Perfluoroalkyl anions

Perfluoroalkyl anions, which form carbenes upon subsequent elimination of a-fluorine, may be generated by cleavage of the carbon-tin and carbon-mercury bonds in, for example, (trifluoromethyl)trimethyltin [56] and phenyl(trifluoromethyl)mercury [57] (Figure 6.40) under very mild conditions. Carbenes may be generated from... 

Perfluoroalkyl anions can, in principle, be generated by the same methods as "normal alkyl or aryl anions - either by deprotonation of a suitable CH-acidic precursor by a strong base or by reductive halogen (usually iodine or bromine) metal exchange (Scheme 2.109). Another method - unique to the "perfluoro world -is addition of fluoride ions or other anions to perfluoroolefins. 

Scheme 2.116 Nucleophilic perfluoroalkylation of aliphatic or aromatic substrates by perfluoroalkyl anions generated by fluoride addition [43, 44] (TDAE = tetrakis(diurethylamino)ethylene).

Direct attack of RpCu on C(3) carbon leads to the most favorable product, probably by a concerted mechanism. The ratio of two isomers is defined by the nature of the halogen in thiophene ring. For example, in the case of the reaction of 3-bromothio-phene and K-perfluorooctyl iodide, 18% of a rearranged product (2-isomer) was formed, whereas in the reaction of 3-iodothiophene, <4% of 2-perfluoro-K-octylthio-phene was formed. The possible reason for 2-isomer formation may be addition of perfluoroalkyl anion to C(2)-C(3) double bond with formation of carbene, which undergoes isomerization into 2-fluoroalkylthiophene. ... 

Perfluoroalkyl cooper reagent also can be generated in situ through the reaction of perfluoroalkyl anions (or their synthetic equivalents) with Cu(I) salts. First part of this section contains a brief review of major types of reagents used for copper mediated... 

Makosza et al. recently reported two-step procedure for selective introduction of CF3 or (CF3)2CF group into heteroaromatic ring, using Reissert type reaction between A -acylated heterocycles and the corresponding perfluoroalkyl anions. 

Trialkyl phosphites have been converted to dialkyl chlorophosphates (32) in a mild and efficient way by tellurium tetrachloride. Tris(dimethylamino)phosphine abstracts iodine from 1-iodoperfluoroalkanes to give metal-free perfluoroalkyl anions which have basic but poor nucleophilic properties. The bicyclic phosphite (33) with chlorine gave a sole product (34) resulting from opening of the five-membered and not the seven-membered ring. ... 

Arsenault G, McAlees A, McCrindle R et al (2007) Analysis of perfluoroalkyl anion fragmentation pathways for perfluoroalkyl carboxylates and sulfonates during liquid chromatog-raphy/tandem mass spectrometry evidence for fluorine migration prior to secondary and tertiary fragmentation. Rapid Commun Mass Spec 21 3803-3814... 

Alkali-metal fluorides and fluoro-olefins provide a convenient source of perfluoroalkyl anions. The exchange of hexafluoropropene with Cs F in the gas phase has been reinvestigated the activity introduced is far less than that introduced into trifluoroacetyl fluoride or sulphur tetrafluoride under similar conditions (see p. 133). The dimerization and trimerization of hexafluoropropene with potassium fluoride or hydrogen fluoride in dimethyl-formamide has been studied, but the structures reported for the trimers... 

Several methods for the preparation of ehain-fluorinated pyridazines relied on the so-called anionic Friedel - Crafts reactions (i.e. aromatic nucleophilic substitution with perfluoroalkyl anions or their synthetic equivalents) with tetra-fluoropyridazine, which was discussed in the corresponding section on chemistry of ring-fluorinated diazines. 

Sodium nitrite in dimethylformamide acts as a nucleophile and reacts with perfluoropropene to generate a perfluoroalkyl nitrite anion The intermediate carbanion undergoes intramolecular nitrosation with loss of carbonyl difluoride to give tnfluoroacetic acid upon hydrolysis [5] (equation 6)... 

TYie, perfluoroalkylations of thiolate anions are interpreted by an mechanism [55, 63, 64] (equation 57). 

Another way to prepare fluorinated sulfides is the photochemical alkylation of sulfides or disulfides by perfluoroalkyl iodides [69, 70, 71] (equations 62-64). Reaction of trifluoromethyl bromide with alkyl or aryl disulfides in the presence of a sulfur dioxide radical anion precursor, such as sodium hydroxymethanesulfi-nate, affords trifluoromethyl sulfides [72] (equation 65). 

Perfluoroalkylation of substituted benzenes and heterocyclic substrates has been accomplished through thermolysis of perfluoroalkyl iodides in the presence of the appropriate aromatic compound Isomeric mixtures are often obtained W-Methylpyrrole [143] and furan [148] yield only the a-substituted products (equation 128) Imidazoles are perfluoroalkylated under LTV irradiation [149] (equation 129). 4-Perfluoroalkylimidazoles are obtained regioselectively by SET reactions of an imidazole anion with fluoroalkyl iodides or bromides under mild conditions [150] (equation 130) (for the SET mechanism, see equation 57)... 

Perfluoroalkylatwn ofpyridines by perfluoroalkyl bromides or iodides occurs m the presence of sulfur dioxide radical anion precursors, such as sodium hydroxy-methanesulfinate [755, 757, 158] (equation 135)... 

Perfluoroalkyl carbanions, generated by reversible nucleophilic addition of a fluoride anion to fluoroalkenes, react with dry benzenediazonium chloride in dimethyl formamide, giving phenylazoperfluoroalkanes in 41-53% yield (Dyatkin et al., 1972). The dianion obtained from 1,2-dinitrobenzene with dipotassium cyclo-octatetraenide reacts in a complex way with arenediazonium salts, forming 4-aryl-azo-2-nitrophenol in 46-58% yield (Todres et al., 1988). 

Neutral b/.v(acyl)Fe(CO)4 complexes have been reported by Stewart et al. (23). The acyl ligands have perfluoroalkyl substituents. These complexes are isoelectronic to the anionic diacyltetracarbonylmanganate species mentioned above. 

Direct electrochemical reduction of perfluoroalkyl halides generates perfluoroalkyl radicals or anions depending on the electrolytic conditions and starting halides. Calas et al. have performed the electrocatalytic addition of perfluoroalkyl iodides to 3-hydroxyalkynes in aqueous KCI emulsion using a... 

Thus, perfluoroalkylated imidazoles are obtained in excellent to good yields (Scheme 3.7) [16, 17]. Similarly, a hindered phenolate anion provides a fluoro-alkylated dimeric product in high yield (Scheme 3.8) [173. 

Nonbranched amino acids substituted by a fluoroalkyl chain on a carbon distant at least one methylene from the amino acid function have been prepared as racemates by various methods." Under nonracemic form, co-perfluoroalkyl norvaline and norleucine (Rf = C2F5 or more) have been prepared by bromination of an anion of a fluorinated chiral oxazolidinone (derived from RfCH2CH2C02H). Substitution of the bromine atom by an azide and subsequent reduction yield the desired amino acids (Figure 5.10)." ... 

The LSR itself consists of a lanthanide ion, commonly europium (Eu3 + ), praseodymium (Pr3+) or ytterbium (Yb3+), and three /1-diketone anions with alkyl or perfluoroalkyl groups Rl and R2 as ligands. Perdeuterated LSRs, which do not give H signals, are commercially available. Incorporation of chiral /J-diketone ligands, mostly derived from substituted camphors, allows chiral recognition. 

Our early work examined the reaction of PCTFE with sulfur, selenium and phosphorous nucleophiles 9 to achieve high levels of functionalization through a well-precedented (in the case of perfluoroalkyl iodides)20"24 one electron transfer, radical anion chain process. While such a reaction demonstrated the feasibility of using one-electron processes for the functionalization of PCTFE, the carbon-sulfur linkage remained susceptable to oxidation. 

Oxygen forms no chains longer than three atoms, and besides the familiar ozone, Ov and its anion. Of, few compounds are known all of them are bis(perfluoroalkyl)... 

All of the C = C bond migrations discussed above involve the shift of an atom, usually fluorine. In one case, a perfluoroalkyl group shift has been observed. Chambers and co-workers reported that perfluoro(4,4-dimethylpent-2-ene) (16) isomerizes almost quantitatively to alkcnc 17 when heated with cesium fluoride in sulfolane at 150— 160 C for 5 hours.36 Based on trapping experiments, the authors concluded that the reaction involves an intcrmolccular transfer of a trifluoromethyl anion. 

Fluorination has a particularly profound effect on the additions of nucleophiles to per-fluorinated alkenes where the intermediate is anionic. Such processes are dramatically assisted by the strongly stabilizing influence of perfluoroalkyl groups substituted at the incipient anionic site.66 Similar to carbocations (see Section 1.4.), the effect of fluorination in such systems is often ambiguous when monofluorination is involved. a-Halogens generally stabilize anions in the order bromine > chlorine > fluorine, which is the exact opposite to the inductive electron-withdrawing order of the substituents. This effect reflects the importance of l7t-repulsion.67... 

Other well-known reactions are those offluorinated olefins with fluoride ion and negatively substituted aromatic compounds leading to the formation of per-fluoroalkylated aromatic compounds The reaction may be considered an anionic version ot a Friedel Crafts process and can result m introduction of one or several perfluoroalkyl substituents [HI] Aromatic substrates include substituted and unsubstituted perfluorobenzenes [131, 212, 213, 214], fluorinated heterocycles [131, 203, 215, 216, 217, 218, 219, 220, 221, 222, 223], perchlonnated heterocycles [224] (equation 44), and other activated aromatic compounds [225] (equation 45) The fluorinated olefins can be linear or cyclic [208] (equation 46)... 

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