Organic and Organometallic Fluorinated Materials for Electronics and Optoelectronics: A Survey on Recent Research

A theoretical investigation for improving the performance of non-fullerene organic solar cells through side-chain engineering of BTR non-fused-ring electron acceptors

In the current quantum chemical study, indacenodithiophene donor core-based the end-capped alterations of the reference chromophore BTR drafted eight A2-A1-D-A1-A2 type small non-fullerene acceptors. All the computational simulations were executed under MPW1PW91/6-31G (d, p) level of DFT. The UV-Vis absorption, open circuit voltage, electron affinity, ionization potential, the density of states, reorganization energy, orbital analysis, and non-covalent interactions were studied and compared with BTR. Several molecules of our modeled series BT1-BT8 have shown distinctive features that are better than those of the BTR. The open circuit voltage (VOC) of BT5 has a favorable impact, allowing it to replace BTR in the field of organic solar cells. The charge carrier motilities for proposed molecules generated extraordinary findings when matched to the reference one (BTR). Further charge transmission was confirmed by creating the complex with a PM6 donor molecule. The remarkable dipole moment contributes to the formation of non-covalent bond interactions with chloroform, resulting in superior charge mobility. Based on these findings, it can be said that every tailored molecule has the potential to surpass chromophore molecule (BTR) in OSCs. So, all tailored molecules may enhance the efficiency of photovoltaic cells due to the involvement of potent terminal electron-capturing acceptor2 moieties. Considering these obtained results, these newly presented molecules can be regarded for developing efficient solar devices in the future.

Applications of Transition Metal-Catalyzed ortho-Fluorine-Directed C-H Functionalization of (Poly)fluoroarenes in Organic Synthesis

The synthesis of organic compounds efficiently via fewer steps but in higher yields is desirable as this reduces energy and reagent use, waste production, and thus environmental impact as well as cost. The reactivity of C-H bonds ortho to fluorine substituents in (poly)fluoroarenes with metal centers is enhanced relative to meta and para positions. Thus, direct C-H functionalization of (poly)fluoroarenes without prefunctionalization is becoming a significant area of research in organic chemistry. Novel and selective methodologies to functionalize (poly)fluorinated arenes by taking advantage of the reactivity of C-H bonds ortho to C-F bonds are continuously being developed. This review summarizes the reasons for the enhanced reactivity and the consequent developments in the synthesis of valuable (poly)fluoroarene-containing organic compounds.

Pd-Catalyzed Oxidative C-H Arylation of (Poly)fluoroarenes with Aryl Pinacol Boronates and Experimental and Theoretical Studies of its Reaction Mechanism

We report the synergistic combination of Pd(OAc)2 and Ag2O for the oxidative C-H arylation of (poly)fluoroarenes with aryl pinacol boronates (Ar-Bpin) in DMF as the solvent. This procedure can be conducted easily in air, and without using additional ligands, to afford the fluorinated unsymmetrical biaryl products in up to 98 % yield. Experimental studies suggest that the formation of [PdL2(C6F5)2] in DMF as coordinating solvent does not take place under the reaction conditions as it is stable to reductive elimination and thus would deactivate the catalyst. Thus, the intermediate [Pd(DMF)2(ArF)(Ar)] must be formed selectively to give desired arylation products. DFT calculations predict a low barrier (5.87 kcal/mol) for the concerted metalation deprotonation (CMD) process between C6F5H and the Pd(II) species formed after transmetalation between the Pd(II)X2 complex and aryl-Bpin which forms a Pd-Arrich species. Thus a Pd(Arrich)(Arpoor) complex is generated selectively which undergoes reductive elimination to generate the unsymmetrical biaryl product.

Supramolecular complexation of C60 with branched polyethylene

Fullerene C60 is a ubiquitous material for application in organic electronics and nanotechnology, due to its desirable optoelectronic properties including good molecular orbital alignment with electron-rich donor materials, as well as high and isotropic charge carrier mobility. However, C60 possesses two limitations that hinder its integration into large-scale devices: (1) poor solubility in common organic solvents leading to expensive device processing, and (2) poor optical absorbance in the visible portion of the spectrum. Covalent functionalization has long been the standard for introducing structural tunability into molecular design, but non-covalent interactions have emerged as an alternative strategy to tailor C60-based materials, offering a versatile and tuneable alternative to novel functional materials and applications. In this work, we report a straightforward non-covalent functionalization of C60 with a branched polyethylene (BPE), which occurs spontaneously in dilute chloroform solution under ambient conditions. A detailed characterization strategy, based on UV-vis spectroscopy and size-exclusion chromatography was performed to verify and investigate the structure of the C60+BPE complex. Among others, our work reveals that the supramolecular complex has an order of magnitude higher molecular weight than its C60 and BPE constituents and points towards oxidation as the driving force behind complexation. The C60+BPE complex also possesses significantly broadened optical absorbance compared to unfunctionalized C60, extending further into the visible portion of the spectrum. This non-covalent approach presents an inexpensive route to address the shortcomings of C60 for electronic applications, situating the C60+BPE complex as a promising candidate for further investigation in organic electronic devices.

Fluorinated Polymer Donors for Nonfullerene Organic Solar Cells

The rapid development of narrow-bandgap nonfullerene acceptors (NFAs) has boosted the efficiency of organic solar cells (OSCs) over 19 %. The new features of high-performance NFAs, such as visible-NIR light absorption, moderate the highest occupied molecular orbitals (HOMO), and high crystallinity, require polymer donors with matching physical properties. This emphasizes the importance of methods that can effectively tune the physical properties of polymers. Owning to very small atom size and strongest electronegativity, the fluorination has been proved the most efficient strategy to regulate the physical properties of polymer donors, including frontier energy level, absorption coefficient, dielectric constant, crystallinity and charge transport. Owing to the success of fluorination strategy, the vast majority of high-performance polymer donors possess one or more fluorine atoms. In this review, the fluorination synthetic methods, the synthetic route of well-known fluorinated building blocks, the fluorinated polymers which are categorized by the type of donor or acceptor units, and the relationships between the polymer structures, properties, and photovoltaic performances are comprehensively surveyed. We hope this review could provide the readers a deeper insight into fluorination strategy and lay a strong foundation for future innovation of fluorinated polymers.

Advances in Continuous Flow Fluorination Reactions

Fluorination reactions are important in constructing organofluorine motifs, which contribute to favorable biological properties in pharmaceuticals and agrochemicals. However, fluorination reagents and reactions are associated with various problems, such as their hazardous nature, high exothermicity, and poor selectivity and scalability. Continuous flow has emerged as a transformative technology to provide many advantages relative to batch syntheses. This review article summarizes recent continuous flow techniques that address the limitations and challenges of fluorination reactions. Approaches based on different flow techniques are discussed, including gas-liquid reactions, packed-bed reactors, in-line purifications, streamlined multistep synthesis, large-scale reactions well as flow photoredox- and electrocatalysis.

Direct synthesis of haloaromatics from nitroarenes via a sequential one-pot Mo-catalyzed reduction/Sandmeyer reaction

Herein, we report the direct synthesis of a wide variety of functionalized aromatic bromides, chlorides, iodides, and fluorides from nitroarenes in a sequential one-pot operation. This protocol is based on an air- and moisture-tolerant dioxomolybdenum-catalyzed reduction of nitroaromatics, employing pinacol as a reducing agent, which enables subsequent diazotization and halogenation steps. This methodology represents a step-economical, practical, and alternative procedure for synthesizing haloaromatics directly from nitroaromatics.

New Approved Drugs Appearing in the Pharmaceutical Market in 2022 Featuring Fragments of Tailor-Made Amino Acids and Fluorine

The strategic fluorination of oxidatively vulnerable sites in bioactive compounds is a relatively recent, widely used approach allowing us to modulate the stability, bio-absorption, and overall efficiency of pharmaceutical drugs. On the other hand, natural and tailor-made amino acids are traditionally used as basic scaffolds for the development of bioactive molecules. The main goal of this review article is to emphasize these general trends featured in recently approved pharmaceutical drugs.

7,7-Difluoropentaphen-6(7H)-one

A new fluorinated pentaphene derivative has been obtained as a potential precursor for fluorinated polycyclic aromatic hydrocarbons. In this work, 7,7-difluoropentaphen-6(7H)-one was prepared from 1,1-difluoroanthracen-2(1H)-one via the Diels–Alder reaction with o-quinodimethane generated in situ from o-bis(dibromomethyl)benzene. The structure of the newly synthesized compound was confirmed by 1H, 13C, 19F NMR, IR and UV/Vis spectroscopy, as well as high-resolution mass spectrometry.

Electrosynthetic C-F bond cleavage

Fluorinated organic compounds are common among pharmaceuticals, agrochemicals and materials. The significant strength of the C-F bond results in chemical inertness that, depending on the context, is beneficial, problematic or simply a formidable synthetic challenge. Electrosynthesis is a rapidly expanding methodology that can enable new reactivity and selectivity for cleavage and formation of chemical bonds. Here, a comprehensive overview of synthetically relevant electrochemically driven protocols for C-F bond activation and functionalization is presented, including photoelectrochemical strategies.

PFAS risk propagation terminology in spatial and temporal scales: Risk intensification, risk attenuation, and risk amplification

Poly- and per fluorinated alkyl substances (PFAS) are man-made chemicals that are used in many industrial applications to improve performance and durability of products. The CF bond is one of the strongest bonds in organic chemistry which makes PFAS highly persistent in the environment. Therefore, PFAS levels have increased in different environmental compartments (air, water, soil) at global scale over time since the early 1950s. Terminology used for describing potential risks and those used in risk communication can be confusing as different disciplines use risk concepts and vocabulary that are different from those used for exposure and/or health risk assessment for hazardous materials. For example, terms such as emergent risk, emerging risk, risk intensification, risk awareness, risk perception, risk attenuation, risk amplification, and risk absorption are often misused or misinterpreted, especially in describing and communicating risks associated with PFAS in the environment or PFAS exposure. In addition, appropriate risk terms associated with psychological, social, institutional, and cultural elements are often misused. Here, appropriate risk terminology for describing and quantifying risks and health risks in reference to PFAS exposure and PFAS related risk propagation in spatial and temporal scales are explained with examples.

PFAS use in electronic products and exposure risks during handling and processing of e-waste: A review

Poly- and perfluorinated alkyl substances (PFAS) have been and are used in electronic products due to their unique properties that improve product quality and performance. Ubiquities and persistence of some PFAS detected in environmental samples (water, soil, air) have attracted much attention and regulatory actions in recent years. This review provides an overview of PFAS use in electronic components; trends in quantities of e-waste generation; PFAS exposure pathways during e-waste handling and processing; reported PFAS in environmental samples and samples of serum, blood, and hair collected from people living near and working at e-waste processing sites. Processes used for manufacturing electronic components (e.g., embedded processes, additive manufacturing) make recycling or materials recovery from discarded electronic units and components very difficult and unfeasible. Exposure during numerous processing steps for materials recovery and scavenging at disposal sites can result in PFAS intake through inhalation, ingestion, and dermal routes. Chemical risk assessment approaches have been continuously evolving to consider chemical-specific dosimetric and mechanistic information. While the metabolic fate of PFAS is not well understood, some PFAS bioaccumulate and bind to proteins (but not to lipids) in biota and humans due to their surface-active characteristics and very low solubility in water and fat. It is difficult to associate the adverse health effects due to exposure to e-waste directly to PFAS as there are other factors that could contribute to the observed adverse effects. However, PFAS have been detected in the samples collected from different environmental compartments (e.g., water, soil, leachate, blood sera, rainwater) at and near e-waste processing sites, landfills, and near electronics and optoelectronics industries indicating that e-waste collection, processing, and disposal sites are potential PFAS exposure locations. Better monitoring of e-waste handling sites and detailed epidemiological studies for at risk populations are needed for assessing potential health risks due to PFAS exposure at these sites.

The Latest FDA-Approved Pharmaceuticals Containing Fragments of Tailor-Made Amino Acids and Fluorine

Nowadays, the selective introduction of fluorine into bioactive compounds is a mature strategy in the design of drugs allowing to increase efficiency, biological half-life and bio-absorption. On the other hand, amino acids (AAs) represent one of the most ubiquitious classes of naturally occurring organic compounds, which are found in over 40% of newly marked small-molecule pharmaceutical drugs and medical formulations. The primary goal of this work is to underscore two major trends in the design of modern pharmaceuticals. The first is dealing with the unique structural characteristics provided by the structure of amino acids featuring an abundance of functionality and the presence of a stereogenic center, all of which bodes well for the successful development of targeted bioactivity. The second is related to fine-tuning the desired activity and pharmacokinetics by selective introduction of fluorine. Historically, both trends were developed separately as innovative and prolific approaches in modern drug design. However, in recent decades, these approaches are clearly converging leading to an ever-increasing number of newly approved pharmaceuticals containing both structural features of amino acids and fluorine.

Catalytic Stereoconvergent Synthesis of Homochiral β-CF3, β-SCF3, and β-OCF3 Benzylic Alcohols

We describe an efficient catalytic strategy for enantio- and diastereoselective synthesis of homochiral β-CF₃, β-SCF₃, and β-OCF₃ benzylic alcohols. The approach is based on dynamic kinetic resolution (DKR) with Noyori–Ikariya asymmetric transfer hydrogenation leading to simultaneous construction of two contiguous stereogenic centers with up to 99.9% ee, up to 99.9:0.1 dr, and up to 99% isolated yield. The origin of the stereoselectivity and racemization mechanism of DKR is rationalized by density functional theory calculations. Applicability of the previously inaccessible chiral fluorinated alcohols obtained by this method in two directions is further demonstrated: As building blocks for pharmaceuticals, illustrated by the synthesis of heat shock protein 90 inhibitor with in vitro anticancer activity, and in particular, needle-shaped crystals of representative stereopure products that exhibit either elastic or plastic flexibility, which opens the door to functional materials based on mechanically responsive chiral molecular crystals.

Au(I) Catalyzed HF Transfer: Tandem Alkyne Hydrofluorination and Perfluoroarene Functionalization

HF transfer reactions between organic substrates are potentially useful transformations. Such reactions require the development of catalytic systems that can promote both defluorination and fluorination steps in a single reaction sequence. Herein, we report a catalytic protocol in which an equivalent of HF is generated from a perfluoroarene | nucleophile pair and transferred directly to an alkyne. The reaction is catalyzed by [Au(IPr)NⁱPr₂] (IPr = N,N′-1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). HF transfer generates two useful products in the form of functionalized fluoroarenes and fluoroalkenes. Mechanistic studies (rate laws, KIEs, density functional theory (DFT) calculations, competition experiments) are consistent with the Au(I) catalyst facilitating a catalytic network involving both concerted S_NAr and hydrofluorination steps. The nature of the nucleophile impacts the turnover-limiting step. The cS_NAr step is turnover-limiting for phenol-based nucleophiles, while protodeuaration likely becomes turnover-limiting for aniline-based nucleophiles. The approach removes the need for direct handling of HF reagents in hydrofluorination and offers possibilities to manipulate the fluorine content of organic molecules through catalysis.

From ferrocene to 1,2,3,4,5-pentafluoroferrocene: halogen effect on the properties of metallocene

The sequentially fluorinated ferrocenes (1-, 1,2-di, 1,2,3-tri, 1,2,3,4-tetra and 1,2,3,4,5-pentafluoroferrocene) have been synthesized from ferrocene. Rather than a 'perfluoro' effect, experimental and computational analysis of the complete series robustly demonstrates a linear additive effect of fluorine on the electrochemical and spectroscopic properties of ferrocene.

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors-Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties

Organic solar cells are on the dawn of the next era. The change of focus toward non-fullerene acceptors has introduced an enormous amount of organic n-type materials and has drastically increased the power conversion efficiencies of organic photovoltaics, now exceeding 18%, a value that was believed to be unreachable some years ago. In this Review, we summarize the recent progress in the design of ladder-type fused-ring non-fullerene acceptors in the years 2018-2020. We thereby concentrate on single layer heterojunction solar cells and omit tandem architectures as well as ternary solar cells. By analyzing more than 700 structures, we highlight the basic design principles and their influence on the optical and electrical structure of the acceptor molecules and review their photovoltaic performance obtained so far. This Review should give an extensive overview of the plenitude of acceptor motifs but will also help to understand which structures and strategies are beneficial for designing materials for highly efficient non-fullerene organic solar cells.

Gold N-Heterocyclic Carbene Catalysts for the Hydrofluorination of Alkynes Using Hydrofluoric Acid: Reaction Scope, Mechanistic Studies and the Tracking of Elusive Intermediates

An efficient and chemoselective methodology deploying gold-N-heterocyclic carbene (NHC) complexes as catalysts in the hydrofluorination of terminal alkynes using aqueous HF has been developed. Mechanistic studies shed light on an in situ generated catalyst, formed by the reaction of Brønsted basic gold pre-catalysts with HF in water, which exhibits the highest reactivity and chemoselectivity. The catalytic system has a wide alkyl substituted-substrate scope, and stoichiometric as well as catalytic reactions with tailor-designed gold pre-catalysts enable the identification of various gold species involved along the catalytic cycle. Computational studies aid in understanding the chemoselectivity observed through examination of key mechanistic steps for phosphine- and NHC-coordinated gold species bearing the triflate counterion and the elusive key complex bearing a bifluoride counterion.

Revisiting the Heck Reaction for Fluorous Materials Applications

Installing fluoroalkyl chains on a molecule by the Heck reaction is a versatile method to transform the molecule’s properties that enable unique materials applications. This work further expands the scope of this reaction to thiophenes, which were able to undergo further functionalization and polymerization, highlighting the potential of these molecules in conjugated organic materials.

Infrared Irradiation-Assisted Solvent-Free Pd-Catalyzed (Hetero)aryl-aryl Coupling via C-H Bond Activation

The increasing attention towards environmentally friendly synthetic protocols has boosted studies directed to the development of green and sustainable methods for direct C-H bond arylation of (hetero)arenes. In this context, here the infrared (IR) irradiation-assisted solvent-free Pd-catalyzed direct C-H bond arylation of (hetero)arenes was achieved. Several heteroaryl-aryl coupling reactions were described, also involving heterocycles commonly used as building blocks for the synthesis of organic semiconductors. The reaction tolerated many functional groups on the aromatic nuclei. The IR-irradiation as the energy source compared favorably with thermal heating and, in combination with solvent-free conditions, provided an important contribution to the development of protocols fitting with the principles of green chemistry.

Expanding organofluorine chemical space: the design of chiral fluorinated isosteres enabled by I(i)/I(iii) catalysis

Short aliphatic groups are prevalent in bioactive small molecules and play an essential role in regulating physicochemistry and molecular recognition phenomena. Delineating their biological origins and significance have resulted in landmark developments in synthetic organic chemistry: Arigoni's venerable synthesis of the chiral methyl group is a personal favourite. Whilst radioisotopes allow the steric footprint of the native group to be preserved, this strategy was never intended for therapeutic chemotype development. In contrast, leveraging H → F bioisosterism provides scope to complement the chiral, radioactive bioisostere portfolio and to reach unexplored areas of chiral chemical space for small molecule drug discovery. Accelerated by advances in I(i)/I(iii) catalysis, the current arsenal of achiral 2D and 3D drug discovery modules is rapidly expanding to include chiral units with unprecedented topologies and van der Waals volumes. This Perspective surveys key developments in the design and synthesis of short multivicinal fluoroalkanes under the auspices of main group catalysis paradigms.

Metal-Free C-C/C-N/C-C Bond Formation Cascade for the Synthesis of (Trifluoromethyl)sulfonylated Cyclopenta[b]indolines

A bis(triflyl)ethylation [triflyl = (trifluoromethyl)sulfonyl] inserted into a sequential cyclization cascade resulted in the direct formation of gem-bis(triflyl)ated cyclopenta[b]indolines from anilide-derived allenols and alkenols. This catalyst- and irradiation-free sequence facilitated the efficient preparation of functionalized tricyclic indoline cores bearing two contiguous stereocenters. The formed cyclopenta[b]indolines can be easily transformed into a wide variety of triflylated indolines, including the tetracycle ring system found in polyveoline.

Design and Synthesis of Annulated Benzothiadiazoles via Dithiolate Formation for Ambipolar Organic Semiconductors

Substituted 2,1,3-benzothiadiazole (BTD) is a widely used electron acceptor unit for functional organic semiconductors. Difluorination or annulation on the 5,6-position of the benzene ring is among the most adapted chemical modifications to tune the electronic properties, though each sees its own limitations in regulating the frontier orbital levels. Herein, a hitherto unreported 5,6-annulated BTD acceptor, denoted as ssBTD, is designed and synthesized by incorporating an electron-withdrawing 2-(1,3-dithiol-2-ylidene)malononitrile moiety via aromatic nucleophilic substitution of the 5,6-difluoroBTD (ffBTD) precursor. Unlike the other reported BTD annulation strategies, this modification leads to the simultaneous decrease in both frontier orbital energies, a welcoming feature for photovoltaic applications. Incorporation of ssBTD into conjugated polymers results in materials boasting broad light absorption, dramatic solvatochromic and thermochromic responses (>100 nm shift and a band gap difference of ∼0.28 eV), and improved crystallinity in the solid state. Such physical properties are in accordance with the combined electron-withdrawing effect and significantly increased polarity associated with the ssBTD unit, as revealed by detailed theoretical studies. Furthermore, the thiolated ssBTD imbues the polymer with ambipolar charge transport property, in contrast to the ffBTD-based polymer, which transports holes only. While the low mobilities (10^-4 to 10^-5 cm² V^-1 s^-1) could be further optimized, detailed studies validate that the thioannulated BTD is a versatile electron-accepting unit for the design of functional stimuli-responsive optoelectronic materials.

Organocatalyzed Fluoride Metathesis

A new organocatalyzed fluoride metathesis reaction between fluoroarenes and carbonyl derivatives is reported. The reaction exchanges fluoride (F^-) and alternate nucleophiles (OAc^-, OCO₂R^-, SR^-, Cl^-, CN^-, NCS^-). The approach provides a conceptually novel route to manipulate the fluorine content of organic molecules. When the fluorination and defluorination steps are combined into a single catalytic cycle, a byproduct free and 100% atom-efficient reaction can be achieved.

Tertiary-Amine-Initiated Synthesis of Acyl Fluorides from Carboxylic Acids and CF3 SO2 OCF3

A convenient method for deoxyfluorination of aromatic and aliphatic carboxylic acids with CF₃ SO₂ OCF₃ in the presence of a suitable base at room temperature has been developed. The reaction allows a straightforward access to a variety of acyl fluorides and proves that CF₃ SO₂ OCF₃ is an effective deoxyfluorination reagent for carboxylic acids. The method features simplicity, expeditiousness, high efficiency, ease of handling, good functional group tolerance, a wide range of substrates, excellent yields of products, compatibility of many amine initiators, use of environmentally friendly reagents, and effortless removal of byproducts. This reaction represents the first utilization of trifluoromethyl trifluoromethanesulfonate as a fluorination reagent.

A General Synthetic Approach and Photophysical Properties of Regioselectively Fluorinated [5]- and [6]-Helical Bispiroindenofluorenes

A first series of fluorinated [n]helical compounds (n=5 and 6) with the dihydroindenofluorene scaffold was prepared in 5 or 9 (octafluorinated dihydroindenofluorene) steps and their photophysical properties were determined. Rh-catalyzed intramolecular [2+2+2] cyclotrimerization of triyndiols, which were prepared in a modular fashion from simple starting material such as fluorinated haloarylcarbaldehydes, to the intermediate [n]helical dihydroindeno[2,1-c]fluorene-5,8-diols was the crucial synthetic step and proceeded with high efficacy. Their further transformation gave the desired selectively fluorinated bispirodihydroindeno[2,1-c]fluorenes. Their absorption and emission spectra were recorded. The fluorescence quantum yields were up to 92 % and the emission maxima were red-shifted in comparison with their non-fluorinated counterparts (386-413 nm).

Fluorous phthalocyanines and subphthalocyanines

Incorporating fluorine atoms into a molecule can endow it with various unique properties that enable materials applications. Selective solubility in fluorous solvents is achieved by a high fluorine content and selective partitioning into perfluorinated liquids over organic and aqueous phases provides orthogonal opportunities for chemistry and materials assembly. Although there is a growing number of partially fluorinated molecules, there are insufficient structural design principles to produce diverse fluorous soluble dyes. Herein, we report the synthesis of six fluorous phthalocyanine and subphthalocyanine dyes, and study their properties in the fluorous phase. Phthalocyanines generally display limited solubility and we also observed apparent aggregation in the fluorous phase. However, the nonplanar subphthalocyanines showed greater solubility. Subphthalocyanines also displayed fluorescence in selected solvents, and their emissive properties were investigated. The materials described expand the library of fluorous dyes and provide insights for the design of new molecules with fluorous solubility.

Selective Quadruple C(sp3)-F Functionalization of Polyfluoroalkyl Ketones

The significance of organofluorine compounds has inspired the establishment of numerous methods for the functionalization of rather inert C-F bonds. Despite advances achieved in the manipulation of C(sp²)-F bonds by employing transition-metal catalysts, such as Pd, Rh, Cu, Ni, Ru, and Ir, strategies that address the paucity of effective pathways for selective activation of multiple C(sp³)-F bonds remained challenging. In this context, we present an unprecedented coupling-aromatization-cyclization reaction of polyfluorinated ketones with diverse N- and S-nucleophiles that forms regiodefined perfluoroalkylated naphtho[1,2-b]furan/benzofuran derivatives by harnessing Co-promoted distinctive quadruple C(sp³)-F bonds cleavage relay. This chemistry involving controlled and successive selective defluorination at heteronuclear centers would greatly contribute to the preparation of drug-like heterocycles as well as the late-stage elaboration of biorelevant compounds. Controlled experiments and DFT theoretical studies revealed that the combination of cheap cobalt salt with Cs₂CO₃ enable expeditious C-F functionalization.

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First example of consecutive selective quadruple C(sp³)-F functionalization

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Selectively and controllably partial defluorination at heteronuclear sites

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Conversion to value-added chemicals by using polyfluorocarbons and nucleophiles

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DFT calculations were performed to support mechanistic proposal

Site-Selective Photochemical Fluorination of Ketals: Unanticipated Outcomes in Selectivity and Stability

We report a method for the regioselective photochemical sp³ C-H fluorination of acetonide ketals that presents interesting problems in chemical reactivity. The question of why certain products of the reaction are stable while others are not is addressed, as is the question of why only select α-ethereal hydrogen atoms are targeted in the reaction. We demonstrate that the method can be employed to synthesize unprecedented fluorinated sugars and steroids, and it can also be applied toward the fluorination of carbamates. Though some substrates contain up to eight discrete α-ethereal C-H bonds, we observed site-selectivity in each case, prompting us to investigate potential transition states for the reaction. Finally, a remarkable regiochemical switch upon minor structural modification of a diketal is also analyzed.

Copper-mediated oxidative [3 + 2]-annulation of nitroalkenes and pyridinium imines: efficient synthesis of 3-fluoro- and 3-nitro-pyrazolo[1,5-a]pyridines

An efficient route to pyrazolo[1,5-a]pyridines by Cu(OAc)2-promoted oxidative [3 + 2]-annulation of nitroalkenes with in situ generated pyridinium imines is developed. The reaction with α-fluoronitroalkenes enables the first preparative synthesis of 3-fluoro-pyrazolo[1,5-a]pyridines. Cycloaddition with α-unsubstituted nitroalkenes provides access to 3-nitro-pyrazolo[1,5-a]pyridines in excellent yields. A broad transformation scope was demonstrated. Both electron-rich and electron-deficient nitroalkenes as well as different aminopyridinium salts can be used for the assembly of the target pyrazolo[1,5-a]pyridines. The related aza-heterocycles, namely, pyrazolo[1,5-a]pyrazines and pyrazolo[1,5-b]pyridazines, were successfully prepared via the present methodology. The possible mechanism of the reaction is discussed.

Ring-Opening Lithiation-Borylation of 2-Trifluoromethyl Oxirane: A Route to Versatile Tertiary Trifluoromethyl Boronic Esters

Stereogenic trifluoromethyl-substituted carbon centers are highly sought-after moieties in pharmaceutical and agrochemical discovery. Here, we show that lithiation-borylation reactions of 2-trifluoromethyl oxirane give densely functionalized and highly versatile trifluoromethyl-substituted α-tertiary boronic esters. The intermediate boronate complexes undergo the desired 1,2-rearrangement of the carbon-based group with complete retentive stereospecificity, a process that was only observed in non-polar solvents in the presence of TESOTf. Although the trifluoromethyl group adversely affects subsequent transformations of the α-boryl group, Zweifel olefinations provide trifluoromethyl-bearing quaternary stereocenters substituted with alkenes, alkynes and ketones.

Gold-Catalyzed Hydrofluorination of Internal Alkynes Using Aqueous HF

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

Highly chemoselective difluoromethylative homologation of iso(thio)cyanates: expeditious access to unprecedented α,α-difluoro(thio)amides

The new motif - α,α-difluoromethyl thioamide - has been assembled starting from isothiocyanate (as thioamide precursor) and a formal difluoromethyl-carbanion generated from commercially available TMSCHF2. Upon proper activation of this reagent with potassium tert-amylate, the high-yielding transfer of the difluorinated nucleophile takes place under high chemocontrol. Various sensitive functionalities (e.g. ester, nitrile, nitro, azido groups) can be accommodated across the isothiocyanate core, thus allowing a wide scope. The methodology is highly flexible and adaptable to prepare analogous α,α-difluoromethyl oxoamides by conveniently using isocyanates as the electrophilic building-blocks.

Direct and Chemoselective Synthesis of Tertiary Difluoroketones via Weinreb Amide Homologation with a CHF2-Carbene Equivalent

The homologation of Weinreb amides into difluoromethylketones with a formal nucleophilic CHF₂ transfer agent is reported. Activating TMSCHF₂ with potassium tert-amylate enables a convenient access to the difluorinated homologation reagent, which adds to the acylating partners. The high chemoselectivity showcased in the presence of variously multifunctionalized Weinreb amides, jointly with uniformly high yields, enables the strategy of general applicability without requiring any stabilization element for the putative carbanion.