From fluoroalkenes and

Reaction of perfluoroaLkenes and hypochlorites has been shown to be a general synthesis of perfluoroepoxides (32) (eq. 7). This appears to be the method of choice for the preparation of epoxides from internal fluoroalkenes (38). Excellent yields of HFPO from hexafluoropropylene and sodium hypochlorite using phase-transfer conditions are claimed (34). 

For the synthesis of the title compound, Oxone or 3-chloroperbenzoic acid2 can be used to oxidize the sulfide to the sulfone. The title compound is a key reagent for the preparation of fluoroalkenes from aromatic11 and aliphatic2 aldehydes. Recently, a stereospecific method to (E)- and (Z)-fluoroalkenes was reported using this reagant.12 13 14... 

In general it is very difficult to make any distinction between a concerted process and the involvement of a short-lived carbanion. For clarity a number of alkene rearrangements in the following text are written as two-step processes, but it should be emphasised that they could involve concerted mechanisms. Products arising from substitution with rearrangement are frequently encountered in reactions of cyclic fluoroalkenes and in fluoride-ion-induced rearrangements (Subsection 6, below). 

The hterature concerning reactions between nucleophiles and fluoroaUcenes is now extensive and is included in various reviews [41, 55, 57, 85-92] and books devoted to organofluorine chemistry (see the relevant chapters in the general textbooks listed in Chapter 1, Section 1). Some examples of reactions between fluoroalkenes and an illustrative selection of nucleophiles are recorded in Table 7.6. The many unusual products and the wide scope of these reactions will be apparent even from such a brief overview of the subject. Examples of reactions involving bifunctional nucleophiles are also included, whereas reactions involving initial attack by fluoride ion as the nucleophile are discussed in Subsection 6, below. 

Conversely, when the rate of propagation is faster than chain transfer, products arising from telomerisation and polymerisation are formed in greater concentration. In this section, free-radical addition to fluoroalkenes will be dealt with first, in order to establish... 

By reaction of a 1,1-difluoroethene with tributylphosphane in the presence of boron trifluoride-diethyl ether complex, the vinylphosphonium salt is obtained. On subsequent hydrolysis the selectivity of formation of the Z- and F-isomer is 100%, but it diminishes after the introduction into the alkene. together with the perfluoroalkyl group, of substituents such as phenyl and 4-methoxyphcnyl. In accordance with this methodology, a method of substitution of fluorine by hydrogen at the fluoroolefinic double bond has been developed.194,206 The first stage of this reaction includes the formation of a fluoro-/5-phosphane from the fluoroalkene and tributylphosphane. The decomposition of this /l5-phosphane in the aqueous solvent leads to a fluoroalkene, e.g. formation of l.206... 

The addition of the 5-pentanoate radical from methyl adipate to butadiene has been intensively investigated, because in this way long chain l,n-diacids are easily accessible a total yield of 96% has been claimed for this reaction (Table 8, entry 7). Different Kolbe radicals from acetic acid, monochloroacetic acid, trichloroacetic acid, oxalic acid, methyl adipate and methyl glutarate have been added to ethylene, propylene, fluoroalkenes and dimethyl maleate. In this detailed study the influence of current density, alkene type and alkene concentration on the product yields and product ratios have been discussed. 

A significant advantage of conducting polymerization and oligomerization of fluoroalkanes in carbon dioxide rather than other solvents is the absence of chain transfer to CO2. Radicals generated from fluoroalkene monomers such as tetrafluoroethylene (TFE) are quite electrophilic, and will undergo facile chain transfer to virtually any hydrocarbon that is present in the system. Moreover, highly reactive monomers such as TFE can be handled more safely as... 

Higher fluoroalkenes and difluorocyclopropanes are also sources of CF2. Dalby (59) obtained this radical by the flash photolysis of perfluoropropylene. The kinetics of CF2 formation from the thermal decomposition of perfluorocyclopropane at 526° - 549°K were reported by Atkinson and McKeagan (78). Birchall, Haszeldine and Roberts (79) investigated the thermal decomposition of a series of gem-difluorohalocyclopropanes as sources of CF2. The cyclopropanes studied were placed in the following approximate order of decreasing stability toward CF2 elimination ... 

However, the method has serious drawbacks. During fluorination of the alkenyhnetal species, an alkene is formed as a by-product and it is difficult to separate this from the fluoroalkene [19-22]. Moreover, the fluorination of alkenylmetal species such as alkenylsilane and alkenylborane proceeds non-steieoselectively, and a mixture of stereoisomers is formed [17, 18]. Recently Ritter et al. reported that the fluorination of alkenylboronic acid 9 with SelectfluorT proceeds steieoselectively and (E)- -fluoroalkene 10 can be obtained stereoselectively [23] (Scheme 4). The use of AgOTf is critical for the stereoselective synthesis of fluoroalkene and the formation of undesired alkene was not observed under these conditions. The alkenylsilver species 11 was postulated as an intermediate. 

Difluoroethanol is prepared by the mercuric oxide cataly2ed hydrolysis of 2-bromo-l,l-difluoroethane with carboxyHc acid esters and alkaH metal hydroxides ia water (27). Its chemical reactions are similar to those of most alcohols. It can be oxidi2ed to difluoroacetic acid [381-73-7] (28) it forms alkoxides with alkaH and alkaline-earth metals (29) with alkoxides of other alcohols it forms mixed ethers such as 2,2-difluoroethyl methyl ether [461-57-4], bp 47°C, or 2,2-difluoroethyl ethyl ether [82907-09-3], bp 66°C (29). 2,2-Difluoroethyl difluoromethyl ether [32778-16-8], made from the alcohol and chlorodifluoromethane ia aqueous base, has been iavestigated as an inhalation anesthetic (30,31) as have several ethers made by addition of the alcohol to various fluoroalkenes (32,33). Methacrylate esters of the alcohol are useful as a sheathing material for polymers ia optical appHcations (34). The alcohol has also been reported to be useful as a working fluid ia heat pumps (35). The alcohol is available ia research quantities for ca 6/g (1992). 

In general, the peilluoioepoxides have boiling points that are quite similar to those of the corresponding fluoroalkenes. They can be distinguished easily from the olefins by it spectroscopy, specifically by the lack of olefinic absorption and the presence of a characteristic band between 1440 and 1550 cm . The nmr spectra of most of the epoxides have been recorded. Litde physical property data concerning these compounds have been pubhshed (Table 1). The stmcture of HFPO by electron diffraction (13) as well as its solubility and heats of solution in some organic solvents have been measured (14,15). 

Conjugated, cross-conjugated, and homoconjugated fluoroalkenes react with halogens to yield predominantly 1,4-adducts Results from the reactions of a series of conjugated fluoroalkenes with elemental halogens are summarized in Table 4 In nearly all cases, the fraMs-l,4-addition products are formed exclusively [Il ... 

The procedure described here provides a stereospecific synthesis of (E)- and (Z)-fluoroalkenes from the corresponding (E)- and (Z)-fluorovinyl sulfones. Fluorovinyl sulfones obtained from ketones are, in most cases, readily separable into (E) and (Z) isomers either by crystallization or by chromatography.4 In the example described, only the (E)-fluorovinyl sulfone 1 is formed (which is converted into the (Z)-fluoroalkene 3 with complete retention of configuration). The reaction sequence has been used for the stereospecific synthesis of fluoroalkene nucleosides5 as well as for... 

Hydration of olefins, alkynes and nitriles calls explicitely for the use of aqueous solvents. Indeed, one of the earliest investigations originates from 1969, when hydration of fluoroalkenes were studied with Ru(II)-chloride catalysts (Scheme 9.6). The reaction has no synthetic value but the studies helped to clarify the mechanism of the interaction of olefins with Ru(II)... 

Methyl fluoro(diethoxyphosphono)dithioacetate (34) has been prepared from difluorinated precursors [56], Fluorophosphonothioacetamides (35) derived from this dithioester, have been successfully transformed into highly functionalized fluoroalkenes (36). Judicious selection of the aldehyde coupling partner can lead expeditiously to the preparation of fluoroolefin dipeptide isosteres following elaboration of the carboethoxy group and desulfurization (Scheme 11). 

More recently, radical additions to fluoroethenes have attracted attention. Eguchi et al. [125] applied the Barton decarboxylation procedure to add a range of alkyl radicals to l,l-dichloro-2,2-difluoroethene. Addition was regioselective and the terminal carbon could be hydrolysed to a carboxyl group with silver(I) mediation (Eq. 39). The fluoroalkene is effectively an equivalent for either difluoroacetyl anion or cation synthons, because the adding radical can be approached from either polarity manifold. 

Unsaturated fluorinated compounds are fundamentally different from those of hydrocarbon chemistry. Whereas conventional alkenes are electron rich at the double bond, fluoroal-kenes suffer from a deficiency of electrons due to the negative inductive effect. Therefore, fluoroalkenes react smoothly in a very typical way with oxygen, sulfur, nitrogen and carbon nucleophiles.31 Usually, the reaction path of the addition or addition-elimination reaction goes through an intermediate carbanion. The reaction conditions decide whether the product is saturated or unsaturated and if vinylic or allylic substitution is required. Highly branched fluoroalkenes, obtained from the fluoride-initiated ionic oligomerization of tetrafluoroethene or hexafluoropropene, are different and more complex in their reactions and reactivities. 

It has been shown in ozonizations of fluoroalkenes (vide supra) that fluoro substituents stabilize the ozonides formed from the rearrangement of the initial molozonides. Rather stable ozonide isomers 3 are formed from the trifluoromethylated alkenyl ether 2 as two separable dia-stereomers with isolated yields 27 and 26%. respectively.180 The stability was demonstrated... 

Elimination of hydrogen iodide from polyfluoroalkyl iodides is facile and gives fluoroal-kenes. Hydrogen iodide is easily eliminated by strong bases (e. g., sodium hydroxide) from polyfluoroalkyl iodides to give the fluoroalkenes.8... 

A nucleophilic mechanism can be applied in reductions with complex hydrides of highly fluori-nated aliphatic and alicyclic fluoroalkenes with electron-deficient C = C bonds the hydride anion adds as a strong nucleophilic agent to the more electrophilic carbon atom the intermediate anion can then lose a fluoride ion either from the original C = C bond, or from the allylic position finishing an SN2 displacement of the fluorine. Thus, the reductions of vinylic C-F bonds with hydrides proceed by a nucleophilic addition-elimination mechanism. Displacement of fluorine in highly fluorinated aromatic compounds proceeds by the same mechanism ... 

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