New conditions for the effective synthesis of tri and tetrasubstituted imidazoles catalysed by recyclable indium (III) triflate and magnesium sulfate heptahydrate

Article abstract of DOI:10.3184/174751914X13863406090407

A one-pot three or four component reaction of wide range of aromatic aldehydes, benzil, aliphatic and aromatic primary amines and ammonium acetate is reported for the synthesis of tri/tetra-substituted imidazoles under solvent-free conditions. Indium (III) trifluoromethanesulfonate and magnesium sulfate heptahydrate as two highly efficient and recyclable catalysts perform a key factor to synthesis of imidazole derivatives with high yields.

Full text of DOI:10.3184/174751914X13863406090407

JOURNAL OF CHEMICAL RESEARCH 2014
JANUARY, 41–45
RESEARCH PAPER 41
New conditions for the effective synthesis of tri and tetrasubstituted
imidazoles catalysed by recyclable indium (III) triflate and magnesium
sulfate heptahydrate
Bahador Karamia*, Roghayeh Ferdosianb and Khalil Eskandaric
aDepartment of Chemistry, PO Box 353, Yasouj University, Yasouj, 75918-74831, Iran
bDepartment of Chemistry, Gachsaran Branch, Islamic Azad University, Gachsaran, Iran
cYoung Researchers and Elites Club, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran
A one-pot three or four component reaction of wide range of aromatic aldehydes, benzil, aliphatic and aromatic primary amines
and ammonium acetate is reported for the synthesis of tri/tetra-substituted imidazoles under solvent-free conditions. Indium
(III) trifluoromethanesulfonate and magnesium sulfate heptahydrate as two highly efficient and recyclable catalysts perform a
key factor to synthesis of imidazole derivatives with high yields.
Keywords: catalyst, solvent-free, recyclable, cost effective, imidazole synthesis
Imidazole derivatives have received significant attentions in
recent years due to their pharmaceutical properties.1,2 Therefore,
highly efficient synthesis of these type of compounds in
green procedures have attractive interest for chemists. In this
research, an effective and eco-friendly procedure to synthesise
polysubstituted imidazoles was obtained by using indium (III)
trifluoromethanesulfonate and magnesium sulfate heptahydrate
as a highly efficient and recyclable catalysts under solvent free
conditions. The procedure not only originates the products
in excellent yields with shorter reaction times but also avoids
some problems such as catalyst cost, pollution, handling, and
safety.
properties when used both externally and internally.
Firstly, different methods for the synthesis of imidazoles
(compound 5a for example) were compared (Table 1). This
method not only gives the products in excellent yields with
short reaction times from a simple and safe procedure but also
avoids the problems associated with solvent use, pollution,
catalyst cost and handling.
To obtain optimum conditions for the synthesis of the desired
products, compound 5a was chosen as a model reaction. In the
presence of catalytic amounts of In(OTf)3, the mixture of benzil
(1 mmol),benzaldehyde(1 mmol),ammoniumacetate(1 mmol),
benzylamine (1 mmol) were reacted in different solvents
such as water, ethanol, methanol, chloroform, acetonitrile
and solvent-free conditions. From these experiments, it was
clearly demonstrated that solvent-free is the best condition
to accomplish this reaction (Table 2). The same results were
obtained when MgSO4.7H2O was used as catalyst.
Results and discussion
In connection with our studies on new catalysed organic
reactions,3–5 indium (III) trifluoromethanesulfonate and
magnesium sulfate heptahydrate were found to be powerful,
safe and recyclable catalysts for the one-pot condensation
reactiontotri/tetrasubstitutedimidazolederivatives. Especially,
MgSO4.7H2O is quite environmentally safe and has medicinal
In the absence of catalyst (up to 24 h stirring) with the
same conditions gave the desired product in trace yield
(12%). In catalyst-free conditions, and increasing the reaction
Table 1 Comparison of the results for the synthesis of 1-benzyl-2,4,5-triphenylimidazole (compound 5a) with other catalysts
Time/yield
Catalyst
Mol/%
Solvent/temp. /°C
Ref.
min/%
25/96
In(OTf)3
5
15
0.15 g
10
15
10
21
15
1
20
2 g
0.1
20
10
Solvent free/120
Solvent free/120
Solvent free/130
Solvent free/140
Solvent free/140
MeOH/r.t.
Solvent free/140
MeOH/60
Solvent free/140
CH3CN/r.t.
Present work
Present work
MgSO4.7H2O
50/94
120/91
120/90
120/90
444/79
120/80
510/86
120/85
60/86
NH4H2PO4/Al2O3
K5CoW12O40.3H2Oa
[(CH2)4SO3HMIM][HSO4]b
InCl3.3H2O
6
7
8
9
c
BF3.SiO2
10
11
12
13
14
15
16
17
L-Proline
AlPO4
ZrCl4
d
SiO2
SiO2
Solvent free, MW
CH2Cl2,Solar heat
Solvent free, MW
Solvent free/100
8/87
120/80
4/92
d
TFAe
I2
60/85
aPotassium dodecatugstocobaltate trihydrate.
b3-Methyl-1-(4-sulfonic acid)-butylimidazolium hydrogen sulfate.
cSilica-supported boron trifluoride.
dSilica gel as acidic support.
eTrifluoroacetic acid.
* Correspondent. E-mail: karami@mail.yu.ac.ir
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42 JOURNAL OF CHEMICAL RESEARCH 2014
Table 2 The effect of solvents in synthesis of 1-benzyl-2,4,5-
triphenylimidazole (compound 5a)
temperature (up to 200 °C), there was no improvement in yield.
Therefore, we found that the presence of the catalytic amount of
indium (III) trifluoromethanesulfonate (or magnesium sulfate
heptahydrate) and solvent-free condition are the best conditions
for this synthesis.
In another investigation, we evaluated the quantity of
catalyst required for the synthesis of tetrasubstituted imidazole
derivatives (compound 5a). From this experiment, maximum
yield of product was obtained when 5 mol% of In(OTf)3 or
15 mol% of MgSO4.7H2O were used. While for trisubstituted
imidazoles (6a was chosen as model reaction), the optimum
amount of catalyst is 5 mol% of In(OTf)3 or 10 mol% of
MgSO4.7H2O (Table 3).
Progressofthereactionwasexaminedatvarioustemperatures
in the presence of optimised amounts of catalysts to give the
best yield of product with short reaction times (Table 4). From
Table 4, 120 °C was chosen as optimal temperature in the
presence of In(OTf)3 or MgSO4.7H2O for tri and tetrasubstituted
imidazoles synthesis.
The reaction under optimal conditions with aromatic
aldehydes 1, ammonium acetate (2), benzil (3), aromatic
and aliphatic amine 4, and catalytic amount of In(OTf)3 or
MgSO4.7H2O and gave the tetrasubstituted imidazoles 5,
whereas in the absence of aromatic and aliphatic amine 4,
trisubstituted imidazoles 6 were obtained (Scheme 1.).
All products obtained (Table 5) were characterised by IR,
1H, 13C NMR, MS analyses for novel products (Figs S1–S48,
ESI), and known products were compared with their published
physical properties.
Entry
Solvent
Water
Ethanol
Time/min
Yield/%
46
75
78
49
1
2
3
4
5
6
90
35
40
120
80
25
Methanol
Chloroform
Acetonitrile
Solvent-free
73
96
Table 3 Optimisation of molar ratio of the catalysts in synthesis of tri and
tetrasubstituted imidazoles
Compound Compound
Compound Compound
6a 5a
In(OTf)
6a
5a
MgSO4.7H2O
/mol%
/mol%3 Time/yield Time/yield
Time/yield Time/yield
min/%
min/%
min/%
min/%
1
2
5
10
15
20
60/55
60/80
15/95
30/90
30/90
30/88
60/48
60/75
25/96
25/94
30/92
30/90
2
5
10
15
20
25
60/42
60/75
60/90
60/90
60/85
70/82
60/45
60/65
60/80
50/94
50/92
60/88
Table 4 Optimisation of temperature for model reaction
Compound Compound Compound Compound
6aa 5aa 6ab 5ab
Temp. /°Ca
Temp./°Cb
Time/yield Time/yield
Time/yield Time/yield
min/%
min/%
min/%
min/%
80
20/68
25/90
15/95
25/85
25/80
30/65
30/90
25/96
30/90
30/78
80
60/70
60/80
60/90
60/88
60/75
60/62
60/70
50/94
60/92
60/86
100
120
140
160
100
120
140
160
After determination of the suitable reaction conditions,
the scope of this MCR was examined using various starting
materials under standard conditions. It was found that both
electron rich and electron deficient aldehydes reacted well
(Table 5).
aIn(OTf)3 was used as catalyst.
bMgSO4.7H2O was used as catalyst.
Table 5 Catalytic synthesis of tri/tetra-substituted imidazoles under solvent-free conditions
MgSO4.7H2O
In(OTf)3
Time/yielda
min/%
Compound
Aldehyde
C6H5CHO
4-BrC6H4CHO
4-MeC6H4CHO
4-ClC6H4CHO
2-ClC6H4CHO
3-NO2C6H4CHO
4-MeC6H4CHO
4-OMeC6H4CHO
2-OH-5-BrC6H3CHO
4-Benzyloxy C6H4CHO
2,4-diClC6H3CHO
4-MeC6H4CHO
C6H5CHO
3-BrC6H4CHO
2-OHC6H4CHO
Amine
Time/yielda
min/%
M.p./°Clit.
5a
5b
5c
5d
5e
5f
5g
5h
5i
C6H5CH2NH2
C6H5CH2NH2
C6H5CH2NH2
C6H5CH2NH2
C6H5CH2NH2
C6H5CH2NH2
C6H11NH2
C6H5CH2NH2
4-ClC6H4NH2
C6H5CH2NH2
C6H5CH2NH2
C6H5NH2
50/94
30/92
80/94
60/90
30/88
45/85
45/75
60/86
33/92
80/82
85/80
60/88
60/90
35/85
60/86
60/88
50/85
45/75
55/90
60/80
45/90
50/90
25/96
20/90
50/92
25/92
20/92
30/90
25/88
40/90
25/98
60/96
60/90
30/90
15/95
10/88
15/90
25/92
15/88
20/80
25/97
25/88
10/94
10/92
162–164 (163–165)18
169–170 (170–172)12
156–158 (156–157)19
159–160 (157–158)19
139–140 (140–142)20
150–152b
160–161 (162–164)21
163–165 (164–165)22
156–158b
5j
5k
5l
138–139b
216–219b
182–184 (185–188)11
275–277 (276–278)18
120–122 (118–122)23
209–211 (209–210)24
207–209 (210–211)11
227–230 (228–230)18
6a
6b
6c
6d
6e
6f
6g
6h
6i
–
–
–
–
–
–
–
–
–
–
2-OMeC6H4CHO
4-OMeC6H4CHO
4-Benzyloxy C6H4CHO
Fluorene-2-carboxaldehyde
Indole-3-carboxaldehyde
4-ClC6H4CHO
25
235–236c
283–286b
311–313b
257–259 (257–260)26
308–309 (>295)27
6j
3-NO2C6H4CHO
aRefers to isolated yields.
bNovel compound.
cMelting point of this compound was not reported by author.
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JOURNAL OF CHEMICAL RESEARCH 2014 43
H
O
G
O
R2
O
NH4
H
N
R2NH2
4
Cat.
Solvent-free
120 °C
ii
N
N
CH3COONH4
2
1
Cat.
Solvent-free
120 °C
i
N
G
G
O
6
O
5
3
Cat.: In(OTf)3, i: 5 mol%; ii: 5 mol%, or MgSO4.7H2O, i: 10 mol%; ii: 15 mol%
Scheme 1 Catalytic-assisted synthesis of tri/tetra-substituted imidazole derivatives under solvent-free conditions.
Cl
Br
N
N
OH
5i
N
N
N
O
N
N
O2
ii
ii
ii
5f
5j
H
N
H
N
O
i
i
HN
O
N
N
6i
3
6g
H
O
NH2
O
O
O
ii
Cl
Cl
N
O
NH4
Solvent-free
120 °C
N
Cl
Cat.
Cl
5k
i: Solvent-free, 120 °C, Respective aldehyde, CH3COONH4, 5 mol% In(OTf)3 or 10 mol% MgSO4.7H2O
ii: Solvent-free, 120 °C, Respective aldehyde, Respective primary amine, CH3COONH4, 5 mol% In(OTf)3 or 15 mol%
MgSO4.7H2O
Scheme 2 Catalytic synthesis of novel tri and tetra-substituted imidazole derivatives.
Note that in this work, the six new compounds 5(f, i, j and k)
and 6(g and h) (Scheme 2) were synthesised and characterised
by FT-IR, 1H, 13C NMR, MS analyses, and elemental analysis.
Scheme 3 shows a probable mechanism for the synthesis of
imidazole derivatives (tetrasubstituted imidazole for example)
may be postulated as shown below which recyclability of
catalyst is observed.
As can be seen from Scheme 3, the catalyst (In(OTf)3
for example) activates the carbonyl group of aldehyde 1
to the nucleophilic attack of amine 4 which increases the
interaction between aldehyde and amine with a decrease
in the energy of the transition state. From this interaction,
intermediate 7 was formed and was stabilised by indium
(III) trifluoromethanesulfonate. Following this, the
nucleophilic attack of ammonia which in situ was generated
Recyclability of catalysts
After completion of the reaction, the catalyst, was separated
from the reaction mixture by filtering, washed with diethyl
ether, dried at 120 °C for 1 h, and reused in another reaction.
We found that indium (III) trifluoromethanesulfonate and
magnesium sulfate heptahydrate can be reused several times
(up to five times) without significant loss of activity. The results
of these observations are shown in Table 6 for a model reaction.
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44 JOURNAL OF CHEMICAL RESEARCH 2014
N
O
N
R2
H
G
5
G
1
H
2O
O
O
S
F
In3+
O
F
F
O
H
O
O
3
H
S
In3+
F
N
N
O
G
F
F
3
R2
OH
R2NH2
G
4
O
O
S
O
O
F
O
S
In3+
F
R2
H
O
F
F
R2
H
F
F
O
O
H2N
3
HN
O
O
O
G
7
NH2
G
S
In3+
F
O
8
3
F
F
2
H
2O
NH3
O
O
NH4
2
OH
O
Scheme 3 The suggested mechanism for the synthesis of tetrasubstituted imidazoles.
Tri/tetra-substituted imidazoles synthesis using In(OTf)3 and
MgSO4.7H2O; general procedure
from ammonium acetate (2) to the intermediate 7, gave the
intermediate 8. Condensation of intermediate 8 with activated
benzil (3) by indium (III) trifluoromethanesulfonate and
following dehydration, gave the corresponding imidazoles 5.
For tetrasubstituted imidazoles synthesis, In(OTf)3 (5 mol%)/
MgSO4.7H2O (15 mol%) was added to stirred mixture of aldehyde
(1 mmol), benzil (1 mmol), primary amine (1 mmol), ammonium
acetate (1 mmol) and heated at 120 °C for the time indicated in Table 5.
The progress of reaction was monitored by TLC on silica gel (SILG/
UV 254) plates (n-hexane, ethyl acetate 10:3). After completion of
reaction, the mixture was cooled to room temperature and washed
with water (50 mL) then was filtered to remove the catalyst and the
filtrate was concentrated in vacuum to afford the crude product
which was recrystallised from boiling EtOAc to afford the crystalline
pure product. For trisubstituted imidazoles synthesis primary amine
was replaced with ammonium acetate and progress of reaction was
monitored by TLC on silica gel (SILG/UV 254) plates (n-hexane, ethyl
acetate 5:1).
Experimental
1H, 13C NMR spectra were recorded on a FT-NMR Bruker Avance
1
ultra shield spectrometer (frequency line, 400.13 MHz for H NMR
and 100.62 MHz for 13C NMR.; solvents, CDCl3 and DMSO-d6). FT-IR
spectra were recorded in the matrix of KBr with JASCO FT-IR-680
plus spectrometer. Elemental analyses (C, H, N) were performed
with a Heraeus CHN-O-Rapid analyser. Mass spectra of the products
were obtained with a HP (Agilent technologies) 5937 Mass Selective
Detector. Melting points were measured on an electrothermal KSB1N
apparatus. TLC was performed on TLC-Grade silica gel-G/UV
254 nm plates (n-hexane, ethyl acetate). Chemicals were purchased
from Aldrich, Fluka and Merck chemical companies. Known
compounds were characterised by comparison with authentic samples
and combustion analyses.
5f: IR, ν/cm–1: 3061, 3026, 2308, 1601, 1521, 1497, 1350, 810, 730, 696.
1H NMR (400.13 MHz, DMSO-d6, δ): 5.19 (s, 2H), 6.89 (d, J=6.1 Hz,
2H), 7.21–7.63 (m, 14H), 8.04 (d, J=7.8 Hz, 1H), 8.23 (d, J=7.8 Hz, 1H),
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JOURNAL OF CHEMICAL RESEARCH 2014 45
8.57 (s, 1H). 13C NMR (100.62 MHz, DMSO-d6, δ): 47.4, 122.3, 122.6,
124.7, 125.7, 125.7, 126.7, 127.1, 127.8, 128.0, 128.6, 129.4, 129.93, 130.2,
131.6, 133.0, 133.5, 135.8, 144.2, 147.2. Anal. calcd for C28H21N3O2: C,
77.94; H, 4.91; N, 9.74; found: C, 77.87; H, 4.83; N, 9.62%. MS, m/z: 431
M+, 386, 340, 295, 190, 165, 134, 91, 57.
The authors are grateful from Yasouj University of Iran for
financial support of this work.
Received 9 August 2013; accepted 12 November 2013
Paper 1302116 doi: 10.3184/174751914X13863406090407
Published online: 8 January 2014
5i: IR, ν/cm–1: 3458, 3063, 1659, 1593, 1578, 1211, 1174, 1096. 1H NMR
(400.13 MHz, DMSO-d6, δ): 6.92–8.53 (m, 17H), 13.06 (s, 1H). 13C NMR
(100.62 MHz, DMSO-d6, δ): 115.2, 123.9, 125.5, 127.6, 134.3, 137.3,
139.3, 140.5, 151.3, 164.7, 166.9. Anal. calcd for C27H18BrClN2O: C,
64.62; H, 3.62; N, 5.58; found: C, 64.51; H, 3.53; N, 5.49%. MS, m/z: 502
M+, 267, 214, 193, 165, 75, 57.
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6h: IR, ν/cm–1: 3413, 3055, 1598, 1490, 1451. H NMR (400.13 MHz,
DMSO-d6, δ): 7.13–7.59 (m, 13H), 8.01 (d, J=2.4 Hz, 1H), 8.46 (d,
J=7.2 Hz, 1H), 11.40 (s, 1H), 12.4 (s, 1H). 13C NMR (100.62 MHz,
DMSO-d6, δ): 106.9, 112.1, 120.2, 121.9, 122.4, 124.5, 125.5, 127.4, 128.0,
128.9, 136.7, 144.1. Anal. calcd for C23H17N3: C, 82.36; H, 5.11; N, 12.53;
found: C, 82.29; H, 5.21; N, 12.40%. MS, m/z: 335 M+, 165, 142, 115, 77,
55.
Conclusions
New efficient method for the synthesis of tri/and tetrasubstituted
imidazoles is reported via three- or four-component reaction
in the presence of In(OTf)3/and MgSO4.7H2O catalysts in solid
phase conditions. Numerous tri/and tetrasubstituted imidazole
derivatives with good to excellent yields were obtained.
Electronic Supplementary Information
Spectral data have been deposited in the ESI available through:
stl.publisher.ingentaconnect.com/content/stl/jcr/supp-data.
JCR1302116_FINAL.indd 45
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