Polyfluorinated Aromatics

Preparation and Reactions of Polyfluorinated Aromatic Heterocyclic Compounds Yakobson G G, Petrova, T D, Kobnna, L S Fluorine Chem Rev 7, 115-223 285... 

The difference in the reactivity of benzylic versus aromatic halogens makes it possible to reduce the former ones preferentially. Lithium aluminum hydride replaced only the benzylic bromine by hydrogen in 2-bromomethyl-3-chloro-naphthalene (yield 75%) [540]. Sodium borohydride in diglyme reduces, as a rule, benzylic halides but not aromatic halides (except for some iodo derivatives) [505, 541]. Lithium aluminum hydride hydrogenolyzes benzyl halides and aryl bromides and iodides. Aryl chlorides and especially fluorides are quite resistant [540,542], However, in polyfluorinated aromatics, because of the very low electron density of the ring, even fluorine was replaced by hydrogen using lithium aluminum hydride [543]. 

Where nucleic acids are concerned, the enhanced hydrophobicity of abiotic polyfluorinated aromatic bases (e.g., tetrafluorobenzene or tetrafluoroindole deoxyribose derivatives) was exploited as an alternative to natural hydrogen bonding to achieve selective and stable nucleic acid base pairing in duplex DNA [85], The DNA replication was examined using polyfluorinated-nucleotide analogs as substrates. A DNA polymerase active site was able to process the polyfluorinated base pairs more effectively than the analogous hydrocarbon pairs, demonstrating hydrophobic selectivity of polyfluorinated bases for other polyfluorinated bases [86]. 

As found recently, a stoichiometric equivalent of BrF - a BrF3/Br2 mixture -behaves as a powerful fluorinating agent for polyfluorinated aromatic compounds C6F5X (X=F, CF3, H, OCH3) [84]. Its reaction with F-benzene proceeds at a temperature as low as 0°C to give a mixture of F-cyclohexadiene-1,4 and 4-Br-F-cyclohexane ... 

Fluoro-substituted annotated five-membered heterocycles are available via stepwise nucleophilic displacement reactions of perfluorinated or polyfluorinated aromatic compounds by 1,3-dinucleophiles. On reaction of hexafluorobenzene with the sodium salt of ethyl acetoacetate the 3-ethoxycarbonyl-2-methylcumarone is formed [64DOK( 158)926 69KGS778] (Scheme 29). 

In view of their high electronegativity, fluorine atoms accumulated in the benzene ring substantially increase the electrophilicity of the carbon atoms. This creates conditions for high mobility of the fluorine atoms of polyfluorinated aromatic compounds in nucleophilic substitution reactions and hence for intramolecular nucleophilic cyclizations by the elimination of the fluorine atom ortho to the... 

Hexafluorobenzene, octafluoronaphthalene and a number of other polyfluorinated aromatic compounds reacted with chlorine in SO2CIF at 60 °C in the prince of SbFj to give the ions corresponding with the addition of Cl" to the carbon atom bonded with the fluorine atom... 

Ions having no substituents of the above type exhibit an increased feasibility of such processes. An example is the nitrofluorination of polyfluorinated aromatic compounds with HNOj in HF or with nitronium tetrafluoroborate ... 

Radical cations of hexa-, penta- and tetramethylbenzenes, as well as 1,3,5-tri-and 1,4-di-tert-butylbenzenes have been det ted by ESR in a flow system after inter-.nction with cobalt triacetate in CF3COOH The radical cations of polyfluorinated aromatic compounds proved to be quite stable. Hexafluorobenzene interacted with O2 AsFg in WFj to yield the salt of the hexafluorobenzene radical cation CgF AsFg Octafluoronaphthalene, deca-fluorobiphenyl, hexa-, penta- and 1,2,4,5-tetrafluorobenzenes yield radical cations... 

Besides the earlier demonstrated possibilities for the polyfluorinated aromatic compounds to add the electrophiles Cl" and CHj, the addition of F and Br" has also been effected Thus the interaction of hexafluorobenzene with the... 

Contents of Vol. 7 Nucleophilic Substitution in Polyfluoroaromatic Compounds (L. S. Kobrina) Preparation and Reactions of Polyfluorinated Aromatic Heterocyclic Compounds (G. G. Yakobson, T. D. Petrova, and L. S. Kobrina). 

Coleman, J.P., Fleischmann, M. and Fletcher, D. (1973) Anodic oxidation of polyfluorinated aromatic hydrocarbons in fluorosulfonic acid - the production of stable cation radicals. Elec-trochimica Acta, 18, 331. 

Polyfluorinated a-diketones react with 1,2-diainino compounds, such as ortlio-phenylenediamine, to give 2,3-substituted quinoxalmes [103] Furthermore, the carboxyl function of trifluoropyruvates offers an additional electrophilic center. Cyclic products are obtained with binucleophiles [13, 104] With aliphatic or aromatic 1,2-diamines, six-memhered heterocycles are formed Anilines and phenols undergo C-alkylation with trifluoropyruvates in the ortho position followed by ring closure to form y-lactams and y-lactones [11, 13, 52, 53, 54] (equation 23). 

NMR data on the most common fluorinated aromatics are presented in three categories. Monofluorophenyls and pentafluorophenyls have found the greatest application in synthesis and spectroscopy. Data for polyfluorinated benzenes are also presented. 

However, these compounds are generally unstable. Most imines with a hydrogen on the nitrogen spontaneously polymerize.143 Stable hemiaminals can be prepared from polychlorinated and polyfluorinated aldehydes and ketones, and diaryl ketones do give stable imines Ar2C=NH.144 Aside from these, when stable compounds are prepared in this reaction, they are the result of combinations and condensations of one or more molecules of 12 and/or 13 with each other or with additional molecules of ammonia or carbonyl compound. The most important example of such a product is hexamethylenetetramine145 (11), prepared from ammonia and formaldehyde.146 Aromatic aldehydes give hydrobenzamides ArCH(N=CHAr)2 derived from three molecules of aldehyde and two of ammonia.147... 

In polyfluorinated and especially perfluorinated aromatics, fluorine is hydrolyzed relatively easily. Perfluorochlorobenzene gives perfluoro-4-chlorophenol (2) on treatment with potassium hydroxide in tert-butyl alcohol.33... 

However, the low basicity of polyfluorinated materials usually limits this method to the carbocations originating from nonfluorinated compounds (some alcohols, aromatics, etc.) or such relatively basic fluorinated substrates as mono- and dihaloalkanes, and fluoroethylenes,e.g.,CH2=CF2 [21]. 

The reactivity of polyfluorinated cyclohexadienes toward antimony or niobium pentafluorides has some peculiarities. The equilibrium mixture of 1,4- and 1,3-cyclohexadienes is formed from pure isomers of each and a catalytic amount of MF5 at room temperature where the non-conjugated diene predominates [167], With an excess of SbF5 both isomers disproportionate to give a mixture of aromatic compounds and cyclohexene polyfluoroaromatics and the corresponding cyclohexene [167,168] ... 

The B-G bond of allyl-, alkynyl-, aryl-, and benzylboranes is more easily cleaved than that of alkylboranes. The C-B bond of aromatic boronic acids is stable to water, but polyfluorinated phenylboronic acids are exceptionally sensitive to Me0H-H20-K0H and Me0H-H20-pyridine.488 Allylic organoboranes were hydrolyzed with water at room temperature with complete allylic rearrangement (Equation (102)).489,490 Addition of water resulted in the rapid hydrolysis of benzylic G-B bond of 329 due to the electron-withdrawing effect of Cr(CO)3 group (Equation (103)).491... 

Simons process — Electrochemical polyfluorination reactions of organic compounds are the only efficient way to industrial production of perfluorinated compounds. The reaction proceeds in the solution of KF in liquid HF (b.p. 19.5 °C), where the starting substances as alcohols, amines, ethers, esters, aliphatic hydrocarbons and halo-hydrocarbons, aromatic and heterocyclic compounds, sulfo- or carboxylic acids are dissolved. During anodic oxidation, splitting of the C-H bonds and saturation of the C=C bonds occur and fluorine atoms are introduced. 

Luijk R, Dorland K, Smit P, Govers HAJ (1993), in Polycyclic aromatic compounds", prediction of the gas chromatographic retention behaviour of polybrominated dibenzo-p-dioxins , p. 565-572, Garrigues Ph, Lamotte M (Eds.), Gordon and Breach, Yverdon Weber R, Hagenmaier H (1994), Organohalogen Compounds 19 7-11. Polyfluorinated diben-zodioxins/furans - Synthesis, analysis and formation", Eds. University of Kyoto, Japan... 

Polyfluoroalkylation Some of the chemistry of polyfluoroalkyl anions, generated by reaction of fluoroalkenes with fluoride ion, was discussed in Chapter 7, where the analogy between the role of fluoride ion in fluorocarbon chemistry and the role of the proton in hydrocarbon chemistry was emphasised. This analogy has been extended to include reactions of polyfluorinated anions, generated in the same way, with activated poly-fluoro-aromatic systems in what may be regarded as the nucleophilic counterpart of Friedel-Crafts reactions [119] (Figure 9.50). 

Monofluoro aromatic compounds do not react rapidly with Cjq and do not undergo dehalogenation. Polyfluorinated derivatives, however, react very rapidly. Thus, pentaflu-orophenol was found to react with Caq with a diffusion-controlled rate constant and... 

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