N-propylbenzoguanamine sulfonic acid-functionalized magnetic nanoparticles: A novel and magnetically retrievable catalyst for the synthesis of 1,4-dihydropyridine derivatives

Article abstract of DOI:10.1002/jccs.201800120

The catalytic activity of N-propylbenzoguanamine sulfonic acid stabilized on silica-coated nano-Fe₃O₄ particles (Fe₃O₄/SiO₂-N-propyl-benzoguanamine-SO₃H) were proven to be as a novel magnet

Full text of DOI:10.1002/jccs.201800120

Received: 30 March 2018
Revised: 15 May 2018
Accepted: 16 May 2018
DOI: 10.1002/jccs.201800120
A R T I C L E
N-propylbenzoguanamine sulfonic acid-functionalized magnetic
nanoparticles: A novel and magnetically retrievable catalyst for
the synthesis of 1,4-dihydropyridine derivatives
Masoumeh Gholami Dehbalaei1 | Naser Foroughifar1 | Alireza Khajeh-Amiri2 | Hoda Pasdar1
1Department of Chemistry, Tehran North Branch,
The catalytic activity of N-propylbenzoguanamine sulfonic acid stabilized on
Islamic Azad University, Tehran, Islamic Republic
of Iran
silica-coated nano-Fe3O4 particles (Fe3O4/SiO2-N-propyl-benzoguanamine-SO3H)
were proven to be as a novel magnetic solid acid catalyst for the synthesis of
1,4-dihydropyridine derivatives in a one-pot pseudo-four-component condensation
reaction of barbituric acid, aromatic aldehydes, and ammonium acetate or aniline
2Biomaterial Laboratory, Toxin Research Institute,
Aja University of Medical Sciences, Tehran,
Islamic Republic of Iran
Correspondence
Naser Foroughifar, Department of Chemistry,
with high yield and short reaction times. The structure and magnetic properties of
Tehran North Branch, Islamic Azad University,
Tehran, Islamic Republic of Iran.
the obtained nanoparticles were characterized via Fourier transform infrared spec-
troscopy (IR), field emission scanning electron microscopy (FE-SEM), transmis-
sion electron microscope (TEM), energy dispersive X-ray analysis (EDXA), X-ray
diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis
(DTA) and vibrating sample magnetometry (VSM), atomic absorption spectros-
copy (AAS), and inductively coupled plasma–mass spectrometry (ICP-MS). The
results demonstrated that the average size of the synthesized magnetite nanoparti-
cles is about 25 nm. In addition, the heterogeneous catalyst can be easily recovered
magnetically and can be reused for further runs without significant loss of its cata-
lytic activity.
Email: n_foroughifar@yahoo.com
Funding information
Islamic Azad University-Tehran North Branch;
Research Council of Aja University of Medical
Sciences
KEYWORDS
1,4-dihydropyridine, barbituric acid, green chemistry, hantzsch reaction,
heterogeneous catalyst, MNPs–NPBG–SA
area, low toxicity, good stability, ease of preparation, and
recycling by means of an external magnetic field.[10] One can
1
| INTRODUCTION
The heterogeneous catalysts composed of hybrid organic and
inorganic materials have recently garnered interest from
researchers as they possess the advantages of both homoge-
neous and heterogeneous catalysts.[1–4] The homogeneous
catalysts are more active than heterogeneous catalysts. Due to
solubility in reaction, homogeneous catalysts increase the cat-
alyst bed, but use of these catalysts may not always result in
the pure product of a reaction, and recycling of homogeneous
catalysts is a boring and time-consuming task.[5] Many inves-
tigations have focused on heterogeneous catalysts, especially
magnetic nanoparticles (MNPs), for example, nanoparticles
Fe3O4.[6–9] This issue is due to their unique physical, elec-
tronic, and magnetic properties, in them including high-level
refer to the highly diversified applications of these materials,
including the isolation of metallic ions,[11] magnetic reso-
nance imaging (MRI),[12] drug transfer system,[13] isolation
of protein,[14] and treatment of cancer.[15] MNPs of ferric
oxide demonstrate highly chemical activity and are oxidized
easily in air; therefore, this leads to the lose of magnetic prop-
erties and dispersion of magnetite. Thus, the creation of an
appropriate surface coating is crucially important in order to
restore the stability of the nanoparticles of magnetic ferric
oxide.[16] From an applied viewpoint, in many cases, the pro-
tective shells not only cause stability in MNPs of ferric oxide
but may also include some other uses.[17–20] The Fe3O4 is
usually coated by a protective layer of silica with (Fe3O4/
© 2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–14.
http://www.jccs.wiley-vch.de
1

2
GHOLAMI DEHBALAEI ET AL.
SiO2) structure for better improvement and the prevention of
the accumulation of ferric oxide particles.[21,22] Specifically,
catalysts of various MNPs are widely utilized in organic reac-
tions. Recently, many kinds of inorganic nanomaterials with
various combinations, physical aspects, and functionalities
have been widely synthesized. Among these nanoparticles,
highly biocompatible coordination polymer (Prussian Blue)
nanoparticles with a hollow space and open pores in the shell
are used as an anticancer drug and to deliver drugs, with
potential for diagnostic and imaging applications. Therefore,
the development of new, hollow, inorganic nanoparticles as
potential drug nanocarriers is scientifically important and
technologically useful for biomedical applications.[23]
CAT@ZIF-90 composites can be applied in several fields
and includes a size-sheltering function to catalase and pro-
tects catalase from the inhibitor proteinase K, biomolecular
delivery, size-selective enzyme catalysis, and industrial
wastewater treatment.[24] MSNs nanoparticles with other
metals, metal oxides, and polymers would create new
MSN-based hybrids that have the potential for many emerg-
ing biomedical tools and would help increase the loading of
hydrophobic drugs and control the release timing of the
loaded drugs for drug delivery application.[25] Mesoporous
titania nanoparticles (MTNs) have been successfully applied
in various fields for photoelectronic applications, photocata-
lysts to solve universal energy problems, intracellular imag-
ing, sensors, separation, and fast mass transport.[26,27] By
reducing the number of synthetic phases and using a small
amount of side product with a shorter time of production,
Multicomponent reactions (MCRs) have emerged as an
important and effective tool.[28] Five and six-member hetero-
cyclic compounds have drawn noticeabe attention from the
pharmaceutical chemistry. These compounds show remark-
able medicinal activity through bioactive compounds, and
their synthetic methods have been noticed by pharmaceutical
chemists. The Hantzsch reaction is a classic technique in the
synthesis of 1,4-dihydropyridine, including a condensation
reaction from an aldehyde and 1,3-dicarbonyl and NH3.[29]
Several techniques have been adapted for the synthesis
of dihydropyridine (DHP) using various catalysts, such as
metal triflate catalyst,[30] nano-ZnFe2O4,[31] ionic liquid,[32]
InCl3,[33] 3D printed α-Al2O3,[34] and MNPs-BPAT,[35] and
without catalysts,[36] such as I2,[37] lanthanide oxide,[38]
SiO2/HClO4,[39] and CAN.[40]
be assumed to be important in both theoretical and practical
approaches.
This study has examined the synthesis of new derivatives
of 1,4-dihydropyridine using barbituric acid, aromatic alde-
hydes, and ammonium acetate or aniline in the presence of
MNPs with an acidic factor N-propylbenzoguanamine sul-
fonic acid stabilized on silica-coated nano-Fe3O4 particles
(MNP–NPBG–SA) as a new and efficient catalyst with recy-
cling potential and reusability. The MNP-NPBG-SA catalyst
was prepared by chemical co-precipitation according to the
previous literature.[49] The new derivatives of 1,4-DHP have
been produced with high efficiency and at a minimum reac-
tion time (Scheme 1). This is the first report presented about
the synthesis of MNP-NPBG-SA, and it has been suggested
that this catalyst could be applied to reactions such as
Hantzsch reaction,[2] Michael addition,[50] and others.
2
| RESULTS AND DISCUSSION
2.1 | Characterization of novel MNP—NPBG–SA
catalyst
MNP–NPBG–SA nanoparticles were characterized by fourier
transform infrared (FT-IR) spectroscopy, X-ray diffraction
(XRD), EDAX, transmission electron microscope (TEM),
field emission scanning electron microscopy (FE-SEM), ther-
mogravimetry analysis (TGA), vibrating sample magnetome-
try (VSM), inductively coupled plasma–mass spectrometry
1,4-DHP compounds possess various biological
and medicinal properties including blocking of calcium
canal and antitumor activity, antisclerotic activities,[41]
antidiabetic,[42] anti-inflammatory, and analgesic proper-
ties[43] and for the treatment of cardiovascular diseases.[44]
Barbituric acid (hexahydropyrimidine-2,4,6-trione) is the
structural basis for several drugs, for example, antispas-
modic, soporific, anticonvulsant, anesthetic, and antitumor
drugs.[45–48] It is worth noting that the synthesis of new
derivatives of 1,4-dihydropyridine from barbituric acid may
SCHEME 1 Synthesis of 1,4-dihydropyridine derivatives using novel
MNP–NPBG–SA as a catalyst

GHOLAMI DEHBALAEI ET AL.
3
(ICP-MS), and AAS techniques.[44] Figure 1 illustrates the
FT-IR spectra for Fe3O4 nanoparticles, Fe3O4/SiO2, Fe3O4/
SiO2/N-Propyl-Cl, Fe3O4/SiO2/N-propyl/benzoguanamine and
MNP–NPBG–SA.
stretching modes. In addition, peaks appear in the range
1,495–1,660 cm−1 (C–N in heterocyclic rings) and
3,174–3,410 cm−1 (stretching N–H) indicate the bond for-
mation of benzoguanamine with Fe3O4/SiO2/N-Propyl-Cl
(Figure 1d). In the FT-IR spectra of MNP—NPBG–SA
(spectrum 1e), the presence of the attached sulfonic acid by
a broad peak at 3,692 cm−1 is confirmed. According to the
results, the functional groups on the surface of the MNPs are
grafted properly.
FE-SEM images of MNP–NPBG–SA nanoparticles are
shown to determine the size of morphology (Figure 2). The
diameter of particles is about 25 nm in a spherical shape.
Energy dispersive X-ray spectrometry (EDAX) was
investigated to determine the kinds of elements in MNP–
NPBG–SA. The EDAX result is obtained from the SEM
image, and it has been demonstrated in the SEM highlight-
ing zone. EDAX analysis obviously shows the presence
Spectrum 1a shows the FT-IR spectrum of Fe3O4 nano-
particles at a stretching vibration of around 3,402 and
579 cm−1, which combines the contributions from both sym-
metrical and asymmetrical modes of the surface hydroxyl
groups and Fe–O bonds of iron oxide, respectively
(Figure 1a). Spectrum 1b of Fe3O4/SiO2 shows a peak at
around 1,084 cm−1 which is assigned to the Si–O group and
confirms that the formation of the SiO2 shell and a weak
peak at 1,625 cm−1 (twisting vibration mode of H–O–H
absorbed in the silica shell) are obvious in the spectrum. In
spectrum 1c–e, the presence of the anchored methylene
groups is identified by the weak bands at 2,920 and
3,082 cm−1, related to C–H symmetric and asymmetric
FIGURE 1 Comparison of FT-IR spectra for (a) Fe3O4, (b) Fe3O4/SiO2, (c) Fe3O4/SiO2/N-propyl-cl, (d) Fe3O4/SiO2/N-propyl/benzoguanamine and
(e) MNP–NPBG–SA

4
GHOLAMI DEHBALAEI ET AL.
FIGURE 2 FE-SEM image of MNP–NPBG–SA nanoparticles
of C, N, Fe, O, Si, and S in the MNPs’ catalyst. Thus, the
presence of the S signal in the EDAX spectrum illustrates
that MNP–NPBG–SA nanoparticles have been modified
successfully by SO3H groups. SEM with EDAX spectra is
shown in Figure 3.
The TEM image of MNP–NPBG–SA nanocatalyst is
shown (Figure 4). This study demonstrated a particle size of
approximately 25 nm for the synthesized catalyst.
The crystal structure of MNP–NPBG–SA nanoparticles
is evaluated using the XRD technique (Figure 5). The pat-
terns indicate a crystallized structure at 2θ: 18.2, 30.2, 35.7,
43.2, 53.7, 57.2 and 62.7, which shows diffraction peaks,
corresponding to (111), (220), (311), (400), (422), (511),
and (440), respectively. According to the standard sample
Fe3O4 (JCPDS file no. 98-007-7842), the peaks of MNPs in
the XRD model is corresponded. The average crystal size of
nanoparticle MNP–NPBG–SA is assessed using Debye–
Scherrer’s formula (D = K λ/β cos θ).[51] The crystal size of
MNPs is about 25 nm in the range determined by FE-SEM
analysis. Both the XRD patterns are colored orange for the
sample of MNP–NPBG–SA that shows diffraction peaks in
various angles. Figure 5 demonstrates a pattern of count
peaks. According to the standard sample Fe3O4 (JCPDS file
no. 98-007-7842) colored by blue and coesite (JCPDS file
no. 98-004-5178) by green, the peaks of MNP-NPBG-SA
nanoparticles in XRD model is corresponded. The elimina-
tion and addition of certain peaks because of the interaction
nanoparticle is made the final factor.
Thermal gravimetric analysis (TGA) and differential
thermal analysis (DTA) are used to evaluate the stability of
FIGURE 3 SEM with EDAX spectrum of MNP–NPBG–SA nanoparticles

GHOLAMI DEHBALAEI ET AL.
5
FIGURE 4 TEM images of MNP–NPBG–SA catalyst at different magnifications
MNP–NPBG–SA (Figure 6). The TGA curve shows the
mass loss of MNP–NPBG–SA nanoparticles at T < 250 C
(10 wt%), attributed to the removal of adsorbed solvents and
After the evaluation of features of the MNP–NPBG–SA
nano catalyst, it was used as a heterogeneous catalyst to syn-
thesize the new derivatives of 1,4-dihydropyridine
(Scheme 1). One of the important capabilities of this nano
catalyst is its novelty and ease of recovery from the reaction
mixture using an external magnet, removing the necessity
for filtration or centrifugation and it can be multiple times
without significant performance loss.
ꢀ
surface hydroxyl groups. Using DTA enabled us to find one
ꢀ
sharp endothermic peak at 250 C. The next stage, including
ꢀ
the high amount of weight loss in the range of 250–600 C,
is attributed to the decomposition and evaporation of organic
groups (propyl, benzoguanamine, and SO3H) grafted to the
surface of Fe3O4/SiO2 MNPs.[52] Through the use of DTA,
ꢀ
we recorded endothermic peaks at 310, 430, and 520 C.
2.2 | Synthesis of 1,4-dihydropyridines catalyzed by
MNP–NPBG–SA
Therefore, TGA indicated that 75% of the MNP–NPBG–SA
nanoparticles consists of organic layers and 15% is Fe3O4/
SiO2. Thus, the MNP–NPBG–SA catalyst is stable at around
In order to optimize the reaction conditions, 1,4-dihydropy-
ridine derivatives (4a, 5a) were prepared as a model com-
pound in different amounts of catalyst, in the absence and
presence of various solvents and using different tempera-
tures, through which the reaction of barbituric acid (2 mmol),
aromatic benzaldehyde (1 mmol) and ammonium acetate or
aniline (1.2 mmol) was examined. The results are given in
Table 1. As shown in Table 1, the best result was obtained
using 7 mg of theꢀMNP–NPBG–SA catalyst in ethanol as a
safe solvent at 50 C (Table 1, entry 9).
The conditions optimized for the production of the
1,4-dihydropyridine derivatives were evaluated using the
MNP–NPBG–SA as a catalyst. The reaction of aromatic
aldehydes carrying either electron-donating or electron-
withdrawing substituents with barbituric acid and ammo-
nium acetate is carried out (Table 2).
ꢀ
250 C, confirming that it could be safely used in organic
reactions. Thus, TGA and DTA curves also convey that the
MNPs are successfully coated by organic groups.
To analyze VSM, MNP–NPBG–SA nanoparticles at a
field room temperature of (ꢁ9,000 Oe) are applied
(Figure 7). Magnetic saturation (Ms) for MNP–NPBG–SA
nanoparticles is about 6.15 emu/g. This result shows that
factorized MNPs have a low magnetic property due to the
coated crust compared to the non-coated MNP (73.7 emu/
g).[53] However, MNP–NPBG–SA nanoparticles can be
removed from the solution using an external magnet. Thus,
the strong magnetization of nanoparticles is verified due
external magnetic gravity (Figure 7, left inset).
Finally, in order to quantify the amount of iron in the nano-
catalyst, it was subjected to ICP-MS determination. The corre-
sponding iron loading was found to be 1.79 × 10−4 mmol/g.
In addition, to support the above observation, the sample was
also analyzed through AAS and it was found that the iron con-
tent matched well with the ICP-MS result.
In addition, the reaction of aromatic aldehydes carrying
either electron-donating or electron-withdrawing substituents
with barbituric acid and aniline is carried out (Table 3). From
these results, we see that all reactions proceeded smoothly to
afford the corresponding products to good yields.

6
GHOLAMI DEHBALAEI ET AL.
FIGURE 5 XRD diffraction pattern of MNP–NPBG–SA nanoparticles
A possible mechanism for the synthesis of 1,4-DHP
in the presence of MNP–NPBG–SA as a magnetic solid
acid catalyst is shown in Scheme 2. The reaction is car-
ried out using the acidic hydrogen sulfonic acid group in
the catalyst, and standard Knoevenagel condensation of
aromatic aldehyde and barbituric acid takes place to form
5 as an intermediate. Then 8 attacks 5 via a Michael
addition and the process continues till the target product
is obtained.
external magnetic force and was washed with ethanol and
dried at 60 C for 1 hr. Then, the recovered catalyst was
ꢀ
reused for the next run. The catalytic activity of MNP–
NPBG–SA was examined for five runs and shows that the
catalytic activity as slightly decreased because some of the
MNP–NPBG–SA nanoparticles were not recovered using
the external magnet or may be the result of chemical poison-
ing of the surface of the catalyst during the reaction
(Figure 8).
After five runs, the recovered catalyst had no distinct
change in structure, as shown by comparison of the FT-IR
spectra with that of fresh catalyst (Figure 9).
The FE-SEM image of MNP–NPBG–SA nanoparticles
after recovery after five runs is shown (Figure 10).
2.3 | Catalyst recovery and reusability
The reusability of magnetic catalysts is one of their notewor-
thy advantages which, makes catalysts useful for commercial
applications. In this study, the reusability of the MNP–
NPBG–SA magnetic catalyst was investigated in the synthe-
sis of the 1,4-dihydropyridine derivatives. After completion
of the reaction MNP–NPBG–SA catalyst could be easily
separated from the reaction mixture with the assistance of an
2.4 | Acidity of the MNP–NPBG–SA nanocatalyst
To determine the acid amount on the surface of MNPs–
NPBG–SA, a back titration method was used. The MNP–

GHOLAMI DEHBALAEI ET AL.
7
FIGURE 6 TGA/DTA analysis of MNP–NPBG–SA nanoparticles
FIGURE 7 Measured magnetic hysteresis loops of the MNPs–NPBG–SA. Left inset: The catalyst was dispersed in liquid and captured by the external
magnet
NPBG–SA nanocatalyst (0.01 g) was added to an aqueous
KCl solution (1 M, 10 mL) and the resulting mixture was
sonicated for 30 min, after that, the pH of the solution
decreased to 2, indicating an ion exchange between nanoca-
talyst protons and potassium ions, the magnetic catalyst was
then separated using an external magnet, and the clear solu-
tion was retained for analysis. Two drops of phenolphthalein
solution were then added to the remaining solution and the
resulting mixture was titrated to neutrality using a standard-
ized 0.1 M KOH solution to determine the acid amount on
the magnetic catalyst. The acid amount of the heterogeneous
acidic catalyst was found to be 0.53 mmol/g.
3
| EXPERIMENTAL
3.1 | General
All chemicals were purchased from Merck or Fluka and
were used without further purification. The melting points

8
GHOLAMI DEHBALAEI ET AL.
TABLE 1 Optimization of reaction conditions for preparation of 1,4-dihydropyrirdine derivatives
Entry
1
Catalyst (mg)
Solvent
—
Temp. (ꢀC)
Time (min)
Yield (%)a 4a
Yield (%)a 5a
MNPs–NPBG–SA (3)
MNPs–NPBG–SA (3)
MNPs–NPBG–SA (3)
MNPs–NPBG–SA (5)
MNPs–NPBG–SA (5)
MNPs–NPBG–SA (5)
MNPs–NPBG–SA (7)
MNPs–NPBG–SA (7)
MNPs–NPBG–SA (7)
MNPs–NPBG–SA (7)
MNPs–NPBG–SA (11)
MNPs–NPBG–SA (11)
–
r.t.
30
35
45
45
40
15
15
10
10
15
20
25
60
40
23
45
60
74
79
78
70
91
94
90
76
81
37
45
30
51
58
69
76
80
67
92
95
91
78
83
39
50
2
CH2Cl2
EtOH
H2O
r.t.
3
50
4
r.t.
5
EtOH
EtOH:H2O
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
50
6
Reflux
r.t.
7
8
40
9
50
10
11
12
13
14
Reflux
r.t.
50
50
MNPs–NPBG (7)
50
a
Isolated yield.
TABLE 2 Multicomponent one-pot synthesis of 1,4-dihydropyridine derivatives using MNPs–NPBG–SA as a catalysta
M.p. (ꢀC)
Found reported
301–303
298–300
298–299c
297–300
302–304c
283–285c
295–297
296–298
299–301c
300–302c
300–303
299–302
301–304
298–301
Entry
1
(R)
Product
4a
Time (min)
Yield (%)b
H
10
15
8
94
89
91
93
90
92
84
96
82
95
90
96
91
87
>300[36]
>300[36]
—
2
4-Me
4b
4c
3
4-CH(Me)2
3-NO2
4-N(Me)2
3-OH
4
4d
4e
15
6
>300 [36]
5
—
6
4f
5
—
7
4-F
4g
7
>300 [36]
>300[36]
—
8
4-Cl
4h
4i
12
15
10
15
10
10
8
9
2-Me
10
11
12
13
14
3,4-(OMe)2
3-OMe
3-CH(Me)2
4-Br
4j
—
4k
4l
>300[36]
>300[36]
>300[36]
>300[36]
4m
4n
3-F
a
b
c
Aromatic aldehyde (1 mmol), barbituric acid (2 mmol), ammonium acetate (1.2 mmol) and 7 mg Fe3O4/SiO2-N-propyl-benzoguanamine-SO3H, at 50 ꢀC.
Isolated yield.
New compound.
were uncorrected and measured using capillary tubes on an
electrothermal digital apparatus. IR spectra were recorded on
a Shimadzo (FT)-IR 300 spectrophotometer in KBr. 1H-
NMR (500 and 300 MHz), and 13C-NMR spectra were
obtained on Brucker 125 and 75 MHz spectrometers using
CDCl3 or DMSO-d6 as a solvent with TMS as an internal
standard. The progress of the reaction was monitored by
thin-layer chromatography (TLC) using n-hexane/EtOAc as
an eluent. Nanoparticles were characterized using an X-Pert
Pro MPD XRD diffractometer (Cu-Kα, k = 0.154056 nm)
over the range 2θ = 10–80 using 0.04ꢀ as the step length.
The scanning electron microscope measurement was

GHOLAMI DEHBALAEI ET AL.
9
TABLE 3 Multicomponent one-pot synthesis of 1,4-dihydropyridine
derivatives using MNPs–NPBG–SA as a catalysta
dried at room temperature to afford the title compound.
MNP–NPBG–SA particles were prepared via the procedure
illustrated in Scheme 3.
M.p. (ꢀC)
Time
(min)
Yield
(%)a
Found
reported
Entry
(R)
Product
5a
3.3 | General procedure for synthesis of 1, 4-DHP
derivatives
1
2
3
4
5
6
7
8
9
10
H
10
5
94
85
90
91
88
93
94
90
89
94
204–206c
158–160c
192–194c
210–212c
284–286c
206–208c
205–207c
198–200c
245–247c
280–282c
—
—
—
—
—
—
—
—
—
—
4-Me
5b
4-CH(Me)2
3-NO2
4-N(Me)2
3-OH
5c
7
The mixture of barbituric acid (2 mmol), aromatic benzalde-
hyde (1 mmol), and ammonium acetate or aniline (1.2 mmol)
was added to MNPs–NPBG–SA (7 mg) in 5 mL of ethanol
as the solvent and the reaction mixture was stirred magneti-
5d
5
5e
5
5f
6
4-NO2
4-Cl
5g
10
6
ꢀ
cally at 50 C. The progress of the reaction was followed by
5h
TLC. After the completion of the reaction, the mixture was
cooled to room temperature, and the catalyst was easily sep-
arated by an external magnet. The solvent was evaporated to
afford the crude solid. Finally, the resulting solid was filtered
and then washed with ethanol without further purification
2-Me
5i
15
9
3,4-(OMe)2
5j
a
Isolated yield.
b
Aromatic aldehyde (1 mmol), barbituric acid (2 mmol), aniline (1.2 mmol) and
7 mg Fe3O4/SiO2-N-propyl-benzoguanamine-SO3H, at 50 ꢀC.
ꢀ
c
and dried in an oven at 60 C. The pure 1,4-dihydropyridine
New compound.
derivatives were obtained in excellent yields.
obtained using a Hitachi S-4700 field emission-scanning
electron microscope (FE-SEM). TEM analysis of the catalyst
was recorded using Zeiss-EM10C TEM. The thermogravi-
metric analysis (TGA) and DTA curves were recorded using
Diamond TGA/DTA SII of the Perkin Elmer Company. The
magnetization was measured at room temperature using a
vibrating sample magnetometer (Model 7300 VSM System,
Lake Shore Cryotronic, Inc., Westerville, OH). ICP-MS was
also performed in order to confirm the iron-loading ICP-MS
(Model Elan 6,000 DRC). The iron content in the catalyst
supernatant was estimated through atomic absorption spec-
troscopy (AAS) on a Model novAA-400p atomic absorption
spectrometer.
4
| SELECTED SPECTRAL DATA
4.1 | 5-phenyl-5,10-dihydropyrido[2,3-d:6,5-d0]
dipyrimidine-2,4,6,8(1H,3H,7H,9H)-tetraone (4a)
White solid; m.p: 301–303 C; Yield 94%; 1H NMR
(500 MHz, DMSO-d6) δppm: 5.90 (s, 1H, CH), 7.01–7.11
(m, 5H, Ar-H), 7.12 (s, 1H, NH 1,4-dihydropyridine), and 10.15
(s, 4H, NH); 13C NMR (125 MHz, DMSO-d6) δppm: 31.3,
91.9, 125.3, 127.5, 128.3, 145.4, 151.6, and 166.8.
ꢀ
4.2 | 5-(p-tolyl)-5,10-dihydropyrido[2,3-d:6,5-d0]
dipyrimidine-2,4,6,8(1H,3H,7H,9H)-tetraone (4b)
White solid; m.p: 298–300 C; Yield 89%; 1H NMR
ꢀ
3.2 | General procedure for preparation of MNP–
NPBG–SA
(500 MHz, DMSO-d6) δppm: 2.16 (s, 3H, CH3), 5.84 (s,
1H, CH), 6.84–6.86 (d, 2H, Ar-H, J = 7.95 Hz), 6.89–6.90
Fe3O4 MNPs were prepared by chemical co-precipitation of
Fe3+ and Fe2+ ions as described in the literature.[54] The
Fe3O4 coated with SiO2 was prepared through a modified
sol–gel method.[55] Chloropropyl-modified silica-coated
MNPs were prepared according to a reported procedure.[56]
To a magnetically stirred mixture of the prepared Fe3O4/
SiO2-Chloropropyl (1 g) was added benzoguanamine
(10 mmol, 1.87 g) and triethylamine (10 mmol, 1.39 mL) in
dried toluene (50 mL) and the mixture was sonicated for
2 hr under N2 atmosphere and then stirred for 48 hr under
reflux conditions. The obtained solid was magnetically col-
lected from the solution and washed with water/ethanol
(20:10 mL) thrice and dried in vacuum for 5 hr. To a mixture
of benzoguanamine-modified silica-coated Fe3O4 MNPs
(1 g) in dried CHCl3 (3 mL), chlorosulfonic acid (ClSO3H,
(d, 2H, Ar-H, J = 8.05 Hz), 7.07 (s, 1H, NH1,4-dihydropyridine
D2O-exchangable), 10.0 (s, 4H, NH, D2O-exchangable); 13
,
C
NMR (125 MHz, DMSO-d6) δppm: 21.4, 30.9, 92.0, 127.5,
128.9, 133.9, 142.4, 151.6.
4.3 | 5-(3-nitrophenyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (4d)
White solid; m.p: 297–300 C; Yield 93%; 1H NMR
ꢀ
(500 MHz, DMSO-d6) δppm: 6.04 (s, 1H, CH), 7.03 (s, 1H,
NH 1,4-dihydropyridine), 7.41–7.46 (m, 2H, Ar-H), 7.80 (s, 1H,
Ar-H), 7.88–7.89 (d, 1H, Ar-H, J = 1.5 Hz), and 9.98 (s,
4H, NH); 13C NMR (125 MHz, DMSO-d6) δppm: 31.7,
91.1, 120.6, 121.9, 129.7, 134.6, 148.5, 148.9, 151.5,
and 165.6.
ꢀ
1 mL) was added dropwise at 0 C over 2 hr and then the
mixture was filtered and washed with ethanol (5 mL) and

10
GHOLAMI DEHBALAEI ET AL.
SCHEME 2 Proposed mechanism for synthesis of 1,4-DHP using MNPs–NPBG–SA as catalyst
4.4 | 5-(4-fluorophenyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (4g)
(d, 2H, Ar-H, J = 10.0 Hz), 6.99–7.02 (d, 2H, Ar-H,
J = 10.0 Hz), 7.09 (s, 1H, NH 1,4-dihydropyridine), and 10.05 (s,
4H, NH); 13C NMR (125 MHz, DMSO-d6) δppm: 30.8, 91.8,
114.7, 114.8, 129.09, 129.1, 141.5, 151.5, 159.8, and 161.7.
White solid; m.p: 295–297 C; Yield 84%; 1H NMR
ꢀ
(500 MHz, DMSO-d6) δppm: 5.87 (s, 1H, CH), 6.89–6.91
FIGURE 8 Recyclability of MNPs–NPBG–SA in the synthesis of
FIGURE 9 FT-IR spectra of fresh catalyst and a catalyst that has been
1,4-DHP derivatives
reused five times

GHOLAMI DEHBALAEI ET AL.
11
FIGURE 10 FE-SEM image of MNP–NPBG–SA nanoparticles after recovery after five runs
SCHEME 3 Preparation of N-propylbenzoguanamine sulfonic acid stabilized on silica-coated nano-Fe3O4 particles (MNP–NPBG–SA)
4.5 | 5-(4-chlorophenyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (4h)
4.6 | 5-(3-isopropylphenyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (4l)
White solid; m.p: 296–298 C; Yield 96%; 1H NMR
White solid; m.p: 299–302 C; Yield 96%; 1H
NMR (500 MHz, DMSO-d6) δppm: 1.15 (s, 3H, CH3),
1.17 (s, 3H, CH3), 2.50–2.81 (m, 1H, CH), 5.90 (s,
1H, CH), 6.92–7.01 (m, 4H, Ar-H), 7.11 (s, 1H,
NH1,4-dihydropyridine), and 10.0 (s, 4H, NH); 13C NMR
(125 MHz, DMSO-d6) δppm: 24.3, 24.4, 24.9, 30.9,
ꢀ
ꢀ
(500 MHz, CDCl3) δppm: 5.92 (s, 1H, CH), 7.01–7.03 (d,
2H, Ar-H, J = 8.0 Hz), 7.11 (s, 1H, NH1,4-dihydropyridine),
7.18–7.20 (d, 2H, Ar-H, J = 8.0 Hz), and 10.09 (s, 4H, NH);
13C NMR (125 MHz, CDCl3) δppm: 31.0, 91.6, 128.1,
129.4, 129.7, 144.8, and 151.5.

12
GHOLAMI DEHBALAEI ET AL.
1
33.7, 34.5, 91.9, 126.1, 127.4, 128.0, 129.0, 130.6,
142.9, 145.1, 151.6, and 164.8.
(NH); H-NMR (DMSO-d6, 500 MHz) δppm: 6.05 (s, 1H,
CH), 7.18–7.37 (m, 5H, Ar-H), 7.47–7.82 (m, 3H, Ar-H),
7.93 (s, 1H, Ar-H), and 10.21 (brs, 4H, NH); 13C-NMR
(DMSO-d6, 125 MHz) δppm: 30.9, 90.03, 119.9, 120.9,
121.05, 125.1, 128.9, 129.5, 133.8, 135.8, 147.5, 147.7,
150.5, 164.8, 167.7, and 168.6.
4.7 | 5-(4-bromophenyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (4m)
White solid; m.p: 301–304 C; Yield 91%; 1H NMR
ꢀ
4.12 | 5-(4-[dimethylamino]phenyl)-10-phenyl-
5,10-dihydropyrido[2,3-d:6,5-d0]dipyrimidine-2,4,6,8
(1H,3H,7H,9H)-tetraone (5e)
(500 MHz, DMSO-d6) δppm: 5.85 (s, 1H, CH), 6.92–6.94
(d, 2H, Ar-H, J = 8.2 Hz), 7.06 (s, 1H,, NH1,4-dihydropyridine),
7.27–7.29 (d, 2H, Ar-H, J = 8.4 Hz), and 10.09 (s, 4H, NH);
13C NMR (125 MHz, DMSO-d6) δppm: 31.3, 91.5, 118.2,
129.9, 131.1, 145.2, and 151.6.
−1
ꢀ
White solid; m.p: 284–286 C; Yield 88%; IR (KBr, cm
)
ѵmax: 1,657 and 1,721 (C=O),2,817–2,927 (CH3 str.), 3,071
and 3,192 (NH); 1H-NMR (DMSO-d6, 300 MHz) δppm:
3.09 (s, 6H, 2CH3), 6.74 (s, 1H, CH), 8.12–8.40 (m, 9H,
2Ar-H), 10.9 (s, 2H, NH), and 11.03 (s, 2H, NH); 13C-NMR
(DMSO-d6, 75 MHz) δppm: 33.03, 57.6, 73.6, 90.9, 99.3,
104.7, 109.5, 111.2, 120.0, 139.1, 141.7, 150.3, 154.1,
155.5, 162.7, and 164.7.
4.8 | 5,10-diphenyl-5,10-dihydropyrido[2,3-d:6,5-d0]
dipyrimidine-2,4,6,8(1H,3H,7H,9H)-tetraone (5a)
−1
ꢀ
White solid; m.p: 204–206 C; Yield 95%; IR (KBr, cm
)
ѵmax: 1,696 (C=O), 3,129 and 3,339 (NH); 1H-NMR
(DMSO-d6, 300 MHz) δppm: 5.92 (s, 1H, CH), 7.02–7.48
(m, 5H, Ar-H, symmetric), 10.2 (brs, 1H, NH, symmetric), and
11.12 (brs, 1H, NH, symmetric); 13C-NMR (DMSO-d6,
75 MHz) δppm: 30.8, 67.8, 84.8, 91.1, 120.4, 124.7, 126.7,
127.4, 129.5, 136.8, 150.7, and 164.8.
4.13 | 5-(3-hydroxyphenyl)-10-phenyl-
5,10-dihydropyrido[2,3-d:6,5-d0]dipyrimidine-2,4,6,8
(1H,3H,7H,9H)-tetraone (5f)
−1
ꢀ
White solid; m.p: 206–208 C; Yield 93%; IR (KBr, cm
)
1
ѵmax: 1,690 (C=O), 3,126 and 3,343 (NH), 3,407 (OH); H-
NMR (DMSO-d6, 500 MHz) δppm: 5.83 (s, 1H, CH),
6.41–7.00 (m, 5H, Ar-H), 7.27–7.62 (m, 4H, Ar-H), 10.12
(brs, 4H, NH), and 11.17 (s, 1H, OH); 13C-NMR (DMSO-
d6, 125 MHz) δppm: 30.7, 91.1, 111.5, 113.9, 117.6, 119.8,
123.5, 128.2, 129.4, 138.1, 146.0, 150.7, 151.8, 156.8,
164.1, 165.8, and 167.8.
4.9 | 10-phenyl-5-(p-tolyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (5b)
−1
ꢀ
White solid; m.p: 158–160 C; Yield 85%; IR (KBr, cm
)
ѵmax: 1,691 (C=O), 3,139 and 3,182 (NH); 1H-NMR
(DMSO-d6, 300 MHz) δppm: 2.2 (s, 3H, CH3), 5.9 (s, 1H,
CH), 6.94–7.25 (m, 9H, 2 Ar-H), 10.14 (brs, 2H, NH),
11.16 (brs, 2H, NH); 13C-NMR (DMSO-d6, 75 MHz) δppm:
20.6, 30.3, 61.6, 68.4, 119.2, 122.8, 126.7, 128.1, 128.6,
128.8, 129.4, 129.7, 133.2, 139.2, 140.9, 150.8, 169.6.
4.14 | 5-(4-nitrophenyl)-10-phenyl-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (5g)
−1
ꢀ
White solid; m.p: 205–207 C; Yield 94%; IR (KBr, cm
)
4.10 | 5-(4-isopropylphenyl)-10-phenyl-
5,10-dihydropyrido[2,3-d:6,5-d0]dipyrimidine-2,4,6,8
(1H,3H,7H,9H)-tetraone (5c)
ѵmax: 1,346 and 1,509 (NO2), 1,714 (C=O), 3,149 and 3,400
(NH); H-NMR (DMSO-d6, 300 MHz) δppm: 6.06 (s, 1H,
CH), 7.29–7.39 (m, 9H, 2Ar-H), and 10.34 (brs, 4H, NH);
13C-NMR (DMSO-d6, 75 MHz) δppm: 31.5, 56.2, 90.5,
104.9, 122.2, 122.9, 126.7, 127.9, 129.7, 133.8, 137.3,
145.0, 150.8, 153.9, 155.3, 158.7, 159.4, and 165.0.
1
−1
ꢀ
Yellow solid; m.p: 192–194 C; Yield 90%; IR (KBr, cm )
ѵmax: 1,689 (C=O), 3,140 and 3,408 (NH); 1H-NMR (DMSO-
d6, 300 MHz) δppm: 1.13 (s, 3H, CH3), 1.15 (s, 3H, CH3),
2.77–2.79 (m, 1H, CH), 5.87 (s, 1H, CH), 7.08–7.09 (m, 5H,
Ar-H), 7.28–7.32 (dd, 4H, Ar-H, J = 7.2 Hz), 10.20 (brs, 2H,
NH), and 11.20 (brs, 2H, NH); 13C-NMR (DMSO-d6,
75 MHz) δppm: 23.7, 24.1, 32.6, 73.9, 87.7, 91.0, 120.1,
123.9, 125.3, 126.6, 129.4, 137.3, 150.6, 163.7, and 165.9.
4.15 | 5-(4-chlorophenyl)-10-phenyl-
5,10-dihydropyrido[2,3-d:6,5-d0]dipyrimidine-2,4,6,8
(1H,3H,7H,9H)-tetraone (5h)
−1
ꢀ
Yellow solid; m.p: 198–200 C; Yield 90%; IR (KBr, cm
)
ѵmax: 686–838 (Cl), 1,689 (C=O), 3,146 and 3,400 (NH);
1H-NMR (DMSO-d6, 500 MHz) δppm: 5.88 (s, 1H, CH),
7.03–7.51 (m, 9H, 2Ar-H), and 10.15 (brs, 4H, NH); 13C-
NMR (DMSO-d6, 75 MHz) δppm: 30.5, 56.1, 76.0, 90.6,
106.1, 121.7, 126.1, 127.4, 128.6, 129.1, 129.7, 134.7,
143.4, 150.7, and 163.8.
4.11 | 5-(3-nitrophenyl)-10-phenyl-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (5d)
−1
ꢀ
White solid; m.p: 210–212 C; Yield 91%; IR (KBr, cm
)
ѵmax: 1,301 and 1,525 (NO2), 1,690 (C=O), 3,126 and 3,407

GHOLAMI DEHBALAEI ET AL.
13
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(b) G. Rahimzadeh, S. Bahadorikhalili, E. Kianmehr, M. Mahdavi, Mol.
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2007, 266, 69.
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4.16 | 10-phenyl-5-(o-tolyl)-5,10-dihydropyrido
[2,3-d:6,5-d0]dipyrimidine-2,4,6,8(1H,3H,7H,9H)-
tetraone (5i)
−1
ꢀ
Yellow solid; m.p: 245–247 C; Yield 89%; IR (KBr, cm )
ѵmax: 1,690 (C=O), 2,825–2,852 (CH3, str.), 3,060 and 3,123
1
(NH); H-NMR (DMSO-d6, 500 MHz) δppm: 3.48 (s, 3H,
CH3), 4.96 (brs, 1H, CH), 6.48–6.99 (m, 9H, 2Ar-H), and
11.1 (s, 4H, NH); 13C-NMR (DMSO-d6, 75 MHz) δppm:
20.6, 30.3, 61.6, 68.4, 119.2, 122.8, 126.7, 128.1, 128.6,
128.8, 129.4, 129.7, 133.2, 139.2, 140.9, 150.8, and 169.6.
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S. Toshiaki, K. Takeshi, Cancer Sci. 2003, 94, 308.
4.17 | 5-(3,4-dimethoxyphenyl)-10-phenyl-
5,10-dihydropyrido[2,3-d:6,5-d0]dipyrimidine-2,4,6,8
(1H,3H,7H,9H)-tetraone (5j)
−1
ꢀ
White solid; m.p: 280–282 C; Yield 94%; IR (KBr, cm
)
ѵmax: 1,150–1,389 (OCH3), 1,741 (C=O), 3,136 and 3,224
1
(NH); H-NMR (DMSO-d6, 300 MHz) δppm: 3.79 (s, 3H,
OCH3), 3.86 (s, 3H, OCH3), 7.08 (s, 1H, CH), 7.39–7.84
(m, 8H, 2 Ar-H), 11.16 (s, 2H, NH), and 11.3 (s, 2H, NH);
13C-NMR (DMSO-d6, 75 MHz) δppm: 30.08, 55.5, 55.9,
81.1, 111.1, 115.2, 116.8, 125.3, 131.8, 147.8, 150.2, 153.7,
155.5, 162.4, and 164.0.
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5
| CONCLUSIONS
[22] A. L. Morel, S. I. Nikitenko, K. Gionnet, A. Wattiaux, J. Lai-Kee-Him,
C. Labrugere, B. Chevalier, G. Deleris, C. Petibois, A. Brisson,
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nol. Adv. Mater. 2012, 13, 013003.
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4957.
We have developed a simple and highly efficient protocol for
the synthesis of new derivatives of 1,4-dihydropyridine
through the one-pot pseudo-four-component condensation of
barbituric acid, aromatic aldehydes, and ammonium acetate or
aniline with N-propylbenzoguanamine sulfonic acid, stabilized
on silica-coated nano-Fe3O4 particles (MNP–NPBG–SA) as a
ꢀ
new and reusable heterogeneous catalyst in ethanol at 50 C.
The process offers several advantages, including a green sol-
vent system; mild reaction conditions; use of easily available,
cheap, high yields; shorter reaction time and easy workup;
and reusability of the catalyst. The MNP–NPBG–SA nanoca-
talyst was characterized using FT-IR spectroscopy, XRD, FE-
SEM, EDAX, TEM, VSM, TGA, DTA, ICP-MS, and AAS.
[30] L.-M. Wang, J. Sheng, L. Zhang, J.-W. Han, Z. Fan, H. Tian, C.-T. Qian,
Tetrahedron 2005, 6, 1539.
[31] T. R. Ravikumar Naik, S. A. Shivashankar, Tetrahedron Lett. 2016, 57,
4046.
ACKNOWLEDGMENTS
[32] S.-J. Ji, Z.-Q. Jiang, J. Lu, T.-P. Loh, Synlett 2004, 5, 831.
[33] G. Shanthi, P. T. Perumal, Tetrahedron Lett. 2007, 48, 6785.
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A. Coelhoa, O. Caamaño, A. Gilc, E. Soteloa, Appl. Catal. A Gen. 2017,
530, 203.
We gratefully acknowledge the financial support from the
Research Council of Aja University of Medical Sciences and
Islamic Azad University-Tehran North Branch.
[35] M. A. Bodaghifard, A. Mobinikhaledi, S. Asadbegi, Appl. Organometal.
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ORCID
[36] (a) N. Azizi, A. Mobinikhaledi, A. Khajeh Amiri, H. Ghafuri, Res. Chem.
Intermed. 2012, 38, 2271. (b) H. Niaz, H. Kashtoh, J. A. J. Khan, A. Khan,
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Naser Foroughifar
http://orcid.org/0000-0003-0562-3015
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How to cite this article: Gholami Dehbalaei M,
Foroughifar N, Khajeh-Amiri A, Pasdar H. N-
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