Perfluorinated olefins, reactions

The choice of the desired CM-partner directly influences the choice of the catalyst [147], Comparing the GII and the HII catalysts shows that the latter has access to a much broader spectrum of cross-partners [148], It is possible to use electron deficient cross-partners like acroleine, perfluorinated olefins, acrylonitrile, or other o / -unsaturated carbonyls, whereas GII leads to no reaction or very low conversions due to side-reactions in these cases. 

Perfluorinated olefins have been found to give both vinyl azides and the saturated fluoroazides on reaction with triethylammonium azide apparently the intermediate carbanion tends to abstract a proton in this case. Reaction of hexafluoropropene (28) with sodium azide in DMF leads stereospecifically to the trans azide 29. 

In some instances, perfluorinated olefins can be used for the introduction of perfluoroalkyl group into highly electrophilic heterocycles. For example, reported in patent literature nucleophilic reaction of C2F5 (generated from tetrafluoroethylene... 

Under the influence of anionic catalysts, silyl ethers react with perfluorinated olefins to produce exceptionally high yields of partially fluorinated vinyl ethers. The number of vinyl fluorines substituted can be controlled for a wide variety of fluorinated olefins and silyl ethers. Application of this reaction to difunctional starting materials affords quantitative yields of condensation polymers of moderate molecular weight. 

Since the conversion of fluorinated olefins to vinyl ethers is knownl, it should be emphasized that the principal benefit from the silyl ether chemistry is increased selectivity and yield. Base-catalyzed reaction of alcohols and fluoroolefins almost always gives a mixture of substitution and addition products, but clean substitution occurs with silyl ethers. Homogeneity, which persists during bulk polymerization, is an additional attractive feature. Substitution of the first fluorine in a 1, 2-disubstituted perfluorinated olefin proceeds more rapidly than subsequent fluorine substitution in the product vinyl ether. The 2/1 adducts shown in Scheme 4 are therefore conveniently prepared in excellent yield. On a laboratory scale, these difunctional vinyl ethers permit good control of stoichiometry required for polymer formation. 

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)... 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

Fluorinated carbocations play an important role as intermediates in electrophilic reactions of fluoroolefins and other unsaturated compounds. For example, F-allyl cation 1 was proposed as a reactive intermediate in reactions of HFP with fluoroolefins catalyzed by Lewis acids [7]. The difference in stability of the corresponding allylic cations was suggested as the explanation for regio-specific electrophilic conjugated addition to CF2=CC1CF=CF2 [11]. Allylic polyfluorinated carbocations were proposed as intermediates in the reactions of terminal allenes with HF [53] and BF3 [54], ring-opening reactions of cyclopropanes [55], Carbocations are also an important part of the classic mechanism of electrophilic addition to olefins (see Eq. 2). This section deals with the questions of existence and stability of poly- and perfluorinated carbocations. 

Reactivity of nitrosonium fluorosulfate and trifluoromethansulfonate 0N0S02X (X=F, CF3) is similar to that of nitronium fluorosulfate, although they are less active than the latter. Reaction, which occurs only with fluoroethylenes and perfluorinated vinyl ethers [ 119 -121 ], is of an electrophilic nature it results in low to moderate yields of nitrosoalkyl compounds when the olefin has a limited contact time with the reaction mixture ... 

Two other interesting papers should also be mentioned. Perfluorination of porphyrin was achieved with AgF resulting in a robust catalyst (equation 41), capable of performing around 50 cycles of benzene oxidation or olefin epoxidation with H20281. The second work deals with photolytic reactions of AgF in the presence of Ti02. The formally nucleophilic fluoride behaves as an electrophile and replaces protons in quite a few cases (equation 42)82. 

Pyridinium (trifluoroacetyl)methylide forms [3-1-2] cycloadducts with a wide variety of perfluorinated and partially fluorinated olefins, alkynes, and nitriles [86JFC(34)275]. Photolysis of a mixture of hexafluoro-3-diazobutan-2-one and perfluoro-2-butyne in the gas phase results in the formation of tetrakis(trifluoromethyl)furan a ketocarbene is the key intermediate of this reaction sequence (87JOC2680) (Scheme 79). 

Arnone et al. studied the epoxidation of various olefins 220 with perfluorinated oxaziridine 80 (Equation 10) <1996JOC8805>. Alkyl-substituted olefins are epoxidized with this oxaziridine under particularly mild conditions. Electron-deficient substrates can also be epoxidized, and the more electron deficient the double bond is, the more severe the reaction conditions become. The reaction is chemoselective and stereoselective, with air-alkenes affording air-epoxides. Various complex and polyfunctionalized substrates of natural origin (monoterpenes, sesquiterpenes, and steroids) have been epoxidized effectively with this reagent (Table 18). 

Substituted alkenes as well as terminal olefins and styrene derivatives are epoxidized in high yield and enantiomeric excess under homogeneous reaction conditions. Very recently, the first chiral salen complexes which are selectively soluble in perfluorinated solvents have been synthesized and their application in asymmetric synthesis has been investigated [39,40]. 

Another FBC approach was developed by Knochel and co-workers to oxidize olefins, sulfides, and aldehydes to epoxides, sulfoxides, sulfones, and carboxylic acids (79). They used the Ru and Ni complexes of a perfluorinated 1,3-diketone, obtained in one step in 80 % yield by the condensation of a perfluoromethyl ester and a perfluoromethyl ketone, as catalysts for these oxidation reactions. More importantly, these Ru and Ni complexes were found to be highly soluble in perfluorocarbons (Figure 3). 

Epoxidation of olefins was catalyzed by the ruthenium(II) complex of the above perfluorinated y3-diketone in the presence of 2-methylpropanal (Scheme 50). Unfunctionalized olefins were epoxidized with a cobalt-containing porphyrin complex, and epoxidation of styrene derivatives was catalyzed by chiral salen manganese complexes (248) (Scheme 50). In the latter case, chemical yields were generally high, however, the products showed low enantiomeric excess with the exception of indene (92% ee). [Pd(C7Fi5COCHCOC7Fi5)2] efficiently catalyzed the oxidation of terminal olefins to methyl ketones with f-butylhydroperoxide as oxidant in a benzene-bromoperfluoro-octane solvent system (Scheme 50). In all these reactions, the product isolation and efficient catalyst recycle was achieved by a simple phase separation. 

The concept of fluorous biphase hydroformylation of heavy olefins was introduced by Horvath at Exxon in 1994 [42, 43]. Fluorocarbon-based solvents, especially perfluorinated alkanes and ethers, are of modest cost, chemically inert, and nonpolar and show low intermolecular forces. Most of them are immiscible with water and can be therefore used as the nonaqueous phase. Moreover, their miscibility with organic solvents such as toluene, THF, or alcohols at room temperature is quite low. Only at elevated temperature miscibility occurs. These features allow hydroformylation at smooth reaction conditions at 60-120 °C in a homogeneous system [44]. Upon cooling, phase separation takes place. The catalyst is recovered finally by simple decantation. One of the last summaries in this area was given by Mathison and Cole-Hamilton in 2006 [45]. 

Chambers RD, Findley AA, Philpot PD, Fielding HC, Hutchinson J, Whittaker G (1978) Perfluorinated derivatives of furan via novel cyclisation reactions of perfluoro-olefins. J Chem Soc Chem Commun 431 32... 

Nowadays, there are several alternatives under investigation as fluid for multiphase catalysis, including the resurgence of water, perfluorinated hydrocarbons, and supercritical fluids, in particular CO2. Indeed, the advent of water-soluble organo-metallic complexes, especially those based on sulfonated phosphorus-containing ligands, has enabled various biphasic catalytic reactions to be conducted on an industrial scale, in particular, for the hydroformylation of olefins. 

Perfluoropropene oxide is a convenient, volatile, thermal source of difluoro-carbene, and its use in the preparation of fluorocyclopropanes has been further exemplified, perfluorinated, polyfluorinated, and hydrocarbon olefins being employed as substrates (see also p. 17) it has also been employed to convert perfluorobut-2-yne into 3,3-difluoro-l,2-bis(trifluoromethyl)cyclo-propene. Qose examination of the reaction between the epoxide and a mixture of cis- and rra .r-l-chloro-l,2-difluoroethylene at ca. 200°C has revealed that stereospecific addition of difluorocarbene takes place, but that loss of configuration can subsequently result from slow thermal isomerization of the cyclopropane product. Thermal decomposition of perfluoropropene oxide at 200 "C in the absence of a trap yields mainly perfiuorocyclo-propane and trifluoroacetyl fluoride together with tetrafluoroethylene, perfluoroisobutene oxide, perfluorobut-l-ene, and poly(difluoromethylene). 

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