Insight into the reactions of trifluorovinylsilanes with aromatic aldehydes

Article abstract of DOI:10.1002/ejoc.200800030

The conditions for the selective addition of trialkyl(trifluorovinyl) silanes to the C=O bond of aromatic aldehydes in the presence of cesium fluoride to give the corresponding "silylated" alcohols in high yields was performed. The reactivity of the "sily

Full text of DOI:10.1002/ejoc.200800030

FULL PAPER
DOI: 10.1002/ejoc.200800030
Insight into the Reactions of Trifluorovinylsilanes with Aromatic Aldehydes
Nataliia V. Kirij,[a] Dariya A. Dontsova,[a] Natalya V. Pavlenko,[a] Yurii L. Yagupolskii,*[a]
Harald Scherer,[b] Wieland Tyrra,[b] and Dieter Naumann[b]
Keywords: Trifluoroallylic alcohols / Aldehydes / Elimination / Nucleophilic addition / Stereoselectivity
The conditions for the selective addition of trialkyl(trifluoro-
vinyl)silanes to the C=O bond of aromatic aldehydes in the
presence of cesium fluoride to give the corresponding
“silylated” alcohols in high yields was performed. The reac-
tivity of the “silylated” alcohols in the presence of nucleo-
philic reagents and Brönsted acids was studied. On the basis
of isolated compounds and of intermediates detected by
NMR spectroscopic methods, several reaction pathways are
proposed. Significant differences between the reaction be-
haviour of triethyl(trifluorovinyl)silane and trimethyl(tri-
fluoromethyl)silane under comparable conditions are pointed
out; the differences can be attributed to the highly reactive
trifluorovinyl group. The reactions of the “silylated” alcohols
proceed with high stereoselectivity to give propenes, acid
fluorides and acids of the (E) isomers in better than 98% pu-
rity.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
In 1975, Normant et al. found conditions for obtaining tri-
fluoroallylic alcohols in high yields by the reaction of tri-
fluorovinyllithium with aldehydes and ketones and for their
conversion into α-fluoroalkenoic acid derivatives.[7] Later,
Olah et al. reported an approach to phenyl(trifluorovinyl)-
carbinol on the basis of the reaction of benzaldehyde with
1,3-bis(trimethylsilyl)-1,1,2,2-tetrafluoroethane in the pres-
ence of fluoride ions.[8] In 2002, Matsui et al. reported a
method for synthesis of trifluoroallylic alcohols not by di-
rect trifluorovinylation of aldehydes and ketones but by the
reaction of 3,3,3,4-tetrafluoro-1-propenyl tosylate with ar-
ylmagnesium bromide.[9]
In contrast to trifluoroallylic alcohols, there are only two
reports on the syntheses of the corresponding silyl ethers
mentioned in the literature. In 1985 and 1988, Hiyama et
al. showed that the reaction of benzaldehyde with triethyl-
(trifluorovinyl)silane in the presence of a fluoride-ion
source results in the formation of 3-triethylsiloxy-1,1,2-tri-
fluoro-3-phenylpropene in low yield.[10] It should be noted
that the reactivity of the product obtained was not investi-
gated.
Introduction
Trifluoroallylic alcohols are of great interest as synthons
in fluoroorganic chemistry. That is, (Z)-1,1-difluoro-1,2-di-
halo-2-alkenes obtained by halogenation of 1,1-difluoro-2-
halo-1-alkene-3-ols were applied in the construction of the
C-3 side chain of polyfluorinated synthetic pyretroids.[1]
The reaction of allylic alcohols with anhydrous hydrogen
fluoride leads to the formation of 1,1,1,2-tetrafluoro-2-al-
kenes; some of them exhibit unique biological properties in
the areas of agrochemicals, pharmaceuticals and material
science.[2] Upon treatment with acids, trifluoroallylic
alcohols give, together with alkenes, α-fluoroalkenoic acids
and the corresponding acid fluorides, which serve as precur-
sors to the fluoro analogues of retinals.[3] Starting from the
ethers of trifluoroallylic alcohols, novel optically active
partly gem-fluorinated allylic alcohols can be obtained by
[2,3] Wittig rearrangement.[4]
The first attempt to synthesize trifluoroallylic alcohols
starting from aldehydes and trifluorovinylmagnesium io-
dide was made by Knunyants et al. in 1958.[5] However, they
succeeded to obtain only a fluoride of the corresponding α-
fluoroalkenoic acid and proposed a route for its formation.
These investigations were intensified by Tarrant et al. who
synthesized some trifluoroallylic alcohols starting from al-
dehydes and ketones and trifluorovinyllithium or trifluoro-
vinylmagnesium bromide and isolated them in low yields.[6]
Herein, we report on a selective method to obtain O-
trialkylsilyl aryl(trifluorovinyl)carbinols in high yields and
the conversions of the synthesized compounds under the
influence of fluoride ions. On the basis of the products iso-
lated, we propose a reaction scheme for “silylated” alcohols
in the presence of nucleophilic reagents and Brönsted acids.
[a] Institute of Organic Chemistry, National Academy of Sciences
of Ukraine,
Murmanskaya Str. 5, 02094 Kiev, Ukraine
Fax: +38-044-5732643
Results and Discussion
E-mail: yagupolskii@bpci.kiev.ua
We found that the reaction of p-substituted aromatic al-
dehydes 1 with triethyl(trifluorovinyl)silane (Et3SiCF=CF2)
[b] Institut für Anorganische Chemie, Universität zu Köln,
Greinstrasse 6, 50939 Köln, Germany
Eur. J. Org. Chem. 2008, 2267–2272
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2267

Yu. L. Yagupolskii et al.
FULL PAPER
in the presence of tetramethylammonium fluoride ([Me4N]- the fluoride ion attacks the silicon atom and desilylates
F, 1 equiv.) in dimethoxyethane (DME) or tetrahydrofuran ether 4a to afford alcoholate 5a; the addition of the fluoride
(THF) in the temperature range from –60 °C to room tem- ion to the trifluorovinyl unit of 4a is accompanied by simul-
perature results in the formation of 1-aryl-2,3,3,3-tetrafluo- taneous triethylsilanolate anion elimination with formation
ropropene 2 and the tetramethylammonium salt of p-substi- of olefin 2a (Scheme 3).
tuted α-fluorocinnamic acid 3 (Scheme 1).
Scheme 1.
It should be noted that a similar reaction of trimethyl(tri-
fluoromethyl)silane (Me3SiCF3) with aromatic aldehydes in
the presence of tetramethylammonium fluoride (1 equiv.)
affords trifluoromethyl-containing tetramethylammonium
alcoholates, [Me4N]OCH(Ar)(CF3); subsequent hydrolysis
of the latter yields the corresponding secondary alcohols,
Ar(CF3)CHOH.[11]
Scheme 3.
Such essential differences between Me3SiCF3 and
Et3SiCF=CF2 in similar conversions may be attributed to
the highly reactive trifluorovinyl moiety being sensitive to
further nucleophilic attack by the reaction products primar-
ily formed. To confirm our assumption, we investigated the
reaction of trialkyl(trifluorovinyl)silanes with aromatic al-
dehydes in the presence of fluoride-ion sources under dif-
ferent conditions.
It should be noted that we were not able to detect the
signals of alcoholate 5a in the low-temperature 19F NMR
spectra. Concomitant with its formation, the extreme nucle-
ophilic nature of 5a results in its addition to the double
bond of the trifluorovinyl group of “silylated” alcohol 4a
to give intermediate A, which again eliminates a triethylsil-
anolate anion to give “unsymmetrical” ether 6a (Scheme 4).
We found that the reaction of equimolar quantities of
aromatic aldehydes 1, Et3SiCF=CF2 and CsF affords “si-
lylated” alcohols 4 in better than 95% yield. The reaction
proceeds in DME between –60 °C and room temperature
within 24 h (Scheme 2).
Scheme 4.
Scheme 2.
Keeping this reaction mixture at –45 °C for 80 min fol-
lowed by the addition of water at the same temperature led
to a product mixture of “silylated” alcohol 4a (40%), “un-
symmetrical” ether 6a (50%) and unidentified fluorine-con-
taining byproducts (10%). Ether 6a was isolated from the
mixture in 26% yield (relative to 1a) with 94% purity. An
attempt to purify 6a by vacuum distillation failed. At
135 °C, the substance decomposed into 2a and p-substi-
tuted α-fluorocinnamic acid fluoride 7a as the major prod-
ucts (Scheme 5).
The reaction with a catalytic amount of CsF proceeds
significantly slower, and even after one week 60% of alde-
hydes 1 were recovered unchanged. The use of a catalytic
amount (10–15 mol-%) of [Me4N]F which is, due to its bet-
ter solubility, a stronger nucleophile than CsF for silane ac-
tivation under similar conditions, yielded a complex prod-
uct mixture containing only 50–60% of the targeted “si-
lylated” alcohols 4.
To understand the nature of these conversions, we inves-
tigated the reaction of equimolar quantities of aldehyde 1a
and Et3SiCF=CF2 in the presence [Me4N]F (0.5 equiv.) by
means of low-temperature 19F NMR spectroscopic experi-
ments. The selective formation of “silylated” alcohol 4a in
DME or THF at –60 °C was complete after a reaction time
of 30 min. When the temperature is increased, [Me4N]F at-
tacks the two reactive positions of compound 4a, that is,
the terminal CF2 group and the silicon atom. In contrast, Scheme 5.
2268
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2267–2272

Insight into the Reactions of Trifluorovinylsilanes with Aromatic Aldehydes
An unexpected result was obtained upon purification of well as that of the “silylated” alcohol 4a and the “unsym-
6a by column chromatography on silica gel: “unsymmetri- metrical” ether 6a, is highly reactive toward nucleophiles.
cal” ether 6a rearranged into isomeric “symmetrical” ether The following reactions of ester 9a with alcoholate 5a and
8a, which was isolated in 45% yield and fully characterized fluoride ion led to the formation of intermediates of type
(Scheme 6). However, an explanation for this rearrange- C, which convert into products 2a, 3a and 6a (Scheme 9).
ment cannot be given. Furthermore, the trifluorovinyl
group of 6a appears to be the reactive centre in further
transformations. Attack of the nucleophiles present in the
reaction mixture, that is, alcoholate 5a and the fluoride ion,
at the double bond of 6a initially affords intermediates of
type B, which then decompose into 2a, 6a and 7a. Acid
fluoride 7a also reacts with alcoholate 5a to give ester 9a
Scheme 9.
(19F NMR spectroscopy) (Scheme 7).
In parallel to the reaction of aldehyde 1a with triethyl(tri-
fluorovinyl)silane in the presence of fluoride-ion sources, we
also studied the reaction of “silylated” alcohol 4a with
[Me4N]F. By 19F NMR spectroscopic methods, we detected
the formation of the same products 2a, 3a, 6a and 9a in the
course of the reaction. On the basis of the results obtained,
we conclude that aldehyde 1a reacts with Et3SiCF=CF2 in
the presence of [Me4N]F probably to form “silylated”
alcohol 4a, which undergoes all reaction steps outlined
above in a one-pot procedure (Scheme 10).
Scheme 6.
Scheme 7.
To confirm these assumptions, 7a was synthesized by an
alternative method[7] and treated with silyl ether 4a in the
presence of a catalytic amount of [Me4N]F (10–15 mol-%).
The reaction conditions were chosen to be similar to those
for the reaction of 1a with Et3SiCF=CF2; through this reac-
tion route, 9a was formed in quantitative yield (19F NMR
spectroscopy) (Scheme 8).
Scheme 10.
In comparative studies, Me3SiCF=CF2 was found to be
much more reactive. Upon reaction with aldehyde 1a in the
presence of [Me4N]F (0.5 equiv.) in DME or THF, the ex-
clusive formation of final products 2a, 3a and 7a were con-
firmed by low-temperature 19F NMR spectra recorded at
–40 °C. However, in diethyl ether, the reaction of aldehyde
1 (1 equiv.) with Me3SiCF=CF2 (1.1 equiv.) and a catalytic
amount of [Me4N]F afforded “silylated” alcohol 10 in bet-
ter than 80% yield of the crude product (Scheme 11),
Scheme 8.
Compound 9a was isolated in 67% yield and fully char-
acterized. The 19F NMR spectroscopic data of ester 9a ob-
tained as described above are in full accordance with those
of the reaction product 9a involved in Scheme 7. It should
be noted that the trifluorovinyl group of compound 9a, as Scheme 11.
Eur. J. Org. Chem. 2008, 2267–2272
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2269

Yu. L. Yagupolskii et al.
FULL PAPER
whereas the total amount of compounds 2, 3, 6 and 9 in versions under the action of both nucleophilic and electro-
the reaction mixture did not exceed 15%. philic reagents. Products 4 are unique due to the presence
Our studies on the conversions of “silylated” alcohol 4a of two reactive centres; both of them can be involved in
under action of fluoride ions were accompanied by investi- conversions depending on the purpose. The presence of a
gations of its reactivity towards Brönsted acids. As it is silyl protecting group for the hydroxy functionality makes
known, the “silylated” alcohols are deprotected by acids to compounds 4 absolutely stable upon storage, unlike the free
give the free alcohols. However, when “silylated” alcohol 4a alcohols. It also should be noted that all reactions of “si-
is treated with H[BF4], HCl or HBr, it is converted into lylated” alcohols 4 studied are highly stereoselective; the
propenes 2a, 11a or 12a, respectively. In this case, minor obtained propenes, acid fluorides and acids are (E) isomers
amounts of 7a and 13a are always detected in the reaction with more than 98% purity. This reaction peculiarity can be
mixtures (19F NMR spectroscopy) (Scheme 12).
also used for the purposeful synthesis of compounds with
definite steric configuration.
Experimental Section
General Remarks: All reactions were carried out under a dry argon
atmosphere by using Schlenk techniques. The following products
were synthesized according to literature procedures: Me3-
SiCF=CF2,[12] Et3SiCF=CF2,[12] [Me4N]F,[13] 2-fluoro-3-p-tolylal-
lylic acid fluoride (7a).[7] All solvents were purified according to
literature procedures.[14] Rf values refer to TLC carried out on 25-
mm silica-gel plates (Merck F254). 1H, 13C, 19F and 29Si NMR
were recorded with Bruker Avance300 and Avance400 spectrome-
ters. The assignment of quaternary C, CH, CH2 and CH3 as well
as C, CF, CF2 and CF3 atoms were made on the basis of DEPT
experiments. Chemical shifts are referenced relative to external
standards Me4Si (for 1H, 13C and 29Si) and CCl3F (for 19F and
29Si). Mass spectra (EI, 20 eV) were obtained with a Finnigan
MAT 95 spectrometer. Melting points were measured in one-end-
open glass capillaries and are uncorrected. Column chromatog-
raphy was carried out by using 60–240 mesh silica gel at atmo-
spheric pressure. C, H, N and F analyses were performed with
HEKAtech Euro EA 3000 and Analytikjena Spekol 1100 instru-
ments.
Scheme 12.
We suppose that “silylated” alcohol 4a in the presence of
an acid is initially converted into free alcohol 14a. Further
protonation of the oxygen atom induces the elimination of
water to give carbocation D as an intermediate. The stabili-
zation of the latter can be accomplished either by the reac-
tion with a halide ion to form the corresponding propene
or with water to give acid fluoride 7a and finally acid 13a
(Scheme 13).
General Procedure for the Synthesis of 1-Triethylsiloxy-2,3,3-tri-
fluoro-1-aryl-2-propenes (4): To a solution of 1 (10 mmol) in dime-
thoxyethane (DME) (50 mL) at –60 °C was added Et3SiCF=CF2
(2.16 g, 11 mmol) and CsF (1.52 g, 10 mmol). The mixture was
stirred for 1 h at –30 °C and then for 23 h at room temperature.
Cesium fluoride was filtered off and the filtrate was concentrated
in vacuo. The residue was purified by distillation under reduced
pressure.
1-Triethylsiloxy-2,3,3-trifluoro-1-(4-tolyl)prop-2-ene (4a): Yield
2.75 g (87%). B.p. 80 °C/0.09 Torr. 1H NMR (300.13 MHz, CDCl3,
3
3
Scheme 13.
25 °C): δ = 0.69 (q, JH,H = 7.7 Hz, 6 H, CH2Si), 1.00 (t, JH,H
7.7 Hz, 9 H, CH3CH2), 2.40 (s, 3 H, CH3C6H4), 5.52 [dm, JH,F
=
=
3
It should be noted that in reactions of 4a with acids un-
der anhydrous conditions the corresponding propene is
formed nearly exclusively. Earlier, this fact was noticed in
the reaction of alcohol 14 with water-free complex
HF·THF,[2] which resulted in propene 2. A similar reaction
of “silylated” alcohol 4a with gaseous HCl afforded pro-
pene 11a as a major product.
32.2 Hz, 1 H, CH], 7.21 (m, 2 H, Ar-Hortho), 7.25 (m, 2 H, Ar-
Hmeta) ppm. 13C NMR (75.47 MHz, CDCl3, 25 °C): δ = 4.6
(CH2Si), 6.5 (CH3CH2), 21.1 (CH3C6H4), 67.8 (CH), 126.0 (2 C,
2
Ar-Cortho), 129.1 (2 C, Ar-Cmeta), 129.7 (ddd, 1JC,F = 241 Hz, JC,F
2
= 48 Hz, JC,F = 12 Hz, =CF), 136.0 (Ar-Cipso), 137.9 (Ar-Cpara),
1
1
2
153.5 (ddd, JC,F = 318 Hz, JC,F = 276 Hz, JC,F = 45 Hz, =CF2)
ppm. 19F NMR (282.4 MHz, CDCl3, 25 °C): δ = –104.3 (dd, JF,F
2
3
2
= 80.6 Hz, JF,Fcis = 31.7 Hz, =CFF), –120.8 (dd, JF,F = 80.6 Hz,
3JF,Ftrans = 115 Hz, =CFF), –186.3 (ddd, JF,Ftrans = 115 Hz, JF,H
3
3
3
= 32.2 Hz, JF,Fcis = 31.7 Hz, =CF-) ppm. 29Si NMR (59.63 MHz,
Conclusions
CDCl3, 25 °C): δ = 22.6 (s) ppm. MS (EI): m/z (%) = 287 (100)
[M – C2H5]+. C16F3H23OSi (316.43): calcd. C 60.73, F 18.01, H
7.33; found C 60.61, F 17.93, H 7.28.
The reaction of equimolar amounts of aromatic alde-
hydes 1, Et3SiCF=CF2 and CsF proceeds selectively to af-
ford “silylated” alcohols 4 in excellent yields. Compounds
1-Triethylsiloxy-2,3,3-trifluoro-1-(4-fluorophenyl)prop-2-ene
(4b):
4 attract significant attention as synthons for further con- Yield: 2.76 g (86%). B.p. 75 °C/0.3 Torr. 1H NMR (300.13 MHz,
2270
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2267–2272

Insight into the Reactions of Trifluorovinylsilanes with Aromatic Aldehydes
3
CDCl3, 25 °C): δ = 0.69 (q, JH,H = 7.7 Hz, 6 H, CH2Si), 0.99 (t, (2 mL) was added to convert byproducts 4a and 9a into 7a, 11a
3
3JH,H = 7.7 Hz, 9 H, CH3CH2), 5.51 (dm, JH,F = 25.2 Hz, 1 H, and 13a. The mixture was stirred for ca. 4 d at room temperature
CH), 7.08 (m, 2 H, Ar-Hortho), 7.42 (m, 2 H, Ar-Hmeta) ppm. 13C
NMR (75.47 MHz, CDCl3, 25 °C): δ = 4.5 (CH2Si), 6.5 (CH3CH2),
67.4 (CH), 127.8 (2 C, Ar-Cortho), 115.3 (2 C, Ar-Cmeta), 130.8
(=CF), 134.7 (Ar-Cipso), 162.5 (Ar-Cpara), 152.4 (=CF2) ppm. 19F
until the reaction was complete (monitored by 19F NMR spec-
troscopy). All volatile compounds were evaporated in vacuo
(0.4 Torr) at 40 °C. The residue was dissolved in THF (10 mL) and
aqueous NaOH (10%, 5 mL) and Bu4NHSO4 (30 mg) were added
to neutralize acrylic acid 13a and the corresponding fluoride 7a.
The mixture was stirred for ca. 2 h at room temperature. After the
reaction was complete (monitored by TLC on silica-gel-coated
plates by using pentane as eluent), THF was evaporated, and the
product was extracted with hexane (5 mL). The extract was washed
with water (2ϫ5 mL), dried (MgSO4) and concentrated in vacuo
to yield 0.5 g (26%) of 6a (94% purity). 1H NMR [300.13 MHz,
(CD3)2CO, 25 °C]: δ = 2.30 (s, 3 H, CH3C6H4), 2.31 (s, 3 H,
NMR (282.4 MHz, CDCl3, 25 °C): δ = –103.9 (dd, 2JF,F = 80.5 Hz,
2
3JF,Fcis = 32 Hz, =CFF), –114.3 (m, 4-FC6H4), –120.7 (dd, JF,F
=
3
3
80.5, JF,Ftrans = 114.5 Hz, =CFF), –186.1 (ddd, JF,Ftrans = 114.5,
3JF,Fcis = 32, JF,H = 25 Hz, =CF-) ppm. 29Si NMR (59.63 MHz,
3
1
CDCl3, 25 °C): δ = 22.8 (d, JSi,C = 60 Hz) ppm. MS (EI): m/z (%)
= 291 (100) [M – C2H5]+. C15F4H20OSi (320.40): calcd. C 56.23, F
23.72, H 6.29; found C 56.34, F 23.77, H 6.31.
General Procedure for the Synthesis of 2,3,3-Trifluoro-1-trimethyl-
siloxy-1-aryl-2-propenes (10): To a solution of 1 (1.4 mmol) in di-
ethyl ether (7 mL) at –30 °C was added Me3SiCF=CF2 (0.24 g,
1.54 mmol) and [Me4N]F (13 mg, 0.14 mmol). The mixture was
stirred for 1 h at –30 °C and then overnight at room temperature.
The precipitate formed was filtered off, the solvent was evaporated
in vacuo and pentane (6 mL) was added to the residue. The pentane
solution was decanted and concentrated in vacuo. The residue was
purified by distillation under reduced pressure.
3
4
CH3C6H4),6.03 (dtm, JH,F = 24.8 Hz, JH,H = 2.3 Hz, 1 H, CH-
3
CF), 6.25 (d, JH,F = 35.6 Hz, 1 H, CH=CF), 7.08 (m, 2 H, Ar-
Hmeta), 7.12 (m, 2 H, Ar-Hmeta), 7.28 (m, 2 H, Ar-Hortho), 7.37 (m,
2 H, Ar-Hortho) ppm. 13C NMR [75.47 MHz, (CD3)2CO, 25 °C]: δ
= 20.3 (1 C, CH3C6H4), 20.5 (1 C, CH3C6H4), 69.6 (1 C, CH-CF),
109.8 (1 C, CH=CF), 118.1 (1 C, CF2-O), 126.2 (1 C, CF2=CF),
126.2 (2 C, Ar-Cortho), 127.8 (1 C, Ar-Cipso), 128.9 (4 C, Ar-Cmeta),
129.1 (2 C, Ar-Cortho), 131.1 (1 C, Ar-Cipso), 138.4 (2 C, Ar-Cpara),
146.2 (1 C, CH=CF), 152.4 (1 C, CF2=CF) ppm. 19F NMR
2
2,3,3-Trifluoro-1-trimethylsiloxy-1-(4-tolyl)prop-2-ene (10a): Yield:
0.29 g (75%). B.p. 65–66 °C/2 Torr. 1H NMR (300.13 MHz, c-
C6D12, 25 °C): δ = 0.15 (s, 9 H, CH3Si), 2.29 (s, 3 H, CH3C6H4),
[282.4 MHz, (CD3)2CO, 25 °C]: δ = –76.9 (ddd, JF,F = 154 Hz,
4
3JF,F = 12.7 Hz, JF,H = 3.6 Hz, CFFO; ABX spin system), –77.7
2
3
2
(dd, JF,F = 154 Hz, JF,F = 14.0 Hz, CFFO), –102.5 (ddd, JF,F
=
3
71.9 Hz, 3JF,Fcis = 33.3 Hz, 4JF,H = 1.7 Hz, =CFF), –119.0 (dd, 2JF,F
= 71.9 Hz, JF,Ftrans = 115.7 Hz, =CFF), –130.3 (dt, JF,H
5.46 (dm, JH,F = 25 Hz, 1 H, CH), 7.07 (m, 2 H, Ar-Hortho), 7.27
(m, 2 H, Ar-Hmeta) ppm. 13C NMR (75.47 MHz, c-C6D12, 25 °C):
3
3
=
=
2
3
3
3
δ = –0.3 (CH3Si), 21.2 (CH3C6H4), 68.8 (dt, JC,F = 22 Hz, JC,F
35.6 Hz, JF,F = 13.2 Hz, CF=CH), –186.7 (ddd, JF,Ftrans
115.7 Hz, 3JF,Fcis = 33.3 Hz, JF,H = 24.8 Hz, =CF) ppm. MS (EI):
m/z (%) = 386 (20) [M]+, 294 (100) [M – C6H4CH3]+, 185 (40)
[CH3C6H4 – CH(CF=CF2)]+.
3
= 3 Hz, CH), 126.7 (2 C, Ar-Cortho), 129.5 (2 C, Ar-Cmeta), 130.1
1
2
2
(ddd, JC,F = 244 Hz, JC,F = 48 Hz, JC,F = 12 Hz, =CF), 136.6
1
1
(Ar-Cipso), 138.1 (Ar-Cpara), 153.5 (ddd, JC,F = 318 Hz, JC,F
=
276 Hz, JC,F = 45 Hz, =CF2) ppm. 19F NMR (282.4 MHz, c-
2
Preparation of Bis[1,1,2-trifluoro-3-(4-methylphenyl)prop-2-enyl]
Ether (8a): 6a (0.3 g, 0.78 mmol) in pentane was passed through
the column with silica gel to yield 0.135 g of 8a (45%). Rf = 0.29
(pentane). 1H NMR (300.13 MHz, CDCl3, 25 °C): δ = 2.40 (s, 6
H, CH3C6H4), 6.38 (d, 3JH,F = 36 Hz, 2 H, CH), 7.23 (m, 4 H, Ar-
Hortho), 7.49 (m, 4 H, Ar-Hmeta) ppm. 13C NMR (75.47 MHz,
2
3
C6D12, 25 °C): δ = –105.5 (ddd, JF,F = 82 Hz, JF,Fcis = 33 Hz,
4JF,H = 2 Hz, =CFF), –122.1 (ddd, JF,F = 82 Hz, JF,Ftrans
=
2
3
4
3
115 Hz, JF,H = 3 Hz, =CFF), –185.7 (ddd, JF,Ftrans = 115 Hz,
3JF,Fcis = 33 Hz, 3JF,H = 25 Hz, =CF) ppm. 29Si NMR (59.63 MHz,
1
c-C6D12, 25 °C): δ = 19.3 (d, JSi,C = 59 Hz) ppm. MS (EI): m/z
(%) = 274 (45) [M]+, 259 (100) [M – CH3]+. C13F3H17OSi (274.35):
2
3
CDCl3, 25 °C): δ = 21.4 (2 C, CH3C6H4), 111.0 (q, JC,F = JC,F
=
calcd. C 56.91, F 20.78, H 6.25; found C57.02, F 20.83, H 6.28.
1
2
3 Hz, 2 C, CH), 116.8 (td, JC,F = 271 Hz, JC,F = 43 Hz, 2 C,
CF2), 123.6 (d, JC,F = 7 Hz, 4 C, Ar-Cortho), 127.2 (d, JC,F
3.5 Hz, 2 C, Ar-Cipso), 129.5 (4 C, Ar-Cmeta), 139.6 (d, JC,F
4
3
2,3,3-Trifluoro-1-(4-fluorophenyl)-1-trimethylsiloxyprop-2-ene (10b):
=
=
Yield: 0.30 g (77%). B.p. 85 °C/12 Torr. 1H NMR (300.13 MHz,
6
3
1
2
CDCl3, 25 °C): δ = 0.19 (s, 9 H, CH3Si), 5.49 (dm, JH,F = 25 Hz,
2.5 Hz, 2 C, Ar-Cpara), 145.8 (dt, JC,F = 268 Hz, JC,F = 36 Hz, 2
C, CF) ppm. 19F NMR (282.4 MHz, CDCl3, 25 °C): δ = –74.6 (dm,
1 H, CH), 7.08 (m, 2 H, Ar-Hortho), 7.40 (m, 2 H, Ar-Hmeta) ppm.
13C NMR (75.47 MHz, CDCl3, 25 °C): δ = –0.3 (CH3Si), 67.3
(CH), 115.3 (2 C, Ar-Cmeta), 127.8 (2 C, Ar-Cortho), 128.8 (=CF),
134.4 (Ar-Cipso), 152.4 (=CF2), 162.6 (Ar-Cpara) ppm. 19F NMR
(282.4 MHz, CDCl3, 25 °C): δ = –103.3 (ddd, 2JF,F = 80 Hz, 3JF,Fcis
3JF,F = 10 Hz, 4 F, CF2; ABX spin system), –131.3 (dtm, JF,H
=
2
3
36 Hz, JF,F = 10 Hz, 2 F, CF) ppm. MS (EI): m/z (%) = 386 (20)
[M]+, 294 (100) [M
– –
C6H4CH3]+, 185 (40) [CH3C6H4
CH(CF=CF2)]+. C20F6H16O (386.33): calcd. C 62.18, F 29.51, H
4.17; found C 62.03, F 29.44, H 4.13.
4
= 33 Hz, JF,H = 2 Hz, =CFF), –114.2 (m, 4-FC6H4), –120.3 (ddd,
3
4
2JF,F = 80 Hz, JF,Ftrans = 116 Hz, JF,H = 4 Hz, =CFF), –186.5
Preparation of 2,3,3-Trifluoro-1-(4--tolyl)allyl 2-Fluoro-3-(4-tolyl)-
acrylate (9a): To a mixture of 7a (0.46 g, 2.5 mmol) and 4a (0.79 g,
2.5 mmol) in DME (20 mL) at –40 °C was added [Me4N]F (30 mg,
0.32 mmol). The mixture was stirred for 1 h at –20 °C and then
overnight at room temperature. The precipitate formed was filtered
off, the filtrate was concentrated, and the residue was dissolved in
a minimum amount of pentane and precipitated upon cooling to
3
3
3
(ddd, JF,Ftrans = 116 Hz, JF,Fcis = 33 Hz, JF,H = 25 Hz, =CF)
ppm. MS (EI): m/z (%) = 278 (50) [M]+, 263 (100) [M – CH3]+.
C12F4H14OSi (278.32): calcd. C 51.78, F 27.31, H 5.07; found C
51.67, F 27.37, H 5.04.
Preparation of 1,1,2-Trifluoro-3-(4-methylphenyl)prop-2-enyl 2,3,3-
Trifluoro-1-(4-methylphenyl)prop-2-enyl Ether (6a): To a solution
of 1a (0.6 g, 5 mmol) in DME (20 mL) at –60 °C was added yield 0.61 g (67%) of 9a. M.p. 64–66 °C. 1H NMR [300.13 MHz,
Et3SiCF=CF2 (1.08 g, 5.5 mmol) and [Me4N]F (0.23 g, 2.5 mmol).
The mixture was stirred for 80 min at –45Ϯ5 °C, then cold water
(8 mL) was added, and the products were extracted with diethyl
ether (2ϫ6 mL). The combined ether phases were washed with
water (6 mL), dried (MgSO4) and concentrated in vacuo. The resi-
due (1.05 g) was dissolved in CHCl3 (5 mL), and 35% aqueous HCl
(CD3)2CO, 25 °C]: δ = 2.37 (s, 3 H, CH3C6H4), 2.39 (s, 3 H,
3
3
CH3C6H4), 6.77 (dm, JH,F = 26 Hz, 1 H, CH-CF), 7.17 (d, JH,F
= 36 Hz, 1 H, CH=CF), 7.3 (2 H, Ar-Hmeta), 7.31 (2 H, Ar-Hmeta),
7.49 (2 H, Ar-Hortho), 7.67 (2 H, Ar-Hortho) ppm. 13C NMR
[75.47 MHz, (CD3)2CO, 25 °C]: δ = 20.2 (1 C, CH3C6H4), 20.5 (1
C, CH3C6H4), 69.3 (1 C, CH-CF), 118.8 (1 C, CH=CF), 125.8 (1
Eur. J. Org. Chem. 2008, 2267–2272
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2271

Yu. L. Yagupolskii et al.
FULL PAPER
C, CF2=CF), 126.8 (2 C, Ar-Cortho), 128.1 (1 C, Ar-Cipso), 129.4 (2
(HBF4, HCl or HBr). The mixture was stirred at room temperature
C, Ar-Cmeta), 129.6 (2 C, Ar-Cmeta), 130.5 (2 C, Ar-Cortho), 130.9 (1 until the reaction was complete. Reaction control was monitored
C, Ar-Cipso), 139.2 (1 C, Ar-Cpara), 140.7 (1 C, Ar-Cpara), 145.7 (1 by 19F NMR spectroscopy. Spectral data of 11a[16] and 12a[17]
2
C, CH=CF), 153.4 (1 C, CF2=CF), 159.6 (d, JC,F = 35 Hz, 1 C, correspond with literature data.
C=O) ppm. 19F NMR [282.4 MHz, (CD3)2CO, 25 °C]: δ = –102.2
2
3
4
(ddd, JF,F = 70 Hz, JF,Fcis = 32 Hz, JF,H = 2 Hz, CFF), –116.6
(ddd, 2JF,F = 70 Hz, 3JF,Ftrans = 114 Hz, 4JF,H = 3 Hz, CFF), –127.8
Acknowledgments
3
3
(d, JF,H = 36 Hz, CH=CF), –187.0 (ddd, JF,Ftrans = 114 Hz,
3JF,Fcis = 32 Hz, JF,H = 26 Hz, CF=CF2) ppm. MS (EI): m/z (%)
3
The generous financial support of this work by the DFG (grant
436 UKR 113) is gratefully acknowledged.
= 364 (20) [M]+, 272 (100) [M – C6H4CH3]+, 185 (40) [CH3C6H4 –
CH(CF=CF2)]+. C20F4H16O2 (364.33): calcd. C 65.93, F 20.86, H
4.43; found C 66.08, F 20.79, H 4.40.
[1] M. Fujita, T. Hiyama, Tetrahedron Lett. 1986, 27, 3659–3660.
[2] a) J. T. Welch, S. Eswarakrishnan, Fluorine in Bioorganic Chem-
istry, John Wiley & Sons, New York, 1991; b) R. E. Bank, B. E.
Smart, J. C. Tatlov (Eds.), Organo-Fluorine Chemistry – Prin-
ciple and Commercial Applications, Plenum, New York, 1994.
[3] T. Shinada, N. Sekiya, K. Bojkova, Tetrahedron 1999, 55, 3675–
3686.
[4] T. Itoh, K. Kudo, N. Tanaka, K. Sakabe, Y. Tokagi, H. Kihara,
Tetrahedron Lett. 2000, 41, 4591–4595.
[5] R. N. Sterlin, R. D. Yatsenko, I. L. Knunyants, Khim. Nauka
Prom-st. 1958, 3, 540–542.
[6] a) P. Tarrant, P. Johncock, J. Savory, J. Org. Chem. 1963, 28,
839–843; b) F. G. Drakesmith, R. D. Richardson, P. Tarrant, J.
Org. Chem. 1968, 33, 286–291.
[7] J. F. Normant, J. P. Foulon, D. Masure, R. Sauvetre, J. Villieras,
Synthesis 1975, 122–125.
[8] A. K. Judin, G. K. S. Prakash, D. Deffieux, M. Bradley, R.
Bau, G. A. Olah, J. Am. Chem. Soc. 1997, 119, 1572–1581.
[9] K. Funabiki, K. Sawa, K.-i. Shibata, M. Matsui, Synlett 2002,
7, 1134–1136.
[10] a) M. Fujita, T. Hiyama, J. Am. Chem. Soc. 1985, 107, 4085–
4087; b) M. Fujita, M. Obayashi, T. Hiyama, Tetrahedron 1988,
44, 4135–4145.
[11] a) G. K. S. Prakash, A. K. Yudin, Chem. Rev. 1997, 97, 757–
786; b) R. P. Singh, J. M. Shreeve, Tetrahedron 2000, 56, 7613–
7632.
[12] J. Burdon, P. Coe, I. B. Haslock, R. L. Powell, Chem. Commun.
1996, 49–50.
[13] A. A. Kolomeitsev, F. U. Seifert, G.-V. Röchenthaler, J. Fluor-
ine Chem. 1995, 71, 47–49.
[14] D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of
Laboratory Chemicals, 2nd ed., Pergamon, Oxford, 1980.
[15] E. Elkik, C. Francesch, Bull. Soc. Chim. Fr. 1986, 3, 423–428.
[16] V. N. Korotchenko, A. V. Shastin, V. G. Nenajdenko, E. S. Ba-
lenkova, Tetrahedron 2001, 57, 7519–7527.
Preparation of 2,3,3,3-Tetrafluoro-1-(4-tolyl)prop-1-ene (2a) and 2-
Fluoro-3-(4-tolyl)acrylic Acid (13a): To a mixture of 1a (1 g,
8.3 mmol) and Et3SiCF=CF2 (1.82 g, 9.1 mmol) in DME (40 mL)
at –55Ϯ5 °C was portionwise added [Me4N]F (0.78 g, 8.3 mmol)
over 1.5 h. The mixture was stirred for 1 h at –30 °C and then over-
night at room temperature. The precipitate formed (tetramethyl-
ammonium salt of 2-fluoro-3-p-tolylacrylic acid, 3a) was filtered,
washed with aqueous HCl (5%, 7 mL) and water (2ϫ7 mL), then
dissolved in aqueous NaOH (10%, 7 mL). Insoluble impurities
were filtered off, and the filtrate was acidified with 5% aqueous
HCl to the isotonic point. The precipitate formed was filtered and
dried to yield 0.70 g (47%) of 13a. Physical and spectral character-
istics of 13a correspond to literature data.[15] The filtrate of the
reaction mixture was concentrated in vacuo, and pentane (6 mL)
was added to the residue. The pentane solution was decanted, and
the solvent was evaporated in vacuo. The residue was purified by
distillation under reduced pressure to yield 0.53 g (31%) of 2a
(E/Z
=
98:2). B.p. 78 °C/12 Torr. (E) isomer: 1H NMR
(300.13 MHz, CDCl3, 25 °C): δ = 2.44 (s, 3 H, CH3C6H4), 6.38 (d,
3
3JH,F = 36 Hz, 1 H, CH), 7.26 (d, JH,H = 8 Hz, 2 H, Ar-Hortho),
7.52 (d, 3JH,H = 8 Hz, 2 H, Ar-Hmeta) ppm. 13C NMR (75.47 MHz,
2
3
CDCl3, 25 °C): δ = 21.3 (CH3C6H4), 111.4 (quint, JC,F = JC,F
=
3.5 Hz, CH), 119.0 (qd, 1JC,F = 271 Hz, 2JC,F = 41 Hz, CF3), 126.9
(d, JC,F = 3.9 Hz, Ar-Cipso),129.6 (Ar-Cmeta), 129.7 (d, JC,F
3
4
=
1
2
7.4 Hz, Ar-Cortho), 144.4 (dq, JC,F = 266 Hz, JC,F = 38 Hz, CF)
ppm. 19F NMR (282.4 MHz, CDCl3, 25 °C): δ = –72.0 (d, JF,F
=
3
2
3
11 Hz, 3 F, CF3), –133.3 (dq, JF,H = 36 Hz, JF,F = 11 Hz, 1 F,
CF) ppm. (Z) isomer: 19F NMR (282.4 MHz, CDCl3, 25 °C): δ =
–66.8 (d, 3JF,F = 10 Hz, 3 F, CF3), –125.7 (dq, 2JF,H = 21 Hz, 3JF,F
=
11 Hz, 1 F, CF) ppm. MS (EI): m/z (%) = 204 (100) [M]+. C10F4H8
(204.16): calcd. C 58.83, F 37.23, H 3.95; found C 58.69, F 37.38,
H 3.88.
[17] V. G. Nenajdenko, G. N. Varseev, V. N. Korotchenko, A. V.
Shastin, E. S. Balenkova, J. Fluorine Chem. 2004, 125, 1339–
1345.
General Procedure for the Reactions of 4a with Brönsted Acids: To
a solution of 4a (0.40 g, 1.26 mmol) in diethyl ether or dioxane
(10 mL) was added an excess amount of the appropriate acid
Received: January 10, 2008
Published Online: March 25, 2008
2272
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2267–2272