Reactions of novel unsaturated fluorocarbons

Article abstract of DOI:10.1016/S0022-1139(00)00246-3

Novel fluorinated mono-enes and di-enes have been synthesised via telomerisation reactions using (CF₃)₂CFI with CF₂=CH₂ and also with CF₂=CFH. Cyclo-additions with diazomethane occur readily to give Δ¹ or Δ² pyrazolines, depending on the system, and nucleophilic attack occurs with methanol and with fluoride ion. In the latter case, stable carbanions have been observed. A novel free-radical route to seven-membered rings, arising from cyclo-addition of dimethyl- and diethyl-ethers to the diene [(CF₃)₂C=CHCF₂-]₂ (3), has been developed.

Full text of DOI:10.1016/S0022-1139(00)00246-3

Journal of Fluorine Chemistry 104 (2000) 239±246
Reactions of novel unsaturated ¯uorocarbons
Richard D. Chambers*, Martin Salisbury
University of Durham, Department of Chemistry, South Road, Durham, DH1 3LE, UK
Received 10 December 1999; accepted 28 January 2000
Abstract
Novel ¯uorinated mono-enes and di-enes have been synthesised via telomerisation reactions using (CF3)2CFI with CF2=CH2 and also
with CF2=CFH. Cyclo-additions with diazomethane occur readily to give D1 or D2 pyrazolines, depending on the system, and nucleophilic
attack occurs with methanol and with ¯uoride ion. In the latter case, stable carbanions have been observed. A novel free-radical route to
seven-membered rings, arising from cyclo-addition of dimethyl- and diethyl-ethers to the diene [(CF3)2C=CHCF2±]2 (3), has been
developed. # 2000 Elsevier Science S.A. All rights reserved.
Keywords: Fluorinated alkene; Fluorinated diene; Pyrazoline; Free-radical addition; Stable carbanion; Cyclic ether
1. Introduction
tuted site at the double-bond in 1. This implies that the
process involves partial nucleophilic attack by the methy-
lene site on 1 as indicated in 4, because we have already
demonstrated that attack by other nucleophiles occurs exclu-
sively at the (CF3)CH= site in this molecule [2].
The double bonds in di-ene 3 are electronically closely
similar to the double-bond in 1 and consequently 3 reacts
with diazomethane in a similar way giving 7 (Scheme 3). In
this case, the product appeared to be solely in the D1
pyrazoline form 7 although it is not wholly clear why
rearrangement to the D2 isomer does not occur. However,
it is useful to note that the CH2 sites in 7 have one less
neighbouring acidifying ¯uorine atom than the correspond-
ing CH2 group in 5.
We have previously described the synthesis of model
compounds that relate to co-polymers of 1,1-di¯uoroethene
and hexa¯uoropropene, via telomerisation reactions using
iodoper¯uoroalkanes and 1,1-di¯uoroethene. In this work,
processes leading to the novel mono-enes 1 and 2 and di-ene
3 were described and these are outlined in (Scheme 1)
[1,2]. Here, we describe some further chemistry of these
unusual unsaturated systems, and also we include the synth-
esis of some analogous systems derived from tri¯uor-
oethene.
2. Results and discussion
Like other ¯uorinated alkenes [4], di-ene 3 reacts readily
with nucleophilic free-radicals e.g. those derived from
methanol and from ethers (Scheme 3). With methanol, only
a mono-addition product 8 is obtained but with ethers, a
fascinating cyclisation process occurs, which provides a new
approach to the construction of seven-membered rings. The
products of reaction of dimethyl- and diethyl- ether are the
oxepanes 9 and 10, respectively, indicated in (Scheme 3),
formed via an intramolecular `back-biting' hydrogen atom
transfer step, i.e. 12, 13, shown in (Scheme 4). This general
process is now well established [5,6] but it has not hitherto
been exploited in ring formation. The ring-closure stage, 13,
13a, (Scheme 4), is a 7-exo-trig, which is obviously favoured
and is consistent with Baldwin's rules [7].
In an earlier paper [3], we demonstrated that per¯uor-
oalkyl groups directly attached to a double bond enhance
reactivity towards diazomethane, whereas a ¯uorine atom
has little effect relative to hydrogen. Consistent with these
earlier ®ndings, compound 1 reacted readily with diazo-
methane, giving a mixture of the D1 and D2 pyrazolines 5
and 6, in the ratio of 3:5, respectively, (Scheme 2). It is
noteworthy that the addition is regioselective, with the
methylene site of diazomethane attacking the least substi-
* Corresponding author. Tel.: ‡44-191-374-3120;
fax: ‡44-191-384-4737.
Reaction of mono-ene 2 with methoxide in methanol
promotes elimination of hydrogen ¯uoride, no doubt via
E-mail address: r.d.chambers@durham.ac.uk (R.D. Chambers)
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 0 ) 0 0 2 4 6 - 3

240
R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
Scheme 1.
Scheme 2.
Scheme 3.

R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
241
Scheme 4.
deprotonation of the extremely acidic (CF3)2CH site, fol-
lowed by loss of ¯uoride ion to give 14 which reacts further,
to give the methoxy compound 15, (Scheme 5). However,
we can synthesise the diene 14 by heating 2 with anhydrous
potassium ¯uoride in a sealed system, (Scheme 5). This
potentially valuable new di-ene reacts with ¯uoride-ion, in
the presence of tetraglyme at ambient temperature, to give a
stable, observable allyl anion 16. The important feature of
the 19F NMR spectrum of 16 is the signal at dFˆ 45.5 ppm
(relative intensity, 6) which arises from two tri¯uoromethyl
groups directly attached to the carbanion centre, while
signals arising from the =CF2 in 14 disappeared. The
signals, in 16, are entirely consistent with the chemical
shifts of closely related observable carbanions that we have
described previously [8,9], (Scheme 5). In comparison with
the neutral precursor 14, the ¯uorine resonance associated
with tri¯uoromethyl groups adjacent to the charge in the
anion 16, i.e. CF3C are deshielded on formation of the ion.
Furthermore, the signal associated with the vinylic ¯uorine
contained in the cyclopentene ring in 16 is also deshielded,
clearly indicating delocalisation of charge in the anion.
Indeed, this is the ®rst example of an observable ¯uorinated
carbanion where a ¯uorine atom is formally directly
attached to a charged site, although more charge probably
resides on the (CF3)2C site. Thus, when the ion 16 was
trapped with bromine, 17a was formed, i.e. with bromine
attacking the (CF3)2C site, although we are unable to rule
out the presence of small amounts of the alternative isomer
17b. Because the product 17 is a very crowded system, it is
relatively unstable and an analytically pure sample could not
be isolated, (Scheme 5).
We have also synthesized analogous telomers to those
described in (Scheme 1), using tri¯uoroethene in place of
1,1-di¯uoroethene. The overall process leading to the
mono-ene 19 [10] and the new saturated compound 20 is
outlined in (Scheme 6). The compound 20 is less reactive
towards Lewis acid induced elimination of hydrogen ¯uor-
ine, i.e. using antimony penta¯uoride, than the correspond-
ing compound derived from 1,1-di¯uoroethene (see
Scheme 1) and, therefore, elimination from 20 required
the use of caesium ¯uoride or tributylamine (Scheme 7).
However, whether caesium ¯uoride or tributylamine was
used, cyclisation of the presumed intermediate di-ene 23
occurred, giving eventually 21 and 22 (Schemes 7 and 8). As
indicated, tributylamine gave a mixture of 21 and 22
whereas caesium ¯uoride gave only 21. The latter has, in
effect, more stabilising per¯uoroalkyl groups attached to the
double-bond [9].
The terminal per¯uorinated alkene 19 is readily iso-
merised to the thermodynamically more stable isomer 24,
using catalytic amounts of caesium ¯uoride. Hydrogen and
¯uorine atoms directly attached to a double bond have little
in¯uence on reactivity towards diazomethane [3] and, there-
fore, compound 24, (Scheme 9), reacts with diazomethane
in a similar fashion to compound 1 in (Scheme 2). In this
case, however, only the D2 isomer 25 was observed and this
is consistent with the increased acidity of the CH2 group in
the D1 isomer 25a, promoting rearrangement. Therefore, in

242
R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
Scheme 5.
Scheme 6.
Scheme 7.

R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
243
Scheme 8.
the series that we have described here, the occurrence of the
D1 isomer decreases with apparent increase in acidity of the
CH2 in the various D1 isomers.
Furthermore, the CF2 signal is also deshielded, with respect
to appropriate neutral model compounds, while the signal
arising from the tri¯uoromethyl group in CF3CF2C is
signi®cantly shielded (dF 87.5 ppm) with respect to the
corresponding signal from CF3C sites, (Scheme 9). These
observations, for both ions 16 and 28, con®rm the trends that
we have noted previously, that shielding and deshielding for
observable anions alternate in the series C -CF(de-
shielded)-CF (shielded).
The double-bond in 24 is extremely susceptible to nucleo-
philic attack and it reacted even with neutral methanol at
208C to give 26 and 27, (Scheme 9). Also, reaction of 24
with caesium ¯uoride in tetraglyme gave the stable obser-
vable carbanion 28, (Scheme 9). This ion is analogous to the
poly¯uoro-t-butyl anion that we have described previously
[8,9] and the ¯uorine resonance associated with CF3C in
28 occurs at dF 42.0 ppm (cf. 45.8 for (CF3)3C ).
No further chemistry was carried out on 24 because the
extreme reactivity of this compound towards nucleophiles
Scheme 9.

244
R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
parallels that of the highly toxic per¯uoroisobutene,
(CF3)2C=CF2, and we must therefore assume 24 to have
a similarly high level of toxicity.
consist of two components with similar retention times
which were identi®ed as i) 4,5,5-tris (tri¯uoromethyl)-4,
5-dihydro-3H-pyrazole (5), dH 4.8 (2H, AB, J 20, NCH2),
5.0 (1H, m, C(CF3)H); dF 60.7 (3F, m, C(CF3)H), 71.9
‡
and 72.9 (6F, m, C(CF3)2; m/z 274 (M 55%), 266
‡
3. Experimental
(M 28, 21%) and 4,5,5-tris (tri¯uoromethyl)-4,5-dihy-
dro-1H-pyrazole (6), dH 5.0 (1H, m, C(CF3)H), 6.6 (1H,
br, N=CH), 7.8 (1H, br, NH); dF 60.7 (3F, m, C(CF3)H),
71.9 and 72.9 (6F, m, C(CF3)2; m/z 274 (M 65%), 164
It should be assumed that all unsaturated ¯uorinated
compounds are potentially toxic, especially those that are
extremely susceptible to nucleophilic attack. Appropriate
safe-handling procedures e.g. vacuum systems, sealed ves-
sels and high-grade fumes-cupboards, should be employed
when working with these compounds.
Infrared spectra were recorded on a Perkin±Elmer
577 Infrared Spectrophotometer. Solid samples were
recorded as KBr discs, liquids as contact ®lms between
KBr plates and volatile samples in a cylindrical cell with
KBr windows.
1H and 19F NMR spectra were recorded on a Varian
EM36OL spectrometer operating at 60 and 56.4 MHz,
respectively, at the ambient probe temperature (408C) and
on a BruÈker HK90 with Fourier Transform facility at
elevated temperatures. Chemical shifts are quoted in ppm
relative to TMS and CFCl3. Carbon (13C) spectra were
recorded on a BruÈker WH-360 operating at 90.6 MHz.
Chemical shifts are quoted in ppm relative to TMS.
Mass spectra were recorded on a V.G. 7070E spectro-
meter equipped with electron-impact, negative ion (NH3
gas) and chemical ionization (i-C4H10) facilities together
with a capilliary column gas chromatograph. Spectra were
also recorded on a VG Micromass 12B spectrometer ®tted
with a Pye 104 gas chromatograph.
Gas liquid chromatographic analyses were carried out on
Varian Aerograph Model 920 or Pye Unicam GCD chro-
matographs using columns packed with diisodecylphthalate
(10 and 20%) on chromasorb P (column A), 20% Krytox
(per¯uoropolyoxypolylene) on chromasorb P (column K)
and Silicon elastomer (5, 10 and 20%) on chromasorb P
(column O). Preparative scale gas liquid chromatography
was performed on a Varian Aerograph Model 920 using
columns A, K and O.
‡
(M C(CF3)2NH, 18%); nmax cm 1, 1750 (s), 1290 (s br),
‡
1200 (s br).
3.1.2. Reaction of 3,6-dihydrohexadecafluoro-2,7-
dimethylocta-2,6-diene (3) with diazomethane
Compound 3 (1 g, 2.2 mmol) and diazomethane gave a
white solid (1.1 g) which was recrystallised from dichlor-
omethane and identi®ed as 1,2-di-(5,5-bistri¯uoromethyl-
4,5-dihydro-3H-4-pyrazolo)-tetra¯uoroethane (7), (Found:
C, 28.4; N, 11.2; F, 59.9. C12H6F16N requires C, 28.2; N,
11.0; F, 59.6%); dH 3.2 (2H, m, CH(CF2 ), 4.4 and 5.3 (4H,
AB, J 18, NCH2); dF 65.0 and 69.0 (6F, m, C(CF3)2), ca.
109.7 (4F, overlapping ABs, (CF2)2±); m/z (CI/i-butane)
‡
‡
1
511 ((M‡1) , 73%), 483 ((M‡1) 28, 16%); nmax cm
,
1600 (br w), 14009 (w), 1250 (s br), 1200 (s br).
3.2. Reactions of 3,6-dihydrohexadecafluoro-2,7-
dimethylocta-2,6-diene (3) induced by g-radiation
Mixtures of (3) with methanol, dimethylether and diethy-
lether sealed in glass tubes under vacuum were irradiated by
g-radiation until reaction was complete. The volatile reac-
tion products were separated from polymeric residues by
reduced pressure distillation, then pure samples of the
products were obtained by preparative scale glc.
3.2.1. Reaction of 3,6-dihydrohexadecafluoro-2,7-
dimethylocta-2,6-diene (3) with methanol
Compound 3 (1.9 g, 4.5 mmol) and methanol (0.3 g,
10 mmol) yielded 3-hydroxymethyl-hexa¯uoro-2,7-dime-
thyloct-6-ene (8), m.p. 738C (from dichloromethane),
(Found: C, 29.5; H, 1.1. C11H6F16O requires C, 28.8; H,
1.3, F, 60.8%); dH 3.2 (1H, m, CF2CH{CH2OH}{CH-
(CF3)2}), 3.4 (2H, m, CF2CH{CH2OH}{CH(CF3)2}), 4.0
(1H, m, CF2CH{CH2OH}{CH(CF3)2}), 5.9 (1H, t Jˆ13,
=CHCF2); dF 61.0 (3F, m, =CCF3), 65 to 67 (9F, m,
=CCF3 and ±CH(CF3)2), 124.3 (4F, m, 2ÂCF2); m/z (CI/i-
3.1. Reactions with diazomethane
Diazomethane was prepared by the method of de Boer
and Becker [11]. Stirred solutions of the substrates in diethyl
ether were cooled to 08C and diazomethane in ether was
slowly added until the yellow colour persisted. The reaction
mixture was allowed to warm to room temperature and the
solvent was removed by vacuum distillation. The crude
product was puri®ed by vacuum transfer.
‡
butane) 459 ((M‡1) , 9%).
3.2.2. Reaction of 3,6-dihydrohexadecafluoro-2,7-
dimethylocta-2,6-diene (3) with dimethyl ether
Compound 3 (1.3 g, 3.1 mmol) and dimethyl ether (0.3 g,
6 mmol) yielded 3,6-bis (2H-hexa¯uoro-2-propyl)-4,4,5,5-
tetra¯uorooxepane (9), dH 3.3±4.0 (broad); dF 60 to
64(12F, m, 4ÂCF3), 112 to 122 (4F, overlapping
3.1.1. Reaction of 2H-nonafluoro-(3-methylbut-2-ene) (1)
with diazomethane
Compound 1 (5.0 g, 22 mmol) and diazomethane yielded
5.0 g of a colourless liquid which was shown by GLC to
‡
ABs, CF2); m/z (CI/i-butane) 473 ((M‡1) , 8%).

R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
245
3.2.3. Reaction of 3,6-dihydrohexadecafluoro-2,7-
dimethylocta-2,6-diene (3) with diethyl ether
dropwise to a stirred suspension of CsF (0.5 gm) in dry
tetraglyme (2 ml). After about 10 min, the 19F NMR was
recorded and found to be different from that of the starting
material 14. Most noteworthy was the resonance at
45.5 ppm, which is indicative of the formation of a
carbanion, (6F, C (CF3)2) [8,9] (16). Other resonances
were at 61.0 and 62.4 (6F, >C(CF3)2), 109.0 (1F,
=CF), 122.6 (2F, CFHCF2CF=), 210.8 (1F, CFH),
(Scheme 5). After several hours, additional resonances
appeared and that at 45.5 ppm disappeared, indicating
decomposition of the carbanion.
Compound 3 (3.0 g, 7.0 mmol) and diethyl ether (0.5 g,
7 mmol) yielded 2,7-dimethyl-3,6-bis-(2H-hexa¯uoro-2-
propyl)-4,4,5,5,-tetrahydrooxepane (10), (Found: C, 33.7;
H, 2.1, F, 61.3. C14H12F16O requires C, 33.6; H, 2.4, F,
60.8%); dH 1.3±1.7 (8H, m, 2CH3 and 2(CF3)2CHCH), 3.3
(2H, m, 2C(CH3)H), 3.9 (2H, m, 2(CF3)2CH); dF 61 to
67 (12F, m, 4ÂCF3), 120 to 123 (4F, overlapping ABs,
‡
2ÂCF2); m/z (CI/i-butane) 501 ((M‡1) , 33%); m/z (EI)
‡
249 (M (CF3)2H, 8%).
3.3. Reactions of 1-(2H-hexafluoro-2-propyl)-3-hydro-
decafluoro-2,2-dimethylcyclopentene (2)
3.3.2.2. Reaction of 16 with bromine. The carbanion 16
was generated as described above and then bromine (ca.
0.5 g, 3.3 mmol) was slowly added to the stirred mixture.
After stirring for a further hour, water was added and the
fluorocarbon layer was separated. Analytical scale GLC
showed the reaction product to consist of starting material
14 and 1-(2-bromohexafluoro-2-propyl)-3-hydrofluoro-2,2-
3.3.1. Reaction of 2 with methoxide
Freshly cut sodium (0.1 g, 5 mmol) was added to dry
methanol (5 ml) and stirred at room temperature for 1 h
under dry nitrogen, after which 2 (2 g, 4 mmol) was added
over a period of 10 min. with further stirring. After about
30 min, the reaction mixture was poured into water and the
organic components were extracted with dichloromethane.
Solvent was distilled from the dried DCM solution and the
residue was distilled under reduced pressure to give a
colourless liquid (1.4 g) which was shown by GLC to
consist of two main components. Each of these was isolated
by preparative scale GLC and identi®ed as starting material
and 1-(2-methoxytetra¯uoropropyl-2-enyl)-3H-deca¯uoro-
2,2-dimethylcyclopentene (15), (Found: C, 31.8; H, 0.8, F,
63.6. C11H4F14O requires C, 31.6; H, 0.96, F, 63.6%); dH 3.8
‡
dimethylcyclopentene (17), m/z 425 (M Br, 9%), 275
‡
(M C(CF3)2Br, 1.0%), 231 (C(CF3)2Br (Brˆ81), 0.5%,
229 (C(CF3)2Br (Brˆ79), 0.5%. (NB A pure sample of (17)
could not be obtained due to its instability).
3.3.2.3. Preparation and reactions of telomers of
heptafluoro-2-iodopropane and trifluoroethene. Telomers
of heptafluoro-2-iodopropane and trifluoroethene were
prepared by the method described for the telomerisation
of 1,1-difluoroethene with heptafluoro-2-iodopropane [2]
and the products were identified by comparing their
physical properties and spectra with those of these same
telomers described in the literature [10]. 2H-1-iodode-
cafluoro-3-methylbutane (18) was dehydroiodinated using
powdered potassium hydroxide as described in the literature
[10] to give perfluoro-3-methylbut-1-ene, (19).
2
3
(3H, s, OCH3), 5.4 (1H, dd, JHFˆ48, JHFˆ15, C(CF3)2-
CFHCF2); dF 57.8 (3F, m, =CCF3), 65.3 and 70.0 (6F,
br, >C(CF3)2), 71.0 (1F, d, Jˆ12.5, acyclic =CF), 111.9
3
(2F, overlapping ABs, CF2), 119.8 (1F, t, JFFˆ12.5,
‡
cyclic ˆCF), 210.9 (1F, m, CFHCF2); m/z 418 (M ,
100%).
3.3.2.4. Coupling of 2H-1-iododecafluoro-3-methylbutane
(18) to give 3,6-dihydroeicosafluoro-2,7-dimethyloctane
(20). A sealed glass tube, charged with 18 (19 g,
26 mmol) and mercury (10 ml), was shaken while being
exposed to a 1 kW UV lamp for 7 days. After this treatment,
volatile material (5.8 g) was separated from other products
by vacuum transfer and identified as 3,6-dihydroei-
cosafluoro-2,7-dimethyloctane (20); (Found: C, 23.1; H,
0.6, F, 75.1. C10H2F20 requires C, 23.9; H, 0.4, F,
3.3.2. Heating 2 with potassium fluoride
Compound 2 (2.0 g, 4.7 mmol), in the vapour phase, was
passed through a bed of anhydrous potassium ¯uoride
heated to 3008C and the products (1.8 g) were collected
in a trap at 1968C. The trapped material was shown by
GLC to consist of two components which were separated by
preparative scale GLC and identi®ed as starting material and
1-(penta¯uoropropyl-2-enyl)-3H-deca¯uoro-2,2-dimethyl-
cyclopentene (14) (Found: C, 29.3. C10HF15 requires C,
2
75.7%); dH 5.1 (d, JHFˆ40, CFH); dF 74.0 and 77.7
2
3
4
29.6%); dH 5.0 (1H, ddd, JHFˆ48, JHFˆ15, JHF 5,
C(CF3)2CFHCF2); dF 60.0 (3F, br, =CCF3), 66.7 and
71.0 (6F, br, >C(CF3)2), 68.3 (2F, m, acyclic =CF2),
113.2 (2F, overlapping ABs, CF2), 117.2 (1F, t,
3JFFˆ14.0, cyclic =CF), 211.6 (1F, m, CFHCF2); m/z
(12F, br, 4ÂCF3), 114.8 (4F, br, CF2), 186.0 (2F, m, 2Â
‡
(CF3)2CF), 216.0 (2F, br, 2ÂCFH); m/z 483 (M 19).
3.4. Reactions of 3,6-dihydroeicosafluoro-2,7-
dimethyloctane (20)
‡
406 (M , 20%).
3.4.1. Reaction with tri-n-butylamine
3.3.2.1. Reaction of 1-(pentafluoropropyl-2-enyl)-3H-
decafluoro-2,2-dimethylcyclopentene (14), with caesium
fluoride. Compound 14 (1.0 g, 2.5 mmol) was added
A mixture of 20 (1.0 g, 2 mmol) and tri-n-butylamine
(0.8 g, 5.6 mmol) was stirred together for 12 h at 1258C.
Volatile material, removed from the reaction vessel by

246
R.D. Chambers, M. Salisbury / Journal of Fluorine Chemistry 104 (2000) 239±246
vacuum transfer, was found to consist of two components in
almost equal amounts. These were separated by preparative
scale GLC and identi®ed as per¯uoro-2-(prop-2-yl)-3,3-
dimethylcyclopentene (21); dF 65.7 (6F, br, 2ÂCF3),
scale GLC showed the reaction product to consist of
unreacted methanol and an approximately equimolecular
mixture of 2-methoxy-nona¯uoro-3-methylbutane (26); dH
3
3.6 (1H, sept, JHFˆ7, (CF3)2CH, 3.7 (3H, s, OCH3); dF
3
4
75.7 (6F, dq JFFˆ24, JFFˆ5, CF(CF3)2), 107.3 (1F,
m, cyclic =CF), 121.0 and 123.0 (4F, m, CF2CF2-
C(CF3)2), 181.3 (1F, m, CF(CF3)2); m/z (negative ion)
462 (M 11%): and per¯uoro-3-(prop-2-yl)-4,4,-dimethyl-
cyclopentene (22); dF 74.6 (6F, br, 2CF3), 75.0 and
77.8 (6F, m, CF(CF3)2), 118.6 (2F, m, CF2C(CF3)2),
123.3 (2F, m, 2Â=CF), 188.1 and 188.5 (2F, m,
CF(CF3)2 and >CFCF(CF3)2); m/z (negative ion) 462
(M 33%).
60.0 and 64.7 (6F, br, (CF3)2CH), 77.5 (3F, d, 3JFFˆ8,
3
CCF3FOCH3), 130.6 (1F, q, JFFˆ8, CCF3FOCH3); m/z
‡
282 (M ), and 2-methoxy-nona¯uoro-3-methylbut-2-ene
(27), dH 4.0 (3H, s, OCH3); dF 60.0 to 64.0 (br m,
‡
3ÂCF3); m/z 262 (M ).
3.5.3. Reaction with caesium fluoride Ð carbanion
formation
Compound 24 (1.0 g, 4 mmol) was added to a stirred
suspension of CsF (0.5 g) in tetraglyme. After 1 h, the 19F
NMR spectrum indicated formation of a stable anion (28):
dF 42.0 (6F, C(CF3)2), 85.7 (3F, CF2CF3), 95.0 (2F,
CF2CF3) (Scheme 9).
3.4.2. Reaction with caesium fluoride
A mixture of 20 (0.3 g, 0.6 mmol), CsF (0.1 gm) and
sulpholane (0.3 ml) was sealed in a NMR tube using
vacuum line techniques and heated to 1408C for 3 h. After
this treatment, 19F NMR showed that all of 20 had been
converted into 21.
Acknowledgements
3.4.2.1. Isomerisation of perfluoro-3-methylbut-1-ene (19).
A mixture of 19 (5.0 g, 20 mmol), CsF (0.5 g) and
sulpholane (10 ml), in a sealed tube, was heated to 1008C
for 2 h with occasional shaking. After this treatment, the
tube was cooled, opened and the volatile products were
removed by vacuum transfer to give a colourless liquid
(4.5 g) which was identified as perfluoro-3-methylbut-2-ene
(24).
We thank the Ausimont Company, Milan, for ®nancial
support and Dr. John Hutchinson for valuable discussions.
References
[1] G.C. Apsey, R.D. Chambers, P. Odello, J. Fluorine Chem. 77 (1996)
127.
[2] G.C. Apsey, R.D. Chambers, M.J. Salisbury, J. Fluorine Chem. 40
(1988) 261.
3.5. Reactions of perfluoro-3-methylbut-2-ene (24)
[3] M.R. Bryce, R.D. Chambers, G. Taylor, J. Chem. Soc., Perkin Trans.
1 (1984) 509.
3.5.1. Reaction with diazomethane
[4] R.D. Chambers, S.L. Jones, S.J. Mullins, A. Swales, P. Telford,
M.L.H. West, in: J.T. Welch (Ed.), Selective Fluorination in Organic
and Bioorganic Chemistry, American Chemical Society, Washington,
DC, 1991.
Compound 24 (1.8 g, 7.2 mmol) was treated with diazo-
methane as outlined above and there was isolated a colour-
less liquid (1.5 g) identi®ed as 4,5,5-tris (tri¯uoromethyl)-4-
¯uoro-4,5-dihydro-1H-pyrazole (25); dH 6.8 (1H, br, CH),
7.5 (1H, br, NH; dF 68.3 to 71.0 (6F, br m, (CF3)2C<),
75.2 (3F, t, 3JFFˆ14, >CFCF3), 163.7 (1F, m, >CFCF3);
[5] H. Muramatsu, H. Kimoto, K. Inukai, Bull. Chem. Soc. Japan 42
(1969) 1155.
[6] R.D. Chambers, B. Grievson, N.M. Kelly, J. Chem. Soc., Perkin
Trans. 1 (1985) 2209.
‡
m/z (CI/i-butane) 293 (M ‡1, 17%); nmax cm 1, 1600 (w
[7] J.E. Baldwin, J. Chem. Soc., Chem. Commun. (1976) 734.
[8] A.E. Bayliff, M.R. Bryce, R.D. Chambers, R.S. Mathews, J. Chem.
Soc., Chem. Commun. (1985) 1018.
br), 1220 (s br).
[9] A.E. Bayliff, R.D. Chambers, J. Chem. Soc., Perkin Trans. 1 (1988)
201.
3.5.2. Reaction with methanol
A mixture of 24 (1.8 g, 7.2 mmol) and methanol (0.7 g,
21.6 mmol), sealed in a glass ampoule using vacuum tech-
niques, was shaken at room temperature for 6 h. Analytical
[10] G.L. Flemming, R.N. Haszeldine, A.E. Tipping, J. Chem. Soc.,
Perkin Trans. 1 (1973) 574.
[11] T.J. de Boer, H.J. Backer, Org. Synth. 34 (1954) 96.