Decarboxylative julia-kocienski gem-difluoro-olefination of 2-pyridinyl sulfonyldifluoroacetate

Article abstract of DOI:10.1002/ejoc.201301654

The decarboxylation of potassium 2-pyridinyl sulfonyldifluoroacetate and its subsequent reaction with aldehydes was found to be an efficient approach for the Julia-Kocienski reaction under mild conditions to give gem-difluoro olefins in moderate to excell

Full text of DOI:10.1002/ejoc.201301654

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201301654
Decarboxylative Julia–Kocienski gem-Difluoro-Olefination of 2-Pyridinyl
Sulfonyldifluoroacetate
Xiao-Ping Wang,[a,b] Jin-Hong Lin,[a] Ji-Chang Xiao,*[a] and Xing Zheng[b]
Keywords: Fluorine / Decarboxylation / Sulfur / Olefination / Aldehydes
The decarboxylation of potassium 2-pyridinyl sulfonyldi-
fluoroacetate and its subsequent reaction with aldehydes
was found to be an efficient approach for the Julia–Kocienski
reaction under mild conditions to give gem-difluoro olefins
in moderate to excellent yields. Owing to its high stability in
the pure state and its easy decarboxylation in polar solvents,
potassium 2-pyridinyl sulfonyldifluoroacetate is expected to
be an efficient gem-difluoro-olefination reagent.
(CF2=C).[3] Traditional methods, including organometal-
lic[3c,4] and elimination[5] approaches and Julia,[6] Horner–
Introduction
The installation of fluorine or fluorine-containing func- Wadsworth–Emmons,[7] and Wittig reactions,[8] require the
tional groups into organic molecules usually has a profound tedious multistep synthesis of the fluorinated precursors,
effect on the physical, chemical, and biological properties of the presence of base, careful handling of the reagents owing
the target molecules.[1] As an important class of fluorinated to their sensitivity to moisture, and the use of environmen-
compounds, gem-difluoro olefins have the potential to be tally unfriendly reagents. We previously found that the de-
used in a wide range of research areas, such as medical and carboxylative Wittig reaction was an efficient approach for
agricultural chemistry and material sciences.[2] Owing to the synthesis of gem-difluoro olefins.[9] As an extension of
their versatility, considerable effort has been directed our studies on this chemistry,[9,10] we describe the decarbox-
towards the search for efficient and general methods for the ylative Julia–Kocienski reaction of aldehydes with 2-pyrid-
construction of the gem-difluorovinylidene moiety inyl sulfonyldifluoroacetate to afford gem-difluoro olefins.
Scheme 1. Julia gem-difluoro-olefination.
The classic Julia gem-difluoro-olefination reaction em-
[a] Key Laboratory of Organofluorine Chemistry, Shanghai
–
ploys PhSO2CF2 as the nucleophile, which is generated
in situ from PhSO2CF2H[6a–6c] or PhSO2CF2Br[6d] by de-
protonation or single-electron transfer, respectively. In these
approaches, desulfonylation is problematic because it needs
multistep treatment or the use of the toxic reagent Na(Hg)
[Scheme 1, Eq. (1)]. Recently, Hu and co-workers found
that difluoromethyl 2-pyridinyl sulfone could act as a
Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, China
E-mail: jchxiao@sioc.ac.cn
http://xiaojichang.sioc.ac.cn/
[b] Institute of Pharmacy and Pharmacology, University of South
China,
Hengyang, Hunan 421001, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301654.
928
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 928–932

Decarboxylative Julia–Kocienski gem-Difluoro Olefination
powerful gem-difluoro-olefination reagent. This approach is Table 1. Optimization of the reaction conditions for the gem-di-
fluoro-olefination.[a]
quite promising because the transformation is applicable to
both aldehydes and ketones, but strong base was required
–
to generate 2-PySO2CF2 at low temperature [Scheme 1,
Eq. (2)].[6e] In this communication, we report the decarbox-
ylation of potassium 2-pyridinyl sulfonyldifluoroacetate
and its subsequent reaction with aldehydes to give gem-di-
fluoro olefins under mild conditions [Scheme 1, Eq. (3)].
Entry
1/2[b]
T [°C]
Solvent
Yield[c] [%]
No base is needed in this simple and convenient conversion.
1
2
3
4
5
6
7
8
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1.5:1
2:1
3:1
1:2
60
60
60
60
60
80
40
r.t.
40
40
40
40
40
DMF
DMSO
CH3CN
THF
1,4-dioxane
DMF
63
63
15
trace
0
63
63
15
63
93
93
93
75
Results and Discussion
Potassium 2-pyridinyl sulfonyl-difluoroacetate (1) could
be easily synthesized from the reaction of 2-pyridinethiol
and ethyl bromodifluoroacetate, followed by oxidation and
hydrolysis (Scheme 2). The salt is stable under air atmo-
sphere. Thermal analysis (DSC-TGA) showed no decompo-
sition below 100 °C (see the ESI), demonstrating relatively
good thermal stability. However, as shown by 19F NMR,
slow decomposition via decarboxylation commenced in the
presence of polar solvent such as DMF even at room tem-
perature, which means decarboxylation of salt 1 in solvent
could happen under mild conditions. The high stability in
pure state and easy decarboxylation in polar solvent sug-
gested this salt could be stored for a long time and gem-
difluoro-olefination could be achieved under mild condi-
tions, which is indeed the case.
DMF
DMF
DMF
DMF
DMF
DMF
DMF
9[d]
10
11
12
13
[a] Reaction conditions: salt 1 and aldehyde in solvent (2 mL) at
40 °C for 2 h, followed by 3 n HCl (1.2 mL) for 2 h. [b] Molar ratio.
[c] Determined by 19F NMR spectroscopy with trifluoromethylben-
zene as an internal standard;. [d] The reaction was run for 6 h.
The substrates scope of the gem-difluoro-olefination re-
action of salt 1 with aldehydes was then explored under the
optimized reaction conditions (Table 1, entry 10). As shown
in Scheme 3, the reaction tolerated various functional
groups and gave the corresponding gem-difluoro olefins in
moderate to excellent yields. Examination of electronic sub-
stituent effects (see 3a–i) showed that electron-withdrawing
groups on the phenyl ring (as in 3a–e) in the substrates led
to better results, presumably as a result of the stronger elec-
Scheme 2. The synthesis of potassium 2-pyridinyl sulfonyl-di-
fluoroacetate.
With stable salt 1 in hand, we then attempted the gem- trophilic ability of these substrates. The reaction is not quite
difluoro-olefination with aldehydes. The reaction mixture sensitive to steric hindrance. With two methyl groups in the
of salt 1 with 4-bromobenzaldehyde in DMF was stirred ortho position of the phenyl ring, a moderate yield of 3g was
at 60 °C for 2 h and then quenched with 3 n HCl. With still obtained. In the cases of 2-naphthyl or heteroaromatic
(trifluoromethyl)(benzene) as an internal standard, analysis substrates 3j–l, the conversion gave the desired products in
of the organic phase by 19F NMR spectroscopy showed good yields. The transformation proceeded smoothly for an
that the product was obtained in 63% yield (Table 1, en- α,β-unsaturated aldehyde, even though the yield of 3m was
try 1). The transformation in DMSO gave the same result lower. The reaction was also applicable to enolizable ali-
(Table 1, entry 2). With the use of a less polar solvent, the phatic aldehydes. The low yield of 3n is probably due to
yield decreased dramatically (Table 1, entries 3–5), and no enolization of the aldehyde in the presence of salt 1, which
desired product was detected in 1,4-dioxane (Table 1, en- could be considered as a weak base. gem-Difluoro-ole-
try 5). We next screened other conditions in DMF. The ex- fination of ketones proceeded sluggishly, and only trace
amination of the reaction temperature (Table 1, entries 6–8) amounts of the products were detected by GC–MS.
showed that slight heating (40 °C) was necessary (Table 1,
As for the reaction mechanism, it is reasonable to con-
entry 7). If the temperature was lowered to room tempera- ceive a pathway involving the condensation of the aldehyde
–
ture, the conversion was suppressed greatly (Table 1, en- with 2-PySO2CF2 , which is generated in situ by decarbox-
try 8). Prolonging the reaction time to 6 h gave the same ylation of salt 1 (Scheme 4). The condensation gives inter-
yield as that obtained after 2 h (Table 1, entry 9 vs. 1). The mediate A, followed by rearrangement to afford more stable
amount of salt 1 had a strong effect on the reaction. By salt B. If the conversion into salt B is completed, the reac-
increasing the amount to 1.5 equiv., the yield improved sig- tion is quenched by acid. Protonation of salt B leads to
nificantly (Table 1, entry 10 vs. 1), but any further increase intermediate C, which results in enhanced leaving ability of
in the amount of 1 gave the same results (Table 1, entries 11 the 2-pyridyloxyl group. Decomposition of intermediate C
and 12). In contrast, an excess amount of aldehyde resulted gives the final product. The mechanism is supported by the
in poor results (Table 1, entry 13).
experimental observation of the formation of salt B by 19F
Eur. J. Org. Chem. 2014, 928–932
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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929

X.-P. Wang, J.-H. Lin, J.-C. Xiao, X. Zheng
SHORT COMMUNICATION
–
Scheme 3. gem-Difluoro-olefination of aldehydes with PySO2CF2CO2 K+. Reaction conditions: Salt 1 (0.9 mmol) and aldehyde
(0.6 mmol) in DMF (2 mL) at 40 °C for 2 h, followed by 3 n HCl (1.2 mL) for 2 h, yields of the isolated products are given.
NMR spectroscopy {δ = –128.7 ppm [(ABq)d, δAB
=
Experimental Section
157.3 ppm, Jd = 11.8 Hz, 2 F]} and ESIMS {m/z = 375.5,
377.5 [M – K]–; calcd. 375.9, 377.9} before the reaction sys-
tem of salt 1 with 4-bromobenzaldehyde was quenched with
acid, which is consistent with the results obtained by Hu
and co-workers.[6e]
General Information: 1H NMR and 13C NMR spectra were re-
corded at 400 or 300 and 100 MHz, respectively, with tetramethyl-
silane as the internal standard. 19F NMR spectra were recorded at
376 MHz with CFCl3 (positive for downfield shifts) as the external
standard. All solvents were purified by standard methods. Flash
column chromatography was performed by using 300–400 mesh sil-
ica gel.
Preparation of Potassium 2-Pyridinyl Sulfonyl-difluoroacetate (1): A
solution of pyridine-2-thiol (16 g, 0.14 mol, 1.0 equiv.) in DMF
(70 mL) was added dropwise over a period of 5 h at 0 °C under an
atmosphere of N2 to a suspension of NaH (60 wt.-%, 6.04 g,
0.15 mol, 1.07 equiv.) in DMF (100 mL). Upon completion of the
addition, the reaction mixture was warmed up to room temperature
and stirred for another 0.5 h. BrCF2CO2C2H5 (28 g, 0.14 mol,
1.0 equiv.) was added. The resulting mixture was stirred overnight.
Upon completion of the conversion, the reaction was quenched by
water (100 mL), followed by extraction with Et2O (100 mL ϫ3).
The organic phase was washed with brine and then dried with an-
hydrous Na2SO4. After the solution was filtered, the solvent was
evaporated under vacuum to give a yellow oil. CCl4 (120 mL), H2O
(300 mL), NaIO4 (100 g, 0.47 mol), and ruthenium trichloride hy-
drate (20 mg) were added to a solution of this oil in CH3CN
Scheme 4. Proposed mechanism for the gem-difluoro-olefination of
aldehydes.
Conclusions
In summary, we found that the generation of 2- (120 mL). The mixture was stirred over a period of 36 h at room
–
temperature. Upon completion of the oxidation, H2O (300 mL) was
added to quench the reaction. The mixture was extracted with di-
ethyl ether (200 mL ϫ3). The combined organic phase was washed
successively with saturated NaHCO3 and NaCl solution and then
dried with anhydrous Na2SO4. After the solution was filtered and
the solvent was evaporated under vacuum, the residue was sub-
jected to silica gel column chromatography (petroleum ether/ethyl
acetate, 4:1 v/v) to give a colorless liquid (10 g). KOH (2 g,
0.035 mol) was added to a solution of this colorless liquid (10 g) in
MeOH (20 mL). The mixture was stirred at room temperature for
6 h. After filtration and concentration, the pure product was ob-
PySO2CF2 through the decarboxylation of potassium 2-
pyridinyl sulfonyldifluoroacetate was an efficient method
for the Julia–Kocienski gem-difluoro-olefination of alde-
hydes. Potassium 2-pyridinyl sulfonyldifluoroacetate exhib-
its good stability in the pure state and readily undergoes
decarboxylation in polar solvents under mild conditions,
which suggests that this salt might be expected to be a con-
venient gem-difluoro-olefination reagent. Investigation into
the application of potassium 2-pyridinyl sulfonyldifluoro-
acetate in other reactions is currently underway.
930
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 928–932

Decarboxylative Julia–Kocienski gem-Difluoro Olefination
tained as a white solid (9.8 g, 0.035 mol, 25% yield over 3 steps),
5.23 (dd, J = 27.4, 2.0 Hz, 1 H), 2.33 (s, 3 H), 2.29 (s, 6 H) ppm.
19F NMR (376 MHz, CDCl3): δ = –83.86 (dd, J = 34.0, 27.4 Hz,
m.p. 142 °C. 1H NMR (300 MHz, D2O): δ = 8.77 (s, 1 H), 8.29–
8.14 (m, 2 H), 7.94–7.77 (m, 1 H) ppm. 13C NMR (100 MHz, 1 F), –87.52 (dd, J = 34.0, 2.0 Hz, 1 F) ppm.
D2O): δ = 161.2 (t, J = 22.9 Hz), 150.9, 150.2, 133.9, 130.3, 127.2,
1-(Benzyloxy)-4-(2,2-difluorovinyl)benzene (3h):[8e] Colorless oil,
115.3 (t, J = 301.6 Hz) ppm. 19F NMR (282 MHz, D2O): δ =
109 mg, 74% yield. 1H NMR (400 MHz, CDCl3): δ = 7.50–7.28
(m, 5 H), 7.24 (d, J = 8.7 Hz, 2 H), 6.93 (d, J = 8.7 Hz, 2 H), 5.19
(dd, J = 26.4, 3.7 Hz, 1 H), 5.04 (s, 2 H) ppm. 19F NMR (376 MHz,
CDCl3): δ = –84.49 (dd, J = 36.4, 26.4 Hz, 1 F), –86.29 (dd, J =
36.4, 3.7 Hz, 1 F) ppm.
–106.02 (s, 2 F) ppm. IR (KBr): ν = 3097, 3063, 1682, 1582, 1456,
˜
1371, 1339, 1145, 1111, 995, 806, 789, 737, 602, 546 cm–1. MS
(ESI): m/z = 236 [M – K]–. C7H4F2KNO4S (275.27): calcd. C 30.54,
N 5.09, H 1.46; found C 30.48, N 5.09, H 1.56.
General Procedure for the gem-Difluoro-Olefination of Aldehydes:
Potassium 2-pyridinyl sulfonyldifluoroacetate (1; 248 mg,
0.9 mmol) was added to a solution of 4-bromobenzaldehyde
(110 mg, 0.6 mmol) in DMF (2 mL). The mixture was stirred at
40 °C for 2 h. The reaction was quenched with aqueous saturated
ammonium chloride (1.2 mL), followed by 3 n HCl (1.2 mL). The
resulting mixture was stirred at 40 °C for another 2 h. After cooling
to room temperature, the mixture was diluted with diethyl ether
(10 mL), washed with H2O (5 mL ϫ3), dried with Na2SO4, and
concentrated under reduced pressure. The residue was purified by
column chromatography (hexane) to afford pure product 3a.
1-(2,2-Difluorovinyl)-4-methoxybenzene (3i):[9] Colorless oil, 66 mg,
65% yield. H NMR (400 MHz, CDCl3): δ = 7.25 (d, J = 8.8 Hz,
2 H), 6.87 (d, J = 8.8 Hz, 2 H), 5.20 (dd, J = 26.4, 3.8 Hz, 1 H),
3.79 (s, 3 H) ppm. 19F NMR (376 MHz, CDCl3): δ = –84.75 (dd,
J = 36.9, 26.4 Hz, 1 F), –86.54 (dd, J = 36.9, 3.8 Hz, 1 F) ppm.
1
2-(2,2-Difluorovinyl)naphthalene (3j):[6e] White solid, 100 mg, 87%
1
yield. H NMR (400 MHz, CDCl3): δ = 7.86–7.73 (m, 4 H), 7.54–
7.42 (m, 3 H), 5.44 (dd, J = 26.2, 3.8 Hz, 1 H) ppm. 19F NMR
(376 MHz, CDCl3): δ = –81.94 (dd, J = 30.7, 26.2 Hz, 1 F), –83.66
(dd, J = 30.7, 3.8 Hz, 1 F) ppm.
2-(2,2-Difluorovinyl)benzofuran (3k):[9] Colorless oil, 96 mg, 89%
1-Bromo-4-(2,2-difluorovinyl)benzene (3a):[9] Colorless oil, 117 mg,
1
yield. H NMR (400 MHz, CDCl3): δ = 7.60–7.33 (m, 2 H), 7.31–
1
90% yield. H NMR (400 MHz, CDCl3): δ = 7.46 (d, J = 8.5 Hz,
7.10 (m, 2 H), 6.62 (s, 1 H), 5.40 (d, J = 25.1 Hz, 1 H) ppm. 19F
NMR (376 MHz, CDCl3): δ = –76.05 (dd, J = 25.1, 16.4 Hz, 1 F),
–82.30 (d, J = 16.4 Hz, 1 F) ppm.
2 H), 7.19 (d, J = 8.5 Hz, 2 H), 5.23 (dd, J = 25.9, 3.6 Hz, 1 H)
ppm. 19F NMR (376 MHz, CDCl3): δ = –81.35 (dd, J = 29.2,
25.9 Hz, 1 F), –83.16 (dd, J = 29.2, 3.6 Hz, 1 F) ppm.
2-(2,2-Difluorovinyl)benzo[b]thiophene (3l): White solid, 107 mg,
91% yield, m.p. 79–80 °C. H NMR (400 MHz, CDCl3): δ = 7.80
1-Chloro-4-(2,2-difluorovinyl)benzene (3b):[11] Colorless oil, 98 mg,
94% yield. H NMR (400 MHz, CDCl3): δ = 7.29 (d, J = 8.7 Hz,
2 H), 7.24 (d, J = 8.7 Hz, 2 H), 5.22 (dd, J = 25.9, 3.6 Hz, 1 H)
ppm. 19F NMR (376 MHz, CDCl3): δ = –81.71 (dd, J = 29.9,
25.9 Hz, 1 F), –83.50 (dd, J = 29.9, 3.6 Hz, 1 F) ppm.
1
1
(dd, J = 7.7, 0.9 Hz, 1 H), 7.72 (dd, J = 7.7, 0.9 Hz, 1 H), 7.40–
7.29 (m, 2 H), 7.20 (s, 1 H), 5.63 (dd, J = 25.6, 1.8 Hz, 1 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 156.5 (dd, J = 299.3, 291.0 Hz),
139.5 (t, J = 2.5 Hz), 139.5, 132.4 (dd, J = 7.7, 6.6 Hz), 124.5,
124.4, 123.2, 122.6 (dd, J = 7.2, 4.7 Hz), 122.0, 78.3 (dd, J = 33.4,
16.5 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ = –78.90 (dd, J =
25.6, 23.1 Hz, 1 F), –84.80 (dd, J = 23.1, 1.8 Hz, 1 F) ppm. IR
1,3-Dibromo-5-(2,2-difluorovinyl)benzene (3c): Colorless oil,
1
150 mg, 84% yield. H NMR (400 MHz, CDCl3): δ = 7.53 (t, J =
1.6 Hz, 1 H), 7.39 (d, J = 1.6 Hz, 2 H), 5.18 (dd, J = 25.3, 3.3 Hz,
1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.7 (dd, J = 300.3,
291.3 Hz), 135.3, 133.9 (dd, J = 7.6, 6.2 Hz), 132.5 (t, J = 1.9 Hz),
129.1 (dd, J = 7.0, 3.6 Hz), 128.6 (d, J = 1.3 Hz), 123.2, 80.6 (dd,
J = 30.9, 13.2 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ = –78.68
(dd, J = 25.5, 25.3 Hz, 1 F), –80.64 (dd, J = 25.4, 3.3 Hz, 1 F)
(KBr): ν = 3073, 2650, 1951, 1916, 1727, 1520, 1456, 1343, 1303,
˜
1159, 931, 874, 844, 747, 727, 673, 520 cm–1. GC–MS (EI): m/z =
196 [M]+. HRMS (EI): calcd. for C10H6F2S 196.0158; found
196.0159.
(E)-(4,4-difluorobuta-1,3-dien-1-yl)benzene (3m):[9] Yellow oil,
49 mg, 51% yield. 1H NMR (400 MHz, CDCl3): δ = 7.45–7.11 (m,
5 H), 6.65 (dd, J = 15.9, 10.9 Hz, 1 H), 6.46 (d, J = 15.9 Hz, 1 H),
5.11 (ddd, J = 24.1, 10.9, 1.0 Hz, 1 H) ppm. 19F NMR (376 MHz,
CDCl3): δ = –85.37 (dd, J = 26.2, 24.1 Hz, 1 F), –87.09 (dd, J =
ppm. IR (KBr): ν = 1724, 1586, 1549, 1415, 1348, 1243, 1177, 1108,
˜
969, 854, 746 cm–1. GC–MS (EI): m/z = 298 [M]+. HRMS (EI):
calcd. for C8H4Br2F2 295.8648; found 295.8651.
1-(2,2-Difluorovinyl)-4-(trifluoromethyl)benzene (3d):[4b] Colorless
1
oil, 100 mg, 80% yield. H NMR (400 MHz, CDCl3): δ = 7.59 (d, 26.2, 1.0 Hz, 1 F) ppm.
J = 8.2 Hz, 2 H), 7.44 (d, J = 8.2 Hz, 2 H), 5.33 (dd, J = 25.7,
(4,4-Difluorobut-3-en-1-yl)benzene (3n):[9] Colorless oil, 52 mg, 48%
yield. H NMR (400 MHz, CDCl3): δ = 7.39–6.90 (m, 5 H), 4.14
(dt, J = 25.4, 7.7 Hz, 1 H), 2.67 (t, J = 7.7 Hz, 2 H), 2.30 (q, J =
7.7 Hz, 2 H) ppm. 19F NMR (376 MHz, CDCl3): δ = –89.04 (d, J
= 47.4 Hz, 1 F), –91.08 (dd, J = 47.4, 25.4 Hz, 1 F) ppm.
3.5 Hz, 1 H) ppm. 19F NMR (376 MHz, CDCl3): δ = –62.83 (s, 3
F), –79.82 (t, J = 25.7 Hz, 1 F), –81.47 (dd, J = 25.7, 3.5 Hz, 1 F)
ppm.
1
1-(2,2-Difluorovinyl)-3-nitrobenzene (3e):[9] White solid, 110 mg,
99% yield. 1H NMR (400 MHz, CDCl3): δ = 8.19 (s, 1 H), 8.09 (d,
J = 8.0 Hz, 1 H), 7.65 (d, J = 8.0 Hz, 1 H), 7.52 (t, J = 8.0 Hz, 1
H), 5.39 (dd, J = 25.2, 3.0 Hz, 1 H) ppm. 19F NMR (376 MHz,
CDCl3): δ = –79.02 (t, J = 25.2 Hz, 1 F), –80.74 (dd, J = 25.2,
3.0 Hz, 1 F) ppm.
Supporting Information (see footnote on the first page of this arti-
cle): Copies of the differential scanning calorimetry/thermogravi-
metric analysis of potassium 2-pyridinyl sulfonyldifluoroacetate;
1
copies of the H NMR, 19F NMR, and 13C NMR spectra of the
final compounds.
4-(2,2-Difluorovinyl)-1,1Ј-biphenyl (3f):[9] White solid, 108 mg, 84%
1
yield. H NMR (400 MHz, CDCl3): δ = 7.65–7.57 (m, 4 H), 7.53–
Acknowledgments
7.31 (m, 5 H), 5.34 (dd, J = 26.2, 2.7 Hz, 1 H) ppm. 19F NMR
(376 MHz, CDCl3): δ = –81.91 (t, J = 26.2 Hz, 1 F), –83.84 (d, J
= 26.2 Hz, 1 F) ppm.
The authors thank the National Natural Science Foundation of
China (NSFC) (grant numbers 21032006, 21172240), the 973 Pro-
gram of China (grant number 2012CBA01200), and the Chinese
2-(2,2-difluorovinyl)-1,3,5-trimethylbenzene (3g):[9] Colorless oil,
70 mg, 64% yield. 1H NMR (400 MHz, CDCl3): δ = 6.94, (s, 2 H), Academy of Sciences for financial support.
Eur. J. Org. Chem. 2014, 928–932
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X.-P. Wang, J.-H. Lin, J.-C. Xiao, X. Zheng
SHORT COMMUNICATION
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