Recent Advances in Transition‐Metal‐Mediated Chelation‐ Assisted Sulfonylation of Unactivated C−H Bonds

Ring-Opening Sulfonylation of Cyclic Sulfonium Salts with Sodium Sulfinates under Transition-Metal- and Additive-Free Conditions

Incorporating a sulfonyl group into parent molecules has been shown to effectively improve their synthetic applications and bioactivities. In this study, we present a straightforward and practical approach for the ring-opening reaction of alkenyl-aryl sulfonium salts with sodium sulfinates to produce a range of sulfur-containing alkyl sulfones. This method offers the benefits of mild reaction conditions, easily accessible raw materials, wide substrate applicability, good functional group compatibility, and operational simplicity. Importantly, the resulting products can be readily converted into sulfoxides, sulfones, sulfoximines, and some heterocyclic compounds.

Nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes to access allenes and dienes

The radical-mediated difunctionalization of 1,3-enynes facilitates rapid access to structurally diverse allenes and dienes. Whereas, owing to the existence of multiple active sites in conjugated 1,3-enynes, regulating selectivity in difunctionalized addition via a single transition-metal-catalyzed radical tandem process remains elusive. Herein, we disclose an intriguing protocol of substrate-controlled nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes with the assistance of sulfonyl chlorides and arylboronic acids. This valuable synthetic utility respectively delivers a series of highly functionalized and synthetically challenging allenyl sulfones and dienyl sulfones from fine-tuned 1,3-enynes by one step, which provides a facile approach for complex sulfone-containing drug molecules synthesis.

Electrochemical Sulfonylation/Cyclization of N-Alkenylacrylamides with Sodium Sulfinates or Sulfonyl Hydrazides

Two general protocols for the regioselective electrochemically enabled sulfonylation cyclization of N-alkenylacrylamides with sodium sulfinates or sulfonyl hydrazides were described. These methods were carried out under mild, chemical oxidant-free, and transition-metal-free conditions with a broad substrate scope and good functional group tolerance to provide sulfonyl-containing 4-pyrrolin-2-ones, which is readily scalable to the gram scale.

Recent advances in palladium-catalyzed sulfonylation via SO2 insertion

The importance of sulfonyl-group-containing compounds, such as sulfonamides, sulfones, sulfinate esters, and sulfonyl fluorides, in pharmaceuticals, bioactive molecules, and natural products cannot be overstated. The new development of palladium-catalyzed sulfonylation via SO2 insertion represents a crucial advancement in organic synthesis, enabling the direct α,α-difunctionalization of SO2 and providing efficient access to an array of structure-diverse sulfonyl-containing compounds. Although there have been numerous reviews about SO2 insertion, many of them only cover specific aspects of palladium-catalyzed reactions, leading to an oversight of some important works. Besides, these reviews often lack detailed discussions and systematic conclusion on reaction mechanisms, and fail to comprehensively summarize the significant research achievements in palladium-catalyzed reactions over the past few years. Herein, we aim to systematically consolidate the recent advances in palladium-catalyzed sulfonylation via SO2 insertion, elucidate the underlying reaction mechanism, and highlight some unsolved challenges in this segment. This review seeks to serve as a valuable resource for researchers, assisting in the continued development of palladium-catalyzed sulfonylation methodologies.

Palladium-Catalyzed Tsuji-Trost-Type Reaction of 3-Indolylmethylacetates with O, and S Soft Nucleophiles

The chemical valorization of widespread molecules in renewable sources is a field of research widely investigated in the last decades. In this context, we envisaged that indole-3-carbinol, present in different Cruciferae plants, could be a readily available building block for the synthesis of various classes of indoles through a palladium-catalyzed Tsuji-Trost-type reaction with O and S soft nucleophiles. The regiochemical outcome of this high-yielding functionalization shows that the nucleophilic substitution occurs only at the benzylic position. Interestingly, with this protocol, the sulfonyl unit could be appended to the indole nucleus, providing convenient access to new classes of molecules with potential bioactivity.

Direct C-H Sulfuration: Synthesis of Disulfides, Dithiocarbamates, Xanthates, Thiocarbamates and Thiocarbonates

In light of the important biological activities and widespread applications of organic disulfides, dithiocarbamates, xanthates, thiocarbamates and thiocarbonates, the continual persuit of efficient methods for their synthesis remains crucial. Traditionally, the preparation of such compounds heavily relied on intricate multi-step syntheses and the use of highly prefunctionalized starting materials. Over the past two decades, the direct sulfuration of C-H bonds has evolved into a straightforward, atom- and step-economical method for the preparation of organosulfur compounds. This review aims to provide an up-to-date discussion on direct C-H disulfuration, dithiocarbamation, xanthylation, thiocarbamation and thiocarbonation, with a special focus on describing scopes and mechanistic aspects. Moreover, the synthetic limitations and applications of some of these methodologies, along with the key unsolved challenges to be addressed in the future are also discussed. The majority of examples covered in this review are accomplished via metal-free, photochemical or electrochemical approaches, which are in alignment with the overraching objectives of green and sustainable chemistry. This comprehensive review aims to consolidate recent advancements, providing valuable insights into the dynamic landscape of efficient and sustainable synthetic strategies for these crucial classes of organosulfur compounds.

Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C-H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C-H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience.

Recent advances in selective mono-/dichalcogenation and exclusive dichalcogenation of C(sp2)-H and C(sp3)-H bonds

Organochalcogen compounds are prevalent in numerous natural products, pharmaceuticals, agrochemicals, polymers, biological molecules and synthetic intermediates. Direct chalcogenation of C-H bonds has evolved as a step- and atom-economical method for the synthesis of chalcogen-bearing compounds. Nevertheless, direct C-H chalcogenation severely lags behind C-C, C-N and C-O bond formations. Moreover, compared with the C-H monochalcogenation, reports of selective mono-/dichalcogenation and exclusive dichalcogenation of C-H bonds are relatively scarce. The past decade has witnessed significant advancements in selective mono-/dichalcogenation and exclusive dichalcogenation of various C(sp2)-H and C(sp3)-H bonds via transition-metal-catalyzed/mediated, photocatalytic, electrochemical or metal-free approaches. In light of the significance of both mono- and dichalcogen-containing compounds in various fields of chemical science and the critical issue of chemoselectivity in organic synthesis, the present review systematically summarizes the advances in these research fields, with a special focus on elucidating scopes and mechanistic aspects. Moreover, the synthetic limitations, applications of some of these processes, the current challenges and our own perspectives on these highly active research fields are also discussed. Based on the substrate types and C-H bonds being chalcogenated, the present review is organized into four sections: (1) transition-metal-catalyzed/mediated chelation-assisted selective C-H mono-/dichalcogenation or exclusive dichalcogenation of (hetero)arenes; (2) directing group-free selective C-H mono-/dichalcogenation or exclusive dichalcogenation of electron-rich (hetero)arenes; (3) C(sp3)-H dichalcogenation; (4) dichalcogenation of both C(sp2)-H and C(sp3)-H bonds. We believe the present review will serve as an invaluable resource for future innovations and drug discovery.

Distal-C-H Functionalization of Biphenyl Scaffolds Assisted by Easily Removable/Recyclable Aliphatic Nitrile Templates

We present here the distal-C-H activation/functionalization of biphenyl scaffolds using aliphatic nitrile templates. The approach has demonstrated good to exclusive meta selectivities over a wide range of olefination and acetoxylation substrates. In addition, bis-olefination has been accomplished in a one-pot, sequential manner. Notably, this technique highlights the diversification of pharmaceuticals and natural products. Consequently, the temporary directing aliphatic template has been recovered quantitively from the coupled product.

Ruthenium(II)-Catalyzed Remote C-H Sulfonylation of 2-Pyridones

Herein, a ruthenium-mediated remote C-H mono- and disulfonylation of 2-pyridones with arylsulfonyl chlorides is developed. The catalytic system consisting of a [Ru(p-cymene)Cl2]2 catalyst and KOAc additive allows 2-pyridones to undergo C3,C5-disulfonylation in 1,4-dioxane, and C5-sulfonylation when the C3-position of 2-pyridones is blocked. The successful transformation of the products and late-stage modification of estrone further highlighted the potential utility and significance of this synthetic protocol. Preliminary mechanistic studies indicated that the remote regioselectivity might be dictated via chelation-assisted ruthenation.

Radical approaches to C-S bonds

Organosulfur functionalities are ubiquitous in nature, pharmaceuticals, agrochemicals, materials and flavourants. Historically, these moieties were introduced almost exclusively using ionic chemistry; however, radical-based methods for the installation of sulfur-based functional groups have recently come to the fore. These radical methods have enabled their late-stage introduction into complex molecules, avoiding the need to preserve labile organosulfur moieties through multistep synthetic sequences. Here, we discuss homolytic C-S bond-forming processes, with a particular emphasis on radical substitution approaches to sulfide, disulfide and sulfinyl products, and the use of sulfur dioxide and its surrogates to build sulfonyl products. We also highlight the mechanistic considerations that we hope will guide further development of radical-based strategies compatible with the various organosulfur moieties that feature in modern chemistry.

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.

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.

Ligand-Enabled Gold-Catalyzed C(sp2)-S Cross-Coupling Reactions

Herein we report C(sp²)-S cross-coupling reactions of aryl iodides and arylsulfonyl hydrazides under ligand-enabled, Au(I)/Au(III) redox catalysis. This strategy operates under mild reaction conditions, requires no prefunctionalized aryl coupling partner, and works across several aryl iodides. The utility of this protocol is highlighted through the synthesis of various medicinally relevant biaryl sulfones. The reaction mechanism is supported with control experiments, mass spectrometry, and NMR studies.

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.

Rhodium(III)-catalyzed oxidative annulation of isoquinolones with allyl alcohols: synthesis of isoindolo[2,1-b]isoquinolin-5(7H)-ones

An efficient rhodium(III)-catalyzed direct C-H oxidative annulation of isoquinolones with allyl alcohols as C1 synthons has been successfully developed. This protocol enables the straightforward synthesis of structurally diverse isoindolo[2,1-b]isoquinolin-5(7H)-ones with high atom economy, tolerates a broad spectrum of functionalities, and is applicable to one-pot operation from readily available N-methoxybenzamides.

Transition metal catalysed direct sulfanylation of unreactive C-H bonds: an overview of the last two decades

Transition metal catalysed direct sulfanylations of unreactive C-H bonds have become a unique and straightforward synthetic strategy in late-stage C-S bond formation of relevant complex molecules. Such transformations have represented...

Applications of DABSO as an SO2 Gas Surrogate in Organic Synthesis

1,4-Diazabicyclo[2.2.2]octane bis(sulfur dioxide), DABCO.SO2, or DABSO, a bench-stable colorless solid, is industrially produced by the reaction of DABCO with the condensed and bubbled sulfur dioxide gas at low temperatures. However,...

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed to add water as the solvent, and it featured mild reaction condition,...

α-Selective C(sp3)-H Thio/Selenocyanation of Ketones with Elemental Chalcogen

A facile method is disclosed for the synthesis of α-thio/selenocyanato ketones through regioselective C-H thio/selenocyanation of ketones. The advantages include the use of easily available starting materials, high efficiency, simple operation, and easy scale-up. Control experiments provide evidence that the reaction proceeded via a radical way, while kinetic isotope effect experiments reveal that the cleavage of the C-H bond serves as the rate-limiting step.

Double C-S bond formation via multiple Csp3-H bond cleavage: synthesis of 4-hydroxythiazoles from amides and elemental sulfur under metal-free conditions

A novel and efficient approach for the synthesis of 4-hydroxythiazoles from amides and elemental sulfur has been developed. In the presence of P₂O₅, DMSO and HMPA, this metal-free protocol proceeds smoothly and tolerates a spectrum of functional groups. Furthermore, this strategy involves the process of double Csp³-S bond formation through the cleavage of multiple Csp³-H bonds for the first time.

Recent Progress and Emerging Technologies towards a Sustainable Synthesis of Sulfones

Sulfones play a pivotal role in modern organic chemistry. They are highly versatile building blocks and find various applications as drugs, agrochemicals, or functional materials. Therefore, sustainable access to this class of molecules is of great interest. Herein, the goal was to provide a summary on recent developments in the field of sustainable sulfone synthesis. Advances and existing limitations in traditional approaches towards sulfones were reviewed on selected examples. Furthermore, novel emerging technologies for a more sustainable sulfone synthesis and future directions were discussed.

Palladium-Catalyzed Distal m-C-H Functionalization of Arylacetic Acid Derivatives

Herein, we present m-C-H olefination on derivatives of phenylacetic acids by tethering with a simple nitrile-based template through palladium catalysis. Notably, the versatility of the method is evaluated with a wide range of phenylacetic acid derivatives for obtaining the meta-olefination products in fair to excellent yields with outstanding selectivities under mild conditions. Significantly, the present strategy is successfully exemplified for the synthesis of drugs/natural product analogues (naproxen, ibuprofen, paracetamol, and cholesterol).

The Renaissance of Alkali Metabisulfites as SO2 Surrogates

The upsurge of interest in the development of methodologies for the construction of sulfur-containing compounds via the use of expedient reagents has established sustainable tools in organic chemistry. This review focuses on sulfonylation reactions using inorganic sulfites (Na2S2O5 or K2S2O5) as the sulfur dioxide surrogates. Compared to the bis-adduct with DABCO, which is an excellent surrogate of gaseous SO2, the use of sodium or potassium metabisulfites as SO2 surrogates are equally efficient. The objective of the current review is to exemplify recent sulfonylation reactions using inorganic sulfites. For better understanding, the review is categorized according to the mode of reactions: transition-metal-catalyzed SO2 insertion, metal-free SO2 insertion, and visible-light-mediated SO2 insertion. All the reactions in each of the sections are illustrated with selected examples with a pertinent explanation of the proposed mechanism.

1 Introduction

2 Outlines of the Reactions Involving SO2 Insertion

2.1 Transition-Metal-Catalyzed SO2 Insertion

2.2 Transition-Metal-Free SO2 Insertion

2.3 Visible-Light-Mediated SO2 Insertion

3 Conclusion and Outlook

Decatungstate-Catalyzed C(sp3)-H Sulfinylation: Rapid Access to Diverse Organosulfur Functionality

Here we report the direct conversion of strong, aliphatic C(sp3)-H bonds into the corresponding alkyl sulfinic acids via decatungstate photocatalysis. This transformation has been applied to a diverse range of C(sp3)-rich scaffolds, including natural products and approved pharmaceuticals, providing efficient access to complex sulfur-containing products. To demonstrate the broad potential of this methodology for the divergent synthesis of pharmaceutically relevant molecules, procedures for the diversification of the sulfinic acid products into a range of medicinally relevant functional groups have been developed.

Oxidation Potential-Guided Electrochemical Radical-Radical Cross-Coupling Approaches to 3-Sulfonylated Imidazopyridines and Indolizines

Oxidation potential-guided electrochemical radical-radical cross-coupling reactions between N-heteroarenes and sodium sulfinates have been established. Thus, simple cyclic voltammetry measurement of substrates predicts the likelihood of successful radical-radical coupling reactions, allowing the simple and direct synthetic access to 3-sulfonylated imidazopyridines and indolizines. The developed electrochemical radical-radical cross-coupling reactions to sulfonylated N-heteroarenes boast the green synthetic nature of the reactions that are oxidant- and metal-free.

Complementary Site-Selective Sulfonylation of Aromatic Amines by Superacid Activation

Under superacidic conditions, aniline and indole derivatives are sulfonylated at low temperature with easy-to-access arenesulfonic acids or arenesulfonyl hydrazides. By modification of the functional-group directing effect through protonation, this method allows nonclassical site functionalization by overcoming the innate regioselectivity of electrophilic aromatic substitution. This superacid-mediated sulfonylation of arenes is complementary to existing methods and can be applied, through protection by protonation, to the late-stage site-selective functionalization of natural alkaloids and active pharmaceutical ingredients.

Regioselective C-H Thioarylation of Electron-Rich Arenes by Iron(III) Triflimide Catalysis

A mild and regioselective method for the preparation of unsymmetrical biaryl sulfides using iron(III) catalysis is described. Activation of N-(arylthio)succinimides using the powerful Lewis acid iron(III) triflimide allowed the efficient thiolation of a range of arenes, including anisoles, phenols, acetanilides, and N-heterocycles. The method was applicable for the late-stage thiolation of tyrosine and tryptophan derivatives and was used as the key step for the synthesis of pharmaceutically relevant biaryl sulfur-containing compounds such as the antibiotic dapsone and the antidepressant vortioxetine. Kinetic studies revealed that while N-(arylthio)succinimides bearing electron-deficient arenes underwent thioarylation catalyzed entirely by iron(III) triflimide, N-(arylthio)succinimides with electron-rich arenes displayed an autocatalytic mechanism promoted by the Lewis basic product.

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.

Synthesis of C3-sulfone substituted naphthols via rhodium(III)-catalyzed annulation of sulfoxonium ylides with alkynylsulfones

C-H activation of sulfoxonium ylides catalyzed by rhodium(iii) with subsequent annulation by alkynylsulfones was accomplished. This methodology offers a step-economical approach for assembling C3-sulfone-substituted naphthols with a high level of regioselectivity that is complementary to previous protocols. The approach has an extensive substrate spectrum and broad functional group tolerance.

Rhodium(III)-catalyzed oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols

An efficient Rh(iii)-catalyzed C-H oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols by merging tandem C-H and C-C cleavage was developed. This transformation features mild reaction conditions, high regioselectivity, and excellent functional group compatibility. The resulting β-aryl ketone derivatives can be readily transformed into 7-azaindole-containing π-extended polycyclic heteroarenes.

Ruthenium-catalyzed coupling of α-carbonyl phosphoniums with sulfoxonium ylides via C–H activation/Wittig reaction sequences

A Ru(ii)-catalyzed coupling of various α-carbonyl phosphoniums with sulfoxonium ylides has been realized for the facile synthesis of 1-naphthols in good to excellent yields.

Cp*Ir(iii)- and Cp*Rh(iii)-catalyzed C(sp2)–H amination of arenes using thioethers as directing groups

A mild and selective Cp*Ir(iii)- and Cp*Rh(iii)-catalyzed direct C(sp²)–H amination of arenes and three types of nitrene precursor reagents is reported, with the assistance of a thioether directing group.

A simple removable aliphatic nitrile template 2-cyano-2,2-di-isobutyl acetic acid for remote meta-selective C–H functionalization

The remote meta-selective C–H functionalization of arenes using first aliphatic nitrile template 2-cyano-2,2-di-isobutyl acetic acid under mild conditions is presented.

Pd-Catalyzed Directed Thiocyanation Reaction by C-H Bond Activation

The Pd-catalyzed directed thiocyanation reaction of arenes and heteroarenes by C-H bond activation was achieved. In the presence of an electrophilic SCN source, this original methodology offered an efficient tool to access a panel of functionalized thiocyanated compounds (21 examples, up to 78 % yield). Post-functionalization reactions further demonstrated the synthetic utility of the approach by converting the SCN-containing molecules into value-added scaffolds.