Catalysis for fluorination and trifluoromethylation

Highly Enantioselective Decarboxylative Difluoromethylation

Organofluorine molecules that contain difluoromethyl groups (CF2H) at stereogenic centers have gained importance in pharmaceuticals due to the unique ability of CF2H groups to act as lipophilic hydrogen bond donors. Despite their potential, the enantioselective installation of CF2H groups into readily available starting materials remains a challenging and underdeveloped area. In this study, we report a nickel-catalyzed decarboxylative difluoromethylation reaction that converts alkyl carboxylic acids into difluoromethylated products with exceptional enantioselectivity. This Ni-catalyzed protocol exhibits broad functional group tolerance and is applicable for synthesizing fluorinated bioisosteres of biologically relevant molecules.

Cobalt-catalyzed reductive cross-coupling: a review

Transition-metal-catalyzed reductive cross-coupling is highly efficient for forming C-C bonds. It earns its limelight from its application by coupling unreactive electrophilic substrates to synthesize a variety of carbon-carbon bonds with various hybridizations (sp, sp2, and sp3), late-stage functionalization, and bioactive molecules' synthesis. Reductive cross-coupling is challenging to bring selectivity but promising approach. Cobalt is comparatively more affordable than other highly efficient metals e.g., palladium and nickel but cobalt catalysis is still facing efficacy challenges. Researchers are trying to harness the maximum out of cobalt's catalytic properties. Shortly, with efficiency achieved combined with the affordability of cobalt, it will revolutionize industrial applications. This review gives insight into the core of cobalt-catalyzed reductive cross-coupling reactions with a variety of substrates forming a range of differently hybridized coupled products.

Redox-neutral decarboxylative coupling of fluoroalkyl carboxylic acids via dual metal photoelectrocatalysis

Given the importance and beneficial characteristics of aliphatic CF3 chiral compounds in modern chemistry, efficient strategies for their synthesis are highly sought after. While α-CF3 carboxylic acid is an emerging and easily accessible CF3-containing synthon, its use as a source of fluoroalkyl is highly challenging due to its high oxidation potential. Herein, we disclose a photoelectrocatalytic method for the direct and enantioselective decarboxylative cross-coupling of α-CF3 carboxylic acids. Key to our approach is the strategic integration of the LMCT-induced decarboxylative process with classical nickel catalysis. This strategy enables the efficient synthesis of aliphatic chiral CF3 compounds with a broad range of substrates.

BiX3-Mediated Hydrohalogenations of HDDA Benzynes: An Approach to Polycyclic Aryl Halides

Here we demonstrate the hydrohalogenation reactions of HDDA benzynes promoted by BiX3 reagents for the generation of complex aryl halides. All three bismuth(III) halides can act as the source for their respective halides, i.e., Cl- or Br- or I-. The regiochemical preference for hydrohalogenation is dependent on the nature of the substituent present at the diyne terminus but neither on the linker nor on the BiX3 reagent. The substrate scope for this transformation is broad in terms of the tethers A-B-C and the substituents R1 and R2.

Asymmetric Remote Aldol Cyclization Reaction to Synthesize Trifluoromethylated Heterospirocyclic Frameworks

The highly enantioselective organocatalytic synthesis of dihydropyran spirocyclic compounds bearing di- and trifluoromethyl groups by aldol cyclization reaction via trienamine using cyclic 2,5-dienones and different di- and trifluoromethylketones is described. Using a bifunctional aminothiourea catalyst, trifluoromethyl-functionalized dihydropyran spirocyclic products were obtained with good yields and enantioselectivities. Subsequent transformation with H2 and Pd/C has allowed the synthesis of the tetrahydropyran structure with three stereocenters. The plausible reaction mechanism was investigated by computational methods.

Oxidative Aminotrifluoromethylation of 1,4-Naphthoquinone

A strategy for convenient and precise oxidative aminotrifluoromethylation of 1,4-naphthoquinone with the Togni reagent and amines has been demonstrated via a radical process. This method allows efficient access for the preparation of a wide range of CF3-functionalized 1,4-naphthoquinones under mild conditions, and its application in late-stage modification of drug molecules is achieved. Mechanistic studies indicate that 1,4-naphthoquinone serves as both a substrate and a catalyst and that the Togni reagent plays a dual role of a substrate and an oxidant. As a result, the title reaction can take place in the dark without external catalysts and oxidants.

Dialkylation of CF2 unit enabled by cobalt electron-shuttle catalysis

The incorporation of difluoromethylene (CF2) group into chemical molecules often imparts desirable properties such as lipophilicity, binding affinity, and thermal stability. Consequently, the increasing demand for gem-difluoroalkylated compounds in drug discovery and materials science has continued to drive the development of practical methods for their synthesis. However, traditional synthetic methods such as deoxofluorination often confront challenges including complicated substrate synthesis sequences and poor functional group compatibility. In this context, we herein report a metal electron-shuttle catalyzed, modular synthetic methodology for difluoroalkylated compounds by assembling two C(sp3) fragments across CF2 unit in a single step. The approach harnesses a difluoromethylene synthon as a biradical linchpin, achieving the construction of two C(sp3)-CF2 bonds through radical addition to two different π-unsaturated molecules. This catalytic protocol is compatible with broad range of coupling partners including diverse olefins, iminiums, and hydrazones, supporting endeavors in the efficient construction of C(sp3)-rich difluoroalkylated molecules.

Visible Light-Promoted Aromatization-Driven Deconstructive Fluorination of Spiro Carbocycles

A visible light-promoted aromatization-driven deconstructive fluorination of spiro carbocycles is presented. A series of spiro dihydroquinazolinones reacted efficiently with NFSI under visible light irradiation to afford the 2-(4-fluoroalkyl)quinazolin-4(3H)-ones in good yields with excellent functional group tolerance. A radical pathway involving C-C bond cleavage and F atom transfer is proposed for the reaction. In addition, the ring-opening chlorination of spiro dihydroquinazolinones with NCS was also applicable.

Electrochemical Decarboxylative Cross-Coupling with Nucleophiles

Decarboxylative cross-coupling reactions are powerful tools for carbon-heteroatom bonds formation, but typically require pre-activated carboxylic acids as substrates or heteroelectrophiles as functional groups. Herein, we present an electrochemical decarboxylative cross-coupling of carboxylic acids with structurally diverse fluorine, alcohol, H2O, acid, and amine as nucleophiles. This strategy takes advantage of the ready availability of these building blocks from commercial libraries, as well as the mild and oxidant-free conditions provided by electrochemical system. This reaction demonstrates good functional-group tolerance and its utility in late-stage functionalization.

Substituent-Controlled Copper-Catalyzed Trifluoromethylation of 1,7-Dienes: Synthesis of Mono- and Bis-trifluoromethylated Benzoxepines

A copper-catalyzed trifluoromethylation of benzene-linked 1,7-dienes with 1-trifluoromethyl-1,2-benziodoxole via a radical cascade cyclization process for the synthesis of mono- and bis-trifluoromethylated benzoxepines is developed. The selectivity depends on substituents on the double bond of the allyl group in 1,7-dienes. The large-scale operation and late-stage functionalization of bioactive molecules reveal the promising utility of this protocol.

Visible-Light-Induced Domino Perfluoroalkylation/Cyclization to Access Perfluoroalkylated Quinazolinones by an EDA Complex

The electron donor-acceptor (EDA) complexes have been extensively studied, which formed an electronically excited state, obviating the need for an exogenous photocatalyst. Herein, we report a mild and efficient strategy for photoinduced radical domino perfluoroalkylation/cyclization using N,N,N',N'-tetramethylethane-1,2-diamine (TMEDA) as an electron donor. This protocol could be well expanded to access various polycyclic quinazolinones containing perfluoroalkyl groups, exhibiting photocatalyst-free, good functional group tolerance, and environmentally friendly features.

Base-Promoted Nucleophilic Phosphorylation of Benzyl Fluorides via C(sp3)-F Cleavage

Herein, a transition-metal-free phosphorylation of benzyl fluorides with P(O)-H compounds is disclosed. In the presence of tBuOK, various benzyl fluorides react with P(O)-H compounds to produce the corresponding benzyl phosphine oxides, phosphinates, and phosphonates in good to high yields. This base-promoted phosphorylation reaction offers a facile and general strategy for the construction of a C(sp3)-P bond.

Direct Synthesis of 2-Hydroxytrifluoroethylacetophenones via Organophotoredox-Mediated Net-Neutral Radical/Polar Crossover

Alkene difunctionalization is a very attractive tool in synthetic organic chemistry. Herein, we disclose an operationally and practically simple method to access 2-hydroxytrifluoroethylacetophenones from styrene derivatives via photoredox catalysis. This light-mediated transformation promotes the generation of the 1-hydroxy-2,2,2-trifluoroethyl carbon-centered radical as key synthon, which undergoes Giese addition with styrenes followed by a Kornblum oxidation process. The presented method is not only mild and cost-effective, but also utilizes an organic photocatalyst and DMSO as oxidant. Experimental investigations support the operative mechanism via net-neutral radical/polar crossover.

Metal- versus ligand-centered reactivity of a cobalt-phenylenediamide complex with electrophiles

A new series of [CoIII-CF3]n+ complexes supported by a bidentate redox-active ligand is presented. The cationic [Co-CF3]+ complex was first obtained by reacting [CpCo(tBuUreaopda)] (Cp = cyclopentadienyl, opda = o-phenylenediamide) with an electrophilic trifluoromethyl source, for which the redox-active phenylenediamide ligand serves as a 2e- reservoir to generate [CpCp(tBuUreabqdi)(CF3)]+ (bqdi = benzoquinonediimine). Electrochemical studies of [Co-CF3]+ revealed two reversible 1e- reductions. Chemical reduction with 1 or 2 equiv. reducing agent enabled isolation of the neutral and anionic complexes, respectively, where the [CoIII-CF3] bond remains intact in all three oxidation states (n = +1, 0, -1). Structural analysis shows systematic changes to the redox-active ligand backbone upon reduction, consistent with sequential ligand-centered electron transfer in the series [bqdi]0 to [s-bqdi]˙- to [opda]2-. In contrast, the reaction of [CpCo(tBuUreaopda)] with alkyl triflates resulted in ligand-centered alkylation at the ureayl groups instead of the targeted Co-alkyl bond formation, suggesting less favorable bond formation at cobalt and greater nucleophilic accessibility of the ligand compared to the metal center.

Engineering non-haem iron enzymes for enantioselective C(sp3)-F bond formation via radical fluorine transfer

In recent years there has been a surge in the development of methods for the synthesis of organofluorine compounds. However, enzymatic methods for C-F bond formation have been limited to nucleophilic fluoride substitution. Here, we report the incorporation of iron-catalysed radical fluorine transfer, a reaction mechanism that is not used in naturally occurring enzymes, into enzymatic catalysis for the development of biocatalytic enantioselective C(sp 3)-F bond formation. Using this strategy, we repurposed (S)-2-hydroxypropylphosphonate epoxidase from Streptomyces viridochromogenes (SvHppE) to catalyse an N-fluoroamide directed C(sp 3)-H fluorination. Directed evolution has enabled SvHppE to be optimized, forming diverse chiral benzylic fluoride products with turnover numbers of up to 180 and with excellent enantiocontrol (up to 94% e.e.). Mechanistic investigations showed that the N-F bond activation is the rate-determining step, and the strong preference for fluorination in the presence of excess NaN3 can be attributed to the spatial proximity of the carbon-centered radical to the iron-bound fluoride.

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

Visible light-mediated difluoromethylation/cyclization in batch and flow: scalable synthesis of CHF2-containing benzimidazo- and indolo[2,1-a]isoquinolin-6(5H)-ones

We report here a practical and cost-effective method for the synthesis of CHF2-containing benzimidazo- and indolo[2,1,a]-isoquinolin-6(5H)-ones through a visible light-mediated difluoromethylation/cyclization cascade. The method, which affords functionalized multifused N-heterocyclic scaffolds in moderate to high yields under mild reaction conditions, is also easily scalable using low-cost 3D printed photoflow reactors.

Synthesis and application of well-defined [Ph4P]+[Cu(CF2CF3)2]- complex as a versatile pentafluoroethylating reagent

We herein describe the preparation and application of a new bispentafluoroethylated organocuprate [Ph4P]+[Cu(CF2CF3)2]-. This complex has demonstrated a remarkable range of reactivities towards carboxylic acids, diazonium salts, organic halides, boronic esters, terminal alkynes and (hetero)arenes as a versatile pentafluoroethylating reagent. The construction of C(sp3)-/C(sp2)-/C(sp)-CF2CF3 bonds can therefore be achieved using a single reagent.

Chemoenzymatic Synthesis of Fluorinated Mycocyclosin Enabled by the Engineered Cytochrome P450-Catalyzed Biaryl Coupling Reaction

Installing fluorine atoms onto natural products holds great promise for the generation of fluorinated molecules with improved or novel pharmacological properties. The enzymatic oxidative carbon-carbon coupling reaction represents a straightforward strategy for synthesizing biaryl architectures, but the exploration of this method for producing fluorine-substituted derivatives of natural products remains elusive. Here, in this study, we report the protein engineering of cytochrome P450 from Mycobacterium tuberculosis (MtCYP121) for the construction of a series of new-to-nature fluorine-substituted Mycocyclosin derivatives. This protocol takes advantage of a "hybrid" chemoenzymatic procedure consisting of tyrosine phenol lyase-catalyzed fluorotyrosine preparation from commercially available fluorophenols, intermolecular chemical condensation to give cyclodityrosines, and an engineered MtCYP121-catalyzed intramolecular biphenol coupling reaction to complete the strained macrocyclic structure. Computational mechanistic studies reveal that MtCYP121 employs Cpd I to abstract a hydrogen atom from the proximal phenolic hydroxyl group of the substrate to trigger the reaction. Then, conformational change makes the two phenolic hydroxyl groups close enough to undergo intramolecular hydrogen atom transfer with the assistance of a pocket water molecule. The final diradical coupling process completes the intramolecular C-C bond formation. The efficiency of the biaryl coupling reaction was found to be influenced by various fluorine substitutions, primarily due to the presence of distinct binding conformations.

Fluorine-Effect-Enabled Photocatalytic 4-Exo-Trig Cyclization Cascade to Access Fluoroalkylated Cyclobutanes

Cyclobutanes are popular structural units in bioactive compounds and versatile intermediates in synthetic chemistry, but their synthesis is challenging owing to high ring strain. In this study, a novel method for highly regio- and diastereoselective synthesis of fluoroalkylcyclobutanes bearing vicinal quaternary and tertiary stereocenters is realized by a photocatalytic 4-exo-trig cyclization cascade of thioalkynes or trifluoromethylalkenes. Density functional theory calculations reveal that a unique fluorine effect, arising from hyperconjugative π→σ*C-F interactions, accounts for the regio-reversed radical addition at the sterically hindered alkene carbon, which facilitates an unprecedented 4-exo-trig ring closure. This chemistry enables the direct and controllable construction of medicinally valuable quaternary-carbon-containing cyclobutanes from readily available raw materials, nicely complementing the existing methods.

Tetrafluoroisopropylation of alkenes and alkynes enabled by photocatalytic consecutive difluoromethylation with CF2HSO2Na

Direct assembly of complex fluorinated motifs from simple fluorine sources is an attractive frontier of synthetic chemistry. Reported herein is an unconventional protocol for achieving tetrafluoroisopropylation by using commercially available CF2HSO2Na as a convenient source of the tetrafluoroisopropyl [(CF2H)2CH] group, which finds widespread applications in life science and material science. Visible-light-induced hydrotetrafluoroisopropylation of alkenes and carbotetrafluoroisopropylation of alkynes have been thus developed. Various structurally diverse α-tetrafluoroisopropyl carbonyls and cyclopentanones are selectively constructed under mild conditions. A photocatalytic triple difluoromethylation cascade, driven by consecutive reductive radical/polar crossover processes, leads to the direct assembly of a tetrafluoroisopropyl moiety from CF2HSO2Na. This C1-to-C3 fluoroalkylation protocol provides a practical strategy for the rapid construction of polyfluorinated compounds that are otherwise difficult to access, thus significantly enhancing the boundary of fluoroalkylation chemistry.

Borane-Catalyzed Coupling of Diazooxindoles and Difluoroenoxysilanes to Tetrasubstituted Monofluoroalkenes

A highly stereoselective coupling reaction of diazooxindoles with difluoroenoxysilanes catalyzed by Lewis acidic boranes has been developed. The reaction proceeded at ambient temperature under transition metal-free conditions with wide functional group tolerance. By using this simple procedure, a series of tetrasubstituted monofluoroalkenes can be accessed in good yield with high selectivity.

Ruthenium-Catalyzed Meta-Selective Trifluoroisopropylation of Arenes

This work reports the mild and efficient Ru-catalyzed trifluoroisopropylation of arenes using 2-bromo-1,1,1-trifluoropropane. Various bioactive molecules, such as purine and nucleoside derivatives, were well-suited for this transformation, affording the corresponding products in moderate-to-good yields. This method provides an efficient strategy for synthesizing trifluoroisopropyl molecules for drug discovery.

Electron Donor-Acceptor Complex Driven Photocatalyst-Free Trifluoromethylation of Heterocycles

Heterocyclic trifluoromethylation is efficiently initiated through a photochemical reaction utilizing an electron donor-acceptor (EDA) complex, proceeding smoothly without the use of photocatalysts, transition-metal catalysts, or additional oxidants. This method has been optimized through extensive experimentation, demonstrating its versatility and efficacy across various substrates, including quinoxalinones, coumarins, and indolones. Notably, this approach enables the practical synthesis of trifluoromethylated quinoxalinones on a gram scale. Mechanistic investigations that incorporate radical trapping and ultraviolet/visible spectroscopy, confirmed the formation of the an EDA complex and elucidated the reaction pathways. This study highlights the crucial role of EDA photoactivation in trifluoromethylation, significantly expanding the application scope of EDA complexes in chemical synthesis.

Tunable molecular editing of indoles with fluoroalkyl carbenes

Building molecular complexity from simple feedstocks through precise peripheral and skeletal modifications is central to modern organic synthesis. Nevertheless, a controllable strategy through which both the core skeleton and the periphery of an aromatic heterocycle can be modified with a common substrate remains elusive, despite its potential to maximize structural diversity and applications. Here we report a carbene-initiated chemodivergent molecular editing of indoles that allows both skeletal and peripheral editing by trapping an electrophilic fluoroalkyl carbene generated in situ from fluoroalkyl N-triftosylhydrazones. A variety of fluorine-containing N-heterocyclic scaffolds have been efficiently achieved through tunable chemoselective editing reactions at the skeleton or periphery of indoles, including one-carbon insertion, C3 gem-difluoroolefination, tandem cyclopropanation and N1 gem-difluoroolefination, and cyclopropanation. The power of this chemodivergent molecular editing strategy has been highlighted through the modification of the skeleton or periphery of natural products in a controllable and chemoselective manner. The reaction mechanism and origins of the chemo- and regioselectivity have been probed by both experimental and theoretical methods.

Chemoselective Synthesis of α-Halo-α,α-difluoromethyl Ketones from Trimethyl(phenylethynyl)silane

Here, we describe a novel strategy for chemoselective synthesis of α-halo-α,α-difluoromethyl ketones (-COCF3 and -COClCF2 motifs) from trimethyl(phenylethynyl)silane under catalyst-free and mild conditions. Commercially available Selectfluor or additional NaCl as halogen reagent was employed to complete this transformation, thereby demonstrating the potential synthetic value of this new reaction in organic synthesis.

Structure-Activity Relationship Studies in a Series of Xanthine Inhibitors of SLACK Potassium Channels

Gain-of-function mutations in the KCNT1 gene, which encodes the sodium-activated potassium channel known as SLACK, are associated with the rare but devastating developmental and epileptic encephalopathy known as epilepsy of infancy with migrating focal seizures (EIMFS). The design of small molecule inhibitors of SLACK channels represents a potential therapeutic approach to the treatment of EIMFS, other childhood epilepsies, and developmental disorders. Herein, we describe a hit optimization effort centered on a xanthine SLACK inhibitor (8) discovered via a high-throughput screen. Across three distinct regions of the chemotype, we synthesized 58 new analogs and tested each one in a whole-cell automated patch-clamp assay to develop structure-activity relationships for inhibition of SLACK channels. We further evaluated selected analogs for their selectivity versus a variety of other ion channels and for their activity versus clinically relevant SLACK mutants. Selectivity within the series was quite good, including versus hERG. Analog 80 (VU0948578) was a potent inhibitor of WT, A934T, and G288S SLACK, with IC50 values between 0.59 and 0.71 µM across these variants. VU0948578 represents a useful in vitro tool compound from a chemotype that is distinct from previously reported small molecule inhibitors of SLACK channels.

Photoinduced metal-free trifluoro/perfluoroalkylation of heteroarenes

A practical and straightforward protocol to access trifluoromethylated/perfluoroalkylated heteroarenes via radical-type nucleophilic substitution rather than typical radical-type electrophilic substitution is described here. The substrate scope was observed to be broad and diverse-covering arenes, heteroarenes (containing N, O, S), bioactive cores, and allylic cores. Mechanistic studies confirmed a radical-mediated reaction pathway.

Regio- and Stereoselective Hexafluoroisopropoxylation and Trifluoroethoxylation of Allenamides

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio- and stereoselective manner in good to moderate yields under mild conditions.

Electrochemical Reductive Cross-Coupling of Alkyl or Alkenyl Halides with gem-Difluoroalkenes

Herein, we describe an electroreductive cross-electrophile coupling protocol for the construction of valuable monofluoroalkenes from easily accessible alkyl or alkenyl halides with gem-difluoroalkenes. The reaction can be conducted under sustainable and mild conditions delivering valuable and functionalized monofluoroalkenes with excellent Z-selectivity. The protocol's most notable advantage is the in situ release of nickel catalyst from the inexpensive electrodes without the addition of extra hazardous metal catalyst and superstoichiometric reductant.

Photoredox Nucleophilic (Radio)fluorination of Alkoxyamines

Herein, we report a photoredox nucleophilic (radio)fluorination using TEMPO-derived alkoxyamines, a class of substrates accessible in a single step from a diversity of readily available carboxylic acids, halides, alkenes, alcohols, aldehydes, boron reagents, and C-H bonds. This mild and versatile one-electron pathway affords radiolabeled aliphatic fluorides that are typically inaccessible applying conventional nucleophilic substitution technologies due to insufficient reactivity and competitive elimination. Automation of this photoredox process is also demonstrated with a user-friendly and commercially available photoredox flow reactor and radiosynthetic platform, therefore expediting access to labeled aliphatic fluorides in high molar activity (Am) for (pre)clinical evaluation.

Synthesis of CHF2-Containing Heterocycles through Oxy-difluoromethylation Using Low-Cost 3D Printed PhotoFlow Reactors

We report here a highly straightforward access to a variety of CHF2-containing heterocycles, including lactones, tetrahydrofurans, tetrahydropyrans, benzolactones, phthalanes, and pyrrolidines, through a visible light-mediated intramolecular oxy-difluoromethylation under continuous flow. The method, which relies on the use of readily available starting materials, low-cost 3D printed photoflow reactors, and difluoromethyltriphenylphosphonium bromide used here as a CHF2 radical precursor, is practical and scalable and provides the desired products in moderate to excellent yields and excellent regio- and stereoselectivities.

Ligand-Enabled Oxidative Fluorination of Gold(I) and Light-Induced Aryl-F Coupling at Gold(III)

MeDalphos Au(I) complexes featuring aryl, alkynyl, and alkyl groups readily react with electrophilic fluorinating reagents such as N-fluorobenzenesulfonimide and Selectfluor. The ensuing [(MeDalphos)Au(R)F]+ complexes have been isolated and characterized by multinuclear NMR spectroscopy as well as X-ray diffraction. They adopt a square-planar contra-thermodynamic structure, with F trans to N. DFT/IBO calculations show that the N lone pair of MeDalphos assists and directs the transfer of F+ to gold. The [(MeDalphos)Au(Ar)F]+ (Ar = Mes, 2,6-F2Ph) complexes smoothly engage in C-C cross-coupling with PhCCSiMe3 and Me3SiCN, providing direct evidence for the oxidative fluorination/transmetalation/reductive elimination sequence proposed for F+-promoted gold-catalyzed transformations. Moreover, direct reductive elimination to forge a C-F bond at Au(III) was explored and substantiated. Thermal means proved unsuccessful, leading mostly to decomposition, but irradiation with UV-visible light enabled efficient promotion of aryl-F coupling (up to 90% yield). The light-induced reductive elimination proceeds under mild conditions; it works even with the electron-deprived 2,6-difluorophenyl group, and it is not limited to the contra-thermodynamic form of the aryl Au(III) fluoride complexes.

Photoredox-Catalyzed Acylchlorination of α-CF3 Alkenes with Acyl Chloride and Application as Masked Access to β-CF3-enones

We disclose a photocatalytic strategy that simultaneously addresses the construction of trifluoromethylated quaternary carbon centers and the preparation of β-CF3-enones through radical difunctionalization of α-CF3 alkenes with acyl chlorides. This method is characterized by its broad functional group compatibility, high efficiency, and atom economy. The versatility of this transformation is poised to broaden the applications of α-CF3 alkenes, providing new pathways for the rapid assembly of structurally diverse fluorinated compounds.

Cross-coupling of organic fluorides with allenes: a silyl-radical-relay pathway for the construction of α-alkynyl-substituted all-carbon quaternary centres

Controlling the transformation of versatile and reactive allenes is a considerable challenge. Herein, we report an efficient silylboronate-mediated cross-coupling reaction of organic fluorides with allenes to construct a series of sterically demanding α-ethynyl-containing all-carbon quaternary centers (ACQCs), using catalyst-free silyl-radical-relay reactions to selectively functionalize highly inert C-F bonds in organic fluorides. The key to the success of this transformation lies in the radical rearrangement of an in situ-generated allenyl radical to form a bulky tertiary propargyl radical; however, the transformation does not show efficiency when using the propargyl isomer directly. This unique reaction enables the cross-coupling of a tertiary carbon radical center with a C(sp2)-F bond or a benzylic C(sp3)-F bond. α-Ethynyl-containing ACQCs with (hetero)aromatic substituents and benzyl were efficiently synthesized in a single step using electronically and sterically diverse organic fluorides and allenes. The practical utility of this protocol is showcased by the late-stage functionalization of bioactive molecules and the modification of a liquid crystalline material.

Catalytic Asymmetric Difluoroalkylation Using In Situ Generated Difluoroenol Species as the Privileged Synthon

A robust and practical difluoroalkylation synthon, α,α-difluoroenol species, which generated in situ from trifluoromethyl diazo compounds and water in the presence of dirhodium complex, is disclosed. As compared to the presynthesized difluoroenoxysilane and in situ formed difluoroenolate under basic conditions, this difluoroenol intermediate displayed versatile reactivity, resulting in dramatically improved enantioselectivity under mild conditions. As demonstrated in catalytic asymmetric aldol reaction and Mannich reactions with ketones or imines in the presence of chiral organocatalysts, quinine-derived urea, and chiral phosphoric acid (CPA), respectively, this relay catalysis strategy provides an effective platform for applying asymmetric fluorination chemistry. Moreover, this method features a novel 1,2-difunctionalization process via installation of a carbonyl motif and an alkyl group on two vicinal carbons, which is a complementary protocol to the metal carbene gem-difunctionalization reaction.

Copper-Mediated Cyclization of Terminal Alkynes with CF3-Imidoyl Sulfoxonium Ylides To Construct 5-Trifluoromethylpyrroles

A copper-mediated [3 + 2] cyclization of CF3-imidoyl sulfoxonium ylides and terminal alkynes has been demonstrated. This work provides a practical approach for assembling 5-trifluoromethylpyrroles with the merits of a broad substrate scope, good functional tolerance, and mild reaction conditions. Control experiments and DFT studies indicate that this reaction may involve the addition of π-bonds of terminal alkynes by copper-carbene radicals and hydrogen migration.

BF3-Promoted Ring Expansion of Iminylphosphiranes and Acylphosphiranes for Divergent Access to 1,2-Azaphospholidines and 1,2-Dihydrophosphetes

Ring expansion of strained small rings provides an efficient method for the synthesis of various high-value carbocycles and heterocycles. Here we report BF3·Et2O as both an activating reagent and fluorine source, enabling ring expansion of phosphirane and P-F bond formation. Treatment of 1-iminylphosphirane complexes with BF3·Et2O resulted in 1,2-azaphospholidines, while the reaction of 1-acylphosphirane complexes with BF3·Et2O afforded 1,2-dihydrophosphetes. The reaction path was tuned by the nucleophilicity of the N and O atoms toward the intermediate phosphenium cation.

The Role of Small Molecules Containing Fluorine Atoms in Medicine and Imaging Applications

The fluorine atom possesses many intrinsic properties that can be beneficial when incorporated into small molecules. These properties include the atom's size, electronegativity, and ability to block metabolic oxidation sites. Substituents that feature fluorine and fluorine-containing groups are currently prevalent in drugs that lower cholesterol, relieve asthma, and treat anxiety disorders, as well as improve the chemical properties of various medications and imaging agents. The dye scaffolds (fluorescein/rhodamine, coumarin, BODIPY, carbocyanine, and squaraine dyes) reported will address the incorporation of the fluorine atom in the scaffold and the contribution it provides to its application as an imaging agent. It is also important to recognize radiolabeled fluorine atoms used for PET imaging in the early detection of diseases. This review will discuss the many benefits of incorporating fluorine atoms into small molecules and give examples of fluorinated molecules used in the pharmaceutical industry and imaging techniques.

Iodine(III)-promoted oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent

A metal-free protocol for oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent has been developed using (diacetoxyiodo)benzene (PIDA) as an oxidant. This three-component strategy enables one-step construction of 3,4-disubstituted maleimides in good yields with high functional group tolerance. Both experimental and theoretical studies support the proposed radical reaction mechanism.

Electrochemistry-enabled residue-specific modification of peptides and proteins

Selective chemical reactions at precise amino acid residues of peptides and proteins have become an exploding field of research in the last few decades. With the emerging utility of bioconjugated peptides and proteins as drug leads and therapeutic agents, the design of smart protocols to modulate and conjugate biomolecules has become necessary. During this modification, the most important concern of biochemists is to keep intact the structural integrity of the biomolecules. Hence, a soft and selective biocompatible reaction environment is necessary. Electrochemistry, a mild and elegant tunable reaction platform to synthesize complex molecules while avoiding harsh and toxic chemicals, can provide such a reaction condition. However, this strategy is yet to be fully exploited in the field of selective modification of polypeptides. With this possibility, the use of electrochemistry as a reaction toolbox in peptide and protein chemistry is flourishing day by day. Unfortunately, there is no suitable review article summarizing the residue-specific modification of biomolecules. The present review provides a comprehensive summary of the latest manifested electrochemical approaches for the modulation of five redox-active amino acid residues, namely cysteine, tyrosine, tryptophan, histidine and methionine, found in peptides and proteins. The article also highlights the incredible potential of electrochemistry for the regio- as well as chemoselective bioconjugation strategy of biomolecules.

Selective Access to Functional Fluoroenones via Palladium-Catalyzed Selenofluoroalkylacylation of Terminal Alkynes

The trifluoromethylacyl group (-COCF3) is an important motif and widely studied in catalysis, medicinal chemistry, and materials science. Herein, a novel palladium-catalyzed selenofluoroalkylacylation of terminal alkynes with commercially available fluoroalkyl anhydride and diorganyl diselenides to afford β-seleno and aryl/alkyl disubstituted enones under mild conditions is disclosed. In addition, selenodifluoroacetylations and selenoperfluoroacetylations are also suitable for this reaction. Mechanistic studies reveal that this reaction proceeds via an oxidative radical-polar crossover process.

Iodonium based regioselective double nucleophilic alkene functionalization of a hydrofluoroolefin scaffold

Herein, we report a modular regioselective alkene difunctionalization strategy based on the use of hydrofluoroolefin (HFO) gas as fluorous feedstock material. The transformation of the HFO gas to iodonium salt creates vicinal electrophilic sites readily available for a broad range of nucleophiles.

Synthesis of Fluoromethylated Chromones and Their Heteroatom Analogues via Sodium Fluoromethanesulfinate-Enabled Direct Fluoromethylation

An array of biologically interesting tri/difluoromethylated chromones and their heteroatom analogues were conveniently synthesized from the reaction of chromones and their heteroatom analogues with CF3SO2Na or HCF2SO2Na in the presence of tert-butyl hydroperoxide under mild conditions. A mechanistic pathway involving the generation of the electrophilic tri/difluoromethyl radical, followed with the radical substitution of chromones and their heteroatom analogues, was postulated.

Brønsted Acid-Catalyzed Dehydrative Nazarov-type Cyclization of CF3-Substituted 3-Indolylallyl Alcohols: Divergent Synthesis of 1-Trifluoromethylated Cyclopenta[b]indoles

An expedient and efficient synthetic method for the divergent synthesis of 1-trifluoromethylated cyclopenta[b]indoles that relies on Brønsted acid-catalyzed dehydrative Nazarov-type cyclization of CF3-substituted 3-indolylallyl alcohols is described. Two classes of 1-trifluoromethylated cyclopenta[b]indoles can be easily accessed simply by changing the NH-protecting group of indoles. With arylsulfonyl protected 3-indolylallyl alcohols as starting materials, the reaction provided the arylsulfonyl protected 1-trifluoromethylated cyclopenta[b]indoles in good to excellent yields, whereas pivaloyl (Piv) protected substrates led to the formation of NH-free 1-trifluoromethylated cyclolopenta[b]indoles with another alkenyl isomer. This protocol features tunable chemoselectivity, operational simplicity, excellent functional group compatibility, and mild metal-free conditions.

Transition-Metal-Catalyzed Directed C-H Functionalization in/on Water

Directing group assisted C-H bond functionalization using transition-metal-catalysis has emerged as a reliable synthetic tool for the construction of regioselective carbon-carbon/heteroatom bonds. Off late, "in/on water directed transition-metal-catalysis", though still underdeveloped, has appeared as one of the prominent themes in sustainable organic chemistry. This article covers the advancements, mechanistic insights and application of the sustainable directed C-H bond functionalization of (hetero)arenes in/on water in the presence of transition-metal-catalysis.

Influence of Metal Identity and Complex Nuclearity in Kumada Cross-Coupling Polymerizations with a Pyridine Diimine-Based Ligand Scaffold

Cross-coupling polymerizations have fundamentally changed the field of conjugated polymers (CPs) by expanding the scope of accessible materials. Despite the prevalence of cross-coupling in CP synthesis, almost all polymerizations rely on mononuclear Ni or Pd catalysts. Here, we report a systematic exploration of mono- and dinuclear Fe and Ni precatalysts with a pyridine diimine ligand scaffold for Kumada cross-coupling polymerization of a donor thiophene and an acceptor benzotriazole monomers. We observe that variation of the metal identity from Ni to Fe produces contrasting polymerization mechanisms, while complex nuclearity has a minimal impact on reactivity. Specifically, Fe complexes appear to catalyze step-growth Kumada polymerizations and can readily access both Csp2-Csp3 and Csp2-Csp2 cross-couplings, while Ni complexes catalyze chain-growth polymerizations and predominantly Csp2-Csp2 cross-couplings. Thus, our work sheds light on important design parameters for transition metal complexes used in cross-coupling polymerizations, demonstrates the viability of iron catalysis in Kumada polymerization, and opens the door to novel polymer compositions.

Selective Defluoroalkylation and Hydrodefluorination of Trifluoromethyl Groups Photocatalyzed by Dihydroacridine Derivatives

The selective functionalization of trifluoromethyl groups through C-F cleavage poses a significant challenge due to the high bond energy of the C(sp3)-F bonds. Herein, we present dihydroacridine derivatives as photocatalysts that can functionalize the C-F bond of trifluoromethyl groups with various alkenes under mild conditions. Mechanistic studies and DFT calculations revealed that upon irradiation, the dihydroacridine derivatives exhibit high reducibility and function as photocatalysts for reductive defluorination. This process involves a sequential single-electron transfer mechanism. This research provides valuable insights into the properties of dihydroacridine derivatives as photocatalysts, highlighting the importance of maintaining a planar conformation and a large conjugated system for optimal catalytic activity. These findings facilitate the efficient catalytic reduction of inert chemical bonds.

The perfluoroalkylthiolation/decarbonylation reaction of 1,3-diketones with perfluoroalkanesulfenic acids

The perfluoroalkylthiolation/decarbonylation reactions of 1,3-dicarbonyl compounds with in situ formed perfluoroalkanesulfenic acids were achieved. Using trifluoromethanesulfonic acid as an additive, a series of α-perfluoroalkylthiolated arylethanones were obtained in moderate to good yields. A possible mechanism was proposed based on the reaction results and control experiments.

Cooperative Photoredox and N-Heterocyclic Carbene Catalyzed Fluoroaroylation for the Synthesis of α-Trifluoromethyl-Substituted Ketones

α-Trifluoromethylated ketones have attracted significant attention as valuable building blocks in organic synthesis. Such compounds are generally accessed through trifluoromethylation of ketones. Here we report an alternative disconnection approach for the construction of α-CF3 carbonyl compounds by using aroyl fluorides as bifunctional reagents for fluoroaroylation of gem-difluoroalkenes through cooperative photoredox and N-heterocyclic carbene (NHC) catalysis. This strategy bypasses the use of expensive or sensitive trifluoromethylation reagents and/or the requirement for ketone pre-functionalization, thus enabling an efficient and general synthetic method to access α-CF3 -substituted ketones. A wide variety of gem-difluoroalkenes and aroyl fluorides bearing a diverse set of functional groups are eligible substrates. Notably, the developed methodology also provides rapid access to mono- or difluoroalkyl ketones. Mechanistic studies reveal that merging photoredox catalysis with NHC catalysis is essential for the reaction.