Synthesis and Characterization of 2‐Pyridylsulfur Pentafluorides

Copper-Initiated Regiodivergent Chloropentafluorosulfanylation of 1,3-Enynes under Substrate Control

A copper-catalyzed regiodivergent chloropentafluorosulfanylation strategy for 1,3-enynes using SF5Cl has been developed. The regioselectivity is dictated by the structural and substitution patterns of 1,3-enynes, enabling facile access to three classes of SF5-containing products: propargylic chlorides, 1,3-dienes, and allenes. The reaction systems involve radical species, where the transfer of a chlorine atom from SF5Cl to a carbon radical is considered the predominant pathway. Diverse types of SF5- building blocks can be synthesized through simple functional group transformations.

Fluoroalkylated hypervalent sulfur fluorides: radical addition of arylchlorotetrafluoro-λ6-sulfanes to tetrafluoroethylene

Fluorinated groups are essential hydrophobic groups in drug design. Combining a carbon-free tetrafluoro-λ6-sulfanyl (SF4) group with a polyfluoroalkyl group (RF) provides SF4RF groups, exhibiting high hydrophobicity with a short carbon chain. In this study, various aryltetrafluoro(polyfluoroalkyl)-λ6-sulfanes (ArSF4RF) were synthesized through the radical addition of arylchlorotetrafluoro-λ6-sulfanes (ArSF4Cl) to tetrafluoroethylene. In addition, quantification of hydrophobic constants (πPh) indicated that the SF4 group is considerably more hydrophobic than a difluoromethylene (CF2) group. Further transformation reactions revealed the stabilities and reactivities of these novel fluorinated groups. The high hydrophobicity and synthetic utility of the SF4RF group lead to the potential applications of the SF4RF group in the pharmaceutical field.

Oxidative Fluorination of Selenium and Tellurium Compounds using a Thermally Stable Phosphonium SF5 - Salt Accessible from SF6

Fluorinated group 16 moieties are attractive building blocks in synthetic chemistry but only few synthetic methods are available to prepare them. Herein, we report a new oxidative fluorination reagent capable of stabilizing reactive fluorinated anions. It consists of an SF₅ ^- anion and a chemically inert phosphonium cation and is exceptionally thermally stable. Accordingly, it was used to generate the SeF₅ ^- and TeF₅ ^- anions from the elemental chalcogens and to prepare the unknown tetrafluoro(phenyl)-λ⁵ -selenate PhSeF₄ ^- and -tellurate PhTeF₄ ^- from the corresponding diphenyl dichalcogenides. In addition, we show that further derivatization of [PhTeF₄ ]^- by oxidation to trans-PhTeF₄ O^- and subsequent alkylation gives access to a new class of trans-(alkoxy)(phenyl)tetrafluoro-λ⁶ -tellanes (trans-PhTeF₄ OR), thus providing an approach to introduce the functional group into organic molecules.

Oxidative Fluorination of Heteroatoms Enabled by Trichloroisocyanuric Acid and Potassium Fluoride

In synthetic method development, the most rewarding path is seldom a straight line. While our initial entry into pentafluorosulfanyl (SF₅) chemistry did not go according to plan (due to inaccessibility of reagents such as SF₅Cl at the time), a “detour” led us to establish mild and inexpensive oxidative fluorination conditions that made aryl‐SF₅ compound synthesis more accessible. The method involved the use of potassium fluoride and trichloroisocyanuric acid (TCICA)—a common swimming pool disinfectant—as opposed to previously employed reagents such as F₂, XeF₂, HF, and Cl₂. Thereafter, curiosity led us to explore applications of TCICA/KF as a more general approach to the synthesis of fluorinated Group 15, 16, and 17 heteroatoms in organic scaffolds; this, in turn, prompted SC‐XRD, VT‐NMR, computational, and physical organic studies. Ultimately, it was discovered that TCICA/KF can be used to synthesize SF₅Cl, enabling SF₅ chemistry in an unexpected way.

Structural Investigation of Magnesium Complexes Supported by a Thiopyridyl Scorpionate Ligand

Herein, we report the synthesis of a series of heteroleptic magnesium complexes stabilized with the scorpionate ligand tris(2-pyridylthio)methanide (Tptm). The compounds of the general formula [Mg(Tptm)(X)] (1-X; X = Cl, Br, I) were obtained via protonolysis reaction between the proligand and selected Grignard reagents. Attempts to isolate the potassium derivative K(Tptm) lead to decomposition of Tptm and formation of the alkene (C₅H₄N-S)₂C=C(C₅H₄N-S)₂, and this degradation was also modelled using DFT methods. Compound 1-I was treated with K(CH₂Ph), affording the degradation product [Mg(Bptm)₂] (2; Bptm = {CH(S-C₅NH₃)₂}⁻). We analyzed and quantified the steric properties of the Tptm ligand using the structural information of the compounds obtained in this study paired with buried volume calculations, also adding the structural data of HTptm and its CF₃-substituted congener (HTptm^CF3). These studies highlight the highly flexible nature of this ligand scaffold and its ability to stabilize various coordination motifs and geometries, which is a highly desirable feature in the design of novel organometallic reagents and catalysts.

(Hetero)aryl-SVI Fluorides: Synthetic Development and Opportunities

(Hetero)arylsulfur compounds where the S atom is in the oxidation state VI represent a large percentage of the molecular functionalities present in organic chemistry. More specifically, (hetero)aryl‐S^VI fluorides have recently received enormous attention because of their potential as chemical biology probes, as a result of their reactivity in a simple, modular, and efficient manner. Whereas the synthesis and application of the level 1 fluorination at S^VI atoms (sulfonyl and sulfonimidoyl fluorides) have been widely studied and reviewed, the synthetic strategies towards higher levels of fluorination (levels 2 to 5) are somewhat more limited. This Minireview evaluates and summarizes the progress in the synthesis of highly fluorinated aryl‐S^VI compounds at all levels, discussing synthetic strategies, reactivity, the advantages and disadvantages of the synthetic procedures, the proposed mechanisms, and the potential upcoming opportunities.

Ethynyl-SF4-Pyridines: Reagents for SF4-Alkynylation to Carbonyl Compounds

The trans-tetrafluoro-λ⁶-sulfanyl (SF₄) unit is medicinally attractive because of its high electronegativity, lipophilicity, and unique hypervalent structure. The trans-SF₄ unit can characteristically connect two independent molecules linearly. However, there is no example of the use of this unit for medicinal chemistry due to difficulties in synthesis. We report the first synthesis of (ethynyl-trans-tetrafluoro-λ⁶-sulfanyl)pyridines (t-ethynyl-SF₄-pyridines) and their use as versatile reagents for the first direct SF₄-alkynylation to carbonyl compounds. The addition reaction of t-ethynyl-SF₄-pyridines to the carbonyl group in the presence of MeLi smoothly afforded pyridine-SF₄-propargylic tertiary and secondary alcohols in high yields.

Synthesis of an Eccentric Electron-Deficient Fluorinated Motif, Tetrafluoro-λ6-sulfanyl gem-Difluorocyclopropenes

Fluoro-functionalization is now recognized as a critical strategy in drug discovery; however, the accessible fluoro-functional groups are limited. We herein introduce an eccentric, fully fluorinated motif, trans-tetrafluoro-λ⁶-sulfanyl gem-difluorocyclopropene 2. This novel motif is highly lipophilic and polarized, enabling a connection of two independent groups via three continuous atoms with a large angle of pseudo cis configuration. The target motif was synthesized via a [2+1] cycloaddition of electron-deficient (hetero)aryl-SF₄-alkynes 1 with an electrophilic difluorocarbene source.

In situ ortho-lithiation/functionalization of pentafluorosulfanyl arenes

A general method for ortho-functionalization of pentafluorosulfanyl arenes has been developed. ortho-Lithiation with lithium tetramethylpiperidide at -60 °C in the presence of silicon, germanium, and tin electrophiles affords trapped products in moderate to high yields. Precise temperature regimes and the presence of electrophiles during lithiation are important for successful reactions, since the pentafluorosulfanyl group acts as a competent leaving group at temperatures above -40 °C. Fluoro, bromo, iodo, enolizable keto, cyano, ester, amide, and unsubstituted amino functionalities are compatible with the reaction conditions. Conversion of 2-dimethylsilylpentafluorosulfanyl benzene to 2-halosubstituted derivatives, useful as starting materials in cross-coupling chemistry, was also demonstrated.

When SF5 outplays CF3: effects of pentafluorosulfanyl decorated scorpionates on copper

Polyfluorinated, electron-withdrawing, and sterically demanding supporting ligands are of significant value in chemistry. Here we report the assembly and use of a bis(pyrazolyl)borate, [Ph2B(3-(SF5)Pz)2]- that combines all such features, and involves underutilized pentafluorosulfanyl substituents. The ethylene and carbonyl chemistry of copper(i) supported by [Ph2B(3-(SF5)Pz)2]-, a comparison to the trifluoromethylated counterparts involving [Ph2B(3-(CF3)Pz)2]-, as well as copper catalyzed cyclopropanation of styrene with ethyl diazoacetate and CF3CHN2 are presented. The results from cyclopropanation show that SF5 groups dramatically improved the yields and stereoselectivity compared to the CF3.

Synthesis and Reactivity of a Bioinspired Molybdenum(IV) Acetylene Complex

The isolation of a molybdenum(IV) acetylene (C₂H₂) complex containing two bioinspired 6-methylpyridine-2-thiolate ligands is reported. The synthesis can be performed either by oxidation of a molybdenum(II) C₂H₂ complex or by substitution of a coordinated PMe₃ by C₂H₂ on a molybdenum(IV) center. Both C₂H₂ complexes were characterized by spectroscopic means as well as by single-crystal X-ray diffraction. Furthermore, the reactivity of the coordinated C₂H₂ was investigated with regard to acetylene hydratase, one of two enzymes that accept C₂H₂ as a substrate. While the reaction with water resulted in the vinylation of the pyridine-2-thiolate ligands, an intermolecular nucleophilic attack on the coordinated C₂H₂ with the soft nucleophile PMe₃ was observed to give a cationic ethenyl complex. A comparison with the tungsten analogues revealed less tightly bound C₂H₂ in the molybdenum variant, which, however, shows a higher reactivity toward nucleophiles.

Synthesis and [3,3]-sigmatropic rearrangements of 5-(pentafluorosulfanyl)-pent-3-en-2-ol, its homologues, and trifluoromethyl analogues

The synthesis of aliphatic (pentafluoro-λ6-sulfanyl)(SF5)-substituted compounds is more challenging than that of the related CF3-substituted analogues. Previous investigations of [3,3]-sigmatropic rearrangements of γ-SF5-substituted allylic alcohols failed to yield 3-SF5-substituted carboxylic acid derivatives. Herein, we present the synthesis of a series of 1-SF5-alk-1-en-3-ols and our efforts to apply them in Johnson-Claisen, ester enolate-Claisen, and Ireland-Claisen rearrangements. Unfortunately, these reactions failed to include the 1-SF5-substituted 1,2-double bond, although successful reactions of analogous CF3-allylic alcohols were reported. Further experiments revealed that bulkiness rather than electronic properties of the SF5 group prevented [3,3]-sigmatropic rearrangements. Indeed, the introduction of a competing second vinyl group into the system (1-SF5-penta-1,4-dien-3-ol) confirmed that a Johnson-Claisen rearrangement was successful (92% yield of methyl 7-SF5-hepta-4,6-dienoate) with incorporation of the unsubstituted 4,5-double bond while the 1-SF5-substituted 1,2-double bond remained unchanged. Efforts to apply 1-(SF5CF2)-substituted 1,2-double bond systems, which are similar to CF3 analogues in steric requirements, in Johnson-Claisen or ester enolate-Claisen rearrangements failed because of the instability of the SF5CF2 substituent under various reaction conditions. On the other hand, when the SF5 group was separated from the reaction center by a CH2 group instead (5-SF5-pent-3-en-2-ol), Johnson-Claisen rearrangements using six orthoesters provided the target 2-substituted 3-(CH2SF5)-hex-4-enoates in 55-76% yields as ∼1 : 1 mixtures of diastereomers. As an example to demonstrate the utility of these products, methyl 3-(CH2SF5)-hex-4-enoate was reduced, and the formed alcohol was oxidized to the aldehyde. Finally, initial experiments showed that the synthetic sequence developed for SF5 compounds is also applicable for analogous CF3-substituted allylic alcohols (5-CF3-pent-3-en-2-ol) and their Johnson-Claisen rearrangement.

Chemoselective Hydro(Chloro)pentafluorosulfanylation of Diazo Compounds with Pentafluorosulfanyl Chloride

Pentafluorosulfanyl chloride (SF₅ Cl) is the most prevalent reagent for the incorporation of SF₅ group into organic compounds. However, the preparation of SF₅ Cl often relies on hazardous reagents and specialized apparatus. Herein, we described a safe and practical synthesis of a bench-stable and easy-to-handle solution of SF₅ Cl in n-hexane under gas-reagent-free conditions. The synthetic application of SF₅ Cl was demonstrated through the unprecedented reaction with diazo compounds. The chemoselective hydro- and chloropentafluorosulfanylations of α-diazo carbonyl compounds were developed in the presence of K₃ PO₄ or copper catalyst, respectively. These reactions provide a direct and efficient access to various α-pentafluorosulfanyl carbonyl compounds of high value for potential applications.

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds

The analysis of crystal structures of SF5 - or SF4 -containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms. Moreover, a number of repeating structural motifs formed by contacts between SF5 groups was identified, including different supramolecular dimers and infinite chains. Among SF4 -containing molecules, the study focused on SF4 Cl compounds, including the first solid-state structure analyses of these reactive species. Additionally, electrostatic potential surfaces of a series of Ph-SF5 derivatives were calculated, pointing out the substituent influence on the ability of F⋅⋅⋅X contact formation (X=F or other electronegative atom). Interaction energies were calculated for different dimeric arrangements of Ph-SF5 , which were extracted from experimental crystal structure determinations.

Oxygen Atom Transfer Reactivity of Molybdenum(VI) Complexes Employing Pyrimidine- and Pyridine-2-thiolate Ligands

Four dioxidomolybdenum(VI) complexes of the general structure [MoO₂L₂] employing the S,N-bidentate ligands pyrimidine-2-thiolate (PymS, 1), pyridine-2-thiolate (PyS, 2), 4-methylpyridine-2-thiolate (4-MePyS, 3) and 6-methylpyridine-2-thiolate (6-MePyS, 4) were synthesized and characterized by spectroscopic means and single-crystal X-ray diffraction analysis (2-4). Complexes 1-4 were reacted with PPh₃ and PMe₃, respectively, to investigate their oxygen atom transfer (OAT) reactivity and catalytic applicability. Reduction with PPh₃ leads to symmetric molybdenum(V) dimers of the general structure [Mo₂O₃L₄] (6-9). Kinetic studies showed that the OAT from [MoO₂L₂] to PPh₃ is 5 times faster for the PymS system than for the PyS and 4-MePyS systems. The reaction of complexes 1-3 with PMe₃ gives stable molybdenum(IV) complexes of the structure [MoOL₂(PMe₃)₂] (10-12), while reduction of [MoO₂(6-MePyS)₂] (4) yields [MoO(6-MePyS)₂(PMe₃)] (13) with only one PMe₃ coordinated to the metal center. The activity of complexes 1-4 in catalytic OAT reactions involving Me₂SO and Ph₂SO as oxygen donors and PPh₃ as an oxygen acceptor has been investigated to assess the influence of the varied ligand frameworks on the OAT reaction rates. It was found that [MoO₂(PymS)₂] (1) and [MoO₂(6-MePyS)₂] (4) are similarly efficient catalysts, while complexes 2 and 3 are only moderately active. In the catalytic oxidation of PMe₃ with Me₂SO, complex 4 is the only efficient catalyst. Complexes 1-4 were also found to catalytically reduce NO₃^- with PPh₃, although their reactivity is inhibited by further reduced species such as NO, as exemplified by the formation of the nitrosyl complex [Mo(NO)(PymS)₃] (14), which was identified by single-crystal X-ray diffraction analysis. Computed ΔG^⧧ values for the very first step of the OAT were found to be lower for complexes 1 and 4 than for 2 and 3, explaining the difference in catalytic reactivity between the two pairs and revealing the requirement for an electron-deficient ligand system.

Pyridine tetrafluoro-λ6-sulfanyl chlorides: spontaneous addition to alkynes and alkenes in the presence or absence of photo-irradiation

A radical addition reaction of Py-SF₄Cl to alkynes and alkenes provide pyridine-SF₄-alkenes and pyridine-SF₄-alkanes under blue LED light irradiation or absence of light irradiation in CPME or without solvent.

Synthesis of aryl and heteroaryl tetrafluoro-λ6-sulfanyl chlorides from diaryl disulfides using trichloroisocyanuric acid and potassium fluoride

A catalyst-free method for the synthesis of (Het)ArSF₄Cl by using trichloroisocyanuric acid and potassium fluoride in acetonitrile is disclosed.

An eccentric rod-like linear connection of two heterocycles: synthesis of pyridine trans-tetrafluoro-λ6-sulfanyl triazoles

The trans-tetrafluoro-λ6-sulfane (SF4) group has been utilized as a unique three-dimensional building block for the linear connection of two independent N-heterocycles, pyridines and triazoles. The linearly connected heterocyclic compounds were synthesized by thermal Huisgen 1,3-dipolar cycloaddition between previously unknown pyridine SF4-alkynes and readily available azides, providing a series of rod-like SF4-connected N-heterocycles in good to excellent yields. X-ray crystallographic analysis of the target products revealed the trans-geometry of the SF4 group, which linearly connects two independent N-heterocycles. This research will open the field of chemistry of SF4-connected heterocyclic compounds.

SF5-Pyridylaryl-λ3-iodonium salts and their utility as electrophilic reagents to access SF5-pyridine derivatives in the late-stage of synthesis

Electrophilic pentafluorosulfanyl (SF₅) heteroarylation of target molecules using novel reagents is described. Unsymmetrical diaryliodonium reagents 1 having 2-SF₅-pyridine have been synthesized in good yields. They are efficient electrophilic reagents for carbon and heterocentered nucleophiles, producing the corresponding SF₅-pyridine derivatives in good to excellent yields.

Synthesis of pyridine trans-tetrafluoro-λ6-sulfane derivatives via radical addition

Pyridine-trans-SF₄-alkenes or -alkanes have been synthesized for the first time via the radical addition reactions of pyridine-trans-SF₄Cl to alkynes or alkenes in good to high yields.

IF5 affects the final stage of the Cl–F exchange fluorination in the synthesis of pentafluoro-λ6-sulfanyl-pyridines, pyrimidines and benzenes with electron-withdrawing substituents

SF₅-(hetero)arenes having electron-deficient groups were efficiently synthesized by oxidative chlorotetrafluorination followed by a S_Ni-type Cl–F exchange reaction using IF₅.

Silver-induced self-immolative Cl–F exchange fluorination of arylsulfur chlorotetrafluorides: synthesis of arylsulfur pentafluorides

Cl–F exchange fluorination of (Het)ArSF₄Cl without fluorinating reagents is disclosed.

Synthesis and nucleophilic aromatic substitution of 3-fluoro-5-nitro-1-(pentafluorosulfanyl)benzene

3-Fluoro-5-nitro-1-(pentafluorosulfanyl)benzene was prepared by three different ways: as a byproduct of direct fluorination of 1,2-bis(3-nitrophenyl)disulfane, by direct fluorination of 4-nitro-1-(pentafluorosulfanyl)benzene, and by fluorodenitration of 3,5-dinitro-1-(pentafluorosulfanyl)benzene. The title compound was subjected to a nucleophilic aromatic substitution of the fluorine atom with oxygen, sulfur and nitrogen nucleophiles affording novel (pentafluorosulfanyl)benzenes with 3,5-disubstitution pattern. Vicarious nucleophilic substitution of the title compound with carbon, oxygen, and nitrogen nucleophiles provided 3-fluoro-5-nitro-1-(pentafluorosulfanyl)benzenes substituted in position four.