Silica-bonded S-sulfonic acid: A recyclable catalyst for the synthesis of trisubstituted imidazoles under solvent-free conditions

Article abstract of DOI:10.1002/cjoc.201090129

Trisubstituted imidazoles have been synthesized in high yields in the presence of silica-bonded S-sulfonic acid as a catalyst. The reaction was carried out at 130 °C under solvent-free conditions. The reaction work-up is simple and the catalyst is easily separated from the products by filtration.

Full text of DOI:10.1002/cjoc.201090129

FULL PAPER
Silica-bonded S-Sulfonic Acid: A Recyclable Catalyst for the
Synthesis of Trisubstituted Imidazoles under Solvent-free
Conditions
Niknam, Khodabakhsh*
Mohammadizadeh, Mohammad R.
Saberi, Dariush
Mirzaee, Salimeh
Chemistry Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
Trisubstituted imidazoles have been synthesized in high yields in the presence of silica-bonded S-sulfonic acid
as a catalyst. The reaction was carried out at 130 ℃ under solvent-free conditions. The reaction work-up is simple
and the catalyst is easily separated from the products by filtration.
Keywords silica-bonded S-sulfonic acid, trisubstituted imidazole, aldehyde, catalyst, solvent-free
Introduction
The imidazole moiety is present in wide naturally
occurring molecules10 and pharmaceutically active
compounds.11 Among these, 2,4,5-trisubstituted imida-
zoles are of great interest because of their chemical and
biological activities, making them common structures in
numerous synthetic compounds11 and therapeutic
agents.12 Because of this, numerous classical methods
for their synthesis have been reported.13-15 In these pro-
cedures, a 1,2-diketone, an aldehyde and ammonium
acetate were condensed in the presence of a strong
The development of heterogeneous catalysts for or-
ganic synthesis has become a major area of research.
The potential advantages of these materials over homo-
geneous systems (simplified recovery, reusability and
the potential for incorporation in continuous reactors
and microreactors) can lead to novel and environmen-
tally benign chemical procedures for academia and in-
dustry.1 From this viewpoint, catalytic reactions lead to
valuable processes, since the use of stoichiometric re-
agents that are often toxic poses inherent limitations
from both an economical and an environmental view-
points and in specific relation to product purification
and waste management.2 Application of solid acids in
organic transformation has important roles, because
these species have many advantages such as simplicity
in handling, decreased reactor and plant corrosion prob-
lems, and more environmentally safe disposal.3-9 It is
clear that green chemistry not only requires the use of
environmentally benign reagents and solvents, but also
the recovery and reuse of the catalyst. One way to
overcome the problem of recyclability of the traditional
acid catalyst is to chemically anchor the reactive center
onto a large surface area inorganic solid carrier to create
a new organic-inorganic hybrid catalyst.4 In these types
of solids, the reactive centers are highly mobile similar
to homogeneous catalysts and at the same time these
species have the advantage of being recyclable in the
same fashion as heterogeneous catalysts. In view of this,
several types of solid sulfonic acid functionalized silica
(both amorphous and ordered) have been synthesized
and applied as an alternative to traditional sulfonic acid
resins and homogeneous acids in catalyzing chemical
transformations.3-9
protic acid (such as H3PO4,16 H2SO4,17 and HOAc18,19
)
or other catalysts in HOAc,14 under reflux conditions.
The products were isolated by neutralization of the re-
action mixture. The solvent used for these syntheses has
usually been a polar organic solvent, such as ethanol,
methanol, acetic acid, DMF or DMSO, with the result
that the isolation and recovery procedures are compli-
cated. These processes also generate significant wastes
containing the catalysts, which have to be recovered,
treated and disposed of in environmentally acceptable
ways.
Recently, a few research groups have reported
one-pot condensation of α-hydroxy ketone or
α-keto-oxime or 1,2-diketone, aldehyde and NH4OAc
on solid supports under microwave irradiation.20-22
However, in spite of their potential utility, most of these
methods not only involve high temperature (180—200
℃) but also the reactions have been carried out in
HOAc. The other methods utilizing ionic liquids,23,24
silica sulfuric acid,25 alum,26 Zr(acac)4,27 tetrabutylam-
monium bromide,28 and polymer-supported zinc chlo-
ride29 have also been described. One important aspect of
clean technology is the use of environmentally friendly
catalysis typically involving the use of solid acid cataly-
sis. Employing such approaches will lead to minimal
*
E-mail: niknam@pgu.ac.ir and khniknam@gmail.com
Received August 1, 2009; revised November 2, 2009; accepted November 16, 2009.
Chin. J. Chem. 2010, 28, 663— 669
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Niknam et al.
FULL PAPER
pollution and waste material, and application of such
catalysts to fine chemical manufacturing is likely to be
especially important in future.
Table 1 Model condensation of benzaldehyde with benzil and
ammonium acetate in the presence of different amounts of
SBSSA under heating and solvent-free conditionsa
Amount of catalyst/
g
Time/ Temperature/ Yieldb/
Entry
Results and discussion
min
60
60
60
60
60
60
60
45
40
30
30
30
60
℃
%
15
20
35
20
50
80
92
92
93
93
93
95
95
1
2
—
130
150
180
80
Recently, we have reported the preparation of sil-
ica-bonded S-sulfonic acid (SBSSA) and its application
as catalyst to the preparation of acylal,5 quinoxaline,6
and coumarin derivatives7 (Scheme 1).
In our continued interest in the development of a
highly expedient methodology for the synthesis of fine
chemicals and heterocyclic compounds of biological
importance,30-35 we report here the synthesis of trisub-
stituted imidazoles in the presence of SBSSA under
solvent-free conditions (Scheme 2).
In a primary study, we have chosen the condensation
reaction of benzil with benzaldehyde and ammonium
acetate as a model reaction in the presence of different
catalytic amounts of SBSSA under solvent-free condi-
tions. The results are summarized in Table 1.
—
3
—
4
0.2
5
0.1
100
130
130
130
130
130
130
130
150
6
0.2
7
0.1
8
0.05
0.03
0.01
0.005
0.002
0.1
9
10
11
12
13
a The molar ratio of aromatic aldehyde∶1,2-diketone∶NH4OAc
As indicated in Table 1, the best results have been
obtained at 130 ℃ with a catalytic amount of 0.002 g
(0.068 mol%) of SBSSA, aldehyde (1 mmol),
1,2-diketone (1 mmol), and ammonium acetate (6 mmol)
under solvent-free conditions. The yield of reaction with
increasing amount of SBSSA or temperature is not con-
siderably increased. It is important to note that in the
absence of catalyst the reaction yield is decreased to
35% even at 180 ℃ after 1 h (Table 1, Entry 3).
used was 1∶1∶6 respectively. b Isolated yield.
of 2,4,5-triarylimidazoles with different groups.
Encouraged by this achievement, we extended the
reaction to condensation of benzoin and NH4OAc with a
range of aromatic aldehydes under similar conditions
(Scheme 3), furnishing the respective corresponding
imidazoles in good to excellent yields (Table 3).
The possibility of recycling the catalyst was exam-
ined using the reaction of benzil, 4-methylbenzaldehyde
and ammonium acetate under optimized conditions.
Upon completion, the reaction mixture was filtered and
the solid was washed with ethanol, and recycled catalyst
was saved for the next reaction. The recycled catalyst
could be reused three times without any further treat-
ment. No observation of any appreciable loss in the
catalytic activity of SBSSA was observed (Table 2, En-
try 2).
A wide range of aromatic aldehydes were employed
and all imidazoles were obtained in high to excellent
yields, and a general method was observed that tolerates
both electron-withdrawing and electron-donating con-
stituents. Another important aspect is that various func-
tionalities such as thioether, halide, etc., survived under
the present reaction conditions. To evaluate the general-
ity of this method, we also concentrated our study on
different benzils (Table 2, Entries 9—17). The results
illustrate the high ability of this method for the synthesis
Scheme 1 Preparation of silica bonded S-sulfonic acid
Scheme 2 SBSSA catalyzed synthesis of trisubstituted imidazoles at 130 ℃ under solvent-free conditions
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Chin. J. Chem. 2010, 28, 663— 669

Catalyst for the Synthesis of Trisubstituted Imidazoles
Table 2 Synthesis of trisubstituted imidazole derivatives catalyzed by SBSSA at 130 ℃ under solvent-free conditionsa
Entry
1
R1
R2
H
Product
Time/min
Yieldb/%
95
30
2
3
4
5
6
H
H
H
H
H
25, 25, 30, 30c
88, 86, 84, 84c
30
30
30
30
90
89
90
89
7
H
85
92
8
MeO
MeO
MeO
MeO
MeO
MeO
80
60
90
92
94
89
90
89
9
10
11
12
13
90
80
120
90
Chin. J. Chem. 2010, 28, 663— 669
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Niknam et al.
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Continued
Entry
14
R1
R2
Product
Time/min
70
Yieldb/%
MeO
95
15
16
F
F
90
90
92
88
17
F
80
91
a The molar ratios of 1,2-diketone∶aldehyde∶ammonium acetate used were 1∶1∶6 in the presence of 0.002 (g) of SBSSA. b Isolated
yield. c The reaction was accomplished in the presence of reused SBSSA as catalyst.
Table 3 Synthesis of trisubstituted imidazole via the reaction of α-hydroxy ketone, aldehydes and ammonium acetate catalyzed by
SBSSA at 130 ℃ under solvent-free conditionsa
Entry
R1
R2
H
Product
Time/min
Yieldb/%
95
1
80
2
3
4
5
6
H
H
H
H
H
70
90
90
80
80
88
90
89
90
89
a The molar ratios of α-hydroxy ketone∶aldehyde∶ammonium acetate used were 1∶1∶6 in the presence of 0.002 (g) of SBSSA. b Iso-
lated yield.
Conclusion
cal for multi-component reactions. We believe that the
present methodology could be an important addition to
the existing methodologies.
In conclusion, heterogeneous conditions, easy and
clean work-up and high yields make this method practi-
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Chin. J. Chem. 2010, 28, 663— 669

Catalyst for the Synthesis of Trisubstituted Imidazoles
Scheme 3 Preparation of trisubstituted imidazoles using aromatic aldehyde, α-hydroxy ketone and ammonium acetate
Experimental
128.73, 129.45, 133.65, 145.21.
2-(4-Bromophenyl)-4,5-diphenylimidazole (Table
2, Entry 4): m.p. 262—264 ℃ (Lit.26 252—254 ℃);
1H NMR (CDCl3/DMSO-d6, 500 MHz) δ: 7.12—7.19
(m, 6H), 7.39 (d, J＝8.5 Hz, 2H), 7.43 (d, J＝7.1 Hz,
4H), 7.87 (d, J＝8.5 Hz, 2H), 12.12 (brs, 1H); 13C NMR
(CDCl3/DMSO-d6, 125 MHz) δ: 122.27, 127.50, 128.42,
128.66, 130.00, 131.87, 145.57.
General
Chemicals were purchased from Merck, Fluka and
Aldrich chemical companies. IR spectra were run on a
1
Perkin Elmer FT-IR Spectrum BX instrument. H and
13C NMR spectra were run on a Bruker Ultrashield 400
(400 MHz) spectrometer, or a Bruker Avance 500 (500
MHz) spectrometer. Melting points were recorded on a
Melting Point SMP1 apparatus in open capillary tubes
and are uncorrected. With TLC using silica gel
SILG/UV 254 plates the progress of reaction was fol-
lowed. Most of the products are known and character-
2-(4-Methylthiophenyl)-4,5-diphenylimidazole
(Table 2, Entry 5): m.p. 244—246 ℃ (Lit.26 242—244
1
℃); H NMR (CDCl3/DMSO-d6, 500 MHz) δ: 2.31 (s,
3H), 7.00—7.12 (m, 8H), 7.33—7.39 (m, 4H), 7.83 (d,
J ＝ 8.5 Hz, 2H), 11.90 (brs, 1H); 13C NMR
(CDCl3/DMSO-d6, 125 MHz) δ: 15.76, 126.23, 126.44,
127.75, 128.57, 138.74, 146.19.
1
ized by comparison of their spectral (IR, H NMR),
TLC and physical data with those reported in the litera-
ture.19,24-29,36-38
4,5-Diphenyl-2-(2-tolyl)imidazole (Table 2, Entry
6): m.p. 204—206 ℃ (Lit.26 198—202 ℃); H NMR
1
General procedure for the synthesis of trisubstituted
imidazole derivatives
(CDCl3/DMSO-d6, 500 MHz) δ: 2.61 (s, 3H), 7.20—
7.24 (m, 5H), 7.25—7.30 (m, 5H), 7.56 (m, 3H), 7.63 (d,
J ＝ 7.6 Hz, 1H), 11.40 (brs, 1H); 13C NMR
(CDCl3/DMSO-d6, 125 MHz) δ: 21.47, 126.01, 127.33,
128.36, 128.72, 128.78, 129.60, 130.92, 131.35, 137.35,
147.04.
To a mixture of aromatic aldehyde (1 mmol),
1,2-diketone (1 mmol) and ammonium acetate (6 mmol)
was added silica-bonded S-sulfonic acid (0.002 g) and
the resulting mixture was heated at 130 ℃. The solid
materials residue was then washed with acetone and the
solvent was evaporated to give the crude product. For
further purification it was crystallized from 9∶1 (V∶V)
acetone-water mixture to afford pure product.
2-(3-Indolyl)-4,5-diphenylimidazole (Table 2, En-
1
try 7): m.p. 302—305 ℃; H NMR (DMSO-d6, 400
MHz) δ: 7.05—7.16 (m, 3H), 7.23—7.28 (m, 3H), 7.37
(d, J＝7.8 Hz, 3H), 7.44 (d, J＝7.3 Hz, 2H), 7.56 (d, J
＝7.1 Hz, 2H), 7.93 (d, J＝2.5 Hz, 1H), 8.40 (d, J＝8.6
Hz, 1H), 11.29 (s, 1H), 12.20 (brs, 1H); 13C NMR
(DMSO-d6, 100 MHz) δ: 106.79, 111.58, 119.68, 121.48,
121.84, 123.74, 125.06, 126.84, 128.15, 128.67, 136.24,
143.69, 145.27, 171.66; IR (neat) ν: 3412.71, 3055.71,
1621.86, 1598.56, 1491.27, 1451.65, 1336.66, 1208.91,
1182.28, 1049.08, 940.61, 854.56, 761.99, 749.63,
Spectral data
2,4,5-Triphenylimidazole (Table 2, Entry 1): m.p.
271 — 273 ℃ (Lit.26 272 — 273 ℃ ); 1H NMR
(CDCl3/DMSO-d6, 500 MHz) δ: 7.13—7.14 (m, 2H),
7.20 (t, J＝7.2 Hz, 5H), 7.27—7.30 (m, 2H), 7.46 (d,
J＝7.0 Hz, 4H), 7.98 (d, J＝7.7 Hz, 2H), 12.00 (brs,
1H); 13C NMR (CDCl3/DMSO-d6, 125 MHz) δ: 125.95,
127.34, 128.48, 128.64, 128.82, 130.95, 146.64.
－
1
696.11 cm . Anal. calcd for C23H17N3: C 82.36, H 5.11,
N 12.53; found C 82.17, H 5.17, H 12.29.
4,5-Diphenyl-2-(4-tolyl)imidazole (Table 2, Entry
4,5-Di(4-anisyl)-2-phenylimidazole (Table 2, Entry
2): m.p. 236—238 ℃ (Lit.11 232—235 ℃); H NMR
1
8): m.p. 110—112 ℃ (Lit.37 202—203 ℃); H NMR
1
(CDCl3/DMSO-d6, 500 MHz) δ: 2.03 (s, 3H), 6.86—
6.91 (m, 4H), 6.96 (t, J＝7.2 Hz, 4H), 7.21 (d, J＝7.4
Hz, 4H), 7.64 (d, J＝8.1 Hz, 2H), 11.89 (brs, 1H); 13C
NMR (CDCl3/DMSO-d6, 125 MHz) δ: 21.44, 125.66,
127.13, 128.07, 128.22, 128.44, 129.33, 138.03, 146.52.
2-(4-Chlorophenyl)-4,5-diphenylimidazole (Table
2, Entry 3): m.p. 263—265 ℃ (Lit.36 266—268 ℃);
1H NMR (CDCl3/DMSO-d6, 500 MHz) δ: 6.89—6.95
(m, 6H), 7.01 (d, J＝8.5 Hz, 2H), 7.19 (d, J＝7.1 Hz,
4H), 7.72 (d, J＝8.5 Hz, 2H), 12.00 (brs, 1H); 13C NMR
(CDCl3/DMSO-d6, 125 MHz) δ: 127.03, 128.16, 128.47,
(DMSO-d6, 400 MHz) δ: 3.77 (s, 6H), 6.95 (d, J＝8.1
Hz, 4H), 7.35 (t, J＝7.3 Hz, 1H), 7.44—7.48 (m, 6H),
8.07 (d, J＝7.3 Hz, 2H), 12.54 (brs, 1H); 13C NMR
(DMSO-d6, 100 MHz) δ: 55.07, 113.84, 125.02, 127.98,
128.62, 128.93, 130.49, 144.78, 158.30, 172.02.
4,5-Di(4-anisyl)-2-(4-tolyl)imidazole (Table 2,
Entry 9): m.p. 102—104 ℃ (Lit.37 212—215 ℃); H
1
NMR (DMSO-d6, 400 MHz) δ: 2.35 (s, 3H), 3.77 (s,
6H), 6.86—6.99 (m, 4H), 7.27 (d, J＝8.1 Hz, 2H), 7.44
(d, J＝8.3 Hz, 4H), 7.95 (d, J＝8.1 Hz, 2H), 12.43 (brs,
1H); 13C NMR (DMSO-d6, 100 MHz) δ: 20.87, 55.07,
Chin. J. Chem. 2010, 28, 663— 669
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Niknam et al.
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113.81, 124.99, 127.83, 129.18, 137.36, 144.93, 157.77,
172.01.
4.90.
4,5-Di(4-fluorophenyl)-2-(4-tolyl)imidazole (Table
1
4,5-Di(4-anisyl)-2-(4-chlorophenyl)imidazole
(Table 2, Entry 10): m.p. 122—124 ℃; 1H NMR
(DMSO-d6, 400 MHz) δ: 3.77 (s, 6H), 6.84—7.01 (m,
4H), 7.38—7.50 (m, 4H), 7.53 (d, J＝8.8 Hz, 2H), 8.08
(d, J ＝ 8.8 Hz, 2H), 12.01 (brs, 1H); 13C NMR
(DMSO-d6, 100 MHz) δ: 55.07, 113.75, 113.79, 114.02,
126.64, 128.71, 129.35, 132.44, 143.69, 172.01; IR
(neat) ν: 2932.21, 2835.92, 1650.62, 1613.37, 1573.65,
1494.35, 1297.54, 1247.29, 1178.54, 1029.62, 831.13,
2, Entry 15): m.p. 243—245 ℃; H NMR (DMSO-d6,
400 MHz) δ: 2.36 (s, 3H), 7.19—7.27 (m, 4H), 7.29 (d,
J＝8.1 Hz, 2H), 7.50—7.54 (m, 4H), 7.95 (d, J＝8.1 Hz,
2H), 12.66 (brs, 1H); 13C NMR (DMSO-d6, 100 MHz) δ:
20.89, 125.17, 129.27, 144.29, 145.61, 170.32; IR (neat)
ν: 3047.66, 1612.10, 1517.42, 1499.79, 1219.84,
1154.86, 1094.16, 970.89, 823.93, 728.59, 658.72,
－
1
609.69 cm . Anal. calcd for C22H16F2N2: C 76.29, H
4.66, N 8.09, F 10.97; found C 76.07, H 4.75, N 7.91, F
10.83.
2,4,5-Tri(4-fluorophenyl)imidazole (Table 2, Entry
16): m.p. 162—164 ℃; 1H NMR (DMSO-d6, 400 MHz)
δ: 7.28—7.44 (m, 6H), 7.66—7.72 (m, 4H), 8.15 (dd,
J ＝ 8.8, 5.5 Hz, 2H), 12.73 (brs, 1H); 13C NMR
(DMSO-d6, 100 MHz) δ: 115.72, 115.94, 116.09, 116.31,
123.09, 124.50, 128.65, 129.01, 129.82, 158.66, 162.35;
IR (neat) ν: 1606.13, 1513.02, 1498.80, 1220.23,
－
1
729.04, 639.69 cm . Anal. calcd for C23H19ClN2O2: C
70.68, H 4.90, N 7.17, Cl 9.07; found C 70.49, H 5.04,
N 6.99, Cl 8.89.
4,5-Di(4-anisyl)-2-(4-fluorophenyl)imidazole
(Table 2, Entry 11): m.p. 126—129 ℃; 1H NMR
(DMSO-d6, 400 MHz) δ: 3.77 (s, 6H), 6.83—7.04 (m,
4H), 7.30 (t, J＝8.8 Hz, 2H), 7.44 (d, J＝7.6 Hz, 4H),
8.10 (dd, J＝8.8, 5.5 Hz, 2H), 12.53 (brs, 1H); 13C
NMR (DMSO-d6, 100 MHz) δ: 55.04, 113.79, 113.91,
115.47, 127.15, 127.18, 143.98, 160.74, 163.17, 172.02;
IR (neat) ν: 2933.24, 1650.05, 1614.17, 1551.75,
1509.43, 1498.37, 1242.47, 1171.29, 1030.63, 833.59,
－
1
1156.08, 1095.86, 965.90, 830.00, 740.76, 659.24 cm .
Anal. calcd for C21H13F3N2: C 71.99, H 3.74, N 8.00, F
16.27; found C 71.78, H 3.87, N 7.89, F 16.05.
4,5-Di(4-fluorophenyl)-2-(3-indolyl)imidazole
(Table 2, Entry 17): m.p. 303—305 ℃; 1H NMR
(DMSO-d6, 400 MHz) δ: 6.93—7.01 (m, 4H), 7.10—
7.14 (m, 2H), 7.26 (d, J＝7.82 Hz, 1H), 7.34—7.43 (m,
4H), 7.78 (d, J＝2.5 Hz, 1H), 8.27 (d, J＝7.3 Hz, 1H),
11.19 (s, 1H), 12.12 (brs, 1H); 13C NMR (DMSO-d6,
100 MHz) δ: 106.68, 115.20, 119.70, 121.41, 121.85,
123.75, 125.00, 128.63, 130.27, 135.56, 143.69, 163.65,
165.27; IR (neat) ν: 3425.31, 3055.92, 1614.17, 1591.07,
1515.87, 1503.57, 1409.97, 1334.10, 1225.69, 1157.76,
1093.83, 936.77, 835.74, 750.20, 741.96, 725.28,
－
1
808.11, 729.48, 660.80, 608.77 cm . Anal. calcd for
C23H19FN2O2: C 73.78, H 5.11, N 7.48, F 5.07; found C
73.56, H 5.18, N 7.27, F 4.88.
4,5-Di(4-anisyl)-2-(4-methylthiophenyl)imidazole
(Table 2, Entry 12): m.p. 112—114 ℃; 1H NMR
(DMSO-d6, 400 MHz) δ: 2.47 (s, 3H), 3.72 (s, 6H),
6.84—6.94 (m, 4H), 7.29 (d, J＝8.3 Hz, 2H), 7.39 (d,
J＝8.6 Hz, 4H), 7.95 (d, J＝8.3 Hz, 2H), 12.42 (brs,
1H); 13C NMR (DMSO-d6, 100 MHz) δ: 21.05, 55.07,
113.84, 113.89, 125.47, 125.83, 127.07, 138.05, 144.49,
172.02; IR (neat) ν: 2960.60, 2837.95, 1650.20, 1613.39,
1573.89, 1503.20, 1390.47, 1298.51, 1251.79, 1180.16,
－
1
657.93, 608.49 cm . Anal. calcd for C23H15F2N3: C
74.38, H 4.07, N 11.31, F 10.23; found C 74.19, H 4.15,
N 11.10, F 10.02.
－
1
1029.22, 837.93, 724.34, 637.61 cm . Anal. calcd for
C24H22N2O2S: C 71.62, H 5.51, N 7.95, S 7.97; found C
71.41, H 5.63, N 6.77, S 7.81.
Acknowledgement
4,5-Di(4-anisyl)-2-(2-thienyl)imidazole (Table 2,
Entry 13): m.p. 137—139 ℃ (Lit.38 139.5—140.5 ℃);
1H NMR (DMSO-d6, 400 MHz) δ: 3.77 (s, 6H), 6.85—
7.04 (m, 4H), 7.12—7.14 (m, 1H), 7.42 (d, J＝8.6 Hz,
4H), 7.53 (dd, J＝5.0, 1.3 Hz, 1H), 7.66 (dd, J＝3.5, 1.0
Hz, 1H), 12.61 (brs, 1H); 13C NMR (DMSO-d6, 100
MHz) δ: 55.07, 113.83, 114.00, 123.83, 125.88, 127.84,
128.16, 129.49, 129.75, 134.20, 140.90, 172.02.
We are thankful to the Persian Gulf University Re-
search Council for the partial support to this work, Prof.
E. J. Thomas research group for running FT-IR, and
NMR, and Dr Mohammad Reza Shamsaddini for his
helpful comments.
References
4,5-Di(4-anisyl)-2-(3-indolyl)imidazole (Table 2,
Entry 14): m.p. 136—139 ℃; 1H NMR (DMSO-d6, 400
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7.20 (m, 2H), 7.44—7.51 (m, 5H), 7.97 (d, J＝2.52 Hz,
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