TiO2-SiO2 nanocomposite-promoted efficient cyclocondensation reaction of arylmethylidenepyruvic acids with dimedone in aqueous media

Article abstract of DOI:10.1002/jccs.201800057

This work focuses on the successful synthesis of 4-aryl-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acids through a condensation reaction of arylmethylidenepyruvic acids with ammonium acetate and dimedone using a catalytic amount of TiO₂–SiO₂ nanocomposite (15 mol%) at room temperature in aqueous media. The principal advantage of this procedure is the relatively high yields (94–98%) with short reaction times (2 hr), under mild reaction conditions and with low environmental impact.

Full text of DOI:10.1002/jccs.201800057

Received: 12 February 2018
DOI: 10.1002/jccs.201800057
Revised: 12 April 2018
Accepted: 9 May 2018
A R T I C L E
TiO2-SiO2 nanocomposite-promoted efficient cyclocondensation
reaction of arylmethylidenepyruvic acids with dimedone in
aqueous media
Sepehr Sadegh-Samiei1 | Shahrzad Abdolmohammadi2
1Department of Chemistry, East Tehran Branch,
This work focuses on the successful synthesis of 4-aryl-7,7-dimethyl-5-oxo-
Islamic Azad University, Tehran, Iran
2Young Researchers and Elite Club, East Tehran
Branch, Islamic Azad University, Tehran, Iran
1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acids through a condensation reaction
of arylmethylidenepyruvic acids with ammonium acetate and dimedone using a
catalytic amount of TiO2–SiO2 nanocomposite (15 mol%) at room temperature in
aqueous media. The principal advantage of this procedure is the relatively high
yields (94–98%) with short reaction times (2 hr), under mild reaction conditions
and with low environmental impact.
Correspondence
Sepehr Sadegh-Samiei, Department of Chemistry,
East Tehran Branch, Islamic Azad University, PO
Box 18735-138, Tehran, Iran.
Email: sepehr.samiei@gmail.com
KEYWORDS
aqueous media, quinolone, recyclability of catalyst, TiO2–SiO2 nanocomposite
acids 4 through a condensation reaction of arylmethylidene-
pyruvic acids 1, which is easily prepared according to a known
1
| INTRODUCTION
procedure,[22] with ammonium acetate 2 and dimedone 3 using
a catalytic amount of the TiO2–SiO2 nanocomposite (15 mol
%) at room temperature in aqueous media (Scheme 1).
In the past few years, the use of nanostructured metal oxide
catalysts in organic synthesis has been preferred because of
their special features such as high surface area with low coor-
dination sites.[1–5] Among these catalysts, titanium dioxide
nanoparticles (TiO2 NPs) have received special interest as a
new and efficient catalyst in several organic and inorganic
transformations because of its superior properties such as high
catalytic activity, nontoxicity, easy availability, moisture sta-
bility, and reusability.[6–14] In particular, the TiO2–SiO2 nano-
composite with its unique characteristics such as electronic
properties and large specific surface area can be used as a new
and versatile heterogeneous catalyst.[15]
Scaffolds based on quinolones have been extensively
studied because of a variety of chemical and biological impor-
tance. They have been reported to exhibit several effective
biological activities such as antibacterial,[16] antimicrobial,[17]
kinase inhibitory,[18] and cytotoxic.[19] Moreover, the major
antibiotic classes contain the 4-quinolone framework in their
structures.[20] Several of synthesized 2,4-disubstituted polyhy-
droquinolines have been found to exhibit promising in vivo
antihyperglycemic activity.[21]
2
| RESULTS AND DISCUSSION
To find the optimal reaction conditions, we started our
experiments by the model reaction of phenylmethylidene-
pyruvic acid (1a), ammonium acetate (2), and dimedone (3),
under various reaction conditions including the amount of
catalyst and different solvents. In order to confirm the cata-
lytic efficiency of the TiO2–SiO2 nanocomposite, the model
reaction was carried out in the absence of any catalyst. In the
absence of the catalyst, the reaction did not proceed to com-
pletion even after 7 hr stirring in water at room temperature
(Table 1, entry 1). Then we carried out the model reaction
using different amounts of the catalyst. However, the best
results were obtained when using 15 mol% of the TiO2–
SiO2 nanocomposite in H2O at room temperature (Table 1,
entry 2–4). Thus, our next effort was focused on the
appraisal of the catalytic efficiency of the TiO2–SiO2 nano-
composite against two commercial nanopowders, namely
Here, we focus on the successful synthesis of 4-aryl-7,
7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic
© 2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–5.
http://www.jccs.wiley-vch.de
1

2
SADEGH-SAMIEI AND ABDOLMOHAMMADI
G
TABLE 2 Effects of reaction media for the synthesis of
4-phenyl-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acid, 4a
O
O
O
Yield (%)a,b
TiO2/SiO2 Nanocomposite
(15 mol %)
Entry
Solvent
Neat
Time (hr)
OH
NH4OAc
+
+
O
H2O, R.T.
1
2
3
4
5
6
5
3
2
2
4
2
48
64
71
95
55
69
O
HOOC
N
H
G
EtOH
MeOH
H2O
3
4
1
2
SCHEME 1 Synthesis of quinolinecarboxylic acids 4a-h
CH2Cl2
DMF
TiO2 NPs (10–30 nm, anatase-TiO2), and SiO2 NPs (20 nm,
non-porous). As shown in Table 1, when the reaction was
performed using 20 mol% of two these commercial nano-
powders alone under the same reaction conditions, the
desired product 4a was obtained in 84 and 78% yields,
respectively. Doping of SiO2 into TiO2 could effectively pre-
vent the growth of TiO2 particles, which may have been due
to the formation of the Ti–O–Si bond and to the presence of
amorphous SiO2 around TiO2[23]; thus a large specific
surface area of particles in composite could be obtained
resulting in their enhanced catalytic activities. Study on the
catalytic potential of the TiO2–SiO2 nanocomposite showed
that the reaction time and the catalyst loading decreased,
along with higher yield of the product (Table 1, entries 3, 5,
and 6).
a
Isolated yield.
b
Reaction conditions: a mixture of phenylmethylidenepyruvic acid (1 mmol),
ammonium acetate (1.2 mmol), dimedone (1 mmol), and TiO2–SiO2 nanocom-
posite (15 mol%) was stirred at room temperature.
950 cm−1 reveals that the TiO2 species are embedded into
SiO2 matrix within the TiO2/SiO2 nanocomposite. The broad
peak appearing at 3,100–3,600 cm−1 is assigned to the
stretching mode of the hydroxyl groups (free or bonded),
which is confirmed from the weak absorption observed at
about 1,620 cm−1
.
The X-ray diffraction (XRD) pattern of synthesized
nanocomposite, which is presented in Figure 2, shows the
existence of the anatase phase of TiO2 in the amorphous
silica matrix. The average particle size of the TiO2–SiO2
nanocomposite was about 5 nm, based on Debye–Scherrer
equation.
The transmission electron microscopy (TEM) image of
synthesized nanocomposite was also carried out, which
showed that all composites had a grainy structure with parti-
cle sizes of about 5 nm (Figure 3). The chemical composi-
tion of as-prepared nanocomposite was determined by X-ray
fluorescence (XRF) technique, and the results show that the
molar ratio was 1:1.
While evaluating the effect of the reaction media on the
above reaction, it was found that the yields were poor in
EtOH, MeOH, CH2Cl2, DMF, and also under neat condi-
tions, while H2O was a favorable medium (Table 2).
The TiO2–SiO2 nanocomposite in the molar ratio of 1:1
was prepared by a procedure reported earlier.[24] The FT-IR
spectrum of the TiO2–SiO2 nanocomposite (Figure 1) shows
three characteristic peaks at around 1,100, 950, and
650 cm−1. The peaks at 650 and 1,100 cm−1 are representa-
tive of the TiO2 and SiO2 matrixes, respectively, in nano-
composite. The peak at around 950 cm−1 is ascribed to the
stretching of the Si–O species of Si–O–Ti or Si–O defect
sites that are formed by the inclusion of Ti4+ ions into the
SiO2 matrix. Thus, the appearance of the peak at around
In order to extend the scope of this new method, we used
several phenyl-substituted methylidenepyruvic acids for their
reaction with ammonium acetate and dimedone. In all cases,
the reactions were successful, giving the corresponding
products in high to excellent yields (Table 3).
TABLE 1 Screening of the effective amount of the catalyst for the synthesis
of 4-phenyl-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic
acid, 4a
Catalyst
(mol% with respect to TiO2)
Time
(hr)
Yield
Entry
(%)a,b,c
1
2
3
4
5
6
No catalyst
7
3
2
2
4
5
Trace
73
Nano-TiO2–SiO2 (10%)
Nano-TiO2–SiO2 (15%)
Nano-TiO2–SiO2 (20%)
Nano-TiO2 (20%)
95
96
84
Nano-SiO2 (20%)
78
a
Isolated yield.
b
Reaction conditions: a mixture of phenylmethylidenepyruvic acid (1 mmol),
ammonium acetate (1.2 mmol), and dimedone (1 mmol) in H2O (3 mL) was
stirred at room temperature.
c
According to the molar ratio of TiO2 to SiO2 in the composite (1:1), the catalyst
loadings in mol% with respect to TiO2 were calculated to be 16, 24, and 32 mg
for 10, 15, and 20 mol% of catalyst, respectively.
FIGURE 1 FT-IR spectrum of the as-prepared TiO2–SiO2 nanocomposite

SADEGH-SAMIEI AND ABDOLMOHAMMADI
3
FIGURE 2 XRD patterns of the as-prepared
TiO2–SiO2 nanocomposite
The recyclability of the catalyst was also examined under
the optimized reaction conditions for the synthesis of 4a. The
recovered catalyst was used in four consecutive runs with
only a moderate decrease in catalytic activity (Figure 4).
The catalytic mechanism of the TiO2–SiO2 nanocompo-
site in accelerating the above cyclocondensation reaction is
provided in Scheme 2. This pathway is initiated by the
condensation of dimedone 3 with ammonium acetate 2 to
generate the enaminone 5. Then TiO2 NPs participated in
the subsequent Michael addition of 5 to arylmethylidene-
pyruvic acid 1 to give intermediate 7. Further intermolecular
cyclization of 7 afforded the products 4 after dehydration.
The structures of compounds 4(a–h) were confirmed by
dimedone. Compared to previous methods,[25,26] this method
has the advantages of high yields, mild reaction conditions,
short reaction time, simple reaction setup, and the use of an
inexpensive, recyclable, and nontoxic catalyst.
4
| EXPERIMENTAL
All chemicals used in this work were purchased from Merck
and Fluka and used without further purification. Melting
points were determined on an Electrothermal 9100 appara-
tus, and are uncorrected. IR spectra were obtained on an
1
ABB FT-IR (FTLA 2000) spectrometer. H NMR and 13C
1
IR, H NMR, and 13C NMR spectroscopic data and also by
NMR spectra were recorded on a Bruker DRX-300
AVANCE spectrometer at 300 and 75 MHz, respectively,
using TMS as internal standard and DMSO (d6) as solvent.
Elemental analyses were carried out on a Foss Heraeus
CHN-O rapid analyzer. Powder XRD data were obtained on
a Philips X’Pert diffractometer using Cu Kα radiation
(λ = 1.54 Å). The composition analysis of catalyst was car-
ried out by XRF using an Oxford ED 2000 instrument. TEM
images of the catalyst were obtained on a Philips EM208
transmission electron microscope.
elemental analyses. Selected spectroscopic data are given in
general procedure section. The synthesized catalyst was fully
characterized by FT-IR, XRD, TEM, and XRF techniques.
3
| CONCLUSIONS
In conclusion, we have demonstrated that the TiO2–SiO2
nanocomposite could efficiently catalyze the reaction of
arylmethylidenepyruvic acids, ammonium acetate, and
TABLE 3 TiO2–SiO2 nanocomposite-catalyzed synthesis of
4-aryl-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic
acids 4a–h
Mp (ꢀC)
Product
4a
G
Yield (%)a,b
Obsd.
Lit.
H
95
97
98
94
97
96
97
98
223–225
266–268
251–252
243–244
259–261
248–249
258–260
240–242
—
4b
Br
—
4c
Cl
250–252[25]
4d
F
—
4e
OH
OCH3
CH3
NO2
—
4f
248–250[25]
259–261[25]
—
4g
4h
a
Isolated yield.
b
Reaction conditions: a mixture of arylmethylidenepyruvic acid (1 mmol),
ammonium acetate (1.2 mmol), dimedone (1 mmol), and TiO2–SiO2 nanocom-
posite (15 mol%) in H2O (3 mL) was stirred at room temperature for 2 hr.
FIGURE 3 TEM image of the as-prepared TiO2–SiO2 nanocomposite

4
SADEGH-SAMIEI AND ABDOLMOHAMMADI
O
OH
96
94
92
90
88
86
84
82
80
O
G
SiO2
Ti
1
G
O
O
O
O
O
NH4OAc
+
O
N
O
H2N
H
O
3
2
5
O
H2N
TiO2 NPs
SiO2
6
G
G
O
H2O
O
HOOC
HO
N
H
N
H
HOOC
1
2
3
4
4
7
Number of cycle
SCHEME 2 Proposed mechanism for the formation of 4
FIGURE 4 Recyclability of the TiO2–SiO2 nanocatalyst in the synthesis
of 4a
4.3 | Selected spectroscopic Data
4.3.1
| 7,7-Dimethyl-4-phenyl-5-oxo-1,4,5,6,7,8-hexahydro-
4.1 | General procedure for the preparation of TiO2–
2-quinolinecarboxylic acid (4a)
SiO2 nanocomposite catalyst
1
ꢀ
White solid, yield: 0.28 g (95%), mp 223–225 C. H NMR
(300 MHz, DMSO-d6): δ 0.91 (3H, s, CH3), 0.99 (3H, s,
CH3), 1.97 (1H, d, J = 15.9 Hz, H-6), 2.10 (1H, d,
J = 15.9 Hz, H-60), 2.46 (2H, m, H-8, H-80), 4.48 (1H, d,
J = 5.0 Hz, H-4), 5.89 (1H, d, J = 4.8 Hz, H-3), 6.65 (5H,
m, HAr), 8.59 (1H, s, NH), 13.00 (1H, s, COOH) ppm. 13C
NMR (75 MHz, DMSO-d6): δ 27.2, 29.1, 30.9, 35.8, 49.9,
105.1, 117.0, 126.7, 127.5, 129.1, 133.7, 142.8, 152.4,
163.4, 193.6 ppm. IR (KBr): νmax 3,359, 2,960, 2,870,
1,704, 1,660, 1,565 cm−1. Anal. Calcd. for C18H19NO3
(297.35): C, 72.71; H, 6.44; N, 4.71. Found: C, 72.92; H,
6.52; N, 4.58.
First, titanium tetrachloride (2 mL) was added dropwise into
the deionized water (200 mL) in an ice-water bath with
strong magnetic stirring. After the hydrolysis was complete,
the released HCl was neutralized by adding dilute NH4OH
to adjust the pH to 7. The produced solid was filtered and
washed with distilled water. The precipitate was dispersed in
a 0.3 M HNO3 aqueous solution (200 mL) to remove all the
chloride ions.ꢀThe mixture was then refluxed under strong
stirring at 70 C for 16 hr, as the titania sol was prepared.
Tetraethylorthosilicate (25 mL) was added dropwise into the
ꢀ
above sol and stirred at 70 C for about 0.5 hr. Finally, the
TiO2–SiO2 nanocomposite powder was filtered and washed
with distilled water and then dried in air at ambient tempera-
ture.[24] The synthesized catalyst was fully characterized by
FT-IR, XRD, TEM, and XRF techniques.
4.3.2
| 4-(4-Bromophenyl)-7,7-dimethyl-5-oxo-
1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acid (4b)
1
ꢀ
White solid, yield: 0.37 g (97%), mp 266–268 C. H NMR
(300 MHz, DMSO-d6): δ 0.90 (3H, s, CH3), 0.97 (3H, s,
CH3), 1.95 (1H, d, J = 16.0 Hz, H-6), 2.16 (1H, d,
J = 16.0 Hz, H-60), 2.45 (2H, m, H-8, H-80), 4.54 (1H, d,
J = 5.2 Hz, H-4), 5.88 (1H, d, J = 5.2 Hz, H-3), 7.18 (2H,
d, J = 8.0 Hz, HAr), 8.35 (2H, d, J = 8.0 Hz, HAr), 8.60
(1H, s, NH), 13.21 (1H, s, COOH) ppm. 13C NMR
(75 MHz, DMSO-d6): δ 27.0, 29.4, 31.6, 36.0, 50.0, 104.9,
116.5, 127.0, 129.2, 130.6, 131.5, 144.0, 151.7, 163.6,
194.1 ppm. IR (KBr): νmax 3,365, 3,320, 2,961, 2,860,
1,700, 1,663, 1,564 cm−1. Anal. Calcd. for C18H18BrNO3
(376.25): C, 57.46; H, 4.82; N, 3.72. Found: C, 57.60; H,
4.93; N, 3.95.
4.2 | General method for the preparation of
compounds 4a–h
A mixture of arylmethylidenepyruvic acids 1a–h (176, 255,
211, 194, 192, 206, 190, 221, 1 mmol), ammonium acetate
2 (92 mg, 1.2 mmol), dimedone 3 (122 mg, 1 mmol), and the
TiO2–SiO2 nanocomposite (21 mg, 15 mol%) in H2O (3 mL)
was stirred at room temperature for 2 hr. The progress of the
reaction was monitored with thin-layer chromatography
(TLC) in 2:1 ethyl acetate/n-hexane as TLC solvent. Upon
completion of the reaction, the reaction mixture was filtered,
the solid mass was diluted with DMF (2 mL), and the mixture
was centrifuged at 2,000–3,000 rpm, for 5 min to remoꢀve the
nano-TiO2–SiO2 catalyst for reusing after drying at 80 C for
several hours under vacuum. The organic solution was then
poured into ice-cold water (5 mL), filtered, and washed with
aqueous ethanol to afford the pure product 4.
4.3.3
| 7,7-Dimethyl-4-(4-fluorophenyl)-5-oxo-
1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acid (4d)
1
ꢀ
White solid, yield: 0.30 g (94%), mp 243–244 C. H NMR
(300 MHz, DMSO-d6): δ 0.90 (3H, s, CH3), 0.99 (3H, s,

SADEGH-SAMIEI AND ABDOLMOHAMMADI
5
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4.3.4
| 7,7-Dimethyl-4-(4-hydroxyphenyl)-5-oxo-
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1
ꢀ
White solid, yield: 0.30 g (97%), mp 259–261 C. H NMR
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4.3.5
| 7,7-Dimethyl-4-(4-nitrophenyl)-5-oxo-
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1,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acid (4h)
1
ꢀ
White solid, yield: 0.34 g (98%), mp 240–242 C. H NMR
(300 MHz, DMSO-d6): δ 0.92 (3H, s, CH3), 0.96 (3H, s,
CH3), 1.95 (1H, d, J = 16.1 Hz, H-6), 2.12 (1H, d,
J = 16.1 Hz, H-60), 2.45 (2H, m, H-8, H-80), 4.52 (1H, d,
J = 5.1 Hz, H-4), 5.87 (1H, d, J = 5.1 Hz, H-3), 7.83 (4H, s,
HAr), 8.55 (1H, s, NH), 13.03 (1H, s, COOH) ppm. 13C NMR
(75 MHz, DMSO-d6): δ 27.1, 29.2, 31.8, 37.4, 50.3, 105.0,
115.9, 124.8, 131.8, 132.0, 144.3, 147.6, 151.8, 163.1,
193.9 ppm. IR (KBr): νmax 3,363, 2,959, 2,856, 1,702, 1,661,
1,564 cm−1. Anal. Calcd. for C18H18N2O5 (342.35): C,
63.15; H, 5.30; N, 8.18. Found: C, 63.03; H, 5.22; N, 8.33.
[25] S. Balalaie, S. Abdolmohammadi, B. Soleimanifard, Int. J. Org. Chem.
2012, 2(3), 276.
[26] S. Abdolmohammadi, Chin. Chem. Lett. 2012, 23, 1003.
ACKNOWLEDGMENT
How to cite this article: Sadegh-Samiei S,
Abdolmohammadi S. TiO2-SiO2 nanocomposite-
promoted efficient cyclocondensation reaction of aryl-
methylidenepyruvic acids with dimedone in aqueous
media. J Chin Chem Soc. 2018;1–5. https://doi.org/
10.1002/jccs.201800057
This work was supported by the East Tehran Branch Islamic
Azad University Research Council.
ORCID
Sepehr Sadegh-Samiei
http://orcid.org/0000-0001-9239-1595
http://orcid.org/0000-0001-8187-9624
Shahrzad Abdolmohammadi