A convenient and efficient method for incorporation of pentafluorosulfanyl (SF5) substituents into aliphatic compounds

Photo-induced hydroxypentafluorosulfanylation of alkenes with SF5Cl and oxygen gas and their further derivatization

Fluorinated or fluoroalkylated alcohols are common structural motifs in biologically active molecules, natural products, and pharmaceuticals. However, pentafluorosulfanyl (SF5) alcohols, a unique class of SF5 compounds that serve as synthetically valuable building blocks, are difficult to prepare with current methodologies. In this article, we present a single-step, metal-free, and photo-induced hydroxypentafluorosulfanylation of styrenes or α,β-unsaturated esters/amide, producing a series of structurally diverse pentafluorosulfanyl alcohols with up to 89% yields. This reaction is mild and operationally simple, using molecular oxygen as the hydroxy source. The protocol is suitable for a wide range of alkenes, including natural products and drug molecule derivatives. The formed SF5 alcohol units can be readily converted into diverse functionalized SF5 compounds, such as α-SF5 ketones, SF5 diols, and SF5 cyclic carbonates. The potential applications of these SF5 compounds in pharmaceutical and material sciences are vast, making this research a step forward in the field.

Pentafluorosulfanylation of Acrylamides: The Synthesis of SF5-Containing Isoquinolinediones with SF5Cl

We disclose herein an efficient and facile method for the synthesis of SF5-containing isoquinolinediones with an all-carbon quaternary stereocenter via intramolecular pentafluorosulfanylation of acrylamides using SF5Cl as a pentafluorosulfanylation reagent. The protocol proceeds under mild reaction conditions and enjoys a broad substrate scope, wide functional group compatibility, and high atom- and step-economy. A radical mechanism involving the SF5 radical cascade addition/cyclization of acrylamides is proposed.

Palladium-Catalyzed Regioselective Synthesis of 2-SF5 -Indenols and Further Derivatizations

A palladium-catalyzed synthesis of 2-SF5 -indenols has been developed by reacting commercially available boronic acid derivatives and readily accessible SF5 -alkynes. The present methodology is fully regioselective thanks to the intrinsic polarization of SF5 -alkynes. A selection of downstream functionalizations has been performed to highlight the versatility of 2-SF5 -indenols and indenones as platforms for the design of more complex SF5 -containing molecules.

Tracking SF5 I in the Iodopentafluorosulfanylation of Alkynes

In the vibrant field of SF5 chemistry, SF5 X reagents (X=F, Cl, Br) are at the heart of current investigations in radical pentafluorosulfanylation reactions. SF5 I is the missing link whose existence has not been reported despite its potential as SF5 donor. This study reports the formal addition of the hitherto unknown SF5 I reagent to alkynes by means of a combination of SF5 Cl/KI/18-crown-6 ether. The exclusive regio- and stereoselective synthesis of unprecedented (E)-1-iodo-2-(pentafluoro-λ6 -sulfanyl) alkenes was achieved. A consensus was reached through computational and mechanistic studies for the realistic formation of SF5 - anion but not SF5 I in solution and the rational involvement of SF5 ⋅ and iodine radicals in the iodo pentafluorosulfanylation reaction.

Strain-Release Pentafluorosulfanylation and Tetrafluoro(aryl)sulfanylation of [1.1.1]Propellane: Reactivity and Structural Insight

We leveraged the recent increase in synthetic accessibility of SF5 Cl and Ar-SF4 Cl compounds to combine chemistry of the SF5 and SF4 Ar groups with strain-release functionalization. By effectively adding SF5 and SF4 Ar radicals across [1.1.1]propellane, we accessed structurally unique bicyclopentanes, bearing two distinct elements of bioisosterism. Upon evaluating these "hybrid isostere" motifs in the solid state, we measured exceptionally short transannular distances; in one case, the distance rivals the shortest nonbonding C⋅⋅⋅C contact reported to date. This prompted SC-XRD and DFT analyses that support the notion that a donor-acceptor interaction involving the "wing" C-C bonds is playing an important role in stabilization. Thus, these heretofore unknown structures expand the palette for highly coveted three-dimensional fluorinated building blocks and provide insight to a more general effect observed in bicyclopentanes.

Recent Advances in the Synthesis and Medicinal Chemistry of SF5 and SF4Cl Compounds

This short review covers the most important advances published in the literature during the last five years, concerning the synthesis, chemical modifications, and applications of SF5 and SF4Cl compounds in medicinal/bioorganic chemistry and materials science.

1 Introduction

2 Methods for Incorporation/Manipulation of SF4Cl/SF5 Groups

2.1 Nonaromatic SF5 Compounds via Direct Pentafluorosulfanylation of Alkenes and Alkynes

2.2 SF4Cl- and SF5-Aryl/Heteroaryl Derivatives

3 Synthesis of SF5/SF4Cl/SF4-Substituted Small Molecules

3.1 Heterocycles

3.2 Amines and Amino Acids

3.3 α-SF5 ketones

3.4 Miscellaneous Alkyl-, Alkenyl-, and Aryl-SF5 Compounds

4 Medicinal/Biological Applications

4.1 Anticancer Compounds

4.2 Antibacterial and Antiparasitic Compounds

4.3 Central Nervous System

4.4 Miscellaneous Biological Activity

5 Materials Science Applications

6 Conclusion

(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-SVI 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 SVI 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-SVI compounds at all levels, discussing synthetic strategies, reactivity, the advantages and disadvantages of the synthetic procedures, the proposed mechanisms, and the potential upcoming opportunities.

Regioselective Synthesis of Pyridine-SF4-Methyl Ketones via Hydration of Pyridine-SF4-Alkynes

Herein, we report the metal-free hydration of pyridine-SF₄-alkynes, under acidic conditions and with reaction durations ranging from 5 min to 10 h at room temperature, to synthesize pyridine-SF₄-methyl ketones in yields of 59-93%. Further, we demonstrate the synthetic applications of the synthesized pyridine-SF₄-methyl ketones, such as chlorination, NaBH₄ reduction, Baeyer-Villiger oxidation, and the generation of enol-triflates. These compounds hold promise as useful building blocks in the syntheses of a wide range of SF₄-containing drug candidates.

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.

Photoinitiated anti-Hydropentafluorosulfanylation of Terminal Alkynes

A photoinitiated anti-hydropentafluorosulfanylation of terminal alkynes using SF₅ Cl and (TMS)₃ SiH as the hydrogen atom donor is reported. This transformation generates selectively (Z)-(1-alken-1-yl)pentafluoro-λ⁶ -sulfanes (Z:E : >85:15), thus allowing the preparation of this previously unknown geometrical isomer. DFT calculations highlight that the selectivity is due to the intrinsic preference of SF₅ -substituted vinylic radicals to adopt a cis geometry, and to increased steric contacts during the transition structures leading to the minor (E)-products.

Radical 1,5-Chloropentafluorosulfanylation of Unactivated Vinylcyclopropanes and Transformation into α-SF5 Ketones

The radical 1,5-chloropentafluorosulfanylation of vinyl cyclopropanes (VCPs) initiated by Et₃B/O₂ affords allylic pentafluorosulfanyl/homoallylic chloride products through the ring-strain release of the cyclopropane. The VCP substitution pattern was investigated. The utility of this reaction was illustrated in post-transformation of the C═C bond by ozonolysis, giving access to valuable α-SF₅ carbonyl compounds.

Synthesis and Physicochemical Properties of 2-SF5-(Aza)Indoles, a New Family of SF5 Heterocycles

Structural diversity in heterocyclic chemistry is key to unlocking new properties and modes of action. In this regard, heterocycles embedding emerging fluorinated substituents hold great promise. Herein is described a strategy to access 2-SF₅-(aza)indoles for the first time. The sequence relies on the radical addition of SF₅Cl to the alkynyl π-system of 2-ethynyl anilines followed by a cyclization reaction. A telescoped sequence is proposed, making this strategy very appealing and reproducible on a gram scale. Downstream functionalizations are also demonstrated, allowing an easy diversification of N- and C3-positions. Ames test, pK _a, log P, and differential scanning calorimetry measurements of several fluorinated 2-Rf-indoles are also disclosed. These studies highlight the strategic advantages that a C2-pentafluorosulfanylated motif impart to a privileged scaffold such as an indole.

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.

Photoredox Catalytic Pentafluorosulfanylative Domino Cyclization of α-Substituted Alkenes to Oxaheterocycles by Using SF6

Virtually inert sulfur hexafluoride becomes a precious pentafluorosulfanylation agent, if properly activated by photoredox catalysis, to access α-fluoro and α-alkoxy SF5 -compounds. This advanced protocol converts SF6 in the presence of alkynols as bifunctional C-C- and C-O-bond forming reagents directly into pentafluorosulfanylated oxygen-containing heterocycles in a single step from α-substituted alkenes. The proposed mechanism is supported by theoretical calculations and gives insights not only in the pentafluorosulfanylation step but also into formation of the carbon-carbon bond and is in full agreement with Baldwin's cyclization rules. The key step is a radical type 5-, 6- respectively 7-exo-dig-cyclization. The synthesized oxaheterocycles cannot be simply prepared by other synthetic methods, show a high level of structural complexity and significantly expand the scope of pentafluorosulfanylated building blocks valuable for medicinal and material chemistry.

Amine-borane complex-initiated SF5Cl radical addition on alkenes and alkynes

The SF5Cl radical addition on unsaturated compounds was performed using an air-stable amine-borane complex as the radical initiator. This method showed to be complementary to the classic Et3B-mediated SF5Cl addition on alkenes and alkynes. A total of seven alkene and three alkyne derivatives were tested in the reaction, with yields ranging from 3% to 85%.

Photoredox Catalytic α-Alkoxypentafluorosulfanylation of α-Methyl- and α-Phenylstyrene Using SF6

SF6 was applied as pentafluorosulfanylation reagent to prepare ethers with a vicinal SF5 substituent through a one-step method involving photoredox catalysis. This method shows a broad substrate scope with respect to applicable alcohols for the conversion of α-methyl and α-phenyl styrenes. The products bear a new structural motif with two functional groups installed in one step. The alkoxy group allows elimination and azidation as further transformations into valuable pentafluorosulfanylated compounds. These results confirm that non-toxic SF6 is a useful SF5 transfer reagent if properly activated by photoredox catalysis, and toxic reagents are completely avoided. In combination with light as an energy source, a high level of sustainability is achieved. Through this method, the proposed potential of the SF5 substituent in medicinal chemistry, agrochemistry, and materials chemistry may be exploited in the future.

Generation of ortho-SF5-Benzyne and Its Diels-Alder Reactions with Furans: Synthesis of 1-SF5-Naphthalene, Its Derivatives, and 1,6(1,7)-Bis-SF5-naphthalenes

Generation of ortho-SF₅-benzyne was achieved by a lithiation/elimination sequence starting from 2-fluoro-SF₅-benzene. The highly reactive ortho-SF₅-benzyne intermediate was trapped by furan or 2-methylfuran in situ, and the obtained stable Diels-Alder adducts were subjected to the series of further chemical transformation, which led to the formation of previously unknown 1-SF₅-naphthalene and its derivatives with bromo, amino, hydroxy, and methyl substituents, including bis-SF₅-substituted naphthalenes. NMR spectroscopy experiments revealed characteristic through-space coupling between the SF₅-group's equatorial fluorines and proton/carbon nuclei of -H, -CH₃, and -OH substituents in the peri-position to the SF₅-group of 1-SF₅-naphthalenes.

SF5-Enolates in Ti(IV)-Mediated Aldol Reactions

The F···Ti bonding in the transition structures determines high trans- and syn-diastereoselectivities for aldol reactions of SF5-acetates with aldehydes in the presence of TiCl4 in the non-nucleophilic solvent CH2Cl2. Such bonding is canceled in nucleophilic solvents where opposite cis-stereochemistry is observed. The potential of thus obtained stereoisomeric SF5-aryl acrylates as dipolarophiles in the preparation of SF5-containing heterocycles is demonstrated.

State-Specific Reactions of Cu(+)((1)S,(3)D) with SF6 and SF5Cl

State-specific reactions of Cu(+)((1)S,(3)D) were carried out in a selected ion drift cell apparatus with SF6 and SF5Cl. Copper ions were prepared in a glow discharge utilizing Ne as the working gas. Analysis of Cu(+) states using ion mobility mass spectrometry (IMS) indicated the presence of both Cu(+)(3d(10)) and Cu(+)(3d(9)4s(1)) configurations attributable to the (1)S ground and (3)D first excited states of this metal ion, respectively. State-specific product formation in reactions of these ions with the two neutral substrates of interest here was determined using IMS along with both known and calculated energetic requirements for product formation. These experiments indicate that Cu(+)((1)S) associates with both SF6 and SF5Cl; however, the process is approximately four times as efficient with the latter neutral under these conditions. Association is also observed as a minor product between Cu(+)((3)D) and both neutral reactants. Inefficient formation of SF3(+) occurs as the sole bimolecular product from SF6 via Cu(+)((3)D). In contrast, Cu(+)((3)D) reacts with SF5Cl in rapid parallel bimolecular processes yielding SF3(+) and CuCl(+). These results also indicate that CuCl(+) initiates additional higher-order processes which result in SF5(+) and SF4Cl(+). The energetics associated with the formation of SF3(+) suggest that a copper halide neutral byproduct must also be formed, requiring a more complex mechanism than simple dissociative charge-transfer.

The involvement of the trisulfur radical anion in electron-catalyzed sulfur insertion reactions: facile synthesis of benzothiazine derivatives under transition metal-free conditions

An efficient and practical synthesis of benzothiazine by K₂S initiated sulfur insertion reaction with enaminones via electron catalysis is developed. This protocol provides a new, environment-friendly and simple strategy to construct benzothiazine derivatives via formation of two C-S bonds under transition metal-free, additive-free and oxidant-free conditions. K₂S not only provides the sulfur insertion source, but also ignites the reaction through the formation of a trisulfur radical anion and electrons in DMF.

Palladium-mediated borylation of pentafluorosulfanyl functionalized compounds: the crucial role of metal fluorido complexes

Model reactions such as the oxidative addition of SF₅ aromatics at [Pd(PiPr₃)₂] and subsequent fluorination and borylation steps led to the development of catalytic processes for the borylation of SF₅ compounds.

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF5-substituted phenylboronic esters and iodobenzenes

Pyridine promotes dediazoniation of aryldiazonium tetrafluoroborates. The formed aryl radicals were trapped with B2pin2, iodine, or tetrahydrofuran to afford boronic esters, iodobenzenes and benzenes, respectively. The application to the synthesis of (pentafluorosulfanyl)phenylboronic esters, iodo(pentafluorosulfanyl)benzenes and (pentafluorosulfanyl)benzene is shown.