Silica-anchored proline-copper(I) as an efficient and recyclable catalyst for the Sonogashira reaction

Article abstract of DOI:10.1055/s-2008-1072562

A novel silica-anchored proline-copper(I) organic-inorganic hybrid material as an efficient catalyst for the Sonogashira reaction was developed. Terminal alkynes were reacted with aryl iodides and bromides smoothly in the presence of a proline-functionalized silica-anchored copper(I) catalyst in DMF to afford the corresponding cross-coupling products in good to excellent yields. Furthermore, silica-anchored proline-copper(I) catalyst was recovered and recycled by a simple filtration of the reaction solution and reused for six times without significant decreases in activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1072562

PAPER
1367
Silica-Anchored Proline–Copper(I) as an Efficient and Recyclable Catalyst for
the Sonogashira Reaction
Recyclable
C
ata
u
lyst for the
S
l
onoga
i
shira Reactio
W
n
ang,a Lei Wang,*a,b Pinhua Lia
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
Fax +86(561)3802069
Received 10 December 2007; revised 29 January 2008
To some extent, supported catalyst can facilitate both the
isolation and recycling of the catalyst by filtration thus
providing environmentally cleaner processes. The devel-
opment of organic reagents grafted onto silica gel has at-
Abstract: A novel silica-anchored proline–copper(I) organic–
inorganic hybrid material as an efficient catalyst for the Sonoga-
shira reaction was developed. Terminal alkynes were reacted with
aryl iodides and bromides smoothly in the presence of a proline-
functionalized silica-anchored copper(I) catalyst in DMF to afford tracted increasing attention in recent years because
the corresponding cross-coupling products in good to excellent
industry seeks more environmentally friendly chemical
manufacturing processes.7 However, applications that
yields. Furthermore, silica-anchored proline–copper(I) catalyst was
recovered and recycled by a simple filtration of the reaction solution
involve the Sonogashira reaction have been less widely
and reused for six times without significant decreases in activity.
investigated, and usually employ a polystyrene-based
support medium rather than a silica-based support.8
Key words: Sonogashira coupling reaction, organic–inorganic hy-
brid material, silica-anchored proline–copper(I) catalyst, heteroge-
Most recently, in our preliminary investigation, the prep-
aration of highly active 3-[(2-aminoethyl)amino]propyl-
functionalized silica-anchored palladium copper(II) cata-
lyst and subsequently its uses as an efficient and recycla-
ble catalyst for the Sonogashira reaction, Heck reaction,
and Ullmann diaryl etherification were reported.9
neous catalysis, terminal alkynes, aryl iodides, aryl bromides
Stephens and Castro first discovered that diarylacetylenes
can be prepared by treating aryl iodides with cuprous
acetylides in refluxing pyridine under nitrogen in 1963.1
Later, Cassar observed that acetylene or monosubstituted
acetylenes were converted into aryl- and vinyl-substituted
acetylene derivatives by reaction with aryl and vinyl ha-
lides in the presence of a nickel or palladium-triarylphos-
phine complex along with a base, in 1975. With the
palladium-triphenylphosphine complexes, the conversion
could be carried out catalytically under mild conditions.2
Subsequently, Sonogashira et al. combined these two pro-
cedures into a cross-coupling reaction of terminal alkynes
with aryl and alkenyl halides catalyzed by the palladium
complexes in the presence of a catalytic amount of CuI
and an amine (as solvent or in large excess), bearing his
name in 1975.3 Since then, the Sonogashira reaction has
become the most important method to prepare arylalkynes
and conjugated enynes, which are precursors for natural
products, pharmaceuticals, and molecular organic materi-
als.4 At present, the palladium complex is the most com-
monly used catalyst for this coupling reaction. In addition,
Au, Ag, Ru, Cu, Ni, In, etc. can also be used as catalysts
for this transformation.5 However, the high cost of transi-
tion-metal catalysts coupled with the toxic effects has lim-
ited its development and application. The development of
inexpensive and nontoxic catalyst has gained more and
more attention nowdays.6
In this paper, we report on a novel silica-anchored pro-
line–copper(I) as an efficient catalyst for the Sonogashira
reaction. Terminal alkynes were reacted with aryl iodides
and bromides smoothly to afford the corresponding cross-
coupling products in good to excellent yields. It is impor-
tant to note that the silica-anchored proline–copper(I) cat-
alyst could be recovered and recycled by a simple
filtration of the reaction solution and could be reused up
to six times without significant loss of its activity.
The synthesis of silica-anchored proline–copper(I) cata-
lyst is illustrated in Scheme 1. This was readily prepared
through a four-step procedure. The silica gel (100–200
mesh, from Aldrich) was reacted with (4-chlorometh-
yl)phenyltrichlorosilane in anhydrous toluene at 140 °C
for 24 hours to afford the 4-chloromethylphenyl function-
alized silica gel. The loading of the modified silica was
readily quantified via CHN microanalysis and found to be
1.12 mmol/g. The obtained 4-chloromethylphenyl func-
tionalized silica gel then reacted with 1-(tert-butoxycar-
bonyl)-4-hydroxypyrrolidine-2-carboxylic acid in the
presence of NaH in anhydrous THF under reflux for 12
hours to afford the organic-inorganic hybrid material. The
Boc protective group in the organic-inorganic hybrid ma-
terial was deprotected through a standard method by shak-
ing with a CF3CO2H–CH2Cl2 solution (1:1) at room
temperature for three hours. The modified silica was fil-
tered and subsequently neutralized by washing with Et3N.
The solid was washed with dichloromethane, methanol,
and diethyl ether, respectively, and dried under vacuum at
SYNTHESIS 2008, No. 9, pp 1367–1372
x
x
.
x
x
.2
0
0
8
Advanced online publication: 27.03.2008
DOI: 10.1055/s-2008-1072562; Art ID: F22707SS
© Georg Thieme Verlag Stuttgart · New York

1368
Z. Wang et al.
PAPER
HO
N
COOH
OH
OH
OH
O
O
O
Cl3SiC6H4CH2Cl
toluene
Boc
Si
CH2Cl
NaH, THF
silica
silica
O
O
O
O
1) TFA, CH2Cl2
2) CuI/DMF
Si
O
O
Si
O
O
O
silica
silica
N
N
COOH
H
OH
Boc
Cu(I)
Scheme 1
Table 1 Effect of Copper Source on the Sonogashira Reactiona
Cu salt (5 mol%)
MeO
MeO
I
+
K2CO3, DMF
Entry
Copper source
Yield (%)b
1
2
3
4
5
CuSO4
Cu(OAc)2
CuI
trace
43
92
CuBr
81
CuCl
73
a Reaction conditions: phenylacetylene (102 mg, 1.0 mmol), 4-iodoanisole (234 mg, 1.0 mmol), silica-anchored proline–copper(I) catalyst (58
mg, contains 0.05 mmol of Cu), and K2CO3 (276 mg, 2.0 mmol) in DMF (2 mL) at 110 °C with stirring for 8 h.
b Isolated yield.
room temperature to afford a white solid. The obtained ride as copper sources. Meanwhile, moderate yield (43%
white solid was then reacted with copper(I) iodide in N,N- yield) of the product was observed with copper(II) acetate
dimethylformamide at room temperature for four hours to as the copper source and no desired product was generated
generate the silica-anchored proline–copper(I) catalyst. when copper(II) sulfate was used as the copper source.
The copper metal amount of the silica-anchored proline–
Encouraged by this result, we continued our research to
copper(I) catalyst was found to be 5.48 wt% based on
improve the yield of the product by optimization of the re-
AAS analysis.
action conditions, for example, by studying the effect of
For our optimization of reaction conditions, the Sono- base on the reaction. From Table 2, we can see that the
gashira coupling reaction of phenylacetylene with 4-io- Sonogashira coupling reaction can occur in the presence
doanisole was chosen as a model reaction. In our initial of the bases we tested, except cesium carbonate. The or-
screening experiments, the effects of various copper ganic bases, such as piperidine and triethylamine can be
sources, bases, solvents, reaction time, and temperature also used in the reaction, but only low yields (36 and 47%,
on the yields of the model cross-coupling reaction were respectively) of the product were obtained. Potassium car-
examined.
bonate was found to be the most effective one in the reac-
tion. The other bases, such as KF, K3PO4, Na2CO3, and t-
BuOK were subsequently less effective (Table 2,
entries1–8).
As shown in Table 1, the effect of copper source on the
Sonogashira coupling reaction under the reaction condi-
tions, which involved potassium carbonate as a base in
N,N-dimethylformamide at 110 °C for 8 hours, was sur- We next turned our attention to investigate the effect of
veyed. Among the copper sources tested, a high yield solvent on the coupling reaction. When the reactions were
(92%) of the desired cross-coupling product was isolated conducted in N,N-dimethylformamide, dimethyl sulfox-
when copper(I) iodide was used as copper source, where- ide, and ethanol, good to excellent yields (92, 88 and 80%,
as good yields (81 and 73%, respectively) of the product respectively) of products were isolated. Use of acetoni-
were obtained with copper(I) bromide and copper(I) chlo-
Synthesis 2008, No. 9, 1367–1372 © Thieme Stuttgart · New York

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Recyclable Catalyst for the Sonogashira Reaction
1369
Table 2 Effect of Base on the Sonogashira Reactiona
anchored Cu(I) cat.
base, DMF
MeO
I
+
MeO
Entry
Base
Yield (%)b
1
2
3
4
5
6
7
8
piperidine
Et3N
36
47
K2CO3
KF
92
57
K3PO4
Na2CO3
Cs2CO3
t-BuOK
82
80
trace
78
a Reaction conditions: phenylacetylene (102 mg, 1.0 mmol), 4-iodoanisole (234 mg, 1.0 mmol), silica-anchored proline–copper(I) catalyst (58
mg, contains 0.05 mmol of Cu), and base (2.0 mmol) in DMF (2 mL) at 110 °C with stirring for 8 h.
b Isolated yield.
Table 3 Effect of Solvent on the Sonogashira Reactiona
anchored Cu(I) cat.
MeO
I
+
MeO
K2CO3, solvent
Entry
Solvent
DMF
Temp (°C)
Yield (%)b
1
2
3
4
5
6
110
110
78
92
88
80
58
30
24
DMSO
EtOH
MeCN
dioxane
toluene
81
100
110
a Reaction conditions: phenylacetylene (102 mg, 1.0 mmol), 4-iodoanisole (234 mg, 1.0 mmol), silica-anchored proline–copper(I) catalyst (58
mg, contains 0.05 mmol of Cu), and K2CO3 (276 mg, 2.0 mmol) in solvent (2 mL) at the temperature indicated in Table 3 for 8 h.
b Isolated yield.
trile, dioxane, and toluene as solvents led to slower reac- The electron-deficient aryl iodides and bromides can be
tions (Table 3, entries1–6).
nearly completely converted into products (Table 4, en-
tries 4, 9, 10, 14, and 16). But the yield from 3-nitro-
substituted iodobenzene was slightly lower than that of its
4-nitro analogue, probably due to the steric hindrance in
the 3-nitro-substituted iodobenzene (Table 4, entry 4 vs.
entry 5). For electron-neutral aryl iodide, high yield of
product was also obtained (Table 4, entry 1), but only
moderate yield of the product was isolated for less rela-
tively active bromobenzene as substrate (Table 4, entry
12). This catalytic system was equally efficient for elec-
tron-rich aryl iodides. Good yields of products (90 and
93% yield, respectively) were observed for 4-iodoanisole
and 4-iodotoluene as organic halide sources (Table 4, en-
tries 2 and 3). The catalytic system was also effective for
2-bromopyridine, which generated the corresponding
product in good yield (Table 4, entry 11). To evaluate the
During the course of our further optimization of the reac-
tion conditions using 5 mol% loading of silica-anchored
proline–copper(I) catalyst, the reactions were generally
completed in a matter of hours, but the time, as expected,
was inversely proportional to the temperature. A reaction
temperature of 110 °C was found to be optimal. Thus, the
optimized reaction conditions for this reaction are silica-
anchored proline–copper(I) catalyst (5% mol) and potas-
sium carbonate (2.0 equiv) in N,N-dimethylformamide at
110 °C for 8 h.
Under the optimized reaction conditions, the reaction of a
wide variety of aryl halides and terminal alkynes under-
went Sonogashira coupling smoothly, which generated
the corresponding products in good to excellent yields.
Synthesis 2008, No. 9, 1367–1372 © Thieme Stuttgart · New York

1370
Z. Wang et al.
PAPER
the solution was vacuum-filtered using a sintered glass
funnel and washed with CH2Cl2, Et2O, EtOH, and hexane,
respectively. After drying, it can be reused directly with-
out further purification. The silica-anchored proline–cop-
per(I) catalyst can be recovered, recycled, and reused for
six consecutive trials without loss of its activity (Table 5).
Table 4 Silica-Anchored Proline–Copper(I)-Catalyzed Sonogash-
ira Reactiona
anchored Cu(I) cat.
R1X
+
R2C
CH
R2C
CR1
K2CO3, DMF
R2C≡CH
Entry R1X
Yield (%)b
In conclusion, a highly efficient silica-anchored proline–
copper(I) catalyst has been successfully applied to the
cross-coupling of aryl halides, including aryl iodides and
bromides with terminal alkynes and the reactions generat-
ed the corresponding products in good to excellent yields.
The use of silica-supported catalyst permitted the product
to be easily separated from the catalyst. Furthermore, the
silica-anchored catalyst could be recovered and recycled
by a simple filtration of the reaction solution and reused
for six consecutive trials without significant loss of activ-
ity.
1
2
PhI
PhC≡CH
93
92
93
95
85
94
90
93
91
90
86
62
67
92
71
96
4-MeOC6H4I
4-MeC6H4I
4-O2NC6H4I
3-O2NC6H4I
PhI
PhC≡CH
3
PhC≡CH
4
PhC≡CH
5
PhC≡CH
6
4-MeC6H4C≡CH
n-C6H13C≡CH
n-C8H17C≡CH
PhC≡CH
7
PhI
8
PhI
Melting points were recorded on a WRS-2B melting point apparatus
9
4-CNC6H4Br
4-MeCOC6H4Br
2-bromopyridine
PhBr
1
and are uncorrected. All H NMR spectra were recorded on a 300
10
11
12
13
14
15
16
PhC≡CH
MHz Bruker FT-NMR spectrometer. Chemical shifts are given as d
values with reference to TMS as internal standard. IR spectra were
obtained by using a Nicolet NEXUS 470 spectrophotometer. The
CHN analysis was performed on a Vario El III elementary analyzer.
Products were purified by flash chromatography on 230–400 mesh
silica gel.
PhC≡CH
PhC≡CH
4-MeOC6H4Br
4-O2NC6H4Br
4-MeC6H4Br
4-O2NC6H4I
PhC≡CH
All chemicals were purchased from commercial suppliers (Aldrich,
USA and Shanghai Chemical Company, China) and used without
purification prior to use. Activation of silica by using concentrated
H2SO4 and HNO3 was done according to the literature.9
PhC≡CH
PhC≡CH
4-MeC6H4C≡CH
Silica-Anchored Proline-Copper(I) Catalyst
a Reaction conditions: terminal alkyne (1.0 mmol), organic halide (1.0
mmol), silica-anchored proline–copper(I) catalyst (58 mg, contains
0.05 mmol of Cu), and K2CO3 (276 mg, 2.0 mmol) in DMF (2 mL) at
110 °C for 8 h.
In a 100 mL round-bottomed flask were introduced successively an-
hyd toluene (60 mL) and (4-chloromethyl)phenyltrichlorosilane
(7.8 g). After stirring the solution for 10 min, activated silica (20.0
g) was added. Then the mixture was refluxed for 24 h at 140 °C. The
mixture was filtered and the solid was washed with EtOH (50 mL)
in a Soxhlet extractor for 5 h, washed with Et2O (60 mL), and dried
under reduced pressure at 80 °C. The loading of the modified silica
was readily quantified via CHN microanalysis and found to be 1.12
mmol/g. Under N2, an oven-dried round-bottomed flask was
charged with anhyd THF (150 mL), 1-(tert-butoxycarbonyl)-4-hy-
droxypyrrolidine-2-carboxylic acid (2.80 g, 12.1 mmol), and NaH
(1.02 g, 60%, 25.5 mmol). The mixture was stirred for 1.5 h, then
the above functionalized silica (10 g) was added and the mixture
b Isolated yield.
scope of this methodology, we also performed the Sono-
gashira coupling reactions involving aliphatic alkynes.
All of them coupled with iodobenzene in high efficiency
(Table 4, entries 7 and 8).
The recyclability of the silica-anchored proline–copper(I)
catalyst was also investigated. After the reaction was over, was refluxed for 12 h. The solution was filtered and the solid was
Table 5 Successive Trials Using Recovered Silica-Anchored Proline–Copper(I) Catalysta
recycled
anchored Cu(I) cat.
MeO
I
+
MeO
K2CO3, DMF
Entry
Yield (%)b
Entry
Yield (%)b
1
2
3
92
89
91
4
5
6
88
89
88
a Reaction conditions: phenylacetylene (102 mg, 1.0 mmol), 4-iodoanisole (234 mg, 1.0 mmol), recycled silica-anchored proline–copper(I) cat-
alyst (58 mg, contains 0.05 mmol of Cu), and K2CO3 (276 mg, 2.0 mmol) in DMF (2 mL) at 110 °C for 8 h.
b Isolated yield.
Synthesis 2008, No. 9, 1367–1372 © Thieme Stuttgart · New York

PAPER
Recyclable Catalyst for the Sonogashira Reaction
1371
washed with H2O (30 mL), EtOH (30 mL), and then dried overnight
under reduced pressure at 60 °C. In a round-bottom flask were in-
troduced successively CH2Cl2 (10 mL), CF3CO2H (8 mL), and the
N-Boc-proline functionalized silica (4 g). The mixture was shaken
for 0.5 h, and the silica was filtered, washed with Et3N (5 mL),
CH2Cl2 (10 mL), MeOH (10 mL) and Et2O (10 mL), and then dried
overnight under reduced pressure at r.t. A white solid was obtained.
The loading of this modified silica was quantified via CHN mi-
croanalysis and found to be 0.91 mmol/g. In a small Schlenk tube,
the silica-anchored proline (1.0 g, containing 0.91 mmol proline
units) was mixed with CuI (0.191 g, 1.0 mmol) in DMF (5 mL). The
mixture was stirred for 4 h under N2 at r.t. The solution was filtered
and the solid was washed with acetone (3 mL) and MeOH (3 mL),
and the solid was dried under reduced pressure at r.t. for 16 h, af-
fording the silica-anchored proline–copper(I) catalyst as a pale blue
powder (1.05 g). The copper metal amount of the silica-anchored
proline–copper(I) catalyst was found to be 5.48 wt% based on AAS
analysis.
1H NMR (300 MHz, CDCl3): d = 8.20 (d, J = 9.00 Hz, 2 H), 7.65 (d,
J = 9.00 Hz, 2 H), 7.57–7.54 (m, 2 H), 7.40–7.38 (m, 3 H).
(3-Nitrophenyl)phenylacetylene
Mp 68–69 °C (Lit.14 mp 68–70 °C).
IR (KBr): 3082, 2237, 1529, 1514, 1442, 1351, 901, 758, 691 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.36 (s, 1 H), 8.15 (d, J = 9.00 Hz,
1 H), 7.81 (d, J = 7.50 Hz, 1 H), 7.57–7.52 (m, 3 H), 7.39–7.37 (m,
3 H).
1-Phenyldec-1-yne
Oil.15
IR (film): 3059, 2956, 2930, 2857, 2256, 1598, 1490, 1466, 901,
755, 691 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.43–7.38 (m, 2 H), 7.29–7.21 (m,
3 H), 2.39 (t, J = 6.96 Hz, 2 H), 1.68–1.56 (m, 2 H), 1.49–1.30 (m,
10 H), 0.89 (t, J = 6.54 Hz, 3 H).
Sonogashira Reaction Using Silica-Anchored Proline–
Copper(I) Catalyst; General Procedure
1-Phenyloct-1-yne
Oil.16
Under N2, an oven-dried two-necked round-bottomed flask contain-
ing a stir bar was charged with organic halide (1.0 mmol), terminal
alkyne (1.0 mmol), silica-anchored proline–copper(I) catalyst (58
mg, containing Cu 0.05 mmol), K2CO3 (276 mg, 2.00 mmol) and
DMF (2 mL). The mixture was heated and stirred at 110 °C for 8 h.
After cooling to r.t., the mixture was vacuum-filtered using a sin-
tered glass funnel and washed with CH2Cl2 (3 mL). The combined
organics were dried (Na2SO4), filtered, concentrated, and the resi-
due was purified by flash chromatography on silica gel to give the
desired cross-coupling product.
IR (film): 3073, 2946, 2923, 2246, 1590, 1498, 1467, 755, 691 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.42–7.39 (m, 2 H), 7.33–7.25 (m,
3 H), 2.41 (t, J = 6.99 Hz, 2 H), 1.69–1.57 (m, 2 H), 1.52–1.32 (m,
6 H), 0.90 (t, J = 6.86 Hz, 3 H).
(4-Methoxyphenyl)phenylacetylene
Mp 59–61 °C (Lit.17 mp 57–61 °C).
IR (KBr): 3059, 2186, 1593, 1511, 1440, 1247, 1028, 834, 754
cm–1.
1H NMR (300 MHz, CDCl3): d = 7.53–7.45 (m, 4 H), 7.33–7.30 (m,
3 H), 6.85 (d, J = 7.80 Hz, 2 H), 3.82 (s, 3 H).
Recyclization of Silica-Anchored Proline–Copper(I) Catalyst
After carrying out the reaction, the mixture was vacuum-filtered us-
ing a sintered glass funnel, and washed with CH2Cl2 (2 mL), Et2O
(2 mL), EtOH (2 mL), and hexane (3 mL), respectively. After dry-
ing in an oven at 60 °C for 4 h, the catalyst can be reused directly
without further purification.
(4-Cyanophenyl)phenylacetylene
Mp 109–111 °C (Lit.18 mp 108.5–109.5 °C).
IR (KBr): 3059, 2227, 2214, 1603, 1502, 1443, 843, 762 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.65–7.59 (m, 4 H), 7.56–7.53 (m,
2 H), 7.39–7.37 (m, 3 H).
Diphenylacetylene
Mp 61–62 °C (Lit.10 mp 60–62 °C).
IR (KBr): 3056, 2311, 1450, 961, 763, 691 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.52–7.50 (m, 4 H), 7.37–7.10 (m,
6 H).
2-(2-Phenylethynyl)pyridine
Oil.19
IR (film): 2986, 2239, 1598, 1535, 1493, 963, 754, 689 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.60 (dd, J = 5.10, 0.90 Hz, 1 H),
7.68–7.59 (m, 3 H), 7.51 (dd, J = 8.10, 0.90 Hz, 1 H), 7.37–7.33 (m,
3 H), 7.23–7.19 (m, 1 H).
Phenyl-p-tolylacetylene
Mp 71–73 °C (Lit.11 mp 72–73 °C).
IR (KBr): 3058, 2241, 1593, 1510, 1440, 915, 818, 754, 690 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.53–7.50 (m, 2 H), 7.42 (d,
J = 7.80 Hz, 2 H), 7.33–7.31 (m, 3 H), 7.12 (d, J = 7.80 Hz, 2 H),
2.35 (s, 3 H).
(4-Nitrophenyl)-p-tolylacetylene
Mp 156–157 °C (Lit.20 mp 157 °C).
IR (KBr): 3059, 2188, 1598, 1501, 1490, 1357, 808 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.23 (d, J = 8.61 Hz, 2 H), 7.66 (d,
J = 7.43 Hz, 2 H), 7.42 (d, J = 7.44 Hz, 2 H), 7.21 (d, J = 7.82 Hz,
2 H), 2.41 (s, 3 H).
(4-Acetylphenyl)phenylacetylene
Mp 95–96 °C (Lit.12 mp 94–96 °C).
IR (KBr): 3059, 2189, 1679, 1602, 1593, 1484, 1442, 1358, 834,
759 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.91 (d, J = 8.41 Hz, 2 H), 7.58 (d,
J = 8.41 Hz, 2 H), 7.54–7.52 (m, 2 H), 7.36–7.33 (m, 3 H), 2.57 (s,
3 H).
Acknowledgment
We gratefully acknowledge the financial support by the National
Natural Science Foundation of China (No. 20772043, 20572031).
(4-Nitrophenyl)phenylacetylene
Mp 120–122 °C (Lit.13 mp 120–121 °C).
IR (KBr): 3066, 2175, 1602, 1593, 1442, 1358, 834, 759 cm–1.
References
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Synthesis 2008, No. 9, 1367–1372 © Thieme Stuttgart · New York

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