An efficient synthesis of 1-aryl-3-(indole-3-yl)-3-(2-aryl-1,2,3-triazol-4- yl)propan-1-one catalyzed by a bronsted acid ionic liquid

Article abstract of DOI:10.3390/molecules15129197

An efficient synthesis of novel 1-aryl-3-(indole-3-yl)-3-(2-aryl-1,2,3- triazol-4-yl)propan-1-ones from indoles and 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl) propan-1-one using a Bronsted acid ionic liquid [Sbmim][HSO₄] as catalyst is described. Sat

Full text of DOI:10.3390/molecules15129197

Molecules 2010, 15, 9197-9204; doi:10.3390/molecules15129197
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
An Efficient Synthesis of 1-Aryl-3-(indole-3-yl)-3-(2-aryl-1,2,3-
triazol-4-yl)propan-1-one Catalyzed by a Brønsted Acid
Ionic Liquid
Chen-Jiang Liu 1,2,* and Chuan-Ji Yu 2
1
Physics and Chemistry Detecting Center, Xinjiang University, 830046 Urumqi, China
2
Key Laboratory of Oil and Gas Fine Chemicals Ministry of Education, School of Chemistry and
Chemical Engineering, Xinjiang University, 830046 Urumqi, China;
E-Mail: cjxyycj@126.com (C-J.Y.)
* Author to whom correspondence should be addressed; E-Mail: pxylcj@126.com;
Tel.: +86-991-8581211; Fax: +86-991-8582807.
Received: 11 October 2010; in revised form: 3 December 2010 / Accepted: 7 December 2010 /
Published: 10 December 2010
Abstract: An efficient synthesis of novel 1-aryl-3-(indole-3-yl)-3-(2-aryl-1,2,3-triazol-4-
yl)propan-1-ones from indoles and 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one using a
Brønsted acid ionic liquid [Sbmim][HSO4] as catalyst is described. Satisfactory results
with excellent yields and short reaction time were obtained in the experiments. The catalyst
could be recovered conveniently and reused efficiently.
Keywords: Brønsted acidic ionic liquid; Michael reaction; indoles; 1,2,3-triazole
Introduction
In recent years, β-indolylketones have received much attention because they represent an important
substructure in both biologically active compounds and natural products [1]. A simple and direct
approach for their synthesis involves the conjugate addition of indole and α,β-unsaturated ketones in
the presence of either protic or Lewis acids. During the last decade, several improved methods have
been reported for the preparation of these compounds using various catalysts such as FAP [2], I2 [3],
Zn-HAP [4], CAN [5], InBr3 [6], PTSA [7], Bi(NO3)3 [8], HfCl4 and ScCl3 [9], PVSA [10], pyrrolidine
and HClO4 [11], GaI3 [12], Zr(OTf)4 [13], Bi(OTf)3 [14] and so on. However, several of these reported

Molecules 2010, 15
9198
procedures suffer from the drawbacks such as strong acidic conditions, long reaction times, complex
handling and low yields of products. Hence, new efficient and green procedures are still in strong
demand. Recently, ionic liquids (ILs) have been widely used as environmentally benign reaction media
in organic synthesis owing to their unique properties of nonvolatility, nonflammability, and
recyclability [15,16]. In particular, the synthesis of task-specific ILs with special functions according to
the requirements of a specific reaction has become an attractive field [17,18]. Recently, Yang et al. [19]
reported the use of the Brønsted acid ionic liquid [Sbmim][HSO4] as catalyst for the hydrolysis of
soybean isoflavone glycosides. In this process [Sbmim][HSO4] has good catalytic activities which are
similar to those of sulfuric acid, giving a conversion of glycitin of more than 90%.
Due to their unique biological properties, 1,2,3-triazole derivatives have attracted much attention
[20]. In this work, we studied the possibility to synthesize 1-aryl-3-(indol-3-yl)-3-(2-aryl-1,2,3-triazol-
4-yl)propan-1-ones using 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one as substrates instead of
ordinary α,β-unsaturated ketones and employing the Brønsted acid ionic liquid [Sbmim][HSO4] as
catalyst (Scheme 1). Herein, an efficient and practical method for the synthesis of target compounds is
described and none of them has been reported yet in the literature.
Scheme 1. The synthesis of 1-aryl-3-(indol-3-yl)-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-
ones catalyzed by the ionic liquid [Sbmim][HSO4].
R
O
4
N
O
N
N
R
1
N
[Sbmim][HSO ]
4
R
4
N
N
+
2
R
N
R
CH CN or Solvent-Free
3
3
R
R
3
R
2
R
1
N
R
1
2
3
SO H
=
[Sbmim][HSO ]
3
4
N
N
HSO
4
Results and Discussion
Initially, to evaluate the effect of the catalyst [Sbmim][HSO4] under different reaction conditions,
the reaction of indole and 1-phenyl-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one was selected as a
model reaction. The results were presented in Table 1. It was clear that the best solvent was
acetonitrile and the best molar ratio of IL/substrate is 10% (Table 1, entry 3). The influence of the
reaction time on the yield was also investigated as shown in Table 1, entries 3, 8–12. It was found that
a higher yield occurred when the reaction time was 3 h (Table 1, entry 11), although, the yield did not
change significantly when the reaction time was increased from 1 h to 5 h. For the purpose of saving
energy, we chose 1 h as the reaction time. Hence, the best conditions employed a 0.1:1:1 mole ratio of
[Sbmim][HSO4], indole and 1-phenyl-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one at 80 °C for 1 h
using acetonitrile as solvent.
The recycling performance of TSIL [Sbmim][HSO4] was also investigated in the reaction of indole
and 1-phenyl-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one. After the separation of product, the filtrate
containing catalyst was distilled under vacuum to remove water and the resulting catalyst was reused
directly for the next run.

Molecules 2010, 15
9199
Table 1. Effect of the catalyst [Sbmim][HSO4] in the reaction of indole and 1-phenyl-3-(2-
phenyl-1,2,3-triazol-4-yl)propan-1-one under different conditions. a
Entry
Solvent
[Sbmim][HSO4] (mol %)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
Ethyl acetate
Methanol
10
10
10
none
2.5
5
15
10
10
10
10
10
4
4
4
4
4
4
4
0.5
1
70
87
95
0
79
91
94
79
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
9c
10
11
95, 92, 90
2
3
5
98
99
97
12
a
Reaction conditions: indole (2 mmol), 1-phenyl-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (2
mmol) and catalyst in solvent (10 mL), 80 °C; b Isolated yield; c catalyst was recycled three times.
As shown in Table 1, Brønsted acidic ionic liquid [Sbmim][HSO4] can be recycled at least three
times without any significant decrease in catalytic activity, the yields ranged from 95% to 90% (entry
9c). This indicated that the ionic liquid [Sbmim][HSO4] was an efficient and recyclable catalyst for the
reaction. In order to check the generality of the procedure, a variety of substituted indoles were reacted
with 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one. In general, the reaction proceeded easily under
the optimum conditions described above and the adducts were isolated in excellent yields (Table 2).
Table 2. [Sbmim][HSO4]-catalyzed synthesis of 1-aryl-3-(indole-3-yl)-3-(2-aryl-1,2,3-
triazol-4-yl)propan-1-one.
Yields (%)b
Entry R
R1
R2
R3
R4
Mp (°C)a
Ac
93
98
97
95
96
93
97
89
97
95
Bc
89
97
92
96
93
87
95
86
94
97
3a
3b
3c
3d
3e
3f
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
H
H
H
H
H
H
5-Br
H
H
H
H
H
H
H
H
H
H
H
4-Br
H
148–150
157–159
188–191
140–143
143–146
144–147
163–165
165–168
142–144
136–138
4-CH3
4-OCH3
4-Cl
4-Br
2,4-Cl2
H
3g
3h
3i
H
H
H
H
2-Cl
4-OCH3
3j
CH3
H
H
a Melting points were uncorrected; b Isolated yield; c Method A: [Sbmim][HSO4] (0.02 mmol), 1-aryl-3-
(2-aryl-1,2,3-triazol-4-yl)propan-1-one (2 mmol), indoles (2 mmol), acetonitrile (10 mL), 80 °C, 1 h;
Method B: [Sbmim][HSO4] (0.02 mmol), 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one (2 mmol),
indoles (2 mmol), solvent-free, 90 °C, 1 h.

Molecules 2010, 15
9200
The results obtained indicated that the electron donating or withdrawing groups at the indole ring
did not seem to affect the reaction significantly in terms of yields. As environmental consciousness in
chemical research and industry has increased, the challenge for a sustainable environment has called
for clean procedures that can avoid the use of organic solvents. Hence, we also examined the reaction
of indoles and 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one under solvent-free condition, and the
products were obtained in excellent yields (Table 2).
A proposed reaction mechanism for the conjugate addition of indole to 1-phenyl-3-(2-phenyl-1,2,3-
triazol-4-yl)propan-1-one is presented in Scheme 2. The catalyst [Sbmim][HSO4] coordinates with the
oxygen atom of 1-phenyl-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (2) to give intermediate 4. The
electron rich β-position of indole ring then attacks the electron deficient conjugated carbon-carbon
double bond of 4 to afford 5, followed by a hydrogen transfer to yield 6. Finally 6 rearranged to give
target compound 3a and [Sbmim][HSO4] catalyzes the next cycle.
Scheme 2. The proposed mechanism of synthesizing β-indolyketones catalyzed by ionic
liquid [Sbmim][HSO4].
O
N
N
SO H
N
3
N
O
N
N
N
HSO
4
N
2
+
HO
N
N
H
3a
N
N
4
SO
3
N
N
HSO
4
N
OH
N
N
OH
N
N
N
N
N
H
H
SO
N
H
3
1
N
N
H
HSO
4
6
5
Conclusions
In summary, we have reported an efficient and simple method for synthesis of a series of novel 1-
aryl-3-(indol-3-yl)-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one using 1-aryl-3-(2-aryl-1,2,3-triazol-4-
yl)propan-1-one instead of ordinary α,β-unsaturated ketones as substrate and employing Brønsted
acidic ionic liquid [Sbmim][HSO4] as catalyst. The corresponding adducts were synthesized in short
reaction times successfully and isolated in excellent yields. It is an important supplement to the
existing methods for the synthesis of β-indolylketones.
Experimental
General
1
All compounds were characterized by IR, H-NMR spectra and elemental analysis. The IR spectra
1
were obtained as potassium bromide pellets with a FTS-40 spectrometer (BIO-RAD, U.S.A). The H-

Molecules 2010, 15
9201
NMR spectra were obtained on a Varian Inova-400 spectrometer using CDCl3 or DMSO-d6 as solvent
(as indicated under each entry below) and TMS as an internal standard, chemical shifts are given in
ppm. Elemental analyses (C, H, N) were performed on a Perkin-Elmer Analyzer 2400. Melting points
were determined using a Büchi B-540 instrument. All melting points are uncorrected. The Brønsted
acid ionic liquid [Sbmim][HSO4] was synthesized according to a previous literature method [19]. 1-
aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one (2) was synthesized according to a previous literature
report [21].
General procedure for the synthesis of 1-aryl-3-(indol-3-yl)-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-ones
3a-3j
A mixture of indole (2 mmol), 1-aryl-3-(2-aryl-1,2,3-triazol-4-yl)propan-1-one (2 mmol) and
[sbmim][HSO4] (0.2 mmol) was heated at 80 °C in acetonitrile (10 mL) or 90 °C under solvent-free
conditions for 1 h with stirring (Scheme 1). The completion of the reaction was monitored by TLC.
After cooling, the reaction mixture was poured onto crushed ice (30 g). The resulting precipitate was
filtered under suction, and then recrystallized from ethanol to afford the pure product. The results are
summarized in Table 2. Data of the compounds are shown below:
1-Phenyl-3-(indol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3a): Red powder. 1H-NMR
(DMSO-d6) δ: 3.87 (dd, J = 6.0, 6.0 Hz, 1H, CH), 4.18 (dd, J = 8.4, 8.4 Hz, 1H, CH), 5.15 (t, 1H,
J = 7.2 Hz, CH), 6.96–8.06 (m, 16H, ArH), 10.97 (s, 1H, NH); IR: ν 3342, 1680, 1594, 1457, 1357,
748 cm–1; Anal. Calcd. for C25H20N4O: C, 76.51; H, 5.14; N, 14.28. Found: C, 76.36; H, 5.18; N, 14.22.
1-(4-Methylphenyl)-3-(indol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3b): Light yellow
1
powder. H-NMR (DMSO-d6) δ: 2.37 (s, 3H, CH3), 3.82 (dd, J = 6.0, 6.4 Hz, 1H, CH), 4.12 (dd,
J = 8.4, 8.4 Hz, 1H, CH), 5.13 (t, 1H, J = 7.2 Hz, CH), 6.96–8.01 (m, 15H, ArH), 10.96 (s, 1H, NH);
IR: ν 3359, 1674, 1595, 1456, 1337, 736 cm–1; Anal. Calcd. for C26H22N4O: C, 76.83; H, 5.46; N,
13.78. Found: C, 76.71; H, 5.51; N, 13.72.
1-(4-Methoxylphenyl)-3-(indol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3c): Light yellow
1
powder. H-NMR (DMSO-d6) δ: 3.78 (dd, J = 6.4, 6.4 Hz, 1H, CH), 3.84 (s, 3H, OCH3) 4.08 (dd,
J = 8.4, 8.8 Hz, 1H, CH), 5.12 (t, 1H, J = 7.2 Hz, CH), 6.95–8.04 (m, 15H, ArH), 10.95 (s, 1H, NH);
IR: ν 3348, 2901, 1668, 1595, 1457, 1338, 735 cm–1; Anal. Calcd. for C26H22N4O2: C, 73.92; H, 5.25;
N, 13.26. Found: C, 73.81 ; H, 5.32; N, 13.39.
1-(4-Chlorophenyl)-3-(indol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3d): Light yellow
1
powder. H-NMR (DMSO-d6) δ: 3.85 (dd, J = 6.0, 6.0 Hz, 1H, CH), 4.17 (dd, J = 8.8, 8.8 Hz, 1H,
CH), 5.12 (t, 1H, J = 7.2 Hz, CH), 6.96–8.17 (m, 15H, ArH), 10.97 (s, 1H, NH); IR: ν 3395, 1678,
1586, 1490, 1338, 737 cm–1; Anal. Calcd. for C25H19N4OCl: C, 70.34; H, 4.49; N, 13.12. Found: C,
70.48 ; H, 4.55; N, 13.01.
1
1-(4-Bromophenyl)-3-(indol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3e): Red powder. H-
NMR (DMSO-d6) δ: 3.84 (dd, J = 6.0, 6.0 Hz, 1H, CH), 4.16 (dd, J = 8.4, 8.4 Hz, 1H, CH), 5.12 (t,

Molecules 2010, 15
9202
1H, J = 7.2 Hz, CH), 6.96–8.10 (m, 15H, ArH), 10.96 (s, 1H, NH); IR: ν 3389, 1677, 1583, 1491,
1338, 737 cm–1; Anal. Calcd. for C25H19N4OBr: C, 63.70; H, 4.06; N, 11.89. Found: C, 63.81; H, 4.11;
N, 11.75.
1-(2,4-Dichlorophenyl)-3-(5-bromoindol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3f): Light
yellow powder. 1H-NMR (DMSO-d6) δ: 3.77 (dd, J = 6.0, 6.4 Hz, 1H, CH), 4.04 (dd, J = 8.4, 8.8 Hz,
1H, CH), 5.03 (t, 1H, J = 7.6 Hz, CH), 7.16–8.06 ( m, 13H, ArH), 11.20 (s, 1H, NH); IR: ν 3323, 1689,
1581, 1461, 1340, 817, 753 cm–1; Anal. Calcd. for C25H17N4OCl2Br: C, 55.58; H, 3.17; N, 10.37.
Found: C, 55.68; H, 3.10; N, 10.25.
1
1-Phenyl-3-(2-methylindol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3g): Red powder. H-
NMR (400 MHz, DMSO-d6) δ: 2.44 (s, 3H, CH3), 3.81 (dd, J = 6.8, 6.8 Hz, 1H, CH), 4.25 (dd, J = 7.2,
7.6 Hz, 1H, CH), 5.09 (t, 1H, J = 7.6 Hz, CH), 6.85–8.01 (m, 15H, ArH), 10.84 (s, 1H, NH); IR (KBr):
ν 3368, 2971, 1679, 1595, 1460, 1336, 752 cm–1; Anal. Calcd. for C26H22N4O: C, 76.83; H, 5.46; N,
13.78. Found: C, 76.91; H, 5.41; N, 13.89.
1-Phenyl-3-(2-methylindol-3-yl)-3-(2-(4-bromophenyl)-1,2,3-triazol-4-yl)propan-1-one (3h): Red
1
powder. H-NMR (DMSO-d6) δ: 2.45 (s, 3H, CH3), 3.82 (dd, J = 6.8, 7.2 Hz, 1H, CH), 4.23 (dd,
J = 7.2, 7.6 Hz, 1H, CH), 5.07 (t, 1H, J = 7.2 Hz, CH), 6.84–7.99 (m, 14H, ArH), 10.84 (s, 1H, NH);
IR: ν 3378, 2898, 1675, 1593, 1489, 739 cm–1; Anal. Calcd. for C26H21N4OBr: C, 64.34; H, 4.36; N,
11.54. Found: C, 64.45; H, 4.30; N, 11.72.
1-(2-Chlorophenyl)-3-(2-methylindol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3i): Red
1
powder. H-NMR (DMSO-d6) δ: 2.39 (s, 3H, CH3), 3.70 (dd, J = 6.8, 6.8 Hz, 1H, CH), 4.18 (dd,
J = 8.0, 8.4 Hz, 1H, CH), 5.02 (t, 1H, J = 7.6 Hz, CH), 6.83–7.94 (m, 14H, ArH), 10.88 (s, 1H, NH);
IR: ν 3380, 1692, 1588, 1460, 1354, 746 cm–1; Anal. Calcd. for C26H21N4OCl: C, 70.82; H, 4.80; N,
12.71. Found: C, 70.65; H, 4.83; N, 12.87.
1-(4-Methoxylphenyl)-3-(1-methylindol-3-yl)-3-(2-phenyl-1,2,3-triazol-4-yl)propan-1-one (3j): Light
yellow powder. 1H NMR (DMSO-d6) δ: 3.72 (s, 3H, CH3) 3.76 (dd, J = 6.0, 6.0 Hz, 1H, CH), 3.84 (s,
3H, OCH3), 4.09 (dd, J = 8.4, 8.8 Hz, 1H, CH), 5.11 (t, 1H, J = 7.2 Hz, CH), 6.99–8.03 (m, 15H,
ArH); IR: ν 3348, 2909, 1682, 1596, 1464, 731 cm–1; Anal. Calcd. for C27H24N4O2: C, 74.19; H, 5.54;
N, 12.84. Found: C, 74.35; H, 5.59; N, 12.99.
Acknowledgements
We gratefully acknowledge support from the National Natural Science Foundation of China (No.
20862016, 20662009).
References
1. Zhan, Z.P.; Yang, R.F.; Lang, K. Samarium triiodide-catalyzed conjugate addition of indoles with
electron-deficient olefins. Tetrahedron Lett. 2005, 46, 3859-3862.

Molecules 2010, 15
9203
2. Tahir, R.; Banert, K.; Sebti, S. Friedel–Crafts-type conjugate addition of indoles using fluorapatite
doped zinc bromide as efficient solid catalyst. Appl. Catal. A Gen. 2006, 315, 147-149.
3. Banik, B.K.; Fernandez, M.; Alvarez, C. Iodine-catalyzed highly efficient Michael reaction of
indoles under solvent-free condition. Tetrahedron Lett. 2005, 46, 2479-2482.
4. Tahir, R.; Banert, K.; Solhy, A.; Sebti, S. Zinc bromide supported on hydroxyapatite as a new and
efficient solid catalyst for Michael addition of indoles to electron-deficient olefins. J. Mol. Catal.
A Chem. 2006, 246, 39-42.
5. Ko, S.K.; Lin, C.C.; Tu, Z.J.; Wang, Y.F.; Wang, C.C.; Yao, C.F. CAN and iodine-catalyzed
reaction of indole or 1-methylindole with α,β-unsaturated ketone or aldehyde. Tetrahedron Lett.
2006, 47, 487-492.
6. Bandini, M.; Cozzi, P.G.; Giacomini, M.; Melchiorre, P.; Selva, S. Sequential one-pot InBr3-
catalyzed 1,4- then 1,2-nucleophilic addition to enones. J. Org. Chem. 2002, 67, 3700-3704.
7. Ji, S.J.; Wang, S.Y. An expeditious synthesis of β-indolylketones catalyzed by p-toluenesulfonic
acid (PTSA) using ultrasonic irradiation. Ultrason. Sonochem. 2005, 12, 339-343.
8. Srivastava, N.; Banik, B.K. Bismuth nitrate-catalyzed versatile Michael reactions. J. Org. Chem.
2003, 68, 2109-2114.
9. Kawatsura, M.; Aburatani, S.; Uenish, J. Catalytic conjugate addition of heterocyclic compounds
to α,β-unsaturated carbonyl compounds by hafnium salts and scandium salts. Tetrahedron 2007,
63, 4172-4177.
10. Ekbote, S.S.; Panda, A.G.; Bhor, M.D.; Bhanage, B.M. Polyvinylsulfonic acid as a novel
Brønsted acid catalyst for Michael addition of indoles to α,β-unsaturated ketones. Catal.
Commun. 2009, 10, 1569-1573.
11. Li, D.P.; Guo, Y.C.; Ding, Y.; Xiao, W.J. Organocatalytic C3-selective Friedel–Crafts alkylations
of indoles with α,β-unsaturated ketones. Chem. Commun. 2006, 799-801.
12. Huang, Z.H.; Zou, J.P.; Jiang, W.Q. Gallium(III) triiodide catalyzed conjugate addition of indoles
with α,β-unsaturated ketones. Tetrahedron Lett. 2006, 47, 7965-7968.
13. Shi, M.; Cui, S.C.; Li, Q.J. Zirconium triflate-catalyzed reactions of indole, 1-methylindole, and
pyrrole with α,β-unsaturated ketone. Tetrahedron 2004, 60, 6679–6684.
14. Reddy, A.V.; Ravinder, K.; Goud, T.V.; Krishnaiah, P.; Raju, T.V.; Venkateswarlu, Y. Bismuth
triflate catalyzed conjugate addition of indoles to α,β-enones. Tetrahedron Lett. 2003, 44,
6257-6260.
15. Welton, T. Room-Temperature Ionic Liquids. Solvents for synthesis and catalysis. Chem. Rev.
1999, 99, 2071-2083.
16. Pârvulescu ,V.I.; Hardacre, C. Catalysis in ionic liquids. Chem. Rev. 2007, 107, 2615-2665.
17. Ranu, B.C.; Banerjee, S. Ionic liquid as catalyst and reaction medium. The dramatic influence of a
task-specific ionic liquid, [bmIm]OH, in Michael addition of active methylene compounds to
conjugated ketones, carboxylic esters, and nitriles. Org. Lett. 2005, 7, 3049-3052.
18. Qiao, K.; Hagiwara, H.; Yokoyama, C. Acidic ionic liquid modified silica gel as novel solid
catalysts for esterification and nitration reactions. J. Mol. Catal. A Chem. 2006, 246, 65-69.
19. Yang, Q.W.; Wei, Z.J.; Xing, H.B.; Ren, Q.L. Brønsted acidic ionic liquids as novel catalysts for
the hydrolyzation of soybean isoflavone glycosides. Catal. Commun. 2008, 9, 1307-1311.

Molecules 2010, 15
9204
20. Hao, L.; Hui, X.P.; Zhang, Z.Y.; Guan, Z.W.; He, Y.L.; Yu, H.J. Studies on semisynthesis and
antibacterial activity of 3-heterocyclicthiomethyl cephalosporins. Chem. J. Chin. Univ. 1999, 20,
1564-1569.
21. Li, F.; Xie, Z.F.; Liu, F.M. Syntheses and fluorescent property of 5-(2-Phenyl-1,2,3-triazoly)-3-
aryl pyrazoline derivatives. Chem. J. Chin. Univ. 2006, 6, 1058-1061.
Sample Availability: Available from the authors
© 2010 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).