Synthesis of Novel Organosiliconsulfur-Containing Tetrasubstituted Imidazoles Sonocatalyzed by LaxSr1-xFeyCo1-yO3 Nanoperovskites

Article abstract of DOI:10.1080/00397911.2015.1009552

The one-pot synthesis of tetrasubstituted imidazoles by use of a series of La_xSr1-_xFe_yCo1-_yO₃ perovskites as catalysts is described. The La_0.8Sr_0.2Fe_0.34Co_0.66O₃ nanocatalyst had the greatest activity in the heterogeneous cyclocondensation of an aldehyde, benzil, ammonium acetate, and a primary aromatic amine in water under ultrasonic irradiation. Some of the derivatives generated during this work were utilized as substrates for the synthesis in good yields of novel multifunctional tetrasubstituted imidazoles with Me₃Si, C=S, and SH groups, via nucleophilic attack of tris(trimethylsilyl)methyllithium (TsiLi) at the carbon of carbon disulphide.

Full text of DOI:10.1080/00397911.2015.1009552

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Synthesis of Novel Organosiliconsulfur-Containing
Tetrasubstituted Imidazoles Sonocatalyzed by
LaxSr1 - xFeyCo1 - yO3 Nanoperovskites
Kazem D. Safaa, Maryam Allahvirdinesbata & Hassan Namazib
a Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
b Laboratory of Dendrimers and Nano-Biopolymers, Faculty of Chemistry, University of
Tabriz, Tabriz, Iran
Accepted author version posted online: 18 Feb 2015.
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To cite this article: Kazem D. Safa, Maryam Allahvirdinesbat & Hassan Namazi (2015): Synthesis of Novel Organosiliconsulfur-
Containing Tetrasubstituted Imidazoles Sonocatalyzed by LaxSr1 - xFeyCo1 - yO3 Nanoperovskites, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, DOI: 10.1080/00397911.2015.1009552
To link to this article: http://dx.doi.org/10.1080/00397911.2015.1009552
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Synthesis of Novel Organosiliconsulfur-Containing Tetrasubstituted Imidazoles
Sonocatalyzed by LaxSr1−xFeyCo1−yO3 Nanoperovskites
Kazem D. Safa1, Maryam Allahvirdinesbat1, Hassan Namazi2
1Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz,
Iran, 2Laboratory of Dendrimers and Nano-Biopolymers, Faculty of Chemistry,
University of Tabriz, Tabriz, Iran
Corresponding author, E-mail: dsafa@tabrizu.ac.ir
Abstract
The one-pot synthesis of tetrasubstituted imidazoles by use of a series of perovskites
LaxSr1−xFeyCo1−yO3 as catalysts is described. The La0.8Sr0.2Fe0.34Co0.66O3 nanocatalyst
had the highest activity in the heterogeneous cyclocondensation of an aldehyde, benzil,
ammonium acetate and a primary aromatic amine in water under ultrasonic irradiation.
Some of the derivatives generated during this work were utilized as substrates for the
synthesis in high yields of novel multifunctional tetrasubstituted imidazoles with Me3Si,
C=S, and SH groups, via nucleophilic attack of tris(trimethylsilyl)methyllithium (TsiLi)
at the carbon of carbon disulphide
KEYWORDS: LaxSr1−xFeyCo1−yO3 perovskites, Imidazoles, Ultrasonic irradiation,
MCRs, Organosiliconsulfur
1

INTRODUCTION
The incorporation of organosilicon moieties into drug structures has been used to
improve pharmacological potency, to modify selectivity toward a given target, to change
metabolic rates, and to increase lipophilicity. Lipophilicity can provide several
physiological benefits, including increased bioavailability and tissue and cell
penetration.[1–3] The chemistry of compounds containing silicon and sulfur attached to the
same or neighbouring carbons offers opportunities, particularly in the broad area of
organic synthesis, not available if work is restricted to compounds containing only one of
these elements.[4]
Cyclizations via one-pot multicomponent coupling reactions (MCRs) are widely used for
the preparation of heterocycles.[5,6] Imidazoles are important in biological systems, e.g.
as histidine, histamine, biotin, and components in drugs (e.g. Losartan, Olmesartan,
Eprosartan, and Trifenagrel) and pesticides. Some of these compounds could also be
used as organic optical materials, in molecular switches and organic light-emitting diodes
(OLEDs). Several methods for their preparation have been reported. Some of these are
associated with one or more disadvantages, such as use of expensive reagents, harmful
organic solvents, prolonged reaction times, or unsatisfactory yields.[7–16] Ultrasound
techniques are proving to be efficient and selective for improving traditional reactions
that require long reaction times.[11,17–20]
In organic syntheses, metal oxide [20,21] catalysts are alternatives for noble metal
catalysts. Perovskites are mixed metal oxides with the general formula ABO3.
2

Lanthanides and/or alkaline earth metal ions usually occupy the A-site position, and first
row transition metals the B-site position. Both A and B cations can be partially
substituted, leading to multicomponent oxides A1−xA′xB1−yB′yO3. Partial substitution of
the A site causes lattice defects and abnormal valences in B site cations that usually
enhance catalytic activity. Partial substitution of the B site brings about synergistic
effects and influences the stability of the crystalline structure.[22] For example,
AB0.5B´0.5O3 (A2BB´O6) is the most common ternary perovskite and Gallagher et al.
have reported high activities for LaMn0.5Cu0.5O3 in the oxidation of CO. The synergistic
effect was explained by the combination of two functions, the activation of oxygen by
manganese oxide and that of CO by copper ions. Levasseur and Kaliaguine have studied
the catalytic combustion of CH3OH, CO, and CH4 over La1-yCeyCo1-xFexO3
perovskites.[23] Herein we describe the effect of the mole fractions of various cations i.e.
Fe, Co, and Sr on the catalytic performance of LaxSr1−xFeyCo1−yO3 nanoperovskites for
synthesis of imidazole derivatives. We report the development of the
La0.8Sr0.2Fe0.34Co0.66O3 catalytic system for convenient and efficient preparation of
tetrasubstituted imidazoles in cyclocondensations of aldehyde, benzil, ammonium acetate
and primary aromatic amine in water under ultrasonic irradiation and have synthesized a
series of new tetrasubstituted imidazoles containing Me3Si, C=S, and SH groups by use
of (Me3Si)3CLi and CS2.
RESULTS AND DISCUSSION
Nanostructured LaxSr1−xFeyCo1−yO3 perovskite mixed oxides, prepared by the sol−gel
combustion,[22] were tested as catalysts for the synthesis of tetrasubstituted imidazole
3

derivatives which are used for preparation of mercaptobis(trimethylsilyl)thiones
containing highly substituted imidazoles. A one-pot four-component condensation of 4-
methylbenzaldehyde (1 mmol) with aniline (1 mmol), benzil (1 mmol) and ammonium
acetate (1.1 mmol) was used as a model for the synthesis of 1,4,5-triphenyl-2-p-tolyl-1H-
imidazole (1a). The reaction was carried out in the presence of catalytic amount (10 wt%)
of catalyst in water under high intensity ultrasound irradiation. The desired product (1a)
was obtained with 50% yield after 60 min. However, the reaction proceeded rather slowly
and no significant catalysis was observed. Incorporation of various metals such as Sr and
Co into LaFeO3 to give the perovskites LaxSr1−xFeyCo1−yO3 has led to improved yields.
We showed that cyclocondensation was improved significantly by Sr substitution. The
highest catalytic activity was observed when the mole fraction of lanthanum was around
0.8 and the mole fraction of strontium about 0.2. The inclusion of iron and cobalt ions at
the B site improved catalyst activity further. In addition, cobalt was better than iron
incorporation. The catalyst showed highest catalytic activity when the mole fraction of
iron was lower than 0.5 (Table 1). The best results (95% yield, after 5 min) were obtained
in the presence of 3 wt % of La0.8Sr0.2Fe0.34Co0.66O3 in aqueous medium under ultrasound
irradiation (Table 1, entry 10). This result is in agreement with our working hypothesis
that a higher concentration of acidic sites gives higher yields. When other solvents such
as acetonitrile, ethanol, THF, and methanol were used, the reactions were slower and the
yields lower.
The reactions of various aldehydes, benzil, amines, and ammonium acetate were
examined in the presence of La0.8Sr0.2Fe0.34Co0.66O3 (3 mol%) in water under ultrasound
4

irradiation. In all cases, the requisite imidazole derivatives were obtained within three to
six minutes in excellent yields (Table 2). Most of the tetrasubstituted imidazoles are
known compounds and their identity was confirmed by IR, NMR, elemental analyses and
melting points.[24, 38-41]
A plausible mechanism for the catalytic activity of La0.8Sr0.2Fe0.34Co0.66O3 is postulated in
Scheme 1. La0.8Sr0.2Fe0.34Co0.66O3 activates the carbonyl group of an aldehyde to
facilitate the formation of diamine intermediate A. This catalyst also activates the
diketone to facilitate the condensation with intermediate A to give imidazol-5-ol
intermediate C which, upon elimination of water, is transformed into the desired 1,2,4,5-
tetrasubstituted imidazole.
We have recently used bulky tris(trimethylsilyl)methyllithium (TsiLi) as a reagent for the
preparation of vinylsilanes, epoxysilanes, halovinylsilanes, silyl ethers, etc.[25–31] To show
the usefulness of the imidazoles generated during this study, imidazoles containing three
different functional groups viz –mercapto, trimethylsilyl and thiocarbonyl–, have been
made via nucleophilic attack of TsiLi at the carbon of CS2 at -46 °C.
(Bromomethyl)phenyl-imidazoles 2a–2d were synthesized according to Scheme 2.
Bromination of the benzylic methyl group(s) in compounds 1a–1d was achieved by use
of N-bromosuccinimide (NBS) in CCl4 in the presence of a catalytic amount of α,α -
azobisisobutyronitrile (AIBN) at 50–52 °C. The crude products were used directly for the
synthesis of thiones 3a–3d by reaction with tris(trimethylsilyl)methyllithium and CS2 at
-46 °C, in short reaction times and with excellent yields. Furthemore, treatment of TsiLi
5

and CS2 with bromopropoxy-imidazoles 2f and 2g was investigated. These compounds
were synthesized by treatment of the hydroxyl-imidazoles 1f and 1g with K2CO3 and
dibromopropane in DMF (Scheme 2). Reaction of TsiLi and CS2 with 2f and 2g
proceeded slowly and after 1h gave a poor yield. In contrast, the reactions of
iodopropoxy-imidazoles were rapid and quantitative. Iodopropoxy-imidazoles were
obtained by addition of potassium iodide (1.1 eq) to 2f or 2g in boiling acetone (Scheme
2). The crude products were directly used for the synthesis of thiones 3f and 3g.
The pathway for the formation of organosiliconsulfur-containing tetrasubstituted
imidazoles is assumed to be by C-to-S migration of the SiMe3 group, the formation of a
carbanion (b) as in a Brook rearrangement and then conversion to the enethiolate (c). The
resulting product 3 shows that the migration of sulfur to the central carbon of C(SiMe3)2
has occurred. It seems likely that the product 3 forms through the intermediates (d)–(g)
and after hydrolysis of (g) (Scheme 3).[32-36]
CONCLUSION
We have reported La0.8Sr0.2Fe0.34Co0.66O3-catalyzed four-component one-pot syntheses of
multi-substituted imidazoles in water under ultrasound irradiation in excellent yields. The
simple procedures combined with easy recovery and reuse of this catalyst make this
method economically and environmentally benign. The organosiliconsulfur-containing
tetrasubstituted imidazoles 3a–3d, 3f and 3g were obtained in good yields. These
synthetic intermediates are potential compounds for incorporation into silver
6

nanoparticles (AgNPs) by reaction with terminal-thiol groups. We shall investigate this
possibility and discuss our results in future communications.
EXPERIMENTAL
Chemicals were either prepared in our laboratory or purchased from Merck, Fluka and
Aldrich. Commercial products were used without further purification. The 1H 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 FT-IR 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.
Typical Procedure For The Synthesis Of 1-(4-Fluorophenyl)-4,5-Diphenyl-2-P-
Tolyl-1H-Imidazole (1b)
The perovskite-type oxides were prepared as described by Niaei and co-workers.[22] In a
typical procedure, a mixture of benzil (1 mmol), 4-methylbenzaldehyde (1 mmol), amine
(1 mmol), and ammonium acetate (1.1 mmol) as ammonia source and 3 mol% of
La0.8Sr0.2Fe0.34Co0.66O3 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
7

at 20% power of the processor. After completion of the reaction (monitored by TLC,
within 3–6 min), the solid product was filtered off, washed with water, dried and
recrystallized from ethanol. The supported reagent was washed three times with ethanol
and dried under vacuum before reuse. The product was identified as 1-(4-fluorophenyl)-
4,5-diphenyl-2-p-tolyl-1H-imidazole (1b) by spectral data.
White powder (96%), mp 188–190 °C, IR (KBr,cm−1): νmax = 3058 (Ar–H), 2962 (C–H),
1602, 1508, 1444 (C=C), 960, 775, 730. 1H NMR (CDCl3, 400 MHz) δH: 2.36 (s, 3H,
CH3), 6.96–7.00 (m, 2H, Ar–H), 7.03–7.07 (m, 2H, Ar–H), 7.11 (d, 2H, J = 8.0 Hz, Ar–
H), 7.14–7.17 (m, 2H, Ar–H), 7.21–7.32 (m, 6H, Ar–H), 7.35 (d, 2H, J = 8.0 Hz, Ar–H),
7.63 (d, 2H, J = 7.2 Hz, Ar–H). 13C NMR (CDCl3, 100 MHz) δC: 20.24 (CH3), 114.95,
115.17, 125.58, 126.32, 126.41, 127.01, 127.12, 127.41, 127.79, 127.88, 128.99, 129.08,
129.50, 129.58, 130.07, 132.19, 133.30, 137.16, 137.31, 146.12, 159.59, 162.06 (Ar).
Anal.Calc. for C28H21FN2: C, 83.14; H, 5.23; N, 6.93%. Found: C, 83.09; H, 5.14; N,
6.81%.
Typical Procedure For The Synthesis Of 2-(4-(Bromomethyl)Phenyl)-1-(4-
Fluorophenyl)-4,5-Diphenyl-1H-Imidazole (2b)
Compound 2b was prepared by reacting compound 1b (1 mmol) with N-
bromosuccinimide (NBS) (1 mmol) in 70 mL of carbon tetrachloride under argon
atmosphere. To initiate the reaction, 10 mol % of , -azobisisobutyronitrile (AIBN) was
added and the reaction mixture was stirred at 50–52 °C. The optimum reaction time for
2b was observed to be 2 days. Then the reaction mixture was cooled to 10 °C, and the
8

precipitated succinimide was filtered off. The solution was washed with water three
times, the organic phase dried over Na2SO4, and the solvent evaporated under vacuum.
For example, crude product 2b was purified by column chromatography (silica gel,
hexane/ethylacetate mixture (10:1, v/v)) to afford bromo-methyl imidazole 2b.
White powder (73%), mp 152–154 °C, IR (KBr, cm−1): νmax = 3058 (Ar–H), 2924 (C–H),
1603, 1509, 1446 (C=C), 1225, 825, 777, 733, 698, 532. 1H NMR (CDCl3, 400 MHz) δH:
4.49 (s, 2H, CH2–Br), 6.99–7.09 (m, 4H, Ar–H), 7.16 (dd, J = 1.6 Hz, J = 7.8 Hz, 2H,
Ar–H), 7.24–7.34 (m, 8H, Ar–H), 7.44 (d, J = 8.3 Hz, 2H, Ar–H), 7.60–7.63 (m, 2H, Ar–
H). 13C NMR (CDCl3, 100 MHz) δC: 31.98 (CH2–Br), 115.165, 115.39, 125.77, 126.32,
127.19, 127.48, 127.94, 128.01, 128.12, 128.99, 129.07, 129.22, 130.05, 131.95, 133.03,
136.78, 159.75, 162.23 (Ar). Anal.Calc. for C28H20BrFN2: C, 69.57; H, 4.17; N, 5.80%.
Found: C, 69.45; H, 4.09; N, 5.72%.
Typical Procedure For The Synthesis Of 1-(4-(3-Bromopropoxy)Phenyl)-2-(4-
Chlorophenyl)-4,5-Diphenyl-1H-Imidazole (2f)
A mixture of (1 mmol) imidazole derivative (1f) and (1 mmol) 1,3-dibromopropane in the
presence 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
9

bromopropoxy-imidazole was collected then the solvent was removed under reduced
pressure.
Yellow powder (64%), mp 175–177 °C, IR (KBr, cm−1): νmax = 3059 (Ar–H), 2925 (C–
1
H), 1637, 1510, 1468 (C=C), 1239, 1169, 1090, 930, 694. H NMR (CDCl3, 400 MHz)
δH: 2.02–2.09 (m, 2H, CH2–CH2–CH2), 3.48 (t, J = 6.5 Hz, 2H, CH2–Br), 3.94 (t, J 6.0
Hz, 2H, O–CH2), 6.73–6.76 (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: 28.35 (CH2–CH2–CH2), 31.36 (CH2–Br), 65.97 (O–
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 (Ar).
Anal.Calc. for C30H24BrClN2O: C, 66.25; H, 4.45; N, 5.15%. Found: C, 66.33; H, 4.38;
N, 5.31%.
Typical Procedure For The Synthesis Of 3-(4-(1-(4-Fluorophenyl)-4,5-Diphenyl-1H-
Imidazol-2-Yl)Phenyl)-1-Mercapto-1,1 Bis(Trimethylsilyl)Propane-2-Thione (3b)
Tris(trimethylsilyl)methyllithium, (Me3Si)3CLi was prepared as described by Gröbel and
co-worker.[37] To a stirred solution of tris(trimethylsilyl)methyllithium (1 mmol) in THF,
carbon disulfide (1.2 mmol) in 2 mL THF was added at -46 °C (cyclohexanone/N2) under
argon atmosphere. The mixture was stirred for 5 min and then 2-(4-
(Bromomethyl)phenyl)-1-(4-fluorophenyl)-4,5-diphenyl-1H-imidazole (2b) (1 mmol)
was added at this temperature and the stirring is maintained (-46 °C→0 °C) to the end of
the reaction that followed by TLC. The mixture was poured into water and extracted with
10

CH2Cl2. The organic layer was washed with water, dried with Na2SO4 and filtered. The
solvent was evaporated and the residue was purified by preparative TLC on silica gel
using n-hexane/ethylacetate (v/v: 10:2) as eluent to give the product (3b).
A yellow sticky solid (96%), IR (KBr, cm−1): νmax = 3060 (Ar–H), 2955 (C–H), 1605,
1561, 1508, 1482, 1447 (C=C), 1409, 1151 (C=S), 1253, 916, 855 (C–Si), 1028 (C–S).
1H NMR (CDCl3, 400 MHz) δH: 0.18 (s, 18H, SiMe3), 3.14 (bs, 1H, S–H), 4.45 (s, 2H,
CH2), 6.94–7.00 (m, 4H, Ar–H), 7.11 (d, J = 6.8 Hz, 2H, Ar–H), 7.13–7.28 (m, 10H, Ar–
H), 7.61 (d, J = 7.1 Hz, 2H, Ar–H). 13C NMR (CDCl3, 100 MHz) δC: -1.18 (SiMe3), 41.27
(CH2), 55.40 (C(SiMe3)2SH), 115.04, 115.27, 126.33, 127.17, 127.31, 127.46, 127.59,
127.77, 127.84, 127.89, 127.96, 127.98, 128.95, 129.04, 129.96, 130.05, 130.25, 132.00,
137.56, 146.28, 159.66, 162.13 (Ar), 214.28 (C=S). Anal. Calc. for C36H39FN2S2Si2: C,
67.67; H, 6.15; N, 4.38%. Found: C, 67.44; H, 6.29; N, 4.53%.
5-(4-(2-(4-Chlorophenyl)-4,5-Diphenyl-1H-Imidazol-1-Yl)Phenoxy)-1-Mercapto-1,1
Bis(Trimethylsilyl)Pentane-2-Thione (3f)
A yellow sticky solid (95%), IR (KBr, cm−1): νmax = 3060 (Ar–H), 2955 (C–H), 1592,
1481, 1423 (C=C), 1410, 1149 (C=S), 1251, 915, 852 (C–Si), 1029 (C–S). 1H NMR
(CDCl3, 400 MHz) δH: 0.19 (s, 18H, SiMe3), 2.11–2.17 (m, 2H, CH2–CH2–CH2), 3.17
(bs, 1H, S–H), 3.37 (t, J = 7.1 Hz, 2H, (CH2–C(SiMe3)2S)), 4.01(t, J = 6.10 Hz, 2H, O–
CH2), 6.80 (d, J = 7.9 Hz, 2H, Ar–H), 6.98 (d, J = 8.1 Hz, 2H, Ar–H), 7.16 (d, J = 6.2 Hz,
2H, Ar–H), 7.23–7.32 (m, 8H, Ar–H), 7.43 (d, J = 7.9 Hz, 2H, Ar–H), 7.61 (d, J = 7.4,
2H, Ar–H). 13C NMR (CDCl3, 100 MHz) δC: -1.18 (SiMe3), 28.69 (CH2), 38.43 (CH2–
11

C(SiMe3)2S), 54.09 (C(SiMe3)2SH), 65.35 (O–CH2), 113.84, 125.68, 126.35, 126.82,
127.02, 127.18, 127.39, 128.36, 128.13, 128.77, 128.89, 129.09, 129.59, 129.63, 130.09,
133.42, 137.13, 145.79, 157.67 (Ar), 213.95 (C=S). Anal. Calc. for C38H43ClN2OS2Si2:
C, 65.25; H, 6.20; N, 4.00%. Found: C, 65.31; H, 6.41; N, 3.88%.
ACKNOWLEDGMENT
We thank Dr. J.D. Smith for his helpful comments. The authors are thankful to those who
contributed to enhancing this project, especially Dr. A. Niaei, Dr. D. Salari and Mrs
Samira Arefi Oskoui.
SUPPLEMENTAL MATERIAL
Full experimental detail, and 1H and 13C NMR spectra, for this article can be accessed on
the publisher’s website.
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15

Table 1 Optimization of the reaction conditions
Entry Catalyst (mol %)
Time (min)
Yield (%)a
1
LaFeO3(10)
60
40
40
30
30
30
10
10
10
5
50
57
60
71
65
67
78
87
95
95
20
2
La1Fe0.5Co0.5O3(5)
3
La1Fe0.66Co0.34O3(5)
La0.9Sr0.1Fe0.5Co0.5O3(5)
La0.9Sr0.1Fe0.82Co0.18O3(5)
La0.9Sr0.1Fe0.66Co0.34O3(5)
La0.8Sr0.2 Fe0.66Co0.34O3(5)
La0.8Sr0.2 Fe0.34Co0.66O3(5)
La0.8Sr0.2 Fe0.34Co0.66O3(3)
La0.8Sr0.2 Fe0.34Co0.66O3(3)
-
4
5
6
7
8
9
10
11
120
Reaction conditions: 4-methylbenzaldehyde (1.0 mmol), benzil (1.0 mmol), aniline (1.0
mmol), ammonium acetate (1.1 mmol), and 3 mol% La0.8Sr0.2 Fe0.34Co0.66O3 in water
under ultrasonic irradiation at ambient temperature at 20% power of the processor
aIsolated yield
16

Table 2 Synthesis of highly substituted imidazoles
Entrya
139
Product
1a
R1
R2
Yield(%)b
95
4-Me
4-Me
4-Me
4-Me
H
H
224
1b
1c
4-F
96
340
4-Cl
3-Cl
4-OH
4-OH
4-OH
4-OH
4-Me
4-Me
4-Me
4-Br
4-Me
95
424
1d
1e
94
524
95
624
1f
4-Cl
4-Me
4-OH
4-OH
H
93
724
1g
1h
1i
94
824
92
938
94
1041
1124
1224
1340
aReference
1j
94
1k
1l
4-Cl
4-Me
4-Me
94
93
1m
95
bIsolated yield
17

Scheme 1 Plausible mechanism for the formation of 1,2,4,5-tetrasubstituted imidazoles in
the presence of La0.8Sr0.2Fe0.34Co0.66O3.
18

Scheme 2 Synthesis of organosiliconsulfur-containing tetrasubstituted imidazoles
19

Scheme 3 The proposed mechanism of the reaction of TsiLi, CS2 and halo-methyl
derivatives of imidazoles
20