Synthesis of Novel Organosilicon Compounds Possessing Fully Substituted Imidazole Nucleus Sonocatalyzed by Fe-Cu/ZSM-5 Bimetallic Oxides

Article abstract of DOI:10.1080/00397911.2014.962056

An efficient four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles is described by one-step condensation of an aldehyde, benzil, ammonium acetate, and primary aromatic amine with nanostructure Fe-Cu/ZSM-5 bimetallic oxides in water under ultrasonic irradiation. The short reaction time, good yields, environmental friendly procedure, mild reaction conditions, and convenient operation are important advantage of this protocol. The products generated during the study have been utilized as substrates for synthesis of organosilicon-containing imidazoles. Synthesis of tris(triorganosilyl)methylimidazole derivatives were carried out using organolithium reagent (Me₃Si)₃CLi, prepared via metalation of (Me₃Si)₃CH with methyllithium in tetrahydrofuran, in excellent yields. GRAPHICAL ABSTRACT.

Full text of DOI:10.1080/00397911.2014.962056

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Synthesis of Novel Organosilicon Compounds Possessing
Fully Substituted Imidazole Nucleus Sonocatalyzed by
Fe-Cu/ZSM-5 Bimetallic Oxides
Kazem D. Safaa, Aynaz Feyzia, Maryam Allahvirdinesbata, Leila Sarchamia & Parvaneh
Nakhostin Panahib
a Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
b Department of Chemistry, Faculty of Science, University of Zanjan, Iran
Accepted author version posted online: 14 Oct 2014.
To cite this article: Kazem D. Safa, Aynaz Feyzi, Maryam Allahvirdinesbat, Leila Sarchami & Parvaneh Nakhostin Panahi
(2014): Synthesis of Novel Organosilicon Compounds Possessing Fully Substituted Imidazole Nucleus Sonocatalyzed by Fe-Cu/
ZSM-5 Bimetallic Oxides, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, DOI: 10.1080/00397911.2014.962056
To link to this article: http://dx.doi.org/10.1080/00397911.2014.962056
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Synthesis of Novel Organosilicon Compounds Possessing Fully Substituted
Imidazole Nucleus Sonocatalyzed by Fe-Cu/ZSM-5 Bimetallic Oxides
Kazem D. Safa1, Aynaz Feyzi1, Maryam Allahvirdinesbat1, Leila Sarchami1, Parvaneh
Nakhostin Panahi2
1Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz,
Iran, 2Department of Chemistry, Faculty of Science, University of Zanjan, Iran
Corresponding author: Email: dsafa@tabrizu.ac.ir
Abstract
An efficient four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles is described
by one-step condensation of an aldehyde, benzil, ammonium acetate and primary
aromatic amine with nanostructure Fe-Cu/ZSM-5 bimetallic oxides in water under
ultrasonic irradiation. The short reaction time, good yields, environmental friendly
procedure, mild reaction conditions and convenient operation are important advantage of
this protocol. The products generated during the study have been utilized as substrates for
synthesis of organosilicon-containing imidazoles. Synthesis of
tris(triorganosilyl)methylimidazole derivatives were carried out using organolithium
reagent (Me3Si)3CLi, prepared via metalation of (Me3Si)3CH with methyllithium in THF,
in excellent yields.
1

KEYWORDS: Substituted Imidazoles, Ultrasonic irradiation, Fe-Cu/ZSM-5,
Organosilicon
INTRODUCTION
Strategy of incorporating organosilicon moieties to molecules can provide a wealth of
chemical diversity and biological function for drugs discovery. [1] Silicon-containing
analogues are ordinarily more lipophilic than their carbon analogues, which can provide
several physiological benefits, including an increase bioavailability and better tissue and
cell penetration. Therefore the attachment of organosilyl groups has been led to augment
biological activity and reduce toxicity in a bid to enhance the therapeutic value of
existing drugs.[2,3] In recent years organosilicon compounds containing bulky ligands
such as (HMe2Si)3C or (Me3Si)3C, attached to metals or metalloid, have been widely used
which led to synthesis of stable compounds in novel chemistry.[4-7] Multicomponent
reactions are powerful tools in modern drug discovery processes, because they are an
important source of molecular diversity, allowing rapid, automated and high throughput
generation of organic compounds.[8] Imidazole scaffold-containing derivatives have
2

known to be an important five-membered nitrogen-containing heterocycles with
extensive application in many fields such as agrochemical as herbicide, fungicide, and
also as ionic liquids, anion sensors, electrical and optical materials, and photosensitive
compounds in photography. Moreover, they have many pharmacological properties and
play important roles in biochemical processes.[9,10] This versatile applicability highlights
the importance of access to effective synthetic routes to well benign highly substituted
imidazole derivatives. These compounds are generally synthesized in a four-component
condensation of aldehydes, 1,2-diketones, amines, and ammonium acetate in the presence
of various catalysts.[11-14] Ultrasound irradiation assisted organic synthesis (UAOS) is
proving to be more efficient and selectivity for improving the traditional reactions that
require longer reaction time, unsatisfactory yields, expensive reagents and high
temperatures. Now, the uses of acidic zeolites in different areas of the organic chemistry
have grabbed significant levels, not only for the possibility to perform environmentally
benign synthesis, but also for the good yields.[20] Various metal-supported zeolites such
as Cu-modified zeolites (H–USY, HY, H–Beta, Mordenite and ZSM-5), have been
successfully used in organic-chemical chemistry.[8] Herein we wish to report a mild,
simple, efficient, eco-friendly, economic method for preparation of fully substituted
imidazole derivatives in water under ultrasound irradiation via heterogeneous catalyzed
multicomponent reactions using Fe-Cu/ZSM-5. In continuation of our research interest in
the synthesis of useful heterocyclic compounds possessing imidazole core and
importance of organosilicon compounds, we have synthesized a series of new fully
substituted imidazoles containing bulky organosilicon groups, using (Me3Si)3CLi, in
which three organosilyl groups are attached to the central carbon atom.
3

RESULTS AND DISCUSSION
In an initial study, we focused on systematic evaluation of different transition metal
oxides supported on H-ZSM-5 for the model reaction of benzaldehyde (l mmol), benzil
(1mmol), 4-hydroxyaniline (1mmol) and NH4OAc (1.1 mmol), as ammonia source, in
water under ultrasonic irradiation (high intensity) (Table 1). In the absence of catalyst,
the reaction was incomplete even after 2 hr of sonication, though formation of a small
amount of 1a (20%) was observed. When the model reaction was carried out in the
presence of M/ZSM-5 (M: Co, Mn, Cr, Cu, V, Zn, Ni and Fe) monometallic catalysts
(5w.%) in water, the desired product 1a was isolated with 70% yield using Cu/ZSM-5.
However, no significant acceleration was observed. Based on our studies, incorporation
of different transition metals into copper-containing H-ZSM-5 was fabricated a series of
M-Cu/ZSM-5 (M: Cr, Mn, Co, Ni, V, Zn and Fe) bimetallic catalysts. Further the study
of catalytic ability of Fe-Cu/ZSM-5 catalyst showed that incorporating Fe over Cu/ZSM-
5 increased the product yield to 99% and reducing the reaction time (2 min) with
decrease the catalyst loading (3w.%). The reaction, performed under conventional stirring
without ultrasound, required a reaction time (30-60 min) clearly longer than those require
when ultrasound was used (2-6 min). (Table 1) The maximum activity of Fe-Cu/ZSM-5
for the synthesis of imidazoles can be attributed to the favorable synergetic effects of iron
and copper over H-ZSM-5. It is worthy to note that, ultrasound with frequencies less than
50 kHz and by used of solid catalysts in the reaction mixture has resulted in increase in
the reaction rate because of the local rise in the temperature and pressure due to the
cavitation of some bubbles next to the surface of the catalyst/reactants.[15] We
investigated the effect of various solvents on a model reaction under ultrasound
4

irradiation (ultrasonic probe). As can be seen from Table 2, the polar solvents afforded
better yield than the nonpolar ones and the best result was obtained in aqueous medium in
which Fe-Cu/ZSM-5 catalyst worked most efficiently by phasing out of the desired
product.
The requisite tetrasubstituted imidazoles were obtained using Fe-Cu/ZSM-5 catalyst
within two to four minutes in excellent yields. Aromatic aldehydes bearing either
electron-donating or electron-withdrawing groups reacted successfully and gave the
corresponding products in high yields. For more examination of the effect of ultrasound
irradiation in this reaction, comparison of the reaction under two methods, ultrasound
irradiation (method A) and reflux conditions (method B) were carried out. As shown in
Table 1, method A in comparison with method B is better in both yields and the reaction
times. The reason may be the phenomenon of cavitation produced by ultrasound
irradiation. Ultrasound-assisted reactions proceed by acoustic cavitation phenomenon,
that is, the formation, growth, and collapse of bubbles in the liquid medium. During the
collapse of a cavity, high local temperatures and pressures arise which lead to increase in
the rate of reactions.[15-19] Fully substituted imidazoles were prepared by the wide range
of substituted aldehydes under optimized reaction conditions in high to excellent yields
(Table 3, method A). Some of the compounds (1a, 1c, 1d, 1f, 1g, 1i, 1l) were confirmed
by IR, 1H NMR, 13C NMR and elemental analysis and other known compounds were
confirmed by making a comparison with the reported melting point in the literature.[25-28]
In the case of benzoin, comparable yields are possible as that of diketone only with
longer reaction times. After the completion of the reaction, the catalyst was washed with
5

water and ethanol. It was found that the catalyst could be reused for the next cycle
without any appreciable loss of its activity.
In our efforts to exemplify the usefulness of compounds generated during this study,
some of these compounds have been used for preparing highly substituted imidazoles
bearing bulky organosilicon groups using tris(organosilyl)methylmetals, with three
organosilyl groups attached to the central carbon atom. We have recently reported the
preparation and reaction of some compounds bearing organosilicon moieties.[4-7,21,22] Now
we were interested in extending these organosilicon groups in biological important
heterocyclic compounds with imidazole core. Therefore, we investigated the synthesis of
imidazoles bearing bulky organosilicon groups in the lateral side chain with ether bond.
Thus, some of bromoalkoxy-imidazoles were synthesized by treatment of the hydroxyl-
imidazoles with K2CO3 and dibromoalkanes in DMF (Scheme 1). The precursor for our
work was tris(trimethylsilyl)methane, (Me3Si)3CH, prepared from the reaction between
CHCl3, Li and Me3SiCl in THF. The solvated organolithium reagent, (Me3Si)3CLi, which
was obtained by treatment of (Me3Si)3CH with MeLi under reflux in THF [4,23], reacts
with bromoalkoxy-imidazoles in THF to give bulky organosilicon groups-containing
highly substituted imidazoles (Scheme 1). All of spectroscopic results indicated that the
nucleophilic substitution on bromo-imidazoles was complete.
CONCLUSION
This work demonstrates a novel, green, highly efficient and environmentally
methodology for the synthesis of fully substituted imidazole derivatives (1a-1l) in the
6

presence of Fe-Cu/ZSM-5 bimetallic oxides nanocatalyst via heterogeneous cyclo-
condensation of benzil with various aromatic aldehydes, ammonium acetate and various
aromatic amines in water under ultrasound irradiation. The bromo-imidazole derivatives
have been shown to be excellent substrate for obtaining the organosilicon-containing
imidazoles. (Me3Si)3C- groups were attached to the imidazoles by nucleophilic
substitution with (Me3Si)3CLi. Highly substituted imidazoles bearing bulky organosilicon
groups were obtained in excellent yields.
EXPERIMENTAL
Chemicals And Apparatus
Chemicals were either prepared in our laboratory or purchased from Merck, Fluka and
1
Aldrich. Commercial products were used without further purification. The H NMR and
13C NMR spectra were recorded with a Bruker FT-400 MHz spectrometer at room
temperature and with CDCl3 and/or DMSO-d6 as solvent. The FTIR spectra were
recorded on a Bruker Tensor 270 spectrometer. The reactions were carried out using an
ultrasonic processor probe (SONOPULS Ultrasonic homogenizers). The Elemental
analyses were carried out with an Elementar vario EL III instrument. The abbreviations
used for NMR signals are: s = singlet, d = doublet, t = triplet and m = multiplet. Melting
points were recorded on a Büchi B-545 apparatus in open capillary tubes and are
uncorrected.
PROCEDURE FOR PREPARATION OF NANOCATALYSTS
7

H-ZSM-5 obtained from Zeochem Int. with Si/Al = 50 was used for preparation of the
catalysts. All mono and bimetallic nanocatalysts were prepared through the excess-
solution impregnation method. The aim of this procedure is to deposit metal oxide on the
zeolite surface, whereas a proton exchange is not explicitly intended and with this
technique an accurate load of metal can be adjusted. The precursors of different metals
were NH4VO3, Zn(NO3)2.6H2O, Cu(NO3)2.3H2O, Ni(NO3)2.6H2O, Co(NO3)2.6H2O,
Cr(NO3)3.9H2O, Fe(NO3)3.9H2O, and Mn(NO3)2.4H2O. The metal content was kept at 5
wt.% for monometallic catalysts and for bimetallic catalysts the second metal content was
kept at 3 wt.%. At first, determined amount of precursors was dissolved in 30 mL of
mixture of distilled water and ethanol with volume ratio of 50%, and then the support of
H-ZSM-5 was added into the solution and suspension was stirred at 45 °C until the
solvent was totally evaporated. Subsequently, the catalysts were dried in an oven at 100
°C overnight and then calcinated at 550 °C for 4 h. Under these conditions complete
decomposition of metal nitrate into metal oxide occurs.[24]
TYPICAL PROCEDURE FOR THE SYNTHESIS OF 4-(2-(4-
CHLOROPHENYL)-4,5-DIPHENYL-1H-IMIDAZOL-1-YL)PHENOL (1C)
In a typical procedure, a mixture of benzil (1 mmol), 4-chlorobenzaldehyde (1 mmol), 4-
hydroxyaniline (1mmol), and ammonium acetate (1.1 mmol) as ammonia source and
3wt.% of Fe-Cu/ZSM-5 in 3 ml water was introduced in a 20 mL heavy walled pear-
shaped two necked flask with nonstandard tapered outer joint. The flask was attached to a
12 mm tip diameter probe and the reaction mixture was sonicated at ambient temperature
at 20% power of the processor. After completion of the reaction (monitored by TLC,
8

within 2-5 min), the solid product was filtered washed with water, dried and
recrystallised from ethanol. The supported reagent was washed thrice with water and
ethanol and dried under vacuum before reuse. The product was identified as 4-(2-(4-
chlorophenyl)-4,5-diphenyl-1H-imidazol-1-yl)phenol (1c) by spectral data. Spectral Data
White powder (99%), M.P. >280 °C, IR (KBr, cm−1): υmax = 3416, 3054, 2926, 1595,
1513 , 1478, 1440, 745, 695. 1H NMR (DMSO-d6, 400 MHz) δH: 6.67 (d, J = 8.4 Hz, 2H,
Ar-H), 7.05 (d, J = 8.4 Hz, 2H, Ar-H), 7.14-7.43 (m, 12H, Ar-H), 7.47 (d, J = 7.5 Hz,
2H, Ar-H), 9.82 (s, 1H, Ar-OH). (DMSO-d6, 100 MHz) δC: 115.69, 126.33, 126.46,
127.55, 128.15, 128.27, 128.37, 128.43, 129.37, 129.71, 129.74, 130.44, 131.10, 131.89,
132.98, 134.37, 136.76, 144.96, 157.42. Anal.Calc. for C27H19ClN2O: C, 76.68; H, 4.53;
N, 6.62%. Found: C, 76.49; H, 4.61; N, 6.58%.
TYPICAL PROCEDURE FOR THE SYNTHESIS OF 1-(4-(4-BROMOBUTOXY)
PHENYL)-2-(4-CHLOROPHENYL)-4,5-DIPHENYL-1H-IMIDAZOLE (2C)
In a typical procedure, a mixture of (1 mmol) 4-(2-(4-chlorophenyl)-4,5-diphenyl-1H-
imidazol-1-yl)phenol (1c) and (1 mmol) 1,4-dibromobutane in present of K2CO3 in 100
ml of dry DMF was stirred at room temperature for 24 h. Then DMF solvent was
evaporated in vacuum, and the residue was taken up in CH2Cl2 (50 ml) and the extract
was washed with brine (30 ml) and then dried (Na2SO4). After filtration, the solvent
evaporated, and the residue was purified by silica gel column chromatography using
hexane/ethylacetate (75:25, v/v). Fraction containing 1-(4-(4-bromobutoxy) phenyl)-2-(4-
9

chlorophenyl)-4,5-diphenyl-1H-imidazole (2c) was collected then the solvent was
removed under reduced pressure.
Spectral Data
White powder (64%), M.P. = 148-150 °C, IR (KBr, cm−1) = 3057, 2927, 1650, 1605,
1
1562, 1541, 1511, 1475, 1417, 1244, 1167, 1091, 1014, 777, 754, 725, 695, 657, 542. H
NMR (CDCl3, 400 MHz): δH 1.90-1.96 (m, 2H, CH2), 2.02-2.09 (m, 2H, CH2), 3.48 (t, J=
6.5 Hz, 2H, CH2), 3.94 (t, J= 6.0 Hz, 2H, CH2), 6.72-6.76 (m, 2H, Ar-H), 6.91-6.95 (m,
2H, Ar-H).7.11-7.14 (m, 2H, Ar-H), 7.16-7.26 (m, 8H, Ar-H), 7.36-7.39 (m, 2H, Ar-H),
7.55-7.57 (m, 2H, Ar-H). 13C NMR (CDCl3, 100 MHz): δC 26.74, 28.35, 32.37, 65.97
(CH2), 113.73, 125.54, 125.63, 126.29, 126.97, 127.16, 127.34, 127.36, 128.05, 128.34,
128.57, 129.01, 129.47, 130.05, 130.30, 133.16, 133.28, 137.24, 144.84, 157.49.
Anal.Calc. for C31H26BrClN2O: C, 66.74; H, 4.70; N, 5.02%. Found: C, 66.63; H, 4.88;
N, 5.31%.
TYPICAL PROCEDURE FOR THE SYNTHESIS OF 1-(4-(5,5,5-
TRIS(TRIMETHYLSILYL)PENTYLOXY)PHENYL)-2-(4-CHLOROPHENYL)-
4,5-DIPHENYL-1H-IMIDAZOLE (3C)
Tris(trimethylsilyl)methyllithium, (Me3Si)3CLi was prepared as described by Gröbel and
co-workers.[23] To a stirred solution of (Me3Si)3CLi (5 mmol) in THF was added 1-(4-(4-
bromobutoxy) phenyl)-2-(4-chlorophenyl)-4,5-diphenyl-1H-imidazole (2c) (5 mmol) in
10 ml THF at 0 °C. The mixture was stirred for another 10 min at room temperature. The
mixture was poured into ammonium chloride solution (50 ml) and extracted with CH2Cl2
0

(2×20 ml). The organic phase was washed with water (100 mL) and dried (Na2SO4), and
the solvent was removed in vacuum to yield a white solid.
Spectral data
1-(4-(5,5,5-TRIS(TRIMETHYLSILYL)PENTYLOXY)PHENYL)-2-(4-
CHLOROPHENYL)-4,5-DIPHENYL-1H-IMIDAZOLE (3C)
White powder (91%), M.P. = 168-170 °C, IR (KBr, cm−1) = 3059, 2958, 1618, 1541,
1512, 1473, 1256, 1094, 840, 620. 1H NMR (CDCl3, 400 MHz): δH 0.10 (s, 27H, SiMe3),
1.62-1.66 (m, 6H, 3 CH2), 3.85 (t, J= 5.9 Hz, 2H, CH2), 6.69 (d, J= 8.8 Hz, 2H, Ar-H),
6.88 (d, J = 8.8 Hz, 2H, Ar-H), 7.06 (dd, J = 1.7 Hz, J = 7.42 Hz, 2H, Ar-H), 7.11-7.23
(m, 8H, Ar-H), 7.33 (d, J= 8.5 Hz, 2H, Ar-H), 7.50 (d, J= 7.2 Hz, 2H, Ar-H). 13C NMR
(CDCl3, 100 MHz): δC 1.72 (SiMe3), 4.43 (C(SiMe3)3), 25.46, 29.51, 29.83, 66.60 (CH2),
113.95, 126.18, 126.37, 126.59, 127.28, 127.50, 127.53, 128.02, 128.24, 128.42, 128.81,
128.87, 129.38, 129.68, 130.09, 130.12, 133.00, 137.04, 157.31. Anal.Calc. for
C41H53ClN2OSi3: C, 69.40; H, 7.53; N, 3.95%. Found: C, 69.48; H, 7.32; N, 3.79%.
SUPPORTING INFORMATION
Full experimental detail, 1H and 13C NMR spectra can be accessed on the publisher’s
website.
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3

Table 1. Comparison of temperature, yield, reaction time and frequency with or without
ultrasound irradiation for the synthesis of 1aa
entry catalyst
without sonication
with sonication
a
temp.(°C)/time(min)/yieldb freq.(Hz)
(%)
/time(min)/yieldb(%)
1
2
3
4
5
6
7
8
9
Cu/ZSM-5
100/60/68
100/60/67
100/60/65
100/60/60
100/60/55
100/60/52
100/60/51
100/60/47
50/30/70
50/30/69
50/30/65
50/30/63
50/30/59
50/30/58
50/30/55
50/30/52
20/2/99
Fe/ZSM-5
Cr/ZSM-5
Co/ZSM-5
V/ZSM-5
Ni/ZSM-5
Zn/ZSM-5
Mn/ZSM-5
Fe-Cu/ZSM- 70/30/96
5
10
11
Cr-Cu/ZSM- 70/30/94
5
20/3/97
20/3/97
Co-
70/30/93
Cu/ZSM-5
4

12
13
14
15
V-Cu/ZSM- 70/30/90
20/5/94
20/5/93
20/5/93
20/6/91
5
Ni-Cu/ZSM- 70/30/88
5
Zn-
70/35/87
Cu/ZSM-5
Mn-
70/40/84
Cu/ZSM-5
H-ZSM-5
-
16
17
100/60/20
50/15/45
50/2hr/20
100/2days/10
aThe reaction conditions: benzaldehyde (1 mmol), benzil (1 mmol), 4-hydroxyaniline (1
mmol), ammonium acetate, (1.1 mmol), and (5wt.% from monometallic catalyst) and
(3wt.% from bimetallic catalyst), 3 ml solvent under ultrasound irradiation.
bIsolated yields.
5

Table 2. Synthesis of 4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenol (1a) using (3wt.%) Fe-
Cu/ZSM-5 monometallic catalysta
entrya solvent
Time
(min)
20
yield (%)b
1
2
3
4
5
6
Acetonitrile
58
54
45
40
99
74
Ethanol
22
CH3COOCH3
THF
15
20
Water
2
Acetonitrile/
Water
10
7
8
Ethanol/ Water
CH3COOCH3/
Water
4
8
78
80
9
THF/ Water
CH2Cl2
10
30
65
35
10
aThe reaction conditions: benzaldehyde (l mmol), benzil (1mmol), 4-hydroxyaniline
(1mmol) and NH4OAc (1.1 mmol), catalyst (3w.%), 3 ml solvent under ultrasound
irradiation.
bIsolated yield.
6

Table 3. Synthesis of tetrasubstituted imidazoles catalyzed by Fe-Cu/ZSM-5 nanocatalyst
entr produ R1
R2
yielda (%)
Benzil
Time (min)
Benzil
y
ct
Benzoin
Benzoin
99 93
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
H
4-
2
2
2
2
2
2
3
8
8
8
8
8
8
8
OH
4-
4-
97 92
99 93
97 90
98 93
97 91
98 92
OH
Me
4-Cl 4-
OH
4-
4-
OH
4-
OH
H
Me
4-Cl 4-
Me
4-Br
1g
4-
Me
7

8
1h
1i
4-
4-
4
3
2
3
3
8
8
8
8
8
97 89
99 94
98 93
98 89
97 88
Me
4-
Me
3-Cl
9
Me
H
10
11
12
1j
4-
Me
4-Cl
1k
1l
4-
Me
4-
4-F
Me
aIsolated yields
8

Scheme 1. Synthesis of organosilicon-containing imidazoles
9