Sulfamic Acid-functionalized Nano-titanium dioxide as a Novel and Highly Efficient Heterogeneous Nanocatalyst for One-pot and Solvent-free Synthesis of Hexahydroquinolines

Article abstract of DOI:10.1002/jccs.201600802

Hexahydroquinolines are synthesized via one-pot, four-component condensation of 1,3-cyclic diketones, aromatic aldehydes, malononitrile, and ammonium acetate in the presence of sulfamic acid-functionalized nano-titanium dioxide as a novel type of heteroge

Full text of DOI:10.1002/jccs.201600802

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Sulfamic Acid-functionalized Nano-titanium dioxide as a Novel and Highly Efficient
Heterogeneous Nanocatalyst for One-pot and Solvent-free Synthesis
of Hexahydroquinolines
*
Elham Tabrizian and Ali Amoozadeh
Department of Organic Chemistry, Faculty of Chemistry, Semnan University, Semnan 35131-19111, Iran
(Received: October 30, 2016; Accepted: December 18, 2016; DOI: 10.1002/jccs.201600802)
Hexahydroquinolines are synthesized via one-pot, four-component condensation of 1,3-cyclic dike-
tones, aromatic aldehydes, malononitrile, and ammonium acetate in the presence of sulfamic
acid-functionalized nano-titanium dioxide as a novel type of heterogeneous nanocatalyst. The opti-
mized reaction condition is achieved using response surface method (Box–Behnken design [BBD]).
Operational simplicity, low cost, nontoxic nature, and high reusability of the catalyst together with
simple work-up and excellent product yields are the main advantages of this methodology. Also,
the nanocatalyst can be recovered easily by centrifugation and reused efficiently for at least seven
consecutive runs.
Keywords: Heterogeneous nanocatalyst; Sulfamic acid-functionalized nano-titanium dioxide; 2,4-
Toluene diisocyanate; Hexahydroquinoline; Experimental design.
INTRODUCTION
Multicomponent reactions (MCRs), as a one-pot
In the last decade, worldwide, momentum toward
the replacement of hazardous and corrosive homogene-
ous catalysts by heterogeneous ones has increased to
meet environmental and safety concerns through green
chemistry.9–15 So, the design and application of hetero-
geneous catalysts is developing rapidly. The several
advantages of heterogeneous catalysts include their eco-
friendly nature, simplicity of storage and handling,
noncorrosiveness, low waste disposal problem, and pro-
longed reusability.16,17 Today, the use of nanomaterials
as catalyst supports has considerably increased because
of their large surface to volume ratio, which makes
them ideal candidates as heterogeneous catalysts for
chemical syntheses.18,19
convergent strategy, are considered an invaluable
approach to drug discovery as well as for the synthesis
of important complex organic compounds from readily
available and ordinary starting materials. In these reac-
tions, three or more components are combined in a sin-
gle step to prepare the corresponding product in high
yield without the isolation of any intermediates or the
appearance of any byproducts, which results in saving
time and atom economy. So, special attention has been
paid in designing and discovering heterocyclic com-
pounds using this powerful strategy instead of conven-
tional sequential, multistep reactions.1–4
Quinolines containing
a
1,4-dihydropyridine
Very recently, our group reported a novel and
unique strategy for immobilizing chlorosulfonic acid on
the surface of nanoparticles by applying 2,4-toluene dii-
socyanate (TDI) as a regioselective and covalently
bound linker.20 TDI acts as a bridge between the sup-
port and sulfonic acid groups to increase the lifetime
and recyclability of the hybrid nanocatalyst (Scheme 1).
This hybrid nanocatalyst was characterized by Fourier
transform infrared (FT-IR) spectroscopy, field effect
scanning electron microscopy (FE-SEM), X-ray
nucleus are one of the most valuable heterocycles
because of their vast biological and pharmacological
properties such as their analgesic, anti-inflammatory,
antitubercular, and antithrombotic activities,5–8 so their
synthesis is an ongoing research area among synthetic
chemists. The convenient synthetic approach for the
preparation of hexahydroquinolines consists of a one-
pot, four-component condensation of 1,3-cyclic dike-
tones, aromatic aldehydes, malononitrile, and an
ammonia source.
*Corresponding author. Email: aamozadeh@semnan.ac.ir
J. Chin. Chem. Soc. 2017
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Article
Tabrizian and Amoozadeh
N
C O
Table 1. Parameter levels and coded values of BBD
O
C
H
Toluene diisocyanate
dry toluene, 95 °C, 6h
n-TiO2
n-TiO2
n-TiO2
n-TiO2
O
N
CH3
OH
Levels
Low
(−1)
Central
(0)
High
(+1)
N
C
O
NH2
CH3
H2O/Acetone
(1/1)
O
C
O
C
H
N
H
Independent variables
n-TiO2
O
CH3
O
N
30 °C, 2h
X1: Catalyst amount (g)
X2: Temperature (ꢀC)
X3: Time (min)
0.005
50
10
0.010
80
30
0.015
110
50
O
S
NH2
CH3
HN
OH
O
C
O
C
O
CH3
H
N
Chlorosulfonic acid
H
n-TiO2
O
O
N
dry CH2Cl2, rt, 30 min
Scheme
1. Preparation
functionalized
NHSO3H).
of
sulfamic
n-TiO2
acid-
(n-TiO2-
On the basis of polynomial response surface mod-
els for yield, X1 had the most linear effect on the prod-
uct yield, and therefore the amount of catalyst can be
considered as the main factor in the progress of the
reaction.
diffraction (XRD), and thermogravimetric analysis
(TGA).20 Furthermore, based on ion-exchange pH
analysis results, the loading of the sulfonic acid sites
was found to be about 1 mmol H+/g of the catalyst.
The superiority of this nanocatalyst consists in its sim-
ple preparation and high recyclability, ease of work-up
procedure, high product yields, short reaction time, and
mild reaction conditions.
Y
= −218:46 + 9003:23X1 + 4:41X2 + 2:90X3
+ 10:03X1X2 + 19:62X1X3 + 0:01X2X3
ðyieldÞ
−4:58 × 105X12 −0:03X22 – 0:05X3
2
RESULTS AND DISCUSSION
The main object of this design is the determination
In this paper, in continuation of our studies on
of the best reaction conditions. Based on the experimen-
tal design by using Design-Expert 7.0.0, the model-
predicted optimum yield is 95%, with the optimal proc-
ess conditions of catalyst amount 0.012 g at 80ꢀC
within the reaction time of 32 min (Figure 1).
applying
green
catalysts
for
organic
transformations,21–27 we investigate the catalytic activ-
ity of nano (n)-TiO2-NHSO3H for the synthesis of hex-
ahydroquinolines (Scheme 2).
With the aim of evaluating the best reaction con-
dition and the influence of different parameters in this
reaction, we considered the Box–Behnken design (BBD)
of response surface method28 and selected the reaction
of dimedone, benzaldehyde, malononitrile, and ammo-
nium acetate as the model reaction. Three variables that
can influence the yield (as the response) are the catalyst
amount (X1), temperature (X2), and reaction time (X3),
which were coded to three levels of −1, 0, and 1, as
shown in Table 1.
Table 2. Conditions of predicted experiments in BBD
Run
X1
X2
X3
Yield (%)
1
2
3
4
5
6
7
8
0.015
0.005
0.010
0.010
0.010
0.010
0.015
0.010
0.005
0.015
0.005
0.015
0.010
0.005
0.010
0.010
0.010
50.00
110.00
80.00
80.00
110.00
80.00
80.00
50.00
50.00
110.00
80.00
80.00
110.00
80.00
80.00
50.00
80.00
30.00
30.00
30.00
30.00
50.00
30.00
50.00
10.00
30.00
30.00
10.00
10.00
10.00
50.00
30.00
50.00
30.00
39.77
73
92.1
92
91.09
95.42
90.06
20.2
32.55
86.24
36.65
47.1
42.33
71.76
90.88
43.89
93.68
Based on the BBD strategy, 17 experimental runs
were carried out at random (Table 2).
9
10
11
12
13
14
15
16
17
Scheme 2. n-TiO2-NHSO3H-catalyzed synthesis of
hexahydroquinolines.
2
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TiO2-NHSO3H as a Novel Heterogeneous Nanocatalyst
The formation of hexahydroquinolines is sug-
gested to involve the following mechanism (Scheme 3):
Knoevenagel condensation, Michael addition, and
intramolecular ring closure as the three main steps. Ini-
tially, the sulfonic acid groups of the catalyst activate
the aldehyde (II) to form the intermediate (IV) through
Knoevenagel condensation of malononitrile (I) with
(II). Then, (VII), which is formed by the condensation
of 1,3-cyclic diketone (V) and ammonium acetate (VI),
readily reacts with (IV), leading to the Michael addition
product (VIII). Finally, intramolecular N-cyclization
takes place (IX), which converts to the final product
(X). The role of the acidic groups of n-TiO2-NHSO3H
is depicted in every step of the mechanism.
In recent years, there has been growing interest
regarding the recyclability and reusability of heteroge-
neous catalysts. In this regard, the reusability of
n-TiO2-NHSO3H was evaluated for the model reaction
under optimized reaction conditions (Figure 2). The
catalyst was separated after each run by centrifugation,
washed three times with ethanol and acetone (5 mL),
dried in an oven at 90ꢀC, and reused in subsequent
runs. It was found that the nanocatalyst could be reused
effectively for at least seven runs with negligible deterio-
ration in activity, which is attributed to the stable func-
tionalized groups on the catalyst.
The changes in structural and morphological fea-
tures of the recovered catalyst were determined by FT-
IR and FE-SEM methods. As can be seen in Figure 3,
the structure of the recycled catalyst remains the same
as that of fresh one, and according to Figure 4, no obvi-
ous change in the size and morphology of the recovered
nanocatalyst was observed.
In summary, n-TiO2-NHSO3H was successfully
applied as a novel inorganic–organic hybrid nanocatalyst
for the synthesis of hexahydroquinolines via a one-pot,
four-component reaction of 1,3-cyclic diketone, aromatic
aldehyde, malononitrile, and ammonium acetate with
inherent diversity. Solvent-free media, simple work-up,
high product yields, short reaction times, and high reusa-
bility of the catalyst are the main promising points of the
present methodology, which make it an attractive process.
Fig. 1. Optimized parameters resulting from the
model.
To assess the best medium for this transformation,
the model reaction was screened in different polar and
nonpolar solvents such as EtOH, H2O, PEG-400,
CH2Cl2, and PhCH3. Solvent-free media were found to
be the best, which afforded the highest product yield
and purity (Table 3).
Inspired by the satisfactory results obtained from
the model reaction, we employed the optimum condi-
tions for the synthesis of a series of hexahydroquino-
lines to find the scope and specificity of this protocol
(Table 4).
Regardless of the presence of electron-donating or
electron-withdrawing substituents in the ortho, meta, or
para positions of the aromatic aldehyde, the reactions
proceed well to give the desired products in good to
excellent yields (85–97%). Melting points of products
were in accordance with those in the literature,29–31 and
some of the products were well characterized by spec-
tral techniques.
Table 3. Optimization of solventa
Entry
Solvent
Yield (%)
1
2
3
4
5
6
—
95
53
21
EtOH
H2O
PEG-400
CH2Cl2
PhCH3
30
15
Trace
EXPERIMENTAL
Materials and instruments
Commercial reagent grade chemicals were pur-
chased from Aldrich or Merck and used as received.
a Reaction conditions: 1 (1 mmol), 2 (1 mmol), 3 (1 mmol), 4
(2.5 mmol), n-TiO2-NHSO3H (0.012 g) at 80ꢀC, reaction
time: 32 min.
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Article
Tabrizian and Amoozadeh
Melting point (ꢀC)
Table 4. Synthesis of hexahydroquinolines by n-TiO2-NHSO3Ha
Entry
R1=R2
R3
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
4-H
32
40
45
30
28
24
27
20
20
25
32
44
50
31
28
27
28
21
22
25
45
95
90
88
90
87
93
91
95
95
97
95
89
88
90
92
94
90
93
92
96
85
258–260
258–260
276–278
226–228
240–242
259–261
287–288
287–289
250–251
285–287
274–276
292–293
290–292
230–232
284–285
293–295
272–275
291–293
296–298
297–299
260–263
4-CH3
4-OCH3
2-NO2
3-NO2
4-NO2
2-Cl
4-Cl
4-Br
4-F
4-H
4-CH3
4-OCH3
2-NO2
3-NO2
4-NO2
2-Cl
4-Cl
4-Br
4-F
2-Naphthyl
9
H
H
10
11
12
13
14
15
16
17
18
19
20
21
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
a Reaction conditions: 1 (1 mmol), 2 (1 mmol), 3 (1 mmol), 4 (2.5 mmol), n-TiO2-NHSO3H (0.012 g) under solvent-free
condition at 80ꢀC.
b Isolated yield.
The progress of the reaction was monitored by thin-
layer chromatography (TLC) on glass plates coated
with silica gel 60 F254. Melting points were measured
on a Thermo Scientific 9100 melting point apparatus.
FT-IR spectra were recorded using KBr pressed powder
disks on a Shimadzu-8400 spectrometer in the range
400–4000 cm−1. FE-SEM images were obtained on a
Philips XL30 field emission scanning electron micro-
scope (Royal Philips Electronics, Amsterdam, The
Netherlands) instrument operated at a 30 kV accelerat-
ing voltage. NMR spectra were measured on a Bruker
Avance instrument using tetramethylsilane (TMS) as
internal reference.
free medium for an appropriate time followed by TLC
(EtOAc/hexane, 20:80). Upon completion of the reac-
tion (monitored by TLC), hot ethanol (10 mL) was
added to dissolve the product entirely and centrifuged
to filter the catalyst. The products were obtained by
recrystallization from ethanol.
2-Amino-4-(2-nitrophenyl)-5-oxo-1,4,5,6,7,8
hexahydroquinoline-3-carbonitrile
(Entry
4)
M.
p.: 226–228ꢀC; IR (KBr, Cm−1) νmax: 3337, 3462, 3236,
2197, 1684, 1661, 1529, 1365. 1H NMR (300 MHz,
DMSO-d6): δ 1.03–1.07 (m, CH2, 2H), 1.89–2.24 (m,
CH2, 2H), 2.48–2.59 (m, CH2, 2H), 3.38 (s, NH, 1H),
4.94 (s, CH, 1H), 7.15 (s, NH2, 2H), 7.35–7.80 (m, 4H).
13C NMR (75 MHz, DMSO-d6): δ 19.7, 26.4, 30.1,
36.0, 56.4, 113.3, 119.1, 123.7, 127.8, 130.4, 133.4,
139.0, 149.0, 159.1, 164.7, 196.0.
General procedure for the synthesis of
hexahydroquinolines (5)
2-Amino-4-(4-bromophenyl)-5-oxo-1,4,5,6,7,8-hexa-
The catalyst was prepared according to our recent
paper.20 A mixture of 1,3-cyclic diketone (1 mmol),
aromatic aldehyde (1 mmol), malononitrile (1 mmol),
ammonium acetate (2.5 mmol), and n-TiO2-NHSO3H
(0.012 g) were magnetically stirred at 80ꢀC in a solvent-
hydroquinoline-3-carbonitrile
(Entry
9)
M.
p.: 250–251ꢀC; IR (KBr, Cm−1) νmax: 3418, 3332, 3252,
1
2197, 1682, 1657, 1071. H NMR (300 MHz, DMSO-
d6): δ 1.89 (m, 2H, CH2), 2.26 (m, 2H, CH2), 2.54 (m,
4
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TiO2-NHSO3H as a Novel Heterogeneous Nanocatalyst
O
S O H
O
O
H
R3
O
(II)
H O S
R3
O
O H
H
H C N
C
C
N
C
H
C N
(I)
NH
(III)
R3
R3
HN
O
H
C
N
C
N
= nano-TiO2
O C N
CH3
O
H O S
O
O
CN
R1
(IV)
N
H
(X)
NH2
R2
R3
H
R3
NH OAc
H2N
O
HN
O
O
O
4
O
O
H
(VI)
CN
C N
R1
R1
R1 R2
(VII)
R1 R2
R1 R2
(V)
C
N
N H
NH
(VIII)
N
R2
R2
H
O
H O S
O
(IX)
H
O
O S O
Scheme 3. Plausible mechanism for the synthesis of hexahydroquinolines catalyzed by n-TiO2-NHSO3H.
2H, CH2), 3.34 (s, 1H, NH), 4.19 (s, 1H), 7.24 (m, 4H),
7.24 (s, 2H, NH). 13C NMR (75 MHz, DMSO-d6): δ
19.8, 26.5, 35.1, 36.3, 57.7, 113.4, 119.6, 120.1, 129.5,
130.7, 131.2, 132.3, 143.1, 149.5, 164.6, 195.9.
2-Amino-7,7-dimethyl-4-(2-nitrophenyl)-5-
oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (Entry
14) M.p.: 230–232ꢀC; IR (KBr, Cm−1) νmax: 3472,
Fig. 3. FT-IR spectra of fresh and recovered
nanocatalyst.
Fig. 2. Reusability test of n-TiO2-NHSO3H.
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Article
Tabrizian and Amoozadeh
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1
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1H), 4.39 (s, CH, 1H), 7.09 (s, NH2, 2H), 7.29–7.90 (m,
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ACKNOWLEDGMENT
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We gratefully acknowledge the Faculty of Chemis-
try, Semnan University, for supporting this work.
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