Microwave-assisted solvent-free synthesis of (E)-stilbenes

Article abstract of DOI:10.3184/174751912X13320888894748

An efficient synthesis of a series of stilbenes is reported using 4-nitrotoluene and substituted arylaldehydes as starting materials in the presence of Cs₂CO₃ and polyethylene glycol under solvent-free microwave irradiation. Compared with conventional method, this strategy exhibited higher stereoselectivity, shorter reaction times and has a lower environmental impact.

Full text of DOI:10.3184/174751912X13320888894748

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 231
APRIL, 231–234
Microwave-assisted solvent-free synthesis of (E)-stilbenes
Liu-chang Wanga, Jiang Lia, Xi-quan Zhangb, Hong-mei Gub, Bao-lin Lia*
aKey Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, and School of Chemistry &
Chemical Engineering, Shaanxi Normal University, Xi’an 710062, P. R. China
bJiangsu ChiaTaiTianqing Pharmaceutical Co., Ltd. Nanjing 210042, P. R. China
An efficient synthesis of a series of stilbenes is reported using 4-nitrotoluene and substituted arylaldehydes as start-
ing materials in the presence of Cs2CO3 and polyethylene glycol under solvent-free microwave irradiation. Compared
with conventional method, this strategy exhibited higher stereoselectivity, shorter reaction times and has a lower
environmental impact.
Keywords: stilbene derivatives, Cs2CO3, microwave irradiation, arylaldehydes, 4-nitrotoluene
Stilbene-based compounds exist in a variety of plant species
and dietary sources1,2 and are important intermediates in
agrochemical3,4, polymer and pharmaceutical industries.5,6
Investigations on stilbenes have attracted the attention by biol-
ogists and chemists due to their excellent biological activity7,8
and photophysical properties.9,10 Applications of stilbenes have
extended to anti-fungal, cytotoxic, anti-inflammatory and
anti-viral products in the pharmaceutical field.11 Some hydroxyl
substituted (E)-stilbenes, such as resveratrol, piceatannol
(3,4,3′,5′-tetrahydroxy-trans-stilbene),12 and combretastatin
A-413 (Fig. 1), have exhibited superior anti-proliferative and
pro-apoptotic activity in a number of human cancer cell lines.
These compounds have been suggested as potential cancer
chemopreventive/chemoprotective agents based on interfering
with the dynamics of tubulin polymerization, depolymerization
and arresting mitosis.14 The photochemical and photophysical
properties of substituted trans-stilbenes which have been
fundamental to the understanding of the excited-state behavior
of arylalkenes15 provide a fertile field of investigation, in
electroluminescence and light-emitting diodes.16,17
There are several strategies for the synthesis of stilbene
derivatives, including Wittig reactions,18 Pd-catalyzed Heck19,20
and Negishi cross-couplings21. However, these procedures
have some disadvantages including anhydrous requirement,
the use of noble metals and toxic organic solvent, and low
stereoselectivity for the Z/E configuration of C=C bonds. It
is of importance to develop simple and green methods for
the synthesis of stilbenes. In recent years, microwave (MW)
irradiation technology has been widely used to accelerate
chemical reactions because of its molecular-level heating.22,23
Compared with conventional heating method, MW has signifi-
cant advantages giving shortened reaction times and increased
yields.24 In the present work, we report a novel MW assisted
strategy to prepare the stilbene skeleton using the Knoevenagel
condensation of 4-nitrotoluene and arylaldehydes in the
absence of solvent (Scheme 1).
reported the use of 1-butyl-3-methylimidazolium chloroalu-
minate and 1-butylpyridinium chloroaluminate ionic liquids
as Lewis acid catalysts in the Knoevenagel condensation for
the synthesis of electrophilic mono-aryl alkenes.25 Although
Chidambaram’s group used tetrabutylammonium bromide
or crown-ether as a phase transfer catalyst in a condensation
reaction for the preparation of substituted stilbenes,26 noxious
organic solvents and a long reaction time were required for the
process. Herein we present an investigation of the solvent-free
synthesis of stilbenes by the Knoevenagel condensation under
microwave irradiation with a microwave-induced synthesis/
extraction apparatus. The preparation of 3,4,5-trimethoxy-
4′-nitrostilbene from 4-nitrotoluene and 3,4,5-trimethoxybenz-
aldehyde was used as a model reaction in the absence of
a solvent to explore the MW promoted effect. A mixture of
15.0 mmol 3,4,5-trimethoxybenzaldehyde, 18.0 mmol 4-nitro-
toluene, 30.0 mmol anhydrous K2CO3 and 1.7 g polyethylene
glycol 400 (PEG-400) as a phase transfer catalyst27 was intro-
duced into a 50 mL flask. Then the mixture was subjected to
MW irradiation at 600 W instead of the conventional heating
method reported in our previous work.28 Unfortunately, it was
found that 3,4,5-trimethoxybenzaldehyde was not completely
converted to a stilbene even with an extended MW irradiation
time of 30 min or increased working power to 850 W. Low
yield (18.4%, entry 1 in Table 1) and an unknown by-product
in a high ratio were detected by GC/GC-MS. However a better
yield (50.4%) was observed (entry 2 in Table 1) when using
equivalent Cs2CO3 instead of K2CO3 under MW irradiation
at 600 W, 100 °C for 30 min. In order to adequately mix the
reactants, keeping the above condition unchanged, two liquid
Results and discussion
The Knoevenagel condensation has been widely used for the
preparation of substituted alkenes. Harjani and co-workers
Scheme 1 Synthesis of stilbenes from the condensation of
4-nitrotoluene and arylaldehydes
Fig. 1 Structures of resveratrol, piceatannol and combretastatin A-4.
* Correspondent. E-mail: baolinli@snnu.edu.cn

232 JOURNAL OF CHEMICAL RESEARCH 2012
Table 1 Effect of bases on the condensation of 3,4,5-trimeth-
Table 2 Effect of microwave conditions on the yields of 4-
oxybenzaldehyde and 4-nitrotoluene with MW assistancea
nitrostilbenea
Entry
Base
Additive
PEG-400
Yield/%b
Entry
MW conditions
Yield/%b
1
2
3
4
5
6
7
8
K2CO3
Cs2CO3
Piperidine
Pyrrolidine
K2CO3
Cs2CO3
K2CO3
no
no
no
no
1.7 g
1.7 g
no
18.4
50.4
No reaction
No reaction
17.5
Power/W
Temperature/°C Time/min
no
1
2
3
4
600
600
500
500
100 °C
100 °C
90 °C
20
5
5
39.4
52.0
64.2
75.4
Pyrrolidine (1.1 g)
Pyrrolidine (1.1 g)
1.7 g
1.7 g
1.7 g
1.7 g
41.9
no
no
38.4c
90 °C
10
Cs2CO3
81.7c
a Conditions: to pre-mixure of 15.0 mmol benzaldehyde,
18.0 mmol 4-nitrotoluene and 1.7 g PEG-400, 30.0 mmol Cs2CO3
was added. Subsequently, the mixture was irradiated with
MW.
a Conditions: the mixture of 15.0 mmol 3,4,5-trimethoxybenzal-
dehyde, 18.0 mmol 4-nitrotoluene, 30.0 mmol base was heated
at 100 °C for 30 min by MW irradiation with power at 600 W.
b Yields determined by GC analysis.
b Yields were determined by GC/GC-MS.
c Pre-mixing before MW irradiation and the reaction time was
10 min.
On the basis of the above optimised MW condition, we
further investigated the important role of Cs2CO3 in the
improvement of yield and stereoselectivity. 3,4,5-Trimethoxy-
benzaldehyde, benzaldehyde and 2-(trifluoromethyl)benzalde
hyde were selected as substrates, and K2CO3 was used in the
control experiment instead of Cs2CO3. The results indicated
that a lower yield (38.4%), lower E/Z ratio (72: 28) and a mass
of by-product were detected by GC/GC-MS in the synthesis of
3,4,5-trimethoxy-4′-nitrostilbene in the presence of K2CO3,
while higher yield of 81.7% with an excellent stereoselectivity
(E/Z ratio=96: 4) were obtained when Cs2CO3 was used as
a base (entry 1 in Table 3). Both satisfactory yields and high
E/Z ratios were also achieved from other two substrates in the
presence of Cs2CO3 under MW irradiation. The above results
organic bases piperidine29 and pyrrolidine were selected instead
of Cs2CO3. Unfortunately, the reaction did not proceed at
all (entry 3, 4 in Table 1). We believed that the basicity of
piperidine and pyrrolidine were not strong enough to remove
the proton of the activated methyl of 4-nitrotoluene to yield the
carbanion for the nucleophilic addition to the carbonyl of
3,4,5-trimethoxybenzaldehyde. An improved result was not
obtained with K2CO3 or Cs2CO3 as base in the reaction in
the presence of pyrrolidine as additive (entry 5, 6 in Table 1).
In further research, an interesting result was observed through
the following pre-mixing process. Firstly, a mixture of 4-nitro-
toluene, 3,4,5-trimethoxybenzaldehyde and PEG-400 was
heated at 60 °C without adding any base (m.p. of 4-nitrotoluene
is 51.9 °C), and the mixture completely turned into a liquid.
Then K2CO3 or Cs2CO3 was introduced into the above liquid.
Subsequently, the system was irradiated with MW at 600 W
and 100 °C. This pre-mixing strategy led to the starting
materials being completely consumed in a very short time
(10 min) and gave a much higher yield (entry 7, 8 in Table 1).
The experiments suggested that higher yield (81.7%) can
be obtained with Cs2CO3 as base rather than K2CO3 (38.4%).
These results indicated that pre-mixing step and the use
of Cs2CO3 are the most important parameters in the MW
irradiation process.
In order to further increase the yield in the condensation
reaction, benzaldehyde was selected as a model substrate
due to its low cost for optimising the MW conditions including
working power, temperature and irradiation time. Firstly the
starting materials benzaldehyde, 4-nitrotoluene and PEG-400
were heated for pre-mixing. Then the reaction was carried
out in the presence of Cs2CO3 under MW irradiation at 600 W,
100 °C, 20 min. Unfortunately, significant over-reaction
occurred in the experiment. We found that lower power and
temperature (500 W, 90 °C) gave a higher yield of 64.2% than
that of 52.0% under 600 W, 100 °C in 5 min (entry 2, 3 in
Table 2). However, incomplete conversion of benzaldehyde
was detected by GC after MW irradiated for 5 min (500 W,
90 °C). When the irradiation time was prolonged to 10 min,
benzaldehyde was totally consumed, and the yield was up to
75.4% (entry 4 in Table 2). A longer irradiation time than
10 min gave undesired complex products in the reaction
system. Therefore we concluded that the optimised MW
condition was as follows: 500 W, 90 °C for 10 min.
Table 3 Comparisons of yield and stereoselectivity for the
condensation reaction in the presence of K2CO3 or Cs2CO3 under
MW irradiationa
Entry Aromatic aldehyde
1d
K2CO3
Cs2CO3
E/Zb Yield/%c E/Zb Yield/%c
72: 28
38.4
96: 4
81.7
2e
3f
62: 38
62: 38
45.0
83.8
90: 10
88: 12
75.4
94.8
a Conditions: to pre-mixture of 15.0 mmol aromatic aldehyde,
18.0 mmol 4-nitrotoluene and 1.7 g PEG-400, 30.0 mmol Cs2CO3
was added. Subsequently, the mixture was irradiated with
MW.
b E/Z ratios determined by GC-MS.
c Combined yield of both E/Z isomers.
d Power = 600 W, temperature = 100 °C, t = 10 min.
e Power = 500 W, temperature = 90 °C, t = 10 min.
f Power = 500 W, temperature = 80 °C, t = 5 min.

JOURNAL OF CHEMICAL RESEARCH 2012 233
Table 4 Synthesis of stilbene derivatives with microwave-
demonstrated that Cs2CO3 was crucial for the enhanced yield
and stereoselectivity during the microwave-assisted synthesis
of stilbenes.
assistance under optimised conditionsa
Entry
Substrate
MW irradiation
As highlighted in Table 4, the method proved to be success-
ful for a wide range of substituted aromatic aldehydes. We
maintained the molar ratio of aromatic aldehydes or heteroaryl
aldehyde and 4-nitrotoluene at 1: 1.2 in the presence of Cs2CO3
and PEG-400 under solvent-free MW irradiation. All arylalde-
hydes with both electron withdrawing group (EWG) and
electron donating group (EDG) completely condensed with
4-nitrotoluene within 10 minutes under the above optimised
MW reaction conditions and provided a series of new stilbene
derivatives (entry 6–14 Table 4). It was found that the yield of
stilbenes was very sensitive to electronic effects.30,31 Substrates
with EDG such as OCH3 had higher yields, while replacement
of EDG with EWG such as F, Cl and Br led to decreased yields.
The position of the substitutent also affected the condensation
reaction. For instance, arylaldehyde bearing CF3 group at
position-2 gave a higher yield with a lower reaction tem-
perature and shorter time than those with a CF3 group at posi-
tion-3 and position-4 (entries 6-8 in Table 4). The results in
Table 4 also revealed that excellent stereoselectivity for the
E/Z configuration of C=C bonds (E/Z ratio = 75–98%) were
obtained.
In summary, we have demonstrated a facile microwave-
assisted strategy for the preparation of a series of stilbenes
under solvent-free condition. When the mixture of substituted
arylaldehydes and 4-nitrotoluene (molar ratio at 1:1.2) was
heated with microwave irradiation in the presence of Cs2CO3
and polyethylene glycol 400, stilbenes with high E/Z ratio for
the configuration of C=C bonds can be obtained in short time
by Knoevenagel condensation reaction. This novel solvent-
free microwave-assisted strategy provided a green and clean
process for the synthesis of stilbene derivatives.
Time/min
E/Zb
Yield/%c
1
10
96: 4
81.7d
2
3
10
83: 17
92: 8
83.1e
10
52.2f
4
5
10
5
90: 10
98: 2
75.4f
98.5e
6
7
5
88: 12
82: 18
94.8f
72.8e
10
8
9
10
10
83: 17
93: 7
72.1
30.5
Experimental
Unless otherwise stated, all chemicals were purchased from commer-
cial sources and used without purification. H NMR (300MHz) and
10
11
12
10
10
10
93: 7
83: 17
75: 25
69.1
26.7
11.0
1
13C NMR (75 MHz) spectra which were recorded using CDCl3 as a
solvent on a Bruker Avance 300 MHz spectrometer. Chemical shifts
(δ) are reported in parts per million, and coupling constants (J) are in
hertz, using TMS as an internal standard. Data are presented as
follows: chemical shift (ppm), multiplicity (s = singlet, d = doublet,
t = triplet, q = quartet, m = multiplet). The IR spectra were recorded
with a NicoletAvatar 360E.S.P. FT-IR spectrometer using KBr pellets.
GC-MS/GC analysis were performed on Shimadzu GCMS-QP2010
apparatus with RTX-5MS capillary column (30 m × 0.25 mm ×
0.25 µm). The melting points were determined using X-5 micro
melting point instrument (the thermometer was not corrected). High
resolution mass spectra were performed on a MaXis UHR-TOF with
direct injection of the sample. All reactions were performed in a Xian-
ghu microwave-induced synthesis/extraction apparatus (XH-100B),
produced by Beijing Xianghu Science and Technology Development
Co., Ltd, Beijing, P. R. China.
13
14
10
10
94: 6
92: 8
60.9
18.5
Synthesis of stilbene compounds under MW irradiation; general
procedure
A mixture of the aromatic aldehyde (15.0 mmol), 4-nitrotoluene
(18.0 mmol) and PEG-400 (1.7 g) in a 50 mL three neck flask was
heated to melt with magnetic stirring. Then Cs2CO3 (30.0 mmol) was
introduced into the above mixture. The flask was fixed in a micro-
wave-induced synthesis/extraction apparatus and irradiated for 5–
10 min with output power of 500 W or 600 W. The MW reaction was
programmed under a constant temperature (80–100 °C). Then the
reaction mixtures were washed with water for several times to obtain
the crude products. The crude products were analysed by GC and
GC-MS. Isolation of products was carried out by recrystallisation
from ethanol or silica column chromatography.
a The reaction conditions: to pre-mixture of 15.0 mmol aromatic
aldehyde, 18.0 mmol 4-nitrotoluene and 1.7 g PEG-400, 30.0 mmol
Cs2CO3 was added, then the mixture was irradiated with MW at
500 W, 100 °C.
b E/Z ratios were determined by GC-MS analysis.
c Yields were obtained by GC analysis.
d Power = 600 W, temperature = 100 °C.
e Power = 500 W, temperature = 90 °C.
f Power = 500 W, temperature = 80 °C.
trans-3,4,5-Trimethoxy-4′-nitrostilbene (entry 1 Table 4): Yellow
solid; m.p. 193.2–194.8 °C (lit.32, m.p. 192–193 °C).
1
All products were characterised by m.p., H NMR, 13C NMR, IR,
and MS analysis. Selected spectral data for new compounds (entries
6–14) are given as follows.
trans-3,5-Dimethoxy-4′-nitrostilbene (entry 2 Table 4): Yellow
solid; m.p. 134.6–135.3 °C (lit.32, m.p. 134–135°C).

234 JOURNAL OF CHEMICAL RESEARCH 2012
trans-4-Methoxy-4′-nitrostilbene (entry 3 Table 4): Yellow solid;
m.p. 128.1–130.1 °C (lit.33, m.p. 129–130 °C).
trans-4-Fluoro-3-trifluoromethyl-4′-nitrostilbene (entry 14 Table
4):Yellow solid; m.p. 174.5–176.1 °C; 1H NMR (300 MHz, CDCl3) δ:
8.22 (d, 2H, J = 8.3 Hz), 7.78 (d, 1H, J = 6.8 Hz), 7.71 (d, 1H, J = 6.8
Hz), 7.66 (d, 2H, J = 8.3 Hz), 7.21 (d, 1H, J = 16.4 Hz), 7.24 (s, 1H),
7.15 (d, 1H, J = 16.4 Hz); 13C NMR(75 MHz, CDCl3) δ: 164.7, 158.6,
147.2, 142.9, 132.8, 132.0, 130.4, 127.9, 127.1, 125.5, 124.2, 117.7,
117.4; IR: νmax 3073, 3038, 1638, 1617, 1594, 1506, 1430, 1337, 1243,
1127, 1051, 964, 837, 687, 540; HRMS (ESI-TOF) for C15H9F4NO2
[M+Na]: Calcd: 334.0467, found: 334.0453.
trans-4-Nitrostilbene (entry 4 Table 4): Yellow solid; m.p. 155.4–
156.1 °C (lit.34, m.p. 150–155 °C).
trans-2-(4-Nitrostyryl)furan (entry 5 Table 4): Yellow solid; m.p.
130.9–131.9 °C (lit.35, m.p. 128–131 °C).
trans-2-Trifluoromethyl-4′-nitrostilbene (entry 6 Table 4): Yellow
1
solid; m.p. 124.6–126.2 °C; H NMR (300 MHz, CDCl3) δ: 8.23 (d,
2H, J = 8.8 Hz), 7.78 (d, 1H, J = 7.8 Hz), 7.59–7.72 (m, 5H), 7.43 (m,
1H), 7.14 (d, 1H, J = 16.1 Hz); 13C NMR(75 MHz, CDCl3) δ: 146.3,
142.2, 131.2, 129.5, 129.3, 127.9, 127.4, 126.6, 126.3, 125.3, 123.2,
122.6, 121.5; IR: νmax 3076, 1650, 1592, 1514, 1456, 1336, 1317,
1155, 1103, 1037, 960, 850, 830, 760, 683, 530; HRMS (ESI-TOF)
for C15H10F3NO2 [M+Na]: Calcd: 316.0561, found: 316.0547.
This work was supported by Natural Science Foundation of
China (No. 20972090) and Jiangsu Chia Tai Tianqing Pharma-
ceutical Co., Ltd., P. R. China. We are also thankful to Dr
Peng-Na Li for helpful discussions.
trans-3-Trifluoromethyl-4′-nitrostilbene (entry 7 Table 4): Yellow
1
solid; m.p. 121.5–122.9 °C; H NMR (300 MHz, CDCl3) δ: 8.23 (d,
Received 3 January 2012; accepted 23 February 2012
Paper 1201079 doi: 10.3184/174751912X13320888894748
Published online: 17 April 2012
2H, J = 8.4 Hz), 7.80 (s, 1H), 7.50–7.73 (m, 5H), 7.27 (d, 1H, J = 16.4
Hz), 7.24 (d, 1H, J = 16.4 Hz); 13C NMR(75 MHz, CDCl3) δ: 146.7,
142.6, 136.5, 131.1, 129.6, 128.9, 127.6, 126.6, 124.7, 123.7, 123.1,
121.7; IR: νmax 3035, 1636, 1594, 1509, 1446, 1339, 1191, 1121, 1069,
968, 865, 834, 798, 693; HRMS (ESI-TOF) for C15H10F3NO2 [M+Na]:
Calcd: 316.0561, found: 316.0544.
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1
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131.1, 129.7, 128.3, 126.7, 126.6, 125.4, 125.3, 123.7; IR: νmax 3107,
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m.p. 181.4–182.6 °C; H NMR (300 MHz, CDCl3) δ: 8.21 (d, 2H,
J = 8.8 Hz), 7.63 (d, 2H, J = 8.8 Hz), 7.36–7.37 (m, 1H), 7.19 (d, 1H,
J = 16.3 Hz), 7.14 (m, 2H), 7.07 (d, 1H, J = 16.3 Hz); 13C NMR(75
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126.1, 123.2, 122.6, 116.7, 114.1; IR: νmax 3112, 3051, 1636, 1602,
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284.0488.
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1
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2H, J = 8.3 Hz), 7.64 (bs, 1H), 7.61 (d, 2H, J = 8.3 Hz), 7.41 (bs, 1H),
7.20 (m, 1 H), 7.14 (d, 1H, J = 16.2 Hz), 7.09 (d, 1H, J = 16.2 Hz); 13
C
NMR(75 MHz, CDCl3) δ: 159.3, 155.9, 142.6, 133.1, 130.2, 129.1,
128.3, 126.9, 123.7, 123.3 116.7, 116.4; IR: νmax 3072, 3037, 1695,
1635, 1594, 1509, 1345, 1251, 1108, 1055, 969, 864, 835, 811, 735,
702, 577; HRMS (ESI-TOF) for C14H9ClFNO2 [M+Na]: Calcd:
300.0204, found: 300.0192.
trans-3-Bromo-4-fluoro-4′-nitrostilbene (entry 11 Table 4): Yellow
1
solid; m.p. 172.7–173.5 °C; H NMR (300 MHz, CDCl3) δ: 8.21 (d,
2H, J = 8.5 Hz), 7.76 (d, 1H, J = 6.1 Hz), 7.63 (d, 2H, J = 8.5 Hz),
7.43–7.45 (m, 1H), 7.15–7.17 (m, 1H), 7.14 (d, 1H, J = 16.3 Hz), 7.08
(d, 1H, J = 16.3 Hz); 13C NMR(75 MHz, CDCl3) δ: 160.8, 157.5,
147.1, 143.1, 133.9, 131.7, 130.6, 127.6, 126.9, 124.2, 117.0, 116.7;
IR: νmax 3070, 3036, 1635, 1592, 1509, 1341, 1248, 1109, 1042, 967,
865, 834, 810, 698; HRMS (ESI-TOF) for C14H9BrFNO2 [M+Na]:
Calcd: 343.9698, found: 343.9687.
23 J. Salvadori, E. Balducci, S. Zaza, E. Petricci and M. Taddei, J. Org. Chem.,
2010, 75, 1841.
24 P. Lidström, J. Tierney, B. Wathey and J. Westman, Tetrahedron, 2001, 57,
9225.
25 J.R. Harjani, S.J. Nara and M.M. Salunkhe, Tetrahedron Lett., 2002, 43,
1127.
26 N. Taha, Y. Sasson and M. Chidambaram, Appl. Catalysis A: General,
2008, 350, 217.
27 M.-L. Wang and K.-R. Chang, Ind. Eng. Chem. Res., 1990, 29, 40.
28 X.B. Li, L. Wang, X.Q. Zhang, H.M. Gu, J. Guo and B.L. Li, J. Chem. Res.,
2010, 34, 489.
trans-4-Fluoro-3-methyl-4′-nitrostilbene (entry 12 Table 4):Yellow
1
solid; m.p. 114.7–115.6 °C; H NMR (300 MHz, CDCl3) δ: 8.20 (d,
2H, J = 8.8 Hz), 7.62 (d, 2H, J = 8.8 Hz), 7.32–7.39 (m, 2H), 7.17 (d,
1H, J = 16.3 Hz), 7.06 (d, 1H, J = 16.3 Hz), 7.02 (d, 1H, J = 8.4 Hz),
2.31 (s, 3H); 13C NMR(75 MHz, CDCl3) δ: 163.3, 160.0, 146.7, 143.8,
132.1, 130.1, 126.8, 126.1, 125.7, 124.2, 115.7, 115.4, 14.6; IR: νmax
3068, 3034, 2921, 1634, 1587, 1502, 1457, 1339, 1246, 1216, 1107,
969, 866, 836, 808, 748; HRMS (ESI-TOF) for C15H12FNO2 [M+Na]:
Calcd: 280.0750, found: 280.0737.
29 L.-Y. Wang, X.-G. Zhang,Y.-P. Shi and Z.-X. Zhang, Dyes Pigments, 2004,
62, 21.
30 Shengming Ma, S. Yu, Z. Peng and H. Guo, J. Org. Chem., 2006, 71,
9865.
31 M. McConville, O. Saidi, J. Blacker and J. Xiao, J. Org. Chem., 2009, 74,
2692.
32 B. Sun, J. Hoshino, K. Jermihov, L. Marler, J.M. Pezzuto, A. D. Mesecar
and M. Cushman, Bioorg. Med. Chem., 2010, 18, 5352.
33 R. Ketcham, D. Jambotkar and L. Martinelli, J. Org. Chem., 1962, 27,
4666.
34 P. Wan, M.J. Davis and M.A. Teo, J. Org. Chem., 1989, 54, 1354.
35 R.S. Tewari, N. Kumari and P.S. Kendurkar, J. Chem. Eng. Data, 1976, 21,
125.
trans-4-Fluoro-4′-nitrostilbene (entry 13 Table 4): Yellow solid;
1
m.p. 138.0–139.1 °C; H NMR (300 MHz, CDCl3) δ: 8.21 (d, 2H,
J = 8.8 Hz), 7.60 (d, 2H, J = 8.8 Hz), 7.52 (dd, 2H, J = 8.6, 5.5 Hz),
7.20 (d, 1H, J = 16.3 Hz), 7.09 (d, 2H, J = 8.6 Hz), 7.08 (d, 1H,
J = 16.3 Hz); 13C NMR(75 MHz, CDCl3) δ: 164.7, 161.4, 143.7,
132.4, 128.6, 127.5, 126.8, 126.1, 124.2, 116.0; IR: νmax 3108, 3076,
1631, 1589, 1509, 1420, 1337, 1234, 1157, 1108, 976, 845, 818, 748,
709, 685, 528; HRMS (ESI-TOF) for C14H10FNO2 [M+Na]: Calcd:
266.0593, found: 266.0582.

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