Synthesis of polyhydroquinoline derivatives via a four-component Hantzsch condensation catalyzed by tin dioxide nanoparticles

Article abstract of DOI:10.1016/S1872-2067(11)60518-4

Tin dioxide (SnO₂) nanoparticles efficiently catalyzed unsymmetrical four-component Hantzsch condensations of various aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate to form polyhydroquinoline derivatives in excellent yields. This novel method offers several advantages over the traditional method of synthesizing these compounds, including safety, mild conditions, short reaction times, high yields, and an easy workup.

Full text of DOI:10.1016/S1872-2067(11)60518-4

Chinese Journal of Catalysis 34 (2013) 758–763
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
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Article
Synthesis of polyhydroquinoline derivatives via a four‐component
Hantzsch condensation catalyzed by tin dioxide nanoparticles
Seyed Mohammad VAHDATa,*, Fereshteh CHEKINa, Mehdi HATAMIb,
Maryam KHAVARPOURc, Saeed BAGHERYd,e, Ziba ROSHAN‐KOUHIe
a Department of Chemistry, Science and Research Ayatollah Amoli Branch, Islamic Azad University, Amol 678, Iran
b Marine Science Research Institute, Khoramshar University of Marine Science and Technology, Khoramshahr 64199‐43175, Iran
c Chemical Engineering Department, Islamic Azad University, Ayatollah Amoli Branch, P.O. Box 678, Amol, Iran
d Department of Chemistry, College of Science, Bu‐Ali Sina University, Hamadan 65174, Iran
e Young Researchers Club, Science and Research Ayatollah Amoli Branch, Islamic Azad University, Amol 678, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Tin dioxide (SnO2) nanoparticles efficiently catalyzed unsymmetrical four‐component Hantzsch
condensations of various aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate to form
polyhydroquinoline derivatives in excellent yields. This novel method offers several advantages
over the traditional method of synthesizing these compounds, including safety, mild conditions,
short reaction times, high yields, and an easy workup.
Received 30 October 2012
Accepted 8 January 2013
Published 20 April 2013
© 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
Nano tin dioxide catalyst
Hantzsch condensation
Polyhydroquinoline
1,4‐Dihydropyridine
1. Introduction
tion, and hydrothermal and polymeric precursor methods [7].
Because one‐dimensional SnO2 structures (e.g., nanowires and
Tin dioxide (SnO2) exhibits desirable properties such as high
transparency in the visible spectrum, strong physical and
chemical interactions with adsorbed species, catalytic activity
at low temperature, and high thermal stability in air (up to 500
°C) [1]. It is an n‐type semiconducting oxide with a wide band
gap (Eg = 3.6–3.8 eV at 300 K), and it has potential applications
for dye‐based solar cells [2]. It has also been used as a sensing
material for gas mixtures such as CO and O2 [3]. However,
compared with other metal oxides, SnO2 has received little at‐
tention as a catalyst [4], although it has been used to catalyze
the oxidation of organic compounds [5].
nanorods) are expected to find wide applications in many
fields, considerable effort has been directed at fabricating such
structures by means of methods such as thermal oxidation and
molten salt synthesis [8,9].
In this study, which is part of our ongoing investigations di‐
rected toward the development and improvement of new syn‐
thetic methodologies [40,41], we investigated the use of SnO2
nanoparticles to catalyze the formation of polyhydroquinolines
and 1,4‐dihydropyridines (1,4‐DHPs). In recent years, interest
in the synthesis of 1,4‐DHPs has increased, owing to their sig‐
nificant biological activities [10,11]. For example, various
1,4‐DHPs with substituents at the 4‐position have been re‐
ported to possess antiatherosclerotic, vasodilatory, antihyper‐
tensive, hepatoprotective, bronchodilatory, antimutagenic,
SnO2 can be synthesized by means of various techniques, in‐
cluding chemical vapor deposition for the preparation of thin
films [6], precipitation, sol‐gel reactions, carbothermal reduc‐
*Corresponding author. Tel: +98‐121‐2517067; Fax: +98‐121‐2517068; E‐mail: m.vahdat@iauamol.ac.ir, vahdat_mohammad@yahoo.com
DOI: 10.1016/S1872‐2067(11)60518‐4 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 34, No. 4, April 2013

Seyed Mohammad VAHDATet al. / Chinese Journal of Catalysis 34 (2013) 758–763
antitumor, geroprotective, and antidiabetic activities [12–16].
A mixture of dimedone (1.0 mmol), aldehyde (1.0 mmol),
ethyl acetoacetate (1.0 mmol), ammonium acetate (1.0 mmol)
and nano SnO2 catalyst (1 mol%) in ethanol (2 ml) were stirred
at room temperature for an appropriate time. The progress of
the reaction was monitored by TLC (n‐hexan/ethyl acetate 5:1).
After completion of the reaction, the resulting solid (crude
product) was filtered and then recrystallized from etha‐
nol‐water to obtain pure product. The physical data (mp, NMR,
IR) of these known compounds were found to be identical with
those reported in the literature.
Ethyl 4‐(4‐chlorophenyl)‐2,7,7‐trimethyl‐5‐oxo‐1,4,5,6,7,8‐
hexahydroquinoline‐3‐carboxylate (Table 4 entry 3) Yield:
96%; mp 229–231 °C (lit. [46] 230–232 oC). 1H NMR (400 MHz,
DMSO): δ 0.84 (s, 3H, –CH3), 0.99 (s, 3H, –CH3), 1.14 (t, 3H, J=
7.2 Hz, –CH3), 2.06 (dd, 2H, –CH2–), 2.13 (dd, 2H, –CH2–), 2.28
(s, 3H, –CH3), 3.99 (q, 2H, J= 7.3 Hz, –OCH2–), 4.95 (s, 1H, –CH–),
7.08 (d, 2H, J = 9.3 Hz, Ar–H), 7.18 (d, 2H, J = 9.4 Hz, Ar–H), 7.93
(brs, 1H, –NH–).13C NMR (100 MHz, DMSO): δ 14.8, 19.2, 27.4,
29.9, 32.8, 36.6, 40.8, 51.2, 60.1, 77.8, 105.3, 111.5, 128.2, 129.8,
131.7, 146.5, 150.1, 167.8, 195.7; IR (KBr, cm–1) 3275, 3199,
3073, 2931, 2360, 1676, 1604, 1490, 1380, 1214, 1101, 857.
DHPs have found commercial utility as calcium channel block‐
ers (e.g., Nitrendipine, Nifedipine, and Nimodipine) [17]. DHPs
can be synthesized by means of the Hantzsch condensation of
an aldehyde, a β‐ketoester, and ammonia; and replacement of
ammonia by ammonium acetate permits the reaction to be
carried out in aqueous media as well as under solvent‐free
conditions [18,19].
Polyhydroquinolines, which are structurally related to
DHPs, are another important group of nitrogen‐containing het‐
erocycles that have attracted much attention because of their
diverse therapeutic and pharmacological properties, such as
their ability to modulate calcium channels. Polyhydroquino‐
lines have been synthesized under mild conditions augmented
by conventional heating [20,21], microwave irradiation, and
ultrasound [22,23]. In addition, various catalysts have been
evaluated, including FeF3 [24], clay‐supported Ni0 nanoparti‐
cles [25], unsupported nickel nanoparticles [26], sili‐
ca‐supported perchloric acid [27], titanium dioxide nanoparti‐
cles [28], Bakers’ yeast [29], K7[PW11CoO40] [30], scandium(III)
triflate [31], ethylene glycol/MW [32], p‐toluenesulfonic acid
[33], trimethylsilyl chloride [34], palladium nanoparticles [35],
a hafnium(IV) bis(perfluorooctanesulfonyl)imide complex [36],
cerium(IV) ammonium nitrate [37], and iron(III) trifluoroace‐
tate [38].
Despite the availability of these methods, the development
of a mild and efficient catalyst for the synthesis of polyhydro‐
quinolines remains highly desirable. In addition, the possibility
of performing the reaction in aqueous media has attracted
much attention because water is safer, cheaper, and more en‐
vironmentally friendly than organic solvents [39]. A wa‐
ter‐soluble catalyst that could be recycled by separation of the
insoluble products by simple filtration is an especially attrac‐
tive prospect.
Herein, we report a new, convenient, mild, efficient proce‐
dure for the synthesis of polyhydroquinoline derivatives by
means of a SnO2 nanoparticle–catalyzed one‐pot Hantzsch
condensation of various aldehydes, dimedone, ethyl acetoace‐
tate, and ammonium acetate at ambient temperature in etha‐
nol.
Ethyl
4‐(4‐hydroxy‐3‐methoxyphenyl)‐2,7,7‐trimethyl‐5‐
oxo‐1,4,5,6,7,8‐hexahydroquinoline‐3‐carboxylate (Table
4
entry 13). Yield: 96%; mp 212–214 °C (lit. [48] 210–212 °C); 1H
NMR (400 MHz, DMSO): δ 0.93 (s, 3H, – CH3), 1.04 (s, 3H, –CH3),
1.25 (t, 3H, J = 7.2 Hz, –CH3), 1.91–2.18 (dd, 2H, –CH2–),
2.27–2.39 (dd, 2H, –CH2–), 2.27 (s, 3H, –CH3), 3.73 (s, 3H,
–OCH3), 4.06 (q, 2H, J = 7.3 Hz, –OCH2–), 4.71 (s, 1H, –CH–),
6.49–6.77 (m, 3H, Ar–H), 8.07 (brs, 1H, –OH), 8.58 (brs, 1H,
–NH–). 13C NMR (100 MHz, DMSO): δ 15.3, 27.1, 28.8, 33.1, 38.4,
47.6, 52.4, 58.3, 106.7, 109.1, 111.3, 115.1, 121.5, 137.2, 145.6,
147.4, 153.3, 157.1, 167.3, 197.6; IR (KBr, cm–1) 3397, 3285,
3065, 2919, 1688, 1559, 1471, 1267, 1223, 829.
Ethyl 2,7,7‐trimethyl‐5‐oxo‐4‐p‐tolyl‐1,4,5,6,7,8‐hexahydro‐
quinoline‐3‐carboxylate (Table 4 entry 15). Yield: 96%; mp
263–265 °C (lit. [45] 260–261 °C). 1H NMR (400 MHz, DMSO): δ
0.81 (s, 3H, –CH3), 1.07 (s, 3H, –CH3), 1.18 (t, 3H, J = 7.2 Hz,
–CH3), 1.98 (s, 3H, –CH3), 2.03 (dd, 2H, –CH2–), 2.21 (dd, 2H,
–CH2–), 2.41 (s, 3H, –CH3), 4.06 (q, 2H, J = 7.1 Hz, –OCH2–), 5.11
(s, 1H, –CH–), 7.44 (d, 2H, J = 9.2 Hz, Ar–H), 8.15 (d, 2H, J = 9.2
Hz, Ar–H), 8.21 (brs, 1H, –NH–).13C NMR (100 MHz, DMSO): δ
14.3, 18.9, 23.1, 27.1, 28.5, 31.9, 37.6, 40.7, 51.3, 61.9, 77.7,
104.3, 110.9, 122.8, 129.1, 146.5, 150.3, 155.1, 168.1, 197.1; IR
(KBr, cm–1) 3270, 3185, 3075, 2967, 2366, 1669, 1614, 1567,
1490, 1372, 1276, 1151, 875.
2. Experimental
2.1. General procedure for the Hantzsch synthesis of 1,4‐DHPs
A mixture of dimedone (1.0 mmol), an aldehyde (1.0 mmol),
ethyl acetoacetate (1.0 mmol), ammonium acetate (1.0 mmol),
and SnO2 nanoparticles (1 mol%) in ethanol (2 ml) was stirred
at room temperature until the reaction was complete, as indi‐
cated by thin‐layer chromatography (n‐hexane/ethyl acetate
5:1). The crude solid product was filtered and then purified by
recrystallization from ethanol‐water. The physical data (mp,
NMR, IR) of known compounds were identical to the corre‐
sponding literature data.
Ethyl 2,7,7‐trimethyl‐4‐(4‐nitrophenyl)‐5‐oxo‐1,4,5,6,7,8‐
hexahydroquinoline‐3‐carboxylate (Table 4 entry 20). Yield:
98%; mp 244–246 °C (lit. [25] 242–244 °C). 1H NMR (400 MHz,
DMSO): δ 0.84 (s, 3H, –CH3), 1.01 (s, 3H, –CH3), 1.13 (t, 3H, J=
7.2 Hz, –CH3), 2.01 (dd, 2H, –CH2–), 2.15 (dd, 2H, –CH2–), 2.32
(s, 3H, –CH3), 4.01 (q, 2H, J= 7.3 Hz, –OCH2–), 5.10 (s, 1H, –CH–),
7.44 (d, 2H, J = 9.3 Hz, Ar–H), 8.01 (d, 2H, J = 9.4 Hz, Ar–H), 8.12
(brs, 1H, –NH–).13C NMR (100 MHz, DMSO): δ 14.6, 19.3, 27.4,
29.8, 32.9, 37.6, 40.9, 51.1, 60.2, 77.9, 104.5, 110.8, 123.6, 129.3,
146.4, 150.3, 155.3, 167.5, 195.8; IR (KBr, cm–1) 3276, 3189,
3072, 2967, 2360, 1679, 1604, 1557, 1490, 1342, 1276, 1105,
879.
2.2. General procedure for the synthesis of
polyhydroquinolines

Seyed Mohammad VAHDAT et al. / Chinese Journal of Catalysis 34 (2013) 758–763
Table 1
Table 2
Effect of catalyst amount on the yield of the Hantzsch condensation
reaction.
Effect of solvent on the reaction time and yield of the Hantzsch conden‐
sation reaction.
Amount of catalyst (mol%)
0.5
1
2
5
Isolated yield (%)
Solvent
H2O
C2H5OH
CH3CN
THF
Time (min)
Isolated yield (%)
89
94
93
89
87
23
9
12
15
19
71
94
93
91
89
10
Toluene
Reaction conditions: benzaldehyde (1 mmol), dimedone (1 mmol),
ethyl acetoacetate (1 mmol), ammonium acetate (1 mmol), ethanol
volume (2 ml), room temperature.
Reaction conditions: benzaldehyde (1 mmol), dimedone (1 mmol),
ethyl acetoacetate (1 mmol), ammonium acetate (1 mmol), SnO2 nano‐
particles (1 mol%), solvent volume (2 ml), room temperature.
Diethyl 4‐(4‐chlorophenyl)‐2,6‐dimethyl‐1,4‐dihydropyri‐
dine‐3,5‐dicarboxylate (Table 6 entry 2). Yield: 95%; mp
145–147 °C (lit. [53] 144–146 oC). 1H NMR (400 MHz, DMSO): δ
1.23 (t, 6H, J= 7.1 Hz, –CH3), 2.27 (s, 6H, –CH3), 4.17 (m, 4H, J=
5.7 Hz, –OCH2), 4.87 (brs, 1H, –NH–), 5.68 (s, 1H, –CH–), 7.41 (d,
2H, J= 7.9 Hz, Ar–H), 7.57 (d, 2H, J= 7.8 Hz, Ar–H). 13C NMR (100
MHz, DMSO): δ 14.3, 14.9, 45.9, 61.3, 97.6, 127.1, 128.3, 134.8,
143.2, 147.1, 167.8; IR (KBr, cm–1) 3273, 3180, 2967, 1687,
1557, 1495, 1341, 1267, 879.
under these conditions, the reaction was complete within 9 min
(Scheme 1).
We compared the results we obtained with SnO2 nanoparti‐
cles as a catalyst with the results reported in the literature for
various other catalysts in similar reactions (Table 3). Two of
the literature methods required a catalyst ratio of >1 mol%
(entries 4 and 7), and some of the methods required much
longer reaction times (entries 2, 7, and 8).
We next evaluated the substrate scope of the reaction with a
series of aromatic, aliphatic, and heterocyclic aldehydes and
found that all the tested substrates underwent the electrophilic
substitution reaction to produce a wide range of polyhydro‐
quinoline derivatives in good to excellent yields (Table 4). Ar‐
omatic aldehydes with electron‐withdrawing groups on the
aromatic ring (entries 18–21) reacted faster than aldehydes
bearing electron‐donating groups (entries 10, 12, and 15). Ali‐
phatic aldehydes also required relatively long reaction times
(entries 25–28), most likely because of the electron‐donating
and steric effects of the aliphatic moieties.
Diethyl
2,6‐dimethyl‐4‐(4‐nitrophenyl)‐1,4‐dihydropyri‐
dine‐3,5‐dicarboxylate (Table 6 entry 7): Yield: 98%; mp
131–133 °C (lit. [53] 130–132 oC). 1H NMR (400 MHz, DMSO): δ
1.27 (t, 6H, J= 7.3 Hz, –CH3), 2.13 (s, 6H, –CH3), 4.35 (m, 4H, J =
5.9 Hz, –OCH2), 4.85 (brs, 1H, –NH–), 5.79 (s, 1H, –CH–), 7.51 (d,
2H, J= 7.8 Hz, Ar–H), 7.59 (d, 2H, J= 7.8 Hz, Ar–H);13C NMR (100
MHz, DMSO): δ 15.1, 17.8, 45.7, 63.3, 96.6, 128.1, 128.7, 132.5,
145.2, 148.3, 167.5; IR (KBr, cm–1) 3275, 3191, 2975, 1657,
15357, 1491, 1356, 1265, 875.
3. Results and discussion
We evaluated the reusability of the catalysts by carrying out
multiple reactions of dimedone, 4‐nitrobenzaldehyde, ethyl
acetoacetate, and ammonium acetate to form 4at (Table 5).
After completion of each reaction, the product was extracted
with ethanol, and the catalyst was recovered from the aqueous
layer. The SnO2 nanoparticles were more soluble in ethanol
than in water. In this medium, the recovered catalyst could be
reused five times without appreciable loss of catalytic activity.
First, we optimized the reaction conditions for the
four‐component Hantzsch condensation with respect to yield
and reaction rate by varying the catalyst amount (Table 1), the
solvent (Table 2), and the reaction temperature. We obtained
the maximum yield of the desired polyhydroquinolines (94%)
with 1 mol% of catalyst at room temperature in ethanol, and
O
O
O
R
Me
CO2Et
O
O
2
CO2Et
Me
NH4OAc, Nano SnO2 (1mol%)
C2H5OH, r.t.
Me
Me
+
Me
Me
N
H
R
H
O
4
1
3
Scheme 1. SnO2 nanoparticle‐catalyzed synthesis of polyhydroquinolines 4.
Table 3
Comparison of various catalysts in the four‐component Hantzsch condensation.
Entry
Catalyst (mol%)
SnO2/1
Bakers’ yeast‐D‐glucose/200–300 mg
MCM‐41/1
Solvent
C2H5OH
phosphate buffer (pH=7.0)
solvent free
C2H5OH
solvent free
CH3CN/reflux
C2H5OH/reflux
perfluorodecalin (C10F18)
Temperature (°C) Time (min)
Yield (%)
94
Ref.
this work
[29]
[38]
[42]
[43]
[30]
[44]
[36]
1
2
3
4
5
6
7
8
r.t
r.t
9
1440
15
79
89
92
85
80
92
95
90
80
80
—
—
60
ZnO/10
60
10
35
SBA‐Pr‐SO3H/ 0.05 g
K7[PW12CoO40]/1
L‐proline/10
360
180
Hf(NPf2)4/1

Seyed Mohammad VAHDATet al. / Chinese Journal of Catalysis 34 (2013) 758–763
Table 4
SnO2 nanoparticle‐catalyzed Hantzsch synthesis of polyhydroquinoline derivatives from various aldehydes (RCHO).
Entry
1
2
3
4
5
6
7
8
R
C6H5
2‐Cl‐C6H4
Product
4aa
4ab
4ac
4ad
4ae
4af
4ag
4ah
4ai
mp (°C)
203‒205
209‒211
229‒231
240‒242
200‒202
243‒245
185‒187
253‒255
216‒218
228‒230
201‒203
258‒260
212‒214
197‒199
263‒265
181‒183
231‒233
190‒192
175‒177
244‒246
143‒145
203‒205
246‒248
225‒227
143‒145
148‒150
161‒163
165‒167
Reaction time (min)
Yield (%)
94
95
96
96
95
95
96
95
94
95
94
95
96
95
96
96
97
98
97
98
97
94
95
95
91
92
92
91
Ref.
[45]
[34]
[46]
[29]
[47]
[29]
[37]
[45]
[26]
[45]
[34]
[45]
[48]
[20]
[45]
[49]
[27]
[24]
[20]
[25]
[24]
[31]
[50]
[34]
[45]
[45]
[44]
[51]
9
7
6
6
7
6
6
6
9
8
8
7
8
8
6
7
5
2
3
1
2
10
9
10
15
14
15
15
4‐Cl‐C6H4
2,4‐Cl2‐C6H3
3,4‐Cl2‐C6H3
2,6‐Cl2‐C6H3
4‐F‐C6H4
4‐Br‐C6H4
3‐OH‐C6H4
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
4‐OH‐C6H4
4aj
4ak
4al
3‐OMe‐C6H4
4‐OMe‐C6H4
4‐OH‐3‐OMe‐C6H3
3,4,5‐(OMe)3‐C6H2
4‐Me‐C6H4
4‐(Me)2CH‐C6H4
4‐(Me)2N‐C6H4
4‐CF3‐C6H4
4am
4an
4ao
4ap
4aq
4ar
4as
4at
4au
4av
4aw
4ax
4ba
4bb
4bc
4bd
3‐NO2‐C6H4
4‐NO2‐C6H4
4‐CN‐C6H4
cinnamaldehyde
furan‐2‐carbaldehyde
thiophene‐2‐carbaldehyde
CH3CH2
CH3(CH2)2
(CH3)2CH
CH3(CH2)4
The morphologies of fresh SnO2 nanoparticles, a composite
Table 5
Evaluation of catalyst reusability for the synthesis of 4at.
sample containing SnO2 nanoparticles and product, and SnO2
nanoparticles recovered after three reactions were studied by
field emission scanning electron microscopy (Fig. 1). The im‐
ages of the fresh nanoparticles showed spherical grains with
diameters of 30–60 nm with condensed structure and no ag‐
gregation (Fig. 1(a)). The image of the composite sample
Entry
Isolated yield (%)
Catalyst recovery (%)
1
2
3
4
5
98
97
97
96
95
98
96
95
93
90
(b)
(c)
(f)
(a)
(d)
(e)
(h)
(i)
(g)
Fig. 1. Field emission scanning electron microscopy images of fresh SnO2 nanoparticles (a–c), a composite sample containing SnO2 nanoparticles and
reaction product (d–f), and SnO2 nanoparticles recovered after three uses (g–i).

Seyed Mohammad VAHDAT et al. / Chinese Journal of Catalysis 34 (2013) 758–763
R
O
O
O
EtO2C
Me
CO2Et
NH4OAc, SnO2 (1mol%)
C2H5OH, r.t.
+
Me
CO2Et
R
H
N
Me
H
3
2
5
Scheme 2. SnO2 nanoparticle‐catalyzed synthesis of 1,4‐DHPs.
Table 6
SnO2 nanoparticle‐catalyzed three‐component Hantzsch synthesis of 1,4‐DHPs from various aldehydes (RCHO).
Entry
R
Ph
4‐Cl‐C6H5
4‐OH‐C6H5
4‐OMe‐C6H5
4‐Me‐C6H5
Product
5a
5b
5c
5d
5e
5f
5g
5h
mp (°C)
158‒160
145‒147
231‒233
151‒153
137‒139
166‒168
131‒133
120‒122
161‒163
Time (min)
11
7
9
7
8
5
2
14
11
Yield (%)
93
Ref.
[52]
[53]
[53]
[52]
[54]
[54]
[53]
[53]
[52]
1
2
3
4
5
6
7
8
9
95
94
94
95
97
98
93
93
3‐NO2‐C6H5
4‐NO2‐C6H5
cinnamaldehyde
furan‐2‐carbaldehyde
5i
showed the presence of cubic rectangular structures with
lengths of >200 nm for reaction products and the presence of
nanoparticles in the solution. The images of the nanoparticles
recovered from the reaction medium revealed that some ag‐
gregates were present.
We also evaluated the use of SnO2 nanoparticle–catalyzed
three‐component Hantzsch reactions for the efficient synthesis
of 1,4‐DHPs at room temperature (Scheme 2). The condensa‐
tion of 2 mmol of ethyl acetoacetate with 1 mmol of each of
various arylaldehydes and NH4OAc in ethanol in the presence
of SnO2 nanoparticles rapidly furnished the desired 1,4‐DHPs in
high yields (Scheme 2).
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[24] Surasani R, Kalita D, Dhanunjaya‐Rao A V, Yarbagi K, Chandrasek‐

Seyed Mohammad VAHDATet al. / Chinese Journal of Catalysis 34 (2013) 758–763
Graphical Abstract
Chin. J. Catal., 2013, 34: 758–763 doi: 10.1016/S1872‐2067(11)60518‐4
Synthesis of polyhydroquinoline derivatives via a four‐component Hantzsch condensation catalyzed by tin dioxide
nanoparticles
Seyed Mohammad VAHDAT*, Fereshteh CHEKIN, Mehdi HATAMI, Maryam KHAVARPOUR, Saeed BAGHERY, Ziba ROSHAN‐KOUHI
Islamic Azad University, Iran; Khoramshar University of Marine Science and Technology, Iran; Bu‐Ali Sina University, Iran
A simple procedure for the SnO2 nanoparticle‐catalyzed preparation of polyhydroquinoline derivatives in aqueous ethanol at ambient
temperature is described.
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