Visible-Light-Induced Arylthiofluoroalkylations of Unactivated Heteroaromatics and Alkenes

Controllable Double Difluoromethylene Insertions into S-Cu Bonds: (Arylthio)tetrafluoroethylation of Aryl Iodides with TMSCF2Br

A new method of constructing "ArSCF2CF2Cu" from ArSCu and TMSCF2Br (TMS=trimethylsilyl) has been developed. The cross-coupling reactions of the obtained "ArSCF2CF2Cu" with diverse aryl iodides (Ar'I) provide an efficient access to Ar'CF2CF2SAr. Mechanistic studies demonstrate that the "ArSCF2CF2Cu" species were generated through controllable double difluoromethylene insertions into ArS-Cu bonds rather than the 1,2-addition of ArSCu to tetrafluoroethylene.

Visible Light-Induced Metal-Free Fluoroalkylations

Fluoroalkylation is a crucial synthetic process that enables the modification of molecules with fluoroalkyl groups, which can enhance the properties of compounds and have potential applications in medicine and materials science. The utilization of visible light-induced, metal-free methods is of particular importance as it provides an environmentally friendly alternative to traditional methods and eliminates the potential risks associated with metal-catalyst toxicity. This Account describes our studies on visible light-induced, metal-free fluoroalkylation processes, which include the use of organic photocatalysts or EDA complexes. We have utilized organophotocatalysts such as Nile red, tri(9-anthryl)borane, and an indole-based tetracyclic complex, as well as catalyst-free EDA chemistry through photoactive halogen bond formation or an unconventional transient ternary complex formation with nucleophilic fluoroalkyl source. A variety of π-systems including arenes/heteroarenes, alkenes, and alkynes have been successfully fluoroalkylated under the developed reaction conditions.

Silver-catalyzed Radical Cascade Arylthiodifluoromethylation/ Cyclization of Isonitriles for the Synthesis of 6-Phenanthridinyldifluoromethyl Aryl Thioethers

An efficient method for silver-catalyzed radical cascade arylthiodifluoromethylation/cyclization of isonitriles is disclosed. The transformation comprised addition of an arylthiodifluoromethyl radical generated in situ by the oxidative decarboxylation of arylthiodifluoroacetic salts to the isonitrile functionality to construct an ArSCF₂ -C bond, followed by intramolecular cyclization to eventually afford 6-phenanthridinyldifluoromethyl aryl thioethers. The protocol provided a variety of 6-phenanthridinyldifluoromethyl aryl thioethers in medium to excellent yields with a good functional group tolerance under mild reaction conditions.

Synthesis of [1,4]Thiazino[4,3-a]indol-10-one Derivatives through Radical Anti Aza-Michael Addition of 2'-Aminochalcones

An efficient method for the synthesis of [1,4]thiazino[4,3-a]indole derivatives using sodium chlorodifluoroacetate (ClCF₂CO₂Na) and elemental sulfur as the difluoromethylthiolating reagent system has been developed. Three-component reactions of 2'-aminochalcones, sulfur, and ClCF₂CO₂Na under basic conditions using TEMPO as the oxidant afforded [1,4]thiazino[4,3-a]indol-10-ones containing a difluoromethyl thioether moiety in good yields. Four bonds including one C-N, two C-S, and one C-C bonds are selectively formed in the sequential transformation process.

Transition-Metal-Free Decarboxylative Cyclization of N-Arylacrylamides with 2,2-Difluoro-2-(phenylthio)acetic Acid: Synthesis of Thiodifluorooxindole Derivatives

An efficient transition-metal-free decarboxylative cyclization of N-arylacrylamides with 2,2-difluoro-2-(phenylthio)acetic acid for the construction of thiodifluoroindoleone derivatives is described. This strategy features stable and readily available substrates, mild reaction conditions, and transition-metal-free catalysts. Notably, this protocol has successfully applied to synthesis of gem-difluoroalkenes, which exist in numerous biologically active compounds.

Ruthenium-Catalyzed Meta-Selective C-H Difluoromethylation of Phenol Derivatives

With pyrimidine as the directing group, we achieved the meta-selective difluoromethylation of phenol derivatives using ruthenium as a catalyst. This synthetic scheme provided an efficient method for the syntheses of fluorine-containing phenol derivatives. A wide variety of phenol derivatives were well-suited, affording the corresponding products in moderate-to-good yields.

Chalcogenide-Catalyzed Intermolecular Electrophilic Thio- and Halofunctionalization of gem-Difluoroalkenes: Construction of Diverse Difluoroalkyl Sulfides and Halides

Thio- and halodifluoromethylated compounds are an important class of compounds in medicinal chemistry and organic synthesis. Herein, we report a facile method for the construction of these compounds via chalcogenide-catalyzed intermolecular electrophilic thio- and halofunctionalization of gem-difluoroalkenes. Simple treatment of gem-difluoroalkenes with electrophilic sulfur/halogen reagents and various O- or N-nucleophiles affords diverse multifunctionalized thio- and halodifluoromethylated compounds. This reaction features a relatively broad substrate scope, good functional group tolerance, and mild reaction conditions.

Access to Polysubstituted (Furyl)methylthioethers via a Base-Promoted S-H Insertion Reaction of Conjugated Enynones

A convenient and applicable approach to the construction of diverse functionalized (2-furyl)methylthioether derivatives via base-promoted S-H insertion of conjugated enynones with thiophenols or thiols has been developed. This reaction features readily available starting materials, high atom economy, broad substrate scope, and versatile operation. Moreover, the synthetic utility of this method has been demonstrated by the efficient synthesis of the CNKSPR1 inhibitor precursor and late-stage functionalization of glutathione.

Organocatalytic Strategy for Hydrophenolation of Gem-Difluoroalkenes

Gem-difluoroalkenes are an easily accessed fluorinated functional group, and a useful intermediate for elaborating into more complex fluorinated compounds. Currently, most functionalization reactions of gem-difluoroalkenes, with or without a transition metal-based catalyst system, involve the addition or removal of a fluorine atom to generate trifluorinated or monofluorinated products, respectively. In contrast, we present a complementary "fluorine-retentive" reaction that exploits an organocatalytic strategy to add phenols across gem-difluoroalkenes to deliver β,β-difluorophenethyl arylethers. The products are produced in good to moderate yields and selectivities, thus providing a range of compounds that are underrepresented in the synthetic and medicinal chemistry literature.

Fluoroalkenylation of boronic acids via an oxidative Heck reaction

A fluoroalkenylation of boronic acids with fluoroalkyl alkenes has been developed. The Pd-catalyzed oxidative Heck coupling reaction proceeds under an oxygen atmosphere at room temperature, in the absence of a base and/or a ligand, showing excellent practicality of the process. This simple transformation is highly stereoselective to provide only E-isomers. In addition to the general approach using alkenes with functionalized fluoroalkyl reagents, this method, by transferring an aromatic system to the electron-deficient fluoroalkyl alkene, provides an efficient alternative method to yield valuable organofluorines.

Synthesis and Reactivity of α-Cumyl Bromodifluoromethanesulfenate: Application to the Radiosynthesis of [18 F]ArylSCF3

A highly reactive electrophilic bromodifluoromethylthiolating reagent, α-cumyl bromodifluoro-methanesulfenate 1, was prepared to allow for direct bromodifluoromethylthiolation of aryl boron reagents. This coupling reaction takes place under copper catalysis, and affords a large range of bromodifluoromethylthiolated arenes. These compounds are amenable to various transformations including halogen exchange with [18 F]KF/K222  , a process giving access to [18 F]arylSCF3 in two steps from the corresponding aryl boronic pinacol esters.

Progress and prospects in the use of photocatalysis for the synthesis of organofluorine compounds

Data on the synthesis of fluorinated organic compounds by photocatalysis are systematically considered and analyzed. The attention is focused on the mechanisms of photocatalytic reactions and the selectivity problem.

The bibliography includes 173 references.

Exploiting the unusual effects of fluorine in methodology

Fluorination of organic molecules significantly impacts the basic physicochemical properties of small and large biologically active molecules, agrichemicals, and materials. Thus, the development of synthetic reactions to access these substructures is important for many applied fields of chemistry. However, these fluorine-induced perturbations of chemical properties can inhibit standard chemical transformations, which provides unique challenges for synthetic organic chemists. In addition, the physicochemical properties imparted by fluorinated substituents can enable distinct reactivity patterns relative to non-fluorinated substrates, thus making synthetic organofluorine chemistry a fertile ground for developing new, exciting transformations. In this feature article, we detail our experiences in methodology, wherein fluorinated substrates have enabled unique reactivity patterns relative to non-fluorous substrates. Specifically, we highlight the non-standard chemo- and regio-selectivities imparted by fluorinated substrates on Pd-catalyzed coupling reactions, nucleophilic addition reactions of olefins, and Cu-catalyzed decarboxylative fluoroalkylation reactions.

Aggregation-induced visible light absorption makes reactant 1,2-diisocyanoarenes act as photosensitizers in double radical isocyanide insertions

The joint computational and experimental efforts reveal that the organic molecule 1,2-diisocyano-4,5-dimethylbenzene (1) acts as both a reactant and a photosensitizer (PS) in a metal-free reaction with perfluoroalkylhalide (2) to produce 2-perfluoroalkyl quinoxalines (3) under visible light. Both the π-π stacking aggregation in crystals and the solvation in various solvents of PS 1 exhibited visible-light absorption at 466 nm in spite of its smaller coefficient than that of the ultraviolet-light absorption. Such an aggregation-assisted visible-light absorption phenomenon is rationalized by theoretical calculations of the condensed-phase properties with the consideration of the explicit polarization effect from the neighboring molecules. Upon irradiation with different wavelengths, the emission colors changed from navy to bright yellow. Fluorescence lifetime measurements show that the emission of 1 comes from its singlet excited state. The aggregation induced emission when excited at 420 nm has a shorter lifetime (0.45 ns) than that of the emission from isolated molecules (2.71 ns) when excited at 381 nm. It is conceived that the aggregation assisted visible light absorption properties may be general in other photo-reactive molecules, such as 1,4-diisocyano-2,5-dimethylbenzene (4), 1,4-dicyanobenzene (5), and 1,4-diisocyanobenzene (6), which are widely used in many photochemical reactions in the absence of any external photosensitizer.

Visible-light-mediated radical arylthiodifluoromethylation of isocyanides with fluorinated 2-pyridyl sulfones

2-PySO₂CF₂SAr were developed as powerful arylthiodifluoromethylation reagents, and the Stern–Volmer luminescence studies demonstrated that the mechanism might operate via a photoredox cycle consisting of a reductive quenching with Na₂CO₃.

Photoredox-Catalyzed Cross-Coupling of Enamides for the Assembly of β-Difluoroimine Synthons

A photoredox-catalyzed formal C_sp3-C_sp3 cross-coupling reaction of enamides with bromodifluoro compounds is established. The resulting gem-difluoromethylenated γ-imines indicated high stability, excellent E/Z control, and broad functional group tolerance. These synthetic intermediates can efficiently transfer to difluoromethylenated γ-amino acids or δ-amino alcohols. Mechanistic analysis indicates that a radical/SET mechanism proceeding via a difluoroalkyl radical may be involved in the catalytic cycle.

Trifluoroethoxy-Coated Subphthalocyanine affects Trifluoromethylation of Alkenes and Alkynes even under Low-Energy Red-Light Irradiation

Photoredox chemical reactions induced by visible light have undergone a renaissance in recent years. Polypyridyl dyes such as Ir(ppy)3 and Ru(bpy)3 are key catalysts in this event, and blue- or white-light irradiation is required for the chemical transformations. However, it remains a challenge to achieve reactions under the lower energy of red light. We disclose, herein, that trifluoroethoxy-coated subphthalocyanine realizes the red-light-driven trifluoromethylation of alkenes and alkynes with trifluoromethyl iodide in good-to-high yields. Perfluoroalkylations were also achieved under red light. The reaction mechanism is discussed with the support of UV/Vis spectroscopy and cyclic voltammetry of trifluoroethoxy-coated subphthalocyanine. Light irradiation/dark study also supports the proposed mechanism.

Base Catalysis Enables Access to α,α-Difluoroalkylthioethers

A nucleophilic addition reaction of aryl thiols to readily available β,β-difluorostyrenes provides α,α-difluoroalkylthioethers. The reaction proceeds through an unstable anionic intermediate, prone to eliminate fluoride and generate α-fluorovinylthioethers. However, the use of base catalysis overcomes the facile β-fluoride elimination, generating α,α-difluoroalkylthioethers in excellent yields and selectivities.

A Diheteroatom Fluoroalkylation Reagent for Preparation of S- and N-Containing Fluoroalkyl Compounds and Sulfonic Acid Polymer

The first stable diheteroatom fluoroalkylation reagent, 2-((2-azido-1-chloro-1,2,2-trifluoroethyl)thio)pyrimidine (ACTP), has been prepared by a novel method. By using this reagent, various fluorinated thioethers and sulfones have been successfully prepared. The dearylation and dearylation-oxidation of fluoroalkyl 2-pyrimidyl sulfone in one-pot reaction were investigated systematically, and the results demonstrated that both fluoroalkyl sulfinates and sulfonates could be obtained in high yields. In addition, ACTP proved to be useful for the preparation of a fluorinated sulfonic acid proton-exchange membrane.

Visible-light-induced installation of oxyfluoroalkyl groups

(Hetero)aryloxytetrafluoroethylation of heteroaromatics and alkenes has been achieved by visible-light photocatalysis utilizing readily synthesized oxyfluoroalkyl reagents.

Controlled Fluoroalkylation Reactions by Visible-Light Photoredox Catalysis

Owing to their unique biological, physical, and chemical properties, fluoroalkylated organic substances have attracted significant attention from researchers in a variety of disciplines. Fluoroalkylated compounds are considered particularly important in pharmaceutical chemistry because of their superior lipophilicity, binding selectivity, metabolic stability, and bioavailability to those of their nonfluoroalkylated analogues. We have developed various methods for the synthesis of fluoroalkylated substances that rely on the use of visible-light photoredox catalysis, a powerful preparative tool owing to its environmental benignity and mechanistic versatility in promoting a large number of synthetically important reactions with high levels of selectivity. In this Account, we describe the results of our efforts, which have led to the development of visible-light photocatalytic methods for the introduction of a variety of fluoroalkyl groups (such as, -CF₃, -CF₂R, -CH₂CF₃, -C₃F₇, and -C₄F₉) and arylthiofluoroalkyl groups (such as, -CF₂SPh, -C₂F₄SAr, and -C₄F₈SAr) to organic substances. In these studies, electron-deficient carbon-centered fluoroalkyl radicals were successfully generated by the appropriate choice of fluoroalkyl source, photocatalyst, additives, and solvent. The redox potentials of the photocatalysts and the fluoroalkyl sources and the choice of sacrificial electron donor or acceptor as the additive affected the photocatalytic pathway, determining whether an oxidative or reductive quenching pathway was operative for the generation of key fluoroalkyl radicals. Notably, we have observed that additives significantly affect the efficiencies and selectivities of these reactions and can even change the outcome of the reaction by playing additional roles during its course. For instance, a tertiary amine as an additive in the reaction medium can act not only as a sacrificial electron donor in photoredox catalysis but also as a hydrogen atom source, an elimination base for dehydrohalogenation of the intermediate, and also a Brønsted base for deprotonation. In the same context, the selection of solvent is also critical since it affects the rate and selectivity of reactions depending upon its polarity and reagent solubilizing ability and plays additional roles in the process, for example, as a hydrogen atom source. By clearly understanding the roles of additives and solvent, we designed several controlled fluoroalkylation reactions where different products were formed selectively from the same starting substrates. In addition, we could exploit one of the most important advantages of radical reactions, that is, the use of unactivated π-systems such as alkenes, alkynes, arenes, and heteroarenes as radical acceptors without prefunctionalization. Furthermore, fluoroalkylation processes under mild room-temperature reaction conditions tolerate various functional groups and are therefore easily applicable to late-stage modifications of highly functionalized advanced intermediates.