Functionalized ionic liquid as an efficient and recyclable reaction medium for phosphine-free palladium-catalyzed heck reaction

Article abstract of DOI:10.1055/s-2006-942466

A functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([HEmim][BF₄]), was found to be as an efficient and recyclable reaction medium for palladium-catalyzed Heck reaction. The olefination of iodoarenes and bromoarenes with olefins generated the corresponding products in good to excellent yields under phosphine-free reaction conditions. The reaction involved the use of [HEmim][BF₄] as the solvent, potassium phosphate as the base, and palladium acetate as the catalyst. In addition, palladium and ionic liquid could be recovered and recycled for six consecutive trials without significant loss of its reactivity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942466

PAPER
2653
Functionalized Ionic Liquid as an Efficient and Recyclable Reaction Medium
for Phosphine-Free Palladium-Catalyzed Heck Reaction
Functionalized
i
Ionic
L
iquid
a
Z
s
Medium for
P
h
hosphine-Fr
o
e
e
Heck Re
a
uction ,a Lei Wang*a,b
a
Department of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui 235000, P. R. of China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. of China
b
Fax +86(561)3090518; E-mail: leiwang@hbcnc.edu.cn
Received 13 March 2006; revised 6 April 2006
In the last decade, ionic liquids (ILs) have attracted con-
siderable attention as environmentally benign reaction
media because of their many fascinating and intriguing
properties such as high thermal and chemical stability, no
Abstract: A functionalized ionic liquid, 1-(2-hydroxyethyl)-3-
methylimidazolium tetrafluoroborate ([HEmim][BF4]), was found
to be as an efficient and recyclable reaction medium for palladium-
catalyzed Heck reaction. The olefination of iodoarenes and bromo-
arenes with olefins generated the corresponding products in good to measurable vapor pressure, nonflammability, friction re-
excellent yields under phosphine-free reaction conditions. The reac-
duction, antiwear performance, and high loading capacity.
tion involved the use of [HEmim][BF4] as the solvent, potassium
Numerous chemical reactions can be carried out in ionic
phosphate as the base, and palladium acetate as the catalyst. In ad-
liquids.9 In most cases, the ionic liquids can be recycled
dition, palladium and ionic liquid could be recovered and recycled
easily. An attractive feature of ionic liquids is that their
for six consecutive trials without significant loss of its reactivity.
solubilities can be tuned readily, so they can phase sepa-
Key words: Heck reaction, palladium acetate, phosphine-free,
rate from organic as well as aqueous media, depending on
functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazoli-
the choice of cations and anions. Substrate solubility can
um tetrafluoroborate ([HEmim][BF4])
also be tuned.
Functionalized ionic liquids (FILs), containing functional
groups such as amine, amide, nitrile, ether, alcohol, acid,
ester, urea, thiourea, or fluorous chain, into the ionic liq-
uids, have shown great promise not only as alternative
green solvents, but also as bases, acids, or coordinating
ligands for organic transformations in recent years.10
However, the synthesis of functionalized ionic liquid or
ionic metal complex is rather complicated and multistep
procedures have to be used. FILs, based on the imidazoli-
um cation that contain additional hydroxyl group, such as
1-(2-hydroxyethyl)-3-methylimidazolium cation with
three different anions ([BF4]–, [Cl]–, and [PF6]–), and their
derivatives were prepared, and used as soluble supports
for the synthesis of a bioactive pentapeptide, 4-thiazolidi-
nones, 2-thioxotetrahydropyrimidin-4-(1H)-ones and
methyl 6-amino-5-cyano-4-aryl-2-methyl-4H-pyran-3-
carboxylate, as well as for Suzuki coupling, Knoevenagel
and 1,3-dipolar cycloaddition reactions.11 Most recently,
3-butyl-(4)5-hydroxymethyl-1-methyl-3H-imidazol-1-
ium salts were used for Heck reaction.12
The palladium-catalyzed coupling of olefins with aryl or
vinyl halides, known as the Heck reaction, is one of the
most important, reliable, and general reactions for car-
bon–carbon bond formation in organic synthesis.1 This
powerful reaction can lead to the construction of an sp2–sp2
C–C bond at an unfunctionalized olefinic carbon in a sin-
gle transformation employing a wide variety of aryl and
vinyl halide substrates. It may be used for the synthesis of
multifunctional derivatives,2 including bioactive com-
pounds, natural products,3 pharmaceuticals and high-per-
formance materials.4 Palladium compounds, usually as
complexes with phosphine ligands, are very often used as
catalyst precursors in the Heck reactions. Phosphines play
the role of stabilizers of in situ formed soluble Pd(0) com-
plexes, which are generally considered the catalytically
active forms.5 On the other hand, phosphine-free catalysts
have been received great interest recently as a less compli-
cated, environmentally friendly, and cheaper alternative
to phosphine-containing systems.6 A homogeneous Pd
catalyst usually precipitated from the solution and recy-
cling or recovery of the expensive catalyst was difficult.
To overcome this drawback, Pd on carbon and Pd on dif-
ferent metal oxides and hydroxides were used.7 Although
palladium nanoparticles of different origins have been uti-
lized in the Heck arylation of unsubstituted acrylates and
styrene with variable degrees of success, in some cases,
the catalyst recycling was fruitless.8
The ligandless Heck reaction in ionic liquids, in particular
those involving 1,3-dialkylimidazolium salts, has been
studied extensively.13 The use of phosphines,14 nitro-
gen-,15 phosphapalladacycles,16 and N,S-based carbene,17
and N-heterocyclic carbene (NHC) ligands in palladium-
catalyzed Heck reaction have been also investigated.18
However, all of these catalyst systems suffer from draw-
backs of one kind or another, such as the high ligand sen-
sitivity toward air and moisture, and tedious multistep
synthesis; hence the high cost of the ligands, and the use
of various additives.
SYNTHESIS 2006, No. 16, pp 2653–2658
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x.
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x
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0
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Advanced online publication: 04.07.2006
DOI: 10.1055/s-2006-942466; Art ID: F04106SS
© Georg Thieme Verlag Stuttgart · New York

2654
L. Zhou, L. Wang
PAPER
Table 1 Effect of Ionic Liquid on the Heck Reactiona
Here we have explored 1-(2-hydroxyethyl)-3-methylimi-
dazolium tetrafluoroborate ([HEmim][BF4]) (Figure 1), a
functionalized ionic liquid, as an efficient and recyclable
reaction medium for palladium catalyzed Heck reaction.
The olefinations of iodoarenes and bromoarenes with ole-
fins generated the corresponding products in good to ex-
cellent yields under phosphine-free reaction conditions
(Scheme 1). In addition, palladium and ionic liquid could
be recovered and recycled for six consecutive trials with-
out significant loss of its reactivity.
Ph
Pd(OAc)2 (2 mol%)
PhCH CH2
PhI
+
K3PO4, IL
Ph
Entry
Ionic Liquid
Yield (%)b
1
2
3
4
5
6
7
8
[Bmim][BF4]
[Bmim][PF6]
18
13
[Bmim][NO3]
[HEmim][Cl]
[HEmim][BF4]
[HEmim][PF6]
[DHPmim][BF4]
[DHPmim][PF6]
trace
42
OH
N
N
N
N
97
NO3
BF4
Cl
PF6
N
N
N
N
84
Me
[Bmim][PF6]
Me
[Bmim][NO3]
Me
[Bmim][BF4]
Me
[HEmim][Cl]
59
56
OH
OH
OH
PF6
OH
OH
OH
BF4
N
N
N
N
a Styrene (104 mg, 1.00 mmol), iodobenzene (204 mg, 1.00 mmol),
Pd(OAc)2 (4.5 mg, 0.02 mmol), K3PO4 (414 mg, 2.00 mmol) in ionic
liquid (3 mL) at 130 °C for 16 h.
N
N
N
N
BF4
PF6
Me
Me
Me
Me
b Isolated yield.
[HEmim][BF4]
[HEmim][PF6]
[DHPmim][BF4]
[DHPmim][PF6]
Figure 1
of hydroxyl functional group in the alkyl chain consider-
ably modifies its behavior.11a,12a
R
X
Pd(OAc)2 (2 mol%)
K3PO4, IL
Several different bases for the Heck reaction catalyzed by
palladium acetate in [HEmim][BF4] were examined. With
regard to other reaction conditions, K3PO4 was found to
be an excellent base for the reaction,19 and other bases
such as KOH, triethylamine, piperidine, Cs2CO3, NaOAc,
Na2CO3, and K2CO3 were substantially less effective. No
desired product was isolated when NaHCO3 was used as
the base in the reaction because of its weak basicity
(Table 2, entries 1–9).
+
R
R1
R1
X = I, Br
R = Ar, CO2R2,
CN
E product
No Amine !
No Phosphine !
Recoverable IL !
Recoverable Catalyst !
Scheme 1
In our initial screening experiments, the Heck reaction be-
tween iodobenzene with styrene was chosen as a model
reaction for investigation. In the reaction with only
Pd(OAc)2 (2%) in [HEmim][Cl] and K3PO4 as the base at
130 °C after 10 hours, 26% yield of the desired product
was obtained, and 39% yield was obtained after 16 hours.
A significant increase in iodobenzene with styrene con-
versions and the yield of the products were observed when
[HEmim][PF6] instead of [HEmim][Cl] was added to the
reaction as the solvent. Encouraged by this result, we con-
tinued our research to improve the yield of product by the
optimization of reaction conditions.
Table 2 Effect of Base on the Heck Reactiona
Ph
Pd(OAc)2 (2 mol%)
PhCH CH2
PhI
+
[HEmim][BF ]
base,
4
Ph
Entry
Base
Yield (%)b
1
2
3
4
5
6
7
8
9
K3PO4
K2CO3
Na2CO3
KOH
97
38
43
86
71
63
0
A significant effect of ionic liquid was found in the reac-
tion. Only trace or poor yields of the desired products was
observed when the reaction was carried out in
[Bmim][BF4], [Bmim][PF6] (Figure 1), or [Bmim][NO3]
in the presence of Pd(OAc)2 (2%) and K3PO4. Surprising-
ly, a significant increase in the yields of the products were
found as the reactions were performed in functionalized
ionic liquids, such as [HEmim][Cl], [HEmim][BF4],
[HEmim][PF6], [DHPmim][BF4], and [DHPmim][PF6]
(Figure 1). A variety of functionalized ionic liquids were
screened (Table 1, entries 1–8), and the most effective
was found to be [HEmim][BF4] because the introduction
Cs2CO3
NaOAc
NaHCO3
Et3N
76
72
piperidine
a Styrene (104 mg, 1.00 mmol), iodobenzene (204 mg, 1.00 mmol),
Pd(OAc)2 (4.5 mg, 0.02 mmol), base (2.00 mmol) in [HEmim][BF4]
(3 mL) at 130 °C for 16 h.
b Isolated yield.
Synthesis 2006, No. 16, 2653–2658 © Thieme Stuttgart · New York

PAPER
Functionalized Ionic Liquid as Medium for Phosphine-Free Heck Reaction
2655
Table 4 Palladium-Catalyzed Heck Reaction in [HEmim][BF4]a
The effect of the palladium source on the Heck reaction
was also examined. Among the palladium sources tested,
Pd(OAc)2 and Pd(PPh3)4 proved to be the best of choice.
Nanosized Pd on PVP, Pd powder (submicron), Pd(dba)2
and PdCl2 were inferior and led to slower reactions. Use
of Pd(OAc)2 was chosen as palladium source for the fu-
ture investigation because of its lower cost and higher
availability (Table 3, entries 1–6).
R
X
Pd(OAc)2 (2 mol%)
+
R
K3PO4, [HEmim][BF4]
R1
R1
Entry
Olefin
Organic halide
Yield of
coupled
product (%)b
1
2
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhI
97
93
88
93
87
92
91
99
99
92
94
93
96
88
83
90
74
65
57
87
82
76
74
80
52
90
Table 3 Effect of Palladium Source on the Heck Reactiona
4-MeOC6H4I
4-MeC6H4I
4-MeCOC6H4I
4-CF3C6H4I
3-CF3C6H4I
2-CF3C6H4I
4-MeOC6H4I
PhI
Ph
Pd Source (2 mol%)
PhCH
CH2
PhI
+
3
K3PO4, [HEmim][BF4]
Ph
4
Entry
Palladium source (2 mol%)
Pd powder (submicron)
Pd(OAc)2
Yield (%)b
5
1
2
3
4
5
6
77
97
39
64
97
81
6
7
PdCl2
8
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
Pd(dba)2
9
Pd(PPh3)4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
4-MeC6H4I
3-NO2C6H4I
4-NO2C6H4I
4-MeCOC6H4I
4-CF3C6H4I
3-CF3C6H4I
2-CF3C6H4I
4-MeCOC6H4Br
4-CNC6H4Br
PhBr
nanosized Pd on PVP
a Styrene (104 mg, 1.00 mmol), iodobenzene (204 mg, 1.00 mmol),
Pd source (0.02 mmol), K3PO4 (414 mg, 2.00 mmol) in
[HEmim][BF4] (3 mL) at 130 °C for 16 h.
b Isolated yield.
During the course of our further optimization of the reac-
tion conditions, when using 2 mol% of palladium acetate
in [HEmim][BF4], the reactions were generally completed
in a matter of hours, but the time, as expected, was in-
versely proportional to the temperature. A reaction tem-
perature of 130 °C was found to be optimal. Thus, the
optimized reaction conditions for this Heck reaction are:
Pd(OAc)2 (2 mol%) and K3PO4 (2 equiv) in
[HEmim][BF4] at 130 °C for 16 hours.
CO2C2H5
PhCH=CH2
PhCH=CH2
PhCH=CH2
PhCH=CH2
4-EtO2CC6H4Br
4-MeCOC6H4Br
4-NO2C6H4Br
3-NO2C6H4Br
4-CNC6H4Br
PhBr
To examine the versatility of this method, the Heck olefi-
nations of styrene with iodoarenes containing electron-
rich, electron-poor or electron-neutral substituents were
investigated. The results in Table 4 showed that the con-
versions, regioselectivity (>99% trans-products), and
yields were satisfactory under the standard reaction con-
ditions (Table 4, entries 1–7). The olefination of the ha-
loarene was also tolerant of ortho substitution in aryl
iodides and led to the good yields (Table 4, entries 7 and
16). The scope of this catalytic system with other vinyl
substrates, such as ethyl acrylates, and acrylonitrile, was
also examined and good to excellent results were obtained
for iodoarenes under identical conditions (Table 4, entries
8–16, and 26). For activated bromoarenes, good yields of
cross-coupling products were isolated under the present
reaction conditions (Table 4, entries 17–18, and 20–24).
As expected, moderate yields of desired products were
observed for deactivated bromoarenes (Table 4, entries 19
and 25).
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CO2C2H5
CN
4-MeC6H4I
a Olefin (1.00 mmol), organic halide (1.00 mmol), Pd(OAc)2 (4.5 mg,
0.02 mmol), K3PO4 (414 mg, 2.00 mmol) in [HEmim][BF4] (3 mL) at
130 °C for 16 h.
b Isolated yield.
To screen the recyclability of palladium and
[HEmim][BF4], a more practical method was applied to
the reaction between iodobenzene and styrene under
present reaction conditions. When iodobenzene was treat-
ed with styrene with a catalyst loading of 2 mol% palladi-
Synthesis 2006, No. 16, 2653–2658 © Thieme Stuttgart · New York

2656
L. Zhou, L. Wang
PAPER
(E)-Stilbene
um at 130 °C for 16 hours, the desired coupling product
was obtained in 97% isolated yield. After separation of the
Mp 120–122 °C (Lit.20 mp 120 °C).
product and the recovery of ionic liquid containing the IR (KBr): 3020, 1631, 1495, 1451, 1364, 962, 764, 692 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.62–7.60 (m, 4 H), 7.40–7.27
palladium catalyst, fresh starting materials were charged
into the reaction system. The reactions still proceeded
well and no unreacted substrates were detected at the end
of the reaction. The IL containing the palladium catalyst
was recycled six times with no loss of catalytic activity
(Table 5, entries 1–6).
(m, 4 H), 7.24–7.13 (m, 4 H).
(E)-4-Methylstilbene
Mp 121–122 °C (Lit.20 mp 120 °C).
IR (KBr): 3018, 2831, 1632, 1574, 1448, 1365, 969, 809, 749, 690
cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.59 (d, J = 7.6 Hz, 2 H), 7.50
(d, J = 8.0 Hz, 2 H), 7.41–7.24 (m, 3 H), 7.21–7.16 (m, 4 H), 2.31
(s, 3 H).
Table 5 Successive Trials with Recoverable Pd/[HEmim][BF4]a
Ph
recycled Pd and IL
PhCH
CH2
PhI
+
K3PO4
Ph
(E)-4-Acetylstilbene
Mp 149–151 °C (Lit.20 mp 148–150 °C).
Trial
Yield (%)b
Trial
Yield (%)b
IR (KBr): 2897, 1708, 1600, 1517, 1368, 1357, 1265, 1178, 1074,
966, 867, 821, 756, 725, 692 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.97 (d, J = 8.4 Hz, 2 H), 7.75
(d, J = 8.4 Hz, 2 H), 7.66 (d, J = 7.6 Hz, 2 H), 7.43–7.32 (m, 5 H),
2.51 (s, 3 H).
1
2
3
97
96
95
4
5
6
94
94
93
a Styrene (104 mg, 1.00 mmol), iodobenzene (204 mg, 1.00 mmol),
Pd(OAc)2 (4.5 mg, 0.02 mmol), K3PO4 (414 mg, 2.00 mmol) in
[HEmim][BF4] (3 mL) at 130 °C for 16 h.
(E)-4-Cyanostilbene
Mp 117–119 °C (Lit.20 mp 117.4–117.7 °C).
IR (KBr): 2834, 2362, 1602, 1504, 1364, 973 cm–1.
b Isolated yield.
1H NMR (400 MHz, DMSO-d6): d = 7.83 (d, J = 8.4 Hz, 2 H), 7.80
(d, J = 8.4 Hz, 2 H), 7.66 (d, J = 7.6 Hz, 2 H), 7.56 (t, J = 7.4 Hz,
2 H), 7.44 (t, J = 8.4 Hz, 1 H), 7.31 (d, J = 16.5 Hz, 1 H), 7.19 (d,
J = 16.5 Hz, 1 H).
In conclusion, we have presented here an efficient, and
economic catalyst system for Heck reaction by using
[HEmim][BF4] as the solvent, potassium phosphate as the
base, and palladium acetate as the catalyst under phos-
phine-free reaction conditions. The olefination reactions
of olefins with iodoarenes and bromoarenes generate the
corresponding coupling products in good to excellent
yields under the present reaction conditions. Moreover,
palladium and ionic liquid could be recovered and recy-
cled for six consecutive trials without significant loss in
activity.
(E)-Ethyl 3-(4-Methoxyphenyl)prop-2-enoate
Mp 48–50 °C (Lit.20 mp 47–48.8 °C).
IR (KBr): 2981, 1718, 1635, 1517, 1368, 1178, 984, 814 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.62 (m, 3 H), 6.92 (d, J = 8.8
Hz, 2 H), 6.45–6.41 (d, J = 16.0 Hz, 1 H), 4.17 (q, J = 7.2 Hz, 2 H),
3.77 (s, 3 H), 1.32 (t, J = 7.2 Hz, 3 H).
(E)-4-Methoxystilbene
Mp 136–138 °C (Lit.21 mp 135–137 °C).
IR (KBr): 2836, 1605, 1512, 1447, 1365, 1297, 1179, 1030, 967,
828, 689 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.60 (d, J = 6.4 Hz, 2 H), 7.50
(d, J = 8.4 Hz, 2 H), 7.36 (t, J = 7.8 Hz, 2 H), 7.24 (t, J = 6.4 Hz, 1
H), 7.16 (d, J = 16.4 Hz, 1 H), 7.10 (d, J = 16.4 Hz, 1 H), 6.95 (d,
J = 8.8 Hz, 2 H), 3.80 (s, 3 H).
Requisite ionic liquids in this work were prepared via literature pro-
cedures or purchased from commercial sources (Aldrich). Other re-
agents were analytical grade and used as received.
Mps were recorded on a WRS-2 melting point apparatus and are un-
1
corrected. All H NMR spectra were recorded at 300 MHz by a
Bruker NMR spectrometer. Chemical shifts are given as d value in
ppm and referenced to TMS as an internal standard. IR spectra were
obtained by using a Nicolet NEXUS 470 spectrophotometer. Prod-
ucts were purified by flash chromatography on 230–400 mesh silica
gel.
(E)-4-(Trifluoromethyl)stilbene
Mp 132–134 °C (Lit.22 mp 132–134 °C).
IR (KBr): 3025, 2846, 1626, 1554, 1418, 1326, 1167, 1111, 1070,
973, 827 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.58 (m, 4 H), 7.52 (d, J = 7.2 Hz,
2 H), 7.39 (m, 2 H), 7.29 (m, 1 H), 7.18 (d, J = 16.2 Hz, 1 H), 7.09
(d, J = 16.5 Hz, 1 H).
Heck Olefination; General Procedure
Under N2, an oven-dried, two-necked round-bottom flask contain-
ing a stir bar was charged with an organic halide (1.00 mmol), olefin
(1.00 mmol), Pd(OAc)2 (4.5 mg, 0.02 mmol), K3PO4 (414 mg, 2.00
mmol) and [HEmim][BF4] (3 mL). The mixture was heated and
stirred at 130 °C for 16 h. After cooling to r.t., the product was ex-
tracted from the mixture with EtOAc (2 × 5 mL). The combined or-
ganic layers were washed with H2O and brine, dried (MgSO4) and
the solvent evaporated under reduced pressure. The residue was fi-
nally purified by flash chromatography on silica gel to give the de-
sired product (Table 4).
(E)-3-(Trifluoromethyl)stilbene
Mp 65–67 °C (Lit.23 mp 66–67 °C).
IR (KBr): 3039, 2854, 1619, 1558, 1497, 1452, 1342, 1169, 1116,
962, 805, 696 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.96–7.91 (m, 2 H), 7.72–7.60
(m, 4 H), 7.47–7.26 (m, 5 H).
Synthesis 2006, No. 16, 2653–2658 © Thieme Stuttgart · New York

PAPER
Functionalized Ionic Liquid as Medium for Phosphine-Free Heck Reaction
2657
(E)-Ethyl Cinnamate
1H NMR (300 MHz, CDCl3): d = 7.68 (d, J = 15.9 Hz, 1 H), 7.61
(m, 4 H), 6.50 (d, J = 15.9 Hz, 1 H), 4.29 (q, J = 7.2 Hz, 2 H), 1.35
(t, J = 7.0 Hz, 3 H).
Oil.24
IR (film): 3074, 2954, 1709, 1621, 1497, 1312, 772, 687 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.67 (d, J = 16.4 Hz, 1 H),
7.62–7.50 (m, 2 H), 7.41–7.36 (m, 3 H), 6.60 (d, J = 16.0 Hz, 1 H),
4.18 (q, J = 7.2 Hz, 2 H), 1.25 (t, J = 7.0 Hz, 3 H).
(E)-Ethyl 4-Styrylbenzoate
Mp 106.0–107.5 °C (Lit.30 mp 106.0–106.5 °C).
IR (KBr): 3035, 2928, 1711, 1632, 1365, 1277, 1176, 851, 776
cm–1.
1H NMR (400 MHz, DMSO): d = 7.96 (d, J = 8.4 Hz, 2 H), 7.66 (d,
J = 7.6 Hz, 2 H), 7.46–7.30 (m, 5 H), 7.22 (d, J = 16.4 Hz, 1 H),
7.13 (d, J = 16.4 Hz, 1 H), 4.32 (q, J = 7.1 Hz, 2 H), 1.34 (t, J = 7.2
Hz, 3 H).
(E)-Ethyl 3-(4-Methylphenyl)prop-2-enoate
Oil.24
IR (film): 2981, 1713, 1632, 1514, 1412, 1365, 1311, 1175, 984,
814 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.62 (d, J = 16.0 Hz, 1 H),
7.58 (d, J = 8.0 Hz, 2 H), 7.22 (d, J = 8.0 Hz, 2 H), 6.55 (d, J = 16.0
Hz, 1 H), 4.18 (q, J = 7.1 Hz, 2 H), 2.32 (s, 3 H), 1.25 (t, J = 7.0 Hz,
3 H).
(E)-Ethyl 3-(4-Cyanophenyl)prop-2-enoate
Mp 62–64 °C (Lit.31 mp 59–63 °C).
IR (KBr): 3041, 2986, 2226, 1709, 1637, 1415, 1367, 1311, 1179,
1002, 850, 827 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.70 (d, J = 8.4 Hz, 2 H), 7.64 (d,
J = 16.2 Hz, 1 H), 7.59 (d, J = 8.4 Hz, 2 H), 6.53 (d, J = 16.2 Hz, 1
H), 4.28 (q, J = 7.2 Hz, 2 H), 1.35 (t, J = 7.2 Hz, 3 H).
(E)-Ethyl 3-(3-Nitrophenyl)prop-2-enoate
Mp 74–75 °C (Lit.25 mp 74.3–74.6 °C).
IR (KBr): 3075, 2982, 1717, 1644, 1525, 1480, 1354, 1328, 1187,
999, 872, 746, 664 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 8.54 (t, J = 1.6 Hz, 1 H), 8.22
(dd, J = 8.4, 1.6 Hz, 1 H), 8.19 (d, J = 8.0 Hz, 1 H), 7.77 (d,
J = 16.4 Hz, 1 H), 7.70 (t, J = 8.0 Hz, 1 H), 6.83(d, J = 16.0 Hz, 1
H), 4.20 (q, J = 7.2 Hz, 2 H), 1.27 (t, J = 7.0 Hz, 3 H).
(E)-4-Methylcinnamonitrile
Mp 72–73 °C (Lit.32 mp 71–73 °C).
IR (KBr): 3062, 2956, 2216, 1653, 1624, 1618, 1181, 1110, 978,
801 cm–1.
(E)-Ethyl 3-(4-Nitrophenyl)prop-2-enoate
1H NMR (400 MHz, DMSO-d6): d = 7.58 (d, J = 16.4 Hz, 1 H),
7.53–7.23 (m, 4 H), 6.37 (d, J = 16.4 Hz, 1 H), 2.33 (s, 3 H).
Mp 138–140 °C (Lit.25 mp 139–139.8 °C).
IR (KBr): 3075, 2982, 1717, 1644, 1525, 1446, 1354, 1188, 1034,
873, 767, 664 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 8.25 (d, J = 8.8 Hz, 2 H), 8.20
(d, J = 8.8 Hz, 2 H), 7.69 (d, J = 16.0 Hz, 1 H), 6.57 (d, J = 16.0
Hz, 1 H), 4.22 (q, J = 7.0 Hz, 2 H), 1.26 (t, J = 7.0 Hz, 3 H).
(E)-2-(Trifluoromethyl)stilbene
Oil.33
IR (film): 3030, 2850, 1621, 1550, 1428, 1341, 1162, 1113, 965,
815, 695 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.78–7.12 (m, 11 H).
(E)-Ethyl 3-(4-Acetylphenyl)prop-2-enoate
Mp 42–44 °C (Lit.26 mp 44–46 °C).
Acknowledgment
IR (KBr): 3025, 2936, 1713, 1685, 1631, 1410, 1358, 1314, 1266,
1178, 828 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.97 (d, J = 8.4 Hz, 2 H), 7.85
(d, J = 8.4 Hz, 2 H), 7.69 (d, J = 16.0 Hz, 1 H), 6.76 (d, J = 16.0
Hz, 1 H), 4.20 (q, J = 7.1 Hz, 2 H), 2.59 (s, 3 H), 1.27 (t, J = 7.0 Hz,
3 H).
We gratefully acknowledge the financial support by the National
Natural Science Foundation of China (No. 20372024), the Excellent
Scientist Foundation of Anhui Province, China (No. 04046080), the
Scientific Research Foundation for the Returned Overseas Chinese
Scholars, State Education Ministry, China (No. 2002247), the
Excellent Young Teachers Program of MOE, China (No. 2024), and
the Key Project of Science and Technology of State Education
Ministry, China (No. 0204069).
(E)-Ethyl 3-(2-Trifluoromethylphenyl)prop-2-enoate
Oil.27
IR (film): 3084, 2986, 1720, 1632, 1489, 1389, 1317, 1165, 1125,
1037, 980, 766, 652 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.09 (d, J = 15.9 Hz, 1 H), 7.76–
7.45 (m, 4 H), 6.41 (d, J = 15.9 Hz, 1 H), 4.29 (q, J = 7.2 Hz, 2 H),
1.35 (t, J = 6.0 Hz, 3 H).
References
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Oil.28
IR (film): 3065, 2936, 1716, 1644, 1440, 1368, 1338, 1198, 1128,
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Synthesis 2006, No. 16, 2653–2658 © Thieme Stuttgart · New York

2658
L. Zhou, L. Wang
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