Synthesis of pyran derivatives under ultrasound irradiation using Ni nanoparticles as reusable catalysts in aqueous medium

Article abstract of DOI:10.1016/j.crci.2013.05.012

Ni nanoparticles (NPs)-catalysed synthesis of pyran derivatives was achieved by one-pot three-component reactions of aryl aldehydes/ketone, malononitrile and C-H activated compounds in aqueous medium under ultrasound irradiation. The present approach offe

Full text of DOI:10.1016/j.crci.2013.05.012

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CRAS2C-3772; No. of Pages 7
C. R. Chimie xxx (2013) xxx–xxx
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Preliminary communication/Communication
Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium
a
b
a,
Mithu Saha , Babulal Das , Amarta Kumar Pal *
a
Department of Chemistry, North-Eastern Hill University, Mawlai Campus, Shillong 793022, India
b
Department of Chemistry, IIT, Guwahati, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Ni nanoparticles (NPs)-catalysed synthesis of pyran derivatives was achieved by one-pot
three-component reactions of aryl aldehydes/ketone, malononitrile and C–H activated
compounds in aqueous medium under ultrasound irradiation. The present approach offer
several advantages, such as shorter reaction time, higher yields, and environmental
friendliness.
Received 21 February 2013
Accepted after revision 23 May 2013
Available online xxx
Keywords:
ß 2013 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Ultrasonic irradiation
Nickel nanoparticles
4
-Hydroxy coumarin
Pyrazolone
Dimedone
Pyran
1
. Introduction
Metal nanoparticles (NPs) are important due to their
[9], Hantzsch condensation [10], etc. However, more
attention has been paid to nickel catalysts because nickel
is comparatively cheap and more environmentally
friendly. Green chemical reactions have become a promi-
nent issue in recent decades. Reactions in aqueous media
are considerably more safe, non-toxic, environmentally
friendly, and inexpensive. Organic reaction in water has
attracted a great deal of interest in both academic and
industrial research because of environmental concerns
[11].
Pyran derivatives are of considerable interest in
industry as well as in academia owing to their promising
biological and medicinal activity, such as analgesic, anti-
tumour, anti-cancer, anti-inflammatory properties and
also serve as potential inhibitors of human Chk1 kinase
(Fig. 1) [12]. Furthermore, they are also found in
applications as pharmaceutical ingredient and biological
agrochemicals [13].
remarkable properties and potential application in a
variety of areas, such as catalysis, sensors, electronics,
and optics [1]. The last decade has witnessed tremendous
growth in the field of nanoscience and nanotechnology.
The easy accessibility to nanoparticles has prompted
investigations on their application in catalysis. Several
reports showed a remarkable level of their performance as
catalysts in terms of selectivity, reactivity, and improved
yields of product [2]. Metal nanoparticles, such as nickel,
palladium, gold, platinum, etc. have properties that may
well markedly differ from those of their bulk metals [3].
Recently, it has been proved that Ni(0) nanoparticles as
catalysts offer great opportunities for a wide range of
applications in organic synthesis [4], such as Suzuki–
Miyaura cross-coupling [5], hydrogenation [6], oxidative
addition [7], Stille coupling [8], Knoevenagel condensation
Considerable effort has been made towards the synth-
esis of pyran annulated heterocyclic derivatives due to
their wide applications. Recently, a few methods have been
reported by using various catalysts [14–19]. Although
most of these processes offer distinct advantages, at the
*
Corresponding author.
E-mail address: amartya_pal22@yahoo.com (A.K. Pal).
1
631-0748/$ – see front matter ß 2013 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.05.012
Please cite this article in press as: Saha M, et al. Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium. C. R. Chimie (2013), http://dx.doi.org/10.1016/
j.crci.2013.05.012

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CRAS2C-3772; No. of Pages 7
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OH
2.3. General procedure for the synthesis of pyran derivatives
OH
A mixture of carbonyl compounds 1 (1 mmol), mal-
ononitrile 2 (1 mmol) and activated C–H compounds 3–5
(
1 mmol) was poured into a round-bottom flask; nickel
H C
3
CN
nanoparticles (10 mol%), water (2 mL) or water–ethanol
mixture (1:1) (2 mL) [in the case of 4-hydroxy coumarin 5]
were added to it and irradiated in ultrasound for a duration
as mentioned in Table 1. After completion (TLC), the
reaction mixture was cooled, filtered and the solvent was
removed under reduced pressure. The residue was
extracted with ethyl acetate (3 ꢁ 10 mL) and the combined
organic extract was washed with water (3 ꢁ 10 mL), brine
HN
N
O
NH2
Fig. 1. An inhibitor of human Chk 1 Kinase.
same time they suffer from certain drawbacks, such as
longer reaction time, unsatisfactory yields, high costs,
harsh reaction conditions, use of stoichiometric amounts
as well as of environmentally toxic catalysts, and also lack
of recyclability [20].
Ultrasound irradiation has been established as an
efficient technique in synthetic organic chemistry. The
ultrasonic irradiation with its advantages, i.e. convenient
operation, mild reaction conditions, short reaction time
and high efficiency, has become particularly popular in
recent times [21]. In order to enlarge the application of
ultrasound irradiation to the synthesis of heterocyclic
compounds, we wish to report a general, efficient and eco-
friendly procedure for the synthesis of pyran derivatives.
2 4
(10 mL), and dried over anhydrous Na SO . After removing
the solvent, the crude product was purified by column
chromatography over silica gel (60–120 mesh) using
hexane–ethyl acetate as an eluent to afford the pure
products.
2.4. Physical and spectroscopic data for the selected
compound
2.4.1. 4-Methyl benzaldehyde (6b)
ꢀ1
1
IR (KBr): 3475, 3326, 2196, 1656 cm
(CDCl + DMSO-d , 400 MHz): = 1.78 (s, 3H), 2.25 (s,
H), 4.50 (s, 1H), 6.22 (s, 2H), 7.35 (t, J = 7.8 Hz, 5H), 7.65 (d,
.
H NMR
3
6
d
3
1
3
2
. Experimental
J = 8.4 Hz, 4H).
= 12.4, 20.6, 36.6, 60.1, 98.1, 119.7, 120.2, 125.8, 127.3,
128.7, 128.8, 136.2, 137.3, 139.5, 143.6, 145.6, 158.9. ESI–
3 6
C NMR (CDCl + DMSO-d , 100 MHz):
d
2
.1. Materials and methods
+
18 4
MS m/z 343 [M + H] . Anal calcd for C21H N O: C, 73.67; H,
The melting points were determined in open capillaries
5.30; N, 16.36. Found: C, 73.75; H, 5.36; N, 16.48 (Table 1,
entry 2).
and uncorrected. IR spectra were recorded with
a
PerkinElmer Spectrum BX FT-IR apparatus (ymax in
ꢀ
1
1
13
cm ) on KBr disks. H NMR and C NMR (400 MHz and
00 MHz, respectively) spectra were recorded on a Bruker
Avance II-400 spectrometer in CDCl and DMSO- d6
chemical shifts in with TMS as the internal standard).
2.4.2. 2-Chloro benzaldehyde (7k)
ꢀ
1 1
1
IR (KBr): 3317, 2380, 2183, 1659, 1593 cm
(CDCl , 400 MHz): = 8.31(d, J = 8.4 Hz, 1H), 7.76 (d,
. H NMR
3
3
d
(
d
J = 8.0 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.51 (t, J = 7.6 Hz,
1H), 7.42 (t, J = 7.4 Hz, 1H), 7.33 (t, J = 7.8 Hz, 1H), 7.17 (t,
J = 7.2 Hz, 1H), 5.19 (s, 1H), 4.46 (s, 2H), 2.50–2.39 (m, 2H),
Mass spectra were recorded on Waters ZQ-2695. Trans-
mission electron microscope (TEM) spectra were recorded
with a JEOL JSM 100CX device. Scanning electron micro-
scope (SEM) measurements were recorded with a JEOL
JSM-6360. XRD spectra were recorded with a Bruker D8
XRD instrument SWAX. CHN were recorded using a
PerkinElmer 2400, Series II, CHN-OS analyser. Silica gel
G (E-mark, India) was used for TLC. Hexane refers to the
fraction boiling between 60 8C and 80 8C. The ultrasonica-
tion reaction was carried out in JAC 1500 (made in Korea).
2.18–2.07 (m, 2H), 1.05 (s, 3H), 0.99 (s, 3H). ESI–MS m/z
+
345 [M + H] . Anal calcd for C22
H
20
N
2
O
2
: C, 76.72; H, 5.85;
N, 8.13. Found: C, 76.64; H, 5.91; N, 7.96 (Table 1, entry 20).
2.4.3. 4-Nitro benzaldehyde (8c)
ꢀ
1
1
IR (KBr): 3476, 2196, 1719, 1613 cm
(CDCl + DMSO-d , 400 MHz): = 8.07–7.23 (m, 8H), 4.60
(s, 1H), 3.11 (brs, 2H). NMR (CDCl + DMSO-d
00 MHz): = 164.9, 163.3, 159.1, 157.3, 154.7, 151.7,
137.8, 133.7, 129.5, 128.5, 127.7, 123.6, 121.4, 117.7, 107.9,
.
H NMR
3
6
d
C
1
3
3
6
,
1
d
2
.2. X-ray crystallography
+
6
C
2.5, 41.9. ESI–MS m/z 362 [M + H] . Anal calcd for:
: C, 63.16; H, 3.07; N, 11.63. Found: C, 62.87; H,
The X-ray diffraction data were collected at 296 K using
˚
19 11 3 5
H N O
the Mo K
a
radiation (
l
= 0.71073 A) using a Bruker Nonius
2.93; N, 11.54 (Table 1, entry 24).
SMART APEX II CCD diffractometer equipped with a
graphite monochromator. SMART software was used for
data collection and also for indexing the reflections and
determining the unit cell parameters; the collected data
were integrated using SAINT software. The structures were
solved by direct methods and refined by full-matrix least-
squares calculations using SHELXTL software. All non-H
atoms were refined using the anisotropic approximation
3. Result and discussion
As part of our continued activities in this area [22], we
are reporting for the first time a simple and efficient
method for the synthesis of pyran derivatives by a one-pot
multi-component reaction, involving C–H activated com-
pounds, (3–5), malononitrile (2), aryl aldehydes, using
novel and reusable Ni nanoparticles in water under
(CCDC 836545).
Please cite this article in press as: Saha M, et al. Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium. C. R. Chimie (2013), http://dx.doi.org/10.1016/
j.crci.2013.05.012

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3
Table 1
Synthesis of pyran derivatives under ultrasonic irradiation in water.
a
Entry
Ar (1)
Product
Molecular formula of product
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
Benzaldehyde
6a
6b
6c
6d
6e
6f
C H
20
C H
21
C H
20
C H
20
C H
20
C H
20
C H
21
C H
20
C H
20
C H
18
C H
19
C H
19
C H
18
C H
18
C H
18
C H
20
C H
18
C H
19
C H
18
C H
22
C H
19
C H
19
C H
20
C H
19
C H
20
C H
20
C H
20
16
N
N
4
O
O
7
14
11
10
12
14
5
90
88
87
89
90
87
85
88
87
86
83
88
85
90
86
88
91
88
90
87
89
89
86
87
86
87
88
4-Methyl benzaldehyde
4-Fluoro benzaldehyde
4-Nitro benzaldehyde
4-Bromo benzaldehyde
4-Chloro benzaldehyde
4-Cyano benzaldehyde
3-Nitro benzaldehyde
2-Chloro benzaldehyde
Benzaldehyde
18
4
15 FN
15
15 BrN
15ClN
4
O
N
5
O
3
4
O
4
O
6g
6h
6i
15
N
N
5
O
15
5
O
3
10
12
10
15
15
14
5
15 ClN
4
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
7a
7b
7c
7d
7e
7f
18
N
20
N
20
N
2
2
2
O
O
O
2
2
4-Methyl benzaldehyde
4-Methoxybenzaldehyde
4-Fluoro benzaldehyde
4-Nitro benzaldehyde
4-Bromo benzaldehyde
N, N-dimethylaminobenzaldehyde
4-Chloro benzaldehyde
4-Cyano benzaldehyde
2-Chloro benzaldehyde
1-Napthaldehyde
3
17FN
17
17BrN
23
17ClN
17
17ClN
2
O
2
N
3
O
4
2
O
2
5
7g
7h
7i
N
3
O
2
14
15
15
10
12
10
13
14
10
15
6
2 2
O
N
3
O
2
7j
2 2
O
7k
7l
20
N
17
N
12
N
14
N
11
N
14
N
11
N
11
N
2
3
2
2
3
2
3
3
O
O
O
O
O
O
O
O
2
3
3
3
5
4
3
4
Isatin
Benzaldehyde
8a
8b
8c
8d
8e
8f
4-Methyl benzaldehyde
4-Nitro benzaldehyde
4-Methoxybenzaldehyde
4-Cyano benzaldehyde
Isatin
10
a
Isolated yields.
ultrasound irradiation. We started this synthesis by
examining the reaction of pyrazolone (1 mmol), maloni-
trile (1 mmol) and benzaldehyde (1 mmol) in the presence
of nickel nanoparticles in water under ultrasonic irradia-
tion. The formation of the compound was confirmed by
spectral data. IR spectra of compound 6b showed absorp-
were subsequently used and the results are reported in
Table 1. From these results, we could conclude that the
whole reaction proceeds smoothly to afford the corre-
sponding products in satisfactory yield. Aromatic alde-
hydes carrying electron-donating or electron-withdrawing
substituents showed similar reaction behaviour and
reacted efficiently to yield the desired products.
ꢀ1
tion peaks at 3475, 3326 cm , which are due to the NH
ꢀ
1
stretching of the NH
2
group; the peak at 2196 cm
Nickel nanoparticles were prepared by the reduction of
1
corresponds to CN stretching. In the H NMR spectrum, the
two methyl groups present in pyrazolone and in the
nickel chloride hexahydrate (NiCl
2
ꢂ6H
2
O) with hydrazine
hydride in an oil micro-emulsion of water/CTAB (cetyl-
trimethyl ammonium bromide)/1-pentanol at 80 8C for 2 h.
CTAB is used as a stabilizer and hydrazine hydrate as a
benzene ring appeared as a singlet at
respectively. The CH (methine proton) was observed as a
singlet at 4.50, while two protons corresponding to NH
appear as a singlet at 6.22. The nine aromatic protons
appeared at 7.35 and 7.65. The structures of all the
d 1.78 and 2.25,
d
2
d
d
d
compounds were confirmed from spectroscopic data and
found to be comparable in all respect with those of an
authentic sample. We have investigated the effect of
different ultrasonic irradiations, such as low-, medium-
and high-frequency ones, at different temperatures on this
reaction (Fig. 2). From Fig. 2, it is evident that the
maximum yield was obtained by using a higher irradiation
level at 70 8C. To find out the effect of ultrasound
irradiation on this reaction, the model reaction was
performed under the same conditions in the absence of
ultrasound irradiation. It was observed that the reaction
time increased and that product yield decreased consider-
ably. Thus, ultrasounds have a beneficial effect on the
synthesis of pyran derivatives.
To investigate the advantages and limitations of our
methodology, other aldehydes having electron-donating
or electron-withdrawing substituents in the aromatic ring
Fig. 2. Optimization of the reaction conditions. Reagents and conditions:
pyrazolone (1 mmol), malononitrile (1 mmol), benzaldehyde (1 mmol),
Ni NPs (l0 mol%), water (2 mL), ultrasound irradiation.
Please cite this article in press as: Saha M, et al. Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium. C. R. Chimie (2013), http://dx.doi.org/10.1016/
j.crci.2013.05.012

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2
1
1
0000
5000
0000
Ni [1,1,1]
Ni [2.0,0]
5
000
0
Ni [2,2,2]
Fig. 3. TEM image of nickel nanoparticles (a) before use (b) after reuse
(four times).
4
0
50
60
70
80
reducing agent. In this work, the Ni nanoparticles were
prepared from the reported micro-emulsion method [23].
The reduction reaction could be expressed as:
Fig. 5. Powder XRD pattern with characteristic dihedral angels at 44.788,
52.208 and 76.688 corresponding to Ni(0) nanoparticles.
Ni2 þ N
þ
H
4
þ 4HOꢀ ! 2Ni þ N
2
2
2
2
þ 4H O
The growth of Ni nanoparticles was completed after 2 h.
Notable improvement was achieved by using 6 and 8 mol%
of catalyst, but the best result was obtained when we used
10 mol% of the catalyst. Further increase in the catalyst
concentration did not improve the yield (Fig. 7). We also
carried out the reaction without any catalyst, but the
desired product was obtained in poor yields (28%).
To further expand the scope of the present method, we
investigated this one-pot reaction involving dimedone 4
and 4-hydroxy coumarin 5. To our delight, under the above
optimized conditions, the reactions proceeded smoothly
and a variety of the desired pyran derivatives were
obtained in good yields (Scheme 1 and Table 1). This
protocol could be applied to the aryl aldehydes with either
electron-withdrawing groups or electron-donating groups.
As it can be seen from Table 1, the electronic effect of the
substituted benzaldehyde has an insignificant impact on
the conversion. The reaction was also carried out with 1, 2-
diketone (isatin) and the product was obtained in good
yields. The feasibility of employing aliphatic aldehydes
instead of aryl aldehydes in the reaction was also
investigated. Unfortunately, aliphatic aldehydes could
not afford the expected product: the starting material
remained as such.
The particle size and structure of the resultant Ni
nanoparticles have been characterized by transmission
electron microscopy (TEM) (Fig. 3), scanning electron
microscopy (SEM) (Fig. 4), and X-ray diffraction (XRD)
(
Fig. 5) analysis. XRD analysis further supported this result.
o
o
Three peaks for Ni nanoparticles at 2
u
= 44.78 , 52.20 ,
o
7
6.68 , correspond to the (111), (200), (220) lattice planes,
so that the resultant particles are pure elemental Ni
nanoparticles with a face-centred cubic (FCC) structure. No
obvious peak of nickel oxide or hydroxide was detected.
The result is in complete agreement with the reported data
24].
Our attention moved onto investigating the effect of
solvent on the product yield. The reaction was carried out
in various solvents, like water, DCM, THF, acetonitrile, and
toluene. Significant improvement was achieved in DCM
and acetonitrile, but the best result was observed when we
used water as a reaction medium (Fig. 6). In case of 4-
hydroxy coumarin, the reaction was sluggish; this may be
due to the insolubility of 4-hydroxy coumarin in water. In
order to increase the solubility, we have used a 1:1 water–
ethanol mixture.
[
We have studied the effect of the catalyst concentration
on the model reaction. We have varied the concentration of
catalyst from 2 to 10 mol%. The result revealed that when
the reaction was carried out in the presence of 2 and
4
mol% of catalyst, it gave lower yields of the product.
Fig. 6. Effect of solvent on the rate of the reaction and the yield of the
product. Reagent and condition: pyrazolone (1 mmol), malononitrile
(1 mmol), benzaldehyde (1 mmol), Ni NPs (l0 mol%), ultrasound
irradiation, solvent (2 mL).
Fig. 4. SEM image of nickel nanoparticles (a) before use (b) after reuse
four times).
(
Please cite this article in press as: Saha M, et al. Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium. C. R. Chimie (2013), http://dx.doi.org/10.1016/
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5
100
9
0
0
0
0
0
0
0
0
0
8
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
mol %
Fig. 7. Effect of catalyst loading on the reaction yield.
H C
3
N
N
O
Ar
Ph
H C
3
CN
3
N
N
Ph
O
6
NH2
O
4
O
Ar
N
N
))))))
CN
C
C
O
Ultrasonication
Ar-CHO +
O
7
NH2
H O, Ni NPs
2
Or
O
2
OH
NH2
CN
Ar
O
O
N
H
O
O
5
1
O
8
O
Scheme 1.
Furthermore, a crystal of 8b was obtained by careful
recrystallization from a solution of DMF, and the structure
was unambiguously confirmed by X-ray crystallography.
Fig. 8 shows the ORTEP diagram of compound 8b with
probability ellipsoids representation (30%).
methine carbon of 10 is activated by nanoparticles and it
reacts with the C–H-activated compound in a Michael
fashion, giving intermediate 11. Intermediate 11 under-
goes intramolecular cyclization followed by tautomeriza-
tion, affording the pyran derivatives 6.
A plausible mechanism for the reaction is depicted in
Scheme 2. Nickel nanoparticles increase the electrophili-
city of carbonyl carbon of C–H activated compounds as
well as of aryl aldehydes. First, aryl aldehydes and
malononitrile formed the Knoevenagel product 9. The
For practical application of this heterogeneous system,
recovery and reusability of the catalyst were very
important factors. It was observed that, in our present
work, Ni nanoparticles could be recycled and reused for
another four consecutive runs without any noticeable
Please cite this article in press as: Saha M, et al. Synthesis of pyran derivatives under ultrasound irradiation using Ni
nanoparticles as reusable catalysts in aqueous medium. C. R. Chimie (2013), http://dx.doi.org/10.1016/
j.crci.2013.05.012

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change of the product yield. The recovered Ni NPs were
analysed by TEM and SEM imaging (Figs. 3b and 4b). It was
observed that the catalyst could be used up to four runs
without any loss of efficiency. After four runs, the reactivity
decreases, possibly due to the agglomeration of nanopar-
ticles on each exposure. After each run, the reaction
mixture was centrifuged at 4000 rpm for 3 min and
filtered. The residue was washed with deionized water
and dried. The recovered nanoparticles were used again for
another set of reactions (Fig. 9).
4. Conclusion
A novel and efficient three-component condensation
reaction of aryl aldehydes, malononitrile and C–H-acti-
vated compounds has been developed for the synthesis of
pyran annulated heterocycles. In general, improvements in
the rates and product yields are observed when the
reaction is carried out in the presence of Ni NPs under
ultrasonication; the catalyst can be reused up to four
successive runs without any noticeable change in the
product yield.
Fig. 8. Showing the ORTEP diagram of 8b with ellipsoids presented at the 30%
probability level; hydrogen atoms are removed for clarity (CCDC 836545).
Acknowledgements
We thank the Department of Chemistry, Sophisticated
Analytical and Instrumentation Facility (SAIF) of North-
Eastern Hill University and IIT (Guwahati). We acknowl-
edge the financial support from DST-SERB (sanctioned No.:
SERC/F/0293/2012-13). We are also thankful to Dr S. Mitra
and DST-PURSE.
Appendix A. Supplementary data
1
13
Supplementary data (Characterization (IR, H and
C
NMR spectroscopic data and elemental analysis) for the
compound are reported in Table 1 [entries 1–27]) associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.crci.2013.05.012.
Scheme 2. Plausible reaction mechanism.
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j.crci.2013.05.012

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j.crci.2013.05.012