Hydrodefluorination of polyfluoro-2-naphthylamines by Zn in aqueous NH3: A correlation of the product distribution and the computationally predicted regioselectivity of the substrate radical anion fragmentation

Селиванова, Г. А.; Reshetov, Alexey V.; Beregovaya, I. V.; Vasil’eva, N. V.; Bagryanskaya, I. Yu.; Shteingarts, V. D.

doi:10.1016/j.jfluchem.2012.02.012

Cited by 14 publications

(7 citation statements)

References 41 publications

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“…Experimentally, the most extensively studied reductive fragmentation of perfluoroarenes has been accomplished via solvated electrons with dissolving metals (Scheme A). ,− The generally accepted mechanism in this reaction is electron transfer to give the metastable nonplanar radical anion 2b . Anion 2b undergoes unimolecular fragmentation to generate a σ-radical 2c .…”

Section: Perfluoroaryl Radicalsmentioning

confidence: 99%

Visible Light Photocatalysis for the Generation and Use of Reactive Azolyl and Polyfluoroaryl Intermediates

2016

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Photocatalysis offers several mechanistically unique pathways that are not rivaled by mainstream catalysis. Primarily, the ability to convert photochemical energy into single electron oxidation and reduction events provides a new dimension for chemists to consider when choosing how to activate a molecule or approach a complex synthesis. Since most organic molecules do not absorb light in the visible region, they are impervious to direct visible light photochemistry, which provides an opportunity for photocatalysis in which a visible light absorbing compound can serve as a mediator. In this Account, we discuss the consequences of catalyst mediated, photoinduced electron transfer to several classes of reducible arenes. While the bulk of the work discussed within this Account utilizes iridium-based photocatalysts, in principle the chemistry is not limited to this class of photocatalyst, and the principles should be more general. Instead, this Account focuses largely on the consequences of single electron transfer to poly- and perfluorinated arenes and 2-halo azoles. Electron transfer converts these stable molecules into reactive intermediates whose behavior often depends entirely on the identity of the halogen that undergoes substitution. The result is both diverse chemistry and an alternative way of thinking about the chemical reactivity of these motifs. Specifically, we discuss our efforts and those of others to develop strategies for the generation of radicals or radical anions from perfluoroarenes and azoles and the behavior of these intermediates as implied by reactions in which they participate. The divergent pathway is illustrated by 2-bromoazoles, which yield azolyl radicals and can be utilized for addition to π-bonds, while use of the 2-chloroazole substrate leads to an entirely different reaction profile. Under the appropriate reaction conditions, the reactive and transient intermediates are useful coupling partners and often provide unrivaled access to new chemical space. The odd electron species can form challenging bonds with minimal prefunctionalization of the coupling partner. For instance, some of the intermediates can be utilized for C-H functionalizations to selectively make crowded amines or to synthesize biarenes substituted at every ortho position. While photocatalysis is not the only manner of accomplishing electron transfer, the catalytic generation of the reactive species in which the concentration of the transient odd electron species is kept low, provides a synthetic handle that can be used to improve reaction outcomes. This is elegantly demonstrated in a number of examples in which redox sensitive groups located on substrates survive the reaction. In addition, the underlying basic concepts associated with radical anion fragmentation are reviewed and provide the backdrop for discussion throughout the Account.

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Section: Perfluoroaryl Radicalsmentioning

confidence: 99%

Visible Light Photocatalysis for the Generation and Use of Reactive Azolyl and Polyfluoroaryl Intermediates

2016

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“…A broad range of substituted and unsubstituted fluoroarenes undergo HDF upon reduction with elemental zinc; substituents include alkyl, aryl, hydroxyalkyl, carboxy, carboxamide, and N‐carboxylamino groups. The preferred charge localization in the initially formed radical anion determines the regioselectivity of subsequent fluoride elimination to generate an aryl radical 63d,h. Transfer of a second electron reduces the radical to a carbanion that is finally protonated by an external proton source (Scheme ).…”

Section: Reductive Hydrodefluorinationmentioning

confidence: 99%

Synthesis of Fluorinated Building Blocks by Transition‐Metal‐Mediated Hydrodefluorination Reactions

2013

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The activation and functionalization of carbon-fluorine bonds can be considered as a major challenge in organometallic chemistry. The growing demand for means to introduce fluorine into new materials or into biologically active molecules has inspired the development of diverse synthetic strategies. Hydrodefluorination is regarded as a promising approach to access partially fluorinated building blocks from readily available perfluorinated bulk chemicals. We provide an overview of transition-metal-based complexes and catalysts that were developed to mediate hydrodefluorination reactions. Special emphasis will be placed on discussing the underlying mechanistic patterns and their impact on scope and selectivity. In addition, future requirements for further developing this field will be highlighted.

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“…The latter is typical of partially polyfluorinated arenes in general. Of late years, the convenient approach to these compounds was developed extensively based on the selective hydrodefluorination of polyfluoroarenes easily available by other methods. − Among these techniques, of special attention is the reduction by zinc in aqueous ammonia (the simplest reduction system hitherto used for this purpose), which is believed to occur through the formation of polyfluoroarene radical anions (RAs) , followed by their fragmentation with the elimination of fluoride anion. − Thus, the applicability of this system to synthesis is determined by its capability to reduce a polyfluoroarene, while the regioselectivity of the hydrodefluorination is determined by the fragmentation behavior of the respective RA, which justifies the interest to the structure and the properties of polyfluoroarene RAs.…”

Section: Introductionmentioning

confidence: 99%

“…Unfortunately, pentafluoroaniline cannot be hydrodefluorinated in the Zn–aqueous ammonia system at room temperature because of insufficient electron affinity. Nevertheless, the hydrodefluorination becomes possible if one uses the more electrophilic N-acetylpentafluoroanilide due to the suppression of the electron-donating effect of the amine group or a polyfluorinated 2-naphthylamine due to the higher electron affinity of the naphthalene core as compared to the benzene one . However, one cannot rule out that the hydrodefluorination of polyfluoroanilines can be feasible under harsher conditions or as a result of the introduction of substituents raising the benzene ring electron affinity.…”

Section: Introductionmentioning

confidence: 99%

Structure and Stability of Pentafluoroaniline and 4-Aminononafluorobiphenyl Radical Anions: Optically Detected Electron Paramagnetic Resonance, Time-Resolved Fluorescence, Time-Resolved Magnetic Field Effect, and Quantum Chemical Study

et al. 2015

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Radical anions (RAs) are the key intermediates of the selective hydrodefluorination of polyfluoroarenes. We used the techniques of optically detected electron paramagnetic resonance (OD EPR), time-resolved fluorescence, time-resolved magnetic field effect (TR MFE), and the density functional theory to study the possibility of RAs formation from 4-aminononafluorobiphenyl (1) and pentafluoroaniline (2) and estimate their lifetimes and decay channels. To our knowledge, both RAs have not been detected earlier. We have registered the OD EPR spectrum for relatively stable in nonpolar solutions 1(-•) but failed to register the spectra for 2(-•). However, we have managed to fix the 2(-•) by the TR MFE method and obtained its hyperfine coupling constants. The lifetime of 2(-•) was found to be only a few nanoseconds. The activation energy of its decay was estimated to be 3.6 ± 0.3 kcal/mol. According to the calculation results, the short lifetime of 2(-•) is due to the RA fast fragmentation with the F(-) elimination from ortho-position to the amine group. The calculated energy barrier, 3.2 kcal/mol, is close to the experimental value. The fragmentation of 2(-•) in a nonpolar solvent is possible due to the stabilization of the incipient F(-) anion by the binding with the amine group proton.

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Hydrodefluorination of polyfluoro-2-naphthylamines by Zn in aqueous NH3: A correlation of the product distribution and the computationally predicted regioselectivity of the substrate radical anion fragmentation

Cited by 14 publications

References 41 publications

Visible Light Photocatalysis for the Generation and Use of Reactive Azolyl and Polyfluoroaryl Intermediates

Visible Light Photocatalysis for the Generation and Use of Reactive Azolyl and Polyfluoroaryl Intermediates

Synthesis of Fluorinated Building Blocks by Transition‐Metal‐Mediated Hydrodefluorination Reactions

Structure and Stability of Pentafluoroaniline and 4-Aminononafluorobiphenyl Radical Anions: Optically Detected Electron Paramagnetic Resonance, Time-Resolved Fluorescence, Time-Resolved Magnetic Field Effect, and Quantum Chemical Study

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