Unusual β,β′-coupling and β-alkylation of methyl 2,3,3-trifluoropropenoate by lithium diorganocuprates

Article abstract of DOI:10.1016/j.jfluchem.2010.12.003

Methyl 2,3,3-trifluoroprop-2-enoate (1) reacts with lithium diorganocuprates in two ways, by fluorine substitution at C-3 with alkyl or aryl, or by β,β′ C,C-coupling. The reaction product was strongly dependent on the organyl structure: while dibutyl- or diphenylcuprate reacted by C-3 substitution, dimethylcuprate afforded the product of the coupling, dimethyl (Z,Z)-2,3,4,5-tetrafluorohexa-2,4-dienedioate (3). (Z)-Configuration is highly prevailing in 3-alkylated 2,3-difluoropropenoates (77-90% rel.).

Full text of DOI:10.1016/j.jfluchem.2010.12.003

Journal of Fluorine Chemistry 132 (2011) 143–146
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Short communication
Unusual
b, b-alkylation of methyl 2,3,3-trifluoropropenoate
b0-coupling and
by lithium diorganocuprates
a,
Jan Hajduch a,b, Oldrich Paleta
*
ˇ
a
´
Department of Organic Chemistry, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences, 166 10 Prague 6, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Article history:
Methyl 2,3,3-trifluoroprop-2-enoate (1) reacts with lithium diorganocuprates in two ways, by fluorine
substitution at C-3 with alkyl or aryl, or by b,
b0 C,C-coupling. The reaction product was strongly dependent
Received 20 October 2010
Received in revised form 29 November 2010
Accepted 2 December 2010
Available online 8 December 2010
on the organyl structure: while dibutyl- or diphenylcuprate reacted by C-3 substitution, dimethylcuprate
afforded the product of the coupling, dimethyl (Z,Z)-2,3,4,5-tetrafluorohexa-2,4-dienedioate (3). (Z)-
Configuration is highly prevailing in 3-alkylated 2,3-difluoropropenoates (77–90% rel.).
ß 2010 Elsevier B.V. All rights reserved.
Keywords:
Trifluoropropenoate
b,
b0-Coupling
Lithium diorganocuprates
Stereoselectivity
1. Introduction
benzyl trifluoroacrylate by a mixture of a Grignard reagent and
copper(I) bromide.
Trifluoroacrylates have been reported as useful building blocks
in syntheses of lactones or 2,3-difluoro-2,3-unsaturated esters [1–
6], which have been in turn exploited as convenient synthetic
The reaction of MTFA with methyllithium (Scheme 1) was
unsuccessful despite of very mild reaction conditions. A complex
mixture of products was obtained, from which no individual
product was isolated.
intermediates [7–9]. Recently,
b-fluoroalkylation of benzyl tri-
fluoroacrylate by fluorine vinylic substitution using Grignard
reagents in the presence of copper(I) bromide has been reported
[5,6]. In this paper, we report the results of the reaction of methyl
2,3,3-trifluoropropenoate (1) with lithium diorganocuprates.
Depending on the organyl component in the cuprates, unusual
New results were found in the reaction of MTFA (1) with some
lithium diorganocuprates (Scheme 1). The reaction of 1 with lithium
dibutyl-ordiphenylcupratesafforded only b-substitutedproducts6
or 7 with the Z-stereoisomer highly prevailing (Table 1, entry 3 and
5). Very close results to these were obtained in the reaction of benzyl
2,2,3-trifluoroprop-2-enoate with butyl- or phenylmagnesium
bromide in the presence of copper(I) bromide (Table 1, entries 4
and 6) [6]. However, when the substrate 1 was reacted with lithium
dimethylcuprate the substitution dimer 3, dimethyl (Z,Z)-2,3,4,5-
b,
b0 C,C-coupling of the trifluoropropenoate 1 has been observed.
2. Results and discussion
tetrafluorohexa-2,4-dienedioate was formed by a b,
b0 C,C-coupling
We tested the reaction of methyl 2,2,3-trifluoroprop-2-enoate
in the 95% relative yield (Scheme 1; Table 1, entry 1). When a more
bulky lithium di(tert-butyl)cuprate was involved in the reaction
(Table 1, entry 2) the yield of the coupling product 3 was decreased
to 56% rel.
(1, methyl
a,b,b-trifluoroacrylate – MTFA) with several organo-
metallic reagents. The reaction of 1 with methylmagnesium iodide
afforded a mixture of products, from which the dimer 2 was
isolated in the 4.8% yield (Scheme 1). The dimer 2 was the same
product as that obtained by the reaction of MTFA with the fluoride
ion [10,11]. Very probably, fluoride ion was liberated by a reaction
of methylmagnesium iodide with the substrate 1. This result is in a
A coupling of this type has not been observed so far. Several
proposals for substitutions by organocuprates have been published
[12] and the importance of tricoordinated copper compounds
R3Cu(III) in particular reactions has been recognized [12a,13] and
their structure published [14]. The existence of Cu(III) intermediates
in addition or substitution reactions involving dialkylcuprates was
contrast with the recently reported [5,6]
b-fluoroalkylation of
predicted by calculations [12b]. Probably, the
molecules of MTFA (1) proceeds via an intermediate 8 (Scheme 2)
b,
b0-coupling of two
* Corresponding author. Tel.: +420 22044 4284; fax: +420 22044 4288.
E-mail address: Oldrich.Paleta@vscht.cz (O. Paleta).
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.12.003

[
J. Hajduch, O. Paleta / Journal of Fluorine Chemistry 132 (2011) 143–146
F
MeO2C
F3C
CO2Me
F
F
2
(E)/(Z) 88/12
i)
CH3MgI
F
F
CO2Me
F
CH3Li
ii)
mixture of products
1
iii)
R2CuLi
F
CO2Me
R
F
CO2Me
F
CO2Me
F
F
+
+
F
F
R
MeO2C
F
4a-7a
4b-7b
3
(Z,Z)- only
(Z)- 77-90% rel.
(E)- 10-23% rel.
4a, 4b, R = CH3; 5a, 5b, R = C(CH3)3; 6a, 6b, R = C4H9; 7a, 7b, R = C6H5 .
i) Et2O, -10 to 0 °C, then CF3CO2H; ii) THF, -100 °C, 1 h, then CF3CO2H, -100 °C to rt, 2 h; iii) THF, -100 to -
70 °C, 3 h, then CF3CO2H, -70 °C to rt, 2 h
Scheme 1. Reactions of methyl 2,3,3-trifluoroprop-2-enoate with organometallic reagents.
Table 1
Overview of the reactions of trifluoroacrylates 1 with organometallic reagents.
F
CO2Me
F
F
F
F
F
F
R2CuLi
+
+
[TD$LINE]
or RMgBr + CuBr
R
CO2Me
MeO2C
F
F
CO2Y
1
E/Z 4-7
3
Entry
Reagent
Y
Product 3
Products 4–7
Ref.
Yield (% rel.)
Yield (%rel.)
E/Z
1
2
3
4
5
6
Me2CuLi
Me
95 (76)a
4
5
6
5
10/90
23/77
7/93
(t-Bu)2CuLi
Bu2CuLi
Me
Me
Bn
56
0
44
100 (81)a
(77)a
BuMgBr, CuBr
Ph2CuLi
0
14/86
18/82
14/86
[6]
[6]
Me
Bn
0
7
100 (73)a
(90)a
PhMgBr, CuBr
0
a
Isolated yield.
Table 2
possessing three-valent copper central atom combining two units
ofdefluorinatedsubstrate1. Thecouplingoccursonlywhenthealkyl
in a lithium cuprate is not sterically inconvenient. Both butyl
and phenyl substituents coordinated with copper blocked the
3
Overview of JF–F coupling constants for E–Z configurations of the structures.
]
F
F
F
A
F
A
B
b,
b0-coupling probably from steric reasons. A similar steric effect of
B
(E)-
(Z)-
these substituents caused limitations of the Wittig–Horner-type
annulation to quinolinediones [15].
Entry
Substituent
A
Compound
3JF–F (Hz)
Ref.
[16]
[6]
The 19F NMR of the product 3 contains only two signals for the
B
(Z)-
(E)-
[()D$FIG]
fT our fluorine atoms attached to two double bonds (ꢀ120.3 and
1
2
H
H
19.3
19.5
2.4
131.9
128.2
129.4
–
CH3
CO2Me
CO2Me
CO2Bn
CO2Me
CO2Me
CO2Bn
CO2Me
CO2Me
CN
4
6
3
CH3(CH2)3
CH3(CH2)3
C(CH3)3
C6H5
F
F
4
4.4
R
(-)
(+)
[R Cu]
Li
5
5
7
4.0
128.4
128.4
127.6
130.5
140.0
141.1
2
3
1
CO2Me
F
MeO2C
CuIII
6
3.4
- RCu
- LiF
- RF
7
C6H5
6.6
[6]
F
8
Cl
18.0
28.1
26.0
[17]
[10]
[11]
8
9
MeO2C(CF3)CF
NC(CF3)CF
10
Scheme 2. Proposed intermediate in the
b,
b0-coupling.

J. Hajduch, O. Paleta / Journal of Fluorine Chemistry 132 (2011) 143–146
145
ꢀ137.4 ppm), which indicates a high symmetry of the molecule.
commercially available organolithium reagent (ca. 29 mmol in
organic solvent) was added dropwise while stirring. The mixture
waswarmed upto0 8Cduring30 minandstirredforanother30 min.
The mixture was then cooled to ꢀ100 8C, MTFA (ca. 15 mmol) was
added dropwise and the resulting mixture warmed up to ꢀ70 8C
during next 3 h. The reaction was quenched by addition of
trifluoroacetic acid adjusting pH ca. 5. The crude final mixture
was warmed uptor.t. duringnext2 handthenfiltered. Diethylether
(50 mL) was added to the solution, which was washed three times
with saturated water solution of NH4Cl (3 ꢂ 20 mL). Organic layer
was dried over MgSO4 and then filtered. The crude product was
purified by column chromatography (50 g of silica gel, CH2Cl2).
Both signals appear as doublets cleaved by the same coupling
3
constant JFF = 3.7. Very low coupling constants indicate Z-
configuration on the both double bonds as comes out from the
data in Table 2: the coupling constants for the corresponding E-
configurations are incomparably higher than those for Z-config-
urations.
3. Conclusions
A new
b,
b0-coupling of methyl 2,3,3-trifluorprop-2-noate (1)
by some lithium diorganylcuprates, in which sp2 C–F bonds are
cleaved, afforded dimethyl (Z,Z)-2,3,4,5-tetrafluorohexa-2,4-die-
nedioate (3). The reagents possessing more bulky organyls (butyl,
4.4.2. Reaction of MTFA (1) with lithium dimethylcuprate
MTFA (2.13 g, 15.2 mmol), CuI (2.91 g, 15.3 mmol), methyl-
lithium (22 ml, 30.4 mmol, 1.4 M in diethyl ether), product 3
(1.41 g, 5.81 mmol, 76.4%), ratio 3/4 = 95/5; product 4 (5% rel., 4a/
4b = 90/10).
Dimethyl (Z,Z)-2,3,4,5-tetrafluorohexa-2,4-dienedioate (3): 1H
NMR (CDCl3) d d: 53.2 (s, OCH3);
: 3.88 (s, 6H) ppm. 13C NMR (CDCl3)
phenyl) afforded products of the
bC–F substitution.
4. Experimental
4.1. General comments
1
2
2
3
All starting organolithium reagents and CuI were purchased
from Sigma–Aldrich and used without any further treatment. NMR
spectra were recorded on a Bruker WP 80 SY (1H, 80.13 MHz; 19F,
75.4 MHz) or a Varian 300 HC (1H, 300.08 MHz; 13C, 75.46 MHz;
141.0 (dddd, JCF = 273.1, JCF = 13.7, JCF = 12.3, JCF = 3.5, CF);
1
2
3
4
141.0 (dddd, JCF = 273.1, JCF = 33.2, JCF = 22.0, JCF = 3.0, CF);
158.7 (d, 2JCF = 29.5, C55O); ppm. 19F NMR (CDCl3)
d
: ꢀ120.3 (s, 1F,
3JFF = 3.7); ꢀ137.4 (s, 1F, 3JFF = 3.7, CFC55O) ppm. GC–MS (EI): 243
(M+ + 1; 0.6), 243 (M+, 4.1), 183 (100). Anal. Calcd for C8H6F4O4: C,
39.69; H, 2.50. Found: C, 39.58; H, 2.54.
19F, 276.51 MHz) instrument in CDCl3. Chemical shifts
relative to tetramethylsilane (1H, 0.0 ppm), CDCl3 13C, 77.0 ppm)
d (ppm) are
(
or CFCl3 (19F, 0.0 ppm). For recording of 13C NMR spectra the pulse
sequences APT or DEPT were used. Coupling constants J are given in
Hz. Mass spectra were recorded using a combination of Hewlett
Packard GC HP 5890 series II gas chromatograph and a Hewlett
Packard MS HP 5971 mass spectrometer (70 eV, EI). The capillary
column for GC was DB5-MS.
Methyl (Z)-2,3-difluorobut-2-enoate (4a): 1H NMR (CDCl3)
d:
3
4
2.38 (dd, 3H, JHF = 19.5, JHF = 4.1); 3.84 (s, 3H) ppm. 13C NMR
3
(CDCl3)
d
: 15.0 (d, JCF = 1.3, CH3); 52.2 (s, OCH3); 136.8 (dd,
1JCF = 250,7, 2JCF = 18,9, CF); 156.8 (dd, 1JCF = 268.9, 2JCF = 13.7, CF);
161.5 (dd, JCF = 27.3, JCF = 10.3, C55O); ppm. 19F NMR (CDCl3)
d:
2
3
ꢀ99.05 (q, 1F, 3JHF = 19.5); ꢀ154.3 (s, 1F, CFC55O) ppm. GC–MS (EI):
137 (M+ + 1; 3.7), 136 (M+; 63.0), 135 (M+ ꢀ 1; 0.9), 105 (100).
4.2. Reaction of MTFA (1) with methylmagnesium iodide
Methyl (E)-2,3-difluorobut-2-enoate (4b): 1H NMR (CDCl3)
d:
3
4
2.18 (dd, 3H, JHF = 17.1, JHF = 5.8); 3.86 (s, 3H) ppm. 13C NMR
Under argon, a solution of methylmagnesium iodide (6.2 mmol)
in diethyl ether (30 mL) was added dropwise to a solution of MTFA
(6 mmol) in diethyl ether (20 mL) placed in a flask, which was
cooled in ice-salt bath while stirring (magnetic spinbar). The
mixture was reacted for 2 h and then let to warm up to r.t. during
4 h and after that quenched by trifluoroacetic acid. The ethereal
layer was washed with saturated water solution of NH4Cl and dried
over MgSO4. Volatile components were distilled off (rotary
evaporator) and the residue, a complex mixture (TLC) was
chromatographed (CH2Cl2). The only product isolated was dimer
2 of MTFA (20.1 mg, 14.4 mmol, 4,8%) as a mixture of (E)/(Z) = 88/
12 isomers [10].
(CDCl3)
d
: 14.4 (dd, 2JCF = 44.7, 3JCF = 1.1, CH3); 53.1 (s, OCH3); 139.2
1
2
1
2
(dd, JCF = 233.0, JCF = 39.0, CF); 158.9 (dd, JCF = 268.9, JCF = 49.3,
CF); ppm. 19F NMR (CDCl3)
3JHF = 17.1); ꢀ165.9 (dq, 1F, JFF = 128.2, JHF = 4.9, CFC55O) ppm.
GC–MS (EI): 137 (M+ + 1; 3.7), 136 (M+; 56.5), 135 (M+ ꢀ 1; 0.5), 105
(100).
3
d:
ꢀ110.2 (dq, 1F, JFF = 128.2,
3
4
4.4.3. Reaction of MTFA (1) with lithium di-tert-butylcuprate
MTFA (2.01 g, 14.4 mmol), CuI (2.81 g, 14.8 mmol), tert-
butyllithium (16.9 ml, 28.7 mmol, 1.7 M in pentane), complex
mixture of fluorinated products (2.56 g) was obtained, 19F NMR
and GC–MS identified product 3 and product 5 (5a/5b = 77/23), the
ratio of 5/3 = 44/56.
4.3. Reaction of MTFA (1) with methyllithium
Methyl (Z)-3,3-difluoro-4,4-dimethylpent-2-enoate (5a): 19F
3
NMR (CDCl3)
d
: ꢀ107.5 (bs, 1F); ꢀ150.4 (d, 1F, JFF = 4.0, CFC55O)
To a solution of MTFA (524 mg, 3.74 mmol) in THF (15 mL) in a
flask (25 mL), which was cooled to ꢀ100 8C under argon, a solution
of methyllithium in diethyl ether (2.9 mL, 1.4 M, 4.1 mmol) was
added dropwise while stirring. The mixture was stirred for 1 h, then
acidifiedwithtrifluoroaceticacid topH = ꢁ5and thenlettowarmup
to r.t. during 2 h. The mixture was neutralized by a solution of
NaHCO3 and then filtered. Volatile components were distilled off
(rotary evaporator) and the residue subjected to analysis (19F NMR,
TLC), which detected a rich mixture of compounds mostly of polar
ones. The separation was not successful.
ppm. GC–MS (EI): 178 (M+; 3.3), 59 (100).
Methyl (E)-3,3-difluoro-4,4-dimethylpent-2-enoate (5b): 19F
3
NMR (CDCl3)
d
: ꢀ128.1 (d, 1F, JFF = 130.8); ꢀ165.5 (d, 1F,
3JFF = 130.3, CFC55O) ppm. GC–MS (EI): 178 (M+, 5.9), 131 (100).
4.4.4. Reaction of MTFA (1) with lithium dibutylcuprate (Bu2CuLi)
MTFA (1.95 g; 13.9 mmol), CuI (2.71 g, 14.2 mmol), butyl-
lithium (14 ml, 27.9 mmol, 2 M in pentane), product 6 (2 g,
11.2 mmol, 80.9%, 6a/6b = 93/7).
Anal. Calcd for C8H12F2O2: C, 53.93; H, 6.79. Found: C, 53.88; H,
6.85.
4.4. Reaction of MTFA (1) with lithium dialkylcuprates
Methyl (Z)-2,3-difluorohept-2-enoate (6a): 1H NMR (CDCl3)
d:
0.94 (t, 3H, 3JHH = 7.4); 1.33–1.45 (m, 2H); 1.55–1.65 (m, 2H); 2.77
3
3
4
4.4.1. General procedure
(ddt, 2H, JHF = 26.4, JHH = 7.4, JHF = 2.8); 3.85 (s, 3H) ppm. 13C
To a mixture of CuI (ca. 15 mmol) and dry THF (30 mL) in a flask
(50 mL), which was cooled to ꢀ20 8C under argon, a solution of
NMR (CDCl3)
d
: 13.4 (s, CH3); 21.9 (s, CH2); 27.8 (d, 3JCF = 2.3, CH2);
2
4
28.0 (dd, JCF = 20.2, JCF = 1.7, CH2); 52.1 (s, OCH3); 135.8 (dd,

146
J. Hajduch, O. Paleta / Journal of Fluorine Chemistry 132 (2011) 143–146
1JCF = 251.9, 2JCF = 19.5, CF); 160.1 (dd, 1JCF = 272.2, 2JCF = 11.8, CF);
Acknowledgement
2
3
161.6 (dd, JCF = 27.8, JCF = 9.7, C55O); ppm. 19F NMR (CDCl3)
d:
3
3
3
ꢀ106.6 (dt, 1F, JHF = 25.6, JFF = 2.4); ꢀ155.6 (d, 1F, JFF = 2.4,
The research was supported by the Ministry of Education of the
Czech Republic (Project No. MSM 6046137301).
CFC55O) ppm. GC–MS (EI): 179 (M+ + 1; 50), 149 (100).
Methyl (E)-2,3-difluorohept-2-enoate (6b): 1H NMR (CDCl3)
d:
0.94 (t, 3H, 3JHH = 7.4); 1.33–1.45 (m, 2H); 1.55–1.65 (m, 2H); 2.50
(ddt, 2H, JHF = 22.8, JHH = 7.2, JHF = 5.8); 3.86 (s, 3H) ppm. 13C
3
3
4
References
NMR (CDCl3)
d
: 13.4 (s, CH3); 21.9 (s, CH2); 27.1 (d, 3JCF = 3.0, CH2);
ˇ
[1] V.P. Shendrik, O. Paleta, V. Dedek, Collect. Czech. Chem. Commun. 42 (1977)
2
1
27.4 (dd, JCF = 21.7, CH2); 52.1 (s, OCH3); 162.1 (dd, JCF = 272.0,
2JCF = 46.9, CF); ppm, other signals hidden in a noise. 19F NMR
2530–2536.
[2] O. Paleta, A. Pelter, J. Kebrle, Tetrahedron Lett. 35 (1994) 9259–9262.
[3] O. Paleta, A. Pelter, J. Kebrle, Z. Duda, J. Hajduch, Tetrahedron 56 (2000) 3197–
3207.
[4] Y. Wang, L. Lu, D.J. Burton, J. Org. Chem. 70 (2005) 10743–10746.
[5] S. Yamada, M. Noma, T. Konno, T. Ishihara, H. Yamanaka, Org. Lett. 8 (2006) 843–
845.
[6] S. Yamada, M. Noma, T. Konno, T. Ishihara, J. Org. Chem. 73 (2008) 522–528.
[7] O. Paleta, Z. Duda, A. Holy´, Mendeleev Commun. (2001) 17–18.
[8] J. Hajduch, O. Paleta, J. Kvıcala, G. Haufe, Eur. J. Org. Chem. (2007) 5101–5111.
[9] (a) Y. Wang, L. Lu, D.J. Burton, J. Org. Chem. 71 (2006) 3859–3862;
(b) Y. Wang, L. Lu, D.J. Burton, Org. Lett. 8 (2006) 1109–1111;
(c) F. Chanteau, M. Essers, R. Plantler-Royon, G. Haufe, R. Portella, Tetraheron Lett.
43 (2002) 1677–1680.
3
3
(CDCl3)
d
: ꢀ124.4 (dt, 1F, JFF = 128.2, JHF = 23.2); ꢀ166.8 (dt, 1F,
3JFF = 129.4, 4JHF = 6.1, CFC55O) ppm. GC–MS (EI): 179 (M+ + 1; 100).
4.4.5. Reaction of MTFA (1) with lithium diphenylcuprate (Ph2CuLi)
MTFA (2.25 g, 16.1 mmol), CuI (3.08 g, 16.2 mmol), phenyl-
lithium (17.9 ml, 32.2 mmol, 1.8 M in diethyl ether), product 7
(2.34 g, 11.8 mmol, 73.4%, 7a/7b = 82/8).
´ˇ
Anal. Calcd for C10H8F2O2: C, 60.61; H, 4.07. Found: C, 60.70; H,
4.00.
Methyl (Z)-2,3-difluoro-3-phenylprop-2-enoate (7a): 1H NMR
ˇ
[10] O. Paleta, V. Havlu˚ , V. Dedek, Collect. Czech. Chem. Commun. 45 (1980) 415–
d
: 3.77 (s, 3H); 7.34 – 7.81 (m, 5H, arom.) ppm. 13C NMR
422.
(CDCl3)
(CDCl3)
ˇ
[11] J. Svoboda, O. Paleta, V. Dedek, Collect. Czech. Chem. Commun. 45 (1980) 406–
1
2
d
: 52.3 (s, OCH3); 137.2 (dd, JCF = 256.9, JCF = 22.3, CF);
414.
141.1 (m, arom. C); 156.1 (dd, 1JCF = 249.0, 2JCF = 16.9, CF); 160.8 (dd,
[12] (a) E. Nakamura, S. Mori, Angew. Chem. Int. Ed. Engl. 39 (2000) 3750–3771;
(b) A.E. Dorigo, J. Wanner, P. Schleyer, Angew. Chem. 107 (1995) 492–494.
[13] E. Nakamura, M. Yamanaka, S. Mori, J. Am. Chem. Soc. 122 (2000) 1826–
1827.
[14] (a) D. Naumann, T. Roy, K.F. Tebbe, W. Krump, Angew. Chem. Int. Ed. Engl. 32
(1993) 1482–1483;
(b) R. Eujen, B. Hoge, D.J. Brauer, J. Organomet. Chem. 519 (1996) 7–20.
[15] (a) O. Paleta, K. Pomeisl, A. Kla´sek, S. Kafka, V. Kubelka, Beilst. J. Org. Chem. 1 (17)
(2005);
2JCF = 28.4, 3JCF = 8.3, C55O); ppm. 19F NMR (CDCl3)
d: ꢀ101.0 (d, 1F,
3JFF = 3.4); ꢀ149.3 (d, 1F, JFF = 4.9, CFC55O) ppm. GC–MS (EI): 198
3
(M+, 100).
Methyl (E)-2,3-difluoro-3-phenylprop-2-enoate (7b): 1H NMR
(CDCl3)
(CDCl3)
d
: 3.94 (s, 3H); 7.34–7.81 (m, 5H, arom.) ppm. 13C NMR
1
2
d
: 52.5 (s, OCH3); 139.5 (dd, JCF = 244.4, JCF = 44.1, CF);
1
2
(b) K. Pomeisl, J. Kvı´cala, O. Paleta, A. Klasek, S. Kafka, V. Kubelka, J. Havlıcek, J.
´ˇ
´
ˇ
141.2 (m, arom. C); 155.8 (dd, JCF = 260.2, JCF = 39.5, CF); ppm.
ˇ
Signal C55O hidden in a noise. 19F NMR (CDCl3)
d: ꢀ134.6 (d, 1F,
Cejka, Tetrahedron 63 (2007) 10549–10561.
[16] G.J. DenOtter, C. MacLean, J. Magn. Reson. 20 (1975) 11–18.
[17] J. Svoboda, O. Paleta, V. Dedek, Collect. Czech. Chem. Commun. 46 (1981) 1272–
3JFF = 128.4); ꢀ162.4 (d, 1F, 3JFF = 128.0, CFC55O) ppm. GC–MS (EI):
ˇ
198 (M+, 100).
1279.