Fe3O4@SiO2@sulfated boric acid as superparamagnetic and recyclable nanocatalyst-assisted, one-pot, pseudo four-component synthesis of 5-amino-2-aryl-3H-chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile derivatives

Article abstract of DOI:10.1002/jccs.201900044

The catalytic performance of the superparamagnetic nanocatalyst Fe₃O₄@SiO₂@Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis of chromeno[4,3,2-de][1,6]naphthyridine derivatives has been

Full text of DOI:10.1002/jccs.201900044

Received: 4 February 2019
Revised: 13 April 2019
Accepted: 21 April 2019
DOI: 10.1002/jccs.201900044
A R T I C L E
Fe3O4@SiO2@sulfated boric acid as superparamagnetic and
recyclable nanocatalyst-assisted, one-pot, pseudo four-component
synthesis of 5-amino-2-aryl-3H-chromeno[4,3,2-de][1,6]
naphthyridine-4-carbonitrile derivatives
Zeynab Khosravi | Hadi Mohammadi | Hamid Reza Shaterian
Department of Chemistry, Faculty of
Sciences, University of Sistan and
Baluchestan, Zahedan, Iran
Abstract
The catalytic performance of the superparamagnetic nanocatalyst Fe3O4@SiO2@
Correspondence
Hamid Reza Shaterian, Department of
Chemistry, Faculty of Sciences, University
Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis
of chromeno[4,3,2-de][1,6]naphthyridine derivatives has been studied. Chromeno
[4,3,2-de][1,6]naphthyridine derivatives via a pseudo four-component reaction
from aromatic aldehydes (1 mmol), malononitrile (2 mmol), and 20-hydroxyaceto-
phenone in the presence of Fe3O4@SiO2@Sulfated boric acid (0.004 g) as a
nanocatalyst in 3 mL of water as a green solvent at 80ꢀC has been synthesized. The
advantages of this method are higher product yields in shorter reaction times, easy
recyclability and reusability of the catalyst, and easy work-up procedures. The
nanocatalyst was reused at least six times. The nanocatalyst retained its stability in
the reaction, and after reusability, it was separated easily from the reaction by an
external magnet.
of Sistan and Baluchestan, P.O. Box
98135-674, Zahedan, Iran.
Email: hrshaterian@chem.usb.ac.ir
K E Y W O R D S
20-hydroxyacetophenone, chromeno[4,3,2-de][1,6]naphthyridine, Fe3O4@SiO2@Sulfated boric acid,
nanocatalyst, Pseudo four-component reaction, water
nanoparticles (MNPs), which show very particular properties
such as high surface areas and ease separation of the catalyst
1 | INTRODUCTION
by external magnet in work-up stage.[4–6]
Nanomaterials have been widely utilized as solid support mate-
rials for the design of environmentally benign heterogeneous
catalysts for various economic and environmental reactions.[1]
Nano-sized metal particles are readily used and exhibit an
intrinsically high surface area, an attribute that allows excellent
accessibility of substrates to the surface-bound active catalytic
sites.[2] Because of their high surface to volume ratio,
nanoparticles as catalyst interact easily with reactants and inter-
mediates which cause to increase the reaction rate, and conver-
sion of reactants to the desired product(s).[3] One of the
important and significant groups of nanoparticles is magnetic
Magnetic core–shell structures of silica are of great
interest to researchers from a wide range of disciplines,
including catalysis, biotechnology/biomedicine, magnetic
resonance imaging, data storage, and environmental
remediation.[7–10] In recent years, MNPs (e.g., Fe3O4) have
been extensively investigated as an inorganic catalyst sup-
port in the synthesis of organic–inorganic hybrid
catalysts[11–13] because of their good stability, easy synthe-
sis and functionalization, and high surface area, as well as
low toxicity and price.[13–16]
© 2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–8.
http://www.jccs.wiley-vch.de
1

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KHOSRAVI ET AL.
Silica-coated nanoparticles such as Fe3O4@SiO2 can be
easily connected to linker groups, which can functionalized
by a range of different organocatalysts.[17] Function-based
sulfonic acid is a significant branch of MNPs.[18] Various
solid acid catalysts with a variety of acid sites were consid-
ered in many different processes.[19,20]
Multicomponent reactions are a promising design in the
novel combinatorial chemistry due to some advantages such
as their ability to synthesize the desired products with high
atom economy through the reaction of three or more starting
materials in a one-pot procedure. In addition, this technical
skill improves the synthetic efficiency and simplicity of the
formation of complex molecules with respect to the conven-
tional organic reactions.[21–23]
Chromenes and their fused heterocyclic derivatives have
attracted a great deal of interest due to their wide applica-
tions in the field of pharmaceuticals. A literature survey
demonstrated that several catalysts were reported for the
FIGURE 1 FT-IR spectra: (a) Fe3O4@SiO2; (b) Fe3O4@SiO2-Cl;
(c) Fe3O4@SiO2-O-B(OH)2; (d) Fe3O4@SiO2-O-B(OSO3H)2
on the boric acid surface was approved by the absorption
band S–O, and the S=O stretching bands of –SO3H moiety
are asserted with 998–1,220 cm−1 bands in the FT-IR spec-
trum. In addition, in the spectrum of Fe3O4@SiO2-O-B
(OSO3H)2, the peak at 3,405 cm−1 was attributed to the
SO3–H groups.
preparation
of
chromeno[4,3,2-de][1,6]naphthyridine
derivatives.[24–27]
In continuation of our research on organocatalysts
immobilized on nonmagnetic materials and their applications
in organic reactions, especially the synthesis of chromeno
[4,3,2-de][1,6]naphthyridine derivatives,[24,27] here, we
report the preparation of 5-amino-2-aryl-3H-chromeno
[4,3,2-de][1,6]naphthyridine-4-carbonitrile derivatives via
cascade pseudo four-component condensation reaction of
malononitrile (2 mmol) and 20-hydroxyacetophenone
(1 mmol) with various aromatic aldehydes (1 mmol) in the
presence of the catalytic amount of superparamagnetic
Fe3O4@SiO2@Sulfated boric acid as a nanocatalyst under
green conditions in aqueous media (Scheme 1).
2.2 | Optimization of the reaction conditions
To evaluate the activity of the nanocatalyst Fe3O4@SiO2-O-
B(OSO3H)2, the one-pot, pseudo four-component reaction of
benzaldehyde (1 mmol), malononitrile (2 mmol), and 20-
hydroxyacetophenone (1 mmol) in water in the presence of
Fe3O4@SiO2-O-B(OSO3H)2 as a nanocatalyst was selected
as a model (Scheme 2).
First, the reaction was carried out in presence of
Fe3O4@SiO2, Fe3O4@SiO2@Boric acid, Fe3O4@SiO2@
Sulfated boric acid, and without a catalyst at 80ꢀC in aque-
ous media. The results are summarized in Table 1. It was
found that the sequence of activity of the catalysts is:
Fe3O4@SiO2 < Fe3O4@SiO2@Boric acid < Fe3O4@SiO2@
Sulfated boric acid. Comparing the catalyst activity of
Fe3O4@SiO2@Sulfated boric acid as a nanocatalyst with
other catalysts in Table 1, the reaction was completed in
60 min and with 90% yield (Table 1, Entry 4).
2 | RESULTS AND DISCUSSION
2.1 | Catalyst
The FT-IR spectrum of Fe3O4@SiO2-O-B(OSO3H)2 is pres-
ented in Figure 1. The Fe–O stretching vibration was
observed at 550–650 cm−1, and the stretching mode of Si–
To select the appropriate solvent, the activity of
Fe3O4@SiO2@Sulfated boric acid as a nanocatalyst was
investigated in water, water: ethanol mixture, and under
solvent-free conditions. According to the results, the highest
yield of the desired product and maximum performance of
the catalyst was obtained once the reaction was carried out
O-Si showed
a
strong broad peak at about
1,099–1,220 cm−1. The functionalization of SO3H groups
R
R
CN
Fe3O4@SiO2-O-B(OSO3H)2
HO
N
O
+
+
2
CN
H3C
O
Water, 80ºC
H
O
N
CN
Fe3O4@SiO2-O-B(OSO3H)2
NC
N
O
HO
H3C
2
+
+
3
1
2
NH2
CN
N
4a-n
O
H
O
NC
1
2
NH2
3
4a
SCHEME 1 Synthesis of 5-amino-2-aryl-3H-chromeno[4,3,2-de]
[1,6]naphthyridine-4-carbonitrile derivatives in the presence of
Fe3O4@SiO2@sulfated boric acid as a nanocatalyst
SCHEME 2 Synthesis of 5-amino-2-phenyl-3H-chromeno
[4,3,2-de][1,6]naphthyridine-4-carbonitrile

KHOSRAVI ET AL.
3
TABLE 1 Preparation of 5-amino-2-phenyl-3H-chromeno
[4,3,2-de][1,6]naphthyridine-4-carbonitrile in the presence of
Fe3O4@SiO2, Fe3O4@SiO2@boric acid, Fe3O4@SiO2@sulfated boric
acid, and without a catalyst at 80ꢀC in aqueous media
TABLE 3 Optimization conditions of the amount of the
nanocatalyst and the best temperature for the preparation of
5-amino-2-phenyl-3H-chromeno [4,3,2-de][1,6]
naphthyridine-4-carbonitrile in aqueous media
Amount
Time Yield
Catalyst
(g)
Temperature
(ꢀC)
Time
(min)
Yield
(%)a,b
Entry Catalyst
catalyst (g) (min) (%)a,b
Entry
1
2
3
4
Catalyst-free
Fe3O4@SiO2
—
360
110
80
13
80
85
90
1
2
3
4
5
6
7
8
0.003
0.004
0.005
0.006
0.004
0.004
0.004
0.004
80
80
80
80
25
60
70
90
85
81
90
82
78
30
65
77
87
0.004
60
Fe3O4@SiO2@boric acid 0.004
55
Fe3O4@SiO2@sulfated
boric acid
0.004
60
50
960
120
90
aReaction conditions: benzaldehyde (1 mmol), malononitrile (2 mmol), and
20-hydroxyacetophenone (1 mmol) with different catalysts in water (3 mL).
bYield refers to isolated pure products.
55
aReaction conditions: benzaldehyde (1 mmol), malononitrile (2 mmol), and
20-hydroxyacetophenone (1 mmol) in water (3 mL) as solvent.
bYield refers to isolated pure products.
TABLE 2 Preparation of 5-amino-2-phenyl-3H-chromeno
[4,3,2-de][1,6]naphthyridine-4-carbonitrile in the presence of
Fe3O4@SiO2@sulfated boric acid in different solvents
Time Temperature Yield
Fe3O4@SiO2@Sulfated boric acid (4 mg) in water, and the
best result was obtained at 80ꢀC (Table 3, Entry 2).
According to optimal considered conditions, 5-amino-
2-aryl-3H-chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile
derivatives were synthesized using this methodology, and the
results are shown in Table 4.
Entry Solvent
(min) (ꢀC)
(%)a,b
1
2
3
4
5
6
EtOH (3 mL)
110
80
80
80
80
80
80
55
H2O;EtOH(1:2) (3 mL) 90
70
H2O;EtOH(1:1) (3 mL) 80
H2O;EtOH(2:1) (3 mL) 75
77
82
The proposed mechanism for the formation of the prod-
uct is shown in Scheme 3. First, intermediate (I) was formed
through condensation between 20-hydroxyacetophenone
(1) and aryl aldehyde (2). Next, intermediate (II) was
obtained from the condensation of (I) with malononitrile (3).
The intramolecular nucleophilic attack by the OH group
(II) led to the formation of intermediate (III). In the follow-
ing condensation between (III) and another malononitrile
(3), intermediate (IV) was formed. Then, the intramolecular
cyclization of (IV) led to the formation of the final product.
The recyclability of Fe3O4@SiO2@Sulfated boric acid
was examined in the one-pot pseudo four-component syn-
thesis of 5-amino-2-phenyl-3H-chromeno[4,3,2-de][1,6]
naphthyridine-4-carbonitrile (Reaction model). After com-
pletion of the reaction, the reaction mixture was cooled to
room temperature, and the water was separated from the
crude product and the catalyst by simple filtration; ethanol
was added to the solid mixture and heated to separate
Fe3O4@SiO2@Sulfated boric acid using an external magnet.
The catalyst was washed with ethanol thrice and dried. As
was shown in Figure 2, even after six runs, the catalytic
activity and product yield had no significant loss. Thus, this
catalyst can endure reaction conditions and remain stable.
To show the merit of the present work in comparison with
reported results in the literature, we compared the results of
Fe3O4@SiO2@Sulfated boric acid with other reported cata-
lysts in the synthesis of 5-amino-2-phenyl-3H-chromeno
H2O (3 mL)
Solvent-free
60
90
120
71
aReaction conditions: benzaldehyde (1 mmol), malononitrile (2 mmol), and
20-hydroxyacetophenone (1 mmol) with Fe3O4@SiO2@Sulfated boric acid
catalyst.
bYield refers to isolated pure products.
in water as a solvent (Table 2, Entry 5). The formation of
hydrogen bonds between starting reactants and nanocatalyst
in water show a greater effect on the reaction. Moreover, the
rate of reaction was drastically decreased with further
increase of the volume ratio of ethanol to water (Table 2,
Entries 2,3,4).
To find optimum conditions of the amount of the
nanocatalyst and selecting the best temperature for the prepara-
tion of 5-amino-2-phenyl-3H-chromeno[4,3,2-de][1,6]naph-
thyridine-4-carbonitrile in aqueous media, the reaction of
benzaldehyde (1 mmol), malononitrile (2 mmol), and 20-
hydroxyacetophenone (1 mmol) in the presence
Fe3O4@SiO2@Sulfated boric acid nanoparticles as
a
nanocatalyst in water (3 mL) as a solvent was carried out in
different temperatures and also with varying concentrations of
the nanocatalyst (3–6 mg). Table 3 shows that using 4 mg of
Fe3O4@SiO2@Sulfated boric acid in the reaction mixture is
sufficient for achieving the best yield. To find the optimum
temperature, the reaction was performed at different tempera-
tures (Table 3), such as 25, 60, 70, 80, and 90ꢀC, by using

4
KHOSRAVI ET AL.
TABLE 4 Synthesis of 5-amino-2-aryl-3H-chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile derivatives by Fe3O4@SiO2@sulfated boric
acid (4 mg) as a nanocatalyst at 80ꢀC in water (3 mL) as a green solvent
Entry Aromatic aldehydes Products
Time(min) Yield (%)a,b Observed M.p. (ꢀC) Lit. M.p. (ꢀC), reference
60 90 >300
>300, [25]
1
4a
4a
2
80
86
>300
>300, [25]
4b
4b
3
65
89
>300
>300, [25]
4c
4c
4d
4
75
93
>300
>300, [25]
4d
7
80
94
294–296
295–296, [25]
4e
4e
8
65
92
280–282
278–280, [26]
4f
4f

KHOSRAVI ET AL.
5
TABLE 4 (Continued)
Entry Aromatic aldehydes Products
Time(min) Yield (%)a,b Observed M.p. (ꢀC) Lit. M.p. (ꢀC), reference
9
75
96
>300
>300, [25]
4g
4g
10
100
73
285–287
288–290, [25]
4h
4h
70
87
>300
>300, [25]
4i
4i
4j
80
90
>300
>300, [25]
4j
11
12
40
65
94
94
>300
>300
>300, [25]
4k
4k
>300, [25]
4l
4l

6
KHOSRAVI ET AL.
TABLE 4 (Continued)
Entry Aromatic aldehydes Products
Time(min) Yield (%)a,b Observed M.p. (ꢀC) Lit. M.p. (ꢀC), reference
13
55
90
>300
New compound
4m
4m
14
60
88
>300
New compound
4n
4n
aReaction conditions: aryl aldehyde (1 mmol), malononitrile (2 mmol), and 20-hydroxyacetophenone (1 mmol) in water (3 mL) as solvent.
bYields refers to isolated pure products.
FIGURE 2 Reusability of Fe3O4@SiO2@sulfated boric acid as
nanocatalyst
[4,3,2-de][1,6]naphthyridine-4-carbonitrile (Reaction model).
As shown in Table 5, Fe3O4@SiO2@Sulfated boric acid can
act as an effective catalyst with respect to reaction times and
yields of the obtained products. Thus, the present protocol
with the Fe3O4@SiO2@Sulfated boric acid catalyst is con-
vincingly superior to the reported catalytic methods.
3 | EXPERIMENTAL
3.1 | Preparation of Fe3O4@SiO2@sulfated
boric acid
SCHEME 3 Mechanism for the synthesis of 5-amino-2-aryl-3H-
chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile derivatives in the
presence of Fe3O4@SiO2@sulfated boric acid as a nanocatalyst
Fe3O4@SiO2@Sulfated boric acid as a nanocatalyst was syn-
thesized based on the following procedure (Scheme 4).[28]

KHOSRAVI ET AL.
7
TABLE 5 Comparison result of Fe3O4@SiO2@sulfated boric acid with other reported catalysts in the literature for preparation of
5-amino-2-phenyl-3H-chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile
Entry
Catalyst
Catalyst amount
5 mol%
Temperature (ꢀC)
Time (min)
Yield (%)
References
[26]
1
2
3
4
Fe3O4 NPs
Fe3O4 NPs
SiO2
70 (MW)
25
90
88
48
78
90
[26]
[25]
5 mol%
70 (conventional)
0.03 g
80
80
120
60
Fe3O4@SiO2@sulfated boric acid
0.004 g
This work
superparamagnetic silica-encapsulated Fe3O4@SiO2-O-B
(OSO3H)2 as the nanocatalyst
3.2 | General procedure for the direct
synthesis of 5-amino-2-aryl-3H-chromeno
[4,3,2-de] [1,6]naphthyridine-4-carbonitrile
derivatives using Fe3O4@SiO2@Sulfated boric
acid nanoparticles
Fe3O4@SiO2@Sulfated boric acid MNPs (4 mg) were added
to a mixture of aromatic aldehyde (1 mmol), malononitrile
(2 mmol), and 20-hydroxyacetophenone (1 mmol) in water
(3 mL). The reaction mixture was stirred at 80ꢀC in an oil
bath. The reaction was monitored by thin layer chromatogra-
phy (TLC); after completion of the reaction, the reaction mix-
ture was cooled to room temperature, and the water was
separated from the crude product and the catalyst by filtration.
Ethanol was added to the solid mixture and heated to separate
Fe3O4@SiO2@Sulfated boric acid using an external magnet.
The catalyst was washed with ethanol thrice and dried. The
warm ethanoic solution containing crude product was cooled
until the precipitated pure product was formed. The known
pure products were characterized and their physical data com-
pared with those of known compounds. The new unknown
products are characterized as follows:
SCHEME 4 Synthesis of Fe3O4@SiO2-O-B(OSO3H)2 as a
5-amino-2-meta-tolyl-3H-chromeno[4,3,2-de][1,6]naph-
thyridine-4-carbonitrile (4m). Yellow solid; mp > 300ꢀC. IR
(KBr) (νmax/cm−1): 3,482, 3,306, 2,209, 1,599, 1,510,
nanocatalyst
First, superparamagnetic Fe3O4 nanoparticles were facilely
prepared using a chemical coprecipitating method.[28] Second,
Fe3O4 was coated with tetraethyl orthosilicate, (TEOS),
becoming Fe3O4@SiO2. Then, the reaction of thionyl
chloride with Fe3O4@SiO2 formed FE3O4@SiO2–Cl; fol-
lowing this, Fe3O4@SiO2-O-B(OH)2 was formed from the
reaction of Fe3O4@SiO2–Cl with boric acid. Finally,
Fe3O4@SiO2-O-B(OH)2 nanoparticles in 40 mL chloro-
form was ultrasonicated for 30 min, Then, chlorosulfonic
acid was added dropwise, and the resulting reaction mix-
ture was stirred for 4 hr at room temperature. The resulted
brown powder was separated using an external magnet,
washed with ethanol several times to remove the
remaining acid, and dried for 12 hr at 60ꢀC to form a
1
1,356, 758, 1,558, 1,573, 756; HNMR (300 MHz, DMSO-
d6): (δ, ppm): 2.47 (s, 3H, CH3), 7.40 (s, 1H, Ar-H), 7.45 (s,
2H, NH2), 7.47–7.52 (m, 3H, Ar-H), 7.69 (t, J = 7.2 Hz,
1H, Ar-H), 8.20–8.31 (m, 2H, Ar-H), 8.58 (d, J = 7.2 Hz,
1H, Ar-H).13CNMR (75.6 MHz, DMSO-d6): δ = 21.6, 76.1,
102.9, 105.2, 116.9, 117.7, 118.4, 125.4, 125.6, 128.6,
129.1, 131.8, 133.5, 138.2, 138.4, 138.9, 152.2, 155.9,
159.6, 162.2, 162.7 ppm.
5-amino-2-(3-hydroxyphenyl)-3H-chromeno[4,3,2-de]
[1,6]naphthyridine-4-carbonitrile
(4n).Yellow
solid;
mp > 300ꢀC. IR (KBr) (νmax/cm−1): 3,373, 3,472, 2,221,
1
1,558, 1,573, 1,356, 756; HNMR (300 MHz, DMSO-d6):
(δ, ppm): 6.98 (d, J = 6.9 Hz, 1H, Ar-H), 7.37 (s, 2H, NH2),
7.40–7.49 (m, 3H, Ar-H), 7.66 (t, J = 7.5 Hz, 1H, Ar-H),

8
KHOSRAVI ET AL.
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7.81 (d, J = 9.0 Hz, 2H, Ar-H), 8.20 (s, 1H, Ar-H), 8.51 (d,
J = 7.5 Hz, 1H, Ar-H), 9.76 (s, 1H, OH).; 13CNMR
(75.6 MHz, DMSO-d6): δ = 76.1, 102.9, 105.3, 115.0,
117.0, 117.6, 118.2, 118.3, 119.2, 125.6, 130.1, 133.4,
138.8, 139.8, 152.1, 155.8, 158.2, 159.5, 162.2, 162.8 ppm.
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4 | CONCLUSIONS
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Reactions II, Springer, Berlin Heidelberg 2010.
Fe3O4@SiO2@Sulfated boric acid as a heterogeneous
nanomagnetic catalyst has been successfully used for the
pseudo four-component preparation of 5-amino-2-aryl-3H-
chromeno [4,3,2-de][1,6]naphthyridine-4-carbonitrile deriva-
tives under green conditions in aqueous media. Easy
reaction conditions, simple work-up or purification, excel-
lent yields, high purity of the desired product, and short
reaction times are some advantages of this protocol. The
superparamagnetic nanocatalyst is separable and stable in
the reaction conditions without detectable activity loss
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We gratefully acknowledge the University of Sistan and Bal-
uchestan Research Councils for supporting this research.
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