Oxidant-Assisted Sulfonylation/Cyclization Cascade Synthesis of Alkylsulfonylated Oxindoles via the Insertion of SO2

An oxidant-assisted tandem sulfonylation/cyclization of electron-deficient alkenes with 4-alkyl-substituted Hantzsch esters and Na2S2O5 for the preparation of 3-alkylsulfonylated oxindoles under mild conditions in the absence of a photocatalyst and transition metal catalyst is established. The mechanism studies show that the alkyl radicals, which come from the cleavage of the C-C bond in 4-substituted Hantzsch esters under oxidant conditions, subsequently undergo the in situ insertion of sulfur dioxide to generate the crucial alkylsulfonyl radical intermediates. This three-component reaction provides an efficient and facile route for the construction of alkylsulfonylated oxindoles and avoids the use of highly toxic alkylsulfonyl chlorides or alkylsulfonyl hydrazines as alkylsulfonyl sources.

I2/DMSO-mediated oxidative C-C and C-heteroatom bond formation: a sustainable approach to chemical synthesis

The I2/DMSO pair has emerged as a versatile, efficient, practical, and eco-friendly catalyst system, playing a significant role as a mild oxidative system, and thus employed as a good alternative to metal catalysts in synthetic chemistry. Presently, I2/DMSO is a thriving catalytic system that is used in preparing C-C and C-X (X = O/S/N/Se/Cl/Br) bonds, resulting in the formation of various bioactive molecules. Many processes utilize this system, including in situ glyoxal synthesis by diverse sp, sp2, and sp3 functionalities via iodination and subsequent Kornblum oxidation. Focusing on oxidation processes, this study examines the synergistic effect of dimethyl sulfoxide (DMSO) and molecular iodine in improving synthetic techniques. We provide a comprehensive overview of the research progress on the I2/DMSO catalytic system for the formation of C-C and C-heteroatom bonds from 2018 to the present. Additionally, the future prospects of this research field are discussed.

Glyoxylic Acid Monohydrate-Promoted Formation of the C-SO2 Bond Starting from Maleimides/Quinones and Sodium Sulfinates

By using glyoxylic acid monohydrate as a promoter, a wide range of substances containing a C-SO2 bond could be obtained from N-substituted maleimides or quinones and sodium sulfinates. The protocol features mild reaction conditions, short reaction time, and good atomic economics, which provides an alternative protocol for the α-sulfonylation of α,β-unsaturated ketones.

Regio- and Stereoselective Intermolecular Oxysulfonylation of Alkynes with 1,3-Diketones to Access (Z)-β-Sulfonated Enethers

The first multicomponent regio- and stereoselective difunctionalization of alkynes via concomitant C-O and C-S bond formation using 1,3-diketones and sodium sulfinate has been developed for the synthesis of various sulfonated enethers. The viability of this strategy is unveiled by gram-scale, various synthetic modifications and late-stage functionalization. This transformation does not require any prefunctionalization, metal catalysts, and oxidants. The present operationally simple, efficient, and sustainable approach provides various functionalized olefins in a one-pot protocol with high Z-selectivity.

Photoredox catalysis in alkene and alkyne alkylsulfonylations: the construction of Markovnikov selective α-sulfones

Photoredox alkene or alkyne alkylsulfonylation has been achieved with phthalimide esters and sulfinates providing unexpected α-sulfones. Mechanistic studies disclose that the preferential alkyl radical addition to the alkene or the Markovnikov hydrosulfonation of the alkyne should contribute to the formation of the β-alkylated α-sulfones. Moreover, the reaction is easy to operate covering quite large substrate scales including primary, secondary and tertiary alkyl groups and all sorts of terminal aryl alkenes or alkynes. Besides, the reaction was also suitable for the sulfonylation of several drug molecules.

Dehydroxylative Sulfonylation of Alcohols

Described here is the R₃P/ICH₂CH₂I-promoted dehydroxylative sulfonylation of alcohols with a variety of sulfinates. In contrast to previous dehydroxylative sulfonylation methods, which are usually limited to active alcohols, such as benzyl, allyl, and propargyl alcohols, our protocol can be extended to both active and inactive alcohols (alkyl alcohols). Various sulfonyl groups can be incorporated, such as CF₃SO₂ and HCF₂SO₂, which are fluorinated groups of interest in pharmaceutical chemistry and the installation of which has received increasing attention. Notably, all reagents are cheap and widely available, and moderate to high yields were obtained within 15 min of reaction time.

Inexpensive and bench stable diarylmethylium tetrafluoroborates as organocatalysts in the light mediated hydrosulfonylation of unactivated alkenes

In this paper, we present the synthetic potential of diarylmethylium tetrafluoroborates as catalysts for the visible light promoted hydrosulfonylation of unactivated alkenes. For the first time, these salts, which are bench stable and easily preparable on a multi-gram scale, were employed as organocatalysts. Interestingly, a catalyst loading of only 1 mol% allowed sulfone products to be efficiently obtained from good-to-excellent yields with high functional-group tolerance and scalability up to 15 mmol of alkene. The mechanistic study, both experimental and computational, presented here, revealed an alternative mechanism for the formation of the key sulfonyl radical. Indeed, the photoactive species was proved not to be the diarylcarbenium salt itself, but two intermediates, a stable S-C adduct and an ion couple, that were formed after its interaction with sodium benzenesulfinate. Upon absorbing light, the ion couple could reach an excited state with a charge-transfer character which gave the fundamental sulfonyl radical. A PCET (proton-coupled electron transfer) closes the catalytic cycle reforming the diarylcarbenium salt.

Electrochemical Decarbonylative Aminosulfonylation of Alkynes with Sulfinates and N-(Formyl)anilides

An unprecedented electrochemical three-component reaction of phenylacetylene, sulfinate, and N-(formyl)anilide was discovered. The transformation occurs in an undivided cell with a graphite anode and cathode in DMF in the presence of tetrabutylammonium iodide as an electrolyte. The addition of silver(I) oxide and catalytic amounts of iodine facilitated the reaction significantly. The transformation was also carried out under photoredox-catalyzed conditions.

The Application of Sulfonyl Hydrazides in Electrosynthesis: A Review of Recent Studies

Sulfonyl hydrazides are viewed as alternatives to sulfinic acids and their salts or sulfonyl halides, which are broadly used in organic synthesis or work as active pharmaceutical substances. Generally, sulfonyl hydrazides are considered good building blocks and show powerful value in a diverse range of reactions to construct C-S bonds or C-C bonds, and even C-N bonds as sulfur, carbon, or nitrogen sources, respectively. As a profound synthetic tool, the electrosynthesis method was recently used to achieve efficient and green applications of sulfonyl hydrazides. Interestingly, many unique and novel electrochemical syntheses using sulfonyl hydrazides as radical precursors have been developed, including cascade reactions, functionalization of heterocycles, as well as a continuous flow method combining with electrochemical synthesis since 2017. Accordingly, it is necessary to specifically summarize the recent developments of electrosynthesis with only sulfonyl hydrazides as radical precursors to more deeply understand and better design novel electrochemical synthesis reactions. Herein, electrosynthesis research using sulfonyl hydrazides as radical precursors since 2017 is reviewed in detail based on the chemical structures of products and reaction mechanisms.

Copper-catalyzed cross coupling reaction of sulfonyl hydrazides with 3-aminoindazoles

A novel Cu-catalyzed radical-radical cross coupling reaction of 3-aminoindazoles with sulfonyl hydrazides has been disclosed, enabling the production of diverse 1,3-substituted aminoindazoles in good yields. This methodology is distinguished by readily available starting materials, wide substrate scope and operational simplicity. In addition, a gram-scale reaction has been well demonstrated.

Visible Light-Induced Highly Regioselective and Stereoselective Oxysulfonylation of Alkynes for the Synthesis of (E)-β-Phenoxy Vinylsulfones

A highly efficient visible light-induced regioselective and stereoselective oxysulfonylation of alkynes with arylsulfonate phenol esters has been developed. This photocatalyst- and metal-free method proceeds smoothly under very mild conditions and exhibits a broad substrate scope, providing (E)-β-phenoxy vinylsulfones in moderate to excellent yields. Mechanistic studies indicated the involvement of an electron donor-acceptor complex-mediated radical process.

Photomediated Tandem Sulfonyl Addition-Chemoselective N-Cyclization of o-Alkenyl Aryl Ureas: Direct Assembly of Functionalized Dihydroquinazolinones

Photoredox-mediated tandem addition-chemoselective cyclization of o-alkenyl aryl ureas is reported for the synthesis of sulfonyl and activated alkyl-decorated dihydroquinazolinones. By a careful choice of o-alkenyl aryl urea starting materials, we achieved chemoselective N-cyclization in the presence of more reactive amidic oxygen. We have demonstrated the scope of the methodology with a variety of sulfonyl chlorides and activated alkyl halides. Finally, large-scale synthesis of sulfonyl-substituted dihydroquinazolinone showcases the synthetic utility of the methodology.

Hydrosulfonylation of Alkenes with Sulfonyl Imines via Ir/Cu Dual Photoredox Catalysis

Sulfonamides exhibit the advantages of wide prevalence, excellent prefunctionalization capability, and broad functional group compatibility. We report here utilizing sulfonyl imines as sulfonyl radical precursors for hydrosulfonylation of activated alkenes via visible-light irradiation. By preinstallation of functional groups into the sulfonamides and subsequent hydrosulfonylation, a variety of complex sulfones were synthesized with good efficiency under Ir/Cu dual photoredox catalysis. Additionally, this protocol expands the research in late-stage N-S bond modification in sulfonamides.

3-Arylsulfonylquinolines from N-Propargylamines via Cascaded Oxidative Sulfonylation Using DABSO

We report a cascaded oxidative sulfonylation of N-propargylamine via a three-component coupling reaction using DABCO·(SO₂)₂ (DABSO). 3-Arylsulfonylquinolines were obtained by mixing diazonium tetrafluoroborate, N-propargylamine, and DABSO under argon atmosphere in dichloroethane (DCE) for 1 h. In a radical pathway, DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction.

1-Acryloyl-2-cyanoindole: A Skeleton for Visible-Light-Induced Cascade Annulation

1-Acryloyl-2-cyanoindoles were found to be novel and efficient skeletons in visible-light-induced persulfate-promoted cascade cyclization reactions. With this transition-metal-free photocatalytic procedure, various sulfonated/thiocyanated pyrrolo[1,2-a]indolediones were synthesized from 1-acryloyl-2-cyanoindoles with sulfonyl hydrazides/NH₄SCN at room temperature under mild reaction conditions.

Progress in the Electrochemical Reactions of Sulfonyl Compounds

Electrosynthesis has recently attracted more and more attention due to its great potential to replace chemical oxidants or reductants in molecule-electrode electron transfer. Sulfonyl compounds such as sulfonyl hydrazides, sulfinic acids (and their salts), sulfonyl halides have been discovered as practical precursors of several radicals. As electrochemical redox reactions can provide green and efficient pathways for the activation of sulfonyl compounds, studies for electrosynthesis have rapidly increased. Several types of radicals can be generated from anodic oxidation or cathodic reduction of sulfonyl compounds and can initiate fluoroalkylation, benzenesulfonylation, cyclization or rearrangement. In this Review, we summarize the electrosynthesis developments involving sulfonyl compounds mainly in the last decade.

Organic Sulfinic Acids and Salts in Visible Light-Induced Reactions

Sulfinic acids and their salts are a useful source of sulfur-containing structures. Photocatalysis of these compounds with visible light enables to achieve various transformations under mild conditions. This review summarizes visible-light-induced reactions of sulfinic acids and their salts. It is organized by reaction type and brief discussions on plausible reaction mechanisms for typical transformations are presented.

1 Introduction

2 Sulfonylation Reactions

2.1 Sulfonylation of Alkenes

2.2 Sulfonylation of Alkynes

2.3 Sulfonylation of Arenes

2.4 sp3 C–H Functionalization

3 Desulfonylation Reactions

4 Sulfenylation Reactions

4.1 Sulfenylation of Heteroarenes

4.2 Sulfenylation of Carbonyl Chlorides

5 Conclusions

A radical-radical cross-coupling reaction of xanthene with sulfonyl hydrazides: facile access to xanthen-9-sulfone derivatives

A straightforward strategy for direct incorporation of sulfonyl units into a xanthene moiety for accessing xanthen-9-sulfone derivatives in good to excellent yields has been established via metal-free radical-radical cross-coupling reaction of xanthenes and sulfonyl hydrazides. Using easily accessible starting materials, this methodology proceeds efficiently with a high degree of functional group compatibility and with a wide scope of both xanthenes and sulfonyl hydrazides under operationally simple reaction conditions. Mechanistic investigations revealed that sulfonyl radicals could be generated from sulfonyl hydrazides in the presence of TBHP under an oxygen atmosphere.

Visible-light mediated cross-coupling of aryl halides with sodium sulfinates via carbonyl-photoredox/nickel dual catalysis

Photoinduced nickel-catalyzed cross-coupling of arylsulfinates (ArSO2−) with (hetero)aryl halides (Ar’-X) via visible light photoexcitation of 2-chloro-thioxanthen-9-one (Cl-TXO) has been achieved in moderate to excellent yields. This photocoupling exhibited a broad...

Temperature Controlled Di- and Monosulfonylation of Propargyl Alcohols with Sodium Sulfinates: Switchable Access to (E)-Allyl, Vinyldisulfones and Propargyl Sulfones

A switchable di- and monosulfonylation of propargyl alcohols with sodium sulfinates is developed, which successfully affords (E)-allyl, vinyldisulfones and propargyl sulfones in good to excellent yields, respectively. The salient features...

Copper-Catalyzed N-Directed Distal C(sp3)-H Sulfonylation and Thiolation with Sulfinate Salts

We herein report a selective and catalytic C(sp³)-H functionalization approach to access amines bearing organo-sulfonyl and organo-thiol groups. This reaction proceeds through a cascade process of N-radical formation, alkyl radical formation via 1,5-HAT, and C-S bond formation, thereby offering a series of functionalized amines. This method could enable primary, secondary, and tertiary C(sp³)-H sulfonylation and thiolation and also exhibits good functional group tolerance.

Visible-Light-Induced Multicomponent Cascade Cycloaddition of N-Propargyl Aromatic Amines, Cyclobutanone Oxime Esters, and K2S2O5: Access to Cyanoalkylsulfonylated Quinolines

A visible-light-induced cascade cyanoalkylsulfonylation/cyclization/aromatization of N-propargyl aromatic amines with K₂S₂O₅ and cyclobutanone oxime esters for the construction of cyanoalkylsulfonylated quinolines is developed. This cascade transformation features mild reaction conditions, a broad substrate scope, and excellent functional group compatibility, providing a convenient route toward cyanoalkylsulfonylated quinolines via the formation of a C-C bond and two C-S bonds in one step.

Electrochemical sulfonylation of enamides with sodium sulfinates to access β-amidovinyl sulfones

The electrochemical sulfonylation of enamides with sodium sulfinates was developed in an undivided cell in constant current mode, leading to the formation of β-amidovinyl sulfones in moderate to good yields. The catalyst-, electrolyte- and oxidant-free protocol features good functional group tolerance and employs electric current as a green oxidant. Mechanistic insights into the reaction indicate that the reaction may proceed via a radical mechanism.

Hydroxysulfonylation of alkenes: an update

The direct difunctionalization of inexpensive and widely available alkenes has been recognized as a strong and straightforward tool for the rapid fabrication of complex molecules and pharmaceutical targets by introducing two different functional groups on adjacent carbon atoms of common alkene moieties in a single operation. This synthetic strategy avoids the purification and isolation of the intermediates and thus makes synthetic schemes shorter, simpler and cleaner. In this family of reactions, the hydroxysulfonylation of alkenes has emerged as an increasingly promising strategy for the synthesis of β-hydroxysulfones, which are found in many biologically important molecules and widespread applications in organic synthesis. The objective of this review is to illustrate the advancements in the field of hydroxysulfonylation of alkenes with special emphasis on the mechanistic details of the reaction pathways.

The direct difunctionalization of alkenes recognized as a straightforward tool for the rapid fabrication of complex molecules and pharmaceutical targets by introducing two different functional groups on adjacent carbon atoms of common alkene moieties.

Practical Electro-Oxidative Sulfonylation of Phenols with Sodium Arenesulfinates Generating Arylsulfonate Esters

A practical and sustainable synthesis of arylsulfonate esters has been developed through electro-oxidation. This reaction employed the stable and readily available phenols and sodium arenesulfinates as the starting materials and took place under mild reaction conditions without additional oxidants. A wide range of arylsulfonate esters including those bearing functional groups were produced in good to excellent yields. This reaction could also be conducted at a gram scale without a decrease of reaction efficiency. Those results well demonstrated the potential synthetic value of this reaction in organic synthesis.

Divergent reactivity of sulfinates with pyridinium salts based on one- versus two-electron pathways

One of the main goals of modern synthesis is to develop distinct reaction pathways from identical starting materials for the efficient synthesis of diverse compounds. Herein, we disclose the unique divergent reactivity of the combination sets of pyridinium salts and sulfinates to achieve sulfonative pyridylation of alkenes and direct C4-sulfonylation of pyridines by controlling the one- versus two-electron reaction manifolds for the selective formation of each product. Base-catalyzed cross-coupling between sulfinates and N-amidopyridinium salts led to the direct introduction of a sulfonyl group into the C4 position of pyridines. Remarkably, the reactivity of this set of compounds is completely altered upon exposure to visible light: electron donor-acceptor complexes of N-amidopyridinium salts and sulfinates are formed to enable access to sulfonyl radicals. In this catalyst-free radical pathway, both sulfonyl and pyridyl groups could be incorporated into alkenes via a three-component reaction, which provides facile access to a variety of β-pyridyl alkyl sulfones. These two reactions are orthogonal and complementary, achieving a broad substrate scope in a late-stage fashion under mild reaction conditions.

Oxidative Sulfonylation of Hydrazones Enabled by Synergistic Copper/Silver Catalysis

A copper/silver-cocatalyzed protocol for oxidative sulfonylation of hydrazones is demonstrated. A wide range of β-ketosulfones and N-acylsulfonamides are directly synthesized in moderate to good yields. Our work provides a viable method for scalable preparation of β-ketosulfone derivatives that have found wide applications in the pharmaceutical industry.

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

This review highlights the preparation of sodium sulfinates (RSO2Na) and their multifaceted synthetic applications. Substantial progress has been made over the last decade in the utilization of sodium sulfinates emerging as sulfonylating, sulfenylating or sulfinylating reagents, depending on reaction conditions. Sodium sulfinates act as versatile building blocks for preparing many valuable organosulfur compounds through S-S, N-S, and C-S bond-forming reactions. Remarkable advancement has been made in synthesizing thiosulfonates, sulfonamides, sulfides, and sulfones, including vinyl sulfones, allyl sulfones, and β-keto sulfones. The significant achievement of developing sulfonyl radical-triggered ring-closing sulfonylation and multicomponent reactions is also thoroughly discussed. Of note, the most promising site-selective C-H sulfonylation, photoredox catalytic transformations and electrochemical synthesis of sodium sulfinates are also demonstrated. Holistically, this review provides a unique and comprehensive overview of sodium sulfinates, which summarizes 355 core references up to March 2020. The chemistry of sodium sulfinate salts is divided into several sections based on the classes of sulfur-containing compounds with some critical mechanistic insights that are also disclosed.

Nanosized CdS as a Reusable Photocatalyst: The Study of Different Reaction Pathways between Tertiary Amines and Aryl Sulfonyl Chlorides through Visible-Light-Induced N-Dealkylation and C-H Activation Processes

It has been found that the final products of the reaction of sulfonyl chlorides and tertiary amines in the presence of cadmium sulfide nanoparticles under visible light irradiation are highly dependent on the applied reaction conditions. Interestingly, with the change of a reaction condition, different pathways were conducted (visible-light-induced N-dealkylation or sp³ and sp² C-H activation) that lead to different products such as secondary amines and various sulfonyl compounds. Remarkably, all of these reactions were performed under visible light irradiation and an air atmosphere without any additive or oxidant in benign solvents or under solvent-free conditions. During this study, the CdS nanoparticles as affordable, heterogeneous, and recyclable photocatalysts were designed, successfully synthesized, and fully characterized and applied for these protocols. During these studies, intermediates resulting from the oxidation of tertiary amines are trapped during the photoinduced electron transfer (PET) process. The reaction was carried out efficiently with a variety of substrates to give the corresponding products at relatively short times in good to excellent yields in parallel with the use of the visible light irradiation as a renewable energy source. Most of these processes are novel or are superior in terms of cost-effectiveness, safety, and simplicity to published reports.

Synthesis of Vinylic Sulfones in Aqueous Media

A green method for the sulfination of allenic carbonyl compounds to access a wide variety of vinylic sulfones is developed. This reaction works in aqueous media under very mild conditions. This reaction is atom economic. A wide variety of vinylic sulfones could be obtained in moderate to excellent yields with wide functional group tolerance. The efficiency of this method is demonstrated in some reactions where the desired products can be isolated by filtration.

Organic-photoredox-catalyzed three-component sulfonylative pyridylation of styrenes

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of styrenes via organic-photoredox catalysis is described. This metal-free process enables the direct and selective installation of sulfonyl and heteroaryl motifs and tolerates a wide array of functional groups as well as complex molecular scaffolds, that could complement previous methods and would be of interest in pharmaceutical research.

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of alkenes via organic-photoredox catalysis is described.

Visible-light-induced radical cascade cyclization of 1-(allyloxy)-2-(1-arylvinyl)benzenes with sulfonyl chlorides for the synthesis of sulfonated benzoxepines

A visible light photocatalyzed cascade sulfonylation/cyclization of 1-(allyloxy)-2-(1-arylvinyl)benzenes with sulfonyl chlorides for the construction of sulfonated benzoxepines is developed.

Progress and perspectives of electrochemical insights for C–H and N–H sulfonylation

A comprehensive electrosulfonylation study has been carried out via cathodic and anodic approaches for the production of organosulfone and sulfonamide derivatives.

Metal-free C–S coupling of thiols and disulfides

A literature overview on C–S coupling reactions using thiols or disulfides as sulfur surrogates under metal-free conditions is presented. Reagents for the transformations include polyvalent iodines, peroxides, tert-butyl nitrite (TBN), DDQ, and aerial oxygen, among others.