Radical 1-Fluorosulfonyl-2-alkynylation of Unactivated Alkenes

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.

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 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.

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

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.

Aliphatic Sulfonyl Fluoride Synthesis via Decarboxylative Fluorosulfonylation of Hypervalent Iodine(III) Carboxylates

We disclose herein a photocatalytic decarboxylative fluorosulfonylation reaction of various hypervalent iodine(III) carboxylates in combination with 1,4-diazabicyclo[2.2.2]octane-bis(sulfur dioxide) adduct as a sulfonyl source and KHF2 as a desirable fluorine source via a radical sulfur dioxide insertion and fluorination strategy. A one-pot photocatalytic decarboxylative fluorosulfonylation reaction of various carboxylic acids mediated by PhI(OAc)2 was realized, as well. Notably, this transformation can be performed under heating conditions without the need for catalysts.

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.

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.

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.

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.

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.

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.

Sulfonyl fluorides are compounds with potential application in chemical biology and drug discovery, but their preparation can be challenging. Here, the authors present a type of bench-stable fluorosulfonyl radical reagents that enable radical fluorosulfonylation reactions via photoredox catalysis.

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.

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.