Fluoride ion-catalyzed 1,2-desilylative defluorination: Syntheses of 1-substituted 2,2-difluorostyrenes

Article abstract of DOI:10.1021/jo070721h

(Chemical Equation Presented) 1-(3′-Chlorophenyl)-1-trimethylsilyl-1, 2,2,2-tetrafluoroethane has been prepared in an excellent yield by the Mg-promoted defluorinative silylation of 3-chloropentafluoroethylbenzene and transformed to a series of 1-substitu

Full text of DOI:10.1021/jo070721h

1′,1′,4′,4′-tetrafluoro-1, 4-quinodimethane 3, a precursor of the
AF4 polymer (Scheme 1).3
Fluoride Ion-Catalyzed 1,2-Desilylative
Defluorination: Syntheses of 1-Substituted
2,2-Difluorostyrenes
Recently, it was reported that 1,4-desilylative defluorination
of 1-methoxy-1-trimethylsilyloxy-2-trifluoromethyl-2-trimeth-
ylsilyloxyethene 4 proceeds quite smoothly in the presence of
a trace amount (0.2 mol %) of fluoride ion, affording 3,3-
difluoro-2-trimethylsilyloxyacrylate 5 in an excellent yield
(Scheme 1).4 Therefore, the desilylative defluorination reaction
by a catalytic amount of fluoride ion is an efficient synthetic
method for conjugated gem-difluoroalkenes, which are highly
reactive, in general, with nucleophiles such as the fluoride ion.5
There has been no report on 1,2-desilylative defluorination
(transformation of 6 to 7) as shown in Scheme 1.
Yutaka Nakamura and Kenji Uneyama*
Department of Applied Chemistry, Faculty of Engineering,
Okayama UniVersity, Okayama 700-8530, Japan
uneyamak@cc.okayama-u.ac.jp
ReceiVed April 6, 2007
Activation of either an R-trimethylsilyl group or R-fluorine
atom involved in 8 and their replacement with other elements
would provide 1,1-disubstituted 1-aryl-2,2,2-trifluoroethanes,
which would be promising synthetic precursors for 1-substituted
2,2-difluorostyrenes 9 (Scheme 2). On this basis, we describe
here an excellent synthesis of 1-(3′-chlorophenyl)-1-trimethyl-
silyl-1,2,2,2-tetrafluoroethane 8 by Mg(0)-promoted defluori-
native silylation of 3-chlorophenylpentafluoroethane 10 as a
model substrate for pentafluoroethylarenes and divergent trans-
formation of 8 to trifluorostyrene 9a and the related 1-substituted
2,2-difluorostyrenes 9b-d based on the concept of fluoride ion-
catalyzed desilylative defluorination, the first 1,2-elimination
version.
As shown in Scheme 3, 1-(3′-chlorophenyl)-1-trimethylsi-
lyltetrafluoroethane 8 was prepared in an excellent yield by the
Mg(0)-promoted defluorinative silylation of 3-chloropentafluo-
roethylbenzene 10,6 in a Mg-TMSCl-DMPU (1,3-dimethyl-
3,4,5,6-tetrahydro-2(1H)-pyrimidinone) system. As for solvents,
DMPU was excellent, either DMF (81%)7 or NMP (N-methyl-
2-pyrrolidinone) (90%)7 was usable to give 8 in a high yield,
and THF was a poor solvent for the purpose.
Next, transformation of 8 to a series of 1-substituted 2,2-
difluorostyrenes was examined. Fluoride ion-catalyzed 1,2-
desilylative defluorination of 8 (Scheme 4) with a catalytic
amount of TBAT ([n-Bu4N][Ph3SiF2]) would provide 3′-chloro-
1,2,2-trifluorostyrene 9a. The optimization of conditions and
the results are summarized in Table 1.
Yield of 9a was highly dependent on the combination of
solvent and reaction temperature. When CH2Cl2 was used as a
solvent, the desired compound 9a was produced in an excellent
yield (96%). This result clearly demonstrates an excellent
recycling of fluoride ion in the 1,2-desilylative defluorination
reaction. n-Hexane was also an excellent solvent for the purpose,
even though TBAT did not completely dissolve in n-hexane.
1-(3′-Chlorophenyl)-1-trimethylsilyl-1,2,2,2-tetrafluoroethane
has been prepared in an excellent yield by the Mg-promoted
defluorinative silylation of 3-chloropentafluoroethylbenzene
and transformed to a series of 1-substituted 2,2-difluorosty-
renes by fluoride ion-catalyzed 1,2-desilylative defluorina-
tion.
The cleavage of a C-F bond is not easy, in general, due to
the large bond energy (ca. 552 kJ mol-1). However, the bond
breaking does occur rather easily when the CF3 group is attached
to the π-electron system, such as in aryl and carbonyl groups,
since easy electron acceptance into the CF3-attached π-electron
system and subsequent extrusion of a fluoride ion occur to drive
the C-F bond breaking reaction forward. The reactivity and
mechanism on electroreductive cleavage of C-F bonds in
fluoromethylarenes (benzylic fluorides) have been investigated
by several groups.1 Bordeau and co-workers2a,b and Pe´richon
and co-workers2c reported the selective synthesis of PhCF2SiMe3
via an electrochemical reduction of PhCF3 in the presence of
chlorotrimethylsilane and the reaction of PhCF2SiMe3 as a
synthon of the PhCF2 anion.
We have reported Mg(0) metal-promoted benzylic C-F bond
activation of 1,4-bis(trifluoromethyl)benzene 1 as a useful
building block for (1′,1′,4′,4′,4′-pentafluoro-1′-trimethylsilyl)-
1,4-xylene 2, and subsequent 1,6-desilylative defluorination (1,6-
version) of 2 by a catalytic amount of fluoride ion gave
(1) (a) Lung, H. Acta Chem. Scand. 1959, 13, 192-194. (b) Cohen, A.
I.; Keeler, B. T.; Coy, N. H.; Yale, H. L. Anal. Chem. 1962, 34, 216-219.
(c) Coleman, J. P.; Gilde, H. G.; Utley, J. H. P.; Weedon, B. C. L.; Eberson,
L. J. Chem. Soc., Chem. Commun. 1970, 738-739. (d) Coleman, J. P.;
Naser-ud-din; Gilde, H. D.; Utley, J. H. P.; Weedon, Basil C. L.; Eberson,
L. J. Chem. Soc., Perkin Trans. 2 1973, 1903-1908. (e) Andrieux, C. P.;
Combellas, C.; Kanoufi, F.; Saveant, J.-M.; Thiebault, A. J. Am. Chem.
Soc. 1997, 119, 9527-9540.
(2) (a) Clavel, P.; Leger-Lambert, M. P.; Biran, C.; Serein-Spirau, F.;
Bordeau, M.; Roques, N.; Marzouk, H. Synthesis 1999, 829-834. (b) Clavel,
P.; Lessene, G.; Biran, C.; Bordeau, M.; Roques, N.; Trevin, S.; de
Montauzon, D. J. Fluorine Chem. 2001, 107, 301-310. (c) Saboureau, C.;
Troupel, M.; Sibille, S.; Pe´richon, J. J. Chem. Soc., Chem. Commun. 1989,
1138-1139.
(3) (a) Amii, H.; Hatamoto, Y.; Seo, M.; Uneyama, K. J. Org. Chem.
2001, 66, 7216-7218. (b) Preparation of 3 by zinc reduction of 1,4-bis-
(chlorodifluoromethyl)benzene: Dolbier, W. R., Jr.; Asghar, M. A.; Pan,
H. Q.; Celewicz, L. J. Org. Chem. 1993, 58, 1827-1830. (c) Preparation
of 3 by PbBr2Al reduction: Zhu, S.-Z.; Mao, Y.-Y.; Jin, G.-F.; Qin, C.-Y.;
Chu, Q.-L.; Hu, C.-M. Tetrahedron Lett. 2002, 43, 669-671.
(4) Takikawa, G.; Toma, K.; Uneyama, K. Tetrahedron Lett. 2006, 47,
6509-6511.
(5) Uneyama, K. Organofluorine Chemistry; Blackwell Publishing:
Oxford, UK, 2006.
(6) Synthetic method for 10: Carr, G. E.; Chambers, R. D.; Holmes, T.
F. J. Chem. Soc., Perkin. Trans. 1 1988, 921-926.
(7) Yields were determined by 19F NMR integration of products relative
to benzotrifluoride as an internal standard.
10.1021/jo070721h CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/21/2007
5894
J. Org. Chem. 2007, 72, 5894-5897

TABLE 1. Fluoride Ion-Catalyzed Desilylative Defluorination of 8
SCHEME 1. Fluoride Ion-Catalyzed Desilylative
Defluorination
Yield (%)b
entry
solvent
tempa (°C)
9a
11
12
1
CH2Cl2
n-hexane
n-hexane
THF
THF
THF
rt
rt
60
96
92
98 (90)
16
25
79
<1
4
0
43
20
10
1
4
1
10
7
6
2c
3
4
5
6
-40
0
60
a Temperatures of oil, ice-water, and acetone-liquid N2 baths. b NMR
yields were analyzed by 19F NMR integration of products relative to
benzotrifluoride as an internal standard. Yield in parenthesis is an isolated
yield. c Reaction took place in 2 h.
SCHEME 5. Al-Lewis Acid-Catalyzed Defluorinative
Halogenation of 8
SCHEME 2. Synthetic Strategy for 1-Substituted
2,2-Difluorostyrenes
1-Chloro compound 13 was prepared in an excellent yield by
fluorine-chlorine exchange reaction of 8 with Et2AlCl. Interest-
ingly, 1-bromo-2,2-difluorostyrene 9b was directly obtained by
the reaction of 8 with AlBr3. It is suggested that the fluorine-
bromine exchange reaction occurred at the benzylic position
and subsequent 1,2-desilylative defluorination proceeded si-
multaneously under the reaction conditions. A trace amount of
fluoride or chloride ions would be generated, and it would
induce the desilylative defluorination of 1-bromo-2,2,2-trifluoro-
1-(3′-chlorophenyl)-1-trimethylsilylethane generated in situ
(Scheme 5).
SCHEME 3. Defluoro Silylation of Pentafluoroethylarene
10
SCHEME 4. Fluoride Ion-Catalyzed Desilylative
Defluorination of 8
The C-F bond activation with Lewis acids, in particular,
aluminum and boron reagents, is well-known.8 The present
halogen exchange reactions of 8 would be initiated by pulling
out benzylic fluorine as the fluoride ion with aluminum, which
has a strong affinity to the fluorine atom due to its large Al-F
bond energy. Also, it is plausible that the exchange reaction is
(8) Benzotrifluoride: (a) Prakash, G. K. S.; Hu, J.; Simon, J.; Bellew,
D. R.; Olah, G. A. J. Fluorine Chem. 2004, 125, 595-601. (b) Riera, J.;
Castaner, J.; Carilla, J.; Robert, A. Tetrahedron Lett. 1989, 30, 3825-3828.
(c) Castaner, J.; Riera, J.; Carilla, J.; Robert, A.; Molins, E.; Miravitlles, C.
J. Org. Chem. 1991, 56, 103-110. (d) Carilla, J.; Fajari, L; Garcia, R.;
Julia, L.; Marcos, C.; Riera, J.; Whitaker, C. R.; Rius, J.; Aleman, C. J.
Org. Chem. 1995, 60, 2721-2725. (e) Ramchandani, R. K.; Wakharkar,
R. D.; Sudalai, A. Tetrahedron Lett. 1996, 37, 4063-4064. Fluoroalkane:
(f) Olah, G. A.; Kuhn, S. J. Org. Chem. 1964, 29, 2317-2320. (g) Ooi, T.;
Uraguchi, D.; Kagoshima, N.; Maruoka, K. Tetahedron Lett. 1997, 38,
5679-5682. (h) Hirano, K.; Fujita, K.; Yorimitsu, H.; Shinokubo, H.;
Oshima, K. Tetrahedron Lett. 2004, 45, 2555-2557. (i) Begum, S. A.;
Terao, J.; Kambe, N. Chem. Lett. 2007, 36, 196-197. (j) Terao, J.; Begum,
S. A.; Shinohara, Y.; Tomita, M.; Naitoh, Y.; Kambe, N. Chem. Commun.
2007, 855-857. Glycosyl fluoride: (k) Nicolaou, K. C.; Dolle, R. E.;
Chucholowski, A.; Randall, J. L. J. Chem. Soc., Chem. Commun. 1984,
1153-1154. (l) Posner, G. H.; Haines, S. R. Tetrahedron Lett. 1985, 26,
1823-1826. (m) Nicolaou, K. C.; Dolle, R. E.; Papahatjis, D. P. J. Am.
Chem. Soc. 1984, 106, 4189-4192. (n) Macdonald, S. J. F.; Huizinga, W.
B.; McKenzie, T. C. J. Org. Chem. 1988, 53, 3371-3373. (o) Drew. K.
N.; Gross. P. H. J. Org. Chem. 1991, 56, 509-513.
Essentially, no byproduct was observed in n-hexane, although
rather higher temperature was required. In THF, the products
were markedly dependent on the reaction temperature. Dimer
11 would be formed by addition-elimination reaction of the
corresponding R-phenethyl carbanion to 9a at low temperature
(-40 °C). Meanwhile, the higher temperature (60 °C) would
accelerate the elimination of the fluoride ion from the R-phen-
ethyl carbanion leading to 9a as expected in a normal E2
reaction.
It is interesting to see if replacement of an R-fluorine atom
of 8 with chlorine and bromine atoms is possible. The
transformations would widen the scope of the key substrate 8
as a synthetic precursor of 1-substituted 2,2-difluorostyrenes.
J. Org. Chem, Vol. 72, No. 15, 2007 5895

SCHEME 6. Transformation of 13 to 1-Chloro- or
1-Trimethylsilyl-2,2-difluorostyrenes (9c or 9d)
ethylbenzene 10 (4.60 g, 20 mmol) was added dropwise, and then
the mixture was stirred for 5 h. At this time, the 19F NMR yield of
8 was 99%. After filtration of the residual Mg, the DMPU solution
was extracted with n-hexane (20 mL × 4). Hydrolysis of product
12 occurred during filtration. Therefore, quick filtering is strongly
required to avoid the hydrolysis. The n-hexane layer was washed
with ice water and dried over anhydrous MgSO4. Purification by a
short column on silica gel and distillation (40 °C/0.1 mmHg)
afforded 8 (5.20 g, 92%) as a colorless oil: IR (neat) 2968, 1602,
1178, 884, 848 cm-1; 1H NMR (600 MHz, CDCl3) δ 0.17 (s, 9H),
7.22-7.25 (m, 1H), 7.31-7.35 (m, 2H), 7.37 (s, 1H); 13C NMR
(150 MHz, CDCl3) δ -3.6 (d, J ) 2 Hz), 95.1 (dq, J ) 185, 34
Hz), 122.0 (dq, J ) 12, 2 Hz), 124.2 (dd, J ) 14, 2 Hz), 124.8
(dq, J ) 25, 280 Hz), 128.1, 129.7 (d, J ) 2 Hz), 134.7 (d, J ) 4
Hz), 137.0 (dq, J ) 18, 2 Hz); 19F NMR (564 MHz, CDCl3) δ
-36.3 (q, J ) 11 Hz, 1F), 90.1 (d, J ) 11 Hz, 3F); EI MS m/z
(relative intensity) 211 (0.5), 194 (33), 192 (100), 157 (13), 73
(54). Anal. Calcd for C11H13ClF4Si: C, 46.40; H, 4.60. Found: C,
46.45; H, 4.60.
3′-Chloro-1,2,2-trifluorostyrene (9a). 1-(3′-Chlorophenyl)-1-
trimethylsilyl-1,2,2,2-tetrafluoroethane 8 (1.40 g, 5 mmol) was
added to a mixture of TBAT (13 mg, 0.025 mmol) in n-hexane
(10 mL) at 60 °C, and then the resulting mixture was stirred for 10
min at 60 °C. After removal of the solvent from the crude reaction
mixture, distillation of the residue (65 °C/20 mmHg) afforded 9a
(0.87 g, 90%) as a colorless oil: IR (neat) 1760, 1290, 1156, 1004,
782 cm-1; 1H NMR (600 MHz, CDCl3) δ 7.32-7.37 (m, 3H), 7.47
(s, 1H); 13C NMR (150 MHz, CDCl3) δ 122.3 (ddd, J ) 8, 6, 4
Hz), 124.3 (ddd, J ) 7, 7, 4 Hz), 127.7 (ddd, J ) 226, 45, 21 Hz),
128.9 (t, J ) 2 Hz), 129.0 (dd, J ) 22, 7 Hz), 130.0 (d, J ) 1 Hz),
134.9 (d, J ) 2 Hz), 153.9 (ddd, J ) 291, 283, 49 Hz); 19F NMR
(564 MHz, CDCl3) δ -15.5 (dd, J ) 109, 33 Hz, 1F), 49.0 (dd, J
) 67, 109 Hz, 1F), 63.9 (dd, J ) 33, 67 Hz, 1F); EI MS m/z
(relative intensity) 194 (33), 192 (100), 157 (62), 137 (10), 107
(56).
accelerated by an electron-donating trimethylsilyl group since
no reaction occurs on treating non-silylated 10 with Et2AlCl
under the same conditions.
As Burton and co-workers reported that 1-halo-2,2-difluo-
rostyrenes (9b, 9c) were functionalized at the halogen site with
arylboronic acids under Pd(0)-catalyzed coupling reaction
conditions, 1-halo-9 and 1-trimethylsilyl-2,2-difluorostyrenes10
are useful synthetic intermediates. Here again, fluoride ion-
catalyzed 1,2-desilylative defluorination is useful for the
preparation of 1-chloro-2,2-difluorostyrene 9c from 13. As
shown in Scheme 6, the styrene 9c was prepared in an excellent
yield by the use of a trace amount of fluoride ion.
3′-Chloro-1-trimethylsilyl-2,2-difluorostyrene 9d serving as
the 1-aryl-2,2-difluoroethenyl carbanion synthon was produced
in 93% isolated yield by metal Zn reductive dechloro-
defluorination.11
In conclusion, 1-(3′-chlorophenyl)-1-trimethylsilyltetrafluo-
roethane 8 was prepared in an excellent yield by the Mg(0)-
promoted defluorinative silylation of 3-chloropentafluoroeth-
ylbenzene. Furthermore, a variety of 1-substituted 2,2-
difluorostyrenes (9a-d) were obtained in high yields via the
three types of defluorinations (1,2-desilylative defluorination
by a catalytic amount of fluoride ion, C-F bond activation by
aluminum reagents, and metal Zn reductive dechloro-deflu-
orination) suitably designed for the structure of each substrate.
The spectral data were consistent with those reported in ref 9b.
1-(3′-Chlorophenyl)-1-chloro-1-trimethylsilyl-2,2,2-trifluoro-
ethane (13). n-Hexane solution of Et2AlCl (0.92 mol/L) (14.1 mL,
13 mmol) was added to 1-(3′-chlorophenyl)-1-trimethylsilyl-1,2,2,2-
tetrafluoroethane 8 (2.85 g, 10 mmol) at room temperature under
an argon atmosphere, and the resulting mixture was stirred for 30
min. Then, the reaction mixture was quenched with a cold water,
and the organic layer was washed with aqueous NaHCO3 and dried
over anhydrous MgSO4. Purification by distillation (75 °C/0.1
mmHg) afforded 13 (2.95 g, 98%) as a colorless oil: IR (neat)
2968, 1596, 1240, 1168, 848 cm-1; 1H NMR (600 MHz, CDCl3) δ
0.20 (s, 9H), 7.30-7.32 (m, 2H), 7.47-7.50 (m, 1H), 7.62 (br,
1H); 13C NMR (150 MHz, CDCl3) δ -2.5 (d, J ) 2 Hz), 64.3 (q,
J ) 32 Hz), 125.2 (q, J ) 2 Hz), 126.3 (q, J ) 279 Hz), 127.5 (q,
J ) 2 Hz), 128.0, 129.4, 134.4, 136.5 (d, J ) 1 Hz); 19F NMR
(564 MHz, CDCl3) δ 97.7 (s, 3F); EI MS m/z (relative intensity)
212 (11), 210 (74), 208 (100), 173 (19), 133 (17), 73 (77). Anal.
Calcd for C11H13Cl2F3Si: C, 43.86; H, 4.35. Found: C, 44.00; H,
4.23.
3′-Chloro-1-bromo-2,2-difluorostyrene (9b). 1-(3′-Chlorophe-
nyl)-1-trimethylsilyl-1,2,2,2-tetrafluoroethane 8 (1.40 g, 5 mmol)
was added to AlBr3 (1.73 g, 6.5 mmol) in n-hexane (15 mL) at
room temperature, and then the resulting mixture was stirred for
30 min. The reaction mixture was quenched with a cold water. The
organic layer was washed with aqueous NaHCO3 and dried over
anhydrous MgSO4. Purification of the crude products by chroma-
tography on silica gel (n-hexane, Rf ) 0.60) afforded 9b (0.90 g,
71%) as a colorless oil: IR (neat) 1720, 1266, 1170, 992 cm-1; 1H
NMR (600 MHz, CDCl3) δ 7.30-7.33 (m, 2H), 7.37-7.39 (m,
1H), 7.39-7.51 (m, 1H); 13C NMR (150 MHz, CDCl3) δ 78.7 (dd,
J ) 34, 27 Hz), 126.9 (t, J ) 3 Hz), 128.9 (t, J ) 4 Hz), 128.9,
129.7, 133.3 (d, J ) 4 Hz), 134.5, 153.3 (dd, J ) 294, 286 Hz);
19F NMR (564 MHz, CDCl3) δ 78.9 (d, J ) 28 Hz, 1F), 84.9 (d,
Experimental Section
1-(3′-Chlorophenyl)-1-trimethylsilyl-1,2,2,2-tetrafluoroet-
hane (8). A suspension of Me3SiCl (10 mL, 80 mmol) in freshly
distilled DMPU (60 mL) and Mg powder (0.97 g, 40 mmol) was
cooled to 0 °C under an argon atmosphere. 3-Chloropentafluoro-
(9) Synthesis of 1-halo-2,2-difluorostyrenes by Pd-catalyzed cross-
coupling of the CF2dCXZnX type zinc reagent with aryl iodides: (a)
Anilkumar, R.; Burton, D. J. Tetrahedron Lett. 2002, 43, 2731-2733. (b)
Anilkumar, R.; Burton, D. J. J. Org. Chem. 2004, 69, 7083-7091. (c)
Anilkumar, R.; Burton, D. J. Tetrahedron Lett. 2002, 43, 6979-6982. (d)
Anilkumar, R.; Burton, D. J. J. Fluorine Chem. 2005, 126, 833-841. (e)
Anilkumar, R.; Burton, D. J. J. Fluorine Chem. 2004, 125, 561-566. (f)
Anilkumar, R.; Burton, D. J. J. Fluorine Chem. 2005, 126, 457-463.
Application of 1-halo-2,2-difluorostyrenes: (g) Anilkumar, R.; Burton, D.
J. J. Org. Chem. 2006, 71, 194-201.
(10) Synthesis of 1-trimethylsilyl-2,2-difluorostyrene: Okano, T.; Ito,
K.; Ueda, T.; Muramatsu, H. J. Fluorine Chem. 1986, 32, 377-388.
(11) Examples of reductive dechloro-defluorination by metal (Zn,
Mg): (a) Cohen, S. G.; Wolosinski, H. T.; Scheuer, P. J. J. Am. Chem.
Soc. 1949, 71, 3439-3440. (b) Svoboda, J.; Palecek, J.; Dedek, V.;
Mostecky, J. Sb. Vys. Sk. Chem. Technol. Praze, C: Org. Chem. Technol.
1986, C29, 45-54. (c) Okano, T.; Ito, K.; Ueda, T.; Muramatsu, H. J.
Fluorine Chem. 1986, 32, 377-388.
5896 J. Org. Chem., Vol. 72, No. 15, 2007

J ) 28 Hz, 1F); EI MS m/z (relative intensity) 256 (M+ + 4) (17),
254 (M+ + 2) (74), 252 (M+) (51), 173 (68), 138 (100), 87 (22).
Compound 9b is very moisture-sensitive. Hydrolysis of 9b
immediately occurs by contact with air. Therefore, elemental
analysis was unsuccessful.
129.5, 134.0, 136.5 (dd, J ) 10, 2 Hz), 155.6 (dd, J ) 306, 285
Hz); 19F NMR (564 MHz, CDCl3) δ 84.7 (d, J ) 25 Hz, 1F), 92.2
(d, J ) 25 Hz, 1F); EI MS m/z (relative intensity) 248 (10), 246
(27), 154 (16), 115 (56), 77 (100). Anal. Calcd for C11H13ClF2Si:
C, 53.54; H, 5.31. Found: C, 53.30; H, 5.36.
3′-Chloro-1-trimethylsilyl-2,2-difluorostyrene (9d). To the
mixture of Zn dust and Me3SiCl (10 mL, 80 mmol) in distilled
THF heated up to 50 °C under argon atmosphere was added
dropwise 1-(3′-chlorophenyl)-1-chloro-1-trimethylsilyl-2,2,2-trif-
luoroethane 13 (1.50 g, 5 mmol), and then the reaction mixture
was stirred for an additional 2 h at 50 °C. After evaporation of
most of THF under reduced pressure, n-hexane was added to the
residue, and the resulting salt was filtered. After removal of the
solvent from the filtrate, distillation (40 °C/0.1 mmHg) of the
residue afforded 9d (1.15 g, 93%) as a colorless oil: IR (neat) 2960,
1710, 1180, 1110, 890 cm-1; 1H NMR (600 MHz, CDCl3) δ 0.17
Acknowledgment. This work was supported by the Ministry
of Education, Culture, Sports, Science and Technology of Japan
[Grant-in-Aid for Scientific Research (C), No. 17550104]. We
also thank the SC-NMR Laboratory of Okayama University for
1
the H, 13C, and 19F NMR analyses.
Supporting Information Available: Experimental details for
compounds 9c and 10, and 1H, 13C, and 19F NMR data for
compounds 8, 9, 10, 11, and 13. This material is available free of
charge via the Internet at http://pubs.acs.org.
(s, 9H), 6.97-6.98 (m, 1H), 7.10 (s, 1H), 7.23-7.29 (m, 2H); 13
C
NMR (150 MHz, CDCl3) δ -1.1 (t, J ) 2 Hz), 87.1 (dd, J ) 35,
5 Hz), 126.7, 127.2 (dd, J ) 3, 1 Hz), 129.0 (dd, J ) 3, 1 Hz),
JO070721H
J. Org. Chem, Vol. 72, No. 15, 2007 5897