Radical Fluorosulfonylation: Accessing Alkenyl Sulfonyl Fluorides from Alkenes

Synthesis of 1,5-Diamino-Substituted 1,3-Dienes via Rhodium(II)-Catalyzed Tandem Reactions of 1-Cyclopropylethylarenes

Herein, (E,E)-1,5-diamino-1,3-dienes are stereoselectively synthesized from substituted aryl derivatives via a rhodium(II)-catalyzed C(sp3)-H functionalization involving a cascade of cyclopropane ring expansion, cyclobutene formation, cyclobutene to 1,3-diene conversion, and regioselective diamination. Mechanistic studies show this one-pot process proceeds through hydrogen atom transfer (HAT), radical-polar crossover (RPC), elimination, electrocyclic ring-opening, and radical addition, underscoring rhodium(II)'s role in radical-mediated catalysis beyond traditional rhodium(II) nitrenoid chemistry.

Photocatalytic Radical Azido/Fluorosulfonylation of Unactivated Alkenes: Accessing Hubs Bridging CuAAC and SuFEx Click Chemistry

Herein, we describe the successful development of an azido-fluorosulfonylation reaction of alkenes under photoredox catalysis, which could allow the installation of the two "clickable" groups, -N3 and -SO2F, on a C-C double bond, with TMSN3 as the azide source. The utilization of the difunctionalization products is also demonstrated in the construction of a library of 1,2,3-triazolesulfonyl fluoride compounds as well as drug molecule ligation by merging copper-catalyzed azide-alkyne cycloaddition (CuAAC) and sulfur(VI) fluoride exchange (SuFEx), the two generations of click reactions. Mechanistic studies suggest a radical fluorosulfonylation/azidation mechanism and unveil FSO2N3 as a new and potential fluorosulfonyl radical precursor.

Photoredox-Catalyzed Allylic C-H Fluorosulfonylation of Alkenes: Accessing Allyl Sulfonyl Fluorides

This study reported a novel and unprecedented photoredox-catalyzed protocol for direct allylic C-H fluorosulfonylation of alkenes with FABI. This mild protocol exhibited excellent compatibility with various functional groups, broad substrate scope, and promising scalability, enabling convenient access to a wide range of allyl sulfonyl fluorides with exceptional regioselectivity. The synthetic robustness of this strategy was further demonstrated by the late-stage functionalization of natural products and their ligation with other drugs via SuFEx chemistry.

Nickel-Catalyzed Direct Fluorosulfonylation of Vinyl Bromides and Benzyl Bromides for Sulfonyl Fluorides

An efficient nickel-catalyzed direct fluorosulfonylation of vinyl bromides and benzyl bromides under mild reaction conditions has been developed for sulfonyl fluorides utilizing Na2S2O4 and NFSI as the sulfur dioxide and fluorine sources, respectively. This reaction system tolerates organic bromide compounds, such as β-styryl bromides, alkyl vinyl bromides, and benzyl bromides, to achieve corresponding sulfonyl fluorides in moderate to good yields, with convenient operation, mild conditions, broad substrate scope, good functional group compatibility, and excellent retention of configuration to vinyl bromides.

Cyano-Fluorosulfonylation of Unactivated Alkenes by Photoredox and Copper Dual Catalysis

Both fluorosulfonyl and cyano groups are important structural motifs in bioactive molecules. Herein, we report a new difunctionalization reaction of alkenes based on fluorosulfonyl radicals, which allows for the introduction of the fluorosulfonyl and cyano groups into unactivated alkenes in one step. This transformation is enabled by merging photoredox and copper catalysis, featuring visible light catalysis, mild conditions, and good functional group tolerance. Further transformation of products via SuFEx reactions is also demonstrated.

Stereo- and Regioselective Installation of Vinyl Sulfonyl Fluoride onto Indoles without Transition-Metal Catalyst

Herein, we developed a practical method for synthesizing a class of novel and highly valuable indolyl vinyl sulfonyl fluorides. This protocol has carved out a path for constructing a broad range of vinyl sulfonyl fluorinated indoles with exclusive stereo- and regioselectivity through the Friedel-Crafts/elimination reaction without any transition-metal catalyst. This transformation features mild conditions, high efficiency, excellent selectivity, and rich substrate compatibility, highlighting its significant value in medicinal chemistry and many related disciplines.

Fe-Catalyzed Fluorosulfonylation of Alkenes via Sulfur Dioxide Insertion: Synthesis of Lactam-Functionalized Alkyl Sulfonyl Fluorides

A novel Fe-catalyzed fluorosulfonylation of alkenes with Na2S2O4 and N-fluorobenzenesulfonimide (NFSI) for assembling various lactam-functionalized alkyl sulfonyl fluorides is disclosed. In this reaction, Na2S2O4 acts as both an SO2 source and a reductant. Furthermore, the resulting products can be efficiently transformed into valuable chemicals, including sulfonyl esters and sulfonamides, via the sulfur(VI) fluoride exchange (SuFEx) click reaction. Preliminary mechanistic studies suggest that the transformation proceeds through intramolecular radical cyclization, SO2 insertion, sulfite anion formation, and fluorination.

Radical Fluorosulfonamidation: A Facile Access to Sulfamoyl Fluorides

Recently, the introduction of fluorosulfonyl (-SO2F) groups have attracted considerable research interests, as this moiety could often afford enhanced activities and new functions in the context of chemical biology and drug discovery. Herein, we report the design and synthesis of 1-fluorosulfamoyl-pyridinium (FSAP) salts, which could serve as an effective photoredox-active precursor to fluorosulfamoyl radicals and enable the direct radical C-H fluorosulfonamidation of a variety of (hetero)arenes. This method features mild conditions, visible light, broad substrate scope, good group tolerance, etc., and a metal-free protocol is also viable by using organic photocatalysts. Further, FSAP can also be applied to the radical functionalization of alkenes via 1,2-difunctionalization, radical distal migration, tandem radical-polar crossover reactions, etc. In addition, a formal C-H methylamination of (hetero)arenes by combining this radical C-H fluorosulfonamidation with subsequent hydrolysis as well as product derivatization are also demonstrated.

Radical Ring-Opening Fluorosulfonylation of Methylenecyclobutanols via Electron Donor-Acceptor Photoactivation

A visible-light-mediated catalyst- and additive-free method for radical ring-opening fluorosulfonylation of methylenecyclobutanols is reported. Sulfuryl chlorofluoride acts as a FSO2 radical precursor as well as an electron acceptor to form electron donor-acceptor complexes with various methylenecyclobutanol substrates. This method shows fully regioselective and (E)-stereoselective ring-opening processes, providing a variety of FSO2-functionalized γ,δ-unsaturated carbonyls in 38-77% yields. A selection of product diversifications has been studied to demonstrate the versatility of these sulfonyl fluoride products.

Ultrafast Flow Synthesis of o-Functionalized Benzenesulfonyl Fluorides and Subsequent SuFEx Connections via Lithiated Chemistry

Herein we present a flow-based, rapid, and straightforward approach to synthesize diverse functionalized sulfonyl fluorides by harnessing an aryllithium intermediate. The aryllithium intermediate was fully utilized under optimized conditions (0.016 s, -18 °C) to afford various functionalized sulfonyl fluorides and also intramolecular SuFEx cyclization products in high yields (27-94%). Furthermore, the integrated synthesis incorporating subsequent SuFEx connections with even unstable organolithium nucleophiles facilitated one-flow molecular assembly in high yields (42-72%).

Fluorosulfonyl Arylation of Alkynes via Electron Donor-Acceptor Photoactivation

A radical fluorosulfonyl arylation of alkynes with sulfuryl chlorofluoride as the FSO2 radical precursor via electron donor-acceptor photoactivation driven by daylight or a blue light-emitting diode is disclosed. A series of valuable benzo-fused carbocycles and heterocycles have been produced with simple operation under mild conditions in the absence of any external catalysts or additives. The synthetic potential of this protocol has further demonstrated excellent scalability, as well as diverse postderivatizations, including SuFEx reactions and other useful cascade reactions.

Stereoselective Fluorosulfonylation of Vinylboronic Acids for (E)-Vinyl Sulfonyl Fluorides with Copper Participation

A practical synthetic method for the synthesis of vinyl sulfonyl fluorides through copper-promoted direct fluorosulfonylation has been developed. The reaction of the vinylboronic acids with DABSO and then NFSI is performed under mild reaction conditions. This transformation efficiently affords aryl or alkyl vinyl sulfonyl fluorides with good reaction yields, exclusive E-configuration, broad substrate scope, excellent compatibility, and operational simplicity.

Radical Hydro-Fluorosulfonylation of Propargylic Alcohols via Electron Donor-Acceptor Photoactivation

A radical hydro-fluorosulfonylation of propargyl alcohols with FSO2Cl is presented based on the photoactivation of the electron donor-acceptor (EDA) complex. The reaction avoids the requirement for photocatalysts, bases, hydrogen donor reagents, any other additives, and harsh conditions, enabling the facile synthesis of various functionalized γ-hydroxy (E)-alkenylsulfonyl fluorides. These multifunctional sulfonyl fluorides can be further diversified, providing access to various privileged molecules of biological relevance.

Electroreductive hydroxy fluorosulfonylation of alkenes

An electroreductive strategy for radical hydroxyl fluorosulfonylation of alkenes with sulfuryl chlorofluoride and molecular oxygen from air is described. This mild protocol displays excellent functional group compatibility, broad scope, and good scalability, providing convenient access to diverse β-hydroxy sulfonyl fluorides. These β-hydroxy sulfonyl fluoride products can be further converted to valuable aliphatic sulfonyl fluorides, β-keto sulfonyl fluorides, and β-alkenyl sulfonyl fluorides. Further, some of these products showed excellent inhibitory activity against Botrytis cinerea or Bursaphelenchus xylophilus, which could be useful for potent agrochemical discovery. Preliminary mechanistic studies indicate that this transformation is achieved through rapid O2 interception by the alkyl radical and subsequent reduction of the peroxy radical, which outcompete other side reactions such as chlorine atom transfer, hydrogen atom transfer, and Russell fragmentation.

An efficient and mild oxidative approach from thiols to sulfonyl derivatives with DMSO/HBr

A mild and practical method for synthesizing sulfonyl derivatives, which have a wide range of applications in pharmaceuticals, materials, and organic synthesis, was described through the oxidative functionalization of thiols with DMSO/HBr. The simple conditions, low cost and ready availability of DMSO/HBr, as well as the versatility of the transformations, make this strategy very powerful in synthesizing a variety of sulfonyl derivatives including sulfonamides, sulfonyl fluorides, sulfonyl azides, and sulfonates. Mechanistic studies revealed that DMSO served as the terminal oxidant, and HBr acted as both a nucleophile and a redox mediator to transfer the oxygen atom.

Turning sulfonyl and sulfonimidoyl fluoride electrophiles into sulfur(VI) radicals for alkene ligation

Sulfonyl and sulfonimidoyl fluorides are versatile substrates in organic synthesis and medicinal chemistry. However, they have been exclusively used as S(VI)+ electrophiles for defluorinative ligations. Converting sulfonyl and sulfonimidoyl fluorides to S(VI) radicals is challenging and underexplored due to the strong bond dissociation energy of SVI-F and high reduction potentials, but once achieved would enable dramatically expanded synthetic utility and downstream applications. In this report, we disclose a general platform to address this issue through cooperative organosuperbase activation and photoredox catalysis. Vinyl sulfones and sulfoximines are obtained with excellent E selectivity under mild conditions by coupling reactions with alkenes. The synthetic utility of this method in the preparation of functional polymers and dyes is also demonstrated.

Fluorochemicals from fluorspar via a phosphate-enabled mechanochemical process that bypasses HF

All fluorochemicals-including elemental fluorine and nucleophilic, electrophilic, and radical fluorinating reagents-are prepared from hydrogen fluoride (HF). This highly toxic and corrosive gas is produced by the reaction of acid-grade fluorspar (>97% CaF₂) with sulfuric acid under harsh conditions. The use of fluorspar to produce fluorochemicals via a process that bypasses HF is highly desirable but remains an unsolved problem because of the prohibitive insolubility of CaF₂. Inspired by calcium phosphate biomineralization, we herein disclose a protocol of treating acid-grade fluorspar with dipotassium hydrogen phosphate (K₂HPO₄) under mechanochemical conditions. The process affords a solid composed of crystalline K₃(HPO₄)F and K_2-xCa_y(PO₃F)_a(PO₄)_b, which is found suitable for forging sulfur-fluorine and carbon-fluorine bonds.

Advances in the construction of diverse SuFEx linkers

Sulfur fluoride exchange (SuFEx), a new generation of click chemistry, was first presented by Sharpless, Dong and co-workers in 2014. Owing to the high stability and yet efficient reactivity of the S^VI-F bond, SuFEx has found widespread applications in organic synthesis, materials science, chemical biology and drug discovery. A diverse collection of SuFEx linkers has emerged, involving gaseous SO₂F₂ and SOF₄ hubs; SOF₄-derived iminosulfur oxydifluorides; O-, N- and C-attached sulfonyl fluorides and sulfonimidoyl fluorides; and novel sulfondiimidoyl fluorides. This review summarizes the progress of these SuFEx connectors, with an emphasis on analysing the advantages and disadvantages of synthetic strategies of these connectors based on the SuFEx concept, and it is expected to be beneficial to researchers to rapidly and correctly understand this field, thus inspiring further development in SuFEx chemistry.

Visible-light-driven reactions for the synthesis of sulfur dioxide-inserted compounds: generation of S-F, S-O, and S-N bonds

Sulfur dioxide-containing compounds such as sulfonyl fluorides, sulfonyl esters, and sulfonyl amides are important structural frameworks in many natural products, pharmaceuticals, and organic compounds. Thus, synthesis of these molecules is a very valuable research topic in organic chemistry. Various synthetic methods to introduce SO₂ groups into the structure of organic compounds have been developed for the synthesis of biologically and pharmaceutically useful compounds. Recently, visible-light-driven reactions were carried out to create SO₂-X (X = F, O, N) bonds, and their effective synthetic approaches were demonstrated. In this review, we summarized recent advances in visible-light-mediated synthetic strategies for generation of SO₂-X (X = F, O, N) bonds for various synthetic applications along with proposed reaction mechanisms.

Fluorosulfonylvinylation of Unactivated C(sp3)-H via Electron Donor-Acceptor Photoactivation

An electron donor-acceptor (EDA) complex photoactivation strategy for radical fluorosulfonylation is disclosed for the first time. Simply upon blue light irradiation, the FSO₂ radical can be generated efficiently under catalyst-free, base-free, and additive-free conditions, which enables facile access to 6-keto alkenylsulfonyl fluorides from readily available propargyl alcohols and FSO₂Cl. The 6-keto alkenylsulfonyl fluoride motif has been showcased as a versatile SuFEx hub with diverse follow-up derivatizations.

SO2ClF: A Reagent for Controllable Chlorination and Chlorooxidation of Simple Unprotected Indoles

Sulfuryl chlorofluoride was first employed as a versatile reagent for controllable chlorination and chlorooxidation of simple unprotected indoles. Three types of products including 3-chloro-indoles, 3-chloro-2-oxindoles, and 3,3-dichloro-2-oxindoles could be selectively obtained in good to excellent yields by switching the reaction solvents. The present method features easy-to-operate, broad substrate scope, and mild reaction conditions.

Synthesis of Sulfonyl Fluorides Using Direct Chloride/Fluoride Exchange in Potassium Fluoride and Water/Acetone

A multitude of synthetic routes are available for the preparation of sulfonyl fluorides (R-SO₂F) whose discovery is now almost a century old. These syntheses are often limited by the scope, hazardous materials, and elaborate procedures. The simple and mild procedure based on direct chloride/fluoride exchange from a sulfonyl chloride (R-SO₂Cl) starting material in a KF and water/acetone biphasic mixture is investigated. Seventeen examples in high yield (84-100%) with wide scope are described.

Radical Fluorosulfonyl Heteroarylation of Unactivated Alkenes with Quinoxalin-2(1H)-ones and Related N-Heterocycles

The incorporation of sulfonyl fluoride groups into molecules has been proved effective to enhance their biological activities or introduce new functions. Herein, we report a transition-metal-free and visible-light-mediated radical 1-fluorosulfonyl-2-heteroarylation of alkenes, which could allow access to a series of SO₂F-containing quinoxalin-2(1H)-ones, which are a critical structural motif widely present in a number of biologically active molecules. Further application of the method to the modification of other heterocycles and drug molecules as well as ligation chemistry via SuFEx click reactions is also demonstrated.

EnT-Mediated N-S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

Sulfur(VI) fluoride exchange (SuFEx) gives rise to a plethora of high-valent sulfur linkages; however, the availability of (aliphatic) sulfonyl fluoride manifolds lag behind, owing to the limited sources of introducing the SO₂F moiety via a classical two-electron approach. Recently, radical-based methodologies have emerged as a complementary strategy to increase the diversity of accessible click partners. In this work, synthesis of a bench-stable sulfamoyl fluoride reagent is presented, which may undergo sigma-bond homolysis upon visible-light-induced sensitization to form protected β-amino sulfonyl fluorides from alkene feedstocks. Notably, this offers an appealing strategy to access various building blocks for peptido sulfonyl fluorides, relevant in a medicinal chemistry context, as well as an intriguing entry to β-ammonium sulfonates and β-sultams, from alkenes. Densely functionalized 1,3-sultones were obtained by employing allyl alcohols as substrates. Surprisingly, allyl chloride-derived β-imino sulfonyl fluoride underwent S-O bond formation and ring closure to yield rigid cyclopropyl β-imino sulfonate ester under SuFEx conditions. Furthermore, by engaging a thiol-based hydrogen atom donor in the reaction, the reactivity of the same reagent can be tuned toward the direct synthesis of aliphatic sulfonyl fluorides. Mechanistic experiments indicate an energy transfer (EnT)-mediated process. The transient sulfonyl fluoride radical adds to the alkene and product formation occurs upon either radical-radical coupling or hydrogen atom transfer (HAT), respectively.

Electroreductively Induced Radicals for Organic Synthesis

Organic electrochemistry has attracted tremendous interest within the novel sustainable methodologies that have not only reduced the undesired byproducts, but also utilized cleaner and renewable energy sources. Particularly, oxidative electrochemistry has gained major attention. On the contrary, reductive electrolysis remains an underexplored research direction. In this context, we discuss advances in transition-metal-free cathodically generated radicals for selective organic transformations since 2016. We highlight the electroreductive reaction of alkyl radicals, aryl radicals, acyl radicals, silyl radicals, fluorosulfonyl radicals and trifluoromethoxyl radicals.

A General Procedure for the Construction of 2-Alkyl-Substituted Vinyl Sulfonyl Fluoride

A series of compact and multifunctional 2-alkyl-substituted vinyl sulfonyl fluorides were efficiently prepared from the corresponding alkyl iodides and 2-chloroprop-2-ene-1-sulfonyl fluoride (CESF). This Giese-type radical approach provided new and general access to alkenyl sulfonyl fluorides, including structures that would otherwise be challenging to synthesize with previously established methods. A correspondingly large collection of derivatization reactions was also demonstrated on the alkenyl sulfonyl fluorides.

Contrasting the Noncovalent Interactions of Aromatic Sulfonyl Fluoride and Sulfonyl Chloride Motifs via Crystallography and Hirshfeld Surfaces

A heteroaryl sulfonyl(VI) fluoride, 4-chloro-7-fluorosulfonyl-2,1,3-benzoxadiazole, was synthesized from its chloride counterpart (4-chloro-7-chlorosulfonyl-2,1,3-benzoxadiazole) and the X-ray structure analysis of these compounds and the interactions in the solid-state were thoroughly examined. Hirshfeld surface analysis is used to provide a thorough and complete picture of the changes arising from the different halides in the functional groups. Surface analysis reveals that the fluoride does not participate in any hydrogen interactions as opposed to the chloride. However, the fluorine atom is observed to form close interactions with several π bonds. For both moieties, however, the sulfonyl oxygens show comparable interactions with respect to both magnitude and interatomic distances. The Hirshfeld surface analysis is coupled with computational studies to help elucidate the observed interactions that are found from the distinct nitrogen, chlorine, and oxygen atoms present in the molecules, providing new physical insights to the correlation between their structures and properties.

β-Aminosulfonyl Fluorides via Water-Accelerated N-Heterocyclic Carbene Catalysis

Herein, a water-accelerated, N-heterocyclic carbene (NHC)-catalyzed aza-Michael addition reaction was reported to access β-aminosulfonyl fluorides, which are key hubs of the sulfur(VI) fluoride exchange (SuFEx) reaction. As a crucial reaction medium, water considerably enhanced the reaction rate with excellent chemo- and site-selectivity (up to >99 : 1) compared to conventional solvents. In addition, the late-stage ligation of bioactive molecules with the aliphatic β-amino SuFEx hub was demonstrated. Mechanistic studies on experimental, analytical, and computational approaches support noncovalent activation over NHC catalysis "on-water".

Synthesis of 2-arylethenesulfonyl fluorides and isoindolinones: Ru-catalyzed C-H activation of nitrones with ethenesulfonyl fluoride

A novel strategy for the synthesis of 2-arylethenesulfonyl fluorides from nitrones and ethenesulfonyl fluoride (ESF) by the activation of the C-H bond using an inexpensive and readily available Ru-catalyst has been developed. In this process, the directing group can be concomitantly converted to an amide group. Interestingly, changing the substituent of the nitrogen of nitrones from a tert-butyl to a methyl group resulted in the formation of cyclic isoindolinones. Detailed mechanistic studies are also presented.

Photo-organocatalytic Synthesis of β-Keto Sulfonyl Fluorides via Radical Fluorosulfonylation of Vinyl Acetates

A metal-free synthesis of useful β-keto sulfonyl fluorides has been established via radical fluorosulfonylation of ketone-derived vinyl acetates under photoredox organocatalysis by using 1-fluorosulfonyl benzoimidazolium (FABI) as the fluorosulfonyl radical source and oxygen-doped anthanthrene (ODA) as the photocatalyst. A series of aryl and alkyl β-keto sulfonyl fluorides as well as cyclic analogues can be readily obtained in moderate to high yields from widely available ketone starting materials.

Synthesis and 18F Labeling of Alkenyl Sulfonyl Fluorides via an Unconventional Elimination Pathway

A successful Cu-catalyzed addition of both Cl and SO₂OCF₂H groups into alkenes allows us to discover the unusual reactivity of the SO₂OCF₂H group. As opposed to common sulfonic esters (RSO₂-O-R'), in which the R' group is highly electrophilic, the SO₂ moiety demonstrates higher electrophilicity in RSO₂-OCF₂H. The unexpected reactivity is further developed not only as a synthetic tool for well-functionalized alkenyl sulfonyl fluorides but also for the first ¹⁸F labeling of alkenyl sulfonyl fluorides.

A practical fluorosulfonylating platform via photocatalytic imidazolium-based SO2F radical reagent

Sulfonyl fluorides are key components in the fields of chemical biology, materials science and drug discovery. In this line, the highly active SO₂F radical has been employed for the construction of sulfonyl fluorides, but the utilization of gaseous ClSO₂F as radical precursor is limited due to the tedious and hazardous preparation. Meanwhile, the synthesis of sulfonyl fluorides from inert SO₂F₂ gas through a fluorosulfonyl radical (·SO₂F) process has met with inevitable difficulties due to the high homolytic bond dissociation energy of the S(VI)-F bond. Here we report a radical fluorosulfonylation strategy for the stereoselective synthesis of alkenyl sulfonyl fluorides and functional alkyl sulfonyl fluorides with an air-stable crystalline benzimidazolium fluorosulfonate cationic salt reagent. This bench-stable redox-active reagent offers a useful and operational protocol for the radical fluorosulfonylation of unsaturated hydrocarbons with good yield and high stereoselectivity, which can be further transformed into valuable functional SO₂F moieties.

Sulfonyl fluorides have potential application in chemical biology, materials science, and drug discovery, but their preparation remains challenging. Here, the authors report an air-stable fluorosulfonylating reagent that enables the radical fluorosulfonylation, hydrofluorosulfonylation and migratory SO₂F-difunctionalization of unsaturated hydrocarbons to construct a variety of sulfonyl fluoride compounds.

Olefination with Sulfonyl Halides and Esters: Synthesis of Unsaturated Sulfonyl Fluorides

Methanedisulfonyl fluoride, CH2(SO2F)2, transforms aromatic aldehydes into β-arylethenesulfonyl fluorides, useful substrates for the SuFEx "click"-type transformations. The reaction mimics mechanism of the Horner-Wadsworth-Emmons olefination, which runs via addition of the carbanion, followed by cyclization-fragmentation of the four-membered ring intermediate. In the absence of base, electron-rich aldehydes follow an alternative pathway of the Knoevenagel condensation to provide unsaturated 1,1-disulfonyl fluorides. We demonstrate also trapping of elusive ethene-1,1-disulfonyl fluoride, CH2═C(SO2F)2, with 4-(dimethylamino)pyridine (DMAP) that forms zwitterionic adduct, characterized with X-ray studies.

Regioselective conjugate addition of isoxazol-5-ones to ethenesulfonyl fluoride

The highly regioselective conjugate addition of isoxazol-5-ones to ethenesulfonyl fluoride (ESF) has been developed. In the presence of different bases, N2-alkylated and C4-alkylated isoxazol-5-ones with a sulfonyl fluoride group were obtained separately with good to excellent yields. Further transformations with amines and phenol gave sulfonamides and sulfonates. The intriguing combination of isoxazol-5-ones and the sulfonyl fluoride group produces valuable products for drug discovery.

Photoredox catalytic radical fluorosulfonylation of olefins enabled by a bench-stable redox-active fluorosulfonyl radical precursor

Sulfonyl fluorides have attracted considerable and growing research interests from various disciplines, which raises a high demand for novel and effective methods to access this class of compounds. Radical flurosulfonylation is recently emerging as a promising approach for the synthesis of sulfonyl fluorides. However, the scope of applicable substrate and reaction types are severely restricted by limited known radical reagents. Here, we introduce a solid state, redox-active type of fluorosulfonyl radical reagents, 1-fluorosulfonyl 2-aryl benzoimidazolium triflate (FABI) salts, which enable the radical fluorosulfonylation of olefins under photoredox conditions. In comparison with the known radical precursor, gaseous FSO2Cl, FABI salts are bench-stable, easy to handle, affording high yields in the radical fluorosulfonylation of olefins with before challenging substrates. The advantage of FABIs is further demonstrated in the development of an alkoxyl-fluorosulfonyl difunctionalization reaction of olefins, which forges a facile access to useful β-alkoxyl sulfonyl fluorides and related compounds, and would thus benefit the related study in the context of chemical biology and drug discovery in the future.

Regio- and Stereoselective Installation of Bromide onto Vinyl Sulfonyl Fluorides: Construction of a Class of Versatile Sulfur Fluoride Exchange Hubs

A convenient protocol for the exclusively regio- and stereoselective installation of a bromine atom on the 2-arylvinylsulfonyl fluorides using lithium bromide (LiBr) as the bromine source was described, providing (Z)-1-bromo-2-arylethene-1-sulfonyl fluorides (Z-BASF) with versatile reactive handles (bromide, vinyl, and sulfonyl fluoride) in ≤88% yield. Meanwhile, Z-BASF molecules displayed various reactivities in a series of chemical transformations.

Electrochemical Synthesis of β-Keto Sulfonyl Fluorides via Radical Fluorosulfonylation of Vinyl Triflates

Electrochemical synthesis of versatile β-keto sulfonyl fluorides is accomplished by radical fluorosulfonylation of vinyl triflates with FSO₂Cl as the fluorosulfonyl radical source. This electroreductive protocol uses inexpensive graphite felt as electrodes, thus avoiding the use of a sacrificial anode. Moreover, this protocol, featuring metal-free, mild conditions and easy scalability, allows expedient access to valuable β-keto sulfonyl fluorides from readily available precursors, as well as the cyclic ones that are otherwise inaccessible using prior methods.

Functional group divergence and the structural basis of acridine photocatalysis revealed by direct decarboxysulfonylation

The reactivity of the sulfonyl group varies dramatically from nucleophilic sulfinates through chemically robust sulfones to electrophilic sulfonyl halides-a feature that has been used extensively in medicinal chemistry, synthesis, and materials science, especially as bioisosteric replacements and structural analogs of carboxylic acids and other carbonyls. Despite the great synthetic potential of the carboxylic to sulfonyl functional group interconversions, a method that can convert carboxylic acids directly to sulfones, sulfinates and sulfonyl halides has remained out of reach. We report herein the development of a photocatalytic system that for the first time enables direct decarboxylative conversion of carboxylic acids to sulfones and sulfinates, as well as sulfonyl chlorides and fluorides in one step and in a multicomponent fashion. A mechanistic study prompted by the development of the new method revealed the key structural features of the acridine photocatalysts that facilitate the decarboxylative transformations and provided an informative and predictive multivariate linear regression model that quantitatively relates the structural features with the photocatalytic activity.

Radical 1-Fluorosulfonyl-2-alkynylation of Unactivated Alkenes

Sulfonyl fluorides have found widespread use in chemical biology and drug discovery. The development of synthetic methods for the introduction of the sulfonyl fluoride moiety is therefore of importance. Herein, a transition-metal-free radical 1,2-difunctionalization of unactivated alkenes via FSO2 -radical addition with subsequent vicinal alkynylation to access β-alkynyl-fluorosulfonylalkanes is presented. Alkynyl sulfonyl fluorides are introduced as highly valuable bifunctional radical trapping reagents that also serve as FSO2 -radical precursors. The β-alkynyl-fluorosulfonylalkanes obtained in these transformations can be readily diversified by using SuFEx click chemistry to obtain sulfonates and sulfonamides.

Catalytic Decarboxylative Fluorosulfonylation Enabled by Energy-Transfer-Mediated Photocatalysis

Sulfonyl fluorides are useful building blocks in a wide array of fields. Herein, we report a catalytic decarboxylative fluorosulfonylation approach for converting abundant aliphatic carboxylic acids to the corresponding sulfonyl fluorides. This transformation is enabled by simple preactivation as aldoxime esters and energy-transfer-mediated photocatalysis. This operationally simple method proceeds with high functional-group tolerance under mild and redox-neutral conditions.

Sulfonyl fluorides as targets and substrates in the development of new synthetic methods

The advent of sulfur(VI)-fluoride exchange (SuFEx) processes as transformations with click-like reactivity has invigorated research into electrophilic species featuring a sulfur-fluorine bond. Among these, sulfonyl fluorides have emerged as the workhorse functional group, with diverse applications being reported. Sulfonyl fluorides are used as electrophilic warheads by both medicinal chemists and chemical biologists. The balance of reactivity and stability that is so attractive for these applications, particularly the resistance of sulfonyl fluorides to hydrolysis under physiological conditions, has provided opportunities for synthetic chemists. New synthetic approaches that start with sulfur-containing substrates include the activation of sulfonamides using pyrilium salts, the deoxygenation of sulfonic acids, and the electrochemical oxidation of thiols. Employing non-sulfur-containing substrates has led to the development of transition-metal-catalysed processes based on palladium, copper and nickel, as well as the use of SO₂F₂ gas as an electrophilic hub. Selectively manipulating molecules that already contain a sulfonyl fluoride group has also proved to be a popular tactic, with metal-catalysed processes again at the fore. Finally, coaxing sulfonyl fluorides to engage with nucleophiles, when required, and under suitable reaction conditions, has led to new activation methods. This Review provides an overview of the challenges in the efficient synthesis and manipulation of these intriguing functional groups.

Photocatalytic fluorosulfonylation of aliphatic carboxylic acid NHPI esters

SO2 radical insertion/fluorination via a photocatalytic redox strategy is developed, providing an efficient and reliable approach for the synthesis of alkylsulfonyl fluorides.