Antimony Fluoride isomerization

Isomerization of fluoroolefins by a shift of a double bond is catalyzed by halide 10ns [7] The presence of crown ether makes this reaction more efficient [74] Prolonged reaction time favors the rearranged product with an internal double bond (equations 3-5) Isomerization of perfluoro-l-pentene with cesium fluoride yields perfluoro-2-pentenes in a Z ratio of 1 6 [75] Antimony pentafluoride also causes isomenzation of olefins leading to more substituted products [76]... 

The possibility of obtaining stable alkylcarbonium hexafluoro-antimonate salts by interaction of alkyl fluorides with antimony pentafluoride (neat or in sulphur dioxide and later in sulphuryl fluoride or sulphuryl chloride fluoride solution) was then evaluated in detail, extending the investigations to all isomeric C3-, C4-, C5- alkyl fluorides. 

Seven isomeric pentyl fluorides, including neopeniyl fluoride, gave the same tertiary carbonium ion (i.e. dimethylethylcarbonium ion. Table 6). Thus, in the strongly acidic antimony pentafluoride, complete... 

The reaction of 5-substituted l.l,3.3-tetrachloro-1.3-dihydroisoben7.ofui ans (R = H, MeO, halogen) with antimony(lll) fluoride is accompanied by partial isomerization of the starting substrates into 2-(trichloromethyl)-5-substituted benzoyl chlorides followed by fluorination of the cyclic and acyclic compounds. No such isomerization is observed when 1,1,3.3-tetrachloro-... 

Chloroheptafluorobut-l-ene (3) isomcrizes in the presence of antimony(V) fluoride to give an E Z mixture of but-2-ene 4.8 4-Chloroheptafluorobut-l-ene also gives the isomeric but-2-cne (see also Section 5.1.2.2.). 

When w.//-perfluoroalk-l-enes longer than butene [CHF2(CF2)nCF = CF2, n = 2-7] are isomerized under conditions of thermodynamic control, however, mixtures of all possible positional isomers are obtained. Isomerization of these aik-1 -enes with antimony(V) fluoride under conditions of kinetic control yields the corresponding alk-2-enes as an EjZ mixture.20... 

The vapor-phase pyrolysis of pcrfluorohept-1-ene at 400 C in the presence of carbon results in complete conversion into the isomeric hept-2- and hept-3-enes in a ratio of 1 3.4.34 As noted above, mixtures are also obtained with cesium fluoride and letraelhylammonium fluoride. Only the antimony(V) fluoride reaction allows selective rearrangement to the alk-2-ene. 

Perfluorotetrahydronaphthalene 5 is isomerized with antimony(V) fluoride to the corresponding 1.2,3,4-tetrahydronaphthalene 6 quantitatively and at low temperature, indicating that aromatization is favored,3,39... 

Perfluoropenta-1,4-diene (10) isomerizes in the presence of antimony(V) fluoride to an E jZ mixture of 1,3-diene 11.41 Heating 11 at 90 C with antimony(V) fluoride gives cyclodimer 12, presumably via allene intermediate 13. 

Heating with antimony(V) fluoride can result in cyclization to perfluoro(1.2-dialkylcy-clopentenes) (excess SbF5) or to perfluoro(l,2-dialkylcyclobutenes) (catalytic SbF5), as has been reviewed by Krespan and Petrov.21 Thus, heating perfluoroocta-2,6-diene (28) in the presence of a threefold excess of antimony(V) fluoride gives perfluoro(l-ethyl-2-methylcy-clopentene) (29) in 90% yield.22,23 In the presence of a catalytic amount of antimony(V) fluoride, 28 is converted into isomeric cyclobutenes 30 and 31 together with cyclopentene 29. 

The cyclopropanation of a,/S-unsaturated aldehydes and ketones by a-diazocarbonyl compounds to give diacylcyclopropanes 1 is promoted by antimony(V) fluoride. Best yields were obtained when equimolar amounts of diazo compound and Lewis acid were applied. Since the Lewis acid also promotes geometrical isomerization of the 1,2-diacylcyclopropanes so obtained, the diastereomer ratio of the latter depends on the temperature and on the molar ratio of diazo compound and Lewis acid. 

In similar fashion and in contrast to its isomerization by fluoride ion and other bases to perfluoropropionyl fluoride (6), HFPO is transformed by Lewis acids such as antimony pentafluoride ° or aluminum chlorofluoride into another isomer, hexafluoroacetone (20). 

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