Perfluorinated alkenes

Access to a variety of unsaturated perfluorinated telomers is provided by the homoielomenzation of perfluorinated alkenes, generally initiated and catalyzed by fluoride ton [22]... 

Neutral (cyclobutadiene)Fe(CO)3 complexes undergo thermal and photochemical ligand substitution with phosphines, with alkenes such as dimethyl fumarate and dimethyl maleate and with the nitrosonium cation to generate the corresponding (cyclobutadiene)Fe(CO)2L complexes15. These types of complexes are presumably intermediates in the reaction of (cyclobutadiene)Fe(CO)3 complexes with perfluorinated alkenes and alkynes to generate the insertion products 266 or 267 respectively (Scheme 70)15,238. 

A complex reaction between perfluoro 2-methylpent-2-ene and carboxylic acids in the presence of potassium carbonate and Aliquat produces the acid fluoride, as the major product, with variable amounts of the 3-acyloxy perfluorinated alkene [37]. The procedure has little value for the synthesis of either compound. 

A number of transition metal complexes react with alkenes, alkynes and dienes to afford insertion products (see Volume 4, Part 3). A general problem is that the newly formed carbon-metal bond is usually quite reactive and can undergo a variety of transformations, such as -hydride elimination or another insertion reaction, before being trapped by an electrophile.200 Usually, a better stability and lower reactivity is observed if the first carbometallation step leads to a metallacycle. It is worthy to note that the carbometallation of perfluorinated alkenes and alkynes constitutes a large fraction of the substrates investigated with transition metal complexes.20015... 

Sodium amalgam is effective for promoting defluorination (Scheme 14), to produce an interesting series of dienes (38), (40) and (42), especially (38) [7, 8, 36], but tetrakis(dimethylamino)ethene (TDAE) (43) (Scheme 15) is a much safer system to use and, consequently, with the latter reagent, the process may be scaled up [36]. TDAE (43) is successful because its donor capacity is high, i.e. it has been variously described as being similar to that of zinc [37] or to alkali-metals [38] and will react, therefore, with most perfluorinated alkenes or -cycloalkenes. Furthermore, the fact that the dienes (38), (40) and (42) may be isolated derives from the fact that the dienes have more CF= sites than the starting alkenes and consequently their respective reduction potentials vary by... 

Table 2. Reduction potentials of some perfluorinated alkenes and dienes (vs S.C.E.) [36]...

A particularly useful reaction of this type involves the direct formation of hexakis(trifluoromethyl)cyclopentadiene (71) (Scheme 31), or the corresponding cyclopentadienide (72), from the diene (38) by a fluoride ion induced reaction with pentafluoropropene [67-69]. Recent work [54] has shown that very active sources of fluoride ion can be generated by direct reaction of amines, especially TDAE (43), with perfluorinated alkenes or perfluorinated aromatic compounds and these essentially solventless systems promote both oligomerisations (see above) and polyfluoroalkylations. The absence of solvent makes recovery of product very easy, e.g. in high-yielding formation of (73), (74) or (75) (Scheme 32). 

Intermolecular transfer of trifluoromethyl has been demonstrated in the fluoride ion induced rearrangement of the perfluorinated alkene (77) to the isomer (78). Again, the driving force in this process is to produce an isomer (78) with fewer vinylic fluorine sites than in the starting isomer (77). The intermediate trifluoromethyl anion has been trapped with perfluoropyrimidine (79)... 

However, ylides may be generated by reactions of amines with various perfluorinated -alkenes or -cycloalkenes [110] and attack of these ylides also promotes oligomerisation [62, 111, 112] (Scheme 52). 

Finally perfluorinated alkenes, prepared according to various routes (decarboxylation of perfluorinated acids or anhydrides, action of organolithium, magnesium reagents or metallic zinc-copper couple to perfluoroalkyl iodides, oligomerisation of TFE and of HFP, addition of perfluoroalkyl iodides to per-fluoroallyl chloride [304], addition of KF to perhalogenated esters or alkanes... 

The formation of 10 is an example of the addition of chloromethyl ethers to perfluorinated alkenes in the presence of potassium fluoride and a catalytic amount of tetrabutylammonium... 

Vacuum pyrolysis of polytetrafluoroethene gives tetrafluoroethene as virtually the only product [21] this unzipping reaction is almost unique amongst depolymerisation processes. At higher pressures the pyrolysis product contains other perfluorinated alkenes and perfluorocyclobutane, the proportions depending on the exact reaction conditions [22]. 

There are four main general methods [40 2] for the preparation of perfluorinated alkenes, namely dehydrohalogenation, dehalogenation, pyrolysis and halogen exchange reactions of appropriate fluorinated precursors. The overall features of the mechanisms of each of these processes have already been discussed (Chapters 6 and 7, Sections 1 and 11). Representative examples of each of these types of synthesis are collated in Table 7.5 clearly the method of choice for the synthesis of a particular fluoroalkene will depend... 

Also, intermediate peroxides are formed in the oxidation of perfluorinated alkenes, e.g. in the photo-oxidation of perfluoroethene and perfluoropropene for the formation of Fomblin (Ausimont Co.) perfluoro-polyether fluids [198, 199]. 

Mercury photosensitization has been used to synthesize 1,3-dioxolane dimers by dehydrodimerization. For 1,3-dioxolane itself or analogues with substitution at C-2 or C-2 and C-4, radical formation occurs at the C-2 position, whereas when substitution is at the C-4 position radical formation occurs at the 4-position. In most cases, a small amount of product from ring opening was also reported <1996TL6853>. For 2,2-dimethyl-l,3-dioxolane, radical formation occurs at the 4-position, and one common way to achieve this is the use of dimethylzinc in air. Addition of various alkenes and related groups can then be performed, such as addition to tosyl imines <2004JOC1531>, and addition to perfluorinated alkenes and alkenyl ethers <1999JFC(94)141>. 

Poly(tetrafluoro ethylene) and other poly(perfluorinated alkenes)... 

Reactions of perfluorinated alkenes, such as hexafluoropropene, with fluoride ion give perfluoroalkylcarbanions which can act as nucleophiles in S Ar reactions with perfluoroheteroaromatic systems (Fig. 8.13). These reactions are another example of mirror-image chemistry and reflect well-known Friedel-Crafts reactions of hydrocarbon systems that proceed by reaction of the corresponding electrophile and carbocationic intermediates. Poly substitution processes are possible and, indeed, all five fluorine atoms may be replaced upon reaction with an excess of tetrafluoroethylene and fluoride ion. ... 

The Ionic Polymer-Metal Composite (IPMC) is a type of EAP actuator whose use in active catheters has been studied the most [19-22, 27, 28]. An IPMC consists of a polymer electrolyte sandwiched between two thin metal layers and typically has an elastic modulus of 0.1 GPa [10]. Common polymer electrolytes are perfluorinated alkenes with anionic-group-terminated side chains, such as Nafion and Flemion or styrene/divinylbenzene based polymers with ionic groups substituted from phenyl rings [10]. 

Reaction of amidine 585 with perfluorinated alkene 587 led to the formation of amidine 588, which upon heating with alkali gave a mixture of pyrimidines 590 (7 %) and 589 (34 %) (Scheme 126) [354], Pyrimidine 589 was obtained in 78 % yield when the second step of this sequence was performed using DABCO. 

Preparations of these 1,2-bis-electrophiles share some common features. In particular, esters of trifluoropyruvic acid (like MeTFP 1015) are available commercially, but they can be prepared in two steps from an epoxide 1067 (namely, hexafluoropropylene oxide, which is available on industrial scale) [633] (Scheme 228). hi turn, epoxides 1067 are obtained by oxidation of the corresponding perfluorinated alkenes, e.g. with hypochlorite [634]. 

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