L-Proline triflate as an efficient and reusable catalyst for the one-pot synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted imidazoles

Article abstract of DOI:10.3184/030823410X12698803608765

L-Proline triflate has been used as an efficient catalyst for an improved and rapid one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles in good yields. The benefit of this approach is its operational simplicity and the catalyst can be easily recovered and reused without any loss of activity.

Full text of DOI:10.3184/030823410X12698803608765

196 RESEARCH PAPER
APRIL, 196–199
JOURNAL OF CHEMICAL RESEARCH 2010
L-Proline triflate as an efficient and reusable catalyst for the one-pot
synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted
imidazoles
Jianjun Li, Shouwang Lin, Jiajia Dai and Weike Su*
Key Laboratory of Pharmaceutical Engineering of Ministry of Education, College of Pharmaceutical Sciences, Zhejiang University of
Technology, Hangzhou 310014, P. R. China
L-Proline triflate has been used as an efficient catalyst for an improved and rapid one-pot synthesis of 2,4,5-trisubsti-
tuted and 1,2,4,5-tetrasubstituted imidazoles in good yields. The benefit of this approach is its operational simplicity
and the catalyst can be easily recovered and reused without any loss of activity.
Keywords: L-proline triflate, multicomponent reaction, 2,4,5-trisubstituted imidazoles, 1,2,4,5-tetrasubstituted imidazoles
Imidazole derivatives are of considerable interest in the
pharmaceutical industry as well as in academia due to their
promising biological activities such as inhibitors of p38 MAP
kinase,1 B-Raf kinase,2 orally bioavailable HIV-1 protease
inhibitors,3 antitumour,4 therapeutic agents,5 plant growth regu-
lators,6 glucagon receptors7 and antibacterial agents.8 Thus, the
synthesis of this heterocyclic nucleus is of great interest.
Multicomponent reactions (MCRs) are one-pot processes
bringing together three or more components and show high
atom economy and operational simplicity. In recent years,
the synthesis of substituted imidazoles by the application of
MCRs has attracted wide attention, for its great contribution
to the convergent synthesis of complex and important
organic molecules from simple and readily available starting
materials.
Many methods have been developed for the synthesis of
2,4,5-trisubstituted imidazoles 1 by three-component cyclo-
condensation of a 1,2-diketone, α-hydroxyketone or α-ketom-
onoxime with an aldehyde and ammonium acetate, under
InCl3 · 3H2O,9 or tetrabutylammonium bromide (TBAB)10
catalysis. Similarly, the synthesis of 1,2,4,5-tetrasubstituted
imidazoles 2 has been carried out by a component condensa-
tion of a 1,2-diketone, α-hydroxyketone or α-ketomonoxime
with an aldehyde, primary amine and ammonium acetate
using microwaves,11 heteropoly acid,12 BF3/SiO2,13 silica gel/
NaHSO414 or K5CoW12O40 · 3H O15 and ionic liquids.16 Alth-
ough a variety of catalytic syst2ems have been introduced for
this cyclocondensation, many of these methodologies are asso-
ciated with one or more disadvantages such as relatively long
reaction times, environmentally unfriendly catalysts, or the
requirement for excess reagents or catalysts and harsh reaction
conditions.
As indicated in Table 1, the reaction proceeded sluggishly
and led to a poor yield in the absence of catalyst (Table 1, entry
1). Higher yields were obtained when L-proline triflate was
used as the catalyst in comparison to other triflates. Then, the
amount of L-proline triflate was decreased from 10 to 1 mol%,
but the yields of the product plateaued around 84% (Table 1,
entry 8). Hence, a larger amount of catalyst for the reaction
is unnecessary and 5 mol% is the optimal amount (Table 1
entry 7).
The choice of solvent is a very crucial factor for this
condensation. As both protic and aprotic solvents were tested,
it was found that methanol was significantly superior to other
alcoholic solvents (Table 1, entries 10 and 11) and protic sol-
vents were better than aprotic ones. It should be pointed out
that no product was obtained when water was used in this
reaction (Table 1, entry 15).
Next, a variety of aldehydes were examined to widen the
scope of this condensation under the optimised conditions.
The results showed that aromatic aldehydes (Table 2) produced
high yields, whereas aliphatic aldehydes gave lower yields. In
these MCRs, using benzoin instead of benzil also provided the
corresponding substituted imidazoles, but in 5–10% lower
yields.
On the basis of the above results, the reactions were extended
to the synthesis of N-substituted imidazoles via the one-pot,
four component condensation of benzil, aldehyde, primary
amine and ammonium acetate, as depicted in Table 3. A variety
of structurally diverse primary amines were evaluated for this
one-pot synthesis. Both aromatic and aliphatic primary amines
afforded the corresponding imidazoles in satisfactory yields.
Because of its excellent solubility and stability in water,
L-proline triflate can be easily recovered and separated from
the crude reaction product. In order to examine the activity of
recovered catalyst, L-proline triflate was reused more than 4
times (10 mmol scale) for the model reaction (Scheme 1). No
loss in activity was observed.
Recently, ammonium triflates,17–20 which are efficient, cost-
effective catalysts can be easily prepared and have been used
as readily available catalysts in a variety of organic reactions.
In continuation of our previous work on triflates, we report
here an efficient method for the synthesis of highly substituted
imidazoles in the presence of novel types of ammonium
triflates.
Initially, we chose benzil, benzaldehyde and ammonium
acetate (1:1:2) as the substrates in a model reaction to screen
the reaction conditions.
Finally, a possible mechanism is proposed and shown in
Scheme 4. There are two plausible pathways to generate the
product. In pathway I, the reaction proceeds through the
diamine intermediate [A]. It is proposed that the ammonium
triflate moiety19 of the catalyst facilitates the formation of [A]
by increasing the electrophilicity of the carbonyl group of the
Scheme 1
* Correspondent. E-mail: pharmlab@zjut.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2010 197
Table 1 The synthesis of 2, 4, 5-triphenylimidazole under different reaction conditionsa
Entry
Catalyst
Loading/mol%
Solvent
Temp./°C
Time/h
Yieldb/%
1
2
No catalyst
0
5
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
EtOH
i-PrOH
CHCl3
Toluene
CH3NO2
H2O
RT
RT
RT
RT
RT
RT
RT
RT
Reflux
RT
RT
RT
RT
RT
RT
24
12
12
12
12
12
12
12
12
12
12
12
12
24
24
25
72
Diphenylammonium triflate
Dicyclohexylammonium triflate
Tributylamine triflate
L-Proline
3
5
46
4
5
5
73
5
55
6
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
L-Proline triflate
10
5
88
7
89
8
1
84
9
5
85
10
11
12
13
14
15
5
70
5
54
5
40
5
32
5
trace
trace
5
a All reactions were run with 1.0 mmol benzil under different reaction conditions, the ratio of benzil: benzaldehyde: ammonium
acetate was 1: 1: 2.
b Isolated yield based on benzil.
Scheme 2
Table 2 The synthesis of 2, 4, 5-trisubstituted imidazoles with
Table 3 The synthesis of 1,2,4,5-tetrasubstituted imidazoles
a wide variety of aldehydesa
with a wide variety of primary aminesa
Entry R1
Products
Time/h
Yieldb/%
Entry R2
R3
Products Time/h Yieldb/%
1c
2
3
4
5
6
7
8
9
Ph
1a
1b
1c
1d
1e
1f
1g
1h
1i
12
12
13
13
12
15
13
12
13
89,87,89,90,88
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2a
2b
2c
2d
2e
2f
2g
2h
2i
12
12
11
12
12
13
11
13
11
85
83
79
62
76
75
78
76
71
4-NO2C6H4
4-MeOC6H
3,4-(CH O)42C6H3
3,4-(CH3)2C6H3
3-FC6H43
87
82
84
77
43
65
69
67
C6H5CH
4-CH3C62H4
4-ClC6H4
4-MeOC6H
Cyclohexy4l
HOCH2CH2
(CH3)2CH
(CH3) C
2-Thi3ophene
Cyclohexyl
4-NO2C6H4 Ph
a Reaction conditions: benzil: aldehyde: ammonium acetate =
1:1:2.
a Reaction conditions: 1,2-Diketone: aldehyde: primary amine:
ammonium acetate = 1:1:1:1.
b Isolated yield based on benzil.
c The catalyst was reused 4 times.
b Isolated yield based on benzil.
catalyst loading, cost efficiency and simplicity of operation. It
is thus a practical alternative to the existing procedures for the
synthesis of imidazoles.
aldehyde. Then, intermediate [A], in the presence of catalyst,
condenses with benzil to form [D], which in turn is dehydrated
to the trisubstituted imidazole. On the other hand, in pathway
II it is proposed that the aldehyde reacts with the amine to form
an imine intermediate [B], which then condenses with [C] to
form intermediate [D]. The latter is converted to the product by
dehydration.
In summary, the present procedure involving catalysis by
L-proline triflate (5 mol%) provides an efficient method for
the synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-
tetrasubstituted imidazoles by a one-pot, multicomponent
methodology. This protocol affords good yields with low
Experimental
Melting points were measured on a Büchi B-540 capillary melting
point apparatus and are uncorrected. IR spectra were recorded on a
Nicolet Aviatar-370 instrument, spectrometer using samples as KBr
plates. 1H NMR and 13C NMR spectra were recorded on a Varian 400
MHz instrument using DMSO-d6 as the solvent, and chemical shifts
are expressed in parts per million (ppm) using TMS as an internal
standard. Mass spectra were measured with a Trace Finnigan DSQ.
Scheme 3

198 JOURNAL OF CHEMICAL RESEARCH 2010
Scheme 4
High resolution mass spectra (HRMS) were measured on an Agilent
6210 TOF LC/MS using APCI (electrospray ionisation) techniques.
All spectral data of the products were identical to authentic samples.
4,5-Diphenyl-2-(4-nitrophenyl)-1H-imidazole (1b): White solid,
m.p. 237–238 °C (lit.10 M.p. 238–239 °C). IR (KBr, cm−1): 3456,
1
1640. H NMR (DMSO-d6, 400 MHz) δ: 7.24–8.44 (m, 14H), 12.61
(s, 1H). 13C NMR (DMSO-d6, 100 MHz) δ: 126.3, 128.0, 128.4, 128.5,
129.1, 130, 134.8, 135.8, 141.8. MS (ESI) m/z = 341 (M +).
4,5-Diphenyl-2-(4-methoxyphenyl)-1H-imidazole (1c): White solid,
m.p. 229–231 °C (lit.10 M.p. 228 °C). IR (KBr, cm−1): 3432, 1630. 1H
NMR (DMSO-d6, 400 MHz) δ: 3.82 (s, 3H), 7.04 (d, 2H, J = 9.2 Hz),
7.21–7.55 (m, 12H), 8.01(d, 2H, J = 8.4 Hz) 12.51 (s, 1H). 13C NMR
(DMSO-d6, 100 MHz) δ: 55.2, 114.1, 123.1, 126.4, 126.7, 127.0,
127.6, 128.1, 128.3, 128.6, 131.2, 135.3, 136.8, 145.6, 159.4. MS
(ESI): m/z = 326 (M+).
General procedure for the preparation of 2, 4, 5-trisubstituted
imidazoles
In a 50 mL round-bottom flask, benzil (1 mmol), an aldehyde
(1 mmol) and ammonium acetate (2 mmol) were stirred in the pres-
ence of of L-proline triflate (5 mol%) in methanol (5 mL) at room
temperature for the stipulated time. The reaction was monitored by
TLC. After the completion of the reaction, the mixture was diluted
with water and extracted with ethyl acetate. The organic layer was
washed with brine then it was dried over MgSO and evaporated.
Recrystallisation of the residue from ethyl acetate 4or elution from a
silica gel column (ethyl acetate-petroleum ether 1:16) afforded the
pure product.
2-(3,4-Dimethoxyphenyl)-4,5-diphenyl-1H-imidazole (1d): White
solid, m.p. 214–215 °C (lit.9 M.p. 215 °C). IR (KBr, cm−1): 3446,
1
1633. H NMR (DMSO-d , 400 MHz) δ: 3.85 (s, 3H), 3.83 (s, 3H),
3.91 (s, 3H), 6.65–6.70 (6m, 2H) 7.20–7.53 (m, 10H), 7.95(d, 1H,
J = 8.8 Hz) 11.73 (s, 1H). 13C NMR (DMSO-d , 100 MHz) δ: 55.4,
55.6, 98.4, 105.6, 112.0, 126.3, 127.1, 128.1, 6128.5, 129.8, 143.4,
157.2, 168.9. MS (ESI): m/z = 356 (M+).
General procedure for the preparation of 1,2,4,5-tetrasubstituted
imidazoles
In a 50 mL round-bottom flask, benzil (1 mmol), an aldehyde
(1 mmol), a primary amine (1 mmol) and ammonium acetate (1 mmol)
were stirred in the presence of of L-proline triflate (5 mol%) in meth-
anol (5 mL) at room temperature for the stipulated time. The reaction
was monitored by TLC. After completion of the reaction, the mixture
was diluted with water and extracted with ethyl acetate. The organic
layer was washed with brine then it was dried over MgSO and evapo-
rated. Recrystallisation of the residue from ethyl acetat4e or elution
from a silica gel column (ethyl acetate-petroleum ether 1:16) afforded
the pure product.
2-(3,4-Dimethylphenyl)-4,5-diphenyl- 1H-imidazole (1e): White
solid, m.p. 234 °C. IR (KBr, cm−1): 3415, 1617. 1H NMR (DMSO-d6,
400 MHz) δ: 2.27–2.51 (m, 6H), 7.20–7.56 (m, 11H), 7.80 (d, 1H,
J = 7.6 Hz), 7.90 (s, 1H) 12.57 (s, 1H). 13C NMR (DMSO-d6, 100
MHz) δ: 19.2, 19.5, 122.7, 126.2, 126.4, 127.1, 127.6, 128.0, 128.1,
128.4, 128.7, 129.8, 136.5, 145.8. MS (ESI): m/z = 324 (M+). HRMS
(ESI): m/z Calcd for C23H20N2: 324.1626. Found: 324.1610.
4,5-Diphenyl-2-(3-fluorophenyl)-1H-imidazole (1f): White solid,
1
m.p. 285 °C. IR (KBr, cm−1): 3412, 1633. H NMR (DMSO-d6, 400
MHz) δ: 7.20–7.56 (m, 12H), 7.91(m, 2H) 12.82 (s, 1H). 13C NMR
(DMSO-d6, 100 MHz) δ: 111.5, 111.7, 114.8, 115.0, 121.2, 126.6,
127.1, 128.0, 128.2, 128.4, 128.7, 130.9, 132.5, 132.6, 135.0, 137.3,
144.2, 161.3, 163.7. MS (ESI): m/z = 314 (M+). HRMS (ESI): m/z
Calcd for C H15N2F: 314.1219. Found: 314.1210.
General procedure for the preparation of L-proline triflate
L-Proline (20 mmol, 2.3 g) was dissolved in water (10 mL) cooled in
ice-salt bath. Then trifuoromethanesulfonic acid (3.0 g, 20 mmol) in
aqueous solution was added dropwise. The mixture was stirred for 2 h
at 0 °C. The residue was extracted with petroleum ether three times.
The combined organic layers were evaporated under reduced pressure
to afford the pure L-proline triflate 5.0 g (95 % yield).
2-(1,1-D2i1methylethyl)-4,5-diphenyl-1H-imidazole (1g): White
solid, m.p. 198–200 °C. IR (KBr, cm−1): 3325, 1623. 1H NMR
(DMSO-d6, 400 MHz) δ: 1.37 (s, 9H), 7.17–7.45 (m, 10H), 11.82 (s,
1H). 13C NMR (DMSO-d6, 100 MHz) δ: 29.5, 32.6, 127.0, 127.3,
128.0, 128.5, 155.4. MS (ESI): m/z = 276 (M+). HRMS (ESI): m/z
Calcd for C19H20N2: 276.1626. Found: 276.1630.
General procedure for recycling of L-proline triflate
After the completion of the reaction, the mixture was diluted with
water and extracted with ethyl acetate. The organic layer was washed
with water (10 mL). The combined water layers were collected and
concentrated to afford the recycled catalyst.
2,4,5-Triphenyl-1H-imidazole (1a): White solid, m.p. 270–272 °C
(lit.9 M.p. 269 °C). IR (KBr, cm−1): 3446, 1631. 1H NMR (DMSO-d6,
400 MHz) δ: 7.21–7.56 (m, 13H), 8.09 (d, 2H, J = 8.4 Hz) 12.68 (s,
1H). 13C NMR (DMSO-d6, 100 MHz) δ: 125.4, 126.7, 127.4, 127.8,
128.2, 128.4, 128.5, 128.7, 130.4, 131.2, 135.2, 137.3, 137.3, 145.6.
MS (ESI): m/z = 296 (M+).
4,5-Diphenyl-2-(2-thienyl)-1H-imidazole (1h): White solid, m.p.
1
265–267 °C. IR (KBr, cm−1): 3414, 1618. H NMR (DMSO-d6, 400
MHz) δ: 7.15 (d, 1H, J = 3.6 Hz), 7.16-7.69 (m, 11H), 7.70 (d, 1H,
J = 1.2 Hz), 12.80 (br, s, 1H). 13C NMR (DMSO-d , 100 MHz) δ:
124.2, 126.2, 127.2, 127.9, 128.4, 133.9, 141.5. MS (6ESI): m/z = 302
(M+). HRMS (ESI): m/z Calcd for C19H14N2S: 302.0878. Found:
302.0871.
2-Cyclohexyl-4,5-diphenyl-1H-imidazole (1i): White solid, m.p.
1
240–241 °C. IR (KBr, cm−1): 3414, 1633. H NMR (DMSO-d6, 400

JOURNAL OF CHEMICAL RESEARCH 2010 199
MHz) δ: 1.22–1.40 (m, 3H), 1.53–1.62 (m, 2H), 1.67–1.70 (m, 1H),
1.78–1.95 (m, 2H), 1.95–1.99 (m, 2H), 2.65–2.72 (m, 1H), 7.17–
7.47(m, 10H), 11.92(s, 1H). 13C NMR (DMSO-d6, 100 MHz) δ: 25.6,
25.7, 31.5, 37.2, 126.6, 127.4, 128.3, 152.4. MS (ESI): m/z = 302
(M+). HRMS (ESI): m/z Calcd for C21H22N2: 302.1783. Found:
302.1789.
1,2,4,5-Tetraphenylimidazole (2a): White solid, m.p. 215–217 °C
(lit.9 M.p. 216–217 °C). IR (KBr, cm−1) 1600, 1579. 1H NMR (DMSO-
d6, 400 MHz) δ: 7.18–7.20 (m, 1H), 7.23–7.39(m, 17H), 7.40–7.51(m,
2H). 13C NMR (DMSO-d6, 100 MHz) δ: 125.2, 126.5, 127.8, 128.3,
128.5, 128.7, 130.3, 131.1, 135.2, 137.1, 145.5. MS (ESI): m/z = 372
(M+).
(DMSO-d6, 100 MHz) δ: 123.5, 126.4, 126.8, 128.2, 128.5, 128.6,
128.7, 128.8, 129.2, 129.5, 129.8, 131.1, 132.8, 133.9, 135.1, 136.2,
136.3, 137.8, 143.8, 146.7. MS (ESI): m/z = 417 (M+).
We are grateful to the National Natural Science Foundation of
China (No. 20806073), Science & Technology Projects
of Zhejiang (2008C11046) and the Opening Foundation of
Zhejing Provincial Top Key Pharmaceutical Discipline for
financial support.
Received 29 December 2009; accepted 15 March 2010
Paper 100935 doi: 10.3184/030823410X12698803608765
Published online: 30 April 2010
1-Benzyl-2,4,5-triphenyl-1H-imidazole (2b): White solid, m.p.
1
160–162 °C (lit.9 m.p. 159–160 °C). IR (KBr, cm−1): 1601, 1581. H
NMR (DMSO-d6, 400 MHz) δ: 5.16 (s, 2H), 6.77(d, 2H, J = 6.8 Hz),
7.14–7.17 (m, 6H), 7.29–7.31(m, 2H), 7.40–7.47(m, 8H), 7.65–7.67
(m, 2H). 13C NMR (DMSO-d6, 100 MHz) δ: 47.6, 58.0, 125.6, 126.1,
126.2, 127.1, 128.1, 128.5, 128.9, 130.1, 130.5, 130.7, 130.8, 134.5,
136.9, 137.3, 147.1. MS (ESI): m/z = 386 (M+).
1-p-Tolyl-2,4,5-triphenyl-1H-imidazole (2c): White solid, m.p.177–
179 °C. (lit.22 M.p. 183–184 °C). IR (KBr, cm−1): 3447, 1636. 1H
NMR (DMSO-d6, 400 MHz) δ: 2.26 (s, 3H), 7.20–7.39 (m, 17H), 7.48
(d, 2H, J = 7.3 Hz). 13C NMR (DMSO-d , 100 MHz) δ: 20.6, 126.3,
128.1, 128.2, 128.4, 129.6, 130.5, 131.1,6134.1, 134.4, 136.7, 138.1,
146.0. MS (ESI): m/z = 386 (M+).
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1-(4-Chlorophenyl)-2,4,5-triphenyl-1H-imidazole (2d): White
solid, m.p. 197–199 °C (lit.21 M.p. 196–199 °C). IR (KBr, cm−1):
1
3442, 1636. H NMR (DMSO-d6, 400 MHz) δ: 7.16–7.41 (m, 17H),
7.49 (d, 2H, J = 8.8 Hz). 13C NMR (DMSO-d6, 100 MHz) δ: 126.3,
126.6, 128.2, 128.3, 128.4, 128.6, 129.2, 130.2, 130.6, 131.2, 133.3,
134.2, 135.6, 136.9, 146.1. MS (ESI): m/z = 406 (M+).
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1-(4-Methoxyphenyl)-2,4,5-triphenyl-1H-imidazole (2e): White
solid, m.p. 185–186 °C. (lit.23 M.p. 180–182 °C). IR (KBr, cm−1):
3448, 1636. 1H NMR (DMSO-d , 400 MHz) δ: 3.70 (s, 3H), 6.85 (m,
2H, J = 9.2 Hz), 7.17–7.32 (m,613H), 7.49 (d, 2H, J = 7.2 Hz). 13C
NMR (DMSO-d6, 100 MHz) δ: 55.2, 114.1, 126.3, 126.4, 128.2,
128.3, 128.4, 128.5, 129.3, 129.9, 130.5, 131.1, 131.5, 134.5, 136.7,
146.2, 158.9. MS (ESI): m/z = 402 (M+).
1-Cyclohexyl-2,4,5-triphenyl-1H-imidazole (2f): White solid, m.p.
168–169 °C (lit.11 m.p. 167–169 °C). IR (KBr, cm−1): 3442, 1635. 1H
NMR (DMSO-d6, 400 MHz) δ: 0.57 (m, 1H), 0.91–1.01 (m, 2H),
1.40–1.55 (m, 5H), 1.87 (d, 2H, J = 11.2 Hz), 3.92 (m, 1H), 7.05–7.16
(m, 3H), 7.29–7.32 (d, 2H, J = 12 Hz), 7.48–7.62 (m, 10H). 13C NMR
(DMSO-d6, 100 MHz) δ: 24.7, 25.7, 33.0, 57.9, 125.9, 127.9, 128.8,
132.0, 134.7, 146.9. MS (ESI): m/z = 378 (M+).
8
9
M. Antolini, A. Bozzoli, C. Ghiron, G. Kennedy, T. Rossi and A. Ursini,
Bioorg. Med. Chem. Lett., 1999, 9, 1023.
S. Das Sharma, P. Hazarika and D. Konwar, Tetrahedron Lett., 2008, 49,
2216.
10 M.V. Chary, N.C. Keerthysri, S.V.N. Vupallapati, N. Lingaiah and S.
Kantevari, Catal. Commun., 2008, 9, 2013.
11 S. Balalaie and A. Arabanian, Green Chem., 2000, 2, 274.
12 M.M. Heravi, F. Derikvand and F.F. Bamoharram, J. Mol. Catal. A: Chem.,
2007, 263, 112.
13 B. Sadeghi, B.B.F. Mirjalili and M.M. Hashemi, Tetrahedron Lett., 2008,
49, 2575.
2-(2,4,5-Triphenyl-1H-imidazol-1-yl)ethanol (2g): White solid, m.
p.182–183 °C. IR (KBr, cm−1): 3425, 1636. 1H NMR (DMSO-d6,
400 MHz) δ: 3.17–3.37 (m, 2H), 4.00 (m, 2H), 4.90–4.93 (m, 1H),
7.10–7.21 (m, 3H), 7.41 (d, 2H, J = 8 Hz). 13C NMR (DMSO-d6,
100 MHz) δ: 46.5, 59.3, 126.1, 128.0, 128.5, 128.7, 129.1, 129.8,
131.0,131.1, 131.2, 134.7, 136.5, 147.1. MS (ESI): m/z = 340 (M+).
HRMS (ESI): m/z Calcd for C28H N2O: 340.1576. Found: 340.1654.
1-Isopropyl-2,4,5-triphenyl-1H2-2imidazole (2h): White solid, m.
p.179–180 °C (lit.11 M.p. 159–160 °C). IR (KBr, cm−1): 3445, 1634.
1H NMR (DMSO-d6, 400 MHz) δ: 1.04–1.20 (m, 6H), 4.36–4.43 (m,
1H), 7.06–7.16 (m, 2H), 7.23 (d, 2H, J = 7.6 Hz), 7.61–7.64 (m, 11H),
8.09 (d, 1H, J = 7.2 Hz). 13C NMR (DMSO-d6, 100 MHz) δ: 22.9,
49.1, 124.8, 125.0, 125.1, 125.2, 125.9, 127.8, 127.9, 128.9, 129.7,
132.1, 134.8, 136.8, 146.7. MS (ESI): m/z = 338 (M+).
14 A.R. Karimi, Z. Alimohammadi, J. Azizian, A.A. Mohammadi and M.R.
Mohammadizadeh, Catal. Commun., 2006, 7, 728.
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266, 104.
16 S.A. Siddiqui, U.C. Narkhede, S.S. Palimkar, T. Daniel, R.J. Lahoti and
K.V. Srinivasan, Tetrahedron, 2005, 61, 3539.
17 K. Ishihara, S. Nakagawa and A. Sakakura, J. Am. Chem. Soc., 2005, 127,
4168.
18 B. Karimi and M. Ghoreishi-Nezhad, J. Mol. Catal. A: Chem., 2007, 277,
262.
19 T. Funatomi, K. Wakasugi, T. Misaki andY. Tanabe, Green Chem., 2006, 8,
1022.
20 S.Z. Luo, J.Y. Li, H. Xu, L. Zhang and J.P. Cheng, Org. Lett., 2007, 9,
3675.
21 K. Buttke, H. Baumgartel, H.J. Niclas and M. Schneider, J. Prakt. Chem.,
1997, 339, 721.
22 A.E. Siegrist, Helv. Chim. Acta., 1967, 50, 906.
23 J. Heinze, H. Baumgärtel and H. Zimmermann, Chem. Ber., 1968, 101,
3504.
2-(4-Nitrophenyl)-1,4,5-triphenyl- 1H-imidazole (2i): Yellow solid,
m.p. 220–223 °C. (lit.21 m.p. 223–225 °C). IR (KBr, cm−1): 3445,
1634. 1H NMR (DMSO-d6, 400 MHz) δ: 7.19–7.40 (m, 13H), 7.52 (d,
2H, J = 8.8 Hz), 7.60–7.63 (m, 2H), 8.14–8.17 (m, 2H). 13C NMR

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