Perfluoroalkenes electrophilic attack

Problems of orientation of attack and reactivities of fluorinated alkenes arise in a way that is analogous but entirely complementary to the classical problems of electrophilic attack on alkenes. For example, typical of the results that we must be able to account for is the reaction of methoxide in methanol which occurs specifically at the Cp2= site in perfluoropropene (Figure 7.15). Also, there is a very wide range of reactivity with perfluoroalkenes for example, reactions of tetrafluoroethene usually require base catalysis, whereas perfluoroisobutene reacts with neutral methanol. 

For this reason, electrophilic additions such as addition of hydrogen halides are very difficult, as can be seen in Explanations 13, 14, and 15. But because of the low overall electron density, the double bonds in perfluoroalkenes are easily attacked by nucleophiles such as fluoride ion. If perfluoropropene is treated with dry potassium fluoride in a proton-donor solvent such as formamide, the fluoride anion joins the less negative carbon of the double bond and forms a negatively charged intermediate that readily reacts with the proton of formamide to give 2 H-perfluo-ropropane [5/]. Such a nucleophilic addition takes place with other fluorides such as cesium fluoride, tetraethylammonium fluoride, and sil-... 

The nucleophilic phosphorus atom in the bromopcntafluorobenzene/tris(diethylamino)-phosphane system attacks the bromine, affording a phosphonium cation and a carbanion. The subsequent reactions of these species depend on the presence of C-electrophiles. It has been shown that this system is convenient for the introduction of the polyfluoroaryl fragment into polyfluoro aromatic compounds and perfluoroalkenes examples are given by the formation of7-n. - - ... 

Fluorinated epoxides are very important synthetically. Perfluoroalkenes can be oxidized by numerous means to the corresponding epoxides. The most commonly encormtered epoxide is hexafluoropropene oxide (HFPO), which is made from hexafluoropropene and is used in the synthesis of oligomers and as a source of difluorocarbene. HFPO is a colorless, nonflammable gas, boiling at -27.4 °C it can be ring-opened easily by nncleophiles or electrophiles imder a variety of conditions. HFPO can be rearranged by flnoride ion to perfluoropropionyl flnoride and by Lewis acids snch as UO2 to hexafluoroacetone (HFA). Nncleophiles typically attack the most substituted carbon of the epoxide, freeing the oxyanion to lose fluoride or act as a nucleophile itself Some examples of HFPO reactivity are shown in Scheme 3. 

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