A convenient method for the preparation of 2,4,5-triaryl imidazoles using barium chloride dispersed on silica gel nanoparticles (BaCl2-nano SiO2) as heterogeneous reusable catalyst

Article abstract of DOI:10.2174/157017812801264683

A simple and eco-friendly procedure for the synthesis of 2,4,5-triaryl imidazoles by using Barium chloride dispersed on silica gel nanoparticles (BaCl₂-nano SiO₂) as heterogeneous reusable catalyst in high yield under thermal conditions has been described.

Full text of DOI:10.2174/157017812801264683

Letters in Organic Chemistry, 2012, 9, 351-355
351
A Convenient Method for the Preparation of 2,4,5-triaryl Imidazoles Using
Barium Chloride Dispersed on Silica Gel Nanoparticles (BaCl2-nano SiO2)
as Heterogeneous Reusable Catalyst
Mohammad R.M. Shafiee1, Abbas Fazlinia2, Najme Yaghooti3 and Majid Ghashang*,1
1Department of Chemistry, Faculty of Sciences, Najafabad Branch, Islamic Azad University, Najafabad, Esfahan, P.O.
Box 517, Iran
2Department of Chemistry, Neyriz Branch, Islamic Azad University, Neyriz, Iran
3Department of Chemistry, Kerman Branch, Islamic Azad University, Kerman, Iran
Received November 27, 2011: Revised March 12, 2012: Accepted March 12, 2012
Abstract: A simple and eco-friendly procedure for the synthesis of 2,4,5-triaryl imidazoles by using Barium chloride
dispersed on silica gel nanoparticles (BaCl2-nano SiO2) as heterogeneous reusable catalyst in high yield under thermal
conditions has been described.
Keywords: 2,4,5-triaryl imidazole, BaCl2-nano SiO2, heterogeneous catalyst.
INTRODUCTION
The use of heterogeneous solid supported Lewis acid
catalysts instead of their unsupported salts have some
advantages and they are desirable to achieve effective
catalyst handling, product purification and a decrease in
waste production. Some examples of them have been
performed as inexpensive catalysts that can be easily
separated, reused and are not contaminated by the products
[33].
Compounds containing imidazole skeletons exhibit
important biological activities and play important roles in
biochemical processes [1-3]. Also, large classes of imidazole
derivatives are used as ionic liquids [4, 5]. Thus, these
properties have instituted a diverse collection of synthetic
approaches to these heterocycles. A number of routes have
been developed for the synthesis of substituted imidazoles.
In this content, 2,4,5-tri substituted imidazoles are generally
synthesized by multi-component cyclo-condensation of 1,2-
diketones, α -hydroxyketones or α -ketomonoximes with
aldehydes and ammonium acetate which imparted from the
assistance of sterically hindered organic bases such as
DABCO [6], microwave irradiation [7-11], ionic liquids [12,
13] and Brønsted and Lewis acids in the case of liquid [14,
15], solid [16-21] or supported on solid materials such as
silica and alumina [22-26]. Some of these procedures have
certain limitations such as tedious process, long reaction
times and harsh reaction conditions. Moreover, different and
effective literatures for the preparation of highly substituted
imidazoles are present, including hetero-cope rearrangement
[27], four-component condensation of aryl glyoxals, primary
amines, carboxylic acids and isocyanides on Wang resin
[28], reaction of N-(2-oxo)-amides with ammonium
trifluoroacetate [29], reaction of N-alkyl-N-(β-keto)amides
with ammonium acetate [30], cyclo-addition reaction of
mesoionic 1,3-oxazolium-5-olates with N-(arylmethylene)-
benzenesulfonamides [31] and addition of a substituted
amino alcohol to a thioamide and subsequent oxidation with
PDC [32]. Although these reports prepare a wide range of
imidazoles but their procedures are relatively expensive for
use in the laboratory and industry.
Herein BaCl2-nano SiO2 [34, 35] was employed as a
useful catalyst for the synthesis and easy purification of
2,4,5-triaryl imidazole derivatives via one-pot three-
component cyclo-condensation of benzil, ammonium acetate
and aldehydes under thermal conditions in high yields
(Scheme 1).
EXPERIMENTAL
All reagents were purchased from Merck and Aldrich and
used without further purification. All yields refer to isolated
products after purification. Products were characterized by
spectroscopic data (IR, NMR spectra) and melting points
with authentic samples. The NMR spectra were recorded on
a Bruker Avance DEX 400 MHz instrument. The spectra
were measured in DMSO-d6 relative to TMS (0.00 ppm). IR
spectra were recorded on a JASCO FT-IR 460plus
spectrophotometer. All of the compounds were solid and
solid state IR spectra were recorded using the KBr disk
technique. Elemental analysis was performed on a Heraeus
CHN-O-Rapid analyzer. Melting points were determined in
open capillaries with a BUCHI 510 melting point apparatus.
TLC was performed on silica gel polygram SIL G/UV 254
plates.
*Address correspondence to this author at the Department of Chemistry,
Faculty of Sciences, Najafabad Branch, Islamic Azad University, Najafabad,
Esfahan, P.O. Box 517, Iran; Tel: +98-3312291004; Fax: +98-3312291016;
E-mail: ghashangmajid@gmail.com
General Procedure
To a mixture of aldehyde (1 mmol), benzil (1 mmol) and
NH4OAc (3 mmol), BaCl2-nano SiO2 (0.025 g) was added
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

352 Letters in Organic Chemistry, 2012, Vol. 9, No. 5
Shafiee et al.
O
Ar'
H
N
BaCl2-nano SiO2 (Cat)
Ph
Ph
NH OAc
+
Ar'-CHO
+
4
Ph
N
Solvent-free
130 oC
O
Ph
Scheme 1.
and the mixture stirred at room temperature. The progress of
the reaction was monitored by TLC. After completion of the
reaction, the mixture was dissolved in hot ethanol and
filtered. Solvent was evaporated and the corresponding pure
product was obtained after recrystallization in ethanol. The
results are summarized in Table 3.
essential for the product formation. To explore this library,
initially, the reaction of benzil, benzaldehyde and
ammonium acetate was used as a model reaction (Scheme 2),
and a variety of Lewis acid catalysts including magnesium
chloride, Magnesium oxide, magnesium chloride dispersed
on silica (SiO2-MgCl2), calcium chloride dispersed on silica
(SiO2-CaCl2), CaCl2, barium chloride dispersed on silica
(SiO2-BaCl2) and barium chloride dispersed on nano silica
(BaCl2-nano SiO2) were screened under solvent-free
conditions and 100 °C for the synthesis of 2,4,5-triaryl
imidazoles. The results are summarized in Table 1. Under
the same reaction conditions, BaCl2-nano SiO2 exhibited
much better activity than others (Table 1). Therefore, BaCl2-
nano SiO2 was selected as the active component for the
preparation of 2,4,5-triphenyl-1H-imidazole.
Selected Data
2-(4-tert-butylphenyl)-4,5-diphenyl-1H-imidazole
1
m.p: 290-292 °C; H NMR (400 MHz, DMSO-d6): 1.34
(s, 9H), 7.23 (t, J = 7.2 Hz, 1H), 7.32 (t, J = 7.6 Hz, 2H),
7.38 (t, J = 7.2 Hz, 1H), 7.45 (t, J = 7.2 Hz, 2H), 7.51 (m,
4H), 7.57 (d, J = 7.6 Hz, 2H), 8.03 (d, J = 8.4 Hz, 2H), 12.63
(s, 1H, NH); 13C NMR (100 MHz, DMSO-d6): δ = 31.5,
34.9, 125.5, 125.9, 126.9, 127.6, 128.2, 128.3, 128.4, 128.6,
128.9, 129.1, 131.6, 131.7, 135.7, 137.4, 146.0, 146.1, 151.3
ppm; IR (KBr): 3417, 3058, 2963, 2903, 1603, 1586, 1504,
1492, 1450, 1434, 1407, 1392, 1362, 1321, 1268, 1201,
1181, 1156, 1134, 1105, 1071, 1025, 967, 946, 839, 774,
765, 720, 696 cm-1; Found: C, 85.25; H, 6.93; N, 7.99
C25H24N2; requires: C, 85.19; H, 6.86; N, 7.95%].
In order to estimate the catalytic efficiency of BaCl2-nano
SiO2 and to determine the most appropriate reaction
conditions, at first a model study was carried out in the
synthesis of 2,4,5-triphenyl-1H-imidazole using the reaction
of benzil, benzaldehyde and ammonium acetate in different
systems of reaction conditions (Table 2).
Among the various tested amounts of the catalyst and
temperature, the condensation of benzil, benzaldehyde and
ammonium acetate was best catalyzed by 0.025 g of catalyst
(Table 2). In order to improve the yields, we performed
reaction using different quantities of reagents. The best
results were obtained with 1:1:3 molar ratios of benzil, aryl
aldehyde and ammonium acetate, respectively. The results
are summarized in Table 2.
2-(3-bromophenyl)-4,5-diphenyl-1H-imidazole
1
m.p: 308-310 °C; H NMR (400 MHz, DMSO-d6): 7.25
(t, J = 6.8 Hz, 1H), 7.32 (t, J = 6.8 Hz, 2H), 7.40 (t, J = 6.8
Hz, 1H), 7.44-7.59 (m, 8H), 8.10 (d, J = 7.6 Hz, 1H), 8.32 (s,
1H), 12.84 (s, 1H, NH); 13C NMR (100 MHz, DMSO-d6): δ
= 122.6, 124.5, 127.2, 127.6, 128.0, 128.4, 128.7, 128.9,
129.2, 131.3, 131.4, 132.9, 135.4, 137.9, 144.2, 144.3 ppm;
IR (KBr): 3423, 3063, 2963, 2923, 2852, 1602, 1583, 1502,
1478, 1456, 1412, 1379, 1321, 1204, 1132, 1071, 1026, 996,
969, 915, 890, 841, 766, 759, 723, 698 cm-1; Found: C,
67.27; H, 4.11; N, 7.55 C21H15BrN2; requires: C, 67.21; H,
4.03; N, 7.47%].
Using these optimized reaction conditions, the scope and
efficiency of these procedures were explored for the
synthesis of corresponding 2,4,5-triaryl imidazole
derivatives.
Generally, the cyclo-condensation reaction between
benzil, arylaldehydes and ammonium acetate proceeded well
and afforded the desired products (Table 3, Entries 1-23) in
good to excellent yields. As shown in Table 3, the reaction
was successfully compatible with a variety of aryl aldehydes
RESULTS AND DISCUSSIONS
The processes for the preparation of 2,4,5-triaryl
imidazoles are usually carried out in the presence of Lewis
and Brønsted acidic catalysts [7-26] and thermal condition. It
was observed that in a control reaction where no catalyst was
used, no product was formed and the conversion of benzil
was found to be 0% after 5 h. This shows that the catalyst is
having
electron-donating
and
electron-withdrawing
substituents.
In all the cases, aromatic aldehydes containing electron-
withdrawing groups (such as nitro-) gave shorter time than
N
O
Catalyst
+ PhCHO + NH4OAc
N
Solvent-free
H
100 oC
O
Scheme 2. preparation of 2,4,5-triphenyl-1H-imidazole using BaCl2-nano SiO2 as catalyst.

A Convenient Method for the Preparation of 2,4,5-triaryl Imidazoles
Letters in Organic Chemistry, 2012, Vol. 9, No. 5
353
Table 1. Catalyst Screening
Entry
Catalyst
Time (min)
Yield (%)a
1
2
3
4
5
6
-
300
140
300
150
210
170
210
110
120
100
-
MgCl2 (0.02 mmol)
35
25
35
25
15
20
40
42
47
MgO (0.02 mmol)
SiO2-MgCl2 (0.02 g = 0.02 mmol MgCl2)
ZnO (0.02 mmol)
CaCl2 (0.02 mmol)
SiO2-CaCl2 (0.025 g = 0.02 mmol CaCl2)
BaCl2 (0.02 mmol)
7
8
9
SiO2-BaCl2 (0.05 g = 0.02 mmol BaCl2)
BaCl2-nano SiO2 (0.05 g = 0.02 mmol BaCl2)
aIsolated yield; Reaction condition: benzaldehyde (1 mmol), benzyl (1 mmol), and ammonium acetate (3 mmol); solvent-free, 100 °C.
Table 2. Optimization of the Reaction Conditions in the Synthesis of 2,4,5-triphenyl-1H-imidazole Under Solvent-Free Condition
Entry
Catalyst
T (°C)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
0.05
0.05
0.05
0.05
0.1
r.t.
80
300
250
100
12
-
30
47
83
82
86
89
86
75
100
130
130
130
130
130
130
10
0.075
0.025
0.01
0.005
12
15
30
70
aIsolated Yield.
Table 3. Synthesis of 2,4,5-triaryl Imidazoles Using BaCl2-nano SiO2 as Catalyst
Entry
Aldehyde
Amine source
Time (min)
Yield (%)a
1
2
Benzaldehyde
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
15
120
160
120
70
89
80
67
62
68
83
79
70
78
70
86
80
71
79
81
3-Hydroxybenzaldehyde
4-Hydroxybenzaldehyde
4-Methoxybenzaldehyde
4-Methylbenzaldehyde
4-tert-Butylbenzaldehyde
2-Methylbenzaldehyde
2,4-Dimethylbenzaldehyde
2-Methoxybenzaldehyde
2,3-Dimethoxybenzaldehyde
3,4-Dimethoxybenzaldehyde
4-Fluorobenzaldehyde
4-Bromobenzaldehyde
3-Bromobenzaldehyde
2-Bromobenzaldehyde
3
4
5
6
25
7
85
8
100
200
200
120
15
9
10
11
12
13
14
15
10
10
30

354 Letters in Organic Chemistry, 2012, Vol. 9, No. 5
Shafiee et al.
(Table 3). Contd…..
Entry
Aldehyde
Amine source
Time (min)
Yield (%)a
16
17
18
19
20
21
22
23
2-Chlorobenzaldehyde
4-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
2-Nitrobenzaldehyde
3-Nitrobenzaldehyde
Furfural
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
NH4OAc
60
10
89
64
85
80
75
59
80
53
100
30
10
120
220
200
Cyclohexanecarbaldehyde
Butyraldehyde
aIsolated yields. All known products have been reported previously in the literature and were characterized by comparison of IR and NMR spectra with authentic samples [6-26].
that with electron-donating groups (such as methoxy-).
Though meta- and para- substituted aromatic aldehydes gave
good results, ortho-substituted aromatic aldehydes (such as
2-nitrobenzadehyde) gave lower yields and longer reaction
time because of the steric effects. As a result, the reaction of
aliphatic was successfully done to have the product in
moderate yield (Table 3; Entries 22-23).
use of BaCl2-nano SiO2. This catalyst is one of the useful
examples of heterogeneous catalysts which has been
performed as an inexpensive catalyst that can be easily
separated, reused and is not contaminated by the products
and can be prepared from cheap materials. The present
methodology offers several advantages such as excellent
yields, simple procedure and shorter reaction times.
The work-up procedure is very clear-cut, that is, the
products were isolated and purified by simple filtration and
crystallization from ethanol. Our protocol avoids the use of
dry media during the reaction process, making it superior to
the previous methods.
CONFLICT OF INTEREST
Declared none.
The reusability of the catalyst was tested in the synthesis
of 2,4,5-triphenyl-1H-imidazole, as shown in Fig. (1). The
catalyst was recovered after each run, washed 3 times with
CH2Cl2, dried prior to use and tested for its activity in the
subsequent run and fresh catalyst was not added. The
catalyst was tested for 5 runs. It was seen that the catalyst
displayed very good reusability.
ACKNOWLEDGEMENT
The authors are indebted to the Islamic Azad University
– Najafabad Branch for financial support of this research.
REFERENCES
[1]
[2]
[3]
Lambardino,
J.G.;
Wiseman,
E.H.
Preparation
and
antiinflammatory activity of some non-acidic trisubstituted
imidazoles. J. Med. Chem., 1974, 17, 1182-1188.
Maier, T.; Schmierer, R.; Bauer, K.; Bieringer, H.; Buerstell, H.;
Sachse, B. US Patent 1989, 820335; Chem. Abstr., 1989, 111,
19494.
Zhang, C.; Sarshar, S.; Morgan, E.J.; Krane, S.; Rodarte, J.C.;
Benbatoul, K.D.; Dixon, R.; Mjalli, A.M.M. 2,4,5-Trisubstituted
imidazoles: novel nontoxic modulators of P-glycoprotein mediated
multidrug resistance. Part 2. Bioorg. Med. Chem., 2000, 10, 2603-
2605.
90
89
88
87
86
85
84
83
82
81
80
[4]
[5]
[6]
Welton, T. Room-Temperature Ionic Liquids. Solvents for
Synthesis and Catalysis. Chem. Rev., 1999, 99, 2071-2084.
Hermann, W.A.; Kocher, C. N-Heterocyclic Carbenes. Angew.
Chem. Int. Ed., 1997, 36, 2162-2187.
Murthy, S.N.; Madhav, B.; Nageswar, Y.V.D. DABCO as a mild
and efficient catalytic system for the synthesis of highly substituted
1
2
3
4
5
6
imidazoles
via multi-component
condensation
strategy.
Run No.
Tetrahedron Lett., 2010, 51, 5252-5257.
[7]
[8]
Usyatinsky, A.Y.; Khemelnitsky, Y.L. Microwave-assisted
synthesis of substituted imidazoles on a solid support under
solvent-free conditions. Tetrahedron Lett., 2000, 41, 5031-5034.
Wolkenberg, S.E.; Wisnoski, D.D.; Leister, W.H.; Wang, Y.; Zhao,
Z.; Lindsley, C.W. Efficient Synthesis of Imidazoles from
Aldehydes and 1,2-Diketones Using Microwave Irradiation. Org.
Lett., 2004, 6, 1453-1456.
Fig. (1). Reusability of BaCl2-nano SiO2.
CONCLUSION
In conclusion, a reliable, rapid, and environmentally
benign method for synthesizing 2,4,5-triaryl imidazoles has
been developed. Compared to previous reported
methodologies, the present protocol features simple
operations, shorter reaction time, environmental friendliness
and good yields. Another advantage of this protocol is the
[9]
Sparks, R.B.; Combs, A.P. Microwave-Assisted Synthesis of 2,4,5-
Triaryl-imidazole;
A
Novel
Thermally
Induced
N-
Hydroxyimidazole N−O Bond Cleavage. Org. Lett., 2004, 6, 2473-
2475.
Oskooie, H.A.; Alimohammadi, Z.; Heravi, M.M. Microwave-
assisted solid-phase synthesis of 2,4,5-triaryl imidazoles in
[10]

A Convenient Method for the Preparation of 2,4,5-triaryl Imidazoles
Letters in Organic Chemistry, 2012, Vol. 9, No. 5
355
solventless system: An improved protocol. Heteroatom Chem.,
2006, 17, 699-702.
[23]
[24]
Shaabani, A.; Rahmati, A. Silica sulfuric acid as an efficient and
recoverable catalyst for the synthesis of trisubstituted imidazoles. J.
Mol. Catal. A: Chem., 2006, 249, 246-248.
Mukhopadhyay, C.; Tapaswi, P.K.; Drew, M.G.B. Room
temperature synthesis of tri-, tetrasubstituted imidazoles and bis-
analogues by mercaptopropylsilica (MPS) in aqueous methanol:
application to the synthesis of the drug trifenagrel. Tetrahedron
Lett., 2010, 51, 3944-3950.
[11]
[12]
Sparks, R.B.; Combs, A.P. Microwave-Assisted Synthesis of 2,4,5-
Triaryl-imidazole; Novel Thermally Induced N-
A
Hydroxyimidazole N−O Bond Cleavage. Org. Lett., 2004, 6, 2473-
2475.
Siddiqui, S.A.; Narkhede, U.C.; Palimkar, S.S.; Daniel, T.; Lahoti,
R.J.; Srinivasan, K.V. Room temperature ionic liquid promoted
improved and rapid synthesis of 2,4,5-triaryl imidazoles from aryl
aldehydes and 1,2-diketones or α -hydroxyketone. Tetrahedron,
2005, 61, 3539-3546.
Zang, H.; Su, Q.; Mo, Y.; Cheng, B.-W.; Jun, S. Ionic liquid
[EMIM]OAc under ultrasonic irradiation towards the first synthesis
of trisubstituted imidazoles. Ultrason. Sonochem., 2010, 17, 749-
751.
[25]
[26]
Niknam, K.; Deris, A.; Naeimi, F.; Majlecif, F. Synthesis of
1,2,4,5-tetrasubstituted
imidazoles
using
silica-bonded
propylpiperazine N-sulfamic acid as
a
recyclable solid acid
[13]
[14]
catalyst. Tetrahedron Lett., 2011, 52, 4642-4645.
Shaabani, A.; Rahmati, A.; Farhangi, E.; Badri, Z. Silica sulfuric
acid promoted the one-pot synthesis of trisubstituted imidazoles
under conventional heating conditions or using microwave
irradiation. Catal. Commun., 2007, 8, 1149-1152.
Wang, J.; Mason, R.; Derveer, D.V.; Feng, K.; Bu, X.R.
Convenient Preparation of
a
Novel Class of Imidazo[1,5-
[27]
[28]
Lantos, I.; Zhang, W.Y.; Shui, X.; Eggleston, D.S. Synthesis of
imidazoles via hetero-Cope rearrangements. J. Org. Chem., 1993,
58, 7092-7095.
Zhang, C.; Moran, E.J.; Woiwode, T.F.; Short, K.M.; Mjalli,
A.M.M. Synthesis of tetrasubstituted imidazoles via α-(N-acyl-N-
alkylamino)-β-ketoamides on Wang resin. Tetrahedron Lett., 1996,
37, 751-754.
Claiborne, C.F.; Liverton, N.J.; Nguyen, K.T. An efficient
synthesis of tetrasubstituted imidazoles from N-(2-Oxo)-amides.
Tetrahedron Lett. 1998, 39, 8939-8942.
Lee, H.B.; Balasubramanian, S. Solid-Phase Synthesis of N-Alkyl-
N-(β-keto)amides and 1,2,4,5-Tetrasubstituted Imidazoles Using a
Traceless Cleavage Strategy. Org. Lett., 2000, 2, 323-326.
Consonni, R.; Croce, P.D.; Ferraccioli, R.; Rosa, C.L. A new
approach to imidazole derivatives. J. Chem. Res. (S), 1991, 188-
189.
Paone, D.V.; Shaw, A.W. Synthesis of tri- and tetrasubstituted
imidazoles. Tetrahedron Lett., 2008, 49, 6155-6159.
Ertl, G.; Knözinger, H.; Weitkamp, J. Preparation of solid
catalysts, Wiley-VCH: Weinheim, 1999.
Mohammad Shafiee, M.R. Silica Supported Barium Chloride
(SiO2-BaCl2): Efficient and Heterogeneous Catalyst for the
Environmentally Friendly Preparation of N,N'-alkylidene bisamides
under Solvent-free Condition. Can. J. Chem., 2011, 89, 555-561.
Mohammad Shafiee, M.R.; Moloudi, R. Barium chloride dispersed
on silica gel nanoparticles: an efficient catalyst for the preparation
of 2,4,6-triarylpyridines under solvent-free conditions. J. Chem.
Res., 2011, 294-297.
a]pyridines:ꢀ Decisive Role by Ammonium Acetate in
Chemoselectivity. J. Org. Chem., 2003, 68, 5415-5418.
Sarshar, S.; Siev, D.; Mjalli, M.M. Imidazole libraries on solid
support. Tetrahedron Lett., 1996, 37, 835-838.
Kidwai, M.; Mothsra, P.; Bansal, V.; Somvanshi, R.K.;
Ethayathulla, A.S.; Dey, S.; Singh, T.P. One-pot synthesis of
highly substituted imidazoles using molecular iodine: A versatile
catalyst. J. Mol. Catal. A: Chem., 2007, 265, 177-182.
Samai, S.; Nandi, G.C.; Singh, P.; Singh, M.S. L-Proline: an
efficient catalyst for the one-pot synthesis of 2,4,5-trisubstituted
and 1,2,4,5-tetrasubstituted imidazoles. Tetrahedron, 2009, 65,
10155-10161.
Sangshetti, J.N.; Kokare, N.D.; Kotharkara, S.A.; Shinde, D.B.
Ceric ammonium nitrate catalysed three component one-pot
efficient synthesis of 2,4,5-triaryl-1H-imidazoles. J. Chem. Sci.,
2008, 5, 463-467.
Sharma, S.D.; Hazarika, P.; Konwar, D. An efficient and one-pot
synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted
imidazoles catalyzed by InCl3·3H2O. Tetrahedron Lett., 2008, 49,
2216-2220.
Shelke, K.F.; Sapkal, S.B.; Shingare, M.S. Ultrasound-assisted one-
pot synthesis of 2,4,5-triarylimidazole derivatives catalyzed by
ceric (IV) ammonium nitrate in aqueous media. Chinese Chem.
Lett., 2009, 20, 283-287.
Mohammadi, A.A.; Mivechi, M.; Kefayati, H. Potassium aluminum
sulfate (alum): an efficient catalyst for the one-pot synthesis of
trisubstituted imidazoles. Monatsh. Chem., 2008, 139, 935-937.
Sivakumar, K.; Kathirvel, A.; Lalitha, A. Simple and efficient
method for the synthesis of highly substituted imidazoles using
zeolite-supported reagents. Tetrahedron Lett., 2010, 51, 3018-3021.
[15]
[16]
[29]
[30]
[31]
[17]
[18]
[19]
[20]
[32]
[33]
[34]
[35]
[21]
[22]