Europium triflate-catalyzed one-pot synthesis of 2,4,5-trisubstituted-1H- imidazoles via a three-component condensation

Article abstract of DOI:10.1080/00397910701483589

A simple, efficient, and practical procedure for synthesis of 2,4,5-trisubstituted-1H-imidazoles via the condensation of benzoin or acetoin, aromatic aldehydes, and ammonium acetate using europium triflate [Eu(OTf)3] as a novel catalyst in high yields is described. The catalyst can be recovered conveniently and reused at least four times without any loss of activity. Copyright Taylor & Francis Group, LLC.

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Europium Triflate–Catalyzed
One‐Pot Synthesis of
2,4,5‐Trisubstituted‐1H‐imidazoles via a
Three‐component Condensation
a
a
a
a
Chuanming Yu , Min Lei , Weike Su & Yuanyuan Xie
a
College of Pharmaceutical Sciences, Zhejiang University of Technology,
Zhejiang Key Laboratory of Pharmaceutical Engineering , Hangzhou, China
Published online: 05 Oct 2007.
To cite this article: Chuanming Yu , Min Lei , Weike Su & Yuanyuan Xie (2007) Europium Triflate–Catalyzed
One‐Pot Synthesis of 2,4,5‐Trisubstituted‐1H‐imidazoles via a Three‐component Condensation, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:19,
3301-3309, DOI: 10.1080/00397910701483589
To link to this article: http://dx.doi.org/10.1080/00397910701483589
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Synthetic Communications , 37: 3301–3309, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701483589
Europium Triflate–Catalyzed One-Pot
Synthesis of 2,4,5-Trisubstituted-1H-
imidazoles via a Three-component
Condensation
Chuanming Yu, Min Lei, Weike Su, and Yuanyuan Xie
College of Pharmaceutical Sciences, Zhejiang University of Technology,
Zhejiang Key Laboratory of Pharmaceutical Engineering,
Hangzhou, China
Abstract: A simple, efficient, and practical procedure for synthesis of 2,4,5-trisubsti-
tuted-1H-imidazoles via the condensation of benzoin or acetoin, aromatic aldehydes,
3
and ammonium acetate using europium triflate [Eu(OTf) ] as a novel catalyst in
high yields is described. The catalyst can be recovered conveniently and reused at
least four times without any loss of activity.
Keywords: acetoin, aromatic alderhydes, benzoin, europium triflate, 2,4,5-trisubsti-
tuted-1H-imidazoles
Imidazole derivatives are a very interesting class of heterocyclic compounds
[1]
because they are found in many pharmacologically active substances.
number of biologically active therapeutics contain an imidazole ring in their
A
[
chemical structures. For example, it is reported that substituted imidazoles
2]
[3]
can act as glucagon receptor antagonists. Furthermore, the newly designed
[4]
imidazoles show potent anti-candida activity. The interesting biological
properties of imidazoles prompted us to search for a more efficient method
for preparation of this heterocyclic nucleus.
Received December 21, 2006
Address correspondence to Weike Su, College of Pharmaceutical Sciences,
Zhejiang University of Technology, Zhejiang Key Laboratory of Pharmaceutical
Engineering, Hangzhou 310014, China. E-mail: leyme@msn.com
3
301

3
302
C. Yu et al.
Because of their wide range of pharmacological activity and industrial and
synthetic applications, the synthesis of imidazoles has received considerable
attention, and many articles have appeared. Methods of synthesis of imidazoles
include a four-component condensation using Wang’s resin in refluxing
[
5]
acetic acid; condensation of 1,2-diketones, aldehydes, primary amines, and
[6]
[7]
ammonium acetate in phosphoric acid and in acetic acid; using an organ-
[
8]
[9]
4
ocatalyst in acetic acid, as well as in H SO
[
and dimethyl sulfoxide
condensation of benzoin, aldehydes, and ammonium acetate in a
2
10]
(
DMSO);
variety of catalysts, such as molecular iodine,
[13]
MW)/silica gel/NaHSO ,
and condensation of two different isocyanides in the
presence of Cu O. However, many of these procedures suffer from disadvan-
[11]
[12]
[Hbim]BF4,
[15]
MW/Et N,
microwave
and MW/
[14]
(
MW/AcOH,
4
3
[
16]
Al O /NH OAC;
2
3
4
[
17]
2
tages, such as harsh reaction conditions, prolonged reaction times, high reaction
temperature, and low isolation yields, and the catalysts cannot be recovered and
reused in most of the existing methods.
During the past decade, rare-earth metal triflates have been found to be
unique Lewis acids. They are water-tolerant, reusable catalysts, and they can
effectively promote several carbon–carbon and carbon–heteroatom bond
[
18]
formation in good yields.
the use of Eu(OTf) as a catalyst for the preparation of 2,4,5-trisubstituted-1H-
In our most recent work, we have investigated
3
imidazoles 3 by condensation of benzoin or acetoin 1, aromatic aldehydes 2,
and ammonium acetate in alcohol. We found that Eu(OTf)3 as a
recyclable and reused catalyst was a suitable alternative catalyst. Herein, we
report our results as shown in Scheme 1. To the best of our knowledge, this is
the first report on the use of Eu(OTf) as a catalyst for the synthesis of imidazoles.
3
First, the mixture of benzoin 1a, benzaldehyde 2a, and ammonium acetate
was chosen as the model reaction to detect whether the use of Eu(OTf) was
3
efficient. The reaction was carried out simply by mixing Benzoin 1a, benzal-
dehyde 2a, and ammonium acetate in alcohol as solvent in the presence of a
catalytic amount of Eu(OTf) (1 mol%). The mixture was stirred at 608C for
3
1
h, and the 2,4,5-triphenyl-1H-imidazole 3a was obtained in 64% yield.
Encouraged by the result, we studied different reaction parameters, and the
results are summarized in Table 1. Only a trace amount of the target product
was observed when the mixture of benzoin 1a, benzaldehyde 2a, and
ammonium acetate was stirred under similar conditions in the absence of
Eu(OTf) even after heating for 2 h (Table 1, entry 1), thus highlighting the
3
Scheme 1.

Synthesis of 2,4,5-Trisubstituted-1H-imidazoles
3303
Table 1. Condensation of benzoin, benzaldehyde, and ammonium
a
acetate under different reaction conditions
Catalyst
(mol%)
Yield of 3a
b
(%)
Entry
Catalyst
Solvent
1
2
None
Eu(OTf)3
Eu(OTf)3
—
1
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
CHCl3
THF
Trace
64
94,94,93,92
c
3
5
4
5
6
7
8
9
Eu(OTf)
Eu(OTf)
3
3
10
20
5
93
94
62
67
91
32
88
93
82
77
Zn(OTf)2
Cu(OTf)
Y(OTf)
Eu(OTf)3
2
5
3
5
5
1
1
1
1
0
1
2
3
Eu(OTf)
Eu(OTf)
3
3
5
5
DMF
AcOEt
MeCN
Eu(OTf)3
Eu(OTf)
5
3
5
a
The reactions were carried out in the presence of benzoin
5 mmol), benzaldehyde (5 mmol), and ammonium acetate
(
(
12 mmol) in solvent (3 mL) at 608C for 1 h.
Isolated yield.
b
c
Catalyst was reused four times.
role of Eu(OTf) as a promoter. We have changed the amount of the Eu(OTf)3
3
from 1 to 20 mol%, finding that the yield of product 3a was improved as the
amount of Eu(OTf) increased from 1 to 5 mol%. The yield plateaued when
3
the amount of Eu(OTf)3 was further increased from 10 to 20 mol%.
Therefore, 5 mol% of Eu(OTf) was considered to be most suitable.
3
Furthermore, several metal triflates were investigated. Eu(OTf) showed
3
the best catalytic effect, whereas Zn(OTf) and Cu(OTf) showed relatively
2
2
lower catalytic effect. The investigation of reaction medium for the process
revealed that reaction solvent played a significant role in the model reaction.
To determine the most appropriate solvent, the reaction was examined using
ethanol, chloroform, acetonitrile, AcOEt, tetrahydrofuran (THF), and
dimethylformamide (DMF). Ethanol was the best solvent in terms of yields.
The recyclable character of Eu(OTf) was also investigated. Of particular
3
note was the fact that the catalyst was very easy to recover by simple filtration
from the reaction medium and could be reused without any loss of activity
(
Table 1, entry 3). Therefore, the best reaction condition was obtained using
mol% of Eu(OTf) in ethanol at 608C for 1 h.
5
3
Then, we selected the optimized reaction condition to examine the
universality of this catalyst’s application. A series of aromatic aldehydes
was selected to undergo the condensation in the presence of a catalytic
amount of Eu(OTf) (5 mol%) in alcohol at 608C (Table 2). We quickly
3

3
304
C. Yu et al.
a
Table 2. Eu(OTf)
3
-catalyzed synthesis of 2,4,5-trisubstituted-1H-imidazoles
b
c
Entry
1
1
2
Products
Yield (%) Mp (8C)
Benzoin 1a
Benzoin 1a
Benzoin 1a
3a
93
91
88
275–276
2
3
3b
3c
262–263
229–230
4
5
Benzoin 1a
Benzoin 1a
3d
3e
90
92
230–231
253–255
6
7
Benzoin 1a
Benzoin 1a
3f
84
83
263–264
250–251
3g
8
9
Benzoin 1a
Benzoin 1a
3h
3i
Trace
Trace
—
—
1
0
1
Benzoin 1a
Acetoin 1b
3j
82
74
238–239
245–247
1
3k
1
2
3
Acetoin 1b
Acetoin 1b
3l
80
83
223–224
283–285
1
3m
1
4
5
Acetoin 1b
Acetoin 1b
3n
3o
68
64
229–231
199–200
1
a
Reaction conditions: benzoin 1 (5 mmol), aldehydes 2 (5 mmol), and ammonium
acetate (12 mmol) in EtOH (3 mL) at 608C for 1 h.
Isolated yield.
b
c
Melting points were uncorrected.

Synthesis of 2,4,5-Trisubstituted-1H-imidazoles
3305
found that this one-step procedure worked well for a variety of aromatic
aldehydes. The aldehydes carrying electron-donating groups (Table 2,
entries 1–5) worked better than those carrying electron-withdrawing groups
(Table 2, entries 6–9). However, we obtained the main product 1,2,3,4-tetra-
phenyl-pyrazine 4 in 62% yield, when using the aldehydes carrying strong
electron-withdrawing groups (Table 2, entries 8 and 9). Only a trace
amount of imidazoles were observed and could not be isolated.
Although there are several papers reporting the synthesis of imidazole
derivatives using benzoin 1a, there are few reports in the literature using
acetoin 1b as starting material. We found that the reactions could proceed
smoothly when using acetoin 1b in good yields (Table 2, entries 11–15).
A probable mechanism for the synthesis involving benzoin or acetoin 1
may be postulated as shown in Scheme 2. It is possible that the Eu(OTf)3
may promote the formation of an a-amino ketone 5 and aryl aldimine 6,
which then condense to form an imidazoline 7, which is oxidized by air to
the imidazole 3. a-Amino ketone 5 also can undergo dimerization to form
2
,5-dihydro-pyrazine 8, which is oxidized by air to the pyrazine 4. We
have mentioned previously that the aldehydes carrying strong electron-with-
drawing groups always resulted in low yields. The probable reason was
that it was difficult for these aldehydes to form aryl aldimines, which meant
that the reaction could not proceed smoothly to afford the corresponding
products.
In conclusion, we have described a simple and efficient method for the
synthesis of 2,4,5-trisubstituted-1H-imidazoles using Eu(OTf) as a reusable
3
Scheme 2.

3
306
C. Yu et al.
catalyst. The method offers several advantages including high yields, environ-
mentally friendly procedure, short reaction times, simple workup procedure,
and easy isolation and recycling of the catalyst, which make it a useful
process for the synthesis of 2,4,5-trisubstituted-1H-imidazoles. Hence, it is
a useful addition to the existing methods.
EXPERIMENTAL
All reagents were commercial available and used without any purification. The
melting points were recorded on digital melting-point apparatus WRS-1B and
1
are uncorrected. H NMR spectra were recorded on Varian 400-MHz spec-
trometer. IR measurements were carried out with a Nicolet Aviatar-370 instru-
ment. Mass spectra were measured with a Thermo Finnigan LCQ-Advantage.
Elemental analyses (C, H, N, S) were performed on a Fisons EA 1110 CHNS
elemental analyzer.
General Procedure for the Preparation of 2,4,5-Trisubstituted-1H-
imidazoles 3
A mixture of benzoin or acetoin 1 (5 mmol), aryl aldehydes 2 (5 mmol),
ammonium acetate (12 mmol), Eu(OTf) (5 mol%), and EtOH (3 mL) was
3
added to a round-bottomed flask. The mixture was heated to 608C for 1 h.
After cooling to room temperature, the reaction was quenched by AcOEt
(
30 mL) and stirred for 5 min. The solid catalyst was recovered by simple fil-
tration. The catalyst was rinsed with a little amount of AcOEt and dried at
508C for 2 h to give a white solid, which could be reused without loss of
activity. The organic liquid was washed with water (20 mL) and sat. aq. NaCl
20 mL). Then the organic layer was concentrated under reduced pressure to
1
(
give the course products 3. The coarse products were rinsed with a little cool
alcohol to obtain pure compounds 2,4,5-trisubstituted-1H-imidazoles 3.
Data
[
12]
1
2
,4,5-Triphenyl-1H-imidazole (3a): Mp 275–2768C (lit.
2758C). H
NMR (400 MHz, DMSO-d ): d 12.74 (brs, 1H, NH), 8.10 (d, 2H,
6
J ¼ 7.6 Hz, ArH), 7.36–7.55 (m, 13H, ArH). IR (KBr): 3037.9, 1488.6,
2
1
þ
1
461.2, 1128.1, 7125, 697.7 cm . MS (EI): m/z (%) ¼ 296 (46) [M ].
Anal. calcd. for C H N : C, 85.11; H, 5.44; N, 9.45. Found: C, 85.07; H,
21 16 2
5
.41; N, 9.52.
4
,5-Diphenyl-2-(4-hydroxyl-phenyl)-1H-imidazole (3b): Mp 262–2638C
[
19b]
1
(
lit.
268–268.58C). H NMR (400 MHz, DMSO-d ): d 12.41 (s, 1H,
6

Synthesis of 2,4,5-Trisubstituted-1H-imidazoles
3307
NH), 9.70 (s, 1H, OH), 7.90 (d, 2H, J ¼ 8.4 Hz, ArH), 7.54 (d, 2H,
J ¼ 7.6 Hz, ArH), 7.49 (d, 2H, J ¼ 7.2 Hz, ArH), 7.42 (t, 2H, J ¼ 7.6 Hz,
ArH), 7.35 (t, 1H, J ¼ 7.6 Hz, ArH), 7.29 (t, 2H, J ¼ 7.6 Hz, ArH), 7.21
(
t, 1H, J ¼ 7.2 Hz, ArH), 6.85 (d, 2H, J ¼ 8.4 Hz, ArH). IR (KBr): 3285.1,
2
1
3
059.0, 1702.2, 1609.5, 1493.8, 696.7 cm . MS (EI): m/z (%) ¼ 312 (40)
þ
[
M ]. Anal. calcd. for C H N O: C, 80.75;H, 5.16; N, 8.97. Found: C,
2
1 16 2
8
0.70;H, 5.18; N, 8.93.
4
(
,5-Diphenyl-2-(4-methyl-phenyl)-1H-imidazole (3c): Mp 229–2318C
[19a]
lit.
1
229–2318C). H NMR (400 MHz, DMSO-d ): d 12.65 (brs, 1H,
6
NH), 7.99 (d, 2H, J ¼ 8.0 Hz, ArH), 7.53 (d, 4H, J ¼ 7.6 Hz, ArH), 7.28–
7
8
.39 (m, 8H, ArH), 2.35 (s, 3H, CH ). IR (KBr): 3030.1, 1493.9, 1449.7,
3
21
þ
23.3, 764.8, 695.7 cm . MS (EI): m/z (%) ¼ 310 (40) [M ]. Anal. calcd.
for C H N : C, 85.13;H, 5.85; N, 9.03. Found: C, 85.09;H, 5.82; N, 9.09.
22 18 2
4
,5-Diphenyl-2-(4-methoxy-phenyl)-1H-imidazole (3d): Mp 221–2228C
[12] 1
(lit.
2228C). H NMR (400 MHz, DMSO-d ): d 12.53 (brs, 1H, NH),
6
8
.02 (d, 2H, J ¼ 8.0 Hz, ArH), 7.52 (d, 4H, J ¼ 6.8 Hz, ArH), 7.30–7.37
(
m, 6H, ArH), 7.05 (d, 2H, J ¼ 7.6 Hz, ArH), 3.82 (s, 3H, CH ). IR (KBr):
3
2
1
3
028.9, 1613.5, 1493.4, 1249.1, 1030.6, 695.7 cm . MS (EI): m/z
þ
(
%) ¼ 326 (36) [M ]. Anal. calcd. for C H N O: C, 80.96;H, 5.56; N,
2
2 18 2
8
.58. Found: C, 80.94;H, 5.53; N, 8.63.
2
2
-(4-N,N-Dimethyl-amino-phenyl)-4,5-diphenyl-1H-imidazole (3e): Mp
1
[
19b]
56–2578C (lit.
258–2598C). H NMR (400 MHz, DMSO-d ): d 12.35
6
(
brs, 1H, NH), 7.92 (d, 2H, J ¼ 8.4 Hz, ArH), 7.52 (d, 4H, J ¼ 7.2 Hz,
ArH), 7.36 (t, 4H, J ¼ 6.8 Hz, ArH), 7.28 (d, 2H, J ¼ 6.8 Hz, ArH), 6.80
(
d, 2H, J ¼ 8.4 Hz, ArH), 2.96 (s, 6H, CH ). IR (KBr): 3061.6, 1616.4,
3
2
1
þ
1
Anal. calcd. for C H N : C, 81.38;H, 6.24; N, 12.38. Found: C, 81.35;H,
508.5, 1496.7, 764.3, 696.1 cm . MS (EI): m/z (%) ¼ 339 (33) [M ].
23 21 3
6
.21; N, 12.44.
2
-(4-Chloro-phenyl)-4,5-diphenyl-1H-imidazole (3f): Mp 2261–2628C
[19b]
1
(lit.
261–2638C). H NMR (400 MHz, DMSO-d ): d 12.81 (brs, 1H,
6
NH), 8.11 (d, 2H, J ¼ 8.4 Hz, ArH), 7.22–7.58 (m, 12H, ArH). IR (KBr):
2
1
3
060.0, 1603.0, 1458.9, 1092.3, 766.0, 696.7 cm . MS (EI): m/z
þ
(
%) ¼ 330 (36), 332 (12) [M ]. Anal. calcd. for C H ClN : C, 76.24;H,
2
1
15
2
4
.57; N, 8.47. Found: C, 76.20;H, 4.55; N, 8.51.
1
4
NMR (400 MHz, DMSO-d ): d 12.71 (brs, 1H, NH), 8.13 (d, 2H,
,5-Diphenyl-2-(4-flouro-phenyl)-1H-imidazole (3g): Mp 250–2518C. H
6
J ¼ 4.2 Hz, ArH), 7.54 (d, 4H, J ¼ 5.6 Hz, ArH), 7.25–7.40 (m, 8H, ArH).
2
1
IR (KBr): 3029.0, 1493.0, 1231.3, 835.5, 765.2, 695.7 cm . MS (EI): m/z
þ
(
%) ¼ 314 (44) [M ]. Anal. calcd. for C H FN : C, 80.24;H, 4.81; N,
2
1
15
2
8
.91. Found: C, 80.27;H, 4.79; N, 8.86.

3
308
C. Yu et al.
1
4
,5-Diphenyl-2-(2-furyl)-1H-imidazole (3j): Mp 238–2398C. H NMR
(
400 MHz, DMSO-d ): d 12.84 (brs, 1H, NH), 7.81 (d, 1H, J ¼ 1.6 Hz,
6
ArH), 7.50 (d, 4H, J ¼ 7.2 Hz, ArH), 7.20–7.44 (m, 6H, ArH), 6.98 (d, 1H,
J ¼ 3.2 Hz, ArH), 6.65 (dd, 1H, J ¼ 1.6 Hz, J ¼ 3.2 Hz, ArH). IR (KBr):
1
2
2
1
3
057.2, 1602.9, 1500.3, 1485.1, 739.6, 696.7 cm . MS (EI): m/z
þ
(
%) ¼ 286 (29) [M ]. Anal. calcd. for C H N O: C, 79.70;H, 4.93; N,
1
9 14 2
9
.78. Found: C, 79.66;H, 4.91; N, 9.74.
1
4,5-Methyl-2-phenyl-1H-imidazole (3k): Mp 245–2478C.
H NMR
(
400 MHz, DMSO-d ): d 12.27 (brs, 1H, NH), 7.88 (d, 2H, J ¼ 7.2 Hz,
6
ArH), 7.38 (t, 2H, J ¼ 7.2 Hz, ArH), 7.25 (t, 2H, J ¼ 7.2 Hz, ArH), 2.12
(
s, 6H, CH ). IR (KBr): 2918.7, 1597.2, 1465.3, 1404.2, 1126.1,
3
2
1
þ
7
06.9 cm . MS (EI): m/z (%) ¼ 172 (54) [M ]. Anal. calcd. for
C H N : C, 76.71;H, 7.02; N, 16.27. Found: C, 76.65;H, 7.04; N, 16.31.
11 12 2
1
2
-(4-Methoxy-phenyl)-4,5-methyl-1H-imidazole (3l): Mp 223–2248C. H
NMR (400 MHz, DMSO-d ): d 11.83 (s, 1H, NH), 7.77 (d, 2H, J ¼ 8.8 Hz,
6
ArH), 6.96 (d, 2H, J ¼ 8.8 Hz, ArH), 2.15 (s, 6H, CH ). IR (KBr): 2919.9,
3
2
1
1
618.9, 1543.7, 1497.3, 1251.7, 836.5 cm . MS (EI): m/z (%) ¼ 202 (48)
þ
[
M ]. Anal. calcd. for C H N O: C, 71.26;H, 6.98; N, 13.85. Found: C,
1
2 14 2
71.32;H, 6.96; N, 13.81.
4
2
,5-Dimethyl-2-(4-N,N-dimethyl-amino-phenyl)-1H-imidazole (3m): Mp
1
83–2858C. H NMR (400 MHz, DMSO-d ): d 11.74 (brs, 1H, NH), 7.67
6
(
d, 2H, J ¼ 8.4 Hz, ArH), 6.72 (d, 2H, J ¼ 8.4 Hz, ArH), 2.91 (s, 6H, CH ),
3
2
.08 (s, 6H, CH ). IR (KBr): 2914.7, 1616.1, 1493.6, 1225.2, 1006.8,
3
2
1
þ
8
24.2 cm . MS (EI): m/z (%) ¼ 215 (44) [M ]. Anal. calcd. for C H N :
1
3 17 3
C, 72.52;H, 7.96; N, 19.52. Found: C, 72.50;H, 7.99; N, 19.51.
1
4
,5-Dimethyl-2-(4-chloro-phenyl)-1H-imidazole (3n): Mp 229–2318C. H
NMR (400 MHz, DMSO-d ): d 12.20 (brs, 1H, NH), 7.86 (d, 2H,
J ¼ 8.4 Hz, ArH), 7.44 (d, 2H, J ¼ 8.4 Hz, ArH), 2.12 (s, 6H, CH ). IR
6
3
2
1
(
KBr): 2919.0, 1526.7, 1441.0, 1129.2, 1092.8, 833.3 cm . MS (EI): m/z
þ
(
%) ¼ 206 (55), 208 (17) [M ]. Anal. calcd. for C H ClN : C, 63.93;H,
1
1
11
2
5
.36; N, 13.55. Found: C, 63.90;H, 5.33; N, 13.59.
1
4
,5-Dimethyl-2-(4-flouro-phenyl)-1H-imidazole (3o): Mp 199–2008C. H
NMR (400 MHz, DMSO-d ): d 12.03 (brs, 1H, NH), 7.88 (dd, 2H,
J ¼ 8.4 Hz, J ¼ 5.6 Hz, ArH), 7.24 (t, 2H, J ¼ 8.4 Hz, ArH), 2.17 (s, 3H,
6
1
2
CH ), 2.08 (s, 3H, CH ). IR (KBr): 3047.9, 1619.6, 1540.8, 1228.9, 844.4,
3
3
2
1
þ
7
30.5 cm . MS (EI): m/z (%) ¼ 190 (49) [M ]. Anal. calcd. for
C H FN : C, 69.46;H, 5.83; N, 14.73. Found: C, 69.51;H, 5.81; N, 14.70.
1
1
11
2
1
1
,2,3,4-Tetraphenyl-pyrazine (4): Mp 249–2508C. H NMR (400 MHz,
DMSO-d ): d 7.61 (d, 8H, J ¼ 7.6 Hz, ArH), 7.28–7.34 (m, 12H, ArH). IR
6

Synthesis of 2,4,5-Trisubstituted-1H-imidazoles
3309
2
1
(
KBr): 3049.6, 1392.3, 1172.7, 1012.1, 764.6, 695.4 cm . MS (EI): m/z
þ
(
%) ¼ 384 (29) [M ]. Anal. calcd. for C H N : C, 87.47;H, 5.24; N, 7.29.
2
8 20 2
Found: C, 87.45;H, 5.20; N, 7.35.
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