New Chemical Transformations Involving SO2 F2 -Mediated Alcohol Activation

Sulfuryl fluoride is a gas produced on a multi-ton scale for its use as a fumigant. In the last decades, it has gained interest in organic synthesis as a reagent with unique properties in terms of stability and reactivity when compared to other sulfur-based reagents. Sulfuryl fluoride has not only been used for sulfur-fluoride exchange (SuFEx) chemistry but also encountered applications in classic organic synthesis as an efficient activator of both alcohols and phenols, forming a triflate surrogate, namely a fluorosulfonate. A long-standing industrial collaboration in our research group drove our work on the sulfuryl fluoride-mediated transformations that will be highlighted below. We will first describe recent works on metal-catalyzed transformations from aryl fluorosulfonates while emphasizing the one-pot processes from phenol derivatives. In a second section, nucleophilic substitution reactions on polyfluoroalkyl alcohols will be discussed and the value of polyfluoroalkyl fluorosulfonates in comparison to alternative triflate and halide reagents will be brought to light.

Comprehensive Study and Development of a Metal-Free and Mild Nucleophilic Trifluoromethoxylation

Among the general interest in fluorinated compounds, trifluoromethoxylated molecules play a specific role. However, despite this interest, the development of efficient reagents to perform trifluoromethoxylation reactions remains a challenge. Here, 2,4-dinitro-trifluoromethoxybenzene (DNTFB) is used as a trifluoromethoxylating reagent to perform nucleophilic substitution under mild metal-free conditions with different leaving groups, including direct dehydroxytrifluoromethoxylation. A mechanistic study rationalized the reaction and subsequently proposed only three reaction conditions, depending on the reactivity of the starting substrates.

Ruthenium-catalyzed Synthesis of Aryl and Alkenyl Halides from Fluorosulfonates

Aryl and alkenyl halides are widely used as key intermediates in organic synthesis, particularly for the formation of organometallic reagents or as radical precursors. They are also found in pharmaceutical and agrochemical ingredients. In this work, we report the synthesis of aryl and alkenyl halides from the corresponding fluorosulfonates using commercially available ruthenium catalysts. Notably, this is the first conversion of phenols to aryl halides that is efficient with chloride, bromide, and iodide. Fluorosulfonates are readily prepared using sulfuryl fluoride (SO2F2) and less expensive substitutes for triflates. Although aryl fluorosulfonates and their reactions are well known, this is the first report of an efficient coupling of alkenyl fluorosulfonates. To finish, we have demonstrated, by means of representative examples, that the reaction is possible in a one-pot process, starting directly from the phenol or aldehyde.

Exploring F/CF3 substituted oxocarbenium ions for the diastereoselective assembly of highly substituted tetrahydrofurans

Understanding the influence of emerging fluorinated motifs is of a crucial importance in the context of the exponentially growing exploitation of fluorine in many fields. Herein, we report on the dramatic effect of a local partial charge inversion by replacing a CHCH₃ group by a CFCF₃. This strategy allows the diastereoselective reduction of 5-membered ring oxocarbenium ions to access highly substituted tetrahydrofurans.

Traceless N-Polyfluoroalkylation of Weakly Nucleophilic Nitrogen Containing Compounds

Here we report an efficient access to high-value N-polyfluoroalkyl anilines, primary polyfluoroalkylamines and N,N-bis(polyfluoroalkyl)amines, via N-polyfluoroalkylation of sulfonamides and phthalimide derivatives using sulfuryl fluoride (SO2F2). The in situ formation of polyfluoroalkyl fluorosulfonates from commercially available fluorinated alcohols and economical sulfuryl fluoride is highly advantageous given that some polyfluoroalkyl halides are ozone-depleting substances (ODS) regulated by the Montreal protocol. This general method is applied to the polyfluoroalkylation of a variety of sulfonamides, N-sulfonyl carbamates and phthalimide with a wide tolerance of functional groups. The process thus provides viable access for industry to N-(polyfluoroalkyl)anilines as well as primary and secondary N-(polyfluoroalkyl)amines, which are very valuable but not easily accessible building blocks for life science applications.

Direct Deprotonative Functionalization of α,α-Difluoromethyl Ketones using a Catalytic Organosuperbase

The deprotonative functionalization of α,α-difluoromethyl ketones is described herein. Using a catalytic organosuperbase and a silane additive, the corresponding difluoroenolate could be generated and trapped with aldehydes to deliver various α,α-difluoro-β-hydroxy ketones in high yields. This new strategy tolerates numerous functional groups and represents the access to the difluoroenolate by direct deprotonation of the difluoromethyl unit. The diastereoselective version of the reaction was also investigated with d.r. up to 93 : 7. Several transformations were performed to demonstrate the synthetic potential of these α,α-difluoro-β-hydroxy ketones. In addition, this method has been extended to the use of other electrophiles such as imines and chalcogen derivatives, and a difluoromethyl sulfoxide as nucleophile, thus leading to a diversity of difluoromethylene compounds.

One-step Oxidative Monofluorination of Electron-Deficient Sulfoxides to Access Highly Lewis Acidic Sulfur(VI) Cations

The strongly oxidizing, powerful electrophilic fluorination reagent [FXe][OTf] is shown to effect direct oxidative monofluorination of sulfoxides. This one-step, chloride promoter-free methodology provides access to so far inaccessible, yet highly desirable strongly Lewis acidic fluorosulfoxonium cations from electron-deficient and/or sterically demanding sulfoxides that are shown to be practically unreactive towards the previously reported XeF₂ /NEt₄ Cl system. Experimental and density functional theory studies have been conducted to assess the Lewis acidities of the prepared sulfur(VI) cations. Preliminary results obtained with chiral sulfoxides provide early insights into the mechanism of these fluorination reactions.

Study of Carbamoyl Fluoride: Synthesis, Properties and Applications

Carbamoyl fluoride is a fluorinated group that, to this date, remains underexplored, probably due to the lack of data concerning its properties. In this paper, a study of carbamoyl fluoride is presented. Stability studies, in particular under physiological conditions, and lipophilicity measurement were performed. A new easy, safe, inexpensive, and metal-free synthesis method is also described. Finally, a potential use in radiochemistry through a ¹⁸ F/¹⁹ F isotopic exchange is demonstrated.

SO2F2-Mediated N-Alkylation of Imino-Thiazolidinones

The N-alkylation of ambident and weakly nucleophilic imino-thiazolidinones has been developed via substitution with alkyl fluorosulfonates. These reactive electrophiles are obtained through the transformation of nontoxic, economic, and commercially available alcohol derivatives on exposure to SO₂F₂ gas. The use of electron-withdrawing groups and DMAc as solvent affords a (Z)- and N-endocyclic selectivity for the easy introduction of a variety of alkyl and polyfluoroalkyl chains.

Synthesis of 3-Amino-5-fluoroalkylfurans by Intramolecular Cyclization

A synthesis to access rarely described 3-amino-5-fluoroalkylfurans has been developed by cyclization of easily accessible fluorovinamides. This method is rapid and simple and affords the desired furans as hydrochloride salts in quantitative or nearly quantitative yields. It is compatible with four different fluorinated groups (-CF₃, -CF₂CF₃, -CHF₂, and -CF₂Cl) and a wide range of substituents on the amine.

CF3-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

"The extraordinary instability of such an "ion" accounts for many of the peculiarities of organic reactions" - Franck C. Whitmore (1932). This statement from Whitmore came in a period where carbocations began to be considered as intermediates in reactions. Ninety years later, pointing at the strong knowledge acquired from the contributions of famous organic chemists, carbocations are very well known reaction intermediates. Among them, destabilized carbocations - carbocations substituted with electron-withdrawing groups - are, however, still predestined to be transient species and sometimes considered as exotic ones. Among them, the CF3-substituted carbocations, frequently suggested to be involved in synthetic transformations but rarely considered as affordable intermediates for synthetic purposes, have long been investigated. This review highlights recent and past reports focusing on their study and potential in modern synthetic transformations.

Electrophilic fluorosulfoxonium cations as hidden Brønsted acid catalysts in (n + 2) annulations of strained cycloalkanes

A fluorosulfoxonium cation and triflic acid were shown to promote (n + 2) annulations of donor–acceptor cyclopropanes or -butanes with 1,2-dipoles, with different activity and selectivity but a presumed similar role as (hidden) Brønsted acids.

Formation of synthetically relevant CF3-substituted phenonium ions in superacid media

Under superacidic conditions, CF₃-substituted phenonium ions can be generated to furnish original CF₃-substituted dihydrostilbenes of interest.

Synthesis and Use of Trifluoromethylthiolated Ketenimines

The synthesis of trifluoromethylthiolated ketenimines is herein described. They are easily synthesized from the corresponding α-trifluoromethylthiolated oximes upon activation with triflic anhydride and a base. The presumed nitrilium ion resulting from the Beckmann rearrangement is deprotonated to lead to the key intermediate, whose stability brought by the fluorinated substituent was unforeseeable. The reaction of these new building blocks with a variety of nucleophiles affords a vast array of cyclic and acyclic products bearing the valuable SCF₃ moiety.

Deprotonative Functionalization of the Difluoromethyl Group

The functionalization of 3-(difluoromethyl)pyridine has been developed via direct deprotonation of -CHF₂ with a lithiated base and subsequent trapping with various electrophiles in THF. In situ quenching gives access to 3-pyridyl-CF₂-SiMe₂Ph as a new silylated compound, which can be postfunctionalized with a fluoride source to obtain a larger library of 3-(difluoroalkyl)pyridines that could not be accessed via direct deprotonation.

Access towards enantiopure α,α-difluoromethyl alcohols by means of sulfoxides as traceless chiral auxiliaries

A new methodology to access enantiopure α,α-difluoromethyl alcohols is hereby being described. The strategy relies on the use of an enantiopure aryl α,α-difluoromethyl sulfoxide employed as chiral and removable auxiliary for the stereoselective difluoromethylation of carbonyl derivatives. The obtained α,α-difluoro-β-hydroxysulfoxides displayed unprecedented diastereomeric ratios.

A physico-chemical investigation of fluorine-enriched quinolines

A homogenous series of 2,4-bis(fluoroalkyl)-substituted quinolines was synthesized under mild reaction conditions and their physico-chemical (absorption and emission, electrochemistry, and TD-DFT) properties were thoroughly investigated.

Fluoroalkyl Amino Reagents for the Introduction of the Fluoro(trifluoromethoxy)methyl Group onto Arenes and Heterocycles

Fluoroalkyl amino reagents 1a and 2a have been developed from commercially available trifluoromethyl trifluorovinyl ether via a hydroamination reaction with diethylamine or dimethylamine. These reagents can be activated by treatment with a Lewis acid and subsequently used as a mono- or dielectrophile for the introduction of the fluoro(trifluoromethoxy)methyl group, either in Vilsmeier-type acylations of aromatic substrates or in the synthesis of fluorinated pyrazoles from CH-acidic substrates and of bis-fluorinated pyrazoles, all being important building blocks for medicinal and agricultural chemistry.

Fluoroalkyl Amino Reagents (FARs): A General Approach towards the Synthesis of Heterocyclic Compounds Bearing Emergent Fluorinated Substituents

Fluorinated heterocycles are important building blocks in pharmaceutical, agrochemical and material sciences. Therefore, organofluorine chemistry has witnessed high interest in the development of efficient methods for the introduction of emergent fluorinated substituents (EFS) onto heterocycles. In this context, fluoroalkyl amino reagents (FARs)—a class of chemicals that was slightly forgotten over the last decades—has emerged again recently and proved to be a powerful tool for the introduction of various fluorinated groups onto (hetero)aromatic derivatives.

A Major Advance in the Synthesis of Fluoroalkyl Pyrazoles: Tuneable Regioselectivity and Broad Substitution Patterns

A novel approach towards highly functionalized fluoroalkyl pyrazoles was developed by using fluoroalkyl amino reagents in combination with a variety of fluorinated ketimines. Tuneable introduction of fluoroalkyl groups in the 3- and 5-positions was possible by using vinamidinium intermediates or the corresponding enamino ketones after hydrolysis. These high-value building blocks can give rise to a large number of analogues for bioactivity screening and discovering new heterocyclic bioactive ingredients in various life science fields.

A new approach toward the synthesis of 2,4-bis(fluoroalkyl)-substituted quinoline derivatives using fluoroalkyl amino reagent chemistry

The present work describes the unprecedented use of Fluoroalkyl Amino Reagents (FARs) to afford 2,4-bis(fluoroalkyl)-substituted quinoline derivatives in two steps under mild reaction conditions, in good yields and with a very good regioselectivity.