N-Propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride-SBA-15 (SBA-DABCO) as basic mesoporous catalyst for the synthesis of 1,4-dihydropyridine hetrocyclic compounds

Article abstract of DOI:10.1016/j.catcom.2015.06.019

Regarding the green chemistry's goals, the development of mesoporous silica materials as attractive candidates in the search for supporting of catalysts is currently a subject of increasing interest. Therefore, in the present research n-propyl-4-aza-1-azo

Full text of DOI:10.1016/j.catcom.2015.06.019

Catalysis Communications 69 (2015) 179–182
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
n-Propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride-SBA-15
SBA-DABCO) as basic mesoporous catalyst for the synthesis of
,4-dihydropyridine hetrocyclic compounds
(
1
a
b,
Ali Reza Kiasat , Jamal Davarpanah ⁎
a
Chemistry Department, College of Science, Shahid Chamran University, Ahvaz, Iran
Chemistry Department, Production Technology Research Institute—ACECR, Ahvaz, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 May 2015
Received in revised form 21 June 2015
Accepted 23 June 2015
Available online xxxx
Regarding the green chemistry's goals, the development of mesoporous silica materials as attractive candidates in
the search for supporting of catalysts is currently a subject of increasing interest. Therefore, in the present re-
search n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride-SBA-15 (SBA–DABCO) was used as a basic catalyst
for the synthesis of 1,4-dihydropyridine (DHP) derivatives from one pot, three-component condensation of
aromatic aldehydes, ammonium acetate and ethylacetoacetate under solvent-free at 80 °C. This method offers
several advantages, including high yield, short reaction time, simple work-up procedure, ease of separation
and recyclability of the catalyst, as well as the ability to tolerate a wide variety of substitutions in the reagents.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Mesoporous catalyst
Dihydropyridine heterocyclic compounds
DABCO
Multicomponent reaction
Organic–inorganic hybrid silica
1
. Introduction
Taking into account the basic principles of green synthesis, the use of
of constant growth due to their applications in catalysis for a variety of
reactions.
In recent year, silica has attracted significant attention of chemists as
a good support for immobilization of homogeneous catalysts [16].
Perhaps no class of inorganic support has been more widely studied
for catalytic applications than silica. Among these kinds of materials,
mesoporous silica materials such as SBA-15, have attracted much atten-
tion, due to their interesting properties that include tunable pore sizes,
stabilities and shape selectivity. SBA-15 is typically synthesized under
mild conditions, allowing for the incorporation of constituent building
blocks with desired functionalities, leading to numerous functional
SBA-15 that has shown promise for a number of applications [17–20].
On the other hand, dihydropyridines and their derivatives (DHPs)
are very well known for their wide range of biological activities includ-
ing antihypertensive, vasodilator, antimutagenic, antitumor, anticon-
vulsant, antidiabatic, antianxiety, antidepressive, analgesic, seditative,
bronchodilator, hypnotic and anti-inflammatory [21]. Consequently,
several methods have been reported for the promoting preparation
DHP derivatives [22]. Although most of these processes offer distinct ad-
vantages, they suffer from some drawbacks such as low yields, extended
reaction times, harsh reaction conditions, tedious work-up procedures,
toxic solvents and application of expensive or unavailability catalysts.
Moreover, in most of the reported methods, catalysts are not recyclable.
Therefore, to overcome these drawbacks a great deal of efforts is direct-
ed to develop an efficient catalytic system for synthesis of these
compounds.
catalysis is a major tool in green synthesis and engineering [1]. 1,4-
Diazabicyclo[2.2.2]octane (DABCO) is an inexpensive commercially or-
ganic base which has been used as catalyst in different organic
reactions [2–6]. However, in many of the reactions, DABCO has not
been recovered. Thus, search for finding a heterogeneous, recoverable
and reusable derivative of DABCO is very desirable.
Moreover, the DABCO-base ionic liquids are used for metal adsor-
bents from aqueous solutions, stationary phase for chromatography,
ionophores in polymeric membrane ion-selective electrode, optical
and electronic devices field [7–9]. This kind of ionic quaternary ammo-
niums, as well as, other resemblances can be used as highly efficient and
environmentally friendly catalysts in organic synthesis.
High cost and difficulty in recycling limited ionic liquid (IL) applica-
tions to the industrial scale. Furthermore, it has been reported that
supporting or immobilization became a general concept to heterogenized
ILs, which led to more improvements in efficiency compared to homoge-
nous ionic liquids [10,11].
In contrast to the solid acid catalysts, the solid base catalysts are
much less frequently used in heterogeneous catalysts [12–15]. Herein,
supported ionic liquid catalysts (SILCs) are an attractive research area
⁎
Corresponding author.
E-mail address: jamaldavarpanah@gmail.com (J. Davarpanah).
http://dx.doi.org/10.1016/j.catcom.2015.06.019
566-7367/© 2015 Elsevier B.V. All rights reserved.
1

180
A.R. Kiasat, J. Davarpanah / Catalysis Communications 69 (2015) 179–182
Scheme 1. Application of SBA–DABCO as basic mesoporous catalyst for the synthesis of DHP derivatives.
However, a supported DABCO as the catalyst for the synthesis of
distribution were calculated by Brunauer–Emmett–Teller (BET) method
and Barrett–Joyner–Halenda (BJH) model, respectively.
DHPs has not been studied yet. Thus, we envisioned that supported
DABCO ionic liquid may act as base catalyst in the synthesis of DHPs.
By considering all the above-mentioned points, we turned our attention
towards the synthesis of 1,4-dihydropyridine (DHP) derivatives by
inorganic–organic hybrid basic nanocatalyst by supporting DABCO,
SBA–DABCO, as a proficient, mild, harmless to the environment,
recyclable, non-toxic solid base catalyst with good stability towards
humidity.
2.2. Synthesis of 1,4-diazabicyclo[2.2.2]octane-SBA (SBA–DABCO)
First, chloropropyl-grafted SBA-15 (SBA-Cl) was prepared by the di-
rect incorporation of chloropropyl groups through co-condensation of
TEOS and CPTMS, according to the reported method [23]. Then, SBA-Cl
(10.0 g) was added to a flask containing 100 mL of anhydrous toluene
and an excess of DABCO (1 g, 9 mmol). The reaction mixture was
refluxed with stirring for 24 h. Then, the reaction mixture was cooled
to room temperature, transferred to a vacuum glass filter, and washed
with toluene. The SBA chemically bonded with DABCO (SBA–DABCO)
was dried at 50 °C for 8 h.
2
. Experimental
2
.1. General
For the direct synthesis of chloro-functionalized SBA-15,
tetraethylorthosilicate (TEOS) was used as a silica source, 3-
chloropropyltrimethoxysilane (CPTMS) was used as a chloropropyl
2.3. Typical procedure for the preparation of 1,4-DHPs
group source and Pluronic P-123 triblock copolymer (EO20PO70EO20
,
A mixture of aromatic aldehyde (1 mmol), ethylacetoacetate
(2 mmol) and ammonium acetate (1.5 mmol), and SBA–DABCO
(0.05 g) was heated at 80 °C for appropriate time. After satisfactory
completion of the reaction and cooling, the crude product was extracted
MW. 5800) was used as a structure-directing agent, were supplied by
Aldrich. Other chemical materials were purchased from Fluka and
Merck companies and used without further purification. Products
1
were characterized by comparison of their physical data, IR and H-
by CH
2
Cl
2
. The organic solvent was removed by simple evaporation and
O to afford pure corre-
1
3
NMR and C-NMR spectra with known samples. NMR spectra were re-
corded on a Bruker Advance DPX 400 MHz instrument spectrometer
using TMS as internal standard. IR spectra were recorded on a
BOMEM MB-Series 1998 FT-IR spectrometer.
finally crude product recrystallized from EtOH/H
2
sponding 1,4-dihydropyridine derivatives in high yields.
3. Results and discussion
The purity determination of the products and reaction monitoring
were accomplished by TLC on silica gel PolyGram SILG/UV 254 plates.
The particle morphology was examined by SEM (Philips XL30 scanning
electron microscope) and TEM (Zeiss — EM10C — 80 KV). Nitrogen ad-
sorption measurements were conducted at 77.4 K on a Micrometrics
ASAP-2020 sorptionmeter. The specific surface area and the pore size
In continuation to our study about application of heterogeneous
catalysts as green catalyst in the synthesis of biologically relevant
3
400
2900
2400
1900
1400
900
400
-
1
Wavenumber (cm )
Fig. 1. The FT-IR spectra of SBA–DABCO.
Fig. 2. TEM image of SBA–DABCO.

A.R. Kiasat, J. Davarpanah / Catalysis Communications 69 (2015) 179–182
181
Fig. 3. Thermal gravimetric analysis–derivative thermogravimetric analysis (TGA–DTG) of SBA–DABCO.
heterocyclic compounds, herein we report catalytic application
of n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride-SBA-15
analysis (DTA) (Fig. 3), and by their comparisons with that of authentic
sample.
(
SBA–DABCO) as basic mesoporous catalyst for the synthesis of 1,4-
Fig. 1 shows the FT-IR spectra of SBA–DABCO in the 400–3800 cm−1.
The presence of peaks at 473, 801 and 1070 to 1200 cm− was most
probably due to the symmetric and asymmetric stretching vibrations
of framework and terminal Si–O groups. The C–H stretching peaks at
1
dihydropyridine (DHP) derivatives from one pot, three-component
condensation of aromatic aldehydes, ammonium acetate and
ethylacetoacetate under solvent-free conditions at 80 °C (Scheme 1).
Recently, we have obtained a new charged hybrid organic–inorganic
mesoporous silica, n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride-
SBA-15 (SBA–DABCO). The catalyst (SBA–DABCO) was prepared
according to the recently reported method [24] with some modifica-
tions by the direct incorporation of chloropropyl groups through co-
condensation of TEOS and CPTMS and then grafting of DABCO onto
the surface of the mesoporous silica by the simple nucleophilic substitu-
tion reaction. The catalyst has been characterized by a scanning electron
microscope (SEM), Brunauer Emmett Teller (BET), X-ray powder
diffraction (XRD) and elemental analysis (CHN) (see the Supplemental
−
1
1200 to 1250 and 2950 to 2830 cm indicate that the surface of silica is
successfully modified by double-charged diazoniabicyclo[2.2.2]octane
−
1
chloride. A band at 1465 cm
is characteristic of the tertiary
−
1
amine group. The bands around 1635 and 3400 cm
are also due
to the bending vibration of water molecules which were adsorbed
on the surface.
The morphological characterization and the particle size distribution
of SBA–DABCO were performed by measuring TEM (Fig. 2). From the
TEM image, the pore structure and orderly pore arrangement could be
clearly observed and confirmed the long-range, three dimensional and
mesoporous ordering in this organocatalyst.
The TGA–DTG of SBA–DABCO is shown in Fig. 3. It can be observed
from the thermogram that the sample shows a three-stage degradation
pattern over the range of 50–600 °C. The onset of degradation occurred
around 81 °C, which can be attributed completely to the loss of adsorbed
water molecules. The second and third weight losses at about 320
and 480 °C associated to the thermal decomposition of Pr-DABCO.
Thus, the TGA and DTG curves also convey the obvious information
that the surface of silica is successfully modified by double-charged
Materials for Figs. S
troscopy (FT-IR) (Fig. 1), transmission electron microscopy (TEM)
Fig. 2), thermogravimetric analysis (TGA) and differential thermal
1 3 1
–S and Table S ), Fourier transform infrared spec-
(
Table 1
Solvent-free reaction of benzaldehyde, ethylacetoacetate, and ammonium acetate under
different conditions.
Entry
Solvent
T (°C)
Catalyst (g)
Time (min)
Yielda (%)
diazoniabicyclo[2.2.2]octane chloride. Figure S
3
shows the XRD
1
2
3
4
5
6
7
8
9
Ethanol
Acetonitrile
Water
Reflux
Reflux
Reflux
Reflux
130
120
100
25
80
80
80
80
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.1
30
30
30
30
30
7
7
60
7
42
41
44
34
50
86
92
Trace
88
diffractrogram of SBA–DABCO. The peak positions in the sample
remained constant after the functionalization process compare to the
SBA-15. It can be observed the intense peak corresponding to the pore
family and the two additional weak reflections assigned to the
family planes, which are indicative of high hexagonal mesoscopic
order [25,26].
After characterization, the catalytic performance of this basic
organocatalyst has been systematically studied in the rapid and efficient
preparation of 1,4-dihydropyridine (DHP) heterocyclic compounds
through a multicomponent reaction. A model four-component coupling
reaction of benzaldehyde, ethylacetoacetate and ammonium acetate
Toluene
Ethanol–water
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
1
1
1
0
1
2
0.05
0.02
–
7
10
60
96
86
Trace
a
Isolated yield.

182
A.R. Kiasat, J. Davarpanah / Catalysis Communications 69 (2015) 179–182
Scheme 2. Synthesis of 1,4-dihydropyridines.
was examined to determine whether the use of SBA–DABCO was
efficient and to investigate the optimized conditions (Table 1).
After some experiments (Table 1), it was found that the use of benz-
aldehyde (1 mmol), ethyl acetoacetate (2 mmol) and ammonium
acetate (2 mmol) in the presence of SBA–DABCO (0.05 g) under
solvent-free conditions at 80 °C were the best condition.
In order to elucidate the role of catalyst, a control reaction was set up
in the absence of catalyst. It was found that in the absence of catalyst
only trace amounts of the desired product was observed on the TLC
plate even after 1 h of heating. When the reaction was performed in
the presence of SBA–DABCO, it proceeded rapidly to give the desired
product.
4. Conclusion
In the present work, the performance of n-propyl-4-aza-1-
azoniabicyclo[2.2.2]octane chloride-SBA-15 (SBA–DABCO) as basic
mesoporous catalyst for the synthesis of 1,4-dihydropyridine (DHP) de-
rivatives under solvent-free conditions at 80 °C was investigated. The
catalytic system can combine the advantages of homogeneous and het-
erogeneous catalysts and therefore they can be selective, reactive and
recyclable. The attractive features of this method are high yield and
clean reaction, simple procedure, short reaction time, ease of separation
and recyclability of the solid catalyst and performing multicomponent
reaction under solvent-free conditions.
Under the optimized reaction conditions, different substituted 1,4-
dihydropyridine (DHP) heterocyclic compounds were prepared chang-
ing the aromatic aldehyde substituents (Scheme 2). Generally, the reac-
tions that employed aromatic aldehydes bearing electron-withdrawing
or electron-donating functional groups at different positions produced
the corresponding products in good to excellent yields. Both of
the aromatic aldehydes with electron-withdrawing and electron-
donating functionalities were found to be compatible under the op-
timized reaction condition (Scheme 2) (Table 2), because the desired
products were obtained in high yields in relatively short reaction
times.
Acknowledgment
We gratefully acknowledge the support of this work by Production
Technology Research Institute.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.06.019.
The structures of products were determined from their analytical
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1
1
0
1
3
2