Highly efficient and recyclable palladium catalyst anchored on organic-inorganic hybrid material: Application in the Heck reaction

Article abstract of DOI:10.1055/s-2008-1067161

Palladium anchored on organic-inorganic (silica gel) hybrid materials behaves as a very efficient heterogeneous catalyst in the Heck reaction. Iodoarenes and bromoarenes react smoothly with alkenes to afford the corresponding cross-coupling products in good to excellent yields under phosphine- and amine-free reaction conditions in the presence of a palladium anchored on L-proline-functionalized silica gel as catalyst. The silica-supported palladium catalyst can be recovered and recycled by simple filtration of the reaction solution, and used for more than 14 consecutive trials without significant loss of its catalytic activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1067161

PAPER
2405
Highly Efficient and Recyclable Palladium Catalyst Anchored on Organic–
Inorganic Hybrid Material: Application in the Heck Reaction
Reactioniang Liu, Lei Wang,* Pinhua Lia
a
a,b
A
H
pplication of
a
n
A
o
nchored Pa
n
lladium Cata
g
lyst in the He
q
c
k
a
Department of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui 235000, P. R. of China
Fax +86(561)3090518; E-mail: leiwang@hbcnc.edu.cn
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. of China
Received 1 January 2008; revised 21 April 2008
tion as a source of palladium(0). Heterocyclic carbenes
Abstract: Palladium anchored on organic–inorganic (silica gel) hy-
brid materials behaves as a very efficient heterogeneous catalyst in
the Heck reaction. Iodoarenes and bromoarenes react smoothly with
alkenes to afford the corresponding cross-coupling products in good
13
are another interesting class of ligands. Both mono- and
bis-carbene complexes have been shown to give high
turnover numbers in the Heck reaction. The N-, O-, and S-
to excellent yields under phosphine- and amine-free reaction condi- centered ancillary ligands have been recently shown to
tions in the presence of a palladium anchored on L-proline-function- have interesting applications in the Heck reaction. Very
alized silica gel as catalyst. The silica-supported palladium catalyst
can be recovered and recycled by simple filtration of the reaction
solution, and used for more than 14 consecutive trials without sig-
nificant loss of its catalytic activity.
14
15
recent examples include thioureas, imines and oximes,
16
17
18
bispyridines, phenanthrolines, hydrazones, tetra-
1
9
20
21
24
methylguanidines, hydroxyquinolines, oxazolines,
thiosemicarbazones,22 tetrazoles, and bisimidazoles.
23
Key words: Heck reaction, organic–inorganic hybrid material, sil-
ica-anchored proline–palladium catalyst, heterogeneous catalysis,
alkenes, aryl iodides, aryl bromides
These phosphine-free ligands are potentially advanta-
geous for being chemically stable and economically inex-
pensive. In addition, the development of organic reagents
grafted onto silica gels has attracted increasing attention
in recent years, because the industry seeks more environ-
The Heck reaction is among the most important and wide-
ly used reaction for the formation of carbon–carbon
bonds, which allows the arylation, alkylation, or vinyla-
tion of various alkenes through their reaction with aryl, vi-
nyl, benzyl, or allyl halides, acetates or triflates in the
presence of palladium and a suitable base in a single step
2
5
mentally friendly chemical manufacturing processes. At
26
27
the same time, Ma et al. and Guo have found that sim-
ple amino acids can serve as ligands. In our preliminary
investigation, the preparation of highly active 3-[(2-ami-
noethyl)amino]propyl-functionalized silica gel anchored
palladium and its subsequent use as an efficient and recy-
clable catalyst for the Sonogashira reaction, Heck reac-
tion, and Ullmann diaryl etherification were reported.28
1
–8
under mild conditions. However, homogeneous cata-
lysts have been of somewhat limited use, mainly because
of the difficulty of separation from the reaction product,
which in turn may lead to economical environmental
problems especially in the case of expensive or toxic met-
al catalysts. Therefore, the development of polymer-sup-
ported and insoluble transition metal complexes has
attracted a great deal of attention to address this issue. The
classic supported reagents can facilitate both the isolation
and recycling of the catalyst by filtration thus providing
Here, we wish to report the design and synthesis of the
palladium catalysts anchored on organic–inorganic hybrid
materials, which is illustrated in Scheme 1. It was readily
prepared in a three-step procedure. The silica gel (100–
2
00 mesh) was treated with (3-aminopropyl)triethoxysi-
lane in dry toluene at 120 °C for 24 hours to afford the 3-
aminopropyl-functionalized silica gel. The obtained func-
tionalized silica material was then reacted with N-Boc-L-
proline in the presence of N,N¢-dicyclohexylcarbodiimide
in tetrahydrofuran at 60 °C for 72 hours to afford the cor-
responding organic–inorganic hybrid material. The Boc
protective group in the organic–inorganic hybrid material
was then deprotected by using trifluoroacetic acid–dichlo-
romethane solution (1:1) with shaking at room tempera-
ture for three hours, and the solution was filtered and
subsequently neutralized with triethylamine, and dried
under vacuo at room temperature giving a white solid 1.
The obtained white solid then reacted with palladium(II)
acetate in ethanol at room temperature for four hours to
generate the silica-anchored proline–palladium catalyst 2.
The assignments of infrared absorption bands for the sam-
ples, silica-anchored proline 1 was made in comparison
with the IR spectra of the corresponding palladium com-
9
environmentally cleaner processes. Along this line, sev-
eral polymer-supported NHC-Pd catalysts have been de-
veloped by immobilization of the corresponding
1
0
homogeneous complexes on Wang resin, Merrifield res-
1
1a
11b
in, and polystyrene and these combine the advan-
tages of both homogeneous and heterogeneous catalysts
in a number of cross-coupling reactions. In addition, a
number of phosphine-free catalysts have been developed
for the Heck reaction. Among them, the palladacycle cat-
alysts have been shown to have great performance.12
However, increasing evidence points to the view that pal-
ladacycles are catalytically inactive and they simply func-
SYNTHESIS 2008, No. 15, pp 2405–2411
x
x.
x
x
.
2
0
0
8
Advanced online publication: 08.07.2008
DOI: 10.1055/s-2008-1067161; Art ID: F04908SS
Georg Thieme Verlag Stuttgart · New York
©

2
406
H. Liu et al.
PAPER
1
)
N
COOH
Boc
OH
OH
OH
O
O
O
(
EtO)3Si(CH2)3NH2
toluene
NH2
DCC, THF
Si
2) TFA/CH2Cl2
silica
silica
O
O
O
H
N
O
O
O
H
N
Pd(OAc)2, EtOH
Si
Si
HN
O
HN
O
silica
1/ Pd(II)
silica
2
2
1
Scheme 1
plex, 2. The magnitude of Dn [n
– n
], and the yield of the product by optimization of the reaction
Si–O(2)
] was found to be 81 cm and 38 cm , conditions.
1
Si–O(1)
–
1
–1
Dn [n
– n
2
C=O(1)
C=O(2)
respectively, indicating that the coordination effect of NH
and C=O as bidentate ligand with palladium. The amount
of palladium metal in the silica-anchored proline–palladi-
um catalyst 2 was found to be 2.76 wt% based on atomic
absorption spectroscopy (AAS) analysis.
The base played an important role in the Heck reaction. In
the presence of silica-anchored proline–palladium cata-
lyst 2 (1 mol% of Pd), when the reactions were conducted
in N,N-dimethylformamide, several different bases were
tested to optimize the base in Heck reactions. It was found
The Heck reaction of 4-iodoanisole with butyl acrylate that potassium carbonate was the most effective base for
served as a model reaction in our initial screening of the the Heck reaction. Other bases (e.g., Na CO , K PO ,
2
3
3
4
catalytic activity of silica-anchored proline-palladium cat- NaOAc, LiOH, KOH, Et N, Bu N, BuNH , and piperi-
3
3
2
alyst 2. When the model reaction was carried out in N,N- dine) were substantially less effective (Table 1, entries
dimethylformamide at 100 °C for 12 hours with the silica- 1–10).
anchored proline–palladium 2 (1 mol% of Pd) as catalyst,
We then turned our attention to the investigate the effects
and potassium carbonate as base, the corresponding cross-
of the solvent on the coupling reaction. When the reac-
coupling product 3f was isolated in 99% yield. Encour-
tions were conducted in dimethyl sulfoxide and N,N-di-
aged by this result, we continued our research to improve
methylformamide, good to excellent yields (88% and
Table 1 Effect of the Base on the Heck Reactiona
I
CO2n-Bu
catalyst 2 (1 mol%)
+
CO2n-Bu
base, DMF
MeO
MeO
3f
Entry
Base
Isolated yield (%)
1
2
3
4
5
6
7
8
9
K CO
99
78
80
94
67
93
54
56
37
63
2
3
K PO
3
4
Na CO
2
3
Et N
3
LiOH
KOH
NaOAc
piperidine
BuNH2
1
0
Bu N
3
a
4-Iodoanisole (1.0 mmol), butyl acrylate (1.0 mmol), 2 (0.01 mmol of Pd), base (2.0 mmol), DMF (3 mL), 100 °C, 12 h.
Synthesis 2008, No. 15, 2405–2411 © Thieme Stuttgart · New York

PAPER
Application of an Anchored Palladium Catalyst in the Heck Reaction
2407
Table 2 Effect of the Solvent on the Heck Reactiona
I
CO2n-Bu
catalyst 2 (1 mol%)
+
CO2n-Bu
K2CO3, solvent
MeO
MeO
3f
Entry
Solvent, temp
DMF, 100 °C
DMSO, 100 °C
toluene, 100 °C
EtOH, 78 °C
THF, 66 °C
Isolated yield (%)
1
2
3
4
5
99
88
67
49
NR
NR
6
acetone, 56 °C
a
4
-Iodoanisole (1.0 mmol), butyl acrylate (1.0 mmol), 2 (0.01 mmol of Pd), K CO (2.0 mmol), DMF (3 mL), 12 h.
2 3
Table 3 Heck Reactions Catalyzed by Catalyst 2a
9
9%, respectively) of product 3f were obtained. The mod-
erate yields of product 3f were isolated when the reaction
carried out in ethanol and toluene. However, no desired
cross-coupling product 3f was observed during the reac-
tions in tetrahydrofuran and acetone (Table 2, entries
catalyst 2 (1 mol%)
R
ArX
+
R
Ar
K2CO3, DMF
3
Entry Organic halide
Ar
Alkene
Product Isolated yield
(%)
1
–6).
X
R
During the course of our further optimization of the reac-
tion conditions, when using 1 mol% loading of organic–
inorganic anchored-palladium catalyst 2, the reactions
were generally completed in a matter of hours, but the
time, as expected, was inversely proportional to the tem-
perature. A reaction temperature of 100 °C was found to
be optimal. Thus, the optimized reaction conditions for
this reaction are 2 (1 mol%) in N,N-dimethylformamide at
1
2
3
4
5
6
7
8
9
0
Ph
Ph
I
Ph
3a
3b
3c
3d
3e
3f
95
99
90
99
89
99
97
99
92
93
90
89
93
84
90
90
95
88
92
85
87
45
I
CO Bu
2
4-MeC H
I
Ph
6
4
4
4-MeC H
I
CO Bu
6
2
4-MeOC H
I
Ph
6
4
4
4-MeOC H
I
CO Bu
6
2
1
00 °C for 12 hours.
4-O NC H
I
Ph
3g
3h
3i
2
6
4
To examine the versatility of this method, the Heck
alkenation of butyl acrylate with iodoarenes and bromo-
arenes containing electron-rich, electron-poor, and electron-
neutral substituents was investigated (Table 3, entries 2,
4-O
NC
H
I
CO Bu
2
2
6
4
4
3-O NC H
I
CO Bu
2
6
2
1
3-MeC H
I
Ph
Ph
Ph
3j
6
4
4
, 6, 8, 9, 13, 15, 17, 19, and 21). The conversions, regio-
selectivities (>99% trans products), and yields were satis- 11
factory under the standard reaction conditions. The
alkenation of haloarenes was also tolerant of ortho- and
meta-substitution of the aryl iodide and led to the products
2-MeC H I
I
3k
3g
3h
3l
6
4
1
1
1
1
2
3
4
5
4-O NC H
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
2
6
4
4
4-O NC H
CO Bu
2
6
2
3
i–k in good yields (Table 3, entries 9–11). The scope of
4-NCC H
Ph
6
4
4
this catalytic system with other vinyl substrates, such as
styrene (Table 3, entries 1, 3, 5, 7, 10, 11, 12, 14, 16, 18,
and 20) was also examined, and good results were ob- 16
tained under identical conditions. For activated chloro-
arenes (Table 3, entry 22), the cross-coupling product 3g
was isolated in poor yield under the present reaction con-
ditions. Unfortunately, the desired cross-coupling prod- 19
ucts were not isolated for the inactivated chloroarenes
after longer reaction times (36 h) and in the presence of
higher palladium loading (2 mol% of Pd).
4-NCC H
CO Bu
3m
3n
3o
3a
3b
3c
3d
3g
6
2
4-AcC
H
Ph
6
4
1
1
7
8
4-AcC H
CO Bu
6
4
2
Ph
Ph
Ph
CO Bu
2
2
2
0
1
2
4-MeC H
Ph
6
4
4
4-MeC H
CO Bu
6
2
2
4-O NC H
CO Bu
2
6
4
2
a
Alkene (1.0 mmol), organic halide (1.0 mmol), 2 (0.01 mmol of Pd),
K CO (2.0 mmol), DMF (3 mL), 100 °C, 12 h.
2
3
Synthesis 2008, No. 15, 2405–2411 © Thieme Stuttgart · New York

2
408
H. Liu et al.
PAPER
Table 4 Successive Trials by Using Recoverable Catalyst 2a
I
CO2n-Bu
recycled 2 (1 mol%)
+
CO2n-Bu
K2CO3, DMF
MeO
MeO
3f
Entry
Isolated yield (%)
Entry
Isolated yield (%)
1
2
3
4
5
6
99
99
98
98
96
95
96
8
9
95
94
95
94
94
93
91
10
11
12
13
14
7
a
4
-Iodoanisole (1.0 mmol), butyl acrylate (1.0 mmol), 2 (0.01 mmol of Pd), K CO (2.0 mmol), DMF (3 mL), 100 °C, 12 h.
2 3
The recyclability of the silica-anchored palladium catalyst in good to excellent yields under phosphine- and amine-
was also investigated. After reaction, the solution was free reaction conditions. Furthermore, the silica-anchored
vacuum filtered using a sintered glass funnel and washed palladium catalyst 2 could be recovered and recycled by
with dichloromethane (2 mL), diethyl ether (2 mL), etha- simple filtration of the reaction solution and used for more
nol (2 mL), and hexane (2 mL), respectively. After being than 14 consecutive trials without significant loss of its
dried, it can be reused directly without further purifica- catalytic activity.
tion. The catalyst 2 can be recovered, recycled, and reused
for 14 consecutive trials without loss of its activity
Melting points were recorded on a WRS-2B melting point apparatus
and are uncorrected. All H NMR and C NMR spectra were re-
(
Table 4). Meanwhile, the extent of palladium leaching in
1
13
the silica-anchored proline–palladium catalyst 2 was de- corded on 300 MHz Bruker FT-NMR spectrometer; TMS was used
termined. Inductively coupled plasma (ICP) analysis of as an internal standard. IR spectra were obtained by using a Nicolet
NEXUS 470 spectrophotometer. The CHN analysis was performed
the clear filtrates obtained by filtration after the reaction
on a Vario El III elementary analyzer. Products were purified by
flash chromatography on 230–400 mesh silica gel.
indicated that palladium content is less than 0.1 ppm.
However, only trace amount of the desired product was
The chemicals were purchased from commercial suppliers (Aldrich,
isolated for the model reaction by adding substrates to a
USA and Shanghai Chemical Company, China) and were used
filtrate obtained from the filtration of the immobilized cat-
without purification prior to use. Activation of silica gel by using
alyst after the reaction.
concd H SO and HNO was preformed according to the litera-
2
4
3
2
8
In comparison to the similar organic–inorganic hybrid ture.
material supported palladium catalysts reported by our
2
8
Preparation of the Silica-Anchored Palladium Catalyst 2
In a 50-mL round-bottomed flask were introduced successively an-
hyd toluene (20 mL), activated silica gel (3.0 g) and (3-aminopro-
pyl)triethoxysilane (10 mL) and the mixture was refluxed for 24 h.
The mixture was filtered and the solid was washed with acetone and
group previously, there are some advantages of the new-
ly designed catalyst; (i) novel N,O-coordination of silica-
anchored proline with palladium, instead of N,N-coordi-
nation of silica-anchored proline with palladium; (ii) the
activity of this silica-anchored palladium is superior to the CH Cl and dried under reduced pressure at 60 °C; functionalized
2
2
2
8e
supported palladium reported previously by us [for the silica gel (3.26 g) was obtained. The loading of the modified silica
gel was readily quantified via CHN microanalysis and found to be
Heck reaction, the reaction conditions for the present
method: silica-anchored-catalyst 2 (1 mol%), K CO (2
0
.935 mmol/g.
2
3
equiv), DMF, 100 °C, 12 h vs the reaction conditions for In a round-bottomed flask, the obtained functionalized silica (1.0 g,
2
8e
0.935 mmol of 3-aminopropyl/g), Boc-L-Pro (0.236 g, 1.08 mmol),
DCC (0.193 g, 0.935 mmol), and anhyd THF (20 mL) were added.
The mixture was stirring at reflux temperature for 72 h. The hot
the reported method:
silica-AAPTS-Pd (2 mol%),
K CO (2 equiv), DMA, 130 °C, 12 h]; (iii) the life of
present catalyst is longer than that of previously one (for
Heck reaction, 14 consecutive trials without loss of activ-
2
3
mixture was filtered and the solid was washed with H O and hot
EtOH, and then dried under reduced pressure at 60 °C overnight.
2
ity of catalyst for the present method vs 10 consecutive tri- The corresponding silica gel (1.205 g) was obtained.
2
8e
als for the reported method ).
In a round-bottomed flask were introduced successively CH Cl (4
2
2
mL), TFA (4 mL), and the silica gel obtained in the preceding step
1.205 g). After shaking for 3 h, the silica gel was washed with Et N
In conclusion, we have demonstrated that a highly effi-
cient and recyclable palladium catalyst anchored on
organic–inorganic hybrid material was used in the Heck
reaction. Iodoarenes and bromoarenes reacted with alk-
enes to afford the corresponding cross-coupling products
(
3
and CH Cl and then dried under reduced pressure at r.t. overnight
2
2
giving 1 (1.099 g) as a white solid.
–
1
FT-IR (KBr): 1101 (Si–O), 1679 (C=O) cm .
Synthesis 2008, No. 15, 2405–2411 © Thieme Stuttgart · New York

PAPER
Application of an Anchored Palladium Catalyst in the Heck Reaction
2409
In a small Schlenk tube, silica-anchored proline 1 (1.00 g) was
(E)-3-Methylstilbene (3j)
Mp 47–48 °C (Lit. 48.6–49.2 °C).
3
2
mixed with Pd(OAc) (0.112 g, 0.5 mmol) in anhyd EtOH (5 mL).
2
The mixture was stirred for 4 h under N at r.t. The soln was filtered
IR (KBr): 3021, 2921, 1600, 1495, 966, 784, 695 cm–1.
2
and the solid was washed with acetone and MeOH and the solid was
dried under reduced pressure at r.t. for 16 h, leading to a pale yellow
powder, catalyst 2 (1.03 g). The amount of palladium metal in 2 was
found to be 2.76 wt% based on atomic absorption spectroscopy
1
H NMR (300 MHz, CDCl ): d = 7.52–7.50 (m, 2 H), 7.35–7.31 (m,
3
4
H), 7.27–7.22 (m, 2 H), 7.09–7.07 (m, 3 H), 2.38 (s, 3 H).
(
E)-2-Methylstilbene (3k)
(AAS) analysis.
3
1
Mp 31–32 °C (Lit. 30–32 °C).
–
1
FT-IR (KBr): 1020 (Si–O), 1641 (C=O) cm .
–
1
IR (KBr): 2920, 1601, 1495, 1448, 965, 761 cm .
Butyl (E)-3-(4-Methoxyphenyl)prop-2-enoate (3f); Typical Pro-
cedure
1
H NMR (300 MHz, CDCl ): d = 7.58–7.48 (m, 3 H), 7.37–7.16 (m,
3
6
H), 7.01 (d, J = 16.2 Hz, 2 H), 2.36 (s, 3 H).
Under N , an oven-dried 2-necked round-bottomed flask containing
2
a stirrer bar was charged with 4-iodoanisole (1.0 mmol), butyl acry-
(
E)-4-Cyanostilbene (3l)
late (1.0 mmol), 2 (24 mg, contains 0.01 mmol of Pd), K CO (276
30
2
3
Mp 117–119 °C (Lit. 117.4–117.7 °C).
IR (KBr): 3023, 2919, 2226, 1601, 973, 825, 758 cm .
1H NMR (300 MHz, CDCl
): d = 7.77–7.63 (m, 6 H), 7.53–7.42 (m,
mg, 2.00 mmol), and DMF (3 mL). The mixture was heated and
stirred at 100 °C for 12 h. After completion of the reaction, the mix-
ture was cooled to r.t., vacuum filtered using a sintered glass funnel,
and washed with CH Cl . The combined organics were dried
–
1
3
3 H), 7.30 (d, J = 16.3 Hz, 1 H), 7.20 (d, J = 16.2 Hz, 1 H).
2
2
(
Na SO ), filtered, concentrated, and the residue was purified by
2 4
flash chromatography (silica gel) to give the desired cross-coupling
product 3f as a light yellow liquid.
(E)-4-Acetylstilbene (3n)
Light yellow solid; mp 140–141 °C (Lit. 139.5–141.5 °C).
3
4
29
–
1
IR (film): 2959, 2934, 1604, 1463, 983, 828 cm .
IR (KBr): 3019, 1678, 1601, 1492, 1411, 1358, 1266, 1180, 1074,
965, 868, 754, 723, 690 cm .
–
1
1
H NMR (300 MHz, CDCl ): d = 7.64 (d, J = 16.8 Hz, 1 H), 7.47 (d,
J = 8.7 Hz, 2 H), 6.89 (d, J = 8.7 Hz, 2 H), 6.30 (d, J = 15.9 Hz, 1
H), 4.20 (t, J = 6.6 Hz, 2 H), 3.82 (s, 3 H), 1.73–1.63 (m, 2 H), 1.49–
3
1H NMR (300 MHz, CDCl
): d = 7.95 (d, J = 8.1 Hz, 2 H), 7.59–
3
7.53 (m, 4 H), 7.38 (t, J = 7.2 Hz, 2 H), 7.29 (t, J = 6.9 Hz, 1 H),
7.23 (d, J = 15.9 Hz, 1 H), 7.09 (d, J = 16.2 Hz, 1 H), 2.60 (s, 3 H).
1
.37 (m, 2 H), 0.97 (t, J = 7.2 Hz, 3 H).
The Recyclability of 2
After carrying out the reaction, the mixture was vacuum filtered us-
Butyl (E)-Cinnamate (3b)
Light yellow liquid.
3
4
ing a sintered glass funnel, and washed sequentially with CH Cl (3
IR (film): 3068, 2959, 1712, 1638, 1467, 1327, 767, 684 cm–1.
1
2
2
mL), Et O (3 mL), EtOH (3 mL), and hexane (3 mL). The catalyst
2
H NMR (300 MHz, CDCl ): d = 7.79 (d, J = 15.9 Hz, 1 H), 7.63–
was dried in an oven at 60 °C for 4 h and can then be reused directly
without further purification.
3
7
.61 (m, 2 H), 7.49–7.46 (m, 3 H), 6.55 (d, J = 15.9 Hz, 1 H), 4.33
(
t, J = 6.9 Hz, 2 H), 1.85–1.80 (m, 2 H), 1.61–1.48 (m, 2 H), 1.07 (t,
J = 7.3 Hz, 3 H).
(
E)-Stilbene (3a)
2
9
White solid; mp 122–123 °C (Lit. 120–122 °C).
Butyl (E)-3-(4-Methylphenyl)prop-2-enoate (3d)
Light yellow liquid.
IR (film): 3015, 2959, 1712, 1608, 1514, 983, 813 cm–1.
–
1
IR (KBr): 3020, 1597, 1495, 1451, 1364, 963, 762, 691 cm .
34
1
H NMR (300 MHz, CDCl ): d = 7.51 (d, J = 7.2 Hz, 4 H), 7.34 (t,
3
J = 7.3 Hz, 4 H), 7.27–7.24 (m, 2 H), 7.10 (s, 2 H).
1
H NMR (300 MHz, CDCl ): d = 7.75 (d, J = 15.9 Hz, 1 H), 7.53 (d,
3
J = 8.1 Hz, 2 H), 7.29 (d, J = 7.8 Hz, 2 H), 6.50 (d, J = 15.9 Hz, 1
H), 4.20 (t, J = 6.7 Hz, 2 H), 2.48 (s, 3 H), 1.85–1.75 (m, 2 H), 1.61–
(
E)-4-Methylstilbene (3c)
2
9
White solid; mp 121–122 °C (Lit. 120 °C).
1
.51 (m, 2 H), 1.08 (t, J = 7.4 Hz, 3 H).
–
1
IR (KBr): 3023, 2918, 2852, 1601, 1447, 969, 809, 749, 690 cm .
1
H NMR (300 MHz, CDCl ): d = 7.62 (d, J = 8.1 Hz, 2 H), 7.53 (d,
Butyl (E)-3-(4-Nitrophenyl)prop-2-enoate (3h)
Mp 63–65 °C (Lit. 64–65 °C).
3
3
0
J = 8.1 Hz, 2 H), 7.50–7.44 (m, 3 H), 7.39–7.20 (m, 4 H), 2.48 (s, 3
H).
IR (KBr): 3058, 2958, 1709, 1601, 1493, 1308, 982, 759 cm–1.
1
H NMR (300 MHz, CDCl ): d = 8.30 (d, J = 8.7 Hz, 2 H), 7.83 (d,
(
E)-4-Methoxystilbene (3e)
3
3
0
J = 15.7 Hz, 1 H), 7.78 (d, J = 8.7 Hz, 2 H ), 6.67 (d, J = 16.2 Hz, 1
H), 4.34 (t, J = 6.7 Hz, 2 H), 1.85–1.76 (m, 2 H), 1.61–1.50 (m, 2
H), 1.08 (t, J = 7.2 Hz, 3 H).
Light yellow solid; mp 136–138 °C (Lit. 135–137 °C).
IR (KBr): 2962, 1601, 1512, 1446, 1296, 1029, 967, 860, 750, 688
cm .
–
1
1
H NMR (300 MHz, CDCl ): d = 7.50 (d, J = 6.4 Hz, 2 H), 7.46 (d,
Butyl (E)-3-(3-Nitrophenyl)prop-2-enoate (3i)
Mp 55–56 °C (Lit. 56–57 °C).
3
3
5
J = 8.7 Hz, 2 H), 7.34 (t, J = 7.5 Hz, 2 H), 7.24 (t, J = 6.9 Hz, 1 H),
7
.16 (d, J = 16.4 Hz, 1 H), 7.10 (d, J = 16.4 Hz, 1 H), 6.95 (d,
IR (KBr): 3036, 2965, 1712, 1613, 1469, 1347, 961, 745, 673 cm–1.
J = 8.7 Hz, 2 H), 3.83 (s, 3 H).
1
H NMR (300 MHz, CDCl ): d = 8.48–7.66 (m, 5 H), 6.67 (d,
3
J = 15.9 Hz, 1 H), 4.34 (t, J = 6.7 Hz, 2 H), 1.85–1.76 (m, 2 H),
1.61–1.49 (m, 2 H), 1.08 (t, J = 7.2 Hz, 3 H).
(
E)-4-Nitrostilbene (3g)
3
3
Light yellow solid; mp 155–157 °C (Lit. mp 156–157 °C).
–
1
IR (KBr): 2920, 1588, 1510, 1344, 971, 849, 839, 767 cm .
Butyl (E)-3-(4-Cyanophenyl)prop-2-enoate (3m)
Light yellow liquid.
IR (film): 2957, 2887, 2221, 1713, 1640, 1605, 1412, 986, 835 cm–1.
1
30
H NMR (300 MHz, CDCl ): d = 8.33 (d, J = 8.4 Hz, 2 H), 7.74 (d,
3
J = 8.4 Hz, 2 H), 7.52 (d, J = 7.4 Hz, 2 H), 7.49–7.44 (m, 3 H), 7.39
(
d, J = 16.2 Hz, 1 H), 7.22 (d, J = 16.2 Hz, 1 H).
Synthesis 2008, No. 15, 2405–2411 © Thieme Stuttgart · New York

2
410
H. Liu et al.
PAPER
1
H NMR (300 MHz, CDCl ): d = 7.79–7.69 (m, 5 H), 6.60 (d,
(14) (a) Dai, M. J.; Liang, B.; Wang, C. H.; You, Z. J.; Xiang, J.;
Dong, G. B.; Chen, J. H.; Yang, Z. Adv. Synth. Catal. 2004,
346, 1669. (b) Yang, D.; Chen, Y. C.; Zhu, N. Y. Org. Lett.
3
J = 15.9 Hz, 1 H), 4.32 (t, J = 6.6 Hz, 2 H), 1.84–1.74 (m, 2 H),
1
.60–1.47 (m, 2 H), 1.05 (t, J = 7.4 Hz, 3 H).
2
004, 6, 1577. (c) Chen, W.; Li, R.; Han, B.; Li, B. J.; Chen,
Butyl (E)-3-(4-Acetylphenyl)prop-2-enoate (3o)
Y. C.; Wu, Y.; Ding, L. S.; Yang, D. Eur. J. Org. Chem.
2006, 1177.
Light yellow liquid.30
–
1
(15) (a) Grasa, G. A.; Singh, R.; Stevens, E. D.; Nolan, S. P.
J. Organomet. Chem. 2003, 687, 269. (b) Arellano, C. G.;
Corma, A.; Iglesias, M.; Sanchez, F. Adv. Synth. Catal.
IR (film): 2960, 2873, 1736, 1686, 1409, 983, 829 cm .
1
H NMR (300 MHz, CDCl ): d = 7.95 (d, J = 9.1 Hz, 2 H), 7.72 (d,
J = 15.9 Hz, 1 H), 7.64 (d, J = 8.1 Hz, 2 H), 6.53 (d, J = 15.9 Hz, 1
H), 4.23 (t, J = 6.6 Hz, 2 H), 2.61 (s, 3 H), 1.72–1.68 (m, 2 H), 1.49–
3
2004, 346, 1758. (c) Hardy, J. E.; Hubert, S.; Macquarrie, D.
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1
.41 (m, 2 H), 0.97 (t, J = 7.3 Hz, 3 H).
(
16) (a) Buchmeiser, M. R.; Wurst, K. J. Am. Chem. Soc. 1999,
Acknowledgment
1
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We gratefully acknowledge financial support by the National Natu-
ral Science Foundation of China (No. 20772043, 20572031).
(
2
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Application of an Anchored Palladium Catalyst in the Heck Reaction
2411
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Synthesis 2008, No. 15, 2405–2411 © Thieme Stuttgart · New York