Isomerisation reaction of a gem-bis-trifluoromethyl olefin in a basic medium: A kinetic study

Article abstract of DOI:10.1016/S0022-1139(01)00446-8

The rearrangement of 5-phenyl-1,1,1-trifluoro-2-(trifluoromethyl)pent-2-ene to 5-phenyl-1,1,1-trifluoro-2-(trifluoromethyl)pent-3-ene has been studied by ¹⁹F NMR in dimethylsulphoxide (DMSO). This isomerisation is catalysed by a base such as tr

Full text of DOI:10.1016/S0022-1139(01)00446-8

Journal of Fluorine Chemistry 111 -2001) 147±152
Isomerisation reaction of a gem-bis-tri¯uoromethyl ole®n
in a basic medium: a kinetic study
Â
Marc Tordeux, Laurence Marival-Hodebar, Marie-Josee Pouet,
Jean-Claude Halle, Claude Wakselman*
à Â
SIRCOB-CNRS, Batiment Lavoisier, Universite de Versailles Saint Quentin en Yvelines, 45avenue des Etats-Unis, 78035Versailles, France
Received 4 March 2001
Abstract
The rearrangement of 5-phenyl-1,1,1-tri¯uoro-2--tri¯uoromethyl)pent-2-ene to 5-phenyl-1,1,1-tri¯uoro-2--tri¯uoromethyl)pent-3-ene
has been studied by 19F NMR in dimethylsulphoxide -DMSO). This isomerisation is catalysed by a base such as triethylamine. It is apparent
that the ole®n is more stable when the two tri¯uoromethyl groups are placed on a saturated carbon rather than on a vinylic carbon. In the
isomerisation process, the part of triethylamine is to assist the intramolecular hydrogen transfer to give the more stable isomer.
# 2001 Elsevier Science B.V. All rights reserved.
Keywords: Isomerisation; Kinetic; 19F NMR; Tri¯uoromethyl ole®n
1. Introduction
1. The phenyl group was only present in order to obtain high
boiling points for the substrate and the products. Instead of the
expected addition, we observed the isomerisation of 1 to 2 -E
con®guration) [7] in dimethylsulphoxide -DMSO) at room
temperature -Scheme 2).
Inasmuch as the conjugation of the double bond with the
aromatic ring in 2 may be a driving force for the isomerisa-
tion in this case, we also examined the behaviour of the
homologous ole®n 3. Since its isomerisation to 4 -E con-
®guration) also takes place in the presence of potassium
thiophenoxide -91% yield) or triethylamine -quantitative)
The effects of per¯uoroalkyl substitution at double bonds
have remained relatively unexplored. Thermally, a single
tri¯uoromethyl substituent slightly destabilises ethylene [1].
However, the in¯uence of a second tri¯uoromethyl substi-
tuent is not known [2]. In the course of our studies on prenyl
synthons [3] particularly on ¯uorinated analogues of iso-
pentenyl adenines [4±6] we observed two different curious
reactions: the anti-Michael addition of nucleophilic reagents
on b,b-bis-tri¯uoromethyl)acrylic esters, followed by ¯uor-
ide ion elimination and also the isomerisation of bis-tri-
¯uoromethyl ole®ns in a basic medium -Scheme 1).
In order to shed some light on the mechanism of this
latter isomerisation reaction, we have performed a kinetic
study.
‡
whose acidities are similar in DMSO -pka ˆ 9:0 for Et3NH
[8]; 9.8 for PhSH [9]), we must conclude that the above-
mentioned conjugation is not the principal reason for the
isomerisation -Scheme 3).
In order to trap a possible intermediate carbanion, the
same experiments were repeated in the presence of good
electrophiles such as benzaldehyde or diphenyldisulphide.
These attempts were unsuccessful. So elucidation of the
mechanism of this isomerisation needed kinetic investiga-
tions. For this purpose, 19F NMR techniques appeared well
adapted for monitoring the reaction [10]. Indeed, in both
systems, the chemical shifts of the 19F nuclei of the non
equivalent tri¯uoromethyl groups of the starting material
were deshielded in comparison with those for equivalent
tri¯uoromethyl groups of 4. Inasmuch as ®rst kinetic experi-
ments conducted in DMSO-d6 were found to be insuf®-
ciently reproducible, probably because of the adventitious
2. Results
In order to check the eventual addition of mild nucleoph-
iles to the double bond of a simple bis-tri¯uoromethyl alkene
as previously observed with analogous substrates bearing
another electron-withdrawing substituent -Scheme 1), we
®rstexaminedthe actionofpotassiumthiophenoxideonole®n
* Corresponding author. Tel.: ‡33-1392-54411; fax: ‡33-1392-54452.
E-mail address: wakselma@chimie.uvsq.fr -C. Wakselman).
0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 - 0 1 ) 0 0 4 4 6 - 8

148
M. Tordeux et al. / Journal of Fluorine Chemistry 111 72001) 147±152
Scheme 1.
Scheme 2.
Fig. 1. First order substrate dependence of the plots ln{ꢀ‰3Š ‡ ‰4Š†=‰3Š}
versus time.
Scheme 3.
water content of the solvent, we have preferred to run the
kinetics in a DMSO-d6/water mixture. We found that addi-
tion of 10 vol.% of water -i.e. 30% in mole fraction) allows
clean and readily reproducible kinetics. During the accu-
mulations of the free induction decays, we had to take care
to not saturate the memories of the computers owing to the
double height of the end product signal versus these of the
substrate. It is also necessary to use a p/6 pulse width.
Indeed, the three studied tri¯uoromethyl groups did not
have identical relaxation times. We have measured T1
relaxation times for tri¯uoromethyl groups: 2.97 s for the
left signal, 2.69 s for the right signal, 2.8 and 3.4 s in the
cases of deuterated ole®n -vide infra). For product 4, the
relaxation time was about 1 s. We used a delay of 0.5 s
between two accumulations in order to obtain short time
recorded spectra. In such a case, we had only a discrepancy
of 2% between the integrations of the three signals. The time
of running for a spectrum was 13 s.
Isomerisation of 3 to 4 by triethylamine in a DMSO-d6/
water -90/10) mixture was found to be ®rst order substrate
dependent, since the plots of ln{ꢀ‰3Š ‡ ‰4Š†=‰3Š} versus time
were found to be linear with zero intercept -Fig. 1).
So for each experiment conducted at different triethyla-
mine concentration the pseudo ®rst order rate constant kobs.
can be deduced from the slope of the plot -Table 1).
The excellent straight line obtained by plotting kobs.
versus triethylamine concentration -Fig. 2) allowed the
determination at 238C of the ®rst order rate constant
-ks ˆ 1:1  10À3 minÀ1) for the catalytic solvent effect
and the second order rate constant -kEt N ˆ 4:9Â
3
10À2 l minÀ1 molÀ1) due to the base catalysis, according
to the equation, kobs: ˆ ks ‡ kEt N [Et3N].On performing an
3
experiment in a DMSO-d6/D2O -90/10) mixture in the pre-
)
sence of triethylamine -0.329 mol lÀ1, kobs: ˆ 0:0163 minÀ1
we only observed at 30 min few incorporation -ꢁ5%) of
deuterium in the ®nal product, depicted by 19F NMR by
Table 1
Triethylamine concentration and pseudo first order rate constant kobs. at 238C
Entry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Et3N -mol lÀ1
)
0.033
0.23
0.056
0.39
0.063
0.42
0.088
0.53
0.124
0.74
0.139
0.76
0.177
1.03
0.190
1.11
0.199
1.11
0.214
0.17a
0.227
0.18a
0.233
1.23
0.240
1.29
0.308
1.56
kobs. -Â10À2 minÀ1
)
a Reaction with 11.

M. Tordeux et al. / Journal of Fluorine Chemistry 111 72001) 147±152
149
Fig. 2. Determination of rate constants -& ) 3 to 4 in DMSO-d6/H2O -90/
10), -*) 11 to 12 in DMSO-d6/H2O -90/10) and -~ ) 3 to 4 in DMSO-d6/
D2O -90/10).
Scheme 5.
Scheme 4.
the large singlet of 4D at ±66.0 ppm, close to the doublet of 4
from 22 Hz up®eld. So, the main part of this incorporation
may be the result of an isotopic exchange of the tertiary allylic
proton of 4H -Scheme 4).
This important result shows that the tautomeric isomer-
isation of 3 to 4 is essentially an intramolecular process. In
order to demonstrate such an assertion, we have prepared the
analogue of 3, deuterated in its allylic position, i.e. 11 in
Scheme 5, and its isomerisation has been investigated.
Products 6, 7 and 8 were already described [11]. Sodium
phenylpropanoate 5 was heated at 1908C in deuterium oxide
in the presence of sodium methylate; this reaction was
repeated twice and the deuterated acid 6 was obtained with
a 85% overall incorporation of deuterium -mono/bis: 0.3/
0.7; this ratio was calculated from NMR spectral data).
Then, this acid was reduced to alcohol 7 with lithium
aluminum hydride and transformed to the corresponding
bromide 8. From its corresponding phosphonium salt 9, a
phosphorane 10 was prepared in order to react with hexa-
¯uoroacetone over 7 days in benzene at re¯ux. The deut-
erated ole®n 11 was obtained as a mixture of dideuterated
-11DD, 70%) and monodeuterated -11HD, 30%) species
that give 85% of overall incorporation -Scheme 5). The
kinetic of the isomerisation of this 11DD/11HD mixture by
triethylamine were monitored by 19F NMR in the DMSO-d6/
water -90/10) mixture as described for 3.
Scheme 6.
3. Discussion
This important deuterium isotopic effect with the very
small deuterium incorporation is observed when isomerisa-
tion of the proton ole®n 3 by triethylamine was conducted in
the DMSO-d6/D2O -90/10) mixture suggests an 1, 3±migra-
tion of the allylic hydrogen via an intermolecular pathway
[12]. Such a mechanism is well described by a transition
state in which the hydrogen is symmetrically centered
between the triethylamine nitrogen and the carbons involved
in the transfer -Scheme 7).
During these experiments, no change has been detected in
the deuterium incorporation ratio of the product mixture 12
-Scheme 6) and an important isotopic effect kH;Et N=kD;Et N
A similar proton transfer has been already reported by
Cram in the base catalysed rearrangement of 3-phenylbut-1-
ene by an alcoholate [13,14]. This rearrangement has been
interpreted as a competition between intermolecular and
intramolecular pathways -Scheme 8).
3
3
ˆ 6:1 hasbeen observed-kD;Et N ˆ 8  10À3l minÀ1 molÀ1).
3
Since this value corresponds to a 85% deuterium labelled
compound, we could expect a larger isotopic effect, probably
around 7 for the totally deuterated ole®n 11DD.
In our case, the intramolecular pathway is more important
and may be compared to the base catalysed proton transfer

150
M. Tordeux et al. / Journal of Fluorine Chemistry 111 72001) 147±152
1
NMR experiments: H NMR spectra were recorded at
300 MHz on a Bruker AC 300 instrument. TMS was used as
an internal standard. 13C NMR spectra were obtained at
75.5 MHz. 19F NMR spectra were recorded on the Bruker
spectrometer at 282.4 MHz using CFCl3 as reference.
CDCl3 was used as a solvent. T1 experiments were carried
out using the Bruker program. The kinetic program was D1;
ZE; GO ˆ 3; WR#1; IF#1; D2; IN ˆ 2; EXIT.
Delay before the ®rst acquisition -D1), delay between to
spectra -D2) -in seconds) and number of experiments -NE).
For kinetic experiments, values for ln-a=ꢀa À x)) were cal-
culated as: a ˆ sums of signals areas at À59.0, À64.9 and
À66.7 ppm; x ˆ signal area at À66.7 ppm; the temperature
was 238C.
Scheme 7.
5.1. 4-Phenyl-2-7trifluoromethyl)-1,1,1-trifluorobut-
2-ene 1
1-Iodo-2-phenylethane -8 g, 0.034 mmol) and triphenyl-
phosphine -10.5 g, 0.04 mmol) were re¯uxed in toluene
-40 ml) for 24 h. The solvent was evacuated under vacuum
and addition of tetrahydrofuran -THF) -50 ml) precipitated
yellow crystals which were washed with THF to give -2-
Scheme 8.
phenylethyl)triphenylphosphonium
0.026 mol, yield: 77%).
iodide
-12.9 g,
Then, butyllithium -10 mmol, 5 ml, 2 M in hexane) was
added to a suspension of the phosphonium iodide -2.47 g,
5 mmol) in THF -50 ml) at À208C. The deep red solution
was stirred for 30 min at this temperature and an excess of
gaseous hexa¯uoroacetone was introduced at À788C. The
mixture became pale yellow and was stirred for 3 h at this
temperature and one night at room temperature. The reaction
medium was poured into a 1/1 mixture of aqueous ammo-
nium chloride/light petroleum. The organic phase was
washed twice with water -50 ml) and dried over magnesium
sulphate. Then the product was puri®ed by column chro-
Scheme 9.
on 3-ketosteroids induced by an isomerase [15±17]. Indeed,
in that system, 10% or less deuterium atoms were incorpo-
rated into the product from the medium and the isotopic
effect was 4.1 -Scheme 9).
Ê
matography -silica gel 60 A; dichloromethane as eluent) as
4. Conclusion
an oilÃ-0.6 g, 2.4 mmol, yield: 41%). 19F NMR: À58.4 -CF3
cis, q q, JFF 7.1 Hz; J : 0:8 Hz), À64.9 -CF3 trans, qÃq, J:
4
The rearrangement of the ole®n 3 to its isomer 4 is slow in
pure DMSO. This isomerisation is catalysed by a base such
as triethylamine. A related rearrangement of a ¯uorinated
prenyl halide has been observed previously [18]. It is
apparent that the ole®n is clearly more stable when the
two tri¯uoromethyl groups are placed on a saturated carbon
rather than on a vinylic carbon [1]. In the isomerisation
process, the part of triethylamine is to assist the intramole-
cular hydrogen transfer to give a more stable isomer.
1.5 Hz). 1H NMR: 7.4 -5H, m) 6.89 -1H, tÃm, J: 6.8 Hz) 3.78
-2H, d). CIMS -m/z) 254, 185, 165, 91, 77. Anal. calc. for
C11H8F6: C: 51.98, H: 3.17; Found: C: 52.32, H: 3.06%.
This product was not very stable. It could isomerise in
DMSO solution to 1-phenyl-4,4,4-tri¯uoro-3--tri¯uoro-
methyl)but-2-ene [7].
5.2. 1-Phenyl-4,4,4-trifluoro-3-7trifluoromethyl)but-
2-ene 2
Potassium thiophenoxide -0.11 g, 0.78 mmol) in dime-
thylsulphoxide -5 ml) was added to 4-phenyl-1,1,1-tri¯uoro-
2--tri¯uoromethyl)but-2-ene -0.2 g, 0.78 mmol) in DMSO
-5 ml). The resulting mixture was stirred at room tempera-
ture for 1 h. Hydrochloric acid -3.5%, 10 ml) was added and
the resulting mixture was extracted with diethylether
-3 Â 20 ml). The organic phases were washed with water,
5. Experimental Section
-3-Phenyl-propyl)triphenylphosphonium bromide was
provided from Lancaster, gaseous hexa¯uoroacetone and
other compounds from Aldrich and deuterated DMSO
from SDS.

M. Tordeux et al. / Journal of Fluorine Chemistry 111 72001) 147±152
151
dried over magnesium sulphate and evacuated under
vacuum. 1-Phenyl-4,4,4-tri¯uoro-3--tri¯uoromethyl)but-2-
ene -0.12 g, 0.47 mmol, yield: 60%) was ®rst puri®ed by
CIMS -m/z) 254, 185, 165, 91, 77 -spectrum identical to
5-phenyl-1,1,1-tri¯uoro-2--tri¯uoromethyl)pent-2-ene, 3).
Ê
column chromatography -silica gel, 60 A; eluents: pentane
5.5. 2,2-Dideuterio-3-phenylpropanoic acid 6
then pentane/dichloromethane, 7/3) then by preparative thin
Ê
layer chromatography -silica gel, 60 A, 1 mm; dichloro-
1
Sodium 3-phenylpropanoate 5 was prepared by reaction
of 3-phenylpropanoic acid and sodium hydride in ether. The
salt -10.9 g, 0.063 mol), sodium methylate -3.42 g,
0.063 mol) and 10 ml of deuterium oxide were heated at
2008C in a 50 ml autoclave for 24 h. Then, 6 N hydrochloric
acid -100 ml) was added and the organic acid was extracted
with ether -4 Â 100 ml). The organic layer was dried over
magnesium sulphate. The reaction was repeated. After
evacuation of the solvent under vacuum, the HD/DD ratio
of 2,2-dideuterio-3-phenyl-propanoic acid was calculated
from the NMR spectrum by integration of 1H NMR signals
2.42 -0.3H) versus 2.72 ppm -2H). The aromatic ring signal
at 7.16 ppm -5H) was also used as reference.
methane as eluent). 19F NMR: À67.55 -d, J: 7.8 Hz). H
NMR: 7.4 -5H, m) 6.89 -1H, d, J: 16 Hz) 6.08 -1H, dÃd, J: 16,
9.5 Hz) 4.68 -1H, m) CIMS -m/z) CI 254, 185, 165, 91, 77
-spectrum identical to that of 4-phenyl-1,1,1-tri¯uoro-2-
-tri¯uoromethyl)but-2-ene).
5.3. 5-Phenyl-1,1,1-trifluoro-2-7trifluoromethyl)pent-
2-ene 3
Butyllithium -8.66 mmol, 5.41 ml, 1.6 M in hexane) was
added to a suspension of -3-phenyl-propyl)triphenylpho-
sphonium bromide -2 g, 4.43 mmol) in THF -25 ml) at
À208C. The deep red solution was stirred for 30 min at this
temperature and an excess of gaseous hexa¯uoroacetone
was introduced at À788C. The mixture became pale yellow
and was stirred for 3 h at this temperature and one night at
room temperature. The reaction medium was poured into a
1/1 mixture of aqueous ammonium chloride/light petroleum.
The organic phase was washed twice with water -50 ml) and
dried over magnesium sulphate. Then the product was
GC±MS -m/z): 151 -16.8), 152 -36.7), 153 -9.4), 107
-44.7), 106 -100), 105 -37.5).
5.6. 2,2-Dideuterio-3-phenylpropan-1-ol 7
Crude acid 6 and lithium aluminum hydride -4.3 g, 0.11
mol) in ether -300 ml) were re¯uxed for 1 h. Water -5.2 ml),
sodium hydroxide -15%, 5.2 ml) then water -5.2 ml) was
added; the solid was ®ltered. The organic layer was washed
with brine and dried over magnesium sulphate. The reduc-
tion was repeated twice. After evacuation under vacuum, the
crude alcohol -6.2 g) was obtained in a 75% yield.
1H NMR: - with integration) 7.20 -5H), 3.59 -2H), 2.74
-2H), 1.84 -0.3H).
Ê
puri®ed by column chromatography -silica gel, 60 A;
dichloromethane as eluent) as an oil -0.6 g, 2.23 mmol,
Ã
4
yield: 51%). 19F NMR: À59.0 -CF3 cis, q q, JFF 6.9 Hz;
J :0:9 Hz) À64.9 -CF3 trans, qÃq, J : 1:5 Hz). 1H NMR: 7.25
-5H, m) 6.76 -1H, tÃm, J: 7.5 Hz) 2.8 -2H, m) 2.75 -2H, m).
CIMS -m/z) 268, 177, 157, 91, 77. Anal. calc. for C12H10F6:
C: 53.74, H: 3.76; Found: C: 53.64, H: 3.52%.
GC±MS -m/z): 139 -1.1%), 138 -4.7%), 137 -2%), 120
-100%), 119 -90.5%), 107 -16.6%), 91 -44.4%).
This product was not stable in DMSO solution. It iso-
merises slowly to 1-phenyl-5,5,5-tri¯uoro-4--tri¯uoro-
methyl)pent-2-ene.
5.7. 1-Bromo-2,2-dideuterio-3-phenylpropane 8
To the alcohol 7 -5.7 g) in ether -33 ml) was added
phosphorus tribromide -4 ml) and the mixture was stirred
for 24 h, poured on ice, then extracted with ether
-3 Â 30 ml). The organic layer was washed with saturated
sodium hydrogencarbonate -50 ml), with brine -2 Â 50 ml)
and dried over magnesium sulphate. After evacuation of the
solvent under vacuum, the product 8 was isolated in a 77%
yield by column chromatography -silica gel, eluents: chloro-
form, then chloroform/ethyl acetate 80/20).
5.4. 1-Phenyl-5,5,5-trifluoro-4-7trifluoromethyl)pent-
2-ene 4
Potassium thiophenoxide -0.16 g, 1.1 mmol) in dimethyl-
sulphoxide -5 ml) was added to 5-phenyl-1,1,1-tri¯uoro-2-
-tri¯uoromethyl)pent-2-ene 3 -0.3 g, 1.1 mmol) in DMSO
-5 ml). The resulting mixture was stirred at room tempera-
ture for 1 h. Hydrochloric acid -3.5%, 10 ml) was added and
the resulting mixture was extracted with diethylether
-3 Â 20 ml). Organic phases were washed with water, dried
over magnesium sulphate and evacuated under vacuum. 1-
Phenyl-5,5,5-tri¯uoro-4--tri¯uoromethyl)pent-2-ene -0.27 g,
1.0 mmol, yield: 91%) was ®rst puri®ed by column chro-
1H NMR: -with integration) 7.20 -5H), 3.35 -2H), 2.75
-2H), 2.15 -0.3H).
GC±MS -m/z): 201 -25.1%), 200 -19.8%), 199 -33.8%),
198 -18.3%), 91 -100%).
Ê
matography -silica gel, 60 A; eluents: pentane then pentane/
dichloromethane, 7/3) then by preparative thin layer chro-
Ê
eluent). 19F NMR: À67.8 -d, J: 7.8 Hz). 1H NMR: 7.2 -5H,
m) 6.27 -1H, dÃt, J: 15.1, 6.9 Hz) 5.48 -1H, dÃd, J: 15.1,
9.5 Hz) 3.43 -2H, d, J: 6.9 Hz) 4.7 -1H, m) 4.68 -1H, m)
5.8. 2,2-Dideuterio-3-phenylpropyl)triphenyl
phosphonium bromide 9
matography -silica gel, 60 A, 1 mm; dichloromethane as
Bromide 8 -2 g, 0.01 mol), triphenylphosphine, -3 g,
0.011 mol) and a small quantity of sodium iodide were

152
M. Tordeux et al. / Journal of Fluorine Chemistry 111 72001) 147±152
re¯uxed in benzene -30 ml) for 7 days. An oily product was
obtained which was precipitated in THF -20 ml). Crystals
-2.2 g, 4.8 mmol, yield: 48%) were ®ltered and washed with
benzene and pentane.1H NMR: - with integration) 7.78
-15H), 7.25 -5H), 3.85 -2H), 3.0 -2H).
References
[1] B.E. Smart, in: J. F Liebman, V. L. Greenberg -Eds.), Molecular
Structure and Energetics, VCH Publishers, Deerfield Beach, FL,
USA, Vol. 3, 1986, p. 141.
[2] P.E. Lindler, D.M. Lemal, J. Amer. Chem. Soc. 119 -1999) 3267.
[3] V. Martin, H. Molines, C. Wakselman, J. Org. Chem. 57 -1992) 5530.
[4] D. Clemenceau, J. Cousteau, V. Martin, H. Molines, C. Wakselman,
R. Mornet, F. Nogue, M. Laloue, J. Agric. Food Chem. 46 -1998)
1577.
5.9. 2,2-Dideuterio-1,1,1-trifluoro-2-trifluoromethylpent-
2-ene 11
[5] L. Marival-Hodebar, M. Tordeux, C. Wakselman, M. Dias, R.
Mornet, M. Laloue, Israel J. Chem. 39 -1999) 155.
[6] L. Marival-Hodebar, M. Tordeux, C. Wakselman, Mag. Res. Chem.
37 -1999) 579.
Its preparation from the phosphonium bromide 9 -3 g,
6.5 mmol) was similar to that of 3. Compound 11 was
obtained in 85% yield -1.47 g, 5.5 mmol).
19F NMR: À59.0 -3F, d J : 0:9 Hz), À64.9 -3F, d J : 1:5).
1H NMR: - with integration) 7.25 -5H), 6.74 -1H), 3.75
-0.3H), 2.75-2H).
[7] A. Haas, M. Lieb, J. Zwingenberger, Justius Liebigs, Ann. Chem.
-1995) 2027.
[8] I.M. Kolthoff, M.K. Chantooni Jr., S. Bhowmik, J. Amer. Chem. Soc.
90 -1968) 23.
Â
[9] J. Courtot-Coupez, M. Demezet, Bull. Soc. Chim. -1969) 1033.
5.10. 2,2-Dideuterio-1,1,1-trifluoro-2-trifluoro-
methylpent-3-ene 12
[10] J.-C. Cherton, S. Hamm, J.-C. Halle, L. Menguy, M. Beaufour, J.
Fluorine Chem. 107 -2001) 397.
[11] M. Kwart, M. Bechbiel, W. Miles, L.D. Kwart, J. Org. Chem. 47
-1982) 4524.
From kinetic experiments. In the mixture DMSO-d6/H2O:
19F NMR: À66.0 -s), À65.95 -d).1H NMR: 7.21 -5H), 5.43
-1H), 4.72 -0.15H), 3.42 -2H).
[12] J. March -Ed.), Advanced Organic Chemistry: Reactions, Mechanism
and Structure, 4th Edition, Wiley, NY, 1992, p. 226.
[13] D.J. Cram, C.A. Kingsbury, B. Rickborn, J. Amer. Chem. Soc. 83
-1961) 3688.
[14] D.J. Cram, R.T. Uyeda, J. Amer. Chem. Soc. 86 -1964) 5466.
[15] P. Talalay, V.S. Wang, Biochim. Biophys. Acta 18 -1955) 300.
[16] V.S. Wang, F.S. Kawahara, P. Talalay, J. Biol. Chem. 238 -1963) 576.
[17] H. Simon, A. Kraus, Isotopes in Organic Chemistry, in: E. Buncel,
C.C. Lee -Eds.), Isotopes in Hydrogen Transfer Processes, Elsevier,
Amsterdam, Vol. 2, 1976, p. 167 -Chapter 5).
Acknowledgements
This work is part in the frame of the European TMR
program ERB FMRX-CT97-0120 entitled ``Fluorine as a
unique tool for engineering molecular properties.''
[18] V. Martin, H. Molines, C. Wakselman, J. Fluorine Chem. 62 -1993) 63.