On the reactions of trifluorovinylsilanes with aromatic ketones - Expected and some unexpected results

Article abstract of DOI:10.1016/j.jfluchem.2009.11.007

The reactions of aromatic ketones with trialkyl(trifluorovinyl)silanes in the presence of fluoride ions were studied. The conditions for the selective addition of trialkyl(trifluorovinyl)silanes to the carbonyl function of aromatic ketones in the presence

Full text of DOI:10.1016/j.jfluchem.2009.11.007

Journal of Fluorine Chemistry 131 (2010) 184–189
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
On the reactions of trifluorovinylsilanes with aromatic ketones – Expected and
some unexpected results
b
b
N.V. Kirij a, D.A. Dontsova a, N.V. Pavlenko a, Yu.L. Yagupolskii a, , W. Tyrra , D. Naumann
*
a Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanskaya Str. 5, UA-02094 Kiev, Ukraine
b Institut fu¨r Anorganische Chemie, Universita¨t zu Ko¨ln, Greinstrasse 6, D-50939 Ko¨ln, Germany
A R T I C L E I N F O
A B S T R A C T
Article history:
The reactions of aromatic ketones with trialkyl(trifluorovinyl)silanes in the presence of fluoride ions
were studied. The conditions for the selective addition of trialkyl(trifluorovinyl)silanes to the carbonyl
function of aromatic ketones in the presence of cesium fluoride and absence of any solvents to form the
trifluorovinyl containing ‘‘silylated’’ alcohols have been worked out. The analogous reactions in common
organic solvents are not terminated on the stage of ‘‘silylated’’ alcohols formation; consecutive reactions
lead to fluorinated olefins and acids under the influence of fluoride ions.
Received 30 July 2009
Received in revised form 9 November 2009
Accepted 11 November 2009
Available online 11 December 2009
Keywords:
ß 2009 Elsevier B.V. All rights reserved.
Aromatic ketones
Trialkyl(trifluorovinyl)silanes
Trifluoroallylic alcohols
Fluoride ion
Fluorinated olefins
Dedicated to the memory of
Prof. Dr. Lev Moiseevich Yagupolskii.
1. Introduction
proposed a reaction scheme for the transformation of ‘‘silylated’’
alcohols under the influence of nucleophilic agents and Bro¨nsted
Trifluoroallylic alcohols are of great interest as synthons in
fluoroorganic chemistry [1]. However, the possibilities to use
them are strictly limited due to the absence of convenient
synthetic methods. Up to now, there is mentioned only one
method in the literature for the introduction of a trifluorovinyl
group into aliphatic ketones by the reaction with trifluorovinyl-
lithium [2–4]. For aromatic ketones, the reaction of acetophenone
with trifluorovinyllithium yielding the trifluorovinyl containing
alcohol is twice reported [4,5]. It should be noted that the stability
of trifluorovinyllithium, even at low temperature, significantly
limits the applicability of this method. It should also be mentioned
that 1,2-bis(trimethylsilyl)-1,1,2,2-tetrafluoroethane has been
used as a reagent to convert benzaldehyde and acetophenone into
the appropriate trifluorovinyl alcohols [6]. Therefore, the search
for available and shelf-stable reagents serving as trifluorovinyl
group sources is of current interest. Previously, we showed that
aromatic aldehydes react with trialkyl(trifluorovinyl)silanes in
the presence of fluoride ions to form ‘‘silylated’’ trifluoroallylic
alcohols. Furthermore, on the basis of the isolated products, we
acids [7].
In the present paper, we report a new method to obtain
‘‘silylated’’ trifluoroallylic alcohols starting from aromatic ketones
and trifluorovinylsilanes in the presence of fluoride ions, and their
consecutive conversions into fluorinated olefins and acids.
2. Results and discussion
Previously, we elaborated the conditions for the reactions of
aromatic aldehydes with trialkyl(trifluorovinyl)silanes (Alk3SiCF55
CF2) in the presence of cesium fluoride (CsF) in dimethoxyethane
(DME)ortetramethylammonium fluoride([Me4N]F)indiethylether
giving trifluorovinyl containing ‘‘silylated’’ alcohols in high yields
[7]. To complete our study, we investigated the reactions of aromatic
ketones, namely 2,2,2-trifluoroacetophenone 1, benzophenone 2
and acetophenone 3, with trialkyl(trifluorovinyl)silanes in the
presence of fluoride ions. However, we failed to synthesize
trifluorovinyl containing ‘‘silylated’’ alcohols starting from aromatic
ketones under the conditions optimized for aromatic aldehydes as
mentioned above [7].
The reaction of equimolar amounts of 2,2,2-trifluoroacetophe-
none 1 and triethyl(trifluorovinyl)silane in the presence of CsF in
DME or THF in the temperature range from À60 8C to room
* Corresponding author. Tel.: +38 044 559 0349; fax: +38 044 573 2643.
E-mail address: yagupolskii@ioch.kiev.ua (Yu.L. Yagupolskii).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.11.007

N.V. Kirij et al. / Journal of Fluorine Chemistry 131 (2010) 184–189
185
Scheme 1.
temperature results in the formation of E/Z-1,1,1,3,4,4,4-heptafluor-
2-phenyl-but-2-enes 4, 5 [8,9] and cesium salts of E/Z-2,4,4,4-
tetrafluor-3-phenyl-but-2-enoic acids 6, 7 instead of the expected
‘‘silylated’’ alcohol (Scheme 1). Salts 6, 7 can be converted into the
corresponding acids 8, 9 by acidification.
It should be noted that solely aforesaid products are formed and
not the expected ‘‘silylated’’ alcohols irrespective of reagents’ ratio,
the fluoride ion source, the solvent and the reaction temperature.
The yield of the olefins 4 and 5 due to their high volatility was
determined on the basis of 19F NMR spectroscopic data relatively to
fluorobenzene (C6H5F) which was used as an internal standard.
The reaction of benzophenone 2 with triethyl(trifluorovinyl)si-
lane and tetramethylammonium fluoride ([Me4N]F) (molar ratio
1:1:2) in tetrahydrofurane (THF) in the temperature range from
À90 8C to 20 8C leads to the formation of 2,3,3,3-tetrafluoro-1,1-
diphenyl-prop-1-ene 10 [10] in 51% yield; 2-fluoro-3,3-diphenyl-
acrylic acid 11 [3,11] is obtained after acidification of the
corresponding tetramethylammonium salt in 41% yield (Scheme 2).
The use of tetrabutylammonium triphenyldifluorosilicate
([NBu4][Ph3SiF2]) as a fluoride ion source allowed to detect (19
F
NMR) the formation of ꢀ15% of the ‘‘silyl ether’’ 12 among the
other products (Scheme 3).
This observation may serve as a confirmation of the reaction
scheme we proposed previously for the interaction of aromatic
aldehydes with trifluorovinylsilane in the presence of fluoride ions
leading to the initial formation of ‘‘silylated’’ alcohols and their
further conversions to the corresponding olefins and acids under
the influence of fluoride ions [7] (Scheme 4).
Scheme 2.
Scheme 3.

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N.V. Kirij et al. / Journal of Fluorine Chemistry 131 (2010) 184–189
Scheme 4.
Most probably, tertiary trifluorovinyl containing ‘‘silylated’’
further attempts were directed towards the exploration of the
reaction of aromatic ketones with trifluorovinylsilanes and
fluoride ions in absence of any solvent.
alcohols are more reactive in comparison to their secondary
analogues and – under these reaction conditions – immediately
undergo consecutive reactions with fluoride ions once being
formed, thus preventing their isolation.
It should be noted that the fluorinated olefins and acids
obtained in the course of research are of practical interest, but
traditional methods to obtain them hamper from that they are
frequently multi-step and based on commercially unavailable
substrates. Taking into consideration the availability of the
reagents we have used together with good yields of the final
products, the present method may be proposed as an alternative
route to obtain fluorinated olefins and acids.
We found that 2,2,2-trifluoroacetophenone 1 reacts with
trimethyl(trifluorovinyl)silane in the presence of a 20% amount
of CsF at 25 8C during 100 h to give 1,1,1,3,4,4-hexafluoro-1-
trimethylsiloxy-1-phenyl-but-3-ene 13. The degree of conversion
of 2,2,2-trifluoroacetophenone gains 95% with the main product
content in the mixture being 80% (Scheme 5). The ‘‘silylated’’
alcohol 13 was isolated using column chromatography and was
fully characterized.
Using a molar amount of cesium fluoride and rise of the reaction
temperature caused lower amounts of the ‘‘silylated’’ alcohol 13
but a concurrent increase of the formation of the fluorinated olefins
4, 5 and the salts 6, 7. By the way, triethyl(trifluorovinyl)silane does
not react under the chosen conditions; a fact which supports our
It is known that in some cases that performing reactions
without any solvent significantly influence the conversion
procedures and the product formation. As a consequence, our
Scheme 5.
Scheme 6.

N.V. Kirij et al. / Journal of Fluorine Chemistry 131 (2010) 184–189
187
Scheme 7.
Scheme 8.
previously stated suggestion about significant differences between
the reactivity of triethyl- and trimethyl(trifluorovinyl)silanes [7].
The reaction of acetophenone 3 with triethyl(trifluorovinyl)si-
lane in the presence of cesium fluoride in the molar ration 1:1.2:1
at 65 8C during 20 h leads to the selective formation of 3,4,4-
trifluoro-1-triethylsiloxy-1-phenyl-but-3-ene 14 (Scheme 6).
The degree of conversion of acetophenone 3 in the above
reaction does not exceed 80% even if an excess of the silane is used.
It should be also mentioned that using the more reactive
trimethyl(trifluorovinyl)silane in this reaction as well as a decrease
of the amount of cesium fluoride significantly lowers the degree of
conversion of the starting substrate 3.
The desilylation to form ‘‘free’’ alcohols proceeds under the
action either of acids or bases. Among the acids tested for
acidification, the HBF4ÁEt2O complex became the reagent of choice
making it possible to proceed the reaction under anhydrous
conditions. The ‘‘silylated’’ alcohol 13 reacts with HBF4ÁEt2O in
diethyl ether at room temperature selectively to form the
1,1,1,3,4,4-hexafluoro-2-phenyl-but-3-en-2-ol 15 (Scheme 7)
which was monitored by 19F NMR spectroscopic means. Com-
pound 15 was isolated and fully characterized.
In contrast to 2,2,2-trifluoroacetophenone 1, the reaction of
‘‘silylated’’ alcohol 14 with HBF4ÁEt2O under similar conditions is
not terminated on the step of the ‘‘free’’ alcohol; consecutive
reaction leads to fluorinated olefins 16, 17 and acids 18, 19
(Scheme 8). The course of the reaction was monitored by 19F NMR
spectroscopy. Spectral data of 16, 17 [5] and 18, 19 [4] correspond
with literature data.
CsF being widely used in analogous reactions was chosen as a
base. It was found out that the ‘‘silylated’’ alcohol 13 reacts with
CsF in molar ratio 1:1 in DME in the temperature range from
À20 8C to 20 8C to form the expected mixture of the products of its
consecutive conversions, i.e. E/Z-1,1,1,3,4,4,4-heptafluor-2-phe-
nylbut-2-enes 4, 5 in a ratio 9:1 and cesium salts of E/Z-2,4,4,4-
tetrafluor-3-phenylbut-2-enoic acids 6, 7 in a 4:1 ratio (Scheme 9).
The reaction of the ‘‘silylated’’ alcohol 14 with CsF under similar
conditions leads to the selective formation (19F NMR control) of
3,4,4-trifluoro-2-phenyl-but-3-en-2-ol 20 [4,5] (Scheme 10).
It should be noted that our attempts to synthesize the
trifluorovinyl containing ‘‘silylated’’ alcohol starting from benzo-
phenone 2 and trialkyl(trifluorovinyl)silanes in the presence of
fluoride ion without a solvent remained unsuccessful.
Scheme 9.

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N.V. Kirij et al. / Journal of Fluorine Chemistry 131 (2010) 184–189
Scheme 10.
3. Conclusions
4.2. Preparation of 1,1,1,3,4,4-hexafluoro-1-trimethylsiloxy-1-
phenyl-but-3-ene 13
On the basis of the results reported, it can be concluded that
aromatic ketones react with trialkyl(trifluorovinyl)silanes in the
presence of fluoride ions without a solvent to form tertiary
trifluorovinyl containing ‘‘silylated’’ alcohols that can be easily
converted into the corresponding alcohols. The analogous reac-
tions in common organic solvents are not terminated on the stage
of ‘‘silylated’’ alcohols formation but proceed with consecutive
reactions to fluorinated olefins and acids. Such fluorinated
products are of practical interest but are limited by the lack of
commercially available starting materials. The method proposed
enables a one-step synthesis of a set of fluorinated olefins and acids
starting from available organic substrates and is, therefore, highly
perspective.
A mixture of 2,2,2-trifluoroacetophenone 1 (0.87 g, 5 mmol),
Me3SiCF55CF2 (1.16 g, 7.5 mmol) and CsF (0.15 g, 1 mmol) was
stirred for 100 h at 26 Æ 1 8C, and then diethyl ether was added.
Insoluble impurities were filtered off, and diethyl ether and volatile
products were evaporated in vacuum. The residue was purified by
silica gel column chromatography, yielded 1.05 g (64%) of 1,1,1,3,4,4-
hexafluoro-1-trimethylsiloxy-1-phenyl-but-3-ene 13. 1H NMR spec-
tral data (500.13 MHz, CDCl3): d 0.21 (s, 3H, CH3), 7.44 (m, 3H, Ph),
7.63 (m, 2H, Ph). 13C NMR (125.76 MHz, CDCl3): d 0.90 (s, CH3), 78.51
(m, Cq), 123.34 (q, J = 287 Hz, CF3), 127.01 (s, CPh), 128.37 (s, CPh),
128.17 (ddd, J = 241 Hz, J = 41 Hz, J = 19 Hz, CF), 129.51 (s, CPh),
134.75 (d, J = 1.6 Hz,
CPh), 154.39 (ddd, J = 335 Hz, J = 289 Hz,
J = 45 Hz, CF2). 19F NMR (188.14 MHz, CDCl3): d À78.13 (dd, 3F,
J = 12 Hz, J = 10 Hz, CF3), À98.74 (dd, 1F, J = 65 Hz, J = 36 Hz, CF),
À108.42 (ddq, 1F, J = 116 Hz, J = 65 Hz, J = 12 Hz, CF), À177.89 (ddd,
1F, J = 116 Hz, J = 36 Hz, J = 10 Hz, CF). Anal. Calcd for C13H14F6OSi: C,
47.57; H, 4.30; F, 34.73. Found: C, 47.69; H, 4.36; F, 34.84.
4. Experimental
All reactions were carried out under a dry argon atmosphere by
using Schlenk techniques. The following products were synthe-
sized according to literature procedures: Me3SiCF55CF2 [12],
Et3SiCF55CF2 [12], [Me4N]F [13]. Aromatic ketones were purchased
from Acros, HBF4ÁEt2O from Fluka. All solvents were purified
according to literature procedures [14]. NMR spectra were
recorded with the Bruker spectrometers AC 200, Avance 400,
Avance DRX 500 and the Varian spectrometer VXR-300. Chemical
shifts are given in ppm relative to Me4Si (1H, 13C) and CCl3F (19F) as
external standards. Melting points were measured in one-end
open glass capillaries and are uncorrected. Column chromato-
graphy was carried out using 60–240 mesh silica gel at atmo-
spheric pressure. CHNF-analyses were performed with the
apparatus HEKAtech Euro EA 3000 and Analytikjena Spekol 1100.
4.3. Preparation of 3,4,4-trifluoro-1-triethylsiloxy-1-phenyl-but-3-
ene 14
A mixture of acetophenone 3 (0.60 g, 5 mmol), Et3SiCF55CF2
(1.18 g, 6 mmol) and CsF (0.76 g, 5 mmol) was stirred for 20 h at
65 Æ 1 8C, and then hexane was added. Insoluble impurities were
filtered off, and hexane and volatile products were evaporated in
vacuum. The residue was purified by silica gel column chromato-
graphy, yielded 0.81 g (51%) of 3,4,4-trifluoro-1-triethylsiloxy-1-
phenyl-but-3-ene 14. 1H NMR spectral data (500.13 MHz, CDCl3): d
0.69 (q, 2H, J = 8 Hz, CH2), 1.01 (t, 3H, J = 8 Hz, CH3), 1.76 (dd, 3H,
J = 5 Hz, J = 2 Hz, CH3), 7.30 (m, 1H, Ph), 7.37 (m, 2H, Ph), 7.48 (m, 2H,
Ph). 13C NMR (125.76 MHz, CDCl3): d 6.14 (s, CH2), 6.84 (s, CH3), 74.83
(ddd, J = 23 Hz, J = 4 Hz, J = 1.3 Hz, Cq), 125.05 (s, CPh), 127.48 (s, CPh),
128.17 (s, CPh), 132.48 (ddd, J = 239 Hz, J = 43 Hz, J = 15 Hz, CF),
144.86 (s, CPh), 153.3 (ddd, J = 330 Hz, J = 282 Hz, J = 48 Hz, CF2). 19F
NMR (188.14 MHz, CDCl3): d À101.22 (dd, 1F, J = 78 Hz, J = 34 Hz, CF),
À112.51 (ddq, 1F, J = 113 Hz, J = 78 Hz, J = 5 Hz, CF), À177.89 (ddd, 1F,
J = 113 Hz, J = 34 Hz, J = 2 Hz, CF). Anal. Calcd for C16H23F3OSi: C,
60.73; H, 7.33; F, 18.01. Found: C, 60.51; H, 7.26; F, 17.94.
4.1. Preparation of 2,3,3,3-tetrafluoro-1,1-diphenyl-prop-1-ene 10
and 2-fluoro-3,3-diphenyl-acrylic acid 11
To the solution of Et3SiCF55CF2 (1.08 g, 5.5 mmol) in tetrahy-
drofuran (THF) (50 mL) at À90 8C [Me4N]F (0.93 g, 10 mmol) was
added. The mixture was stirred for 0.5 h at À85 Æ 5 8C and then
benzophenone 2 (0.91 g, 5 mmol) was added at À70 8C. The reaction
mixture was allowed to warm to room temperature over 4 h. The
precipitate formed (tetramethylammonium salt of 2-fluoro-3,3-
diphenyl-acrylic acid) was filtered, washed with 5% aqueous HCl
(5 mL), and water (2Â 5 mL), then dissolved in 20% aqueous NaOH
(10 mL). Insoluble impurities were filtered off, and the filtrate was
acidified with 5% aqueous HCl to the isotonic point. The precipitate
formed was filtered, dried and yielded 0.48 g (40%) of 2-fluoro-3,3-
diphenyl-acrylic acid 11. Physical and spectral characteristics of 11
correspond to literature data [3,11].
THF and volatile products were evaporated in vacuum, and
hexane was added to the residue. Insoluble impurities were
filtered off, and hexane was evaporated in vacuum. The residue
was purified by silica gel column chromatography, yielded 0.68 g
(51%) of 2,3,3,3-tetrafluoro-1,1-diphenyl-prop-1-ene 10. Physical
and spectral characteristics of 10 correspond to literature data [10].
4.4. Preparation of 1,1,1,3,4,4-hexafluoro-2-phenyl-but-3-en-2-ol 15
To the solution of 1,1,1,3,4,4-hexafluoro-1-trimethylsiloxy-1-
phenyl-but-3-ene 13 (0.98 g, 3 mmol) in diethyl ether (5 mL)
HBF4ÁEt2O (5 g, 31 mmol) was added. The mixture was stirred at
20 8C until the reaction was completed (monitored by 19F NMR
spectroscopy). To the solution were added diethyl ether (10 mL),
water (20 mL) and NaHCO3 to neutralize HBF4. The product was
extracted with diethyl ether (2Â 10 mL). The combined ether
phases were washed with water (10 mL), dried (MgSO4) and
concentrated in vacuum to yield 0.66 g (86%) of 1,1,1,3,4,4-
hexafluoro-2-phenyl-but-3-en-2-ol 15. 1H NMR spectral data
(299.94 MHz, CDCl3):
d 3.54 (s, 1H, OH), 7.44–7.48 (m, 3H, Ph),

N.V. Kirij et al. / Journal of Fluorine Chemistry 131 (2010) 184–189
189
7.64–7.67 (m, 2H, Ph). 13C NMR (100.62 MHz, CDCl3):
Cq), 123.95 (q, J = 288 Hz, CF3), 126.94 (s, CPh), 129.01 (s, CPh),
128.17 (ddd, J = 241 Hz, J = 40 Hz, J = 20 Hz, CF), 130.24 (s, CPh),
133.59 (s, CPh), 154.97 (ddd, J = 333 Hz, J = 287 Hz, J = 46 Hz, CF2).
d
76.42 (m,
acidified with 5% aqueous HCl to the isotonic point, the oil formed
after acidification was extracted with ethylacetate, dried (MgSO4),
concentrated in vacuum and yielded 0.39 g (55%) of E/Z-2,4,4,4-
tetrafluoro-3-phenyl-but-2-enoic acids 8, 9 (E/Z = 4:1).
19F NMR (188.14 MHz, CDCl3):
d
À76.89 (t, 3F, J = J = 9 Hz, CF3),
À95.96 (dd, 1F, J = 65 Hz, J = 37 Hz, CF), À107.98 (ddq, 1F,
J = 117 Hz, J = 65 Hz, J = 9 Hz, CF), À178.54 (ddd, 1F, J = 117 Hz,
J = 37 Hz, J = 9 Hz, CF). Anal. Calcd for C10H6F6O: C, 47.89; H, 2.36; F,
44.51. Found: C, 47.69; H, 2.29; F, 44.37.
4.6. Preparation of 3,4,4-trifluoro-2-phenyl-but-3-en-2-ol 20
To the solution of 3,4,4-trifluoro-1-triethylsiloxy-1-phenyl-
but-3-ene 14 (0.63 g, 2 mmol) in DME (15 mL) at À20 8C CsF
(0.46 g, 3 mmol) was added. The mixture was stirred for 1 h at
À20 8C and then overnight at room temperature until the reaction
was completed (monitored by 19F NMR spectroscopy). The yield of
3,4,4-trifluoro-2-phenyl-but-3-en-2-ol 20 (0.36 g, 90%) was deter-
mined by 19F NMR experiments (relative to fluorobenzene
(C6H5F)). Spectral characteristics of 20 correspond to literature
data [4].
4.5. Preparation of E-1,1,1,3,4,4,4-heptafluor-2-phenylbut-2-ene 4,
Z-1,1,1,3,4,4,4-heptafluor-2-phenylbut-2-ene 5, E/Z-2,4,4,4-
tetrafluoro-3-phenyl-but-2-enoic acids 8, 9
Method A: To a mixture of 2,2,2-trifluoroacetophenone 1 (0.87 g,
5 mmol) and Et3SiCF55CF2 (1.13 g, 5.75 mmol) in dimethoxyethane
(DME) (50 mL) at À60 8C CsF (0.76 g, 5 mmol) was added. The
mixture was stirred for 1 h at À35 Æ 5 8C and then overnight at room
temperature. The yield of olefines 4 (0.35 g, 27%) and 5 (0.08 g, 6%)
was determined by 19F NMR experiments (relative to fluorobenzene
(C6H5F)). Spectral characteristics of 4 and 5 correspond to literature
data [8,9]. All volatile products and DME were evaporated in vacuum,
and hexane (10 mL) was added to the residue. The precipitate formed,
was filtered, washed with hexane and dried to give the products 6, 7
(cesium salts of E/Z-2,4,4,4-tetrafluoro-3-phenyl-but-2-enoic acids,
0.70 g, 38%). Salts 6, 7 were dissolved in water (15 mL), insoluble
impurities were extracted with diethyl ether (2Â 7 mL), then water
phase was acidified with 5% aqueous HCl to the isotonic point. The oil
formed after acidification was extracted with ethylacetate, dried
(MgSO4), concentrated in vacuum and yielded 0.41 g (35%) of E/Z-
2,4,4,4-tetrafluoro-3-phenyl-but-2-enoic acids 8, 9 (E/Z = 4:1). (E)
Isomer: 1H NMR spectral data (299.94 MHz, CDCl3): d 7.31–7.50 (m, 5
H, Ph). 13C NMR (100.62 MHz, (CD3)2SO): d 120.13 (qd, J = 31.5 Hz,
J = 8.6 Hz, C55), 123.33 (q, J = 275 Hz, CF3), 128.32 (s, CPh), 129.42 (s,
Acknowledgements
The generous financial support of this work by the DFG (grant
436 UKR 113) is gratefully acknowledged. The authors thank Dr.
Harald Scherer (Universita¨t Freiburg) and Dr. Alexander Rozhenko
for their help interpreting the NMR spectra.
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[12] J. Burdon, P. Coe, I.B. Haslock, R.L. Powell, Chem. Commun. (1996) 49–50.
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47–49.
C
Ph), 130.73 (s, CPh), 153.83 (d, J = 274 Hz, CF55), 161.30 (d, J = 34 Hz,
COOH). 19F (188.14 MHz, CDCl3): d À57.54 (d, 3F, J = 10 Hz, CF3),
À104.48 (q, 1F, J = 10 Hz, CF).
Method B: To the solution of 1,1,1,3,4,4-hexafluoro-1-trimethyl-
siloxy-1-phenyl-but-3-ene 13 (0.98 g, 3 mmol) in DME (30 mL) at
À20 8C CsF (0.46 g, 3 mmol) was added. The mixture was stirred for
1 h at À20 8C and then overnight at room temperature. The
precipitate formed was filtered off, the filtrate was concentrated,
and the residue was dissolved in water. The water phase was
[14] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals,
second ed., Pergamon, Oxford, 1980.