Pentafluorophenyl-substituted compounds

The ability of fluoro-2 -phosphanes to transform silyl ethers into fluorides was first observed during a study of the reactions of phosphorus pentafluoride and its derivatives R PF5 (n = 1, 2, 3 R = hydrocarbon group) with trimethylsilyl ethers. Subsequently, this reaction was proposed as a new method for the preparation of C-F compounds from silyl ethers or silicic acid esters with fluoro-A -phosphanes. Pentafluorophenyl-substituted fluoro-A -phos-phanes were found to react similarily, Other workers found that tctrafluoro(phenyl)-A -phos-phane. which was chosen as the most convenient reagent with regard to reactivity and stability, gave considerable amounts of elimination products, especially with primary and cyclic alcohols. Good yields of fluorinated products are obtained when stable carbocations can be formed at the site of substitution, such as in tertiary alcohols, but 2-phcnylethanol. benzyl alcohol and diphcnylmethanol, on the other hand, give only poor yields of fluorinated products ethers and polymers are the main products. ... 

Syndiotactic polystyrene was first obtained only recently by Ishihara et al. [5] in polymerisation with a homogeneous catalyst derived from a transition metal compound such as monocyclopentadienyltitanium trichloride and methylalu-minoxane in toluene. Since then, several authors have reported on the synthesis of syndiotactic polystyrene promoted by different catalysts based on metal hydrocarbyls such as benzyl compounds, half-sandwich metallocenes (e.g. monocyclopentadienyl, monopentamethylcyclopentadienyl and monoindenyl metal derivatives), metal alkoxides, metallocenes and some other compounds. These catalysts are commonly derived from titanium or zirconium compounds, either activated with methylaluminoxane or aluminium-free, such as those activated with tris(pentafluorophenyl)boron, and promote the syndiospecific polymerisation of styrene and substituted styrenes [5-10,21,48-70], Representative examples of the syndiospecific polymerisation of styrene using catalysts based on various titanium compounds and methylaluminoxane are shown in Table 4.2 [6,52,53,56,58],... 

Well-defined substitution patterns in the target molecules can be constructed by a combination of fluorine-free or fluoro-substituted (1,3 ee) components with fluorine-free and fluoro-substituted (1,2 nn) compounds. A representative example for the introduction of fluorine and fluoro-substituted groups into five-membered heterocycles via both educts is the reaction of fluoro-substituted chalcones and pentafluorophenyl hydrazine (88JIC773). 

Another possible route for the nucleophilic substitution of the ort/io-fluorine atom includes intramolecular attack by the hydroxy group of 2-(hydroxyamino)-l-(pentafluorophenyl)ethanol 128. Heating of compound 128 in N,N-dimethylformamide in the presence of sodium fluoride led to cyclizations at the nitrogen to give l,3-dihydroxy-4,5,6,7-tetrafluoro-indoline 130. The latter was readily reduced by zinc in acidic media into 4,5,6,7-tetrafluoroindole 132. The starting amino alcohols 128 and 129 were obtained by the potential-controlled electrochemical reduction of the nitroalcohol 127, which can be prepared directly from pentafluorobenzaldehyde and nitromethane. 

Fluorinated 1,2,4-oxadiazoles find their application in both the pharmaceutical industry and materials science. Recently, 3-substituted 5-pentafluorophenyl-1,2,4-oxadiazoles 2 (Fig. 2) have been used as fluorinated oxadiazole arylating reagents (FOXARs) for the attachment of fluorinated moieties to nucleophilic pendants of polymers [4] and macromolecules [5]. Huorinated 1,2,4-oxadiazoles 3 (Fig. 2) have been employed as reagents to introduce the difluoromethylene moiety into organic compounds [6]. To date, despite the fact that 3- (or 5-) chloro- or bromo- derivatives are known, there is still no literatnre on the synthesis of 1,2,4-oxadiazoles bearing a fluorine atom directly linked to the oxadiazole ring. 

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