Alkenes vinylic fluorides

The fluoropolymer family consists of polymers produced from alkenes in which one or more hydrogens have been replaced by fluorine. The most important members of this family are polytetrafluoroethylene (PTFE) (XLVII), polychlorotrifluoroethylene (PCTFE) (XLVIII), poly(vinyl fluoride) (PVF) (XLIX), poly(vinylidene fluoride) (PVDF) (L) copolymers of... 

Vinyltrimethylstannanes react with xenon difluoride in dichloromethane at room temperature in the presence of equimolar (or a 50 Vo excess) of silver trifluoromethanesulfonate and a catalytical (0.1 equiv) quantity of 2,6-di-/e/7-butyl-4-methylpyridine to form the corresponding vinyl fluorides in high to moderate yields.54 57 The substitution reaction is tolerant to various functional groups, such as ketones, esters, carbamates, ketals, ethers, phenol rings and tertiary alcohols. As byproducts corresponding alkenes have been detected due to pro-tiodestannylation. 

Vinylfluorides.1 This combination results in formation of a reagent BrF (1), which reacts with alkenes by trans-addition to form bromofluorides 2. On elimination of HBr (KOH), the adducts form vinyl fluorides stereospecifically. 

Beside these above fluoroolefins, numerous other fluorinated alkenes have been involved in telomerisation. Most of them are unsymmetrical and thus lead to adducts composed of at least two isomers. Among them, vinyl fluoride and 1,1, 1-trifluoropropene have been attempted with various telogens. 

OL-Methylenecyclohutanones. The reagent reacts regioselectively with activated alkenes (vinyl ethers, silyl enol ethers) to give cyclobutanones. These products undergo ring expansion with diazomethane to cyclopentanones. Both products undergo desilylative elimination in the presence of fluoride ion to form a-methylene ketones. 

Treatment of vinyllin compounds with xenon difluoride in dichloromethane at 25"C results in low yields of the desired vinyl fluorides with the major products being the corresponding alkenes. In addition to the poor yield of the desired compound the reaction times are long (2-3 d). Attempts to increase the reactivity of the vinyltin compounds by the addition of... 

Hydrogenolysis of vinylic fluorides is hardly ever done with the aim of removing fluorine finom a molecule. Rather, it occurs as a usually undesirable side reaction, accompanying reductions of other functions in fluorinated compounds. " It frequently takes place during catalytic hydrogenation of fluorinated alkenes. A clear-cut saturation of the double bonds in polyfluorinated alkenes is rare and usually requires mild reaction conditions,and hydrogenolysis of fluorine without reduction of the double bond in catalytic hydrogenation is unknown. Numerous examples are quoted in the review literature, " and a few samples are shown in Table 1. 

Nonphotochemical cycloadditions of hexafluorothioacetone to alkenes (vinyl ethers, vinyl sulfides, " cyclohexene, and dimethyl maleate " ) have been observed, as illustrated for methyl vinyl ether. The formal addition of thiocarbonyl fluoride to tetrafluorethylene to give hexafluorothietane occurs on thermolysis at 600-700° (lO " mm) of a copolymer of the two components. " QO-Dimethyldithiooxalate undergoes a thermal cycloaddition to quadricyclane to give thietane 51a. ... 

Competing reactions to addition to a-hetero-substituted alkenes are metallation of vinylic or allylic protons (see 5.5.2.3.2) and cleavage of the carbon-hetero-element bond (see 5.5.2.2.1.). a-Metallations occur with vinylic chlorides, fluorides and ethers no addition of RLi occurs with vinyl fluorides, chlorides or ethers. For vinylic sulfides and selenides, whether metallation or addition (or even carbon-heterobond cleavage) occurs depends on the conditions and reagents. Addition of RLi (R = Et or n-Bu, not Ph) occurs to aryl vinyl sulfides ... 

The method employing the sequential alkylation and elimination of sulfoxides, reported above, has been successfully applied to the synthesis of dienes (Scheme 86, entry c), aryl alkenes and dienes (Scheme 47), vinyl sulfides, a,3-unsaturated sulfoxides, vinyl fluorides and vinyl chlorides (Scheme 96, entry a), and 1,1-dichloro-l-alkenes (Scheme 96, entry b). ... 

This method for bromofluorination of ethylenic compounds has been extended by others to symmetrical alkenes,10 terminal allylic alcohols,11 vinyl oxiranes,12 enol esters,13 and vinyl fluorides.14... 

Similar reactions with haloalkenes lead to simultaneous halogenation at the C=C bond. Vinyl chloride reacts at -40 to -20 °C to give a 70% combined yield of (1,2-dichloroethyl)-and (2,2-dichloroethyl)-phosphonic dichlorides, which can be separated in an indirect fashion which results in the loss of the latter ". The reaction has also been applied to vinyl fluoride and vinyl bromide Prop-2-enyl chloride gives a good yield of (2,3-dichloro-propyl)phosphonic dichloride " and 1,2-dichloroethene yields (1,2,2-trichloroethyl)phos-phonic dichloride. Other halogenated alkenes, H2C=CHR, where R is CCI3 or C F2 +i (n = 4,6, 8 or 10), yield only the phosphorodichloridates RCH(CH2Cl)0P(0)Cl2. ... 

Vinyl fluorides. BrF, generated from NBA and HF in ether, adds to alkenes to form t /c-bromofluoroalkanes in high yield. These products are dehydrobromi-nated by KOH either in DMSO (20-25°) or in triethylene glycol (150°). ... 

Synthesis of Vinyl Fluorides. Addition of potassium bis(tri-methylsilyl)amide to /3-fluoro- -silyl alcohols was shown to selectively effect a Peterson-type alkenation reaction to form vinyl fluorides (eq 21). Treatment of a primary -fluoro- -silyl alcohol with KN(TMS)2 led cleanly to the terminal alkene. Use of a sy -substituted secondary alcohol led to the stereoselective formation of the (Z)-substituted alkene (eq 22) reaction of the anft -isomer, however, demonstrated no (Z E) selectivity. 

While partially fluorinated alkenes such as vinyl fluoride and vinylidene fluoride polymerize with the same facility as tetrafluoroethylene, the latter is unique in the class of the perfluoroalkenes with the respect to the ease of polymerization as will be described later. Perfluoroalkenes such as hexafluoropropylene (HFP) and hexafluorobutadiene polymerize only with great difficulty as the result of the steric inhibition in the propagation step [598]. HFP can be converted to high-molar-mass polymer only at pressures above 1000 atm. The polymerizations are carried out most conveniently in a perfluorinated solvent using perfluorinated free-radical initiators [599]. For the polymerization of hexafluorobutadiene, similar conditions are reported [600]. Due to these very drastic polymerization conditions, these oligomers/polymers are not yet commercially applied. 

Vinyl Halides. E- or Z-Vinyl fluorides can be prepared stereospecifically by rra 5-addition of BrF (prepared in situ from NBS and HF- pyridine complex) to alkenes followed by /rans-coplanar elimination of HBr (Scheme 44) in a sequence very similar to one featured in an earlier Report (3,153). Both isomers... 

It would be convenient to start from an alkene and generate the vinyl fluoride through C—H activation... 

Vinyl Halides. A recently reported method for the production of vinyl fluorides from alkenes employs the reaction with iV-bromoacetamide in the presence of HF, as an equivalent to electrophilic addition of the unstable BrF, and subsequent elimination of HBr (Scheme 42). ... 

The reaction can be done intramolecularly. N-Benzyl pent-4-ynamide reacted with tetrabutylammonium fluoride to an alkylidene lactam. Similar addition of a tosylamide-alkene, with a palladium catalyst, led to a vinyl Al-tosyl pyrrolidine. Similar cyclization reactions occur with tosylamide-alkynes. ... 

It should be noted that addition of the tributyltin radical to 1-fluoro-1-(phenylsulfonyl)ethene provides phenyl vinyl sulfone as the only isolated product. However, 2-trimethylsilyl-1-fluoro-1-(phenylsulfonyl)ethene reacts with tributyltin hydride in the presence of AIBN to provide (E)-2-trimethylsilyl-1-fluoro-1-tributylvinylstannane. The vinylstannane is an equivalent for the synthon "H2C=CF " providing a convenient route to 2-fluoro-1-alkenes.8 The trimethylsilyl group can be removed with potassium fluoride in dimethyl sulfoxide-water or oxalic acid-methanol at the end of the reaction sequence. 

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. 

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