Regioselective Gold-Catalyzed Hydration of CF3- and SF5-alkynes

Unlocking the Potential of CF3-Alkynes in Gold-Catalyzed Oxygen Transfer: A Direct Route to Trifluoromethylated Compounds

We report on gold-catalyzed oxygen transfer utilizing, for the first time, electron-deficient trifluoromethylated alkynes as substrates. This double O-transfer process provides a direct and convenient one-step route to difficult-to-obtain trifluoromethylated 1,2-diketones. Due to the relatively mild oxidative reaction conditions (rt to 60 °C, 2,6-dichloropyridine N-oxide as an oxidizer, 3 mol % JohnPhosAuNTf2), various functional substituents were tolerated (19 examples; yields up to 95%). The synthetic utility of the obtained trifluoromethylated dicarbonyl products was further explored, and these studies included one-pot multicomponent syntheses of valuable CF3-substituted indoles and benzofurans.

Synthesis of α-SF5 Ketones by Oxypentafluorosulfanylation of Alkynes with SF5Cl and Oxygen

Herein for the first time, we disclose a practical and straightforward approach to access α-SF5 ketones via direct oxypentafluorosulfanylation of alkynes with SF5Cl and oxygen under acidic conditions by one step. The protocol features mild reaction conditions, broad substrate scope, good functional group compatibility and can be applied to late-state functionalization of complex natural products and pharmaceuticals. A radical mechanism involving SF5 radical addition to triple bonds followed by O2 capture is proposed.

On-Demand Continuous Flow Synthesis of Pentafluorosulfanyl Chloride (SF5Cl) Using a Custom-Made Stirring Packed-Bed Reactor

The pentafluorosulfanyl (SF5-) group has been the subject of a surge of interest in the past decade, but there is still little practicality associated with its synthesis and installation. Herein is reported the first continuous flow synthesis of pentafluorosulfanyl chloride (SF5Cl), the most common reagent for the synthesis of SF5-substituted compounds. The synthesis is based on inexpensive and easy-to-handle reagents: sulfur powder (S8), trichloroisocyanuric acid (TCCA) and potassium fluoride (KF). To this end, a custom-made stirring reactor was designed to allow for fast, safe, and highly efficient on-demand synthesis of SF5Cl. The resulting SF5Cl solution is showcased in the radical addition on alkynes in a telescoped fashion.

1,3-Dipolar Cycloaddition of SF5-Alkynes with Nonstabilized Diazo: Synthesis of Highly Substituted SF5-3H-Pyrazoles

This work presents the 1,3-dipolar cycloaddition of SF5-alkynes with nonstabilized diazo compounds under mild conditions, producing highly substituted SF5-3H-pyrazoles. Eighteen examples are given, with yields of up to 91%. The two regioisomers were obtained in ratios ranging from 27:73 to 73:27. The products can undergo a Van Alphen-Huttel rearrangement. DFT calculations were performed to understand the selectivities and rearrangements.

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.

Gold Trifluoromethyl Complexes as Efficient Regioselective Catalysts in Alkyne Hydration

Gold(III) complexes containing trifluoromethyl ligands are efficient catalysts in the hydration of alkynes, operating at low catalyst loadings, without additives, using environmentally friendly solvents and at mild conditions (60 °C). Hydration of terminal and internal alkynes provides the corresponding ketones in quantitative yields without special precautions as dry solvents or inert atmospheres. Remarkably, hydration of asymmetric internal alkynes proceeds with moderate to notable regioselectivities, providing mixtures of the two possible isomers with ratios up to 90 : 10.

Hydroamination of Triisopropylsilyl Acetylene Sulfur Pentafluoride - a Bench-top Route to Pentafluorosulfanylated Enamines

Synthetic access to a variety of aliphatic and vinylic pentafluorosulfanylated building blocks remains a major challenge in contemporary organofluorine chemistry hampering its investigation in the context of medicinal chemistry, agrochemistry and functional materials. Herein, we report a bench-top protocol to access the virtually unknown class of α-SF5 -enamines under mild reaction conditions in good to excellent yields (up to 95 %). This reaction combines the protodesilylation of the commercially available precursor TASP with the in situ hydroamination of HC≡C-SF5 . The on-site use of highly toxic gases or corrosive reagents is avoided, making access to this motif applicable to a wide chemical audience. The excellent E-diastereoselectivity of this two-step cascade reaction is suggested to be the result of the convergence of the fast Z-/E- isomerization of a vinyl anion as well as the isomerization of the iminium ion. The remarkable thermal stability of these SF5 -enamines encourages further studies of their synthetic utility.

Synthesis of Substituted Pentafluorosulfanylpyrazoles Under Flow Conditions

The development of flow conditions for the synthesis of pentafluorosulfanylpyrazoles is reported. A range of alkyl- and aryl-substituted SF5-alkynes were used in combination with different diazoacetates for this transformation. The corresponding substituted SF5-pyrazoles were obtained in up to 90% yield (average of 74% for 21 examples) as a mixture of isomers (up to 73:27 ratio). Synthetic transformations starting from an SF5-containing pyrazole were also demonstrated.

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.

Expanding Radical Chloropentafluorosulfanylation of Alkynes

The chloropentafluorosulfanylation of alkynes is a delicate but crucial operation for accessing SF5-alkynes that serve as substrates in numerous transformations. Dolbier's procedure using Et3B/O2 was the most efficient approach, while recent efforts make use of other initiators and light activation. We found that THF, as a single stimulus, is sufficient to trigger the reaction of SF5Cl with alkynes. We determined the configuration of Cl/SF5 products and clarified the structure of side-products.

Highly regio- and stereocontrolled preparation of α-(trifluoromethyl)-β-(phenylthio) enamines by the hydroamination of in situ-synthesized 1-(trifluoromethyl)-2-(phenylthio)ethyne

Various nitrogen nucleophiles were easily added to in situ-generated 1-(trifluoromethyl)-2-(phenylthio)ethyne to afford the corresponding trifluoromethyl enamines in good-to-high yields and with high regio- and stereocontrol under very mild conditions.

Pyridinium-Masked Enol as a Precursor for Constructing Alpha-Fluoromethyl Ketones

We present herein a pyridinium-masked enol as a versatile platform to produce ketones bearing tri-, di-, and monofluoromethyl in the presence of [Ir(dF(Me)ppy)]2(dtbbpy)]PF6 under blue light (455 nm) irradiation. By simply changing the F-source, α-trifluoromethyl ketones, α-difluoromethyl ketones, and α-monofluoromethyl ketones could be easily prepared in moderate to excellent yields in one step, making it a practical tool for the synthesis of fluorine-containing ketones. In addition, the pyridinium-masked enol could also be extended to the synthesis of sulfonyl ketones. The findings of the present protocol contribute to the arsenal of fluorine chemistry and might have potential applications in the pharmaceutical and agrochemical industries.

Au(I)-Catalyzed Regioselective Hydrofluorination of Propargylamines Using Aqueous HF

Gold-catalyzed regioselective hydrofluorination of alkynes using aqueous HF has been achieved by employing an amide directing group. For both aryl- and alkyl-substituted propargylamines, the fluorination occurred at the site distal to the amino group.

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 SF5 Cl 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 SF5 Cl, enabling SF5 chemistry in an unexpected way.

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.

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.

Radical Addition of SF5Cl to Cyclopropenes: Synthesis of (Pentafluorosulfanyl)cyclopropanes

With the goal of accessing yet unknown SF₅-cyclopropyl building blocks, the radical addition of SF₅Cl to cyclopropenes was investigated. Addition of the SF₅ radical occurs regioselectively at the less substituted carbon of cyclopropenes and trans to the most hindered substituent at C3, while chlorine atom transfer proceeds with moderate to high levels of diastereocontrol. The carbon-chlorine bond in the resulting adducts can undergo subsequent radical reduction or be involved in a radical cyclization.

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.

Scissoring Enaminone C═C Double Bond by Free Radical Process for the Synthesis of α-Trifluoromethyl Ketones with CF3SO2Na

The C═C double bond cleavage on tertiary enaminones, enabling the formation of a new C-CF₃ bond, has been realized as a practical method for the synthesis of α-trifluoromethyl ketones with only the promotion of TBHP and ambient heating. Control experiments support that the reactions proceed via a featured free radical process. The deuterium labeling experiment employing D₂O indicates that water participated in the product formation by donating the hydrogen atom for the newly generated α-C-H bond in the product.

Drastic fluorine effect: complete reversal of the selectivity in the Au-catalyzed hydroalkoxylation reaction of fluorinated haloalkynes

The gold-catalyzed hydration reaction of haloalkynes is highly regioselective producing 2-halomethylketones as the sole products. Herein, we document a drastic fluorine effect where the reaction of 1-halo-3,3-difluoroalkynes as substrates leads to a complete reversal of selectivity and produces 3,3-difluoroesters as the unique products.

Gold-Catalyzed Hydrofluorination of Internal Alkynes Using Aqueous HF

The gold-catalyzed hydrofluorination reaction of internal alkynes using hydrofluoric acid is reported. Notably, those conditions use one of the most economical sources of HF and are free of additional additives. Both symmetrical and unsymmetrical internal alkynes can be utilized, and the use of alkynes bearing a fluorinated group at the propargylic position as substrates allowed for a regioselective hydrofluorination reaction.