C-H functionalization of alkylarenes is described. The method directly affords the amine hydrochloride salt. Catalyst loadings down to 0.1 mol % in combination with scalability, insensitivity to air and moisture, and no need for column chromatography makes the procedure highly practical. The facile synthesis of the racemate of a blockbuster drug highlights the relevance for the development of pharmaceuticals. Preliminary mechanistic data are also included.

Nickel-Catalyzed Cross-Dehydrogenative Coupling of α-C(sp3)-H Bonds in N-Methylamides with C(sp3)-H Bonds in Cyclic Alkanes

A nickel-catalyzed cross-dehydrogenative coupling reaction of α-C(sp³)-H bonds in N-methylamides with C(sp³)-H bonds from cyclic alkanes has been developed, which offers a cheap transition-metal-catalyzed C-H activation method for amides without the requirement for any extraneous directing group. This new strategy is highly selective and tolerates a variety of functional groups. Mechanistic investigations into the reaction process are also described in detail.

Synthesis of benzyl hydrazine derivatives via amination of benzylic C(sp3)–H bonds with dialkyl azodicarboxylates

Copper(i)/Phen catalysed functionalization of benzylic C–H bonds with dialkyl azodicarboxylates.

Persulfate-promoted oxidative C–N bond coupling of quinoxalinones andNH-sulfoximines

A simple approach for a direct sulfoximination of quinoxalinonesviaK₂S₂O₈-mediated oxidative coupling is reported.