Nonafluoro-tert-butoxylation of Diaryliodonium Salts

Site-Selective Nitration of Arene via Hypervalent Iodine-Mediated C-H Functionalization

We developed a novel nitration method using hypervalent iodine for site-selective C-H functionalization. This technique efficiently synthesizes nitroarenes with high regioselectivity and is scalable, enhancing the late-stage modification of bioactive pharmaceuticals.

Selective radical-type perfluoro-tert-butylation of unsaturated compounds with a stable and scalable reagent

Despite the promising potential of the perfluoro-tert-butyl group in diverse fields such as magnetic resonance imaging, material science and drug design, incorporating this group into organic molecules is still a formidable task, primarily due to its bulky structure and unique fluorine effect. Herein, we describe a stable and scalable reagent for radical-type perfluoro-tert-butylation, which is synthesized in large scale from commercial perfluoro-tert-butanol and a designed benzothiazole hypervalent iodonium salt. Highly E-selective photo-driven C(sp2)-H functionalization of styrene derivatives is achieved in a triplet-triplet energy transfer halted manner, while thermally disfavored Z-products are also accessible by removing the energy antagonist. The application of this method is further demonstrated by late-stage functionalization and divergent synthesis of perfluoro-tert-butylated compounds.

Exploring the Chiral Match-Mismatch Effect in the Chiral Discrimination of Nitriles

This study tackles the challenge of enantiodifferentiation of nitrile compounds, which is typically difficult to resolve using nuclear magnetic resonance (NMR) due to the significant distance between the chiral center and the nitrogen atom involved in molecular interactions. We have developed novel chiral 19F-labeled probes, each featuring two chiral centers, to exploit the "match-mismatch" effect, thereby enhancing enantiodiscrimination. This strategy effectively differentiates chiral analytes with quaternary chiral carbon centers as well as those with similar substituents at the chiral center. Our approach not only provides a novel method for precise probe performance optimization but also offers a rapid and efficient technique for screening reaction conditions in asymmetric synthesis.

[Cu(NHC)(OR)] (R = C(CF3)3) complexes for N-H and S-H bond activation and as pre-catalysts in the Chan-Evans-Lam reaction

The synthesis, isolation, and full characterization of a series of NHC-copper perfluoro-alkoxide complexes are reported. Their exceptional stability resides with the steric hindrance of the nonafluoro-tert-butyl alkoxide moiety, which exhibits a strong electron withdrawing effect. These new Cu(I) complexes are synthons that can permit the activation of acidic N-H and S-H bonds. The well-defined [Cu(IPr)(OC(CF3)3)] was investigated as a pre-catalyst in the Chan-Evans-Lam reaction.

Direct synthesis of N-perfluoro-tert-butyl secondary amines from N-trifluoromethyl secondary amines

N-Perfluoro-tert-butyl (N-PFtB) secondary amines, harboring a unique 19F-reporting moiety linked directly to nitrogen, are highly attractive due to their diverse potential applications. However, their mild and facile synthesis remains a significant challenge. Herein, we present a safe and efficient strategy for the direct synthesis of N-perfluoro-tert-butyl secondary amines from readily available N-trifluoromethyl secondary amines. Experiments and theoretical calculations demonstrate that this novel protocol encompasses three main processes: the elimination of hydrogen fluoride from the N-trifluoromethyl precursor, consecutive addition-elimination conversion of difluoromethyl imine (R-N[double bond, length as m-dash]CF2) to hexafluoropropyl imine (R-N[double bond, length as m-dash]C(CF3)2), and final addition of R-N[double bond, length as m-dash]C(CF3)2 with the in situ generated fluoroform (HCF3). Key advantages of this reaction include the utilization of a single trifluoromethyl source and the N-trifluoromethyl starting material itself as the hydrogen source. Notably, the elimination of hydrogen fluoride, facilitated by CsF, is critical for the success of this approach. This method is compatible with a broad range of functional groups, including heterocyclic compounds. 19F MRI experiments suggest promising prospects for PFtB-labeled secondary amines as 19F MRI contrast agents.

Functional Hexafluoroisopropyl Group Used in the Construction of Biologically Important Pyrimidine Derivatives

A series of versatile 4-((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)pyridine intermediates have been developed to efficiently produce biaryls, amines, ethers, and thioethers. These hydrolysis-stable ether intermediates exhibit reactivity toward electron-donating groups and nucleophiles in cross-coupling and nucleophilic substitution reactions while surpassing the stability of corresponding aryl halides. In comparison to conventional coupling methods, this protocol offers an alternative pathway for accessing natural product and drug-like compounds without the need for metal catalysts. With assistance of this approach, we successfully obtained a potent P-glycoprotein inhibitor 4k (YS-370), a potent epidermal growth factor receptor inhibitor 4l (YS-363), and a promising lysine-specific demethylase 1 inhibitor 5g.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Synthesis of Diaryl Ethers via Hypervalent Iodine-Mediated C-H Functionalization

A hypervalent iodine-reagent-based C-H functionalization strategy was utilized to synthesize diaryl ethers. This method directly transforms various arenes into their corresponding diaryliodonium salts, followed by a C-O coupling reaction to produce structurally diverse diaryl ethers. The efficacy of this approach in the late-stage structural modifications of complex molecules was demonstrated.

19 F-Labeled Probes for Recognition-Enabled Chromatographic 19 F NMR

The NMR technique is among the most powerful analytical methods for molecular structural elucidation, process monitoring, and mechanistic investigations; however, the direct analysis of complex real-world samples is often hampered by crowded NMR spectra that are difficult to interpret. The combination of fluorine chemistry and supramolecular interactions leads to a unique detection method named recognition-enabled chromatographic (REC) 19 F NMR, where interactions between analytes and 19 F-labeled probes are transduced into chromatogram-like 19 F NMR signals of discrete chemical shifts. In this account, we summarize our endeavor to develop novel 19 F-labeled probes tailored for separation-free multicomponent analysis. The strategies to achieve chiral discrimination, sensitivity enhancement, and automated analyte identification will be covered. The account will also provide a detailed discussion of the underlying principles for the design of molecular probes for REC 19 F NMR where appropriate.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

Regioselective Aromatic Perfluoro-tert-butylation Using Perfluoro-tert-butyl Phenyl Sulfone and Arynes

The selective introduction of perfluoro-tert-butyl group (PFtB, the bulkier analogue of CF₃ group) into arenes has long been sought after but remains a formidable task. We herein report the first general synthetic protocol to realize aromatic perfluoro-tert-butylation. The key to the success is the identification of PFtB phenyl sulfone as a new source of PFtB anion, which reacts with arynes in a highly regioselective manner to afford perfluoro-tert-butylated arenes in high yields. The application of the method is demonstrated by the preparation of sensitive ¹⁹F-labeled NMR probes with an extraordinary resolving ability.

Organocatalytic Synthesis of Phenols from Diaryliodonium Salts with Water under Metal-Free Conditions

The metal-free synthesis of phenols from diaryliodonium salts with water was developed by using N-benzylpyridin-2-one as an organocatalyst. In this process, sterically congested, functionalized, and heterocycle-containing iodonium salts were smoothly converted to the desired products, and the clofibrate and mecloqualone derivatives were also synthesized in high yields. In addition, the gram-scale experiment was successfully carried out with 10 mmol of a sterically congested substrate.

Toward Nanomolar Multi-Component Analysis by 19F NMR

The widespread application of nuclear magnetic resonance (NMR) spectroscopy in detection is currently hampered by its inherently low sensitivity and complications resulting from the undesired signal overlap. Here, we report a detection scheme to address these challenges, where analytes are recognized by ¹⁹F-labeled probes to induce characteristic shifts of ¹⁹F resonances that can be used as "chromatographic" signatures to pin down each low-concentration analyte in complex mixtures. This unique signal transduction mechanism allows detection sensitivity to be enhanced by using massive chemically equivalent ¹⁹F atoms, which was achieved through the proper installation of nonafluoro-tert-butoxy groups on probes of high structural symmetry. It is revealed that the binding of an analyte to the probe can be sensed by as many as 72 chemically equivalent ¹⁹F atoms, allowing the quantification of analytes at nanomolar concentrations to be routinely performed by NMR. Applications on the detection of trace amounts of prohibited drug molecules and water contaminants were demonstrated. The high sensitivity and robust resolving ability of this approach represent a first step toward extending the application of NMR to scenarios that are now governed by chromatographic and mass spectrometry techniques. The detection scheme also makes possible the highly sensitive non-invasive multi-component analysis that is difficult to achieve by other analytical methods.

Synthesis of Aryl Perfluorocyclopropyl Ethers via [2 + 1] Cyclopropanation Using TMSCF2Br Reagent

Aryl perfluorocyclopropyl ethers have been synthesized for the first time by [2 + 1] cyclopropanation between aryl trifluorovinyl ethers and a commercially available TMSCF₂Br reagent. This cycloaddition reaction between two fluorine-containing reactants proceeds smoothly in toluene at 120 °C in the presence of a catalytic amount of n-Bu₄NBr, and the reaction tolerates a variety of functional groups. A wide range of aryl trifluorovinyl ethers, easily accessible from phenols, were successfully transformed to aryl perfluorocyclopropyl ethers.

Fluorination Triggers Fluoroalkylation: Nucleophilic Perfluoro-tert-butylation with 1,1-Dibromo-2,2-bis(trifluoromethyl)ethylene (DBBF) and CsF

Perfluoro-tert-butylation reaction has long remained a challenging task. We now report the use of 1,1-dibromo-2,2-bis(trifluoromethyl)ethylene (DBBF) as a practical reagent for perfluoro-tert-butylation reactions for the first time. Through a consecutive triple-fluorination process with DBBF and CsF, the (CF₃ )₃ C^- species can be liberated and observed, which is able to serve as a robust nucleophilic perfluoro-tert-butylating agent for various electrophiles. The power of this synthetic protocol is evidenced by the efficient synthesis of structurally diverse perfluoro-tert-butylated molecules. Multiple applications demonstrate the practicability of this method, as well as the superiority of perfluoro-tert-butylated compounds as sensitive probes. The perfluoro-tert-butylated product was successfully applied in ¹ H- and ¹⁹ F-magnetic resonance imaging (MRI) experiment with an ultra-low field (ULF) MRI system.

Perfluoro-tert-butanol: a cornerstone for high performance fluorine-19 magnetic resonance imaging

As a versatile quantification and tracking technology, 19F magnetic resonance imaging (19F MRI) provides quantitative "hot-spot" images without ionizing radiation, tissue depth limit, and background interference. However, the lack of suitable imaging agents severely hampers its clinical application. First, because the 19F signals are solely originated from imaging agents, the relatively low sensitivity of MRI technology requires high local 19F concentrations to generate images, which are often beyond the reach of many 19F MRI agents. Second, the peculiar physicochemical properties of many fluorinated compounds usually lead to low 19F signal intensity, tedious formulation, severe organ retention, etc. Therefore, the development of 19F MRI agents with high sensitivity and with suitable physicochemical and biological properties is of great importance. To this end, perfluoro-tert-butanol (PFTB), containing nine equivalent 19F and a modifiable hydroxyl group, has outperformed most perfluorocarbons as a valuable building block for high performance 19F MRI agents. Herein, we summarize the development and application of PFTB-based 19F MRI agents and analyze the strategies to improve their sensitivity and physicochemical and biological properties. In the context of PFC-based 19F MRI agents, we also discuss the challenges and prospects of PFTB-based 19F MRI agents.

Fluorine NMR functional screening: from purified enzymes to human intact living cells

The substrate- or cofactor-based fluorine NMR screening, also known as n-FABS (n fluorine atoms for biochemical screening), represents a powerful method for performing a direct functional assay in the search of inhibitors or enhancers of an enzymatic reaction. Although it suffers from the intrinsic low sensitivity compared to other biophysical techniques usually applied in functional assays, it has some distinctive features that makes it appealing for tackling complex chemical and biological systems. Its strengths are represented by the easy set-up, robustness, flexibility, lack of signal interference and rich information content resulting in the identification of bona fide inhibitors and reliable determination of their inhibitory strength. The versatility of the n-FABS allows its application to either purified enzymes, cell lysates or intact living cells. The principles, along with theoretical, technical and practical aspects, of the methodology are discussed. Furthermore, several applications of the technique to pharmaceutical projects are presented.