Isomerization of monohydroperfluoroalkenes

Synthesis and Spectroscopic Characterization of Potassium Polyfluoroalken-1-yltrifluoroborates

“…With R = CF 3 or C 2 F 5 , they can be obtained by the isomerisation of trans-CF 3 CF=CFH or CF 2 =CFCF 2 CF 2 H with SbF 5 [6,7]. This procedure can not be applied to hydroperfluoroalkenes with longer chains because they give a mixture of internal isomers in addition to the desired products [8]. We assumed that the formation of CF 2 =CFLi from CF 3 CFH 2 via CF 3 CFHLi developed by different English groups [9] may have a general character, and that the elimination of LiF from the related intermediate RCF 2 CFHLi may lead to cis-olefins RCF=CFH rather than to trans-olefins.…”

“…After evaporation of the solvent the brownish viscous oil was washed with benzene (3´5 ml) and with CFCl 3 (5´10 ml) and dried in vacuum to yield potassium cis-perfluoroocten-1-yltrifluoroborate (4.8 g, 49%). C 8 Potassium cis-heptafluorobuten-1-yltrifluoroborate (3). A solution of cis-1 H-heptafluoro-1-butene (13.9 g, 76 mmol) in ether (300 ml) was cooled to ±85°C and 2.5 M BuLi in hexane (32 ml, 80 mmol) was added drop by drop within 15 min at £ ±85°C.…”

An efficient stereoselective preparation of cis-perfluoroalkenylzinc reagents [(E)-RFCFCFZnCl] by the metallation of 1H,1H-perfluoroalkanes and their derivatization to cis-1-arylperfluoroalkenes [(Z)-RFCFCFAr]

“…Trans-1-iodo-perfluoroalkenes ((Z)-R F CF CFI) are well known and are prepared either by metallation of the (E)-R F CF CFH, followed by iodinolysis [69,70] or thermal decomposition of the perfluoroalkyl Grignard reagents [71,72]. However, the cis-1-iodoperfluoroalkenes ((E)-R F CF CFI) are less conveniently available and more difficult to synthesize, especially the higher homologues [the higher homologues other than R F = CF 3 , C 2 F 5 ] cannot be prepared by the SbF 5 catalyzed isomerization of ((E)-R F CF CFH) [58,62,63]. Iodinolysis of the cisperfluoroalkenylzinc reagent generated by our in situ metallation method could eventually give to the corresponding cis-1-iodo-perfluoroalkenes.…”

“…The corresponding precursors for the cis-iodide, [(E)-R F CF CHF] are less conveniently available than the trans-isomers. They have been synthesized by the isomerization of (Z)-R F CF CHF (R F = CF 3 , C 2 F 5 -) using SbF 5 [58,62], but this methodology was not feasible for perfluoroalkenes with longer chains due to the formation of internal isomers in addition to the desired product [63]. So the synthesis of (Z)-1-arylperfluoroalkenes is rather difficult and it is useful to develop a methodology that would generate them exclusively in good yield.…”

Introduction of Fluorine

“…Scheme 2.44Fluoride ion-induced rearrangements of perfluoroolefins leading to a reduced number of fluorine atoms bound to sp 2 carbon (R = CF 2 CF 2 CF 2 CF 2 H)[100,101]. The estimated enthalpies of the rearrangements are −5.2 kcal mol −1 in (a) and −15.0 kcal mol −1 in (b) (for R = CH 3 ; calculation at the HF/6-31G*//HF/6-31G* level of theory)[23].…”