An effective and new method for the synthesis of polysubstituted imidazoles by the use of CrCl3.6H2O as a green and reusable catalyst: Synthasis of some novel imidazole derivatives

Article abstract of DOI:10.1002/jccs.201100555

New, efficient and environmentally adapted synthesis of polysubstituted imidazoles in one-pot is found. The multicomponent reaction of various aldehydes, benzil, aliphatic and aromatic primary amines and ammonium acetate under solvent-free condition is explained. The highly efficient role of CrCl₃.6H₂O as catalyst in this synthesis was shown. By this advantage, several polysubstituted imidazoles as pharmaceutical important molecules can be prepared in high yield and high purity. This method is a very easy and a rapid reaction for the synthesis of imidazole derivatives. The crude products recrystallized to afford the crystalline pure products. Furthermore, catalyst exhibited remarkable reusable activity.

Full text of DOI:10.1002/jccs.201100555

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Communication
An Effective and New Method for the Synthesis of Polysubstituted Imidazoles by the
Use of CrCl3.6H2O as a Green and Reusable Catalyst: Synthasis of Some Novel
Imidazole Derivatives
Bahador Karami,a,b,* Khalil Eskandari,a Mahnaz Farahia and Akram Barmasb
aDepartment of Chemistry, Yasouj University, Yasouj, Zip Code: 75918-74831, P.O. Box 353, Iran
bDepartment of Chemistry, Gachsaran Branch, Islamic Azad University, Gachsaran, Iran
(Received: Sept. 15, 2011; Accepted: Nov. 28, 2011; Published Online: Mar. 6, 2012; DOI: 10.1002/jccs.201100555)
New, efficient and environmentally adapted synthesis of polysubstituted imidazoles in one-pot is found.
The multicomponent reaction of various aldehydes, benzil, aliphatic and aromatic primary amines and
ammonium acetate under solvent-free condition is explained. The highly efficient role of CrCl3.6H2O as
catalyst in this synthesis was shown. By this advantage, several polysubstituted imidazoles as pharmaceu-
tical important molecules can be prepared in high yield and high purity. This method is a very easy and a
rapid reaction for the synthesis of imidazole derivatives. The crude products recrystallized to afford the
crystalline pure products. Furthermore, catalyst exhibited remarkable reusable activity.
Keywords: Catalyst; CrCl3.6H2O; Benzil; Polysubstituted imidazoles.
INTRODUCTION
Multicomponent reactions (MCRs) are the special
sought continuously. In the scope of previous works for
synthesis of heterocyclic compounds by inorganic solid ac-
ids,19 in this study, a new method for the synthesis of poly-
substituted imidazoles was obtained by condensation of
benzil with aldehydes, primary amines and ammonium ace-
tate in the presence of CrCl3.6H2O as an effective and green
catalyst in solvent-free condition. (Scheme I).
type of organic reactions which afford complex products
from reaction of three or more simple starting materials in
one pot. Because of atom-economy, convergent character,
operational simplicity, structural diversity and complexity
of the molecules in these reactions, they have attracted
much attention.1,2
The imidazoles and their derivatives are very impor-
tant molecules because they have many applications in
chemical processes, especially in pharmaceuticals.3,4 Vari-
ous substituted imidazoles act as inhibitors of p38 MAP
kinase,5 B-Raf kinase,6 glucagon receptors,7 plant growth
regulators,8 antitumor9 and pesticides.10
Synthesis of polysubstituted imidazoles in
the presence of CrCl3.6H2O as catalyst
Scheme I
Lewis acid catalysts have been of great interest in or-
ganic synthesis.11 There are many methods for the synthe-
sis of polysubstituted imidazoles by the employing of
Lewis acids such as condensation of diones, aldehydes, pri-
mary amines and ammonia in the presence of various acid
catalysts,12-14 N-alkylation of trisubstituted imidazoles,14
condensation of benzil or benzoin acetate with aldehydes,
primary amines and ammonia in the presence of copper ac-
etate,16,17 condensation of o-diamines with aldehydesand in
the presence of Tetrabutylammonium Fluoride (TBAF)18
and etc. The first mention method is the most well-known
and classical method. However, some of these methods, in-
volved long reaction times, and unsatisfactory yields.
Therefore, improvements in these syntheses have been
Herein, we report a simple, rapid and one-pot proce-
dure for the synthesis of tri and tetrasubstituted imidazoles
by the use of CrCl3.6H2O with high yields and short reac-
tion times. Using benzil 1, aromatic aldehydes 2, aromatic
and aliphatic amine 3, ammonium acetate 4 and catalytic
* Corresponding author. Tel: +987412223048; Fax: +987412242167; E-mail: karami@mail.yu.ac.ir
J. Chin. Chem. Soc. 2012, 59, 473-479
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473

Communication
Karami et al.
Table 1. The effect of solvents in synthesis of polysubstituted
imidazoles for model reaction
amount of CrCl3.6H2O under solvent-free condition lead to
tetrasubstituted imidazoles 5, wherease in the absence of
aromatic and aliphatic amine 3, trisubstituted imidazoles
were obtained 5¢ (Scheme I).
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
Water
90
35
46
75
78
49
73
96
Ethanol
Methanol
Chloroform
Acetonitrile
Solvent-free
40
RESULTS AND DISCUSSION
120
80
Firstly, synthesis of 1-benzyl 2,4,5-triphenyl imida-
zoles was chosen as a model reaction (compound 5a) in the
synthesis of polysubstituted imidazoles to determine the
optimum condition for these synthesises. In model reac-
tion, in the presence of CrCl3.6H2O (5 mol%) as catalyst,
the mixture of benzil (1 mmol), benzaldehyde (1 mmol),
ammonium acetate (1 mmol), bnzylamine (1 mmol) carried
out in different solvents such as water, ethanol, methanol,
chloroform, acetonitrile and solvent-free conditions. From
these experiments, it was clearly demonstrated that the sol-
vent-free condition is the best condition to accomplish this
synthesis (Table 1).
30
Table 2. Optimization of molar ratio of the catalyst in synthesis
of tri and tetrasubstituted imidazoles
Trisubstituted
imidazole
Tetrasubstituted
imidazole
CrCl3.6H2O
(mol%)
Entry
Time(min)/Yield(%) Time(min)/Yield(%)
1
2
3
4
5
6
1
2
90/65
70/75
50/90
60/82
65/80
75/78
110/60
40/65
30/96
35/78
70/83
75/85
5
10
15
20
We carried out the model reaction in the absence of
catalyst at solvent-free condition and room-temperature for
24 h, which lead to very poor yield (12%) of product. In the
absence of catalyst for enhance the yield of the desired
product, temperature of the reaction was increased to 200
°C, but no appreciable increment in the product yield was
observed. Therefore, we found that the presence of the cat-
alytic amount of CrCl3.6H2O and solvent-free condition
are the best conditions for this synthesis.
Table 3. Optimization of temperature for model reaction
Trisubstituted
imidazole
Tetrasubstituted
imidazole
Entry Temp. (°C)
Time(min)/Yield(%) Time(min)/Yield(%)
1
2
3
4
5
80
90/82
75/80
50/90
60/85
100/65
110/75
90/80
30/96
40/90
45/70
We also evaluated quantity of required catalyst in
synthesis of imidazole derivatives for model reaction
(compound 5a). It was found that maximum yield (96%)
obtained, when the reaction was loaded with 5 mol% of
CrCl3.6H2O. Same result was obtained from trisubstituted
imidazoles when compound 5¢a was chosen as model reac-
tion (Table 2).
100
120
140
160
ducted the synthesis of polysubstituted imidazoles in the
presence of CrCl3.6H2O as catalyst in solvent-free condi-
tion at 120 °C.
In the following study on the model reactions, we ex-
amined the reactions at various temperatures to find out the
effect of temperature on the progress of reaction in the
presence of optimized amount of catalyst (Table 3). The
maximum rate of reaction was obtained at 120 °C as the op-
timum temperature for tri and tetrasubstituted imidazoles.
As can be seen from Table 3, at 80 °C, reaction was
completed slowly. Increasing temperature to 120 °C, in-
creased the yield of reaction and decreased the time of reac-
tion. When the reaction was heated above 120 °C, so high
temperatures did not further improved yield and decrease
time of reaction.
Comparison of this method with others for the syn-
thesis of 1-benzyl 2,4,5-triphenyl imidazole (compound
5a) as a model reaction is shown in Table 4.14,20–29 These re-
sults show that this catalyst prepared good to excellent con-
ditions for the synthesis of imidazole derivatives than other
catalysts and methods that were reported. This method not
only affords the products in excellent yields but also avoids
the problems associated with catalyst cost, handling,
safety, and pollution.
Reusability of the catalyst
At the end of the reaction, the catalyst was filtered,
According to the archived optimal condition, we con-
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J. Chin. Chem. Soc. 2012, 59, 473-479

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Synthesis of Polysubstituted Imidazoles
Table 4. Comparison of the results for the synthesis of 1-benzyl 2,4,5-triphenyl imidazole (compound
5a) as a model reaction with other catalysts
Time (min)/
Yield (%)
Entry
Catalyst
Mol (%)
Solvent/Temp. (oC)
[Ref.]
1
CrCl3.6H2O
I2
5
Solvent free/120
Solvent free/100
Solvent free/140
Solvent free, MW (150 W)
Solvent free/140
Solvent free, MW
CH2Cl2, Solar heat
Solvent free/140
Solvent free/140
MeOH/60
30/96
60/85
120/90
4/92
This work
[20]
2
10
15
20
10
2 g
0.1
1
3
[(CH2)4SO3HMIM][HSO4]a
TFA b
[21]
4
[22]
5
K5CoW12O40·3H2O c
120/90
8/87
[23]
d
6
SiO2
[24]
d
7
SiO2
120/80
120/85
120/80
510/86
444/79
60/86
[25]
8
AlPO4
[14]
e
9
BF3.SiO2
21
15
10
20
[26]
10
11
12
L-Proline
InCl3.3H2O
ZrCl4
[27]
MeOH/r.t.
[28]
CH3CN/r.t.
[29]
a 3-Methyl-1-(4-sulfonic acid)-butylimidazolium hydrogen sulfate.
b Trifluoroacetic acid.
c Potassium dodecatugstocobaltate trihydrate.
d Silica gel as acidic support.
e Silica-supported boron trifluoride.
washed with diethyl ether, dried at 130 oC for 1 h, and re-
The suggested mechanism for the synthe-
sis of tetrasubstituted imidazoles
Scheme II
used in another reaction. We found that CrCl3.6H2O
showed high catalytic activity with very short reaction
time. Moreover, it can be recovered and reused five times
without significant loss of activity. The results of these ob-
servations for the model reaction are shown in Table 4 and
Figure 1.
A probable mechanism for the synthesis of tetrasub-
stituted imidazoles may be postulated as shown below
(Scheme II).
As can be seen from Scheme II, in the presence of
CrCl3.6H2O as Lewis acid, the carbonyl group of aldehyde
2 is activated and the energy of transition state for nucleo-
philic attack is decreased. Then nucleophilic attack of
amine 3 on the activated carbonyl of aldehydes, resulted to
the formation of imine, and it followed by nucleophilic at-
tack of the insitu generated ammonia from 4 to the imine,
giving the intermediate 6. From condensation of intermedi-
ate 6 with benzil 1 and dehydration of it, corresponding
imidazoles 5 are produced.
Moreover, the probable mechanism for the synthesis
of trisubstituted imidazoles is same with tetrasubstituted
imidazoles but in this case, ammonium acetate was handled
Fig. 1. The reusability of the catalyst for model reac-
tion.
J. Chin. Chem. Soc. 2012, 59, 473-479
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Communication
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Table 5. Reusability results of CrCl3.6H2O on the reaction
process for the model reaction
instead of primary amine.
Product
Total reusability Yield (%)
Time (min)
EXPERIMENTAL
Melting points were measured on an elecrtothermal
KSB1N apparatus. IR spectra were recorded in the matrix
Ph
N
1
2
3
4
5
96
95
95
97
97
30
30
35
45
55
N
Ph
1
of KBr with JASCO FT-IR-680 plus spectrometer. H
NMR and 13C NMR spectra were recorded on a FT-NMR
Bruker Avance ultra shield spectrometer at 400.13 and
100.62 MHz in CDCl3 and DMSO-d6 as solvent in the pres-
ence of tetramethylsilane as internal standard. TLC was
performed on TLC-Grade silica gel-G/UV 254 nm plates.
The products were isolated and characterized by physical
and spectral data and they were compared with authentic
samples (Table 5).
water then was filtered. Obtained products were purified by
crystallization from acetone-water (10:1). The products
were characterized by IR, NMR, and through comparison
of their physical properties with those reported in litera-
ture.14,27,30-39
Hence, general procedure for the synthesis of 2,4,5-
trisubstituted imidazoles is same to the 1,2,4,5-tetrasubsti-
tuted imidazoles, but it needs to 2 mmol of ammonium ace-
tate instead of 1 mmol in the absence of primary amine.
Representative spectral data
General procedure for synthesis of 1,2,4,5-tetrasub-
stituted imidazoles by CrCl3.6H2O
A mixture of aromatic aldehyde (1 mmol), benzil (1
mmol), primary amine (1 mmol), ammonium acetate (1
mmol) and CrCl3.6H2O (5 mol%) were stirred at 120 oC in
solvent-free condition. The progress of reaction was moni-
tored by TLC. After completion of reaction, the mixture
was cooled to room temperature and was solved in 50 mL
Table 5, compound 5a: m.p. 170-172 °C; IR (KBr)
(nmax, cm-1): 3061, 3026, 2308, 1601, 1521, 1497, 1350,
761, 696. 1H NMR (250 MHz, DMSO-d6): d (ppm) 5.13 (s,
Table 6. Synthesis of polysubstituted imidazoles catalyzed by CrCl3.6H2O (5 mol%) under
solvent-free condition at 120 °C
Yielda
Compound
R1
R2NH2
Time (min)
M.p. (oC)/(lit.)
(%)
5a
5b
5c
C6H5
4-Br-C6H4
C6H5CH2NH2
30
25
55
60
25
20
40
50
25
95
85
50
50
10
30
25
100
60
35
140
25
10
96
90
92
85
85
80
75
90
98
96
80
93
90
89
90
92
70
68
97
83
90
91
170-172 30
169-170 14
163-166 31
160-162 31
193-195 32
150-152 b
160-161 33,34
148-151 27
156-158 b
138-139 b
216-219 b
182-184 34
272-273 30
120-122 35
209-211 36
204-206 27
227-230 30
235-236 37
283-286 b
311-313 b
257-259 38
308-309 39
C6H5CH2NH2
4-CH3-C6H4
4-Cl-C6H4
C6H5CH2NH2
5d
5e
C6H5CH2NH2
2-Cl-C6H4
C6H5CH2NH2
5f
3-NO2-C6H4
4-CH3-C6H4
4-OCH3-C6H4
2-OH-5-Br-C6H3
4-Benzyloxy-C6H4
2,4-di-Cl-C6H3
4-CH3-C6H4
C6H5
C6H5CH2NH2
5g
5h
5i
CyclohexylNH2
C6H5CH2NH2
4-Cl-C6H4NH2
5j
C6H5CH2NH2
5k
5l
C6H5CH2NH2
C6H5NH2
---
5'a
5'b
5'c
5'd
5'e
5'f
5'g
5'h
5'i
5'j
3-Br-C6H4
---
2-OH-C6H4
2-OCH3-C6H4
4-OCH3-C6H4
4-Benzyloxy-C6H4
2-Fluorenyle
3-Indolyl
---
---
---
---
---
---
4-Cl-C6H4
---
3-NO2-C6H4
---
a Refers to isolated yields
b Novel compound
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CHEMICAL SOCIETY
Synthesis of Polysubstituted Imidazoles
2H), 7.18-8.41 (m, 22H). 13C NMR (62.69 MHz, DMSO-
d6) d (ppm): 48.29, 126.00, 126.38, 126.81, 128.11,
129.08, 129.58, 129.90, 130.09, 130.98, 131.09, 135.09,
137.57, 148.09.
112.95, 122.40, 124.94, 125.21, 125.71, 126.26, 127.00,
127.49, 127.52, 127.71, 128.02, 128.70, 129.37, 130.03,
130.12, 133.53, 136.64, 136.78, 146.94, 159.04.
Table 5, compound 5i: m.p. 156-158 °C; IR (KBr)
(nmax, cm-1): 3458, 3063, 1659, 1593, 1578, 1211, 1174,
1096. 1H NMR (400.13 MHz, DMSO-d6) d (ppm):
6.92-8.53 (m, 17H), 13.06 (s, 1H). 13C NMR (100.62 MHz,
DMSO-d6) d (ppm): 115.17, 123.92, 125.53, 127.64,
134.31, 137.31, 139.26, 140.54, 151.31, 164.74, 166.94.
Table 5, compound 5j: m.p. 138-139 °C; IR (KBr)
(nmax, cm-1): 2857, 1601, 1575, 1526, 1289, 1247, 1177. 1H
NMR (400.13 MHz, DMSO-d6) d (ppm): 2.18 (s, 2H), 5.06
(s, 2H), 6.83-7.82 (m, 24H). 13C NMR (100.62 MHz,
DMSO-d6) d (ppm): 48.29, 70.03, 115.05, 123.79, 126.06,
126.38, 126.85, 127.41, 127.53, 128.11, 128.16, 128.68,
128.86, 129.89, 130.50, 131.14, 131.23, 134.70, 136.76,
137.75, 137.94, 148.02, 159.33.
Table 5, compound 5b: m.p. 169-170 °C; IR (KBr)
(nmax, cm-1): 3059, 3027, 2938, 1599, 1479, 1358, 1070,
835, 758, 694. 1H NMR (400.13 MHz, DMSO-d6): d (ppm)
4.86 (s, 2H), 6.61-7.46 (m, 21H). 13C NMR (100.62 MHz,
DMSO-d6) d (ppm): 49.41, 125.86, 126.51, 126.78,
127.53, 128.14, 128.25, 128.74, 128.87, 130.48, 130.79,
131.03, 131.79, 137.33.
Table 5, compound 5c: m.p. 163-166 °C; IR (KBr)
(nmax, cm-1): 3060, 3027, 2926, 1600, 1496, 1349, 826, 767,
694. 1H NMR (400.13 MHz, DMSO-d6) d (ppm): 2.08 (s,
3H), 4.91 (s, 2H), 6.61-7.40 (m, 19H). 13C NMR (100.62
MHz, DMSO-d6) d (ppm): 22.52, 49.41, 127.15, 127.47,
127.94, 128.46, 129.22, 129.72, 129.92, 130.10, 130.45,
131.03, 132.23, 138.80, 140.01, 146.34.
Table 5, compound 5k: m.p. 216-219 °C; IR (KBr)
(nmax, cm-1): 3069, 2924, 1557, 1523, 1459, 1092. 1H NMR
(400.13 MHz, DMSO-d6) d (ppm): 2.18 (s, 2H), 7.45-8.41
(m, 13H), 8.64 (d, J = 7.6 Hz, 1H), 8.77 (t, J = 8.4 Hz, 2H).
13C NMR (100.62 MHz, DMSO-d6) d (ppm): 120.88,
121.13, 122.98, 123.47, 123.76, 125.00, 126.03, 126.82,
127.20, 127.39, 127.43, 127.56, 129.00, 129.58, 131.28,
132.31, 133.77, 135.20, 136.93, 145.22.
Table 5, compound 5d: m.p. 160-162 °C; IR (KBr)
(nmax, cm-1): 3059, 3029, 2936, 1600, 1480, 1357, 1089,
835, 758, 693. 1H NMR (400.13 MHz, DMSO-d6) d (ppm):
4.9 (s, 2H), 6.60-7.50 (m, 19H). 13C NMR (100.62 MHz,
DMSO-d6) d (ppm): 48.31, 125.88, 126.55, 127.54,
129.13, 129.31, 130.28, 130.43, 130.74, 131.04, 134.18,
135.04, 136.81, 137.30, 138.22.
Table 5, compound 5e: m.p. 193-195 °C; IR (KBr)
(nmax, cm-1): 3062, 3026, 2930, 1602, 1485, 1349, 1079,
758, 690. 1H NMR (400.13 MHz, DMSO-d6) d (ppm): 4.74
(s, 2H), 6.42-7.42 (m, 19H). 13C NMR (100.62 MHz,
DMSO-d6) d (ppm): 43.17, 126.00, 126.50, 126.68,
127.48, 128.44, 128.69, 128.99, 129.15, 129.36, 129.74,
129.81, 130.33, 130.61, 130.89, 131.08, 131.15, 132.92,
133.80, 134.24, 134.95, 136.80, 137.65, 145.13.
Table 5, compound 5l: m.p. 182-184 °C; IR (KBr)
(nmax, cm-1): 3055, 3022, 2930, 1600, 1495, 1349, 826, 767,
694. 1H NMR (400.13 MHz, CDCl3): d (ppm) 2.34 (s, 3H),
7.07-7.36 (m, 17H), 7.64 (d, J = 7.1 Hz, 2H). 13C NMR
(100.62 MHz, CDCl3) d (ppm): 20.23, 124.24, 125.49,
126.39, 126.67, 126.85, 127.09, 127.12, 127.27, 127.45,
127.77, 127.79, 127.98, 128.46, 129.74, 130.11, 136.23,
137.10, 146.06.
Table 5, compound 5f: m.p. 150-152 °C; IR (KBr)
(nmax, cm-1): 3061, 3026, 2308, 1601, 1521, 1497, 1350,
810, 730, 696.1H NMR (400.13 MHz, DMSO-d6): d (ppm)
5.19 (s, 2H), 6.89 (d, J = 6.15 Hz, 2H), 7.21-7.63 (m, 14H),
8.04 (d, J = 7.8 Hz, 1H), 8.23 (d, J = 7.8 Hz, 1H), 8.57 (s,
1H). 13C NMR (100.62 MHz, DMSO-d6) d (ppm): 47.42,
122.30, 122.59, 124.71, 125.67, 125.73, 126.71, 127.15,
127.84, 127.97, 128.56, 129.36, 129.93, 130.24, 131.57,
132.98, 133.51, 135.78, 144.23, 147.20.
Table 5, compound 5¢b: m.p. 120-122 °C; IR (KBr)
(nmax, cm-1): 3387, 3062, 1584, 1529, 1480, 1241, 1100. 1H
NMR (400.13 MHz, CDCl3) d (ppm): 7.26-7.78 (m, 14H),
9.40 (s, 1H). 13C NMR (100.62 MHz, CDCl3) d (ppm):
121.86, 125.62, 126.02, 126.75, 127.41, 127.70, 127.76,
128.11, 131.05.
Table 5, compound 5¢c: m.p. 209-211 °C; IR (KBr)
(nmax, cm-1): 3450, 3385, 1584, 1529, 1480, 1240, 1098. 1H
NMR (400.13 MHz, CDCl3) d (ppm): 6.92 (d, J = 7.28 Hz,
1H), 7.08 (d, J = 7.7 Hz, 1H), 7.26-7.62 (m, 12H), 9.36 (s,
1H), 12.83 (s, 1H). 13C NMR (100.62 MHz, CDCl3) d
(ppm): 111.39, 116.80, 117.92, 122.00, 126.32, 127.14,
127.38, 128.07, 129.54, 144.67, 156.45.
Table 5, compound 5h: m.p. 148-151 °C; IR (KBr)
(nmax, cm-1): 3063, 3019, 2295, 1609, 1519, 1493, 1354,
696. 1H NMR (400.13 MHz, CDCl3): d (ppm) 3.81(s, 3H),
5.08 (s, 2H), 6.82-7.56 (m, 15H), 7.58 (d, J = 2.3 Hz, 4H).
13C NMR (100.62 MHz, CDCl3) d (ppm): 47.16, 54.26,
Table 5, compound 5¢d: m.p. 204-206 °C; IR (KBr)
J. Chin. Chem. Soc. 2012, 59, 473-479
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Communication
Karami et al.
(nmax, cm-1): 3388, 3062, 2933, 1584, 1530, 1481, 1240,
1099. 1H NMR (400.13 MHz, DMSO-d6) d (ppm): 4.05 (s,
3H), 7.03-7.69 (m, 13H), 8.50 (d, J = 8 Hz, 1H), 10.51 (s,
1H). 13C NMR (100.62 MHz, DMSO-d6) d (ppm): 126.45,
126.83, 127.33, 128.22, 128.59, 129.07, 129.67, 129.91,
130.26, 131.02, 132.98, 133.97.
13.10 (s, 1H), 13C NMR (100.62 MHz, DMSO-d6) d (ppm):
119.40, 122.61, 127.13, 128.44, 128.68, 130.44, 131.17,
131.82, 143.38, 148.37.
CONCLUSION
In this work, we found a thermal exposure synthetic
method for the preparation of polysubstituted imidazoles,
that it is a simple, efficient and green chemistry via multi-
component one-pot reaction in the presence of CrCl3.6H2O
as an inexpensive and eco-friendly catalyst in solvent-free
condition. Furthermore, products were isolated in excellent
yields. Also catalyst efficiently recovered and reused, that
is considered as economic advantages of this synthesis. It is
believed that this procedure will find important applica-
tions in the synthesis of wide range of polysubstituted
imidazoles.
Table 5, compound 5¢e: m.p. 227-230 °C; IR (KBr)
(nmax, cm-1): 3433, 3027, 1613, 1578, 1542, 1248, 1176. 1H
NMR (400.13 MHz, DMSO-d6) d (ppm): 3.87 (s, 3H),
6.98-7.86 (m, 12H), 7.55 (s, 2H), 7.85 (d, J = 8.4 Hz, 2H).
13C NMR (100.62 MHz, DMSO-d6) d (ppm): 55.36,
114.27, 122.78, 126.78, 127.30, 127.80, 128.55, 146.14,
160.16.
Table 5, compound 5¢f: m.p. 235-236 °C; IR (KBr)
(nmax, cm-1): 3054, 3018, 2930, 1608, 1578, 1541, 1230,
1181. 1H NMR (400.13 MHZ, DMSO-d6) d (ppm) 5.16 (s,
2H), 7.11-7.54 (m, 17H), 8.01 (d, J = 8.8 Hz, 2H), 12.51 (s,
1H). 13C NMR (100.62 MHz, DMSO-d6) d (ppm): 69.78,
115.42, 123.82, 126.09, 127.18, 127.52, 128.26, 128.36,
128.63, 128.82, 128.93, 129.10, 135.79, 137.41, 146.06,
158.99.
ACKNOWLEDGEMENT
Financial support from Yasouj University of Iran was
greatly acknowledged.
Table 5, compound 5¢g: m.p. 283-286 °C; IR (KBr)
(nmax, cm-1): 3350, 3054, 2950, 1601, 1532, 1500. 1H NMR
(400.13 MHz, DMSO-d6) d (ppm): 4.01 (s, 2H), 7.33-8.00
(m, 15H), 8.130 (d, J = 7.6 Hz, 1H), 8.32 (s, 1H), 12.733 (s,
1H). 13C NMR (100.62 MHz, DMSO-d6) d (ppm): 39.92,
120.36, 120.68, 122.37, 124.57, 125.64, 126.73, 127.42,
128.28, 128.90, 129.36, 141.23, 141.63, 143.88, 143.95,
146.42.
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