Pentafluorophenylation

Fig. 8. Rephcation. The amino adenosine X and the pentafluorophenyl ester Y form a hydrogen-bonded dimer XY, prior to reaction between the amine and the activated ester groups (shown in the circle). The reaction product is a <7 -amide conformer cis-Z that isomeri2es to the more stable trans- acnide Z. The rephcative process is cataly2ed by the reaction product Z (also referred to as the template). First, a termolecular complex XYZ is formed from X, Y, and Z.

Pentafluorophenylmagnesium bromide or lithium can be converted to other pentafluorophenyl organometabics by reaction with the corresponding metal chloride (237). Bis(pentafluorophenyl)phenylphosphine [5074-71-5] (Ultramark 443), (CgF )2CgH P, is offered commercially as a marker for mass spectral standardi2ation (238). 

Preparation of (14) and treatment with A[,A[-bis(ttimethylsily)fomiamide (BSF) and triethylamine provided (16) in 84% yield via the putative imine intermediate (15). The trifliioromethyl group could be replaced by other moieties such as 2,4,5 trichlorophenyl, pentafluorophenyl, or nonafluorobutyl with increasing effectiveness. 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

Robert Filler, The Pentafluorophenyl Croup Effects on Reactivity of Organic Compounds... 

Xenon difluoride has been used to oxidize a number of antimony compounds [102, 109] in yields ranging from 73 to 98%. Elemental fluorine oxidized tris(pen-tafluorophenyl)stibine to tris(pentafluorophenyl)stibine difluoride in 98% yield [706]. Oxidative fluonnation of stibines has also been accomplished with iodine pentafluoride [707]. 

The KF-S reaction presumably involves attack of a fluonnated caibanion on sulfur, whereas the S-Sbp5 reaction may involve electrophilic attack by a cationic sulfur species on the olefin under the strong Lewis acid conditions Electrophilic attack on a fluonnated olefin may also account for formation of a perfluorinated sulfide from reaction of bis(pentafluorophenyl)disulfide with hexafluoropropylene under superacid conditions [IS5] (equation 28)... 

Triaryl-substituted imines are converted to the corresponding nitrones by peroxyacetic add [87] (equation 79) substitution of one pentafluorophenyl group by a phenyl group at the carbon atom reduces the yield to ca. 20% [[Pg.349]

Oxidation of more lipophihc pentafluorophenyl sulfamimine to the corresponding sulfamyloxaziridine by m-chloroperoxybenzoic acid gives better yields in a shorter tune compared with the nonfluonnated analogue [95] (equation 87)... 

A guanidine obtained from a pentafluorophenyl isocyanide dichloride and aniline is cyclized to a tetrafluorobenzimidazole [106] (equation 92). 

Pentafluorophenylnitrene generated by the photolysis of pentafluorophenyl-azide in toluene at 25 gives pentafluoroaniline and benzyl-substituted anilines At low temperatures (-78 to -196 °C), perfluoroazobenzene also is formed [7] (equation 8)... 

Tns(pentafluorophenyl)phosphine is also replaced when the 4 fluonne reacts with hydrazine [55, 66] (equation 34)... 

Hexafluorabenzene may also add to methylene Lnphenylphosphorane to form a new pentafluorophenyl-bearing yhde Treatment of tins ylide with an acid fluonde or acid anhydride followed by pyrolysis (shown in equation 58) forms the corresponding pentafluorophenylacetylene [66] (equation 58). 

Tnmethylpentafluorophenylsilane reacts with ketones in the presence of cyamde ion to form the silyl eiher denved from the alkoxide created by the addition of the pentafluorophenyl amon to the carbonyl carbon [89] The nucleofugal character of the pentafluorophenyl group is significantly greater than that of the added cyamde ion so that the addihon proceeds under nearly neutral condmons (equation 73)... 

A method for generating a perfluoroarylmagnesium compound is the cleavage of a pentafluorophenyl-metal bond by a nucleophile such as ethyltnagnesium bromide As an example, tetrakis(pentafluorophenyl)tin on reaction with ethyl-magnesium bromide gives a series of products, one of which may result from pentafluorophenylmagnesium bromide [27] (equation 7)... 

Bis(pentafluorophenyl)cadmium complexes have been used to prepare tri-methyl(pentafluorophenyl)tin [4 (equation 15)... 

Several studies have investigated the preparation and properties of trifluo-romethyl and pentafluorophenyl cadmates [132, 733]... 

The arylcopper reagents couple with 1-iodoarylacetylenes to give the unsym-metrical diarylacetylenes [25(S] (equation 176) Reaction with tetrabromoethyl- ene gives bis(pentafluorophenyl)acetylene in 66% yield [25S] (equation 177) Pen-tafluorophenyl copper couples with (bromoethynyl)triethylsilane to give C6F5C=CSi(C2H5)3 in 85% yield [259]... 

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

The additions of phenyl azide and phenylnitrile oxide to pentafluorophenyl-acetylene are also regiospecific [75, 7S] (equation 12). Interestingly, in the latter reaction, phenylacetylene gives regiochemistry that is opposite to that observed for pentafluorophenylacetylene [75]... 

Trifluoromethyl or pentafluorophenyl phosphonates can be produced photo-chemically by irradiation of triethylphosphites with fluorinated iodides [181] (equation 48). 

Pentafluorophenyl derivatives have received wide application in biochemistry as highly selective and efficient protective reagents (for a review, see reference 148)... 

Pentafluorophenyl acetate is a highly selective acetylating reagent, useful for acetylations at hydroxyl and amino groups under mild conditions When applied to the acetylation of amino alcohols, it gives selective formation of H acetyl derivatives at room temperature and M,0 diacetylated products under moderate heating in the presence of triethylamine [149]... 

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. 

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