Application of Fe3O4@SiO2/(CH2)3-[imidazolium-SO3H]Cl as a robust, magnetically recoverable solid acid catalyst for the facile preparation of arylbispyranylmethanes

Article abstract of DOI:10.1139/cjc-2017-0232

In this study, Fe₃O₄@SiO₂/(CH₂)₃-[imidazolium-SO₃H]Cl shows robust promoting capability in the synthesis of arylbispyranylmethane derivatives under mild and green conditions. Arylbispyranyl

Full text of DOI:10.1139/cjc-2017-0232

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Application of Fe3O4@SiO2/(CH2)3-[Imidazolium-SO3H]Cl as a robust magnetically
recoverable solid acid catalyst for the facile preparation of arylbispyranylmethanes
Mohammad Ali Zolfigol,*1 Mahdiyeh Navazeni,1 Meysam Yarie1 and Roya AyaziꢀNasrabadi1
Department of Organic Chemistry, Faculty of Chemistry, Bu‐Ali Sina University, PO Box 6517838683, Hamedan,
Iran.
Correspondence: Mohammad Ali Zolfigol, Email: zolfi@basu.ac.ir & mzolfigol@yahoo.com, Tel.: +98 811
8282807; fax: +98 811 8380709.

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Abstract
In this study, Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl shows robust promoting capability in
the synthesis of arylbispyranylmethane derivatives under mild and green conditions.
Arylbispyranylmethanes were synthesized via efficient threeꢀcomponent reaction of various
aromatic aldehydes with 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone. The nanomagnetic coreꢀshell
catalyst presented effective potential of at least 8 times recycling applicability in the described
synthetic procedure.
Keywords: Magnetically recoverable solid acids, Arylbispyranylmethanes, Multicomponent
condensation, Mild and green conditions.
Running Head: Facile preparation of arylbispyranylmethanes

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Introduction
Nowadays, growing attentions have been focused on the topic of preparation and application of
nanamagnetic coreꢀshell catalysts in the domain of organic functional groups transformations.
Heterogenization and solidification of catalytically active agents onto the surface of Fe3O4 as a
promising magnetic inorganic support lead to generation of stable heterogeneous promoter which
inherit several outstanding utilities viz highly potential of activity and selectivity as in the case of
homogeneous catalysts. Also, they represent good thermal/mechanical stability, nanometer scale,
high loading capacity, excellent accessibility and high surface area to volume ratio [1ꢀ13].
On the other hand, using oneꢀpot multicomponent reactions (MCRs) as a refine and efficient
strategy for carrying out the organic functional groups transformation have appeared as an
influential tool in the toolbox of organic methodologists. Oneꢀpot multicomponent reactions
depict some trustworthy characters such as high degree of atom and step economy, preparation
of elaborate target structures and medicinal active compounds and access to molecular library
through an ecoꢀcompatible route. Moreover, employing of this versatile synthetic tool under
solvent free conditions by applying a recoverable nanomagnetic coreꢀshell catalyst can be
considered as a branch of green chemistry domain [14ꢀ19].
Heterocyclic compounds bearing 4ꢀhydroxy pyranꢀ2ꢀone structural kernels are renowned as
influential organic natural products with excellent potent of therapeutic applications in the field
of medicinal and biological chemistry. They can be applied as antiꢀHIV, antiꢀoxidant, antiꢀviral,
antiꢀdementia, antiꢀdiabetic, antiꢀcoagulant, antiꢀinflammatory and antiꢀplatelet aggregative
agents [20ꢀ24]. Among them, arylbispyranylmethane derivatives are remarkable heterocyclic
privileged scaffold as they can be served as building blocks for the synthesis of organic

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compounds which possess a broad scope of pharmaceutical activities alike antiꢀcoagulant
property and inhibitor for mPGESꢀ1 and 5ꢀLO. Also, 5ꢀsubstituted pyrimidine nucleoside with
arylbispyranylmethane moiety can act as antiviral agent [25ꢀ27]. Some bioactive agents bearing
4ꢀhydroxy pyranꢀ2ꢀone structural scaffold are shown in Figure 1.
Figure 1: Some bioactive agents which bearing 4ꢀhydroxy pyranꢀ2ꢀone structural scaffold.
Hence, owing to their persuasive prevalent pharmaceutical versatility of the
arylbispyranylmethane derivatives [28ꢀ30], synthesis and chemistry of them have attracted much
attention in recent times. Anyway, most of the reported routes for the construction of these target
molecules are connected with some limitations in term of long reaction times, unsatisfactory
yields, harsh reaction conditions, tedious workꢀup, using toxic and unsafe organic solvents.
Therefore, presenting of newer methods for the construction of the arylbispyranylmethane
derivatives by applying a reusable nanomagnetic catalyst is attractive.

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In this report, during the course of our constant research program dedicating of newer and
efficient protocols for the synthesis of heterocyclic molecules using silica sulfuric acid [31ꢀ33]
and nanomagnetic catalysts [34ꢀ42], herein, we wish to report the catalytic application of
Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl as a nanomagnetic and reusable solid acid catalyst
at the preparation of arylbispyranylmethane derivatives. The obtained results have shown in the
Schemes 2.
Scheme 2: Synthesis of arylbispyranylmethane derivatives under mild and ecoꢀfriendly conditions
.
Experimental
General
All materials were obtained from Merck chemical company and used without further
purification. The structural verification of the known products was made by comparison of their
physical properties and spectral data with those of authentic samples reported in the literature.
The reaction progress and purity of the compounds were checked out by using TLC performed
with silica gel SIL G/UV 254 plates. The 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were recorded with a Bruker spectrometer. Melting points were recorded with a Buchi B‐545
apparatus in open capillary tubes.

Page 6 of 16
General procedure for the construction of two magnetically recoverable solid acids
The construction and structural verification of the applied nanomagnetic based heterogeneous
catalyst Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl was explored in our previously reported
method as illustrated in Scheme 3 [43].
General procedure for the synthesis of arylbispyranylmethane derivatives
In a test tube containing a mixture of aromatic aldehydes (1 mmol) and 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀ
pyranꢀ2ꢀone (2 mmol, 0.252 g), 10 mg of Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl 1 as
nanomagnetic catalyst was added. The resulting mixture stirred for proper times under solvent
o
free conditions at 90 C as indicated in Table 2. The progress of the reactions was monitored by
TLC skill using nꢀhexane and EtOAc as eluent system. After completion of the reactions, hot
ethanol was added to the reaction mixtures to dissolve the desired products and also unreacted
starting materials. The nanomagnetic catalyst 1 was not dissolved in used solvent and easily
separated from reaction mixture by applying an external magnet, washed with EtOH and
preserved for next run. Finally, the pure products were obtained via recrystallization from
ethanol with good to excellent yields.
Selected spectral data for arylbispyranylmethane derivatives
3,3'-((2-Chlorophenyl)methylene)bis(4-hydroxy-6-methyl-2H-pyran-2-one) (1c)
Melting point = 156ꢀ157 oC
FTꢀIR (KBr): ν (cmꢀ1)= 3081, 2990, 1709, 1683, 1619, 1571, 1450, 1408, 1308, 997, 826.
δ
(400 MHz, DMSO) 11.22 (brs, 2H, OH), 7.30ꢀ7.28 (m, 1H, Aromatic), 7.18ꢀ7.11 (m, 1H,
H
Aromatic), 5.96 (s, 2H, Olefinic), 5.65 (s, 1H, CH), 2.15 (s, 6H, CH3).

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δ
(101 MHz, DMSO) 166.4, 164.4, 160.5, 139.2, 132.7, 130.1, 128.6, 127.3, 126.2, 100.6,
C
100.4, 34.8, 19.1.
3,3'-((3-Hydroxyphenyl)methylene)bis(4-hydroxy-6-methyl-2H-pyran-2-one) (1d)
Melting point = 226ꢀ227 oC
FTꢀIR (KBr): ν (cmꢀ1)= 3323, 3188, 3093, 1671, 1618, 1562, 1447, 1271, 995, 794.
δ H (400 MHz, DMSO) 11.79 (brs, 2H, OH), 9.17 (brs, 1H, OH), 7.02 (t, J=8 Hz, 1H, Aromatic)
, 6.54 (t, J=8 Hz, 1H, Aromatic), 6.44ꢀ6.42 (m, 2H, Aromatic), 6.11 (s, 2H, Olefinic), 5.94 (s,
1H, CH), 2.21 (s, 6H, CH3).
δ
(101 MHz, DMSO) 168.1, 166.4, 161.3, 157.2, 140.9, 129.1, 117.1, 113.3, 112.7, 101.6,
C
101.3, 33.6, 19.1.
3,3'-((2,4-Dichlorophenyl)methylene)bis(4-hydroxy-6-methyl-2H-pyran-2-one) (1e)
Melting point = 234ꢀ235 oC
FTꢀIR (KBr): ν (cmꢀ1)= 3435, 3216, 1686, 1672, 1633, 1575, 1448, 1409, 1302, 833.
δ H (400 MHz, DMSO) 11.29 (brs, 2H, OH), 7.50 (d, J=4 Hz, 1H, Aromatic), 7.34 (dd, J=4 Hz,
1H, Aromatic), 7.18 (d, J=8 Hz, 1H, Aromatic), 6.02 (s, 2H, Olefinic), 5.62 (s, 2H, CH), 2.22 (s,
6H, CH3).
δ
(101 MHz, DMSO) 166.2, 163.9, 160.5, 138.8, 133.4, 131.5, 130.7, 127.8, 126.3, 100.2,
C
100.2, 34.7, 19.4, 19.2.
3,3'-((2-Nitrophenyl)methylene)bis(4-hydroxy-6-methyl-2H-pyran-2-one) (1h)
Melting point = 235ꢀ236 oC
FTꢀIR (KBr): ν (cmꢀ1)= 3099, 3027, 2944, 1685, 1611, 1568, 1524, 1417, 1357, 996, 850, 728.

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δ
(400 MHz, DMSO) 11.41 (brs, 2H, OH), 7.82 (d, J=8 Hz, 1H, Aromatic), 7.61 (t, J=8 Hz,
H
1H, Aromatic) , 7.47 (t, J=8 Hz, 1H, Aromatic), 7.33 (d, J=8 Hz, 1H, Aromatic), 6.12 (s, 1H,
CH), 6.02 (s, 2H, Olefinic), 2.23 (s, 6H, CH3).
δ
(101 MHz, DMSO) 166.5, 164.0, 160.7, 149.4, 135.5, 132.0, 130.0, 126.8, 123.6, 100.2,
C
100.0, 32.9, 19.2.
4-(Bis(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)methyl)benzonitrile (1j)
Melting point = 218ꢀ221 oC
FTꢀIR (KBr): ν (cmꢀ1)= 3448, 3058, 2226, 1687, 1672, 1626, 1445, 1407, 1298, 1000, 827.
δ
(400 MHz, DMSO) 11.70 (brs, 2H, OH), 7.74 (d, J=8 Hz, 2H, Aromatic), 7.28 (d, J=4 Hz,
H
2H, Aromatic), 6.11 (s, 2H, Olefinic), 5.88 (s, 1H, CH), 2.25 (s, 6H, CH3).
δ
(101 MHz, DMSO) 167.5, 165.3, 161.3, 147.0, 131.8, 128.0, 119.1, 108.2, 100.9, 100.6,
C
35.3, 19.1.
Result and discussion
The preparation and structural confirmation of the employed Fe3O4@SiO2/(CH2)3ꢀ[Imidazoliumꢀ
SO3H]Cl 1 as a nanomagnetic based heterogeneous catalyst were investigated in our previously
reported method as portrayed in Scheme 3 [43].

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Scheme 3: The structure of the applied nanomagnetic based heterogeneous catalyst 1.
In this exploration the catalytic applicability of the Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl
1, was explored for the synthesis of a series of arylbispyranylmethane derivatives. In the first
trial, as in the case of target molecules 1a-m, variable reaction parameters such as load of
catalyst 1, reaction temperature and solvents were checked out upon the reaction of 4ꢀ
chlorobenzaldehyde and 2 equivalent of 4ꢀhydroxyꢀ6ꢀmethylꢀ2ꢀpyrone (Scheme 4). The outcome
data for optimizing of the reaction conditions are presented in Table 1. The resulting data implied
that the best results attained under solvent free conditions in the presence of 10 mg of the
nanomagnetic solid acid catalyst 1 at 90 oC.
Scheme 4: The model reaction for the optimizing of the reaction conditions in the case of 3,3'ꢀ((4ꢀ
chlorophenyl)methylene)bis(4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone) (1a).

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Table 1: Optimizing of the reaction conditions for the synthesis of 3,3'ꢀ((4ꢀchlorophenyl)methylene)bis(4ꢀ
hydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone) (1a)a.
Entry
Solvent
Temperature
(˚C)
Load of catalyst
(mg)
Time
Yield (%)b
(min.)
1
2
ꢀ
80
60
10
10
10
10
ꢀ
47
45
66
56
92
95
40
90
90
85
82
40
55
90
ꢀ
3
ꢀ
100
40
4
-
90
40
5
ꢀ
90
100
40
6
ꢀ
ꢀ
90
7
7
90
15
10
10
10
10
10
40
8
H₂O
Reflux
Reflux
Reflux
Reflux
Reflux
140
120
130
140
120
9
C₂H₅OH
CH₃CN
nꢀHexane
EtOAc
10
11
12
aReaction conditions: 4ꢀchlorobenzaldehyde (1 mmol, 0.144 g), 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone (2 mmol,
0.252 g)., b Isolated yields.
In second place, with optimal reaction conditions in hand, the versatility, limitations and scope of
the presented synthetic manner to arylbispyranylmethane derivatives, the reaction of several type
of arylaldehydes (bearing electronꢀreleasing, electronꢀwithdrawing groups and halogens) and 4ꢀ
hydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone were examined. The collected obtained results in Table 2,
illustrated that direct threeꢀcomponent reactions worked well with a variety of arylaldehydes and
the target molecules were produced with high to excellent yields in relatively short reaction
times.

Page 11 of 16
Table 2: Synthesis of target molecules 1a-m in the presence of nano magnetic catalyst 2a.
Melting point (°C),
[found]Lit.
Entry
Time (min.)
Yield (%)b
Product
R
1
2
40
25
35
50
40
15
20
33
30
50
25
15
17
95
91
90
89
89
94
83
88
82
91
95
93
86
223ꢀ225 [202ꢀ206]37
204ꢀ206 [200ꢀ204]37
156ꢀ157 [155ꢀ158]37
226ꢀ227 [new]
1a
1b
1c
1d
1e
1f
4-Cl
3-NO2
2-Cl
3
4
3-OH
2,4-Cl2
H
5
234ꢀ235 [244ꢀ246]37
213ꢀ215 [213ꢀ216]37
188ꢀ190 [183ꢀ185]37
235ꢀ236 [223ꢀ227]30
188ꢀ190 [174ꢀ176]37
218ꢀ221 [223ꢀ225]37
199ꢀ201 [219ꢀ221]37
217ꢀ218 [212ꢀ215]37
193ꢀ197 [232ꢀ234]37
6
7
1g
1h
1i
4-Me
2-NO2
4-OMe
4-CN
4-F
8
9
10
11
12
13
1j
1k
1l
4-Br
1m
4-NO2
aReaction conditions: arylaldehyde (1 mmol), 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone (2 mmol, 0.252 g)., b Isolated
yields.
In continued, the reusability potential of the Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl as a
nanomagnetic catalyst were successfully examined. After completion of each run, in order to
separation of nanomagnetic catalyst 1, hot EtOH was added to the reaction mixture. Afterwards,
the catalyst was isolated by using an external magnet, washed with ethanol, weighted and
preserved for the following assay. In the presented method for the synthesis of
arylbispyranylmethane derivatives, the reaction of benzaldehyde and 4ꢀhydroxyꢀ6ꢀmethylꢀ2ꢀ
pyrone (target molecule 1f) was selected as model reaction in the presence of nanomagnetic
catalyst Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl. The reusability of the catalyst was

Page 12 of 16
investigated for eight consecutive runs in the period of 15 minutes. The collected data for the
multicomponent synthesis of arylbispyranylmethane derivatives is depicted in Figure 2. The
achieved data indicated that the used nanomagnetic catalyst Fe3O4@SiO2/(CH2)3ꢀ[Imidazoliumꢀ
SO3H]Cl shows excellent potential of reusability in the selected reaction.
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Compound 1f
94
94
94
93
93
93
93
92
Figure 2: Reusability test for both types of the presented multicomponent reactions.
In another assay the plausible mechanistic pathway for the synthesis of 3,3'ꢀ
(phenylmethylene)bis(4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone) 1f is illustrated in Scheme 5. In first
place, 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone attacked to the activated benzaldehyde which was
produced intermediate A via dehydration. In the following step, through the reaction of second
mole of 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone with intermediate A, intermediate B was
generated. At last, tautomerization afforded the desired product 1f.

Page 13 of 16
Scheme 5: Plausible process for the synthesis of target molecule 1f.
Conclusion
In summary, the catalytic activity of Fe3O4@SiO2/(CH2)3ꢀ[ImidazoliumꢀSO3H]Cl as a
magnetically recoverable solid acids catalyst was explored in the synthesis of
arylbispyranylmethane derivatives under mild and green reaction conditions.
Arylbispyranylmethanes were synthesized by a highly efficient threeꢀcomponent reaction of
varied aromatic aldehydes with 4ꢀhydroxyꢀ6ꢀmethylꢀ2Hꢀpyranꢀ2ꢀone. The nanomagnetic coreꢀ
shell catalyst presented effective potential of at least 8 times recycling in the described synthetic
procedure.

Page 14 of 16
Acknowledgments
We are grateful to Bu‐Ali Sina University and Iran National Science Foundation (INSF) for
financial support (Grant Number: 940124) of our research group.
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