Synthesis of silyl-protected terminal thioalkyne-substituted tetraaryl imidazoles: utilization of Ag–Fe/ZSM-5 bimetallic nanooxides for cyclocondensation of polysubstituted imidazoles

Article abstract of DOI:10.1007/s11164-016-2787-1

An improved one-pot and ecofriendly approach to tri- and tetraaryl imidazoles through three- and four-component coupling reactions under neutral and solvent-less solid-phase conditions is presented. A series of nanosized Ag/metal oxide species on H–ZSM-5 support were tested in this procedure, with Ag–Fe/ZSM-5 bimetallic oxide nanoparticles exhibiting excellent catalytic activity for improved efficiency of the one-pot, multicomponent cyclocondensation reaction. The obtained bromoimidazole derivatives were converted into silyl-protected terminal alkynyl thiolate-substituted tetraaryl imidazoles by treatment with lithium 2,2,2-tris(trimethylsilyl)ethanedithioate, produced by reaction of organolithium reagent (Me₃Si)₃CLi with CS₂ at 0?°C. These novel and stable synthetic intermediates are potential compounds for functionalization of imidazoles.

Full text of DOI:10.1007/s11164-016-2787-1

Res Chem Intermed
DOI 10.1007/s11164-016-2787-1
Synthesis of silyl-protected terminal thioalkyne-
substituted tetraaryl imidazoles: utilization of Ag–Fe/
ZSM-5 bimetallic nanooxides for cyclocondensation
of polysubstituted imidazoles
Maryam Allahvirdinesbat1 Mohaddeseh Fozi1
•
•
Kazem D. Safa1 Maryam Alyari1
Parvaneh Nakhostin Panahi2 Aligholi Niaei3
•
•
•
Received: 20 May 2016 / Accepted: 14 October 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract An improved one-pot and ecofriendly approach to tri- and tetraaryl
imidazoles through three- and four-component coupling reactions under neutral and
solvent-less solid-phase conditions is presented. A series of nanosized Ag/metal
oxide species on H–ZSM-5 support were tested in this procedure, with Ag–Fe/ZSM-
5 bimetallic oxide nanoparticles exhibiting excellent catalytic activity for improved
efficiency of the one-pot, multicomponent cyclocondensation reaction. The obtained
bromoimidazole derivatives were converted into silyl-protected terminal alkynyl
thiolate-substituted tetraaryl imidazoles by treatment with lithium 2,2,2-
tris(trimethylsilyl)ethanedithioate, produced by reaction of organolithium reagent
(Me3Si)3CLi with CS2 at 0 °C. These novel and stable synthetic intermediates are
potential compounds for functionalization of imidazoles.
Keywords Imidazole Á MCRs Á Alkynyl thiolation reaction Á Silyl protecting group Á
Triple bond Á Ag/metal nanooxides
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2787-1)
contains supplementary material, which is available to authorized users.
&
Kazem D. Safa
dsafa@tabrizu.ac.ir
1
Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz,
Tabriz 5166614766, Iran
2
3
Department of Chemistry, Faculty of Science, University of Zanjan, Zanjan, Iran
Department of Applied Chemistry and Chemical Engineering, Faculty of Chemistry, University
of Tabriz, Tabriz 5166614766, Iran
123

M. Allahvirdinesbat et al.
Introduction
Silicon-containing analogs have diverse uses in organic chemistry from the most
common application as protecting groups to essential building blocks in natural
products [1]. Silylacetylenes are useful conduits for the most versatile terminal
alkynes in a number of chemical reactions such as Diels–Alder reactions, and
[2 ? 2] and [2 ? 3] cycloadditions [2]. On the other hand, alkynyl thiolates have
emerged as powerful and versatile intermediates in a variety of synthetic
transformations. This is based on the combination of the enhanced reactivity of
the triple bond with a sulfur atom, frequently encountered in biological systems and
materials [3]. S–Csp bonds undergo a large number of reactions such as copper-
catalyzed azide–alkyne cycloaddition and cross-coupling processes [4]. Due to the
applications of Si–Csp and S–Csp bonds as key units in preparation of natural
products and chemical compounds, we focus on biologically important heterocycles
that contain a silyl-protected terminal alkynyl thiolate unit.
Zeolite-catalyzed multicomponent reactions (ZCMCRs) are efficient, environmentally
friendly, and economic tools in organic and medicinal chemistry for synthesis of bioactive
systems [5]. The imidazole scaffold has emerged as an active backbone in natural products
(viz. biotin, the essential amino acid histidine, histamine, and pilocarpine alkaloids) and
several drugs (e.g., naamidine a, olmesartan, losartan, trifenagrel, and eprosartan). Some
imidazole-based derivatives have extensive applications in many fields, e.g., as organic
optical materials, in anion sensors, and as ionic liquids [6–8]. This versatile applicability in
materials science, and organic and medicinal chemistry highlights the importance of
access to convenient synthetic methods for benign imidazole ring-containing derivatives.
Several new routes have been reported for their synthesis. Cyclizations via one-pot
multicomponent coupling reactions (MCRs) [9] represent a useful synthetic route for
preparation of heterocyclic compounds. In recent years, design of cyclocondensation
reactions under neutral and solvent-free solid-phase catalytic conditions has received
enormous attention in the area of green MCR protocols [8, 10, 11].
Silver has long been recognized as a useful and convenient catalyst for a variety
of reactions of commercial and environmental importance [12, 13]. Ag-loaded
catalysts are active and durable at high reaction temperatures, especially in presence
of water and sulfur dioxide [14].
As part of our work devoted to synthesis of highly substituted imidazoles, we
report herein, for the first time, development of an Fe/Ag-modified ZSM-5
nanocatalyst for simple preparation of tri- and tetraaryl imidazoles using an MCR
strategy under solvent-free conditions and synthesis of a series of imidazole
derivatives terminated by trimethylsilylethynylthiolato groups via nucleophilic
reaction of (Me3Si)3CLi with carbon disulfide at 0 °C.
Results and discussion
Due to the significance of imidazole-based derivatives and silicon-containing
analogs as useful building blocks in the chemical and pharmaceutical industry, we
recently prepared a series of highly substituted imidazoles including carbosilane and
silyl ether moieties [15] (route A, Scheme 1).
123

Synthesis of silyl-protected terminal thioalkyne-…
SiMe2R
SiMe2R
SiMe2R
N
N
SiMe2R
SiMe2R
R2
S
iM
e
2R
R2
R=H, Me
N
SiMe2R
SiMe2R
SiMe2R
C
N
N
SiMe2R
SiMe2R
N
B
D
R=H, Me, Ph
R2
R2=H, 4-Cl, 3-Cl, 4-F,
4-Br, 4-Me
H
R2=H
R= Me, Ph
N
N
R2
R1
A
R2
E
F
N
N
R3
R4
N
Si
R2
R5
S
R2=H
N
R2=H, 4-Cl, 4-F, 3-Cl
SH
SiMe3
a)R3=R4=R5=Me
b)R3=R4=R5=Et
c)R3=R4=R5=Ph
d)R3=R4=Me, R5=H
N
Me3Si
N
S
SiMe3
X
e)R3=R4=Me, R5=OMe
X=CH2 R2=H, 3-Cl, 4-F
(
O
CH2
)
n
X=
R=H, ...
in this work
A: if R1=CH3, a) LDA/THF/r.t; b)R3SiCl/THF/0oC or r.t
B: if R1:CH3, a) NBS,CCl4/AIBN/50-52 oC; (RMe2Si)3CLi/THF/r.t
C: if R1 and R2:CH3, a) NBS,CCl4/AIBN/50-52 oC; (RMe2Si)3CLi/THF/r.t
or if R1 and R2: OH, a) Br(CH2)4Br/K2CO3/DMF; b) RMe2Si)3CLi/THF/r.t
D: if R1=CH3, a) DMSO-H2O/IBX/EtOAc; b) RMe2Si)3CLi/THF/r.t
E: if R1:CH3, a) NBS,CCl4/AIBN/50-52 oC; (RMe2Si)3CLi/CS2/THF/-46oC
F: if R1:CH3, a) NBS,CCl4/AIBN/50-52 oC; (RMe2Si)3CLi/THF/0oC
or if R1 and R2: OH, a) Br(CH2)4Br/K2CO3/DMF; b) RMe2Si)3CLi/THF/0oC
Scheme 1 Some of the synthetic strategies for construction of silicon-containing imidazoles
In previous work, silyl-substituted organometallic reagents (RMe2Si)3CLi were
studied for generation of synthetically useful multisubstituted imidazoles containing
bulky organosilicon groups and organosilylvinyl substituent [16] (routes B, C, D,
Scheme 1). In the other paper in this series, we reported the new type of chemistry
of mixed organosulfur-silicon compounds with Me3Si, SH, and C=S groups
proceeding via nucleophilic attack of organometallic reagent (Me3Si)3CLi at carbon
atom of carbon disulfide in presence of several alkyl and benzyl halides possessing
highly substituted imidazole core at -46 °C [17] (route E, Scheme 1). In another
development, we investigated preparation of thioalkyne-substituted thiazolidine-2-
thione derivatives using (Me3Si)3CLi and CS2 at temperature ranging from 0 to
25 °C [4]. In continuation of our investigations on synthesis of novel organosulfur-
silicon compounds, we set out to study the generality of this reaction with several
alkyl and benzyl bromides possessing polysubstituted imidazole core (route F,
Scheme 1). Pursuing this matter further, initially, we optimized the reaction
123

M. Allahvirdinesbat et al.
conditions for synthesis of fully substituted imidazoles for use in synthesis of
imidazole-based silyl-protected terminal alkynyl thiolates.
Due to the wide application of nanosized metal oxides on different supports as
catalysts for a variety of chemical purposes and during the course of our studies
towards development of facile and clean synthetic methodologies for biologically
active compounds [15, 16, 18], we report herein an efficient green MCR protocol for
synthesis of a variety of 2,4,5-triaryl and 1,2,4,5-tetraaryl imidazoles via
cyclocondensation reactions under solvent-free conditions (Scheme 2).
Nanosized Ag/metal-modified ZSM-5 catalysts were tested for preparation of
imidazole-based derivatives. The X-ray power diffraction (XRD) patterns of the H–
ZSM-5 support, Ag/ZSM-5 monometallic catalyst, and Ag–Fe/ZSM-5 bimetallic
catalyst are shown in Fig. 1. All the characteristic peaks corresponding to H–ZSM-5
appeared in the patterns of Ag/ZSM-5 and Ag–Fe/ZSM-5, suggesting that the original
structure of the support was not destroyed during impregnation and calcination. No
peaks due to metal oxides or metal could be detected in the diffractograms registered
for all the metal-promoted samples. This implies that the metal oxide species are very
small and are well dispersed in the support. The results of Transmission electron
microscopy (TEM) analysis of H–ZSM-5 and Ag–Fe/ZSM-5 catalyst are shown in
Fig. 2. The TEM images of the Ag–Fe/ZSM-5 catalyst indicate that nanooxide
species (dark area) are uniformly distributed over H–ZSM-5.
To the best of the authors’ knowledge, use of Ag-based catalysts for synthesis of
triaryl imidazoles has not been reported to date. Thus, we sought to optimize the
reaction condition for formation of 2-(4-fluorophenyl)-4,5-diphenyl-1H-imidazole
(5b) as model reaction via one-pot three-component reaction of 1,2-diketone
(1 mmol), ammonium acetate (2.2 mmol), and 4-fluorobenzaldehyde (1 mmol),
examining the catalytic effect of nanosized Ag/metal-ZSM-5 oxide species, the
weight loadings of transition metal (wt%), the amount of catalysts, temperature, and
time. We first tested this reaction in presence of pure H–ZSM-5 under solvent-free
condition at 120 °C; however, the yield of 5b was low (Table 1, entry 10). Table 1
shows that, when the model reaction was studied in presence of M/ZSM-5 (M: Ag,
Scheme 2 Preparation of 2,4,5-triaryl and 1,2,4,5-tetraaryl imidazoles using metal-supported
nanocatalysts under various reaction conditions
123

Synthesis of silyl-protected terminal thioalkyne-…
Fig. 1 XRD patterns of H–ZSM-5 support, Ag/ZSM-5 monometallic nanostructure, and Ag–Fe/ZSM-5
bimetallic nanostructure
Fig. 2 TEM images of H–ZSM-5 support (a), Ag/ZSM-5 monometallic nanostructure (b), and Ag– Fe/
ZSM-5 bimetallic nanostructure (c)
Mn, Co, Ni, and Fe) supported nanocatalysts (10 wt%) in the same conditions, the
corresponding product 5b was isolated in 40–65 % yield after 3 h. The behavior of
Ag and Fe is very similar, having higher activity than Mn, Co or Ni (Table 1,
entries 1–5).
Ag/ZSM-5 monometallic nanooxide was prepared with different Ag loadings (3,
5, and 8 wt%). The results showed that the cyclocondensation increased with
increasing silver loading, passing through a maximum at loading of 5 wt%.
Additional increase in the Ag loading had no further effect on the cycloconden-
sation. This can be attributed to excessive Ag agglomeration that blocked the pores
inside and inhibited access of reactants to active sites of the support. Therefore, Ag
loading of 5 wt% on H–ZSM-5 was found to be the optimum loading in this
investigation. However, the proposed reaction proceeded rather slowly, and no
remarkable acceleration was observed.
In the present study, an attempt was made to prepare a series of Ag–M/ZSM-5
(M = Co, Mn, Fe, and Ni) zeolite-supported Ag-based multicomponent catalysts
that would improve the catalytic ability of the heterogeneous catalyst for
123

M. Allahvirdinesbat et al.
Table 1 Optimization of reaction conditions
Entry
Catalyst (wt%)
Time (h)
Yield (%)a
1
Mn/ZSM-5 (10)
Co/ZSM-5 (10)
Ni/ZSM-5 (10)
Fe/ZSM-5 (10)
Ag/ZSM-5 (10)
Ag–Mn/ZSM-5 (5)
Ag–Co/ZSM-5 (5)
Ag–Ni/ZSM-5 (5)
Ag–Fe/ZSM-5 (5)
H–ZSM-5 (10)
No catalyst
3
40
2
3
45
3
3
50
4
3
63
5
3
65
6
1
60
7
1
74
8
1
82
9
1
95
10
11
1 day
1 day
30
Trace
Reaction conditions: 1,2-diketone (1 mmol), ammonium acetate (2.2 mmol), and 4-fluorobenzaldehyde
(1 mmol). The metal content was kept at 5 wt% for M/ZSM-5 catalysts and 2 wt% for Ag–M/ZSM-5
catalysts
a
Indicated yields refer to isolated products
preparation of 2,4,5-trisubstituted imidazoles. Furthermore, study of the catalytic
ability of the Ag–Fe/ZSM-5 catalyst showed that incorporating Fe over Ag/ZSM-5
increased the product yield to 95 % and reduced the reaction time (1 h) with
decreased catalyst loading (5 wt%) under solvent-free condition at 120 °C (Table 1,
entry 9). The highest activity of Ag–Fe/ZSM-5 for preparation of triaryl imidazoles
can be attributed to the favorable synergetic effects of silver and iron over H–ZSM-
5, acidity, and reactant adsorption ability on the catalyst surface. Also, we studied
the effect of various solvents such as EtOH, EtOAc, and CH2Cl2 on the model
reaction. Polar solvents and solventless conditions afforded better yield than
nonpolar solvent, with the best result obtained under solvent-free condition with
Ag–Fe/ZSM-5 catalyst.
To further show the applicability of this protocol, 5-(benzyloxy)-4-oxo-4H-
pyran-2-carbaldehyde was tested in the previous reaction. Unfortunately, the
corresponding triaryl imidazole was isolated in poor yield due to formation of
byproducts (Table 2, entry 9). In comparison, synthesis of derivatives 5a–i with a
wide range of substituted diverse aldehydes bearing either electron-withdrawing or
electron-donating groups and heterocyclic substrates was studied under the same
experimental conditions, and the desired derivatives were obtained in high yield
123

Synthesis of silyl-protected terminal thioalkyne-…
Table 2 Synthesis of 2,4,5-triaryl imidazolesa
Reaction conditions: aldehyde (1 mmol), benzil (1 mmol), ammonium acetate (2.2 mmol), and 5 wt%
Ag–Fe/ZSM-5 for preparation of 5a–i under solvent-free condition at 120 °C
a
Indicated yields refer to isolated products
95
95
94
92
100
80
60
40
20
0
60
60
70
Time (min)
80
Isolated Yield (%)
1
2
3
4
Fig. 3 Reusability results for Ag–Fe/ZSM-5 in preparation of 5b
without significant amounts of undesirable byproducts (Table 2). Furthermore, the
reaction conditions are mild enough not to react with acid-sensitive moieties, such
as ethers, which often undergo cleavage in highly acidic media (5e).
123

M. Allahvirdinesbat et al.
In addition to the benefits from the economical point of view, easy recovery and
reusability of catalyst is very significant to avoid waste. Consequently, we tested the
catalytic performance of recycled Ag–Fe/ZSM-5 in the model reaction. As shown in
Fig. 3, the recovered catalyst could be reused three times without appreciable loss of
its activity during storage.
Following the optimized conditions, an array of tetraaryl imidazoles were
synthesized using the same reaction conditions. The substrate scope of the reaction
was evaluated using a variety of amines and aromatic aldehyde derivatives
(Table 3). In all cases, corresponding products were prepared in excellent yield
Table 3 Synthesis of 1,2,4,5-tetraaryl imidazolesa
Reaction conditions: aldehyde (1 mmol), benzil (1 mmol), ammonium acetate (1.1 mmol), amine
(1 mmol), and 5 wt% Ag–Fe/ZSM-5 for synthesis of 6a–k under solvent-free condition at 120 °C
Indicated yields refer to isolated products
a
123

Synthesis of silyl-protected terminal thioalkyne-…
(Table 3) without preparation of any byproducts such as 2,4,5-triaryl imidazoles,
oxidized products of aniline and aldehyde derivatives, which are generally observed
in strong acid media.
A plausible route for the catalytic activity of Ag–Fe/ZSM-5 is postulated in
Scheme 3. Ag–Fe/ZSM-5 nanocatalyst facilitates formation of diamine intermediate
[A] by increasing the electrophilicity of the aldehyde’s carbonyl group. Intermediate
[A], in presence of Ag–Fe/ZSM-5, condenses with diketone to form intermediate
[B], which in turn rearranges to the 2,4,5-triaryl imidazole by a [1, 5] hydrogen shift
(Scheme 3).
Similarly, a plausible mechanism for the preparation of the tetraaryl imidazole
involves the formation of intermediate [C] by reaction of an aldehyde, primary
amine, and ammonium acetate using Ag–Fe/ZSM-5 as catalyst. Intermediate
[C] condenses with diketone to form intermediate [D], to obtain imidazol-5-ol
intermediate [E] that, upon elimination of water, is transformed into the desired
products (Scheme 4).
To extend our investigation, some tetraaryl imidazoles containing triple bond
including sulfur atom and trimethylsilyl group were synthesized through nucle-
ophilic reaction of (Me3Si)3CLi with carbon disulfide at 0 °C.
(Bromomethyl)phenyl-imidazoles 7f, g, i were synthesized according to
Scheme 5. Following use of N-bromosuccinimide (NBS) in CCl4 in presence of
catalytic amount of a,a0-azobisisobutyronitrile (AIBN) at 50–52 °C, bromination
products were obtained, to which we assign the structures 6f, g, i. The crude products
were used directly for preparation of compounds 8f, g, i by reaction with
tris(trimethylsilyl)methyllithium and CS2 at 0 °C, in short reaction time and high
yield. In addition, treatment of TsiLi and CS2 with bromobutoxy-imidazoles 7j,
k was investigated. These compounds were synthesized by treatment of the
hydroxyl-imidazoles 6j, k with K2CO3 and 1,4-dibromobutane in Dimethylfor-
mamide (DMF) (Scheme 5). Reaction of TsiLi and CS2 with 7j, k gave compounds
Scheme 3 Proposed route for
preparation of 2,4,5-triaryl
imidazoles using Ag–Fe/ZSM-5
2 NH4OAc
Ar
Ar
2 NH3
O
NH2
[A]
H2N
H
Ph
O
O
Ph
Ph
Ph
Ph
Ph
N
N
H
-2 H2O
N
Ar
Ar
N
H
[B]
= Ag-Fe/ZSM-5
123

M. Allahvirdinesbat et al.
NH4OAc
NH3
Ar
Ar
Ar
N
R
NH2
O
N
+
RNH2
-H2O
H
RHN
[C]
H
Ph
Ph
O
O
Ar
RHN
Ph
Ph
Ph
Ph
NH
N
N
H
OH
Ph
-HOH
O
Ar
Ar
-H2O
N
R
OH
ph
R
[E]
[D]
= Ag-Fe/ZSM-5
Scheme 4 Proposed route for preparation of 1,2,4,5-tetraaryl imidazoles by Ag–Fe/ZSM-5
MeLi
2h
THF
Me3SiCl + CHCl3 + Li
(Me3Si)3CH
R2
(Me3Si)3CLi
R2
R2
NBS
(Me3Si)3CLi
10% AIBN
CCl4/ 50-52 o
N
N
CS2
N
N
THF/0 o
C
C
N
N
Br
S
7f R2=H
8f R2=H
82%
SiMe3
SiMe3
6f R2=H
7g R2=4-F
7i R2=3-Cl
8g R2=4-F 88%
8i R2=3-Cl 85%
6g R2=4-F
6i R2=3-Cl
S
3
O
Br
O
4
N
N
R1
SiMe3
OH
N
N
7j R1=H
K2CO3
R1
(Me3Si)3CLi
CS2
8j R1=H 79%
DMF/r.t
N
N
S
Br
4
THF/0 o
C
Br
)
(
3
O
Br
SiMe3
O
6j R1=H
R1
4
6k R1=OH
S
N
N
N
)
(
3
N
O
( )
4 Br
7k
O
8k 80%
Scheme 5 Preparation of organosulfur-silicon-containing tetraaryl imidazoles
123

Synthesis of silyl-protected terminal thioalkyne-…
S
S
Me3Si
CS2
R
Br
Me3Si
SiMe3
SiMe3
-
S Li+
R
R
S
Me3Si
Li
0 oC
Me3Si
Me3Si SiMe3
Me3Si
[B]
[A]
-
Li+Br
-
+S
Li
S
-LiSSiMe3
SiMe3
SiMe3
SiMe3
R
S
[C]
RX=alkyl and benzyl bromides possessing polysubstituted imidazole core
Scheme 6 Plausible mechanism for reaction of TsiLi, CS2, and bromoimidazoles
8j, k at 0 °C. All spectroscopic results indicated that the nucleophilic substitution on
bromoimidazoles was complete.
The precursor (Me3Si)3CH was prepared by reaction of Li, chloroform, and
trimethylsilyl chloride in tetrahydrofuran (THF). The solvated organolithium
reagent (Me3Si)3CLi was obtained by treatment of (Me3Si)3CH with methyllithium
under reflux conditions in THF (Scheme 5).
A possible mechanism for the synthesis of trimethylsilylethynylthiolato group-
containing tetraaryl imidazoles is depicted in Scheme 6. First, addition of carbon
disulfide to tris(trimethylsilyl)methyllithium at 0 °C produced lithium 2,2,2-
tris(trimethylsilyl)ethanedithioate (Me3Si)3C(S)SLi (A) as intermediate, which
subsequently reacted with alkyl and benzyl bromides possessing highly substituted
imidazole core (7f, g, i–k) to give (Me3Si)3C(S)SCH2R (B). E2 elimination from
B with nucleophilic attack of Br- at Me3Si, which leads to loss of BrSiMe3 group,
produced C. Intermediate C was unstable with respect to loss of LiSSiMe3 group,
resulting in final products 8f, g, i–k (Scheme 6).
Conclusions
We successfully developed a straightforward and atom-economic green approach
for synthesis of structurally diverse 2,4,5-triaryl and 1,2,4,5-tetraaryl imidazoles,
employing nanosized Ag/metal oxide species on H–ZSM-5 as promoter under
solvent-less condition. The protocol has several advantages such as excellent yield
combined with ease of recovery and reuse of the catalyst, being a waste-free
chemical process with methodological ease due to formation of carbon–carbon and
carbon–nitrogen bonds in a single step. We also describe an efficient synthetic
strategy for silyl-protected terminal alkynyl thiolates from alkyl and benzyl
bromides possessing highly substituted imidazole core at 0 °C. Imidazoles bearing
trimethylsilylethynylthiolato groups are key intermediates for functionalization of
123

M. Allahvirdinesbat et al.
imidazoles through preparation of alkynyl thiolate units. We will study this
possibility and discuss our results in future communications.
Experimental
Materials and techniques
Chemicals were either synthesized in our laboratory or purchased from Fluka, Merck,
and Aldrich. Commercial products were used without further purification. All yields
refer to isolated products. The Fourier transform infrared spectroscopy (FTIR) spectra
1
of the compounds were obtained on a Bruker Tensor 270 spectrometer. H and 13
C
Nuclear magnetic resonance spectroscopy (NMR) spectra were measured with a
Bruker FT-400 MHz spectrometer at room temperature with CDCl3 and/or Dimethyl
sulfoxide (DMSO)-d6 as solvent. The abbreviations used for NMR signals are:
s = singlet, d = doublet, t = triplet, and m = multiplet. Elemental analyses were
performed using an Elementar Vario EL III instrument. Melting points were recorded
on a Bu¨chi B-545 apparatus in open capillary tubes and are uncorrected.
Preparation of catalysts
Ag/ZSM-5 nanooxides with various loadings of Ag (3, 5, and 8 wt%) and other
monometallic nanooxides (with metal content 5 %) were prepared by the incipient
wetness impregnation technique, and other all bimetallic nanooxides with 5 wt% Ag
and 2 wt% transition metal were obtained by the simultaneous impregnation
procedure. The precursors for metals were AgNO3, Co(NO3)2Á6H2O, Fe(NO3)3-
9H2O, Ni(NO3)2Á6H2O, and Mn(NO3)2Á4H2O. H–ZSM-5 support obtained from
Zeochem Int with SiO2/Al2O3 = 50 was used to fabricate the catalysts. Typically,
1 g H–ZSM-5 zeolite was added to aqueous solution containing calculated amounts
of silver nitrate and transition-metal nitrate, followed by continuous stirring at
45 °C until the slurry was completely dry. The prepared samples were dried at
110 °C overnight and calcined at 600 °C for 4 h in air.
Characterization of catalysts
Powder X-ray diffraction patterns of the prepared catalysts were obtained at room
temperature using a D500 diffractometer (Siemens) with Cu Ka radiation
(k = 0.154050 nm) in the 2h range of 5–70° at scan rate of 0.016 s-1. The
morphology of the obtained catalysts was observed by transmission electron
microscopy using a JEOL 2000 (JEOL, Japan) operated at 200 kV.
General procedure for synthesis of 2,4,5-triaryl imidazoles 5a–i
A mixture of benzil (1 mmol), aldehyde (1 mmol), ammonium acetate (2.2 mmol),
and Ag–Fe/ZSM-5 (3 wt%) was heated at 120 °C within 50–70 min. After
completion of the reaction as indicated by thin-layer chromatography (TLC), the
123

Synthesis of silyl-protected terminal thioalkyne-…
reaction mixture was cooled to room temperature. The mixture was dissolved in
ethanol, and supported reagent was separated by filtration. The crude product was
recrystallized from ethanol to afford the pure products. The catalyst was washed
three times with ethanol and dried under vacuum before reuse. The spectroscopic
data of some of the new products are given below.
2-(2-Chlorophenyl)-4,5-diphenyl-1H-imidazole (5c)
White powder; yield 94 %; m.p. = 190–192 °C; FTIR (KBr, cm-1): 3437, 3062,
2956, 1599, 1501, 1477, 1445, 1386, 971, 763, 695, 518. H NMR (400 MHz,
1
CDCl3, ppm): d 7.24–7.45 (m, 9H, Ar–H), 7.56–7.58 (m, 4H, ArH), 8.39 (d,
J = 7.4 Hz, 1H, ArH), 10.11 (s, 1H, N–H). 13C NMR (100 MHz, CDCl3, ppm): d
126.43, 126.51, 126.73, 126.86, 126.90, 127.42, 127.62, 128.55, 129.40, 129.81,
142.16. Anal. Calcd. for C21H15ClN2: C 76.24, H 4.57, N 8.47 %. Found: C 76.01,
H 4.78, N 8.19 %.
4-(4,5-Diphenyl-1H-imidazol-2-yl)phenol (5d)
White powder; yield 96 %; m.p. = 243–244 °C; FTIR (KBr, cm-1): 3616, 3359,
3056, 2976, 1648, 1608, 1546, 1497, 1447, 1359, 1250, 835, 767, 739, 695. H
1
NMR (400 MHz, DMSO-d6, ppm): d 6.80 (d, J = 8.4 Hz, 2H, ArH), 7.16 (t,
J = 7.0 Hz, 1H, ArH), 7.25 (t, J = 7.4 Hz, 2H, ArH), 7.31 (t, J = 7.0 Hz, 1H,
ArH), 7.38 (t, J = 7.5 Hz, 2H, ArH), 7.44 (d, J = 7.1 Hz, 2H, ArH), 7.48 (d,
J = 8.0 Hz, 2H, ArH), 7.85 (d, J = 8.5 Hz, 2H, ArH), 9.77 (s, 1H, O–H), 12.38 (s,
1H, N–H). 13C NMR (100 MHz, DMSO-d6, ppm): d 115.46, 121.66, 126.44,
126.91, 127.10, 127.43, 127.61, 128.22, 128.36, 128.70, 131.33, 135.43, 136.63,
146.12, 157.83. Anal. Calcd. for C21 H16N2O: C 80.75, H 5.16, N 8.97 %. Found: C
80.95, H 5.01, N 9.08 %.
2-(Benzo[d][1,3]dioxol-5-yl)-4,5-diphenyl-1H-imidazole (5e)
White powder; yield 96 %; m.p. = 251–253 °C; FTIR (KBr, cm-1): 3415, 3058,
2973, 2884, 1634, 1605, 1481, 1339, 1237, 1159, 1070, 1038, 934, 814, 767, 733,
697. 1H NMR (400 MHz, CDCl3, ppm): d 5.93 (s, 1H, N–H), 6.02 (s, 2H, O–CH2–
O), 6.85 (d, J = 7.8 Hz, 2H, ArH), 7.29–7.56 (m, 10H, ArH), 7.76 (d, J = 7.4 Hz,
1H, ArH). 13C NMR (100 MHz, CDCl3, ppm): d 58.29, 100.14, 100.35, 105.21,
106.72, 107.46, 107.54, 118.28, 120.20, 123.18, 126.03, 126.35, 126.79, 127.54,
127.58, 130.79, 144.93, 147.16, 147.22. Anal. Calcd. for C22H16N2O2: C 77.63, H
4.74, N 8.23 %. Found: C 77.45, H 4.93, N 7.99 %.
4,5-Diphenyl-2-p-tolyl-1H-imidazole (5g)
White powder; yield 97 %; m.p. = 236–238 °C; FTIR (KBr, cm-1): 3335, 3056,
2948, 2916, 1634, 1576, 1526, 1489, 1453, 1348, 1296, 820, 722, 693, 595. H
1
NMR (400 MHz, CDCl3, ppm): d 2.26 (s, 3H, CH3), 5.55 (s, 1H, N–H), 7.04 (d,
J = 7.5 Hz, 2H, ArH), 7.16 (d, J = 7.5 Hz, 2H, ArH), 7.26–7.38 (m, 7H, ArH),
123

M. Allahvirdinesbat et al.
7.43 (d, J = 6.9 Hz, 1H, ArH), 7.73 (d, J = 7.7 Hz, 2H, ArH). 13C NMR
(100 MHz, CDCl3, ppm): d 20.12, 126.00, 126.49, 127.53, 128.41, 130.61, 134.74.
Anal. Calcd. for C22H18N2: C 85.13, H 5.85, N 9.03 %. Found: C 85.35, H 5.70, N
9.25 %.
3-(4,5-Diphenyl-1H-imidazol-2-yl)-1H-indole (5h)
Red powder; yield 96 %; m.p. = 281–283 °C; FTIR (KBr, cm-1): 3630, 3412,
3053, 2965, 2889, 1665, 1598, 1492, 1449, 1335, 1267, 751, 697, 512. H NMR
1
(400 MHz, DMSO-d6, ppm): d 7.12–7.23 (m, 3H, ArH), 7.30–7.37 (m, 3H, ArH),
7.42–7.46 (m, 3H, ArH), 7.51 (d, J = 7.3 Hz, 2H, ArH), 7.63 (d, J = 7.4 Hz, 2H,
ArH), 7.99 (d, J = 2.4 Hz, 1H, ArH), 8.46 (d, J = 7.4 Hz, 1H, ArH), 11.39 (s, 1H,
N–H (indol)), 12.30 (s, 1H, N–H). 13C NMR (100 MHz, DMSO-d6, ppm): d 38.83,
39.08, 39.29, 39.50, 39.71, 39.92, 40.12, 106.86, 111.70, 119.80, 121.56, 121.96,
123.85, 125.1, 125.82, 126.28, 126.95, 127.49, 128.23, 128.27, 128.79, 131.66,
135.77, 136.32, 143.80. Anal. Calcd. for C23H17N3: C 82.36, H 5.11, N 12.53 %.
Found: C 82.08, H 5.32, N 12.35 %.
General procedure for synthesis of 1,2,4,5-tetraaryl imidazoles 6a–k
A mixture of benzil (1 mmol), aldehyde (1 mmol), ammonium acetate (1.1 mmol),
amine (1 mmol), and Ag–Fe/ZSM-5 (3 wt%) was heated at 120 °C within
50–70 min. After completion of the reaction as indicated by TLC, the reaction
mixture was cooled to room temperature. The mixture was dissolved in ethanol, and
supported reagent was separated by filtration. The crude product was recrystallized
from ethanol to afford the pure products. The catalyst was washed three times with
ethanol and dried under vacuum before reuse. The spectroscopic data of some of the
products were given in Refs. [19, 20].
General procedure for bromination of imidazole derivatives was described in
Refs. [16, 17]; they were used for preparation of silyl-protected terminal alkynyl
thiolates containing tetraaryl imidazoles.
General procedure for preparation of silyl-protected terminal alkynyl
thiolates containing tetraaryl imidazoles
Tris(trimethylsilyl)methyllithium (Me3Si)3CLi was synthesized as described by
¨
Grobel and coworkers [21]. Carbon disulfide (1.2 mmol) in 2 mL THF was added
to a stirred solution of tris(trimethylsilyl)methyllithium (1 mmol) in THF at 0 °C
under argon atmosphere. The mixture was stirred for 5 min, alkyl and benzyl
bromides possessing tetraaryl imidazole core (1 mmol) or bis(bromobutoxy)imida-
zole (0.5 mmol) was added at this temperature, and the stirring was maintained to the
end of the reaction as followed by TLC. The mixture was poured into water and
extracted with EtOAc. The organic layer was washed with water, dried with MgSO4,
and filtered. The solvent was removed in vacuum, 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. Characterization data for the new products are given below:
123

Synthesis of silyl-protected terminal thioalkyne-…
2-(4-((2-(Trimethylsilyl)ethynylthio)methyl)phenyl)-1,4,5-triphenyl-1H-imidazole
(8f)
Yellow sticky solid (82 %). FTIR (KBr, cm-1): 3059, 2957, 2923, 2853, 2091 (C:C),
1740, 1681, 1600, 1495, 1450 (C=C), 1250, 841 (C–Si), 759, 697, 539. H NMR
1
(400 MHz, CDCl3, ppm): d 0.13 (s, 9H, SiMe3), 3.87 (s, 2H, CH2), 6.98–7.15 (m, 4H,
Ar–H), 7.17–7.48 (m, 11H, Ar–H), 7.58 (dd, J = 1.8 Hz, J = 7.3 Hz, 2H, Ar–H),
7.66–7.69 (m, 2H, Ar–H). 13C NMR (100 MHz, CDCl3, ppm): d 1.08 (SiMe3), 38.98
(CH2), 90.85 and 100.92 (C:C), 126.21, 126.36, 126.80, 127.16, 127.33, 127.38,
127.41, 127.54, 127.85, 127.95, 128.15, 128.19, 131.32, 136.34, 138.16. Anal. Calcd.
for C33 H30N2SSi: C 77.00, H 5.87, N 5.44 %. Found: C 77.31, H 5.94, N 5.82 %.
2-(4-((2-(Trimethylsilyl)ethynylthio)methyl)phenyl)-1-(4-fluorophenyl)-4,5-
diphenyl-1H-imidazole (8g)
Yellow sticky solid (88 %). FTIR (KBr, cm-1): 3055, 2956, 2090 (C:C), 1602,
1507, 1444 (C=C), 1250, 843 (C–Si), 774, 699, 657, 528. H NMR (400 MHz,
1
CDCl3, ppm): d 0.13 (s, 9H, SiMe3), 3.88 (s, 2H, CH2), 6.97 (d, J = 8.2 Hz, 2H,
Ar–H), 7.02–7.03 (m, 2H, Ar–H), 7.11 (d, J = 6.4 Hz, 2H, Ar–H), 7.20–7.26 (m,
8H, Ar–H), 7.40 (d, J = 8.1 Hz, 2H, Ar–H), 7.57 (d, J = 7.2 Hz, 2H, Ar–H). 13C
NMR (100 MHz, CDCl3, ppm): d -1.11 (SiMe3), 38.94 (CH2), 90.09 and 101.04
(C:C), 115.16, 115.39, 125.81, 126.37, 127.04, 127.14, 127.21, 127.50, 127.97,
129.05, 129.13, 129.37, 129.45, 129.58, 130.10, 131.98, 133.35, 136.27, 142.21,
145.00, 160.10, 161.07. Anal. Calcd. for C33H29FN2SSi: C 74.40, H 5.49, N 5.26 %.
Found: C 74.28, H 5.54, N 5.02 %.
2-(4-((2-(Trimethylsilyl)ethynylthio)methyl)phenyl)-1-(3-chlorophenyl)-4,5-
diphenyl-1H-imidazole (8i)
Yellow sticky solid (85 %). FTIR (KBr, cm-1): 3030, 2954, 2089 (C:C), 1652,
1491, 1422, 1365 (C=C), 1246, 841 (C–Si), 772, 697, 528, 500. 1H NMR
(400 MHz, CDCl3, ppm): d 0.14 (s, 9H, SiMe3), 3.89 (s, 2H, CH2), 6.98 (d,
J = 8.6 Hz, 1H, Ar–H), 7.11 (d, J = 6.5 Hz, 1H, Ar–H), 7.18–7.32 (m, 14H, Ar–
H), 7.57 (d, J = 6.9 Hz, 2H, Ar–H). 13C NMR (100 MHz, CDCl3, ppm): d -1.11
(SiMe3), 38.95 (CH2), 89.88 and 102.59 (C:C), 125.82, 126.36, 126.48, 127.19,
127.27, 127.55, 127.97, 128.00, 128.34, 128.44, 128.59, 129.85, 130.09, 133.34,
134.54, 135.95, 145.36. Anal. Calcd. for C33H29ClN2SSi: C 72.17, H 5.32, N
5.10 %. Found: C 72.30, H 5.04, N 5.23 %.
1-(4-(4-(2-(Trimethylsilyl)ethynylthio)butoxy)phenyl)-2,4,5-triphenyl-1H-imidazole
(8j)
Yellow sticky solid (79 %). FTIR (KBr, cm-1): 3098, 2926, 2855, 2091 (C:C),
1608, 1512, 1472, 1400 (C=C), 1250, 838 (C–Si), 1104 (C–O–Ar), 696, 621, 469.
1H NMR (400 MHz, CDCl3, ppm): d 0.16 (s, 9H, SiMe3), 1.91–1.92 (m, 4H, 2CH2),
2.79 (t, J = 6.5 Hz, 2H, CH2), 3.93 (t, J = 4.6 Hz, 2H, CH2), 6.73 (d, J = 8.8 Hz,
123

M. Allahvirdinesbat et al.
2H, ArH) 6.94 (d, J = 8.8 Hz, 2H, ArH), 7.11–7.26 (m, 11H, ArH), 7.45 (d,
J = 6.5 Hz, 2H, ArH), 7.58 (d, J = 7.1 Hz, 2H, ArH). 13C NMR (100 MHz,
CDCl3, ppm): d -1.00 (SiMe3), 24.69, 26.67, 28.69, 34.77, 66.37, 90.95 and 101.05
(C:C), 113.05, 125.54, 126.37, 126.85, 127.08, 127.22, 128.67, 129.05, 129.31,
129.74, 130.15, 134.05, 138.00, 146.74, 157.66. Anal. Calcd. for C36H36N2OSSi: C
75.48, H 6.33, N 4.89 %. Found: C 75.21, H 6.09, N 5.01 %.
1,2-Bis(4-(4-(2-(trimethylsilyl)ethynylthio)butoxy)phenyl)-4,5-diphenyl-1H-
imidazole (8k)
Yellow sticky solid (80 %). FTIR (KBr, cm-1): 3059, 2925, 2859, 2090 (C:C),
1675, 1608, 1511, 1469, 1391 (C=C), 1246, 836 (C–Si), 1170, 1100 (C–O–Ar), 738,
695, 469. 1H NMR (400 MHz, CDCl3, ppm): d 0.13 (s, 18H, SiMe3), 2.00–2.03 (m,
8H, 4CH2), 2.05–2.09 (m, 4H, 2CH2), 3.79–3.89 (m, 4H, 2CH2), 6.79–6.85 (m, 4H,
ArH), 6.98 (d, J = 6.5 Hz, 2H, ArH), 7.15–7.30 (m, 8H, ArH), 7.40 (d, J = 8.4 Hz,
2H, ArH), 7.62 (d, J = 7.6 Hz, 2H, ArH). 13C NMR (100 MHz, CDCl3, ppm):
-1.56 (SiMe3), 25.00, 26.67, 28.68, 35.02, 67.69, 67.90, 90.77 and 100.64 (C:C),
113.05, 113.64, 125.49, 126.39, 126.80, 127.10, 127.31, 128.47, 129.29, 130.14,
133.57, 133.58, 136.90, 157.77, 158.00. Anal. Calcd. for C45H52N2O2S2Si2: C
69.90, H 6.78, N 3.62 %. Found: C 69.79, H 6.99, N 3.78 %.
Acknowledgments The authors would like to acknowledge the financial support from the University of
Tabriz and Iranian Nanotechnology Initiative.
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