A facile solvent-free route for one-pot multicomponent synthesis of benzylpyrazolyl coumarins derivatives in presence of effective synergetic catalytic system

Article abstract of DOI:10.14233/ajchem.2019.21986

A combinatorial library of benzylpyrazolyl coumarin derivatives have been synthesized by a green one-pot four-component reaction between aryl hydrazine/hydrazine hydrate (1), ethyl acetoacetate (2), aromatic aldehydes (3) and 4-hydroxycoumarin (4) catalyz

Full text of DOI:10.14233/ajchem.2019.21986

Asian Journal of Chemistry; Vol. 31, No. 6 (2019), 1357-1361
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.21986
A Facile Solvent-Free Route for One-Pot Multicomponent Synthesis of Benzylpyrazolyl
Coumarins Derivatives in Presence of Effective Synergetic Catalytic System
2
NARENDRA R. KAMBLE1,* and VINOD T. KAMBLE
1Department of Chemistry, PDEA’s Waghire College, Saswad-412301, India
2Organic Chemistry Research Laboratory, Department of Chemistry, Institute of Sciences, Nagpur-440008, India
*Corresponding author: E-mail: narendra1499@gmail.com
Received: 7 February 2019;
Accepted: 11 March 2019;
Published online: 29 April 2019;
AJC-19380
A combinatorial library of benzylpyrazolyl coumarin derivatives have been synthesized by a green one-pot four-component reaction
between aryl hydrazine/hydrazine hydrate (1), ethyl acetoacetate (2), aromatic aldehydes (3) and 4-hydroxycoumarin (4) catalyzed by
niobium pentachloride with silver salt under solvent-free conditions has been developed. Experimental simplicity, simple work-up procedure
and solvent-free reaction condition at room temperature are important features of the present protocol.
Keywords: Niobium pentachloride, Silver salt, Benzylpyrazolyl coumarin.
phenprocoumon, coumatetralyl, carbochromen, bromadialone,
offering antibacterial, anti-HIV [9], antiviral [10], anticoagulant
[11], antioxidant [12] and anticancer activities [13]. Moreover,
pyrazolones are regarded as important structural nuclei in many
drugs such as convenient antipyretic and analgesic drugs [14],
whereas edaravone (MCI-186) has been useful for curing brain
[15,16] and myocardial ischemia [17]. In addition, pyrazolones
have kinase inhibitory effects, particularly in the case of
enzymes which catalyze both phosphorylation of serine and
threonine in proteins. They are also used for treating diseases
related to these enzymes, such as rheumatoid arthritis, psoriasis,
bone loss, cancer and other proliferative diseases including
antifungal [18], antimycobacterial [19,20], antibacterial [21],
anti-inflammatory [22], antitumor [23], gastric secretion stimu-
latory [24], antidepressant [25], antifilarial activities [26] and
antitubercular activities [27].
In the present work, a novel route was used for the synthe-
sis of benzylpyrazolyl coumarins (5) with high yields by one
pot four component condensation reaction of hydrazine (1),
ethyl acetoacetate (2), aromatic aldehyde (3) and 4-hydroxy-
coumarin (4) reacted in the presence of a mixture of NbCl5
andAgClO4 as Lewis acid and a combined catalyst under room
temperature and stirring conditions, in short reaction time and
environmentally benign.
INTRODUCTION
Recently, green chemistry has received more attention due
to its great applications and approaches that aim to prevent
pollution and reduce the use of the waste materials that affect
the human health and environment. Therefore, a number of
chemists focused on designing of methodologies to create
chemical protects without toxicity to human health. In this
sense, a green chemistry focuses mainly on chemical syntheses
using novel synthetic methods that provide affordable protects
and services to the human and society [1-5]. To enhance chemical
processes and environment friendly protects, the chemists work-
ing in green chemistry carry out multicomponent reactions
that offer great advantages in the green chemistry, in which
various flow one-pot transformations occur in the same step
to offer the product without a need to segregate or isolate any
compounds produced in the intermediate steps [6-8].
The important synthesized compounds by multicomponent
reactions were these derivatives containing coumarins and
pyrazolone nucleus. 3-Substituted 4-hydroxycoumarin, espe-
cially 3-benzyl substituted 4-hydroxycoumarin derivatives that
are of extreme significance because they exist abundantly in
natural products and exhibit a wide range of biological acti-
vities as they are used in medicinal scaffolds, namely warfarin,
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1358 Kamble et al.
Asian J. Chem.
one (5e): Yield: 93 %, white crystalline solid, m.p.: 225-227
ºC, IR (KBr, νmax, cm–1): 3064, 1651, 1602, 1492, 1177, 1095,
752. 1H NMR (400 MHz, DMSO) δ ppm: 2.44 (s, 3H), 5.72
(s, 1H), 7.17-7.24 (m, 8H), 7.34-7.50 (m, 3H), 7.58-7.91 (m, 3H).
LC-MS (ESI) m/z [M+ + H] = 461.1. C26H19N2O4Cl ([M+H])
458.1, found: 458.8. Elemental analysis calcd. (found) %: C
68.55 (68.07), H 4.57 (4.20); N 6.20 (6.13).
4-((4-Fluorophenyl)(4-hydroxy-2-oxo-2H-chromen-3-
yl)methyl)-1,2dihydro-5-methyl-2-phenylpyrazol-3-one
(5f): Yield: 93 %, white crystalline solid, m.p.: 240-242 ºC,
IR (KBr, νmax, cm–1): 3081, 1656, 1607, 1566, 1499, 1187, 1040,
754. 1H NMR (400 MHz, DMSO) δ ppm: 2.36 (s, 3H), 5.70
(s, 1H), 6.80-6.86 (m, 2H), 7.09-7.19 (m, 5H), 7.31-7.42 (m, 3H),
7.57-7.60 (d, J = 8.1 Hz, 2H), 7.76-7.79 (m, 1H), 12.03 (bs, 1H).
LC-MS (ESI) m/z [M++H] = 442.1. C26H19N2O4F ([M+H])
442.6, found: 442.1. Elemental analysis calcd. (found) %: C
70.58 (70.61), H 4.33 (4.35) and N 6.33 (6.36).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(4-hydroxyphenyl)methyl)-5-methyl-2-phenyl-1H-pyrazol-
3(2H)-3-one (5g):Yield: 88 %, white cream solid, m.p.: 220-
222 ºC, IR (KBr, νmax, cm–1): 3501, 1656, 1607, 1566, 1499,
1187, 1040, 754. 1H NMR (400 MHz, DMSO) δ ppm: 2.36 (s,
3H), 5.70 (s, 1H), 6.80-6.86 (m, 2H), 7.09-7.19 (m, 5H), 7.31-
7.42 (m, 3H), 7.57-7.60 (d, J = 8.1 Hz, 2H), 7.76-7.79 (m, 1H),
12.03 (bs, 1H). LC-MS (ESI) m/z [M++H] = 442.1. C26H20N2O5
([M+H]) 440.9, found: 441.1; Elemental analysis calcd. (found)
%: C 70.18 (70.61); H 4.03 (4.35); N 6.83 (6.36).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(3-hydroxyphenyl)methyl)-5-methyl-2-phenyl-1H-pyrazol-
3(2H)-3-one (5h):Yield: 82 %, white solid, m.p.: 260-264 ºC,
IR (KBr, νmax, cm–1): 3581, 1626, 1637, 1566, 1419, 1187, 1040,
754. 1H NMR (400 MHz, DMSO) δ ppm: 2.36 (s, 3H), 5.70
(s, 1H), 6.80-6.86 (m, 2H), 7.09-7.19 (m, 5H), 7.31-7.42 (m, 3H),
7.57-7.60 (d, J = 8.1 Hz, 2H), 7.76-7.79 (m, 1H), 12.03 (bs,
1H). LC-MS (ESI) m/z [M++H] = 442.1. C26H20N2O5 ([M+H])
440.9, found: 491.1; Elemental analysis calcd. (found) %: C
71.18 (70.61); H 4.63 (4.35); N 6.03 (6.36).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(4-methoxyphenyl)methyl)-5-methyl- 2phenyl-1H-pyrazol-
3(2H)-3-one (5i): Yield: 85 %, yellow crystalline solid, m.p.
199-202 ºC, IR (KBr, νmax, cm-1): 2989, 1693, 1614, 1566,
1512, 1450, 1151, 1021, 756. 1H NMR (400 MHz, DMSO) δ:
2.38 (s, 3H), 3.99 (s, 3H), 4.22 (s, 1H), 6.57-6.59 (m, 3H),
7.14-7.19 (m, 5H), 7.31-7.43(m, 3H), 7.51-7.55 (d, J = 8.1 Hz,
2H), 7.78-7.80 (d, J = 7.8 Hz, 1H) ppm, LC-MS (ESI) m/z
[M+H] = 419.1; C27H22N2O4 ([M+H]) 454.1, found: 454.1.
Elemental analysis calcd. (found) %: C 71.85 (71.38); H 4.18
(4.91); N 6.06 (6.18).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(2,3-dimethoxyphenyl)methyl)-5-methyl-2-phenylpyrazol-
3-one (5j): Yield: 89 %, pale yellow crystalline solid, m.p.:
223-225 ºC, IR (KBr, νmax, cm–1): 2934, 1666, 1613, 1477,
1277, 1181, 1071, 753. 1H NMR (400 MHz, DMSO) δ ppm:
2.35 (s, 3H), 3.53 (s, 3H), 3.69 (s, 3H), 5.82 (s, 1H), 6.73-
7.02 (m, 3H), 7.14-7.38 (m, 6H), 7.61 (bs, 2H), 7.74-7.76 (d, J
= 7.8 Hz, 2H). LC-MS (ESI) m/z [M++ H] = 484.1; C28H24N2O6
([M+H] = 484.1, found: 484.3. Elemental analysis calcd. (found)
%: C 69.41 (69.44); H 4.99 (5.03); N 5.78 (5.80).
EXPERIMENTAL
General procedures for the synthesis of benzylpyrazolyl
coumarin derivatives: In a mixture of 5 mol of ethanol and
5 mL of water, phenyl hydrazine (1 mmol), ethyl acetoacetate
(1 mmol), aromatic aldehyde (1 mmol) and 4-hydroxycoumarin
(1 mmol), 1 mol % of NbCl5 and 3 mol % ofAgClO4 were dis-
solved and stirred at room temperature. After completing the
reaction monitor by thin-layer chromatography, the reaction
mixture was left to be cooled at room temperature. Then, the
reaction mixture was poured into cold water and the crystalline
product was filtered. After that, the product was washed by
water for 2-3 times and, then, dried at the room temperature
and recrystallized from hot ethanol to afford the corresponding
benzylpyrazolyl coumarin derivatives. To recover the catalyst
from the filtrate, the aqueous layer was evaporated under reduced
pressure to yield the final product.All the products were charac-
terized by IR, 1H NMR and mass spectra.
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)
(phenyl) methyl)-5-methyl-2phenyl-1H- pyrazol-3(2H)-3-
one (5a): Yield: 80 %, white crystalline solid, m.p.: 230-232
ºC, IR (KBr, νmax, cm–1): 3062, 2803, 1764, 1720, 1668, 1450,
1174, 1028,750. 1H NMR (400 MHz, DMSO) δ ppm: 1.75 (s,
1H), 2.21 (s, 3H), 5.74 (s, 1H), 7.73-7.80 (m, 4H), 7.18-7.35 (m,
5H), 5.74-7.69 (m, 5H). LC-MS (ESI) m/z [M++H] = 388.1.
C26H20N2O4 ([M+H]) 424.1, found: 424.1. Elemental analysis
calcd. (found) %: C 73.17 (73.15); H 4.25 (4.42); N 6.00 (6.22).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(4-nitrophenyl)methyl)-5-methyl-2-phenylpyrazol-3-one
(5b): Yield: 92 %, pale yellow crystalline solid, m.p.: 248-
250 ºC, IR (KBr, νmax, cm–1): 3073, 1649, 1608, 1560, 1525,
1178, 1039, 748. 1H NMR (400 MHz, DMSO) δ ppm: 2.65 (s,
3H), 6.12 (s, 1H), 7.46-7.78 (m, 9H), 7.94-8.97 (m, 5H). LC-MS
(ESI) m/z [M++H] = 469. C26H19N3O6 ([M+H]) 469.6, found:
469.1. Elemental analysis calcd. (found) %: C 66.02 (66.55);
H 4.28 (4.11); N 8.25 (8.94).
1.2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(3-nitrophenyl)methyl)-5methyl-2-phenyl-1H-pyrazol-3-
(2H)-3-one (5c): Yield: 90 %, yellow crystalline solid, m.p.:
200-202 ºC, IR (KBr, νmax, cm–1): 2918, 1764, 1681, 1521, 1458,
1173, 1043, 756. 1H NMR (400 MHz, DMSO) δ ppm: 2.20 (s,
3H), 5.79 (s, 1H), 7.05-7.07 (m, 4H), 7.11- 7.20 (m, 2H), 7.24-
7.31 (m, 2H), 7.41-7.49 (m, 2H), 7.82-7.89 (m, 2H). LC-MS
(ESI) m/z [M++H] = 434.1. C26H19N3O6 ([M+H]) 469.1, found:
469.8. Elemental analysis calcd. (found) %: C 66.12 (66.33);
H 4.20 (4.00); N 8.95 (8.96).
1,2-Dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)-
(p-tolyl)methyl)-5-methyl-2 phenylpyrazol-3-one (5d):
Yield: 92%, white crystalline solid, m.p. 222-224 ºC, IR (KBr,
ν
max, cm–1): 3081, 1649, 1610, 1494, 1184, 1031, 752. 1H NMR
(400 MHz, DMSO) δ ppm: 2.18 (s, 3H), 2.34 (s, 3H), 5.68 (s,
1H), 6.92-7.19 (m, 7H), 7.31-7.41 (m, 4H), 7.58-7.61 (d, J =
7.8 Hz, 2H), 7.75-7.78 (m, 1H). LC-MS (ESI) m/z [M++H] =
438.1. C27H22N2O4 ([M+H]) 438.5, found: 438.1. Elemental
analysis calcd. (found) %: C 73.06 (73.99); H 5.86 (5.07); N
6.39 (6.42).
4-((4-Chlorophenyl)(4-hydroxy-2-oxo-2H-chromen-3-
yl)(phenyl)methyl)-5-methyl-2phenyl-1H-pyrazol-3(2H)-3-

Vol. 31, No. 6 (2019)
Synthesis of Benzylpyrazolyl Coumarins Derivatives in Presence of Effective Synergetic Catalytic System 1359
TABLE-1
RESULTS AND DISCUSSION
OPTIMIZATION OF THE AMOUNT OF NbCl5 AND ADDITIVE
FOR BENZYLPYRAZOLYL COUMARIN DERIVATIVES
As a part of the current ongoing studies devoted to the
development of practical, safe and environmentally friendly
procedures for synthesizing several important biologically
active organic compounds, a simple and highly efficient route
was used for the synthesis of benzylpyrazolyl coumarins as
shown in Scheme-I.
First, to recognize the optimization of the reaction condi-
tions, phenyl hydrazine (1.0 mmol), ethyl acetoacetate (1.0
mmol), 3-nitrobenzaldehyde (1.0 mmol) and 4-hydroxycou-
marin (1.0 mmol) were, carrying out the reaction without using
any catalyst. Table-1 shows that the reaction completed in a
long period of time (300 min) and it was very sluggish and the
yield of product was very low (10 %) (Table-1, entry 1). Secondly,
for examining and finding out the ideal amounts of the catalysts
NbCl5 and AgClO4, added to the reaction, the reaction was
carried out several times in each which specific amounts of
NbCl5 and AgClO4 were added. Table-1 shows that the best
amounts were 1 mol % of NbCl5 and 3 mol % of AgClO4; the
reaction completed in the shortest period of time (30 min) and
the yield of the product was excellent (90 %) (entry 6).
NbCl5
(mol %)
Additive
(mol %)
Time
(min)
Entry
Yield (%)
1
2
3
4
5
6
7
8
No catalyst No catalyst
300
300
300
100
150
30
10
40
25
70
58
90
88
88
1
–
5
–
1
3
5
–
1
–
5
3
3
5
30
30
Moreover, the efficiency of current method was evalu-
ated by utilizing an extensive variety of aromatic aldehydes
whenever electron withdrawing and electron donating groups
for synthesis of the corresponding benzyl pyrazolyl coumarin
derivatives. The reaction successes efficiently provided exce-
llent yields and tolerated many electron-withdrawing and electron-
donating substituted benzaldehydes (Table-2, entries 1-10).
Finally, we examined the advantage of our catalyst in
synthesis of benzyl pyrazolyl coumarin derivatives used in
OH Ar
O
OH
O
O
NbCl5 + additive
N R
ArCHO
C6H5NHNH2
N
r.t., stirring
O
O
O
O
OEt
H
1
3
4
5a-j
2
Scheme-I
TABLE-2
SUBSTRATES SCOPE OF BENZYLPYRAZOLYL COMPOUND
Entry
Hydrazines
Aldehydes
Products
Time (min)
Yield (%)
CHO
H
N
OH
O
O
N
N
H
NH2
1
30
93
O
5a
NO2
CHO
NO2
H
N
OH
O
NH2
2
35
92
O
N
N
H
O
O
5b
NO2
O
CHO
H
N
OH
O
NH2
3
40
90
N
N
H
NO2
5c

1360 Kamble et al.
Asian J. Chem.
CH3
CHO
H
N
OH
O
NH2
O
N
4
45
88
CH3
N
O
5d
H
Cl
CHO
H
N
OH
O
NH2
5
35
93
O
N
N
H
Cl
O
F
5e
CHO
H
N
OH
O
O
N
NH2
6
40
90
F
N
O
H
5f
OH
CHO
H
N
OH
O
NH2
O
N
N
H
7
8
9
50
60
45
88
85
88
OH
O
5g
5h
OH
CHO
H
N
OH
O
O
NH2
N
N
H
OH
O
OCH3
CHO
H
N
OH
O
NH2
O
N
OCH3
N
O
5i
H
OCH3
OCH3
O
CHO
H
N
OH
O
NH2
10
50
85
OCH3
OCH3
N
N
H
O
5j
the present work to comparison with other results reported in
the literature review to show the advantages of our catalyst
under room temperature condition. the reactants; phenyl hydra-
zine (1.0 mmol), ethyl acetoacetate (1.0 mmol), benzaldehyde
(1.0 mmol) and 4-hydroxycoumarin (1.0 mmol) and 1 mol %
of NbCl5 and 3 mol % ofAgClO4 as catalysts using solvent free
condition comparing with different catalysts as Alg(ACOH)
[28] and Ca(OTf)2 [29] under reflux conditions. After compa-

Vol. 31, No. 6 (2019)
Synthesis of Benzylpyrazolyl Coumarins Derivatives in Presence of Effective Synergetic Catalytic System 1361
14. M. Himly, B. Jahn-Schmid, K. Pittertschatscher, B. Bohle, K. Grubmayr,
ring the combined acid catalyst under various conditions (room
temp., reflux) with these catalysts, it was found that the combined
acid catalyst under neat condition was the best catalyst for
synthesis 1,2-dihydro-4-((4-hydroxy-2-oxo-2H-chromen-3-yl)
(phenyl) methyl)-5-methyl-2-phenyl 1H-pyrazol-3(2H)-one
with respect to the reaction time and the product yield.
F. Ferreira, H. Ebner and C.J. Ebner, Allergy Clin. Immunol., 111, 882
(2003);
https://doi.org/10.1067/mai.2003.163.
15. T. Watanabe, S. Yuki, M. Egawa and H. Nishi, J. Pharmacol. Exp.
Ther., 268, 1597 (1994).
16. H. Kawai, H. Nakai, M. Suga, S. Yuki, T. Watanabe and K.I. Saito, J.
Pharmacol. Exp. Ther., 281, 921 (1997).
17. T.W. Wu, L.H. Zeng, J. Wu and K.P. Fung, Life Sci., 71, 2249 (2002);
https://doi.org/10.1016/S0024-3205(02)01965-3.
18. M.A. Al-Haiza, S.A. El-Assiery and G.H. Sayed, Acta Pharm., 51,
251 (2001).
19. D. Castagnolo, F. Manetti, M. Radi, B. Bechi, M. Pagano, A. De Logu,
R. Meleddu, M. Saddi and M. Botta, Bioorg. Med. Chem., 17, 5716
(2009);
https://doi.org/10.1016/j.bmc.2009.05.058.
20. M. Radi, V. Bernardo, B. Bechi, D. Castagnolo, M. Pagano and M. Botta,
Tetrahedron Lett., 50, 6572 (2009);
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
REFERENCES
1. A. Domling, Chem. Rev., 106, 17 (2006);
https://doi.org/10.1021/cr0505728.
2. J. Zhu and H. Bienayme, Multicomponent Reaction, Wiley-VCH:
Weinheim (2005).
3. D.J. Ramón and M. Yus, Angew. Chem. Int. Ed., 44, 1602 (2005);
https://doi.org/10.1002/anie.200460548.
4. A. Chanda and V.V. Fokin, Chem. Rev., 109, 725 (2009);
https://doi.org/10.1021/cr800448q.
5. M.C. Pirrung and K.D. Sarma, J. Am. Chem. Soc., 126, 444 (2004);
https://doi.org/10.1021/ja038583a.
6. C.-J. Li, Chem. Rev., 93, 2023 (1993);
https://doi.org/10.1021/cr00022a004.
7. C.-J. Li, Chem. Rev., 105, 3095 (2005);
https://doi.org/10.1021/cr030009u.
8. K. Tanaka and F. Toda, Chem. Rev., 100, 1025 (2000);
https://doi.org/10.1021/cr940089p.
9. S. Hesse and G. Kirsch, Tetrahedron Lett., 43, 1213 (2002);
https://doi.org/10.1016/S0040-4039(01)02373-5.
10. B.H. Lee, M.F. Clothier, F.E. Dutton, G.A. Conder and S.S. Johnson,
Bioorg. Med. Chem. Lett., 8, 3317 (1998);
https://doi.org/10.1016/S0960-894X(98)00588-5.
11. J.-C. Jung,Y.-J. Jung and O.-S. Park, Synth. Commun., 31, 1195 (2001);
https://doi.org/10.1081/SCC-100104003.
12. G. Melagraki, A. Afantitis, O. Igglessi-Markopoulou, A. Detsi, M.
Koufaki, C. Kontogiorgis and D.J. Hadjipavlou-Litina, Eur. J. Med.
Chem., 44, 3020 (2009);
https://doi.org/10.1016/j.ejmech.2008.12.027.
13. J.-C. Jung, J.-H. Lee, S. Oh, J.-G. Lee and O.-S. Park, Bioorg. Med.
Chem. Lett., 14, 5527 (2004);
https://doi.org/10.1016/j.tetlet.2009.09.047.
21. F. Moreau, N. Desroy, J.M. Genevard, V. Vongsouthi, V. Gerusz, G. Le
Fralliec, C. Oliveira, S. Floquet, A. Denis, S. Escaich, M. Busemann, K.
Wolf andA.Aschenbrenner, Bioorg. Med. Chem. Lett., 18, 4022 (2008);
https://doi.org/10.1016/j.bmcl.2008.05.117.
22. F.A. Pasha, M. Muddassar, M.M. Neaz and S.J. Cho, J. Mol. Graph.
Model., 28, 54 (2009);
https://doi.org/10.1016/j.jmgm.2009.04.006.
23. C.E. Rosiere and M.I. Grossman, Science, 113, 651 (1951);
https://doi.org/10.1126/science.113.2945.651.
24. D.M. Bailey, P.E. Hansen, A.G. Hlavac, E.R. Baizman, J. Pearl, A.F.
Defelice and M.E. Feigenson, J. Med. Chem., 28, 256 (1985);
https://doi.org/10.1021/jm00380a020.
25. P.M.S. Chauhan, S. Singh and R.K. Chatterjee, Indian J. Chem., 32B,
858 (1993).
26. P. Gunasekaran, S. Perumal, P. Yogeeswari and D. Sriram, Eur. J. Med.
Chem., 46, 4530 (2011);
https://doi.org/10.1016/j.ejmech.2011.07.029.
27. P.P. Ghosh, G. Pal, S. Paul andA.R. Das, Green Chem., 14, 2691 (2012);
https://doi.org/10.1039/c2gc36021g.
28. S.Yaragorla,A. Pareek and R. Dada, Tetrahedron Lett., 56, 4770 (2015);
https://doi.org/10.1016/j.tetlet.2015.06.049.
29. R.K. Pardeshi, S.A. Jadhav, M.G. Shioorkar, A.P. Sarkate and D.B.
Shinde, Chem. Mater. Res., 7, 105 (2015).
https://doi.org/10.1016/j.bmcl.2004.09.009.