Another application of (NH4)42[MoVI 72MoV 60O372(CH3COO)30(H2O)72] as a highly efficient recyclable catalyst for the synthesis of dihy

Article abstract of DOI:10.1002/aoc.3479

In continuation of our previous works on the application of (NH₄)₄₂[Mo^VI ₇₂Mo^V ₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂], a Keplerate-type giant-ball n

Full text of DOI:10.1002/aoc.3479

Full paper
Received: 30 December 2015
Revised: 26 February 2016
Accepted: 28 February 2015
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3479
Another application of (NH4)42
VI
V
[Mo Mo O (CH3COO)30(H2O)72] as a
72
60 372
highly efficient recyclable catalyst for the
synthesis of dihydropyrano[3,2-c]chromenes
Marziyeh Rohaniyan, Abolghasem Davoodnia* and Ahmad Nakhaei
VI
72
In continuation of our previous works on the application of (NH4)42[Mo MoV60O372(CH3COO)30(H2O)72], a Keplerate-type giant-ball
nanoporous isopolyoxomolybdate, as a catalyst for the synthesis of heterocyclic compounds, in this paper, we report another ap-
plication of this attractive catalyst in the synthesis of 2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles via a one-
pot three-component reaction of 4-hydroxycoumarin, aldehydes and malononitrile. The reactions occur in ethanol–water as sol-
vent at room temperature and the process is operative with various aldehydes, giving the corresponding products in high yields.
Other beneficial features of this protocol include short reaction times, simple work-up and the recyclability and reusability of the
catalyst for up to five consecutive runs. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: dihydropyrano[3,2-c]chromenes; giant nanoporous isopolyoxomolybdate; Keplerate; {Mo132
}
(V), bridged by oxygen atoms. They are of proven value in catalysis,
magnetism, materials science and biomedicine,[24–28] because they
are diverse and highly modifiable in size, shape, charge density,
acidity and reversible redox potential. A number of very large
POM anions have been synthesized and structurally characterized.
Beginning with the big-wheel Mo154 anion,[29] Müller’s group have
reported several giant mixed-valence POMs with cyclic (Mo176),[30]
Introduction
Thesynthesisofdihydropyrano[3,2-c]chromeneswithbiologicaland
pharmacologicalpropertiessuchasspasmolytic, diuretic, anticoagu-
lant,anticancerandantianaphylacticactivities[1,2] iscurrentlyofgreat
interest. The reported protocol for the synthesis of dihydropyrano
[3,2-c]chromenes involves the one-pot three-component reaction
of 4-hydroxycoumarin, aldehydes and malononitrile in the presence
capped cyclic (Mo248) )
[31] and basket (Mo116 [32] architectures. Giant
of
a
catalyst such as polymer-supported sulfanilic acid,[3]
nanosized porous Keplerate-type POMs show a large variety of
applications in fundamental and applied science, such as in
modelling passive cation transport through membranes, encap-
sulation, nanoseparation chemistry and magnetic and optics
applications.[33,34] In spite of these valuable properties, to the au-
thors’ knowledge, application of giant nanosized porous POMs as
catalysts in organic transformations has been largely overlooked.[35]
Müller and co-workers, for the first time, reported the synthesis of a
saccharose,[4] H6P2W18O62Á18H2O,[5] poly(ethylene glycol)-grafted
N,N-dimethylaminopyridine-functionalized dicationic ionic liquid
[DMAP-PEG1000-DIL][BF4],[6] magnetic nanocatalyst γ-Fe2O3@HAp-
Si-(CH2)3-AMP,[7] Fe3O4@SiO2-imid-PMAn nanoparticles,[8] RuBr2
(PPh3)4,[9] NaCl,[10] crown ether complex cation ionic liquid,[11]
tetrabutylammonium bromide[12] and (NH4)2HPO4 or S-proline.[13]
While each of these methods has its own advantages, many suffer
from limitations such as prolonged reaction times, the use of rela-
tively expensive catalysts and unsatisfactory yields. Thus the discov-
ery of a new and efficient catalyst with high catalytic activity, short
reaction times, recyclability and simple reaction work-up for the
preparation of dihydropyrano[3,2-c]chromenes is of great interest.
Heterogeneous catalysis has been known for many years and has
become strategically vital for efficient and ecofriendly organic
transformations over the past few decades.[14–17] These catalysts
have many advantages over homogeneous catalysts involving sim-
ple work-up, ease of handling, recoverability and reusability.[18,19]
Catalysts of this type have the potential to make the processes in
which they are applied cleaner, safer, higher-yielding and relatively
inexpensive.[20–23]
Keplerate-type giant-ball nanoporous isopolyoxomolybdate which
VI
was formulated as (NH4)42[Mo MoV60O372(CH3COO)30(H2O)72] and
72
denoted as {Mo132}.[36] Recently, the application of {Mo132} as a cat-
alyst for a series of organic transformations has been reported by
our group. This new reusable catalyst performed well and showed
a high level of catalytic activity in the synthesis of 1,2,4,5-
tetrasubstituted imidazoles, 1,8-dioxooctahydroxanthenes, 1,8-
dioxodecahydroacridines and polyhydroquinolines.[37–39]
*
Correspondence to: Abolghasem Davoodnia, Department of Chemistry, Mashhad
Branch, Islamic Azad University, Mashhad, Iran. E-mail: adavoodnia@mshdiau.ac.
ir; adavoodnia@yahoo.com
Polyoxometalates (POMs) are a large class of metal oxide clusters
of early transition metals, typically W(VI), V(V), Mo(VI), Nb(V) and Ta
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad,
Iran
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

M. ROHANIYAN, A. DAVOODNIA AND A. NAKHAEI
Prompted by these facts and as part of our research on the
development of environmentally friendly methods for the synthesis
of organic compounds using reusable catalysts,[40–51] we report
here another application of {Mo132} as a catalyst in the synthesis
Table 1. Optimization of reaction conditions for synthesis of com-
a
pound 4c catalysed by {Mo132
}
Entry Catalyst (g) Solvent
Temp. (°C) Time (min) Isolated yield (%)
1
—
EtOH
H2O
Reflux
Reflux
r.t.
80
90
70
65
30
23
30
30
20
23
15
15
11
11
10
10
11
12
10
10
20
25
45
40
30
30
70
60
60
60
Trace
Trace
11
12
38
52
45
39
53
51
67
68
81
80
79
94
93
91
92
93
85
86
54
59
58
61
41
49
37
51
of
(4a–n)
2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles
via one-pot three-component reaction of
2
—
a
3
—
EtOH–H2O
EtOH–H2O
—
4-hydroxycoumarin, aldehydes and malononitrile (Scheme 1).
4
—
Reflux
110
5
0.07
0.07
0.03
0.03
0.04
0.04
0.05
0.05
0.06
0.06
0.06
0.07
0.07
0.07
0.08
0.08
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
6
—
130
Experimental
7
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH–H2O
EtOH
r.t.
Chemicals and apparatus
8
Reflux
r.t.
9
All chemicals were available commercially and used without addi-
tional purification. The catalyst was synthesized according to the
literature.[36] Melting points were recorded with a Stuart SMP3 melt-
ing point apparatus. Fourier transform infrared (FT-IR) spectra were
obtained using a Bruker Tensor 27 spectrophotometer as KBr discs.
1H NMR (300 and 400 MHz) spectra were recorded with Bruker 300
and 400 spectrometers.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Reflux
r.t.
Reflux
r.t.
50
Reflux
r.t.
50
General procedure for synthesis of dihydropyrano[3,2-c]
Reflux
r.t.
chromenes 4a–n catalysed by {Mo132
}
Reflux
r.t.
A mixture of 4-hydroxycoumarin (1; 1.0mmol), an aldehyde (2a–n;
1.0 mmol), malononitrile (3; 1.0mmol) and {Mo132} (0.07g) in a
mixture of EtOH–H2O (1:1, 2 ml) as solvent was stirred at room
temperature for the appropriate time. During the procedure, the
reaction was monitored using TLC (n-hexane–ethyl acetate, 3:1).
Upon completion of the transformation, the solvent was
evaporated in vacuo, and hot ethanol (2 ml) was added to the resi-
due. The catalyst was removed by filtration of the hot suspension
and washed with a small portion of hot ethanol (2× 2 ml). After
cooling, the combined filtrate was concentrated by half and
allowed to stand at room temperature. The precipitated solid was
collected by filtration, and recrystallized from ethanol to afford
compounds 4a–n in high yields.
EtOH
Reflux
r.t.
CH3OH
CH3OH
Reflux
r.t.
CH3OH–H2O
CH3OH–H2O Reflux
CH2Cl2
CH2Cl2
CHCl3
CHCl3
r.t.
Reflux
r.t.
Reflux
aReaction conditions: 4-hydroxycoumarin (1; 1 mmol), 4-
chlorobenzaldehyde (2c; 1 mmol) and malononitrile (3; 1 mmol).
Results and discussion
are necessary for the reaction. Table 1 indicates that under solvent-
free conditions and from among the solvents tested such as EtOH,
H2O, MeOH, CH2Cl2 and CHCl3 and using varying amounts of the
catalyst, the reaction proceeds more easily and affords the highest
yield when using 0.07 g of {Mo132} in a mixture of EtOH and H2O at
room temperature (entry 16). No improvement in yields or reaction
times is observed when using higher temperatures or higher
amount of the catalyst.
Under the optimized reaction conditions (0.07 g of {Mo132} in
EtOH–H2O at room temperature), we investigated the scope and
the limitations of the reaction employing a variety of aldehydes.
The results are summarized in Table 2. Obviously, the reaction is
practicable for various aromatic, heteroaromatic and aliphatic alde-
hydes. As evident, all reactions proceed very cleanly to give the cor-
responding dihydropyrano[3,2-c]chromenes 4a–n in high yields
over short reaction times. Melting points, TLC and 1H NMR spectro-
scopic data were used to establish that only one product is formed
in all cases with no undesirable side-products being present after
purification.
The {Mo132} catalyst was characterized using FT-IR and UV–visible
spectroscopies as reported in our previous work.[37] To begin our
study, the reaction of 1 (1.0 mmol), 4-chlorobenzaldehyde (2c;
1.0 mmol) and 3 (1.0mmol) was selected as the test reaction and
various reaction parameters were studied for the formation of
corresponding dihydropyrano[3,2-c]chromene 4c. Trace amounts
or low yields of the product 4c are obtained in the absence of the
catalyst in refluxing EtOH or H2O or in mixture of them at room
temperature or reflux conditions (Table 1, entries 1–4). Also, in the
presence of the catalyst under solvent-free conditions at high tem-
peratures only moderate yields of the product 4c are obtained
(entries 5 and 6). These results indicate that the catalyst and solvent
The ability to recycle and re-use {Mo132} was also studied. For this
purpose, after separation of the catalyst according to the procedure
outlined in the experimental section, the recovered catalyst was
washed with hot ethanol and subsequently dried at 60°C under
Scheme 1. Synthesis of dihydropyrano[3,2-c]chromenes catalysed by
{Mo132}.
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

VI
Another application of (NH4)42[Mo MoV60O372(CH3COO)30(H2O)72]
72
Table 2. {Mo132}-catalysed synthesis of dihydropyrano[3,2-c]
chromenes 4a–na
produce intermediates II and III, respectively. Finally, the products
4a–n are obtained from the latter intermediate after
tautomerization. On the basis of our previous reports,[37,38] it is rea-
sonable to assume that several accessible Mo sites and NH4 groups
in {Mo132} could act as Lewis acid and Brønsted acid centres, respec-
tively, and therefore promote the necessary reactions. The catalyst
would play a significant role in increasing the electrophilic character
of the electrophiles in the reaction.
Entry
R
Products Time Isolated
(min) yield
(%)
M.p. (°C)
Found Reported
1
C6H5
2-ClC6H4
4-ClC6H4
4-FC6H4
3-O2NC6H4
4-O2NC6H4
4-HOC6H4
4-MeOC6H4
2-Thienyl
3-Pyridyl
Me
4a
4b
4c
12
20
10
20
13
10
20
10
12
15
19
25
23
25
92
92
94
90
94
95
90
95
93
91
92
90
93
92
259–261 255–256[4]
266–268 267–269[8]
265–266 263–264[6]
260–261 262–263[6]
266–268 266–267[8]
253–255 252–254[8]
261–262 261–263[8]
243–245 244–246[8]
255–257 256–258[7]
254–256 257–259[11]
227–228 227–229[7]
238–240 239–241[7]
241–243 240–242[8]
251–253 251–253[8]
2
3
Conclusions
4
4d
4e
4f
5
We have found that {Mo132} can be used as a new, reusable and ef-
ficient catalyst for the preparation of a variety of dihydropyrano[3,2-
c]chromenes by one-pot three-component reaction of 4-
hydroxycoumarin, aldehydes and malononitrile. The reaction oc-
curs in ethanol–water at room temperature and furnishes the ex-
pected products in high yields over short reaction times. This
property combined with ease of recovery and catalyst reusability
makes this method an economic, benign and waste-free chemical
process for the synthesis of dihydropyrano[3,2-c]chromenes.
6
7
4 g
4 h
4i
8
9
10
11
12
13
14
4j
4 k
4 l
Et
n-Pr
4 m
4n
i-Pr
aReaction conditions: 4-hydroxycoumarin (1; 1 mmol), an aldehyde
(2a–n; 1 mmol), malononitrile (3; 1 mmol), {Mo132} (0.07 g), EtOH–
H2O (1:1, 2 ml), room temperature.
Acknowledgments/Acknowledgements according to UK/US
spelling of paper
The authors express their gratitude to the Islamic Azad University,
Mashhad Branch for its financial support.
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Appl. Organometal. Chem. (2016)
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sion of this article at the publisher’s web site.
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