SO3H-functionalized nano-MGO-D-NH2: Synthesis, characterization and application for one-pot synthesis of pyrano[2,3-d]pyrimidinone and tetrahydrobenzo[b]pyran derivatives in aqueous media

Article abstract of DOI:10.1002/aoc.4661

An SO₃H-functionalized nano-MGO-D-NH₂ catalyst has been prepared by multi-functionalization of a magnetic graphene oxide (GO) nanohybrid and evaluated in the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone derivati

Full text of DOI:10.1002/aoc.4661

Received: 1 August 2018
DOI: 10.1002/aoc.4661
Revised: 27 September 2018
Accepted: 27 September 2018
F U L L P A P E R
SO3H‐functionalized nano‐MGO‐D‐NH2: Synthesis,
characterization and application for one‐pot synthesis of
pyrano[2,3‐d]pyrimidinone and tetrahydrobenzo[b]pyran
derivatives in aqueous media
Heshmatollah Alinezhad1 | Mehrasa Tarahomi1 | Behrooz Maleki2
| Amirhassan Amiri2
1 Faculty of Chemistry, University of
An SO3H‐functionalized nano‐MGO‐D‐NH2 catalyst has been prepared by multi‐
functionalization of a magnetic graphene oxide (GO) nanohybrid and evaluated
in the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3‐d]pyrimidinone
derivatives. The GO/Fe3O4 (MGO) hybrid was prepared via an improved Hum-
mers method followed by the covalent attachment of 1,4‐butanesultone with
the amino group of the as‐prepared polyamidoamine‐functionalized MGO
(MGO‐D‐NH2) to give double‐functionalized magnetic nanoparticles as the cata-
lyst. The prepared nanoparticles were characterized to confirm their synthesis
and to precisely determine their physicochemical properties. In summary, the
prepared catalyst showed marked recyclability and catalytic performance in
terms of reaction time and yield of products. The results of this study are hoped
to aid the development of a new class of heterogeneous catalysts to show high
performance and as excellent candidates for industrial applications.
Mazandaran, PO Box 47416‐95447,
Babolsar, Iran
2 Department of Chemistry, Faculty of
Sciences, Hakim Sabzevari University,
96179‐76487 Sabzevar, Iran
Correspondence
Heshmatollah Alinezhad, Faculty of
Chemistry, University of Mazandaran, PO
Box 47416‐95447, Babolsar, Iran.
Email: heshmat@umz.ac.ir
Behrooz Maleki, Department of
Chemistry, Faculty of Sciences, Hakim
Sabzevari University, 96179–76487,
Sabzevar, Iran.
Email: malekibehrooz@gmail.com
KEYWORDS
dendrimer, magnetic, pyrano[2,3‐d]pyrimidinones, SO3H‐functionalized nano‐MGO‐D‐NH2,
tetrahydrobenzo[b]pyrans
1 | INTRODUCTION
is directly linked to the synthesis of chemical products
and plays a pivotal role in the development of cleaner tech-
The growing need to eliminate hazardous materials at
their source has become a great motivation for careful
design and selection of appropriate substances that are
environmentally more benign and simultaneously avoid
the necessity of the reduction or disposal of the generated
wastes during the chemical process. This goal which falls
within the scope of green chemistry has been brought into
the spotlight of intensive researches over the past few
decades and has the double advantage of economic bene-
fits and environmental protection by decreasing the usage
of toxic materials and increasing the overall efficiency.
Among the most important aspects of green chemistry,
catalysis has been identified as a fundamental tool which
nologies and chemical manufacturing processes. Catalytic
science may fulfil the essential requirements of green
chemistry by the development of novel catalysts which
have the benefits of lower input energies, higher selectivity
and decreasing toxic agents during the synthesis of certain
chemicals which leads to the implementation of facile and
simpler separation and recycling processes.[1–6]
In organic transformations, catalysts play a significant
role, and most of these are acid catalysts. The most com-
monly used acidic catalysts are sulfuric, hydrochloric, nitric
and phosphoric acids. However, corrosive properties, inabil-
ity to be reused and tough separation are their drawbacks.
Heterogeneous catalysts are superior to homogeneous ones
Appl Organometal Chem. 2019;e4661.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4661

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ALINEZHAD ET AL.
with regard to several important characteristics such as cost‐
effectiveness, recyclability and catalytic performance. Con-
sequently, a great deal of attention has been directed
towards the design and performance analysis of these cata-
lysts in the last few decades and this topic is still a matter
of scientificinterest.[7–11] Anefficient method for the fabrica-
tion of solid acid catalysts is the attachment of catalytically
active compounds onto the surface of various supporting
materials such as inorganic molecules or nanostructures
which leads to the formation of catalytically active hybrid
materials.[12,13] This idea dates back to the pioneering work
of Hara and co‐workers who prepared a carbon‐based solid
acid catalyst through incomplete carbonization of
sulfonated aromaticcompounds, which was furthergeneral-
ized by the interesting work of Wang and co‐workers who
covalently attached sulfonic acid‐containing aryl radicals to
mesoporous carbon and obtained a highly active catalyst
remained unchanged after several sets of experiments
with an average hydrolysis rate of 64% at 70°C for
6 h.[29] GO‐based composites can also be fabricated
through the attachment of bifunctional linkers to the sur-
face of GO. These linkers, such as dendrimers, which
play the role of molecular bridges will provide reactive
sites for anchoring of guest molecules such as acid cata-
lysts and enhance the overall efficiency and lifetime of
the prepared composites.
Dendrimers are characterized as manufactured, to a
great degree branched, nano‐sized and mono‐scatter
macromolecules with
a
globular structure.[30,31]
Dendrimers are known as types of artificial polymers
with unique structural features such as structural homo-
geneity, host–guest potential, high internal porosity,
integrity, controlled composition and biocompatibility.
They have also been broadly investigated for their appli-
cations in cancer diagnosis,[32] drug delivery,[33] cataly-
sis,[34] electrochemical sensors,[35] gene therapy,[36]
adsorption[37] and other areas.[38]
with an acid density of 1.93 mmol H+ g−1 [14,15]
.
With the emergence of nanostructures, many scien-
tists have been intrigued by the fascinating properties of
these materials, such as excellent chemical and mechani-
cal properties, and a great deal of effort has been made to
take advantage of these properties in developing novel
materials in various scientific fields. In this regard,
graphene and its derivatives such as an oxidized form
of graphene – so‐called graphene oxide (GO) – have
drawn considerable attention because of their superior
chemical and mechanical properties.[16–19] As a chemi-
cally modified graphene sheet, GO has been considered
as an efficient alternative to pristine graphene in a wide
range of applications. Because of the presence of hydro-
philic functional moieties such as epoxide, hydroxyl and
carboxylic groups in addition to its very large aromatic
surface, GO has the double advantage of both retaining
the excellent mechanical and thermal properties of
graphene while alleviating the dispersibility problem of
pristine graphene sheets in aqueous media. Consequently,
graphene and its oxidized analogues have been intro-
duced as efficient materials for the preparation of hybrid
composites through introduction of a wide variety of
functionalities which have gained marked popularity in
the literature, both theoretically and experimentally, and
offer promising potential in scientific fields such as
energy research,[20,21] catalysis[22,23] and electrochemical
analysis.[24] Several studies have pointed out the synergis-
tic interactions that GO can have with a wide class of
biomolecules such as enzymes and organic dyes through
covalent or non‐covalent linkages and reported improved
performances in conversion and yields.[25–28] In work by
Ji et al., sulfonated groups were covalently attached to
the surface of GO and the reactivity of this solid acid cat-
alyst was evaluated in the catalytic hydrolysis of ethyl
acetate. It was found that the activity of the catalyst
Due to the diverse biological properties associated with
pyranopyrimidinones and tetrahydrobenzo[b]pyrans, there
is an extensive interest in the synthesis of such compounds.
Tetrahydrobenzo[b]pyrans and their derivatives are an
important class of heterocyclic compounds which have
prominent biological and pharmacological properties such
as antitumour,[39,40] antibacterial,[41] antihypertensive,
hepatoprotective, cardiotonic,[39,42] vasodilatory and
bronchodilatory[43] activities, and hence are introduced as
ideal enhancers having a wide range of therapeutic applica-
tions. In this regard, the objective of the work presented
here was to synthesize a novel solid acid catalyst based on
GO which meets the criteria of green chemistry and to aid
the efficient synthesis of tetrahydrobenzo[b]pyrans and
pyrano[2,3‐d]pyrimidinones via a domino Knoevenagel
cyclocondensation reaction. We utilized magnetic GO as
the supporting material and polyamidoamine (PAMAM)
dendrimers which act as the bifunctional linker for the
anchoring of alkylsultone as the acid catalyst. Further infor-
mation regarding the incorporated chemicals and synthesis
route as well as the evaluation procedures are thoroughly
discussed in the following sections.
2 | EXPERIMENTAL
2.1 | Materials and instrumentation
TLC was conducted using glass plates coated with silica
gel 60 F254 with n‐hexane–ethyl acetate mixture as the
mobile phase to determine the purity of the products.
Melting point measurements of the synthesized samples
were carried out using a Thermo Scientific 9100

ALINEZHAD ET AL.
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apparatus. Fourier transform infrared (FT‐IR) spectro-
scopic measurements were carried out with a Shimadzu
8400 spectrometer in the wavenumbers range 400–
4000 cm−1 using KBr pellets. NMR spectra were recorded
with a Bruker DRX‐400 AVANCE (MA, USA) spectrome-
ter at 400.13 and 100.61 MHz. Field‐emission scanning
electron microscopy (FE‐SEM) images were obtained
with a MIRA3 XMU instrument operating at 25 kV to
study the morphology of samples. Also the MIRA3
XMU scanning electron microscope was equipped with
energy‐dispersive X‐ray (EDX) analysis facility for ele-
mental analysis. Finally, thermogravimetric analysis
(TGA) of the samples was performed with a DuPont
2000 thermal analysis system within the range 30–600°C
using a heating rate of 5°C min−1 under air atmosphere.
2.2 | Preparation of GO/Fe3O4 (MGO)
By oxidizing graphite with a modified Hummers method,
GO was prepared.[44,45] Using an effective chemical pre-
cipitation method, a magnetic GO (GO/Fe3O4 or MGO)
nanocomposite was synthesized. An amount of 30 mg of
GO was added to 10 ml of distilled water and sonicated
for 20 min to form a fully dispersed suspension. The
resulting suspension was heated to 50°C in a nitrogen
atmosphere to remove O2. Then,
a solution of
FeCl2⋅4H2O (80 mg) and FeCl3⋅6H2O (216 mg) was added
to the suspension under ultrasonication for 30 min. After
complete mixing, 1 ml of NH3⋅H2O solution was added
dropwise to the mixture under nitrogen. The mixture
was continually stirred for 40 min at 50°C to continue
SCHEME 1 Preparation of modified PAMAM denrimer (G2)

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ALINEZHAD ET AL.
the reaction and the resulting mixture was cooled to
room temperature. The obtained product was thoroughly
washed with double‐distilled water and the resulting
MGO nanoparticles were separated using a magnet.
aspects of the synthesis route would be beneficial, as illus-
trated in Scheme 1.
2.4 | Functionalization of MGO with
modified PAMAM dendrimer (MGO‐D‐NH2)
2.3 | Preparation of modified PAMAM
MGO (0.3 g) was dispersed in 200 ml of deionized water
by sonication for 30 min. Then, 1‐ethyl‐3‐(3‐
dimethylaminopropyl)carbodiimide hydrochloride (EDC.
HCl; 0.052 g) and N‐hydroxysuccinimide (NHS; 0.015 g)
were added to the solution and stirred for 10 min to
dendrimer
The synthesis of the modified PAMAM dendrimer was
accomplished according to a procedure described in detail
in our previous work.[37] However, a recap of the main
SCHEME 2 Procedures for the preparation of GO/Fe3O4NCs with modified PAMAM dendrimer (MGO‐D‐NH2)

ALINEZHAD ET AL.
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activate the carbonyl groups of MGO. Finally, the modi-
fied PAMAM dendrimer (3 ml) was added dropwise to
the system, and the reaction was allowed to proceed for
24 h at room temperature. The precipitate was collected
using an external magnetic field, washed with deionized
water and ethanol several times and dried in a vacuum
at 70°C. The resulting dark‐brown precipitates of MGO‐
D‐NH2 were ready to use (Scheme 2).
added to the solution and the reaction mixture was mixed
at 100°C for 48 h. Finally, through an external magnetic
field, the resultant particles were separated. The obtained
particles were thoroughly rinsed with toluene and acetone
in order to eliminate the unreacted 1,4‐butanesultone, and
finally vacuum‐dried at 70°C for 24 h (Scheme 3).
2.6 | General procedure for one‐pot
synthesis of tetrahydrobenzo[b]pyrans and
pyrano[2,3‐d]pyrimidinone derivatives
2.5 | Preparation of n‐butylsulfonate‐
functionalized MGO‐D‐NH2
n‐Butylsulfonate‐functionalized MGO‐D‐NH2 (MGO‐D‐
NH‐(CH2)4‐SO3H; 0.02 g) was added to a mixture of alde-
hyde (1 mmol), malononitrile (1.2 mmol), 1,3‐cyclic
MGO‐D‐NH2 (1 g) was dispersed in 25 ml of toluene by son-
ication for 30 min. Then, 0.7 g of 1,4‐butanesultone was
SCHEME 3 Procedures for the preparation of N‐Butylsulfonate‐functionalized MGO‐D‐NH2

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ALINEZHAD ET AL.
diketone (1 mmol) and 5 ml of water–ethanol (4:1, v/v) in a
10 ml round‐bottom flask. Then, the resulting mixture was
stirred at room temperature (see Tables 2 and 3). The reac-
tion progress was monitored using TLC. After completion
of the reaction process, the obtained product was dissolved
by the addition of hot ethanol to the mixture. The incorpo-
rated magnetic catalyst was separated from the product by
the application of a 1.4 T magnetic field followed by pouring
the reaction product onto crushed ice for 10 min. The
resulting product was then filtered and recrystallized from
96% ethanol (3 ml) to afford tetrahydrobenzo[b]pyran and
pyrano[2,3‐d]pyrimidinone derivatives.
IR (KBr disc, ν, cm−1): 3502, 3306, 3170, 2199, 1720, 1668,
1612.
2.8 | Recyclability evaluation of
MGO‐D‐NH‐(CH2)4‐SO3H
The synthesis of 2‐amino‐7,7‐dimethyl‐5‐oxo‐4‐phenyl‐
5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitrile was used
to evaluate the recyclability of MGO‐D‐NH‐(CH2)4‐
SO3H, under optimized conditions. At the end of the reac-
tion, the catalyst was separated using an external mag-
netic field and washed thoroughly with ethanol and
acetone to eliminate any trace of synthesized compound
on the catalyst surface. Finally, the catalyst was dried at
70°C for 1 h.
2.7 | Selected spectral data
2.7.1 | 2‐Amino‐4‐(4‐chlorophenyl)‐7,7‐
dimethyl‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐
chromene‐3‐carbonitrile (4d)
3 | RESULTS AND DISCUSSION
1H NMR (400 MHz, DMSO‐d6, δ, ppm): 0.98 (s, 3H), 1.05 (s,
3H), 2.15–2.26 (m, 2H), 2.40 (s, 2H), 4.12 (s, 1H), 6.60 (brs,
2H, D2O exchangeable), 7.13 (d, 2H), 7.46 (d, 2H). FT‐IR
(KBr, ν, cm−1): 3370,3175, 2190, 1670, 1628, 1500, 1490, 1380.
Based on our interest in the synthesis of novel recoverable
heterogeneous nanocatalysts, we report a novel experi-
mental protocol for the preparation of MGO‐D‐NH‐(-
CH2)4‐SO3H. Scheme 3 shows the preparation of the
nanocatalyst. First, nano‐MGO was synthesized using a
modified Hummers strategy.[44,45] In the following step,
the surface of MGO was functionalized using a modified
PAMAM dendrimer. The hydroxyl groups of carboxylic
acid on the surface of nano‐MGO reacted with NH2 groups
of the modified PAMAM dendrimer to form amide groups.
Finally, MGO‐D‐NH‐(CH2)4‐SO3H was formed by the
reaction between 1,4‐butanesultone with the NH2 groups
of MGO‐D‐NH2 via a ring‐opening process. The catalyst
was characterized using FT‐IR spectroscopy, EDX analy-
sis, FE‐SEM, TGA and acid–base titration.
2.7.2 | 2‐Amino‐7,7‐dimethyl‐4‐(2‐nitro-
phenyl)‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐
chromene‐3‐carbonitrile (4e)
1H NMR (400 MHz, DMSO‐d6, δ, ppm): 0.86 (s, 3H),
1.02 (s, 3H), 1.90–2.21 (m, 2H), 2.33–2.46 (m, 2H), 4.94
(s, 1H), 7.20 (brs, 2H, D2O exchangeable 2H), 7.32–
7.45 (m, 2H), 7.62–7.68 (m, 1H), 7.80–7.84 (dd, 1H).
FT‐IR (KBr disc, ν, cm−1): 3400, 3306, 2200, 1692,
1592, 1505, 1462, 1378.
3.1 | Characterization of MGO‐D‐NH‐
(CH2)4‐SO3H
2.7.3 | 2‐Amino‐7,7‐dimethyl‐4‐(4‐nitro-
phenyl)‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐
chromene‐3‐carbonitrile (4f)
3.1.1 | FT‐IR spectroscopy
1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.04 (s, 3H), 1.18
(s, 3H), 2.26–2.51 (m, 2H), 2.59 (s, 2H), 5.26 (s, 1H), 6.12
(brs, 2H, D2O exchangeable), 7.56 (d, 2H), 8.09 (d, 2H).
FT‐IR (KBr disc, ν, cm−1): 3401, 3307, 2200, 1690, 1598,
1498, 1468, 1375.
The successful attachment of functional groups onto the
surface of the GO was assessed at each step of the catalyst
synthesis through FT‐IR spectra as shown in Figure 1.
The FT‐IR spectrum of GO which is illustrated in
Figure 1a shows a broad peak between 3000 and
3600 cm−1 corresponding to the vibration of O─H groups
and two sharp peaks in the region 1635–1740 cm−1 which
can be attributed to the bending and stretching vibrations
of O─H and C═O of ─COOH groups, respectively. More-
over, the peaks at 1415 and 1131 cm−1 correspond to the
C─O stretching of carboxylic acid and C─OH of alcohol,
respectively, confirming the presence of oxygen
2.7.4 | 7‐Amino‐5‐(2‐chlorophenyl)‐2,4‐
dioxo‐1,3,4,5‐tetrahydro‐2H‐pyrano[2,3‐d]
pyrimidine‐6‐carbonitrile (6l)
1H NMR (400 MHz, DMSO‐d6, δ, ppm): 4.65 (s, 1H), 7.03
(s, 2H), 7.28–7.35 (m, 4H), 10.90 (s, 1H), 11.94 (s, 1H). FT‐

ALINEZHAD ET AL.
7 of 14
FIGURE 1 FT‐IR spectra: (a) GO; (b)
MGO; (c) MGO‐D‐NH2; (d) MGO‐D‐NH‐
(CH2)4‐SO3H
functionalities within the structure of the synthesized
GO. The FT‐IR spectrum of GO/Fe3O4 (Figure 1b) shows
the specific peak at 595 cm−1 relating to the stretching
vibration of the Fe─O bond. In the FT‐IR spectrum of
MGO‐D‐NH2 (Figure 1c), the peaks at 2923 and
2863 cm−1 are assigned to C─H stretching of the alkyl
group in the modified PAMAM component. The charac-
teristic peaks of MGO‐D‐NH2 at 1639, 1547 and
1434 cm−1 are attributed to NH deformation vibration
of primary amine, the coupling of N─H bending and
C─N stretching of amide. Also, the peak at 3435 cm−1
indicates the presence of nitrogen‐containing functional
groups.[65] Two significant peaks at 1037 and 1213 cm−1
confirm the reaction of MGO‐D‐NH2 with 1,4‐
butanesultone that correspond to the symmetric and
asymmetric stretching vibrations of S═O, respectively
(Figure 1d). The effective functionalization of 1,4‐
butanesultone onto the surface of MGO‐D‐NH2 is
evidenced by the FT‐IR results.[66]
thickness, smooth surface and wrinkled edge. After the
combination with Fe3O4 nanoparticles to form MGO
(Figure 2b), there is a much rougher surface, revealing
that many small magnetic nanoparticles had been assem-
bled on the surface of GO layers with a high density. The
FE‐SEM image of MGO‐D‐NH2 (Figure 2c) confirms the
grafting of organic compounds on MGO by increasing
particle sizes.
The EDX analysis of MGO‐D‐NH2 and MGO‐D‐NH‐(-
CH2)4‐SO3H confirmed the presence of C, S, N, Fe and O
atoms (Figure 3).
3.1.3 | Thermogravimetric analysis
TGA can be used to evaluate the thermal stability and
bond formation of materials. The TGA results for MGO,
MGO‐D‐NH2 and MGO‐D‐NH‐(CH2)4‐SO3H are shown
in Figure 4 in the range 30–600°C. It can be seen from
Figure 4a that MGO underwent a mild weight loss below
100°C which can be attributed to the loss of impurities
such as residuals or absorbed solvent. At that point, two
stages of weight loss happened at around 150 and
420°C, representing the decomposition and vaporization
of several functional groups at different sites on GO.
The TGA curve of MGO‐D‐NH2 (Figure 4b) indicated a
weight loss between 200 and 600°C which was assigned
3.1.2 | FE‐SEM and EDX analyses
To study the surface of MGO‐D‐NH2, FE‐SEM analysis
was used (Figure 2). Figure 2a shows a typical FE‐SEM
image of GO obtained using a modified Hummers
method. GO presents a sheet‐like structure with large

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ALINEZHAD ET AL.
FIGURE 2 FE‐SEM images: (a) GO; (b) MGO; (c) MGO‐D‐NH2
FIGURE 4 TGA curves: (a) MGO; (b) MGO‐D‐NH2; (c) MGO‐D‐
NH‐(CH2)4‐SO3H
the TGA curve of MGO‐D‐NH‐(CH2)4‐SO3H as shown
in Figure 4c exhibited an initial ascending behaviour
as the consequence of the buoyancy effect of the instru-
ment. Similar ascending trends in TGA curves have also
been reported in several studies and explained in that
this initial weight gain for the sample and platinum
pan stems from the differences in heat capacity and
thermal conductivity of the purging gas. The weight loss
between 400 and 600°C originated from the decomposi-
tion of the modified PAMAM dendrimer and n‐butyl–
SO3H groups.
FIGURE 3 EDX analysis: (a) MGO‐D‐NH2; (b) MGO‐D‐NH‐
(CH2)4‐SO3H
3.1.4 | Analysis of pH of catalyst
to the modified PAMAM dendrimer. In contrast to the
observed situation for MGO and MGO‐D‐NH2 where
the TGA curves showed an entirely descending trend,
The catalytic active sites of the synthesized MGO‐D‐
NH‐(CH2)4‐SO3H were determined by the method of

ALINEZHAD ET AL.
9 of 14
active‐site titration. Following this aim, 100 mg of catalyst
was selected and stirred with 10 ml of 1 M NaCl solution
for 24 h at room temperature. After that, the pH was calcu-
lated to be about 2.1 which is equivalent to 0.06 mmol g−1
of SO3H groups within the structure of the catalyst.
The nanomagnetic MGO‐D‐NH‐(CH2)4‐SO3H exhib-
ited the best catalytic performance in comparison to the
other catalysts according to the values of time and yield
as presented in Table 1, and retained its optimal condi-
tions. As can be perceived from the values of time and
yield in Table 1, higher performance was achieved using
0.02 g of the catalyst at room temperature in water–
ethanol (4:1, v/v) (entry 5). However, increasing the
amount of catalyst and temperature did not lead to any
improvements in the obtained results (entries 6 and 7).
Having found the optimized reaction conditions based
on the data reported in Table 1, we aimed at assessing the
performance and activity of MGO‐D‐NH‐(CH2)4‐SO3H in
the synthesis of various derivatives of tetrahydrobenzo[b]
pyran (Table 2) and pyrano[2,3‐d]pyrimidinone (Table 3)
by reacting a wide range of arylaldehydes (1 mmol) with 5‐
dimethylcyclohexane‐1,3‐dione (1 mmol) and malononitrile
(1.2 mmol) in the presence of our synthesized catalyst.
To demonstrate the advantages of the synthesized
catalyst, we compared the obtained results for the cata-
lytic activity of MGO‐D‐NH‐(CH2)4‐SO3H with other
reported results for the synthesis of tetrahydrobenzo[b]
pyrans and pyrano[2,3‐d]pyrimidinones using various
catalysts (Table 4). It is evident from Table 4 that
3.2 | Activity assessment of MGO‐D‐NH‐
(CH2)4‐SO3H catalyst
The activity of MGO‐D‐NH‐(CH2)4‐SO3H nanoparticles was
explored in the synthesis of pyrano[2,3‐d]pyrimidinones
and tetrahydrobenzo[b]pyrans by the three‐component
reaction of 1,3‐dicarbonyl and malononitrile with various
aromatic aldehydes (Scheme 4).
The reaction of 5,5‐dimethylcyclohexane‐1,3‐dione
(0.14 g, 1 mmol), benzaldehyde (0.106 g, 1 mmol) and
malononitrile (0.079 g, 1.2 mmol) as a model reaction
was selected to optimize the reaction conditions and
investigated in the presence of several nanocatalysts such
as GO, MGO, MGO‐D‐NH2 and MGO‐D‐NH‐(CH2)4‐
SO3H in various solvents, and at different temperatures.
The results are summarized in Table 1.
SCHEME 4 MGO‐D‐NH‐(CH2)4‐
SO3H–catalyzed synthesis of
tetrahydrobenzo[b]pyrans and pyrano[2,3‐
d]pyrimidinones
TABLE 1 Optimization of reaction conditions for synthesis of tetrahydrobenzo[b]pyran derivative 4a
Entry
Reaction conditions
Time (min)
Yield (%)
1
GO (0.02 g)/water/ethanol (4:1, v/v), 25°C
40
75
35
10
5
65
50
2
Fe3O4 (0.02 g) water/ethanol (4:1, v/v), 25°C
3
MGO (0.02 g)/water/ethanol (4:1, v/v), 25°C
70
4
MGO‐D‐NH2 (0.02 g)/water/ethanol (4:1, v/v), 25°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/water/ethanol (4:1, v/v), 25°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.03 g)/water/ethanol (4:1, v/v), 25°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/water/ethanol (4:1, v/v), 35°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/toluene, 100°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/DMF, 100°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/ethanol, 25°C
MGO‐D‐NH‐(CH2)4‐SO3H (0.02 g)/water, 25°C
75
5
95
6
5
95
7
5
95
8
120
120
5
Trace
40
9
10
11
80
60
62

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ALINEZHAD ET AL.
TABLE 2 Synthesis of tetrahydrobenzo[b]pyran derivatives catalysed by MGO‐D‐NH‐(CH2)4‐SO3H
M.p.
(found)
(°C)
M.p.
(lit.)
(°C)
Time
(min)
Yield
(%)
Entry
Ar
R
4a
4b
4c
4d
4e
4f
C6H5
5
4
5
4
4
3
4
6
6
6
10
6
6
5
4
4
4
3
6
6
5
6
6
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
227–228
217–219
223–225
207–209
223–225
173–175
205–207
206–208
215–217
198–200
179–181
209–211
200–202
211–213
212–214
222–225
196–197
230–232
234–236
189–191
170–172
232–235
198–200
95
95
94
96
97
98
93
94
90
92
85
90
88
94
96
96
97
98
89
90
90
88
89
228–230[46]
217–219[47]
224–225[48]
209–211[46]
224–226[49]
174–176[50]
203–205[51]
206–208[52]
216–218[47]
198–199[47]
178–180[53]
210–212[47]
201–203[49]
213–215[49]
212–214[49]
224–226[46]
196–198[49]
230–232[46]
234–236[54]
190–192[49]
171–174[52]
234–236[49]
199–200[49]
2‐ClC6H4
3‐ClC6H4
4‐ClC6H4
2‐O2NC6H4
4‐O2NC6H4
4‐BrC6H4
4g
4h
4i
4‐(CH3)2NC6H4
4‐H3CC6H4
4‐CH3OC6H4
2‐HOC6H4
4‐HOC6H4
2‐Furfural
C6H5
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
2‐ClC6H4
H
4‐ClC6H4
H
2‐O2NC6H4
4‐O2NC6H4
4‐H3CC6H4
4‐CH3OC6H4
4‐(CH3)2NC6H4
4‐HOC6H4
2‐Furfural
H
H
H
4t
H
4u
4v
4w
H
H
H
TABLE 3 Synthesis of pyrano[2,3‐d]pyrimidinones catalysed by MGO‐D‐NH‐(CH2)4‐SO3H
M.p.
M.p.
(lit.)
(°C)
Time
(min)
(found)
(°C)
Yield
(%)
Entry
Ar
R1
X
6a
6b
6c
6d
6e
6f
4‐NCC6H4
4‐O2NC6H4
4‐O2NC6H4
4‐BrC6H4
4‐BrC6H4
4‐F3CC6H4
4‐F3CC6H4
C6H5
H
H
H
H
H
H
H
H
H
4
3
5
5
6
6
6
5
5
O
O
S
254–256
236–238
234–236
226–228
234–236
250–252
239–241
209–211
214–216
96
98
92
90
89
92
88
94
92
254–256[55]
237–238[55]
235–236[55]
226–227[56]
236[55]
O
S
O
S
250–251[55]
239–240[55]
210–211[56]
214–215[57]
6g
6h
6i
O
O
4‐ClC6H4
(Continues)

ALINEZHAD ET AL.
11 of 14
TABLE 3 (Continued)
M.p.
(found)
(°C)
M.p.
(lit.)
(°C)
Time
(min)
Yield
(%)
Entry
6j
Ar
R1
X
O
S
3‐ClC6H4
3‐ClC6H4
2‐ClC6H4
C6H5
H
6
6
5
5
4
6
5
6
7
6
238–240
235–236
214–216
209–211
211–213
238–240
206–208
220–222
209–211
224–227
90
89
93
92
96
92
94
90
91
92
240–241[55]
237–238[55]
214–215[56]
210[58]
6k
6l
H
H
O
O
O
O
O
O
O
O
6m
6n
6o
CH3
CH3
CH3
CH3
CH3
CH3
CH3
4‐O2NC6H4
2‐ClC6H4
4‐ClC6H4
4‐H3CC6H4
2‐CH3OC6H4
4‐CH3OC6H4
212[59]
238–239[60]
206–208[61]
221–223[62]
209–210[63]
225–227[64]
6p
6q
6r
6s
TABLE 4 Comparison of MGO‐D‐NH‐(CH2)4‐SO3H with some reported catalysts in the synthesis of tetrahydrobenzo[b]pyran and
pyrano[2,3‐d]pyrimidinone
Time
(min)
Yield
(%)
Entry
4a
Product
Conditions
NH4H2PO4/Al2O3/EtOH/reflux[46]
15
10
15
120
20
25
5
86
96
95
96
92
95
95
[PVPH]HSO4/H2O:EtOH (7:3), 80°C[67]
[DABCO‐PDO][CH3COO]/H2O, 80°C[68]
[Ch][OH]/H2O/reflux[69]
H2PO4‐SCMNPs/solvent‐free, 80°C[70]
Fe3O4@Ph‐SO3H/H2O/r.t./ultrasonic condition[71]
MGO‐D‐NH‐(CH2)4‐SO3H/H2O–EtOH (4:1), r.t. (this work)
6h
Diammonium hydrogen phosphate (10 mol %)/EtOH, r.t.[72]
Na2SeO4 (5 mol%)/EtOH, 120°C[73]
120
180
20
81
85
94
94
Nano SiO2 (20 mol%)/H2O, 90°C[74]
MGO‐D‐NH‐(CH2)4‐SO3H/H2O–EtOH (4:1), r.t. (this work)
5
MGO‐D‐NH‐(CH2)4‐SO3H is highly efficient in minimiz-
ing the reaction time, performing at room temperature,
increasing the product yield and elimination of hazard-
ous solvent.
arylidenemalononitrile creates intermediates C or D.
Finally, tautomerization affords the corresponding
products (tetrahydrobenzo[b]pyrans and pyrano[2,3‐d]
pyrimidinones).
A
plausible mechanism for the synthesis of
tetrahydrobenzo[b]pyran and pyrano[2,3‐d]pyrimidinone
derivatives is outlined in Scheme 5. According to the
reaction procedure, initially the MGO‐D‐NH‐(CH2)4‐
SO3H catalyst activates the carbonyl group of the aro-
matic aldehyde by H+ of catalyst. Then, the Knoevenagel
condensation of activated aromatic aldehyde with
malononitrile is completed by the elimination of one
H2O molecule forming arylidenemalononitrile. In the
second step, the nucleophilic (Michael) addition of the
enolizable 1,3‐dicarbonyl compounds (A or B) to
3.3 | Recycling of catalyst
One of the most significant advantages of a heteroge-
neous catalyst for industrial applications is reusability.
A modest decrease in the catalytic activity as shown in
Figure 5 after six runs was evident by the percentage
yields of each recycle. These results indicate the reusabil-
ity of MGO‐D‐NH‐(CH2)4‐SO3H.

12 of 14
ALINEZHAD ET AL.
SCHEME 5 Proposed mechanism for the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3‐d]pyrimidinone
D‐NH‐(CH2)4‐SO3H
nanoparticles
by
double‐
functionalization of MGO with PAMAM dendrimer and
1,4‐butanesultone. The obtained heterogeneous catalyst
shows some excellent properties such as very strong activ-
ity towards the synthesis of tetrahydrobenzo[b]pyrans
and pyrano[2,3‐d]pyrimidinones and sufficient durability
in at least six consecutive reaction cycles without any
notable activity loss, which indicate its promising poten-
tial for industrial applications.
ACKNOWLEDGEMENTS
The authors thank the Research Council of the University
of Mazandaran and Hakim Sabzevari University for sup-
port of this work.
FIGURE
synthesis of 4a
5
Recyclability of MGO‐D‐NH‐(CH2)4‐SO3H for
4 | CONCLUSIONS
ORCID
With the aim of obtaining an efficient and low‐cost
hybrid catalyst, we have successfully synthesized MGO‐
Behrooz Maleki https://orcid.org/0000-0002-0322-6991

ALINEZHAD ET AL.
13 of 14
[29] J. Ji, G. Zhang, H. Chen, S. Wang, G. Zhang, F. Zhang, X. Fan,
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How to cite this article: Alinezhad H, Tarahomi
M, Maleki B, Amiri A. SO3H‐functionalized nano‐
MGO‐D‐NH2: Synthesis, characterization and
application for one‐pot synthesis of pyrano[2,3‐d]
pyrimidinone and tetrahydrobenzo[b]pyran
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