A facile and eco-friendly synthesis of imidazo[1,2-a]pyridines using nano-sized LaMnO3 perovskite-type oxide as an efficient catalyst under solvent-free conditions

Article abstract of DOI:10.1016/j.apcata.2013.10.026

LaMnO₃ perovskite nanoparticles were prepared using a sol-gel method. The physical and chemical properties of the catalyst were determined using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Energy dispersiv

Full text of DOI:10.1016/j.apcata.2013.10.026

Applied Catalysis A: General 470 (2014) 56–62
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
A facile and eco-friendly synthesis of imidazo[1,2-a]pyridines using
nano-sized LaMnO3 perovskite-type oxide as an efficient catalyst
under solvent-free conditions
Tayebeh Sanaeishoara, Haman Tavakkolia,∗, Fouad Mohaveb
a Department of Chemistry, Science and Research Branch, Islamic Azad University, Khouzestan, Iran
b Young Researchers Club, Khouzestan Science and Research Branch, Islamic Azad University, Ahvaz, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 June 2013
Received in revised form 12 October 2013
Accepted 16 October 2013
Available online xxx
LaMnO3 perovskite nanoparticles were prepared using a sol–gel method. The physical and chemical
properties of the catalyst were determined using X-ray diffraction, transmission electron microscopy,
scanning electron microscopy, Energy dispersive X-ray spectroscopy, BET method and Fourier transform
infrared spectroscopy. The XRD results indicated that the LaMnO3 has a good crystalline phase at 600 ◦C.
The BET surface area of the mesoporous perovskite materials (LaMnO3) was 475 m2/g and the average
width of the pores was 8.7 nm. The experimental data revealed that the LaMnO3 particles were nano-
sized. This perovskite-type oxide as a green and reusable catalyst showed excellent catalytic activity
for the synthesis of imidazo[1,2-a]pyridines. LaMnO3 catalyst could be recovered and reused in five
reaction cycles, giving a total TON = 2790 and TOF = 372. The products were prepared under solvent-
free conditions without any additives. Principal features of this simple method include non-hazardous
reaction conditions, low catalyst loading and excellent yields.
Keywords:
Perovskite-type oxide
Nanoparticles
Reusable heterogeneous catalyst
Three-component reactions
Solvent-free
© 2013 Published by Elsevier B.V.
1. Introduction
A wide cross-fertilization bridges heterogeneous catalysis and
materials science in the areas of physicochemical characterization,
Nitrogen-containing heterocycles are abundant in nature and
exhibit diverse and important biological properties [1–4]. Among
them, imidazo[1,2-a]pyridine derivatives display a diverse range
of biological activities such as antimicrobial [5], inhibitors of HIV-1
reverse transcriptase [6], biological activity against colon cancer
[7], potent inhibitor of p38 MAP kinase [8], inhibitor of cyclin
dependent kinases [9] and treatment of anxiety disorders [10]. A
new three-component condensation to approach such fused imid-
azoles was developed simultaneously by Groebke, Bienayme, and
Blackburn in 1998 [11–13]. Since the first reports were published,
various methods have been performed to improve this powerful
MCR (multi component reaction) synthetic methodology. Some of
these methods used acidic catalysts [14–16], some supported acid
catalysts [17–19], in the presence of polar solvents [20–22], ionic
liquids [23] and under catalyst-free [24], neat condition [25,26], and
microwave irradiation [27,28]. However, these methods possess
several disadvantages such as long reaction time [11–13,24,25],
complicated work-up procedure and harsh reaction conditions
[17,27], requirement of excess amount of catalysts [11,12,14], and
low yields [27,29].
solid-state chemistry, and synthetic routes [30–32]. Among mixed
metal oxides, perovskite-type oxides are prominent. Perovskite-
type mixed metal oxides of chemical formula ABO3 (A is a larger
cation than B) have attracted interest over the years owing to their
unique physical and chemical properties [33]. Perovskites have
many possible applications, e.g., in electrical devices [34], as fer-
romagnetic material [35], in membranes for gas separation [36], as
catalysts [37,38], as promising adsorbents [39,40] and in sensors
[41], and the catalytic properties are important in most applica-
tions.
Perovskites also efficiently catalyse organic reactions at very low
catalyst loadings [42–45]. The small amount of precious or active
metal oxides in the perovskite implies very high turnover num-
bers. Furthermore the catalysts are readily removed by filtration,
are recyclable and lead to extremely low leaching into solution
making perovskites an attractive alternative to homogeneous catal-
ysis. An important feature of LaMnO3 and many related perovskites
is their ability to reversibly adsorb and desorb oxygen into the
crystal lattice by continuous and spontaneous changes in Mn oxida-
tion state, without changing the overall bulk crystal structure [46].
Therefore, the present study has investigated fabrication and char-
acterization of perovskite-type oxide nanoparticles LaMnO3 and
determination its efficiency as a promising nanocatalyst for syn-
thesis of imidazo[1,2-a] pyridine derivatives using very low amount
∗
Corresponding author. Tel.: +98 611 4457612; fax: +98 611 4435288.
E-mail address: h.tavakkoli@khouzestan.srbiau.ac.ir (H. Tavakkoli).
0926-860X/$ – see front matter © 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.apcata.2013.10.026

T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
57
of sufficient recyclable catalyst and eliminate the use of auxiliary
substances e.g. solvents, separation agents, etc.
2.5. Preparation of catalyst (KF·ꢁ-Al2O3)
The KF·␥-Al2O3 was prepared by reported method [49]. Sup-
ported KF on ␥-alumina with loadings of 3–15 mmol KF/g was
prepared by the wet impregnation method. ␥-Alumina was added
to a solution of KF in water and the suspension was stirred at room
temperature for 2 h. Water as evaporated at 60 ◦C under reduced
pressure using a rotary evaporator. The catalyst was dried at 100 ◦C
overnight, and pretreated in vacuum at the desired temperature
before testing for any catalytic activity.
2. Experimental
2.1. General remarks
All chemicals and reagents were obtained from Sigma–Aldrich
or Merck and were used without further purification. Several tech-
niques were employed to analyze and validate the synthesized
nanocatalyst. For structural investigation of calcined powder at
650 ◦C X-ray diffraction (XRD) measurements were carried out in
the region of (2ꢀ = 20◦ to 70◦) using CuK␣ radiation on a Rigaku
D/MAX RB XRD diffractometer equipped with a curved graphite
monochromator. The microstructure of powder was examined
using LEO 912AB TEM under a working voltage of 120 kV, while
the morphology and chemical analysis of the particles was inves-
tigated using SEM–EDX technique. The SEM of the type LEO 1450
VP (V = 30 kV) was equipped with an EDX spectrometer of the type
Inca 400 (Oxford Instruments). The melting points of products were
determined with an Electrothermal 9200 melting point appara-
tus. The FT-IR spectra were recorded on a Perkin-Elmer BX-II IR
spectrometer. The 1H NMR and 13C NMR spectra were provided on
Bruker DRX-400 and DRX-300 Avance instruments in CDCl3. The
specific surface area (SSA) of the catalyst was calculated using BET
method from the nitrogen adsorption isotherms obtained at 77 K
on samples outgassed at 250 ◦C with the use of a Micromeritics
Accusorb 2100E apparatus.
2.6. Preparation of catalyst (NH4OAc·Al2O3)
Alumina (ICN Biomedical N-Super 1, 9.23 g) was added to a solu-
tion of ammonium acetate (10 mmol, 0.77 g) in methanol, and the
mixture was stirred at room temperature for 0.5 h. The methanol
was removed by rotary evaporator under reduced pressure, and
the resulting reagent was dried in vacuum (10 mmHg) at room
temperature for 2 h [50].
2.7. Typical procedure for the synthesis of
imidazo[1,2-a]pyridines
To a mixture of aldehyde(1 mmol), amidine(1 mmol) and iso-
cyanide(1 mmol), nano-LaMnO3 (0.0005 g) was added and the
mixture was heated at 35 ◦C for an appropriate time as indicated by
TLC. The mixture was filtered and washed with CH2Cl2 to separate
catalyst. To obtain pure products the solid residue was recrystal-
lized from CH3CN.
All the products (except of 4a, 4b, 4c, 4f and 4 h) are new com-
pounds, which were identified by IR, 1H NMR and 13C NMR spectral
data.
2.2. Preparation of catalyst (LaMnO3)
LaMnO3 (LMO) of the type perovskite oxide were fabricated
by sol–gel method. The appropriate amounts of starting materials
La(NO3)3·6H2O (99.9%) and Mn(CH3COO)2·H2O (99.9%) were dis-
solved in deionized water. Citric acid was then added slowly to
the metal solution at room temperature under constant magnetic
stirring (1000 r/min). The solution was refluxed with stirring for
2 h to convert it to a stable complex. To make a gel, stirring was
continued at ∼70 ◦C for 3 h in water bath. A dry gel was obtained
by placing the sol in an oven and heating slowly to 110 ◦C and then
maintaining the temperature for 8 h. The gel was ground in an agate
mortar to give a powder. LaMnO3 nanoparticles were obtained by
calcinations of the precursors at 650 ◦C for 9 h in air.
2.8. Spectral data of synthesized imidazo[1,2-a]pyridines
2.8.1. N-Cyclohexyl-2-(4-(dimethylamino)phenyl)imidazo[1,2-
a]pyridin-3-amine (4d,
C21H26N4)
Yellow-brown crystal, (0.314 g, 94%); mp: 182–183 ◦C; IR (KBr,
cm−1): 3432(NH), 2926 (CH), 1630 and 1462 (Ar). 1H NMR (CDCl3,
400 MHz): ı = 1.17–1.86 (10H, m, 5 CH2 of CyHex), 3.02 (1 H, m,
CHN of CyHex), 3.02 (6H, s, 2CH3), 3.27 (1H, s, NH), 6.81 (3H, m,
3 CH of Ar), 7.15 (1H, dd, J, 3J = 8.4, 4J = 7.2, CH of Ar), 7.62 (1H,
d, 3J = 8.8, CH of Ar), 7.98 (2H, d, 3J = 6.8, 2 CH of Ar), 8.15 (1H, d,
3J = 6.8, CH of Ar). 13C NMR (CDCl3, 100 MHz): ı = 24.86, 25.81, 34.15,
40.47, 56.80, 111.14, 112.32, 116.77, 122.54, 122.58, 123.36, 123.55,
127.84, 137.10, 141.36, 149.67.
2.3. Preparation of catalyst (FeCl3·nano-SiO2)
The FeCl3·nano-SiO2 was prepared by reported method [47]. In
a 100 mL flask, nano silica gel (25 g) and FeCl3·6H2O (2 g) (8% of
the weight of nano-SiO2) were vigorously stirred by magnetic stir-
rer under solvent-free conditions at room temperature for 24 h to
achieve a homogeneous adsorption. A yellow powder was obtained.
This powder was heated for 1 h at 100 ◦C to give a brownish powder
(“active” FeCl3/nano-SiO2·reagent).
2.8.2. N-Cyclohexyl-2-(9H-fluoren-2-yl)imidazo[1,2-a]pyridin-
3-amine (4e, C26H25N3)
Yellow-brown crystal, (0.360 g, 95%); mp: 172–174 ◦C; IR (KBr,
cm−1): 3222 (NH), 2926 (CH), 1638 and 1444 (Ar). 1H NMR (CDCl3,
400 MHz): ı = 1.18–1.87 (10H, m, 5 CH2 of CyHex), 3.01 (1 H, m, CHN
of CyHex), 3.63 (1H, s, NH), 4.00 (2H, s, CH2), 6.79 (1 H, td, 3J = 6.8,
4J = 0.8, CH of Ar), 7.16 (1 H, m, CH of Ar), 7.34 (1 H, td, 3J = 7.6, 4J = 1.2,
CH of Ar), 7.39 (1 H, m, CH of Ar), 7.58 (1 H, d, 3J = 7.2, CH of Ar),
7.65 (1 H, d, 3J = 8.8, CH of Ar),), 7.81 (2 H, m, 2 CH of Ar), 8.10 (1 H,
dd, 3J = 7.8, 4J = 1.4, CH of Ar), 8.19 (1 H, d, 3J = 6.8, CH of Ar), 8.33 (1
H, d, 3J = 0.4, CH of Ar). 13C NMR (CDCl3, 100 MHz): ı = 24.83, 25.76,
34.21, 37.04, 56.87, 111.51, 117.13, 119.82, 119.92, 122.72, 123.79,
123.94, 124.94, 125.07, 125.55, 126.66, 126.79, 133.01, 136.81,
140.78, 141.51, 141.62, 143.64, 143.66.
2.4. Preparation of catalyst (FeCl3·Al2O3)
The FeCl3·Al2O3 was prepared by reported method [48], by mix-
ing with ∼10% its weightof iron chloride hexahydrate (FeCl3·6H2O)
8 g in acetone (72 mL) and adding 43.2 g neutral Al2O3. The mixture
was stirred at room temperature for 1 h. The acetone was removed
under reduced pressure. The resulting yellow-brown powder was
dried at 120 ◦C for 4 h.

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T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
Fig. 1. XRD patterns of samples of the LMO nanopowder calcinated at 650 ◦C.
Fig. 2. TEM image of the LMO nanoparticles.
2.8.3. 2-(4-Chlorophenyl)-N-cyclohexyl-7-methylimidazo[1,2-
a]pyridin-3-amine (4l,
C
20H22ClN3)
nanopowders is shown in Fig. 2. All the particles display the uniform
quasi-spherical morphology with the average particle size of about
25 nm, which is in a good agreement with the results achieved from
XRD measurement.
Scanning electron microscopy (SEM) of perovskite oxide pre-
pared by the sol–gel method and calcined at 650 ◦C is shown in
Fig. 3. Based on the SEM images, porosity of the surface is evident
and it seems that the particles have grown with uniform size. The
particles size that was propagated on the surface seems to be in the
range of 25–100 nm.
White crystals, (0.333 g, 98%); mp: 208–209 ◦C; IR (KBr, cm−1):
3235 (NH), 2922 (CH), 1644 and 1467 (Ar). 1H NMR (CDCl3,
400 MHz): ı = 1.17–1.82 (10 H, m, 5 CH2 of CyHex), 2.44 (3H, s, CH3),
2.93(1 H, m, CHN of CyHex), 3.86 (1H, br s, NH), 6.79 (1 H, d, 3J = 6.8,
CH of Ar), 7.37 (2 H, m, CH of Ar), 7.48 (1 H, s, CH of Ar), 8.08 (3
H, m, CH of Ar). 13C NMR (CDCl3, 100 MHz): ı = 21.36, 24.81, 25.71,
34.16, 56.90, 114.54, 115.59, 122.02, 124.48, 128.16, 128.60, 132.82,
132.89, 134.89, 135.46, 141.93.
3. Results and discussion
In addition, energy-dispersive X-ray (EDX), as shown in Fig. 4,
confirmed the existence of La, Mn and O ratio as well as the phase-
purity of the nanopowders.
3.1. Characterization of the catalyst
The specific surface area of the catalyst was measured by
means of conventional BET method (Fig. 5). Results showed that
the average of specific surface area of LMO nanoparticle was
475 m2/g. Mesopore volume and mesopore width were obtained
from DR method are 0.27 cm3/g and 8.7 nm, respectively. Accord-
ing to IUPAC classification, N2 adsorption–desorption isotherm of
nanoparticles LMO is type IV. This isotherm is the characteristic of
adsorption–desorption on mesoporous solids. So, it seems that the
large specific surface area of the catalyst is an advantage for the
synthesis of imidazo[1,2-a] pyridine derivatives.
The nanopowders of perovskite-type oxides LaMnO3 were fabri-
cated by sol–gel method in the presence of citric acid as a chelating
agent. The obtained nanoparticles were characterized by XRD, TEM,
SEM, BET and EDX methods.
3.1.1. X-ray diffraction studies
Fig. 1 shows the XRD patterns of the LaMnO3 nanoparticles
prepared by sol–gel method and calcined at 650 ◦C for 9 h. The
diffractograms reveal that the crystalline perovskite structure is
the main phase for synthesized powders. The diffraction peaks at
2ꢀ angels appeared in the order of 23◦, 32.5◦, 41◦, 47◦, 58.5◦ and
68.65◦ and they can be assigned to scattering from the (1 1 0), (1 1 2),
(0 2 2), (2 2 0), (3 1 2) and (4 0 0) planes of the LaMnO3 perovskite
type crystal lattice, respectively. XRD data shows LaMnO3 crystal-
lized in rhombohedral system [51]. No additional peak is seen in
the XRD pattern of the catalyst which reveals the high purity of
the prepared perovskite nanoparticles. The average crystallite size
can be calculated using the XRD peak broadening of the (2ꢀ = 32.5◦)
peak by the well known Scherer’s formula:
0.9ꢂ
ˇhkl cos ꢀhkl
Dhkl
=
(1)
where Dhkl (nm) is the particle size perpendicular to the normal
line of (hkl) plane, ˇhkl is the full width at half maximum, ꢀhkl (Rad)
is the Bragg angle of (hkl) peak, and ꢂ (nm) is the wavelength of X-
ray. The crystallite size of LaMnO3 calcinated at 650 ◦C was about
28 nm.
3.1.2. Morphology, pore structure and surface area
The morphology and the particle size of LaMnO3 nanoparticles
were studied by TEM and SEM methods. The TEM image of these
Fig. 3. SEM images of LMO nanopowders.

T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
59
Table 1
Initial solvent effect studies for synthesis of 3-aminoimidazo[1,2-a]pyridines with
0.2 mol% catalyst.
Entry
Solvent
Temp (◦C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
CH2Cl2
CH3CN
EtOH
MeOH
Acetone
H2O
Toluene
n-Hexane
Ethyl acetate
Solvent-free
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
35
24
24
24
24
24
24
24
24
24
1.5
35
<30
55
55
<30
<30
50
50
45
10
96
Conditions: aminopyridine (1 mmol), benzaldehyde (1 mmol), cyclohexyl iso-
cyanide (1 mmol) and 0.2 mol% nano-LaMnO3 in 2 mL solvent, stirring.
Effective catalysis was demonstrated down to 0.2 mol% (0.0005 g)
of nano-LaMnO3 (Table 2). We observed that taking reaction in the
room temperature gave low yields of the desired products (entry
10). The yield increased sharply when the temperature was raised
from room temperature to 35 ◦C. A further increase in the amount
of catalyst (up to 10 mol%) and of the reaction temperature did
not have any significant effects on the product yield or reaction
time. It should be noted that in the absence of catalyst a very low
amount of the desired product was formed (entry 1). However
other catalysts such as FeCl3·nano-SiO2, FeCl3·Al2O3, KF·␥-Al2O3
and NH4OAc·Al2O3 were examined, which afforded relatively low
yield of compounds and higher catalyst loading. In general Bron-
sted or Lewis acids as well as solid acids promoters give the best
results in terms of yield and reaction time. Moreover, the use of
FeCl3·nano-SiO2, FeCl3·Al2O3 and LaMnO3 as Lewis acid catalysts
afforded the higher yield comparing to basic catalysts. High activity
of the LaMnO3 along with Lewis acidic center depends on the high
surface area and the perovskite structure, these attributes play-
ing a very important role to synthesis desired products, also these
features are the main reasons for LaMnO3 to obtain higher yields
comparing to other catalyst (Table 2). In order to show the effec-
tiveness of the present work with respect to the previous reports,
nano-LaMnO3 was compared with mentioned examples as well
(see entries 7–10).
Fig. 4. Energy dispersive X-ray (EDX) spectrum of the LMO nanoparticles.
Fig. 5. N2 adsorption–desorption isotherm of LMO is calcinated at 650 ◦C.
3.2.2. Catalytic performance
After optimizing the conditions, to explore the scope and limita-
tions of this reaction we studied the reactions of 2-aminopyridine
or 4-methyl-2-aminopyridine 1 and isocyanide 3 with various aro-
matic aldehydes 2 all desired products were formed as shown
in (Table 3). As expected, we have found that the reactions of
electron-withdrawing aldehydes have higher yields compared to
the reactions of electron donating aldehydes. Despite the expec-
tations, reactions of 4-methyl-2-aminopyridine have lower yields
comparing to 2-aminopyridine.
Scheme 1. Synthesis of compounds 4a–4o.
3.2. Catalytic application of LaMnO3 nanoparticles in synthesis of
imidazo[1,2-a] pyridine derivatives
To explore the catalytic activity of this heterogeneous cat-
alyst, we investigated its efficiency in the reaction between
2-aminopyridine, benzaldehyde, and cyclohexyl isocyanide under
solvent-free conditions within 1.5 h at 35 ◦C (Scheme 1). In order
to optimize the reaction conditions, we conducted this reaction
with various solvent systems; it was observed that solvent-free
condition gave the best result in terms of reaction time and yield
(Table 1).
3.2.3. Reusability of catalyst
To evaluate the stability of catalytic activity and the potential for
recycling, we completed several catalytic cycles. When the reaction
was completed, the catalyst was separated by filtration. Then the
catalyst was washed with CH2Cl2 (3 × 5 mL) and subsequently dried
at 50 ◦C to the reused. As shown in Fig. 6 nano-LaMnO3 could be
reused in subsequent reactions without any decrease in catalytic
activity even after five runs. Turn over number (TON) and turn over
frequency (TOF)−o1f 4a after the fifth run were calculated, TON = 2790
and TOF = 372 h and compared to the previous report TON = 453
and TOF = 82.4 h−1 [26].
3.2.1. Catalyst loading
The required quantity of catalyst was probed by perform-
ing the condensation reaction of 2-aminopyridine, benzaldehyde
and cyclohexyl isocyanide at six different nano-LaMnO3 loadings.

60
T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
Scheme 2. A plausible mechanism using nano-LaMnO3.
3.2.4. A plausible mechanism for synthesis of
imidazo[1,2-a]pyridine using LaMnO3
On the basis of the experimental observations and previ-
ously reported mechanism [11–13], the possible pathway for the
formation of imidazo[1,2-a]pyridine over LaMnO3 nanoparticles
can be explained as follows (Scheme 2): Initially, 2-aminopyridine
1 coordinates to the Lewis acidic site present at the catalyst sur-
face (I). The protonation of 2 by the NH-acidic of compound (II)
and the subsequent attack of the resulting nucleophile (III) on the
activated carbonyl of aldehyde 5 afforded (IV). The elimination of
the water leads to iminium salt (V), then it undergoes nucleophilic
addition with the isocyanide 3 to form the isonitrilium interme-
diate (VI), which cyclizes into the imino intermediate (VII). This
intermediate tautomerizes under the reaction conditions to afford
the 3-alkylamino-2-arylimidazo[1,2-a]pyridine (VIII), The inter-
mediate catalyst species (VIII) regenerates the solid catalyst via
elimination of the final product 4.
Fig. 6. Yield refers to isolated products from the aminopyridines (1 mmol), benz-
aldehyde (1 mmol), cyclohexylisocyanide (1 mmol) in the presence of 0.2 mol%
nano-LaMnO3 (0.0005 g) under solvent-free condition.

T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
61
Table 2
Condensation reaction of 2-aminopyridine, benzaldehyde and cyclohexylisocyanide in the presence of different loading of the catalyst under solvent-free conditions.
Entry
Catalyst
Catalyst loading (g)
Temperature (◦C)
Time (h)
Yielda (%)
Refs.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
–
–
r.t.
r.t.
35
35
35
35
2
2
1.5
1.5
1.5
2
3
2
1
1
Trace
40
80
94
35
30
86
94
78
92
60
96
96
96
95
95
95
This work
This work
This work
This work
This work
This work
[17]
[18]
[20]
[26]
This work
This work
This work
This work
This work
This work
This work
FeCl3·nano-SiO2
FeCl3·nano-SiO2
FeCl3·Al2O3
0.02
0.02
0.02
0.02
0.05
0.05
0.05
5b
KF·␥Al2O3
NH4OAc·Al2O3
Clay
Microwave
r.t.
Microwave
35
r.t
35
35
35
35
35
35
Cellulose sulfuric acid
ZnCl2
␥-Fe2O3@SiO2-OSO3H
nano-LaMnO3
nano-LaMnO3
nano-LaMnO3
nano-LaMnO3
nano-LaMnO3
nano-LaMnO3
nano-LaMnO3
1b
0.002
0.0005
0.001
0.002
0.005
0.01
0.02
2
1.5
1.5
1.5
1.5
1.5
1.5
Conditions: 2-aminopyridine 1 mmol, benzaldehyde 1 mmol cyclohexylisocyanide 1 mmol.
a
Isolated yield.
mol%.
b
Table 3
Synthesis of various 3-aminoimidazo[1,2-a]pyridines in the presence of nano-LaMnO3.
Entry
X
R
Product
Yield* (%)
mp (◦C)
TON
TOF (h−1
)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
Me
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
96
95
99
94
95
91
99
97
95
94
91
98
94
94
99
178–180 (174–175) [17]
160–161 (166–169) [25]
185–187 (179–181) [24]
182–183
172–174
154 (154) [52]
176–178
160–161 (168–170) [53]
170–172
191–192 (dec)
198–199
208–209
200–202 (dec)
200–201
2790
2902
3210
3138
3608
2822
3654
2884
2904
3002
3036
3326
3278
3696
3794
372
387
428
418
481
376
487
384
387
400
405
443
437
492
506
4-Me-C6H4
4-Cl-C6H4
4-NMe2-C6H4
2-Fluorenyl
4-OMe-C6H4
4-Br-C6H4
2-Thiophen
Ph
4-Me-C6H4
2,4-Me2-C6H3
4-Cl-C6H4
4-NMe2-C6H4
2-Fluorenyl
4-Br-C6H4
9
10
11
12
13
14
15
204–206
Conditions: aminopyridines (1 mmol), benzaldehydes (1 mmol), cyclohexylisocyanide (1 mmol) and 0.2 mol% nano-LaMnO3 (0.0005 g), stirring at 35 ◦C, 90 min.
*
Isolated yield.
4. Conclusions
References
[1] A. Monge, J.A. Palop, J.C.D. Castillo, J.M. Caldero, J. Roca, G. Romero, J.D. Rio, B.
Lasheras, J. Med. Chem. 36 (1993) 2745–2750.
[2] K. Toshima, R. Takano, T. Ozawa, S. Matsumara, Chem. Commun. 3 (2002)
212–213.
[3] B. Dowlati, D. Nematollahi, M.R. Othman, Int. J. Electrochem. Sci. 7 (2012)
5990–5996.
[4] Y.B. Kim, Y.H. Kim, J.Y. Park, S.K. Kim, Bioorg. Med. Chem. Lett. 14 (2004)
541–544.
[5] C. Desai, N.R. Pandya, M.M. Rajpara, K.V. Joshi, V.V. Vaghani, H.M. Satodiya, Med.
Chem. Res. 21 (2012) 4437–4446.
[6] D. Elleder, T.J. Baiga, R.L. Russell, J.A. Naughton, S.H. Hughes, J.P. Noel, J.A.T.
Young, Virol. J. 9 (2012) 305–311.
[7] N. Dahan-Farkas, C. Langley, A.L. Rousseau, D.B. Yadav, H. Davids, C.B. de Koning,
Eur. J. Med. Chem. 46 (2011) 4573–4583.
[8] K.C. Rupert, J.R. Henry, J.H. Dodd, S.A. Wadsworth, D.E. Cavender, G.C. Olini, B.
Fahmy, J. Siekierka, J. Bioorg, Med. Chem. Lett. 13 (2003) 347–350.
[9] C. Hamdouchi, B. Zhong, J. Mendoza, E. Collins, C. Jaramillo, J.E. De Diego, D.
Robertson, C.D. Spencer, B.D. Anderson, S.A. Watkins, F. Zhanga, H.B. Brooks,
Bioorg. Med. Chem. Lett. 15 (2005) 1943–1947.
[10] S.C. Goodacre, L.J. Street, D.J. Hallett, J.M. Crawforth, S. Kelly, A.P. Owens, W.P.
Blackaby, R.T. Lewis, J. Stanley, A.J. Smith, P. Ferris, B. Sohal, S.M. Cook, A. Pike, N.
Brown, K.A. Wafford, G. Marshall, J.L. Castro, J.R. Atack, J. Med. Chem. 49 (2006)
35–38.
In summary, nanoparticles of perovskite type LaMnO3 were
prepared using sol–gel method in the presence of citric acid
as a chelating agent. The XRD, TEM, SEM and EDX reveal that
the LaMnO3 nanoparticles prepared by calcinating the gel pre-
cursor at 650 ◦C have good crystallinity in perovskite phase
structure. According to electron microscopic images, the nanopar-
ticles exhibit regular morphology with homogeneous particle size
distribution.
In addition, in the present study we developed a green method
for synthesis the imidazo[1,2-a]pyridine derivatives by perovskite-
type oxide LaMnO3 nanoparticles as thermally stable, non-volatile,
efficient recyclable heterogeneous catalyst under solvent-free con-
dition. The advantages of this procedure over earlier reported
processes include excellent yield, short reaction time, and mild con-
dition, very low loading of catalyst and high performance of catalyst
even after five runs.
[11] K. Groebke, L. Weber, F. Mehlin, Synlett 6 (1998) 661–663.
[12] H. Bienayme, K. Bouzid, Angew. Chem. Int. Ed. 37 (1998) 2352–2355.
[13] C. Blackburn, B. Guan, P. Fleming, K. Shiosaki, S. Tsai, Tetrahedron Lett. 39 (1998)
3635–3638.
[14] C. Hulme, Y.S. Lee, Mol. DiversityV 12 (2008) 1–15.
[15] C. Che, J. Xiang, G.X. Wang, R. Fathi, J.M. Quan, Z. Yang, J. Comb. Chem. 9 (2007)
982–989.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.apcata.2013.10.026.

62
T. Sanaeishoar et al. / Applied Catalysis A: General 470 (2014) 56–62
[16] M.A. Mironov, M.I. Tokareva, M.N. Ivantsova, V.S. Mokruskin, Russ. Chem. Bull.
Int. Ed. 55 (2006) 1835–1839.
[17] R.S. Varma, D. Kumar, Tetrahedron Lett. 40 (1999) 7665–7669.
[18] A. Shaabani, A. Maleki, J. Moghimi Rad, E. Soleimani, Chem. Pharm. Bull. 55
(2007) 957–958.
[19] A. Shaabani, E. Soleimani, A. Maleki, Monatsh. Chem. 138 (2007) 73–76.
[20] A.L. Rousseau, P. Matlaba, C.J. Parkinson, Tetrahedron Lett. 48 (2007)
4079–4082.
[37] R. Horyn, R. Klimkiewicz, Appl. Catal., A: Gen. 370 (2009) 72–77.
[38] N. Pal, M. Paul, A. Bhaumik, Appl. Catal., A: Gen. 393 (2011) 153–160.
[39] M. Yazdanbakhsh, H. Tavakkoli, S.M. Hosseini, Desalination 281 (2011)
388–395.
[40] H. Tavakkoli, M. Yazdanbakhsh, Microporous Mesoporous Mater. 176 (2013)
86–94.
[41] A.V. Salker, N.J. Choi, J.H. Kwak, B.S. Joo, D.D. Lee, Sens. Actuators, B: Chem. 106
(2005) 461–467.
[21] A. Shaabani, F. Rezazadeh, E. Soleimani, Monatsh. Chem. 139 (2008) 931–933.
[22] A.T. Khan, R.S. Basha, M. Lal, Tetrahedron Lett. 53 (2012) 2211–2217.
[23] A. Shaabani, E. Soleimani, A. Maleki, Tetrahedron Lett. 47 (2006) 3031–3034.
[24] M. Adib, M. Mahdavi, M.A. Noghani, P. Mirzaei, Tetrahedron Lett. 48 (2007)
7263–7265.
[25] M. Adib, E. Sheikhi, N. Rezaei, Tetrahedron Lett. 52 (2011) 3191–3194.
[26] S. Rostamnia, K. Lamei, M. Mohammadquli, M. Sheykhan, A. Heydari, Tetrahe-
dron Lett. 53 (2012) 5257–5260.
[42] S.V. Ley, M.D. Smith, C. Ramarao, A.F. Stepan, H. Tanaka, US 2005215804., U.S.
Pat. Appl. Pub., 2005.
[43] M.D. Smith, A.F. Stepan, C. Ramarao, P.E. Brennan, S.V. Ley, Chem. Commun.
(2003) 2652–2653.
[44] S.P. Andrews, A.F. Stepan, H. Tanaka, S.V. Ley, M.D. Smith, Adv. Synth. Catal. 347
(2005) 647–654.
[45] S. Lohmann, S.P. Andrews, B.J. Burke, M.D. Smith, J.P. Attfield, H. Tanaka, K.
Kaneko, S.V. Ley, Synlett 8 (2005) 1291–1295.
[27] S.M. Ireland, H. Tye, M. Whittaker, Tetrahedron Lett. 44 (2003) 4369–4371.
[28] Y. Lu, W. Zhang, QSAR Comb. Sci. (2004) 23–31.
[29] C. Blackburn, Tetrahedron Lett. 39 (1998) 5469–5472.
[30] W.R. Moser, Catalytic Chemistry of Solid State Inorganics, New York Academy
of Sciences, New York, 1976.
[46] G. Pilania, P.X. Gao, R. Ramprasad, J. Phys. Chem. C 116 (2012) 26349–26357.
[47] J. Safaei-Ghomi, S. Zahedi, M.A. Ghasemzadeh, Iran. J. Catal.
27–30.
2 (2012)
[48] J.H. Shi, L. Zhou, L.Z. Wang, W. Yan, J. Zhejiang Univ. Tech. 34 (2006)
360–363.
[31] G. Centi, F. Trifiro, Catal. Rev. Sci. Eng. 28 (1986) 165–184.
[32] N. Mizuno, M. Misono, Chem. Rev. 98 (1998) 199–218.
[33] C.D. Chandler, C. Roger, M.J. Hampden-Smith, Chem. Rev. 93 (1993) 1205–1241.
[34] R. Robert, M.H. Aguirre, P. Hug, A. Reller, A. Weidenkaff, Acta Mater. 55 (2007)
4965–4972.
[35] M. Nandia, K. Sarkara, M. Seikhc, A. Bhaumik, Microporous Mesoporous Mater.
143 (2011) 392–397.
[36] H. Aono, E. Traversa, M. Sakamoto, Y. Sadaoka, Sens. Actuators, B: Chem. 94
(2003) 132–139.
[49] V. Raju, R. Radhakrishnan, S. Jaenicke, G.K. Chuah, Catal. Today 164 (2011)
139–142.
[50] T. Aoyama, S. Murata, T. Takido, M. Kodomari, Tetrahedron 63 (2007)
11933–11937.
[51] M. Kakihana, M. Arima, M. Yoshimura, N. Ikeda, Y. Sugitani, J. Alloys Compd.
283 (1999) 102–105.
[52] A. Shaabani, E. Soleimani, A. Maleki, J. Moghimi-Rad, Synth. Commun. 38 (2008)
1090–1095.
[53] A. Shahris, S. Esmati, Synlett 24 (2013) 595–602.