Novel nano-architectured carbon quantum dots (CQDs) with phosphorous acid tags as an efficient catalyst for the synthesis of multisubstituted 4H-pyran with indole moieties under mild conditions

Article abstract of DOI:10.1039/d1ra02515e

In this work, a new nano-structured catalyst with phosphorus acid moieties, synthesized by the reaction of carbon quantum dots (CQDs) and phosphorus acid under refluxing EtOH. The structure and morphology of CQDs-N(CH₂PO₃H₂)₂were fully characterized using various techniques such as Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG) analysis, fluorescence and X-ray diffraction (XRD) measurements. The new CQDs-N(CH₂PO₃H₂)₂catalyst was successfully used for the synthesis of 2-amino-6-(2-methyl-1H-indol-3-yl)-4-phenyl-4H-pyran-3,5-dicarbonitriles by the one-pot reaction of various aromatic aldehydes, 3-(1H-indol-3-yl)-3-oxopropanenitrile derivatives and malononitrile in refluxing EtOH and/or ultrasonic irradiation conditions.

Full text of DOI:10.1039/d1ra02515e

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Novel nano-architectured carbon quantum dots
(CQDs) with phosphorous acid tags as an efficient
catalyst for the synthesis of multisubstituted 4H-
pyran with indole moieties under mild conditions†
Cite this: RSC Adv., 2021, 11, 25995
a
a
Milad Mohammadi Rasooll,a Mahmoud Zarei,
Mohammad Ali Zolfigol,
*
*
Hassan Sepehrmansourie,a Afsaneh Omidi,b Masoumeh Hasani
b
*
c
and Yanlong Gu
In this work, a new nano-structured catalyst with phosphorus acid moieties, synthesized by the
reaction of carbon quantum dots (CQDs) and phosphorus acid under refluxing EtOH. The structure
and morphology of CQDs–N(CH2PO3H2)2 were fully characterized using various techniques such as
Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), scanning
electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG)
analysis, fluorescence and X-ray diffraction (XRD) measurements. The new CQDs–N(CH2PO3H2)2
catalyst was successfully used for the synthesis of 2-amino-6-(2-methyl-1H-indol-3-yl)-4-phenyl-
4H-pyran-3,5-dicarbonitriles by the one-pot reaction of various aromatic aldehydes, 3-(1H-indol-
3-yl)-3-oxopropanenitrile derivatives and malononitrile in refluxing EtOH and/or ultrasonic
irradiation conditions.
Received 30th March 2021
Accepted 28th June 2021
DOI: 10.1039/d1ra02515e
rsc.li/rsc-advances
solid acid catalysts with phosphorous acid functional
groups, such as glycoluril,16 SBA-15,17 a melamine-based
nano catalyst,18 metal–organic frameworks (MOFs)19–21 and
1. Introduction
Carbon quantum dots (CQDs) have recently attracted
comprehensive research interest due to their various phys-
icochemical properties and favorable features such as
biocompatibility, distinctive optical properties and low
cost.1–6 In 2004, Xu et al. developed carbon quantum dots
(CQDs) during the purication of single-walled carbon
nanotubes via a preparative electrophoresis methodology.7
Carbon quantum dots (CQDs) have been used in many
interesting elds of research such as bioimaging, biosens-
ing, catalysis, heavy metal element sensing and
biomolecule/drug delivery.8–13 Also, these nanomaterials
show intense photoluminescence (PL), arising from
quantum-connement effects.14 Materials with phospho-
rous acid tags have been introduced as catalysts, adsor-
bents, inhibitors and extractants.15 Recently a wide variety of
uric acid,22 have been reported for the synthesis of organic
compounds.
Organic compounds with indole scaffolds have diverse bio-
logical and pharmacological applications such as antifungal,
optimal inhibitory, anticholinergic, antihypertensive, antibac-
terial, antiviral, cardiovascular, anticonvulsant and anti-
proliferative activities.23–30 Also, several natural products and
pharmaceutically important compounds which act as anti-
tumor, anticancer, anti-inammatory, hypoglycemic, antipy-
retic or analgesic reagents have indole scaffolds in their
structures.31 Additionally, 4H-pyran derivative structures are an
important category of heterocyclic compounds due to their
biological properties, such as their anticoagulant, anticancer,
antioxidant, spasmolytic, diuretic and anti-anaphylactic activi-
ties (Fig. 1).32–36 2-Amino-4H-pyran derivatives have also been
applied as photoactive materials, cosmetics and pigments.37
Ultrasonic irradiation has been widely applied for the prepara-
tion of organic compounds with biological activity. On the other
hand, ultrasonic irradiation as an efficient strategy for the
preparation of materials in chemical synthesis has received
great attention in chemical processes.38,39 One of the major
advantages of ultrasonic irradiation is the controllability of the
time and energy power.
aDepartment of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University,
Hamedan 6517838683, Iran. E-mail: mahmoud8103@yahoo.com; zol@basu.ac.ir;
mzolgol@yahoo.com; Fax: +988 138380709; Tel: +988 138282807
bDepartment of Analytical Chemistry, Faculty of Chemistry, Bu-Ali Sina University,
Hamedan, Iran. E-mail: hasani@basu.ac.ir
cSchool of Chemistry and Chemical Engineering, Huazhong University of Science and
Technology, 1037 Luoyu Road, Hongshan District, Wuhan, 430074, China. E-mail:
klgyl@hust.edu.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d1ra02515e
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Fig. 1 Structure of pyran compounds with biological properties.
lined stainless-steel autoclave at 200 ꢀC for 6 h. Aer the
reaction was completed, a dark precipitate appeared, which
was ltered by centrifugation (1000 rpm, 20 min). The
carbon quantum dots (CQDs) were dried under vacuum.
Then, in a 25 mL round-bottomed ask connected to a reux
condenser, carbon quantum dots (CQDs) (0.5 g), para-
formaldehyde (4 mmol, 0.12 g), phosphorous acid (2 mmol,
0.164 g), p-TSA (0.01 g) and ethanol (10 mL) were added and
reuxed for 8 hours. A white solid appeared, which was
ltered by centrifugation (1000 rpm, 10 min). The
obtained CQDs–N(CH2PO3H2)2 was dried under vacuum
(Scheme 2).
Scheme
1 Synthesis of 4H-pyran-3,5-dicarbonitrile with indole
moieties using CQDs-N(CH2PO3H2)2.
On the basis of the above-mentioned facts, the synthesis of
4H-pyran-3,5-dicarbonitrile and pyridines with indole moieties
in the presence of reusable solid acid catalysts is our main
research interest. With this aim, CQDs-N(CH2PO3H2)2, as
a novel carbon quantum dot (CQD) nano-catalyst structure with
phosphorus acid tags, was synthesized, characterized and used
in the synthesis of 4H-pyran-3,5-dicarbonitrile with indole
moieties, both in reuxing EtOH and ultrasonic irradiation in
EtOH as a solvent (Scheme 1).
2.2. General procedure for the synthesis of 2-amino-6-(2-
methyl-1H-indol-3-yl)-4-phenyl-4H-pyran-3,5-dicarbonitrile
using CQDs–N(CH2PO3H2)2 as a catalyst
In a 20 mL round-bottomed ask, a mixture of aldehyde (1
mmol), 3-(1H-indol-3-yl)-3-oxopropanenitrile derivatives (1
mmol), malononitrile (1.1 mmol, 0.073 g), CQDs–
N(CH2PO3H2)2(10 mg) as a catalyst and EtOH (10 mL) was stirred
under reux conditions (method A) or under ultrasonic irradia-
tion (method B). Aer the completion of the reaction (monitored
by TLC n-hexane/ethyl acetate; 7 : 3), PEG (10 mL) was added to
2. Experimental
2.1. General procedure for the preparation of CQDs–
N(CH2PO3H2)2
Initially, carbon quantum dots (CQDs) were synthesized by the mixture and the catalyst was separated by centrifugation
adding citric acid (1.05 g, 5.5 mmol), ethane-1,2-diamine (1000 rpm, 10 min). Finally, the mixture was poured into H2O and
(5 mmol, 0.33 mL) and 10 mL H2O under ultrasonic irrita- the precipitate was ltered off. The obtained residue was washed
tion for 30 min.40 Then, this mixture was kept in a Teon- with warm ethanol and dried at 100 ꢀC (Scheme 1).
Scheme 2 Preparation of CQDs–N(CH2PO3H2)2 as the desired catalyst.
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3. Result and discussion
3.1. Synthesis and characterization of the catalyst with
phosphorous acid tags
Since molecules with indole moieties have been considered
as candidates with biological interest41 and we have con-
ducted a literature survey for publishing a comprehensive
review on the subject of bis and tris indolyl methanes,42 we
decided to report a catalytic methodology for the synthesis
of multisubstituted 4H-pyran with indole moieties (Schemes
1 and 2). Here, 2-amino-6-(2-methyl-1H-indol-3-yl)-4-phenyl-
4H-pyran-3,5-dicarbonitriles were successfully synthesized
in the presence of CQDs–N(CH2PO3H2)2, various aromatic
aldehydes, 3-(1H-indol-3-yl)-3-oxopropanenitrile derivatives
and malononitrile both in reuxing EtOH and/or ultrasonic
irradiation conditions.
At rst, the desired catalyst CQDs–N(CH2PO3H2)2 was
prepared according to Scheme 2. This novel nano-structure
catalyst was fully characterized by applying FT-IR spectros-
copy, XRD spectroscopy, FE-SEM, energy dispersive X-ray spec-
troscopy (EDS), transmission electron microscopy (TEM), TG
and uorescence analysis.
The FT-IR spectra of carbon quantum dots (CQDs) and
CQDs–N(CH2PO3H2)2 are compared in Fig. 2. The broad peak
at 2600–3500 cmꢁ1 is related to the OH of the PO3H2 func-
tional groups. The absorption bands at 1015 and 1050 cmꢁ1
are related to P–O bond stretching and the band at 1128 cmꢁ1
is related to P]O. The differences between the FT-IR spectra
of the carbon quantum dots (CQDs) and CQDs-
N(CH2PO3H2)2 veried the structure of the catalyst.
Fig. 3 Fluorescence spectra of the initial CQDs and functionalized
CQDs.
Following this, the uorescence features of the initial
CQDs and functionalized CQDs were investigated for the
evaluation of the synthesized CQDs and the effect of post-
functionalization on the surface of the nal catalyst. As
can be seen in Fig. 3, the initial synthesized CQDs display
a high-intensity emission peak at 450 nm (peak a). But the
uorescence intensity of the functionalized CQDs with
PO3H2 groups is decreased and shied towards longer
wavelengths (the red shi effect). Many factors are effective
for amplifying or attenuating the uorescence intensity by
affecting the resonance system, including structural
rigidity, steric effect interactions, temperature, solvent, pH,
the presence of para-magnetite species, heavy atoms and
electron donor/acceptor groups. It can be proposed that the
presence of larger PO3H2 groups instead of the smaller
proton groups (Scheme 1) can have a negative effect on the
uorescence intensity due to the steric effects. In the other
words, the presence of the large PO3H2 groups, along with
the possible rotation of these groups, reduces the symmetry
of the molecule. So, increasing the mobility of the molecule
will reduce the uorescence intensity of the functionalized
CQDs due to the decreased rigidity and disturbance of the
conjugated system. The decreasing uorescence intensity of
Fig. 2 Comparison of the FT-IR spectra of the CQDs and CQDs– Fig. 4 X-ray diffraction (XRD) pattern of CQDs functionalized with
N(CH2PO3H2)2.
PO3H2 groups.
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the functionalized CQDs compared to that of the initial show different morphologies of these materials. As shown in
CQDs can be a reason for the stabilization of PO3H2 func- the transmission electron microscopy images (Fig. 7), nano-
tional groups on the initial CQD surface. Fig. 3 shows particles of CQDs-N(CH2PO3H2)2 are approximately 5–15 nm
photographic images of the decreased uorescence inten- with a narrow size, which are regularly arranged and not
sity of the initial CQDs aer post-modication with the completely stacked.
PO3H2 groups.
The thermal gravimetric (TG) analysis results for CQDs–
The XRD pattern for CQDs–N(CH2PO3H2)2 is shown in the N(CH2PO3H2)2 are shown in Fig. 8. Two declining stages were
region of 2q ¼ 5–80ꢀ (Fig. 4). The broad peak of CQDs- observed for CQDs–N(CH2PO3H2)2 in Fig. 8. The rst weight loss
N(CH2PO3H2)2 corresponds to the diffraction lines in previously (which includes about 5% weight loss) was related to the
reported literature.43 Therefore, the structure and morphology evaporation of the solvents (organic and water). The second
of the carbon quantum dots (CQDs) is stable aer functionali- weight loss is at 400 ꢀC (includes about 40% weight loss), which
zation with phosphorous acid groups.
is linked to the breaking of the bonds of N–C–PO3H2 of the
The elements that CQDs–N(CH2PO3H2)2 was composed of structure of CQDs–N(CH2PO3H2)2.
were also studied with energy dispersive X-ray (EDX) analysis
(Fig. 5). The structure of the catalyst was veried by the exis-
tence of N, C, O and P atoms.
3.2. Catalytic properties of the catalyst with phosphorous
acid tags
The morphology and particle size of CQDs–N(CH2PO3H2)2
were also studied from the scanning electron microscopy (SEM)
(Fig. 6a and b) and transmission electron microscopy (TEM)
images (Fig. 7). The scanning electron microscopy (SEM) of
CQDs–NH2 (Fig. 6a) and CQDs–N(CH2PO3H2)2 (Fig. 6b) did not
Aer the synthesis and characterization of CQDs–
N(CH2PO3H2)2, it was applied for the synthesis of 2-amino-6-
(2-methyl-1H-indol-3-yl)-4-phenyl-4H-pyran-3,5-
dicarbonitrile derivatives with indole and pyran moieties.
The above-mentioned products were obtained by the
Fig. 5 Energy dispersive X-ray (EDX) analysis of CQDs–N(CH2PO3H2)2.
Fig. 6 Scanning electron microscopy (SEM) images of CQDs–NH2 (a) and CQDs–N(CH2PO3H2)2 (b).
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Fig. 7 Transmission electron microcopy (TEM) images of CQDs–N(CH2PO3H2)2.
of the reaction conditions. The optimization data is listed in
Table 1. As shown in Table 1, the best synthesis of 2-amino-4-
(4-chlorophenyl)-6-(1H-indol-3-yl)-4H-pyran-3,5-dicarbonitrile was
achieved in the presence of 10 mg CQDs–N(CH2PO3H2)2 in EtOH
(5 mL) as the solvent (entry 1, Table 1). The model reaction was
also studied using several solvents such as H2O, CH3CN, n-
hexane, CHCl3, toluene, MeOH, DMF, EtOH, CH2Cl2 and EtOAc
(5 mL), as well as a solvent-free condition, in the presence of
10 mg of CQDs–N(CH2PO3H2)2. The results of the reaction show
that the yield and time were not improved when using other
amounts of catalyst (Table 1, entries 16–18).
Aer optimizing the reaction conditions, CQDs–
N(CH2PO3H2)2(10 mg) was applied to synthesise a good range of
desired compounds using various aromatic aldehydes bearing
electron-donating groups, electron-withdrawing groups and
heterocycles, as well as malononitrile and 3-(1H-indol-3-yl)-3-
oxopropanenitrile derivatives, both in reuxing EtOH or ultra-
sonic irradiation conditions (methods A and B, respectively). As
shown in Table 2 the obtained results indicated that CQDs–
N(CH2PO3H2)2 is appropriate for the preparation of target
molecules in high to excellent yields with short reaction times
(methods A and B).
In the proposed mechanism, the aldehyde is activated with
a proton of the acidic functional groups of CQDs–N(CH2PO3H2)2
and intermediate (I) is prepared by the reaction of malononitrile
with the loss of one molecule of H2O. In the second step, 3-(1H-
indol-3-yl)-3-oxopropanenitrile reacts with intermediate (I) to give
intermediate (II) aer tautomerization. Then, intermediate (II)
gives the desired product aer intramolecular cyclization and the
loss of another molecule of H2O (Scheme 3).
To compare the efficiency of the described CQDs–
N(CH2PO3H2)2 for the synthesis of 2-amino-6-(2-methyl-1H-
indol-3-yl)-4-phenyl-4H-pyran-3,5-dicarbonitrile that was
achieved in the presence of 10 mg of the catalyst by the
reaction of 4-chloro-benzaldehyde (1 mmol, 0.14 g), 3-(1H-
indol-3-yl)-3-oxopropanenitrile (1 mmol, 0.184 g) and malo-
nonitrile (1.1 mmol, 0.073 g) under the above-mentioned
optimized reaction conditions, various organic and inor-
ganic solid acid catalysts for the above reaction were tested
(Table 3). As Table 3 indicates, CQDs–N(CH2PO3H2)2 is the
best choice for the synthesis of 2-amino-6-(2-methyl-1H-
Fig. 8 Thermal gravimetric (TG) analysis of CQDs–N(CH2PO3H2)2.
reaction of 4-chloro-benzaldehyde (1 mmol, 0.14 g), 3-(1H-
indol-3-yl)-3-oxopropanenitrile (1 mmol, 0.184 g) and malo-
nonitrile (1.1 mmol, 0.073 g) as a model for the optimization
Table 1 Effects of different amounts of catalyst, temperature and
solvent (5 mL) on the synthesis of 2-amino-4-(4-chlorophenyl)-6-
(1H-indol-3-yl)-4H-pyran-3,5-dicarbonitrile
Entry Solvent
Catalyst (mg) Temp. (ꢀC) Time (min) Yield (%)
1
2
3
4
5
6
7
8
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
DMF
10
10
10
5
20
—
10
10
10
Reux
50
25
25
45
80
35
30
120
90
120
120
120
100
120
50
89
55
30
70
75
25
60
—
Trace
—
50
—
60
35
—
60
35
45
Reux
Reux
Reux
100
Reux
Reux
Reux
Reux
Reux
Reux
Reux
Reux
100
H2O
CH3CN
9
10
11
12
13
14
15
16
17
18
n-hexane 10
CHCl3 10
Toluene 10
MeOH
CH2Cl2
EtOAc
—
10
10
10
10
10
10
50
120
30
120
50
—
—
25
50
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Table 2 Synthesis of 2-amino-4-(4-chlorophenyl)-6-(1H-indol-3-yl)-4H-pyran-3,5-dicarbonitrile derivatives using CQDs–N(CH2PO3H2)2
under refluxing EtOH (method A) and ultrasonic irradiation (method B)
Method A
Method B
Entry
R1
X
Product
Time (min)
Yield (%)
Time (min)
Yield (%)
MP (ꢀC)
L1
Me
4-OMe
25
87
6
93
263–265
L2
Me
4-Cl
25
89
10
94
268–270
L3
Me
2-Cl
20
88
10
92
236–238
L4
Me
4-NO2
10
90
Immediate
95
284–286 (ref. 46)
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Table 2 (Contd.)
Method A
Method B
Entry
R1
X
Product
Time (min)
Yield (%)
Time (min)
Yield (%)
MP (ꢀC)
L5
Me
3-NO2
10
90
Immediate
95
252–254 (ref. 46)
L6
Me
4-Br
20
88
7
92
267–269 (ref. 46)
L7
Me
3,4-OMe
20
85
8
91
205–207
L8
Me
4-Py
10
85
Immediate
93
226–228
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Table 2 (Contd.)
Method A
Method B
Entry
R1
X
Product
Time (min)
Yield (%)
Time (min)
Yield (%)
MP (ꢀC)
L9
Me
4-CN
30
87
8
92
257–259
L10
Me
3-Py
10
87
Immediate
95
220–222
I1
H
4-Cl
23
85
8
92
254–256 (ref. 46)
I2
H
4-Br
20
86
7
93
210–212 (ref. 44)
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Table 2 (Contd.)
Method A
Method B
Entry
R1
X
Product
Time (min)
Yield (%)
Time (min)
Yield (%)
MP (ꢀC)
I3
H
3-NO2
10
88
Immediate
95
248–250 (ref. 45)
I4
H
4-NO2
10
88
Immediate
94
239–241 (ref. 44)
I5
H
2-Naph
27
80
13
87
205–207 (ref. 45)
I6
H
4-Py
10
87
Immediate
94
220–222
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Table 2 (Contd.)
Method A
Method B
Entry
R1
X
Product
Time (min)
Yield (%)
Time (min)
Yield (%)
MP (ꢀC)
I7
H
4-OMe
20
80
7
94
246–248 (ref. 45)
I8
H
4-CN
15
82
6
93
260–262
I9
H
2,6-Cl
30
65
15
75
238–240
I10
H
3-Py
10
85
Immediate
95
238–240
I11
H
3,4-OMe
20
85
7
90
228–230 (ref. 45)
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Scheme 3 Proposed mechanism for the synthesis of 2-amino-4-(4-chlorophenyl)-6-(1H-indol-3-yl)-4H-pyran-3,5-dicarbonitrile.
Table
3 Synthesis of 2-amino-4-(4-chlorophenyl)-6-(1H-indol-3-
yl)-4H-pyran-3,5-dicarbonitrile the presence of various catalysts using
method A
Entry Catalyst
(mol %) Time (min) Yield (%)
1
2
3
4
5
6
7
FeCl3
H2SO4
Fe3O4
NH4NO3
10
10
80
120
25
20
Trace
25
35
Fig. 9 Recyclability of CQDs–N(CH2PO3H2)2 for the synthesis of 4H-
pyran-3,5-dicarbonitrile derivatives.
10 mg 120
10
10
10
10
90
70
120
80
CF3SO3H
GTBSA47
15
60
MIL-100(Cr)/NHEtN
(CH2PO3H2)2 (ref. 21)
H3[p(W3O10)4]$XH2O
SBA-15/(CH2)3N(CH2PO3H2)
(CH2)2–N(CH2PO3H2)2 (ref. 17b)
[PVI-SO3H]FeCl4 (ref. 48)
p-TSA
8
9
10
10
120
90
Trace
62
10
11
12
13
14
15
16
17
18
10
10
100
120
48
48
50
—
50
—
35
60
65
SSA49
Et3N
10 mg 110
10
10
—
10
120
90
—
MHMHPA18
Nano-SB-[PSIM]Cl50
[Py-SO3H]Cl51
APVPB52
120
10 mg 80
10 mg 70
Fe3O4@Co(BDC)-NH2
(ref. 53)
19
20
21
H3PO3
CQDs
10
60
63
70
89
10 mg 45
CQDs-N(CH2PO3H2)2 (this work) 10 mg 25
Fig. 10 The characterization of the reused catalysts after seven runs
using FT-IR spectroscopy.
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Fig. 11 The characterization of the reused catalysts after seven runs using energy dispersive X-ray analysis (EDX).
indol-3-yl)-4-phenyl-4H-pyran-3,5-dicarbonitrile derivatives;
due to the shorter reaction times, higher yields and amount
References
of applied catalyst. Also, the reusability of CQDs–
N(CH2PO3H2)2 as a catalyst for the preparation of 2-amino-6-
(2-methyl-1H-indol-3-yl)-4-phenyl-4H-pyran-3,5-
1 M. J. Molaei, Anal. Methods, 2020, 12, 1266.
2 M. J. Molaei, Sol. Energy, 2020, 196, 549.
3 X. Kou, S. Jiang, S. J. Park and L. Y. Meng, Dalton Trans.,
2020, 49, 6915–6928.
4 J. M. Katzen, C. Tserkezis, Q. Cai, L. H. Li, J. M. Kim, G. Lee,
G. Yi, W. R. Hendren, E. J. G. Santos, R. M. Bowman and
F. Huang, ACS Appl. Mater. Interfaces, 2020, 12, 19866.
5 G. Kalaiyarasan, J. Joseph and P. Kumar, ACS Omega, 2020, 5,
22278.
dicarbonitrile derivatives was examined in the above reac-
tion. The results show that the catalyst has the potential to be
recycled and reused up to 7 times without a signicant
decrease in its catalytic activity (Fig. 9).CQDs–N(CH2PO3H2)2
was also characterized by FT-IR and energy dispersive X-ray
analysis (EDX) analysis aer its application in the reaction.
These spectra were same as those of the fresh catalyst (Fig. 10
and 11).
6 F. Li, T. Li, C. Sun, J. Xia, Y. Jiao and H. Xu, Angew. Chem., Int.
Ed., 2017, 56, 9910.
7 X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker and
W. A. Scrivens, J. Am. Chem. Soc., 2004, 126, 12736.
8 H. Li, X. He, Z. Kang, H. Huang, Y. Liu, J. Liu, S. Lian,
C. H. A. Tsang, X. Yang and S. T. Lee, Angew. Chem., 2010,
122, 4532.
4. Conclusion
In conclusion, we have designed and introduced CQDs–
N(CH2PO3H2)2 as a novel heterogeneous nano-catalyst. It was
identied using various techniques. CQDs–N(CH2PO3H2)2, as an
9 W. Su, R. Guo, F. Yuan, Y. Li, X. Li, Y. Zhang, S. Zhou and
L. Fan, J. Phys. Chem. Lett., 2020, 11, 1357.
efficient catalyst, was applied for the synthesis of multi substituted 10 B. C. Martindale, G. A. Hutton, C. A. Caputo and E. Reisner, J.
4H-pyran-3,5-dicarbonitrile with indole moieties as candidates
with biological interest. The presented methodology is not suitable
for synthesis of pyridines with indole moieties. A short reaction
time, clean and mild reaction conditions and the recycling of the
catalyst are the major advantages of the presented work.
Am. Chem. Soc., 2015, 137, 6018.
11 B. B. Karakoçak, A. Laradji, T. Primeau, M. Y. Berezin, S. Li
and N. Revi, ACS Appl. Mater. Interfaces, 2021, 13, 277.
12 K. M. Chan, W. Xu, H. Kwon, A. M. Kietrys and E. T. Kool, J.
Am. Chem. Soc., 2017, 139, 13147.
13 X. Xiao, Z. Shao and L. Yu, Chin. Chem. Lett., 2021, 23, 4647.
14 X. Wang, Y. Feng, P. Dong and J. Huang, Front. Chem., 2019,
7, 671.
15 (a) C. Fujun, Y. Ping, L. Xiguang, L. Chunping and
Q. Rongjun, Renewable Energy, 2014, 71, 61; (b) M. F. Mady
and M. A. Kelland, Energy Fuels, 2017, 31, 4603; (c)
A. Kadous, M. Didi and D. Villemin, J. Radioanal. Nucl.
Chem., 2010, 284, 431.
16 S. Moradi, M. A. Zolgol, M. Zarei, D. A. Alonso and
A. Khoshnood, ChemistrySelect, 2018, 3, 3042.
17 (a) M. Zarei, M. A. Zolgol, A. R. Moosavi-Zare,
E. Noroozizadeh and S. Rostamnia, ChemistrySelect, 2018,
Conflicts of interest
There are no conicts to declare.
Acknowledgements
We thank the Bu-Ali Sina University and Iran National Science
Foundation (INSF) (grant number: 98020070) for nancial
support.
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RSC Advances
3, 12144; (b) F. Jalili, M. Zarei, M. A. Zolgol, S. Rostamnia 32 D. Kumar, P. Sharma, H. Singh, K. Nepali, G. K. Gupta,
and A. R. Moosavi-Zare, Microporous Mesoporous Mater.,
2020, 294, 109865.
18 J. Afsar, M. A. Zolgol, A. Khazaei, M. Zarei, Y. Gu,
S. K. Jain and F. Ntie-Kang, RSC Adv., 2017, 7, 36977.
33 Saigal, M. Irfan, P. Khan, M. Abid and M. M. Khan, ACS
Omega, 2019, 4, 16794.
D. A. Alonso and A. Khoshnood, Mol. Catal., 2020, 482, 34 P. K. Singh and O. Silakari, ChemMedChem, 2018, 13, 1071.
110666.
35 S. Gupta, S. Adhikary, R. K. Modukuri, D. Choudhary,
R. Trivedi and K. V. Sashidhara, Bioorg. Med. Chem. Lett.,
2018, 28, 1719.
19 S. Babaee, M. Zarei, H. Sepehrmansourie, M. A. Zolgol and
S. Rostamnia, ACS Omega, 2020, 5, 6240.
20 S. Babaee, M. Zarei, M. A. Zolgol, S. Khazalpour, M. Hasani, 36 S. P. Khare, T. R. Deshmukh, S. V. Akolkar, J. N. Sangshetti,
U. Rinner, R. Schirhagl, N. Norouzi and S. Rostamnia, RSC
Adv., 2021, 11, 2141.
V. M. Khedkar and B. B. Shingate, Res. Chem. Intermed.,
2019, 45, 5159.
21 H. Sepehrmansouri, M. Zarei, M. A. Zolgol, A. R. Moosavi- 37 Z. Tashri, M. Mohammadi-Khanaposhtani, H. Hamedifar,
Zare, S. Rostamnia and S. Moradi, Mol. Catal., 2020, 481,
110303.
22 S. Kalhor, M. Zarei, H. Sepehrmansourie, M. A. Zolgol,
H. Shi, J. Wang, J. Arjomandi, M. Hasanie and
R. Schirhagl, Mol. Catal., 2021, 507, 111549.
B. Larijani, S. Ansari and M. Mahdavi, Mol. Diversity, 2020, 1.
38 (a) P. N. Amaniampong and F. Jerome, Curr. Opin. Green
Sustain. Chem., 2020, 22, 7; (b) J. Amaro-Gahete, R. Klee,
´
´
D. Esquivel, J. R. Ruiz, C. Jimenez-Sanchidrian and
F. J. Romero-Salguero, Ultrason. Sonochem., 2019, 50, 59.
23 (a) A. Varvaresou, A. Tsantili-Kakoulidou, T. Siatra- 39 F. Bigdeli, F. Rouhani, A. Morsali and A. Ramazani, Ultrason.
Papastaikoudi and E. Tiligada, Arzneimittelforschung, 2000, Sonochem., 2020, 62, 104862.
50, 48; (b) J. Slaett, I. Romero and J. Bergman, Synth., 2004, 40 J. Schneider, C. J. Reckmeier, Y. Xiong, M. von Seckendorff,
´
16, 2760; (c) F. Palluotto, A. Carotti, G. Casini, M. Ferappi,
A. Rosato, C. Vitali and F. Campagna, Il Farmaco, 1999, 54,
A. S. Susha, P. Kasak and A. L. Rogach, J. Phys. Chem. C, 2017,
121, 2014.
191; (d) M. Shiri, Chem. Rev., 2012, 112, 3508; (e) M. Shiri, 41 M. Shiri, Chem. Rev., 2012, 112, 3508.
M. A. Zolgol, H. G. Kruger and Z. Tanbakouchian, Chem. 42 M. Shiri, M. A. Zolgol, H. G. Kruger and Z. Tanbakouchian,
Rev., 2010, 110, 2250.
Chem. Rev., 2010, 110, 2250.
24 (a) P. Kutsky, T. M. Dzurilla and A. Sabova, Collect. Czech. 43 H. Kooshki, A. Sobhani-Nasab, M. Eghbali-Arani, F. Ahmadi,
Chem. Commun., 1999, 64, 348; (b) P. Kutschy, M. Dzurilla,
¨ ¨
V. Ameri and M. Rahimi-Nasrabadi, Sep. Purif. Technol.,
2019, 211, 873.
´
´
M. Takasugi, M. Torok, I. Achbergerova, R. Homzova and
´
´
M. Racova, Tetrahedron, 1998, 54, 3549.
44 T. Chen, X. P. Xu and S. J. Ji, J. Heterocycl. Chem., 2013, 50,
25 S. A. Zotova, T. M. Korneeva, V. I. Shvedov, N. I. Fadeeva,
244.
I. A. Leneva, I. T. Fedyakina, M. L. Khristova, 45 N. V. Lakshmi, P. Thirumurugan, K. M. Noorulla and
I. S. Nikolaeva, V. V. Peters and T. A. Gus’kova, Pharm.
Chem. J., 1995, 29, 57.
26 N. V. Lakshmi, P. Thirumurugan, K. M. Noorulla and
P. T. Perumal, Bioorg. Med. Chem. Lett., 2010, 20, 5054.
27 R. D. Dillard, N. J. Bach, S. E. Draheim, D. R. Berry,
P. T. Perumal, Bioorg. Med. Chem. Lett., 2010, 20, 5054.
46 L. Kheirkhah, M. Mamaghani, A. Yahyazadeh and
N. O. Mahmoodi, Appl. Organomet. Chem., 2018, 32, 4072.
47 M. Zarei, H. Sepehrmansourie, M. A. Zolgol, R. Karamian
and S. H. Moazzami Farida, New J. Chem., 2018, 42, 14308.
D. G. Carlson, N. Y. Chirgadze and J. P. Wery, J. Med. 48 H. Sepehrmansourie, M. Zarei, R. Taghavi and M. A. Zolgol,
Chem., 1996, 39, 5119. ACS Omega, 2019, 4, 17379.
28 S. M. Gomha and H. A. Abdel-Aziz, Bull. Korean Chem. Soc., 49 (a) M. A. Zolgol, Tetrahedron, 2001, 57, 9509; (b)
2012, 33, 2985. H. Sepehrmansourie, Iran. J. Catal., 2020, 10, 175.
29 S. Battagba, E. Boldrini, F. D. Settimo, G. Dondio, 50 A. Zare, M. Merajoddin, A. R. Moosavi-Zare, M. Zarei,
C. L. Motta, A. M. Marini and G. Primoore, Eur. J. Med.
Chem., 1999, 34, 93.
M. H. Beyzavi and M. A. Zolgol, Res. Chem. Intermed.,
2016, 42, 2365.
30 L. Garuti, M. Roberti, T. Rossi, M. Castelli and M. Malagoli, 51 A. R. Moosavi-Zare, M. A. Zolgol, M. Zarei, V. Khakyzadeh
Eur. J. Med. Chem., 1998, 33, 43. and A. Hasaninejad, Appl. Catal., A, 2013, 467, 61.
31 (a) M. A. Radwan, E. A. Ragab, N. M. Sabry and S. M. El- 52 E. Noroozizadeh, A. R. Moosavi-Zare, M. A. Zolgol, M. Zarei,
Shenawy, Bioorg. Med. Chem., 2007, 15, 3832; (b) S. L. Zhu,
S. J. Ji, X. M. Su, C. Sun and Y. Liu, Tetrahedron Lett., 2008,
R. Karamian, M. Asadbegy, S. Yari and S. H. M. Farida, J.
Iran. Chem. Soc., 2018, 15, 471.
49, 1777; (c) A. A. Fadda, A. El-Mekabaty, I. A. Mousa and 53 H. Sepehrmansourie, M. Zarei, M. A. Zolgol, S. Babaee and
K. M. Elattar, Synth. Commun., 2014, 44, 1579; (d)
P. Thirumurugan, A. Nandakumar, D. Muralidharan and
P. T. Paramasivan, J. Comb. Chem., 2010, 12, 161.
S. Rostamnia, Sci. Rep., 2021, 11, 5279.
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