Highly efficient synthesis of benzopyranopyridines via ZrP 2O 7 nanoparticles catalyzed multicomponent reactions of salicylaldehydes with malononitrile and thiols

Article abstract of DOI:10.1080/17415993.2014.913291

ZrP₂O₇ nanoparticles as an efficient catalyst have been used for the preparation of benzopyrano[2,3-b]pyridines from the four-component condensation reaction of salicylalde-hydes, thiols, and 2 equiv. of malononitrile under reflux co

Full text of DOI:10.1080/17415993.2014.913291

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Highly efficient synthesis of
benzopyranopyridines via
ZrP2O7 nanoparticles catalyzed
multicomponent reactions of
salicylaldehydes with malononitrile and
thiols
Javad Safaei-Ghomia, Marzieh Kiania, Abolfazl Ziaratia & Hossein
Shahbazi-Alavia
a Department of Organic Chemistry, Faculty of Chemistry,
University of Kashan, 51167 Kashan, I. R. Iran
Published online: 07 May 2014.
To cite this article: Javad Safaei-Ghomi, Marzieh Kiani, Abolfazl Ziarati & Hossein Shahbazi-
Alavi (2014) Highly efficient synthesis of benzopyranopyridines via ZrP2O7 nanoparticles catalyzed
multicomponent reactions of salicylaldehydes with malononitrile and thiols, Journal of Sulfur
Chemistry, 35:4, 450-457, DOI: 10.1080/17415993.2014.913291
To link to this article: http://dx.doi.org/10.1080/17415993.2014.913291
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Journal of Sulfur Chemistry, 2014
Vol. 35, No. 4, 450–457, http://dx.doi.org/10.1080/17415993.2014.913291
Highly efficient synthesis of benzopyranopyridines via ZrP2O7
nanoparticles catalyzed multicomponent reactions of
salicylaldehydes with malononitrile and thiols
Javad Safaei-Ghomi∗, Marzieh Kiani, Abolfazl Ziarati and Hossein Shahbazi-Alavi
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, 51167 Kashan, I. R. Iran
(Received 8 November 2013; accepted 5 April 2014)
ZrP2O7 nanoparticles as an efficient catalyst have been used for the preparation of benzopyrano[2,3-
b]pyridines from the four-component condensation reaction of salicylalde-hydes, thiols, and 2 equiv. of
malononitrile under reflux conditions in ethanol in excellent yields and short reaction times.
SR2
NH2
R1
R
1
CHO
OH
CN
CN
CN
ZrP2O7
2
+
R2SH
+
reflux, ethanol
O
N
NH2
Keywords: ZrP2O7 nanoparticles; salicylaldehydes; benzopyrano[2,3-b]pyridine; one-pot; heterocycles
1. Introduction
Benzopyranopyridines are fused heterocyclic compounds that exhibit anti-bacterial,[1,2] anti-
proliferative,[3] anti-myopic,[4] anti-rheumatic,[5] anti-asthmatic,[6] and cancer chemopreven-
tive [7] activities. Several compounds derived from libraries were identified as inhibitors of
mitogen-activated protein kinase-activated protein kinase 2 and attenuated the production of proin-
flammatory TNFα,[8] and histamine-stimulated gastric acid secretion in animals.[9] Some other
examples of benzopyranopyridine derivatives such as amlexanox and pranoprofen have been
reported as anti-allergic and potent NSAIDs, respectively. Therefore, the development of sim-
ple methods for the synthesis of benzopyranopyridines is of major interest to modern synthetic
organic chemists. In recent years, multicomponent reactions have been extensively utilized to
produce heterocyclic compounds with biological activity. Multicomponent reactions are highly
flexible, convergent, fruitful and atom-efficient processes of high exploratory power that mini-
mize solvent consumption and maximize atom efficiency.[10–17] Multicomponent reactions are
usually designed for the development of environmentally benign synthetic methods. Hence, they
are useful from a green chemistry viewpoint.[18,19] A few catalysts such as K2CO3,[20] Et3N
∗Corresponding author. Email: safaei@kashanu.ac.ir
© 2014 Taylor & Francis

Journal of Sulfur Chemistry 451
[21] and chitosan [22] have been used for the synthesis of benzopyranopyridine derivatives,
but all these methods require a long duration and high temperature. Heterogeneous catalysts have
emerged as economically viable due to their unique catalytic properties [23–25] and nanoparticles
(NPs) as heterogeneous catalysts have received considerable attention in green chemistry. Metal
pyrophosphates are heavily studied materials due to their utility in a variety of applications.[26,27]
For example, zirconium pyrophosphate (ZrP2O7) NPs were used as an excellent catalyst in many
organic reactions.A simple separation and purification process in organic reactions is an advantage
of heterogeneous catalytic systems. Due to their high surface-to-volume ratio, which can carry a
high payload of catalytically active species, NPs show very high catalytic activity and chemical
selectivity under mild conditions.[28–36] Neat processes utilizing eco-friendly and green cat-
alysts that can be simply recycled at the end of reactions has received remarkable attention in
recent years. We report herein a simple and facile procedure for the synthesis of benzopyrano[2,3-
b]pyridines through one-pot three-component reaction of salicylaldehydes, thiols and 2 equiv. of
malononitrile catalyzed by ZrP2O7 NPs under reflux conditions in ethanol (Scheme 1).
SR2
NH2
R1
R1
CHO
CN
CN
CN
ZrP2O7
2
+
R2SH
+
reflux, ethanol
OH
O
N
NH2
Scheme 1. Synthesis of benzopyranopyridines via ZrP2O7 NPs catalyzed multicomponent
reactions of salicylaldehydes with malononitrile and thiols.
2. Results and discussion
The morphology and particle size of ZrP2O7 NPs was investigated by scanning electron
microscopy (SEM) as shown in Figure 1. The SEM image shows particles with diameters in
the range of nanometers. The X-ray diffraction (XRD) pattern of the ZrP2O7 NPs is shown in
Figure 1. SEM images of ZrP2O7 NPs.

452 J. Safaei-Ghomi et al.
Figure 2. The XRD pattern of ZrP2O7 NPs.
Figure 3. TEM image of ZrP2O7 NPs.
Figure 2. The average NP size was estimated from the full-width half-maximum of the peaks
with use of the Debye–Sherrer equation. The results show that ZrP2O7 NPs were obtained with
an average diameter of 11 nm as confirmed by the XRD analysis.
Characterization of nano ZrP2O7 showed the same particle size by transmission electron
microscopy (TEM) (Figure 3).
In order to achieve optimum conditions, we initially investigated the reaction of salicylaldehy-
des, thiols and 2 equiv. of malononitrile in the presence of different catalysts such as DBU, ZnCl2,
FeCl3, morpholine and ZrP2O7 NPs under different conditions (Table 1). Next, we optimized the
required amount of ZrP2O7 NPs; the optimum amount was found to be 5 mol%.
The reaction works well for salicylaldehyde and 5-bromo-2-hydroxybenzaldehyde and different
thiols. All the reactions reached completion within 40–55 min to afford good yields of products.
These products precipitate from refluxing ethanolic solutions and are isolated by easy filtration.
The yields of recrystallized benzopyranopyridines are given in Table 2.
2.1. Proposed mechanism
A plausible mechanism for the preparation of benzopyranopyridines using ZrP2O7 NPs is shown
in Scheme 2.

Journal of Sulfur Chemistry 453
Table 1. Optimization of reaction condition using different catalystsa.
Entry
Catalyst
DBU
ZnCl2
FeCl3
Morpholine
ZrP2O7 NPs
ZrP2O7 NPs
ZrP2O7 NPs
Mol (%)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
30
10
10
10
2
200
100
100
90
50
50
40
18
30
55
80
90
90
5
8
50
aReaction conditions: salicyladehyde (1.5 mmol), malononitrile (3 mmol) and benzenethiol (1.5 mmol).
bIsolated yields.
Table 2. Synthesis of benzopyranopyridine derivatives using ZrP2O7 NPsa.
Entry
R1
R2
Product
Time (min)
Yieldb
m.p. (◦C)
Lit. m.p. (◦C)
1
2
3
4
5
6
7
8
H
H
H
H
Br
Br
Br
Br
Ar
4-Me-Ar
Ar-CH2
2-furyl-methyl
Ar
4-Me-Ar
Ar-CH2
1a
2a
3a
4a
1b
2b
3b
4b
42
47
55
48
40
46
57
46
90
87
82
85
91
88
83
87
221–223
222–224
210–212
230–234
215–217
213–215
206–208
225–227
(220–222)[19]
(223–225)[19]
–
–
–
–
–
–
2-furyl-methyl
aAll the reactions were carried out under reflux conditions in ethanol.
bIsolated yields.
ZrP2O7
O
ZrP2O7
CN
NH
H
CN
+
O
CN
OH
ZrP2O7
R2SH
SR2 NH2
SR2
O
CN
CN
CN
CN
+
O
N
NH2
NH2
ZrP2O7
Scheme 2. Proposed reaction pathway for the synthesis of benzopyranopyridines by ZrP2O7
NPs.
3. Conclusions
In this research, ZrP2O7 NPs were used for mild preparation of benzopyranopyridine derivatives
under reflux conditions in ethanol for the first time. The advantages offered by this method are
satisfactory yields of products using a green and recyclable nanocatalyst, easy workup, short
reaction time and mild reaction conditions.

454 J. Safaei-Ghomi et al.
4. Experimental
All organic materials were purchased commercially from Sigma-Aldrich and Merck and were
used without further purification. All melting points are uncorrected and were determined in a
capillary tube on a Boetius melting point microscope. FT-IR spectra were recorded with KBr
pellets using a Magna-IR, spectrometer 550 Nicolet. NMR spectra were recorded on a Bruker
400 MHz spectrometer with DMSO as solvent and TMS as an internal standard. Powder XRD
was carried out on a Philips diffractometer of X’pert Company. Microscopic morphology of the
products was visualized by SEM (LEO 1455VP). TEM images were obtained on a Philips EM208
TEM with an accelerating voltage of 100 kV.
4.1. Preparation of ZrP2O7 NPs
The catalyst was prepared via a sonochemical method (worked at 20 kHz frequency and 80W
powers) using ZrOCl2 as the zirconium source. The stoichiometric amount of ZrOCl2/8H2O
was first added to 20 mL of distilled water and dissolved with the aid of sonication. Then, H3PO4
(85%) was added dropwise in 20 min and the mixture was sonicated until the precipitation of solids
was finished. When the reaction was completed, a dispersed white precipitate was obtained. The
solid was filtered and washed with distilled water and ethanol several times. Subsequently, the
catalyst was dried at 100◦C for 8 h and calcined at 500◦C for 1 h to obtain pure nano zirconium
pyrophosphate.
4.2. General procedure for the preparation of benzopyranopyridines
To a mixture of a selected salicylaldehyde (1.5 mmol), malononitrile (3 mmol) and a desired thiol
(1.5 mmol) in 5 mL of anhydrous ethanol was added ZrP2O7 NPs (5 mol%) in 2 mL ethanol at
room temperature. The resulting mixture was refluxed for 40–50 min and then allowed to cool to
room temperature. The formed precipitate was isolated by filtration. The product was dissolved
in DMF (3 mL) and the catalyst was filtered. Then, 4 mL water was added to the filtrate which
resulted in the crystallization of the product. The resulting crystalline structure was filtered and
dried with a vacuum pump. The structures of the products were fully established on the basis of
their 1H NMR, 13C NMR and FT-IR spectra.
4.3. 2,4-Diamino-5-phenylsulfanyl-5H-chromeno[2,3-b]pyridine-3-carbonitrile (1a)
Yellow solid, IR (KBr) (vmax/cm−1): 3355, 3429, 2203, 1400–1623; 1H NMR (400 MHz, DMSO-
d6): δ = 5.73(s, 1H), 6.50 (2H, s), 6.74–6.78(3H, m), 6.94 (s, 2H), 7.05–7.11(3H, m), 7.15–
7.30 (m, 3H); 13C NMR (100 MHz, DMSO-d6): δ = 160.9, 159.7, 156.4, 150.9, 137.7, 134.2,
129.7,129.5, 129.2, 128.64, 128.60, 123.9, 121.5, 116.5, 116.01, 86.90, 70.8, 43.12. Anal. calcd
for C19H14N4OS: C 65.88, H 4.074, N 16.17. Found C 65. 82, H 4.09, N 16.07.MS (EI) (m/z):
346 (M+).
4.4. 2,4-Diamino-5-(4-methylphenylsulfanyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile
(2a)
Yellow solid, IR (KBr) (vmax/cm−1): 3457, 3349, 2198, 1400–1623. 1H NMR (400 MHz, DMSO-
d6): δ = 2.19 (s, 3H), 5.66 (s, 1H), 6.46 (br s, 2H), 6.61 (d, J = 7.9 Hz, 2H), 6.79 (d, J = 7.9 Hz,
1H), 6.90 (m, 4H), 7.11; (d, J = 6.8 Hz, 1H), 7.19 (d, J = 7.3 Hz, 2H).13C NMR (100 MHz,
DMSO-d6): δ = 160.25, 160.08, 156.3, 151.33, 138.3, 136.9, 129.8, 128.6, 128.2, 127.0, 123.6,

Journal of Sulfur Chemistry 455
121.8, 116.4, 115.7, 86.3, 70.8, 43.11, 21.2. Anal. calcd for C20H16N4OS: C 66.64, H 4.47, N
15.54. Found C 66. 59, H 4.51, N 15.48.MS (EI) (m/z): 360 (M+).
4.5. 2,4-Diamino-5(benzylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile(3a)
Yellow solid, IR (KBr) (vmax/cm−1): 3377, 3439, 2200, 1400, 1605; 1H NMR (400 MHz, DMSO-
d6): δ = 3.49 (ABq, 2H, J = 12 Hz), 5.48 (1H), 6.55 (bs, 2H), 6.83 (bs, 2H), 7.03–7.21 (m, 7H),
7.33 (m, 2H); 13C NMR (100 MHz, DMSO-d6): δ = 160.2, 159.9, 152.9, 143.7, 136.6, 133.3,
133.2, 129.6, 129.4, 124.3, 124.2,122.8, 119.3, 118.3, 117.6, 87.01, 70.90, 44.01, 37.02. Anal.
calcd for C20H16N4OS: C 66.64, H 4.47, N 15.54. Found C 66. 48, H 4.58, N 15.39.MS (EI)
(m/z): 360 (M+).
4.6. 5-((Furan-2-yl) methylthio)-2,4-diamino-5H-chromeno[2,3-b]pyridine-3-carbonitrile
(4a)
Yellow solid, IR (KBr) (vmax/cm−1): 3386, 3440, 2203, 1397, 1612;1H NMR (400 MHz, DMSO-
d6): δ = 3.51 (ABq, 2H, J = 12 Hz), 5.46(1H), 5.99 (1H), 6.23 (s, 1H), 6.55 (bs, 2H), 6.79 (bs,
2H), 7.10(d, 1H, J = 8 Hz), 7.17 (t, 1H, J = 8 Hz), 7.24(s, 1H), 7.31(t, 2H, J = 8 Hz); 13C NMR
(100 MHz, DMSO-d6): δ = 160.10, 160.3, 157.1, 151.2, 149.4, 142.7, 133.8, 129.7, 129.0, 116.9,
116.5, 111.0, 107.8, 87.9, 71.0, 35.03, 25.9. Anal. calcd for C18H14N4O2S: C 61.70, H 4.03, N
15.99. Found C 61.62, H 4.10, N 15.91. MS (EI) (m/z): 350(M+).
4.7. 2,4-Diamino-5-(benzylthio)-7-bromo-5H-chromeno[2,3-b]pyridine-3-carbonitrile (3b)
Yellow solid, IR (KBr) (vmax/cm−1): 3315, 3441, 2189, 1403, 1653; 1H NMR (400 MHz, DMSO-
d6) δ = 4.06–4.45 (ABq, 2H, J = 12 Hz), 4.67 (1H), 6.48 (s, 1H), 6.88–6.90 (m, 5H), 7.37 (m,6H);
13C NMR (100 MHz, DMSO-d6) δ = 160.80, 160.44, 152.75, 148.22, 137.96, 137.53, 131.05,
129.79, 128.60, 124.41,121.60, 120.90, 118.79, 116.46, 87.22, 35.78, 35.4, 33.34. Anal. calcd
for C20H15N4OSBr: C 54.68, H 3.44, N 12.75. Found C 54.55, H 3.52, N 12.61. MS (EI) (m/z):
439(M+).
4.8. 5-((Furan-2-yl)methylthio)-2,4-diamino-7-bromo-5H-chromeno[2,3-b]pyridine-3-
carbonitrile (4b)
Yellow solid, IR (KBr) (vmax/cm−1):3311, 3442, 2194, 1404, 1655;1H NMR (400 MHz, DMSO-
d6) δ = 4.14–4.56 (ABq, 2H, J = 12 Hz), 4.89 (1H), 6.34 (s, 1H), 6.46 (d, J = 8.3 Hz,1H),
6.78–6.95 (m, 6H), 7.39 (d, 1H, J = 9 Hz), 7.62 (d, 1H);13C NMR (100 MHz, DMSO-d6) δ =
160.5, 155.24, 150.72, 148.21, 143.26, 131.89, 131.12, 125.50, 124.14, 119.41, 118.87, 116.50,
111.49, 108.77, 84.86, 54.27, 36.31, 28.64. Anal. calcd for C18H13N4O2SBr: C 50.39, H 3.05, N
13.06. Found C 50.35, H 2.97, N 13.01.MS (EI) (m/z): 429 (M+).
4.9. Catalyst recovery
In the recycling procedure of ZrP2O7 NPs, DMF was added to dilute the reaction mixture after
terminating the reaction. The catalyst was insoluble in the solvent and was separated by simple
filtration. The recovered ZrP2O7 NPs was washed with ethanol and dried at 70◦C for 2 h. The
separated catalyst was used several times with a slightly decreased activity as given in Table 3.

456 J. Safaei-Ghomi et al.
Table 3. Recycling of ZrP2O7 NPs as catalyst.
Recycle
1
2
3
4
5
Yield (%)
94
92
90
88
85
Funding
The authors are grateful to University of Kashan for supporting this work [grant number 159196/IV].
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