Use of transesterified 1,3-diketoesters in the synthesis of trisubstituted pyrazoles and their biological screening

Article abstract of DOI:10.4314/bcse.v27i1.9

Starting from 2-acetylbenzofuran derivatives 1a-d, methyl/ethyl 4-substituted/unsubstituted benzofuran-2-yl)-2,4-dioxobutanoate 2a-d and 3a-d have been synthesized by Claisen's condensation reaction with diethyloxalate. The transesterified product, 1,3-diketoester 2a-d on condensation with phenyl hydrazine undergo cyclization to afford the corresponding methyl 5-(substituted/unsubstituted benzofuran-2-yl)-1-phenyl- 1H-pyrazole-3- carboxylate 4a-d, which upon further condensation with hydrazine hydrate yielded 5- (substituted/unsubstituted benzofuran-2-yl)-1-phenyl-1H-pyrazole-3- carbohydrazide 5a-d. The structures of the newly synthesized compounds 2a-d, 3a-d, 4a-d and 5a-d were characterized by their elemental analysis and spectral studies such as IR, ¹H NMR, ¹³C NMR and MS. All the synthesized compounds were screened for their antimicrobial activity. Most of the synthesized compounds showed high sensitivity against the selected bacteria and fungi at various concentrations.

Full text of DOI:10.4314/bcse.v27i1.9

Bull. Chem. Soc. Ethiop. 2013, 27(1), 85-94.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v27i1.9
ISSN 1011-3924
 2013 Chemical Society of Ethiopia
USE OF TRANSESTERIFIED 1,3-DIKETOESTERS IN THE SYNTHESIS OF
TRISUBSTITUTED PYRAZOLES AND THEIR BIOLOGICAL SCREENING
Naqui-Jahan Siddiqui1*, Mohammad Idrees1, Niraj T. Khati2 and Madhukar G. Dhonde3
1Department of Chemistry, Government Science College, Gadchiroli – 442 605 (M.S.), India
2Department of Applied Chemistry, Priyadarshini Engineering College, Nagpur (M.S.), India
3Department of Chemistry, Shri Mathuradas Mohata College of Science, Nagpur (M.S.), India
(Received May 14, 2012; revised November 15, 2012)
ABSTRACT. Starting from 2-acetylbenzofuran derivatives 1a-d, methyl/ethyl 4-substituted/unsubstituted
benzofuran-2-yl)-2,4-dioxobutanoate 2a-d and 3a-d have been synthesized by Claisen’s condensation reaction
with diethyloxalate. The transesterified product, 1,3-diketoester 2a-d on condensation with phenyl hydrazine
undergo cyclization to afford the corresponding methyl 5-(substituted/unsubstituted benzofuran-2-yl)-1-phenyl-
1H-pyrazole-3-carboxylate 4a-d, which upon further condensation with hydrazine hydrate yielded 5-
(substituted/unsubstituted benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide 5a-d. The structures of the
newly synthesized compounds 2a-d, 3a-d, 4a-d and 5a-d were characterized by their elemental analysis and
1
spectral studies such as IR, H NMR, 13C NMR and MS. All the synthesized compounds were screened for their
antimicrobial activity. Most of the synthesized compounds showed high sensitivity against the selected bacteria
and fungi at various concentrations.
KEY WORDS: 2,4-Dioxobutanoate, Prazole-3-carboxylate, Pyrazole-3-carbohydrazide
INTRODUCTION
As 1,3-diketoester derivatives have been found very reactive towards organic reagent such as
hydrazine hydrate, phenyl hydrazine, semicarbazide hydrochloride, hydroxyl amine
hydrochloride and hence utilized for the synthesis of substituted pyrazole derivatives[1-3].
Pyrazoles are important class of nitrogen containing five membered heterocyclic compounds.
Compounds with pyrazole ring are of interest due to their broad spectrum of biological activities
like antibacterial [4, 5], antiameobic [6], fungicidal [7, 8], antidiuretic [9], anticancer [10],
potent antidiabetic agent [11], anti-inflammatory [12], antidepressant [13], and antiviral [14].
Moreover N-phenyl pyrazole derivatives play an important role in antitumor screening [15] as
well as potent antimicrobial activity [16, 17]. Some substituted pyrazoles also exhibits cyclo-
oxygenes-2-(Cox2) selective inhibitors [18, 19]. Literature survey indicated that the hydrazone
group plays an important role for the antimicrobial activity. A number of hydrazide-hydrazone
derivatives also have been claimed to possess interesting bioactivity such as antibacterial-
antifungal [20, 21], anti-inflammatory [22], antimalarial [23], anticonvulsant [24],
antituberculosis [25, 26], and anticancer [27] activities. So a few pyrazole carbohydrazide
hydrazone derivatives have also been reported, which have been synthesized by many methods
[28-30]. Encouraged by the importance of pyrazole rings in various pharmacological lead
molecules we thought of incorporating this moiety to our base material for research. As a part
of our continuing interest in heterocyclic chemistry we turned our attention with the aim to
synthesize and evaluate the antimicrobial activities of different trisubstituted pyrazole
derivatives derived from methyl 4-(substituted/unsubstituted benzofuran-2-yl)-2,4-
dioxobutanoate as a stating material.
__________
*Corresponding author. E-mail: naquiphd.2010@gmail.com

86
Naqui-Jahan Siddiqui et al.
RESULTS AND DISCUSSION
The synthesis of the novel compounds 2a-d, 3a-d, 4a-d and 5a-d is described in reaction
scheme. At every stage the purity of the compounds were monitored by TLC technique. The
identities of the newly synthesized compound have been established on the basis of their
1
elemental analysis and spectral data such as IR, H NMR, 13C NMR and mass spectral studies.
All the obtained products were screened for their antimicrobial activities.
R
Reaction Scheme
2
OH
R1
( CH3CO)2O
CH3COONa
OCOCH3
R2
R2
OH
O
OH
O
R
2
H
anhy.AlCl3
R1
CH3
R1
R1
K2CO3
Dry acetone
K2CO3/Dry acetone
R
ClCH2COCH3
R1
ClCH2COCH3
CH3
O
R2
O
1a ....d
DMF
Diethyl Oxalate
Diethyl Oxalate
NaOEt
R
MeONa
Transesterification
R
R1
R1
MeOH/H+
EtOH/H+
O
O
O
OEt
O
OMe
R2
R2
O
O
O
O
3a....d
2a....d
CH3COOH
PhNHNH2
R1
R
O
NH2-NH2.H2O
EtOH
R1
R
NH2
O
NH
O
R2
N
N
OMe
O
R2
N
N
Ph
Ph
5a....d
4a....d
R
H
H
R1
R2
R
R1
H
R2
H
2a
2b
2c
2d
3a
3b
3c
3d
H
H
H
H
Cl
H
H
H
Cl
4a
4b
4c
4d
5a
5b
5c
5d
H
Br
Cl
Cl
H
H
Br
Cl
Cl
H
H
CH3
CH3
CH3
H
H
CH3
H
Cl
H
H
Br
Cl
Cl
H
Br
Cl
Cl
H
CH3
CH3
CH3
CH3
H
Cl
Bull. Chem. Soc. Ethiop. 2013, 27(1)

Use of transesterified 1,3-diketoesters in the synthesis of trisubstituted pyrazoles
87
The syntheses of the key intermediates 2-acetyl substituted/unsubstituted benzofuran 1a-d
were prepared in quantitative yields according to the reference method [31]. The reaction of 1a-
d with diethyl oxalate in presence of sodium methoxide solution as a base and DMF as solvent
afforded 2a-d via transesterification, while the same reaction with sodium ethoxide furnished
1
3a-d. The H NMR and IR spectra of 2a-d exhibited characteristic band of enolic group due to
keto-enol tautomerism of reactive methylene group which was also confirmed by the test with
alcoholic FeCl3 which gave wine red colouration. The IR spectrum of methyl 4-(benzofuran-2-
yl)-2,4-dioxobutanoate 2a showed the –OH stretch of enol form at 3475 cm-1 and C=O
1
stretching in ester group at 1759 cm-1. The H NMR spectrum showed singlet signal at δ 14.24
ppm for one proton of –OH group, confirms the enolic form, singlet signal at δ 3.95 ppm due
to OCH3 confirms the methyl ester and multiplet signals at δ 7.20-7.71 ppm for five aromatic
protons and singlet at δ 7.10 ppm confirms one proton due to the vinylic =CH. The chemical
shift value of the methoxy carbon in 13C NMR is observed at δ 53 ppm (-OCH3), the carbon
atoms connected to methoxy group are observed at the δ 156-167 ppm range, signal δ 167 ppm
is due to C1 carbon in C=O of the ester group whereas C4 carbon in C=O group under the
influence of strong electronegative environment appears downfield at δ 181 ppm, the aromatic
carbons were observed in expected region. The mass spectrum [32] of this product reveals a
molecular ion at m/z 247 [M+H]+ and 269 [M+Na]+ is in consistent with the molecular formula
C13H10O5.
The IR spectra of ethyl 4-[5-chloro-3-methylbenzofuran-2-yl)-2,4-dioxobutanoate 3c
showed –OH stretch at 3632 cm-1 and C=O stretching in ester group at 1724 cm-1, respectively.
1
The H NMR spectrum showed singlet signal at δ 14.79 ppm due to one proton confirms the –
OH group in the enolic form of -OHC=CH- due to keto-enol tautomerism, triplet signal at δ
1.41-1.44 ppm for two proton of -CH2 group, quartet signal at δ 4.38-4.44 ppm confirms
-OCH2CH3 the ethyl ester and multiplet signals at δ 7.26-7.52 ppm for three aromatic protons
and singlet at δ 7.11 ppm confirms one proton due to the vinylic =CH of OHC=CH-. The
chemical shift values of the ethoxy carbons in 13C NMR spectrum is observed at δ 14 ppm
(-OCH2CH3) and 62 ppm (-OCH2CH3), the carbon atoms connected to ethoxy group are
observed at the δ 152-167 ppm range, C4 carbon in C=O group appears at δ 183 ppm while
signal at δ 167 ppm is due to C1 of C=O carbon of the ester group. The molecular ion peak at
m/z 309 M+, 331 [(M +Na)+, 35Cl], 333 [(M+Na)+ ,37Cl]; is in agreement with the molecular
formula C15H13O5Cl.
2a-d on reaction with phenyl hydrazine gave corresponding 4a-d. The IR spectra of methyl
5-(benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate 4a showed absorption band in the
region 1734 cm-1 due to C=O stretching in ester group. The characteristic band at 1618 cm-1
shows strong C=N stretching bands. This is in evidence with the ring closure of pyrazole ring.
1
The H NMR spectrum showed singlet signal at δ 3.97 ppm due to three proton confirms the
–COOCH3 group in the ester, multiplet at δ 7.17-7.54 ppm for ten aromatic proton and one
singlet signals at δ 6.22 ppm for one proton of pyrazole ring. 13C NMR spectrum shows that the
five membered heterocycle pyrazole is formed via cyclization and its signal is characteristically
influenced by the phenyl substituent. The C3 atom of pyrazole is found to resonate at about δ
145 ppm while C5 atom at δ 154 ppm, signal at δ 162 ppm is due to the C=O carbon atom of
ester and methoxy carbon (-OCH3) gives signal at δ 53 ppm. Similarly the mass spectra reveals a
molecular ion peak at m/z 319 [M+H]+ and 341 [M+Na]+ is same as the molecular formula
C19H14O3N2.
Formulation of the reaction product designed as 4a-d, was based upon the comparative
reactivity of two carbonyl groups in 2a-d. The C2 carbonyl group being more reactive than C4
carbonyl group [1], it gets preferably attacked by the nucleophilic reagent such as phenyl
hydrazine to give corresponding hydrazone intermediate which simultaneously undergo ring
Bull. Chem. Soc. Ethiop. 2013, 27(1)

88
Naqui-Jahan Siddiqui et al.
closure with elimination of water molecule from imino proton of hydrazone residue and the
–OH group of enolized C4 carbonyl group.
The reaction of 4a-d, with hydrazine hydrate in ethanol gave 5a-d. Its structure was
supported by IR revealing the presence of C=O group and –NH stretch. The IR spectra of 5-
(benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide 5a showed characteristic absorption
band at 3429 cm-1 indicates the stretch due to –NHNH2 and C=O stretch in –CONHNH2 at
1
1683 cm-1 and C=N stretch in pyrazole ring at 1649 cm-1, respectively. The H NMR spectrum
showed singlet signal at δ 3.69-3.71 ppm due to two proton of –NH2 in –CONHNH2 and a broad
band at δ 8.49 ppm for one proton of –NH in CONHNH2 and multiplet signals at δ 7.17-7.51
ppm for ten aromatic protons and singlet at δ 6.22 ppm is due to one proton of pyrazole. In 13C
NMR spectrum, the absence of signal corresponding to methoxy carbon as in 4a-d at δ 53 ppm
clearly indicates that ester group has been converted to carbohydrazide –CONHNH2, C=O
carbon of carbohydrazide gives signal at δ 162 ppm while the aromatic carbons, C3 and C5 in the
pyrazole ring are at their expected regions. The elemental analysis of this product gave C, 67.50;
H, 4.35; N, 16.88; and mass spectrum reveals a molecular ion at m/z 319 [M+H]+ and 341
[M+Na]+ is in consistent with the molecular formula C18H14O2N4.
The structures of the other novel synthesized compounds, 2b-d, 3b-d, 4b-d and 5b-d were
1
also confirmed by CHN and spectral investigation such as IR, H NMR, 13C NMR, and mass
spectra. Simultaneously, the physical constant, yield, spectroscopic and analytical data are also
mentioned.
Antimicrobial activity
The investigation of the microbial screening data revealed that all the tested compounds showed
variable activities towards the fungus and bacteria used, which showed that these compounds
are biologically active due to the presence of different heterocycles and functional groups. The
test compound 2a, 2b, 2d, 3a, 3b, 3c, 3d, 4a, 4c, 4d, 5b, 5c were found to possess moderate to
high activity, whereas 2c, 4b, 4c, 5a, 5d were found to be poorly active at 300-500 µg/mL, but
inactive at 100 or 200 µg/mL concentration against the fungus Aspergillus niger as given in the
Table 1. Similarly the result of antibacterial activity are also tabulated which clearly indicates
that the synthesized compounds 2a, 3a, 3b, 4a, 4b, 4d, 5a, are highly active, compounds 2b, 3c,
4c, 5b, 5c are moderately active while 2c, 2d, 3d, 5d are poorly active against S. aureus.
Compounds 3b, 3c, 4a, 5b, 5c are highly active, 2b, 2c, 2d, 3a, 3d, 4c, 5a are moderately active
and 2a, 4b, 4d and 5d are poorly active against E. coli.
EXPERIMENTAL
The melting points were recorded in open capillary in paraffin bath and are uncorrected. IR
1
spectra were recorded on a Shimadzu IR Spectrophotometer (KBr, ν max in cm-1). H NMR
and 13C NMR spectra are recorded on a Bruker AM 400 instrument (400 MHz) using
tetramethylsilane (TMS) as an internal reference and DMSO-d6 and CDCl3 as solvent. Chemical
shifts are given in parts per million (ppm). Positive-ion electrospray ionisation (ESI) mass
spectra were obtained with a Waters Micromass Q–TOF Micro, Mass Spectrophotometer.
Elemental analysis (CHN) was done using Elemental analyzer, Vario EL III. All the chemicals
used for the synthesis were of AR grade of Merck, S.D. Fine and Aldrich. The reactions were
monitored by E. Merck TLC aluminum sheet silica gel60F254 and visualizing the spot in UV
cabinet and iodine chamber. The antimicrobial screening of the synthesized compounds were
carried out at microbiology laboratory.
Bull. Chem. Soc. Ethiop. 2013, 27(1)

Use of transesterified 1,3-diketoesters in the synthesis of trisubstituted pyrazoles
89
Table 1. Antimicrobial activity of the synthesized compounds 2a-d, 3a-d, 4a-d and 5a-d.
Antifungal activity
Zone of inhibition in mm
S. aureus
1 mg/mL
*Antibacterial activity
No.
Compound
A. niger
E. coli
µg/mL
300
9
Concentration
100
7
8
-
200
9
400
11
11
9
500
12
13
11
11
16
17
16
14
11
9
1
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
5a
5b
5c
5d
26
21
15
16
25
28
21
17
28
24
20
25
26
20
21
13
-
11
2
9
11
7
14
12
12
14
16
15
13
17
10
13
11
12
17
18
10
-
3
-
4
7
9
9
7
8
7
-
7
8
9
5
11
11
9
15
13
10
10
9
16
15
13
12
10
7
6
7
8
8
9
9
10
11
12
13
14
15
16
-
7
-
7
9
10
8
14
9
7
-
7
8
6
7
8
9
8
-
9
10
10
-
12
12
8
14
15
10
23
-
9
-
-
Kanamycin
Chloramphenicol
DMSO
8
-
9
14
-
18
-
-
32
-
21
-
-
-
-
-
-
General procedure for the synthesis of (1a-d)
2-Hydroxy acetophenone/2-hydroxy benzaldehyde derivatives (10 mmol) were taken in dry
acetone (40 mL) and chloroacetone (10 mmol) was added dropwise at room temperature for 1 h.
Then freshly ignited K2CO3 (15 mmol) was added, the reaction mixture was refluxed on steam
bath for 8 h. K2CO3 was removed by washing with acetone. This combined acetone extract was
distilled on reduced pressure then cooled and kept overnight, product obtained was filtered,
washed with water, dried and recrystallized from ethanol [31].
General procedure for the synthesis of (2a-d)
To a solution of 1a-d (10 mmol) and sodium methoxide (10 mmol) in DMF (100 mL),
diethyloxalate (10 mmol) was gradually added with shaking. The reaction mixture was then
stirred for 12 h at room temperature; the product so obtained was acidified by 1:1 ice-cold HCl,
filtered, washed with water and recrystallized from suitable solvent.
Methyl 4-(benzofuran-2-yl)-2,4-dioxobutanoate
0
(2a) [33]. Yellow crystals, yield: (85%);
m.p.:131-133 C (from DMF or acetone); IR (KBr, ν in cm-1) 3475 (-OH), 3059, 3020 (ArH),
1
2968, 2879 (CH3) 1805, 1759 (C=O, ester), 1624, 1573, 1521 (C=C); H NMR (CDCl3) δ
(ppm): 3.95 (s, 3H, CH3 ),7.20-7.71 (m, 5H, ArH), 7.19 (s, 1H, =CH), 14.24 (s, 1H, -OH); 13C
NMR δ (ppm): 53, 99, 112, 114, 123, 124, 127, 128, 150, 156, 162, 167, 181; ESI(+)-MS: m/z
247 (M+H)+, 269 (M+Na)+; anal. calcd. for C13H10O5: C, 63.41; H, 4.06; found: C, 62.52; H,
4.13.
Bull. Chem. Soc. Ethiop. 2013, 27(1)

90
Naqui-Jahan Siddiqui et al.
Methyl 4-(5-bromobenzofuran-2-yl)-2,4-dioxobutanoate (2b). Yellow crystals, yield: (79%);
0
m.p.: 170-171 C (from DMF or acetone); IR (KBr, ν in cm-1), 3450, 3119(-OH), 3086, 3022
1
(ArH), 2962, 2879 (CH3), 1898, 1732 (C=O ester), 1620, 1570 (C=C); H NMR (CDCl3) δ
(ppm): 3.96 (s, 3H, CH3), 7.20-7.85 (m, 4H, ArH), 7.10 (s, 1H, =CH), 14.28 (s, 1H, -OH),
13C NMR δ (ppm): 53, 99, 112, 113, 117, 125, 129, 131, 151, 154, 162,168, 180; ESI(+)-MS:
m/z 326 (M+H)+, 347 [(M+Na)+, 79Br], 349 [(M+Na)+, 81Br]; anal. calcd. for C13H9O5Br: C,
48.00;H, 2.77; found: C, 47.89; H, 2.59.
Methyl 4-[5-chloro-3-methylbenzofuran-2-yl)-2,4-dioxobutanoate (2c). Yellow crystals, yield:
0
(89 %) m.p.: 178-180 C (from DMF or acetone); IR (KBr, ν in cm-1) 3435, 3132 (-OH), 3016,
1
3086 (ArH), 2956, 2883 (CH3), 1898, 1770, 1728 (C=O, ester), 1635, 1589 (C=C); H NMR
(DMSO) δ (ppm): 2.58-2.65 (s, 3H, CH3), 3.76-3.94 (b, 3H, -OCH3), 7.46-7.73 (m, 4H, ArH,
-OH), 7.12 (s, 1H, =CH). 13C NMR δ (ppm): 9, 53, 99, 113, 120, 125, 128, 130, 146, 152, 162,
168, 180; ESI(+)-MS: m/z 296 (M+H)+, 317 [(M+Na)+, 35Cl], 319 [(M+Na)+ , 37Cl]; anal. calcd.
for C14H11O5Cl: C, 56.95; H, 3.73; found: C, 56.84; H, 3.82.
Methyl 4-[5,7-dichloro-3-methylbenzofuran-2-yl)-2,4-dioxobutanoate (2d). Yellow crystals,
0
yield: (65%); m.p.: 200-202 C (from DMF or acetone); IR (KBr, ν, in cm-1), 3446 (-OH),
1
3122, 3078, 3018 (ArH), 2956 (CH3), 1763, 1734 (C=O, ester), 1635, 1579, 1597 (C=C); H
NMR (CDCl3) δ (ppm): 2.6 (s, 3H, CH3), 3.9 (s, 3H, -OCH3), 7.2-7.5 (m, 3H, ArH), 14.68 (b,
1H, -OH); ESI(+)-MS: m/z 331 (M+2)+, 351[(M+Na)+, 35Cl], 353 [(M +Na)+, 37Cl]; anal. calcd.
for C14H10O5Cl2: C, 51.06; H, 3.03; found: C, 50.73; H, 3.31.
General procedure for the synthesis of (3a-d)
To a solution of 1a-d (10 mmol) and sodium ethoxide (10 mmol) in DMF (100 mL),
diethyloxalate (10 mmol) was gradually added with shaking. The reaction mixture was then
stirred for 12 h at room temperature; the product so obtained was acidified by 1:1 ice-cold HCl,
filtered, washed with water and recrystallized from suitable solvent.
Ethyl 4-(benzofuran-2-yl)-2,4-dioxobutanoate (3a) [34]. Yellow Crystalline, Yield: (55%);
0
m.p.: 63-65 C (from ethanol); IR (KBr, ν in cm-1) 3653, 3455 (OH), 3107, 3080 (ArH), 2980,
2937, 2904, 2874 (CH3), 1786, 1724 (C=O, ester), 1633, 1548 (C=C); anal. calcd. for C14H12O5:
C, 64.61; H, 4.61; found: C, 64.59; H, 4.60.
Ethyl 4-(5-bromobenzofuran-2-yl)-2,4-dioxobutanoate (3b). Yellow crystals, yield: (60%); m.p.:
0
130-131 C (from ethanol); IR (KBr, ν in cm-1) 3423, 3126 (-OH), 3072 (ArH), 2987, 2899
(CH3), 1888, 1724 (C=O, ester), 1627, 1562 (C=C); 1H NMR (CDCl3) δ (ppm): 1.41-1.44 (t, J =
7.12 Hz, 3H, -OCH2CH3), 4.39-4.44 (q, J = 7.16 Hz, 2H, -OCH2CH3), 7.26-7.85 (m, 4H, ArH),
7.09 (s,1H, =CH); ESI(+)-MS: m/z 339 M+, 361 [(M+Na)+,79Br], 363 [(M+Na)+, 81Br]; anal.
calcd. for C14H11O5Br: C, 49.55; H, 3.24; found: C, 49.18; H, 3.31.
Ethyl 4-[5-chloro-3-methylbenzofuran-2-yl)-2,4-dioxobutanoate (3c). Yellow crystals, yield:
0
(60%); m.p.: 145-147 C(from acetone); IR (KBr, ν in cm-1), 3632, 3132 (-OH), 3095 (ArH),
1
2999 (CH3), 1871, 1724 (C=O, ester), 1678, 1639, 1599, 1575 (C=C); H NMR (CDCl3) δ
(ppm): 1.41-1.44 (t, J = 7.12 Hz, 3H, -OCH2CH3), 4.38-4.44 (q, J = 7.16 Hz, 2H, -OCH2CH3),
2.59 (s, 3H, CH3), 7.11(s, 1H, =CH), 7.26-7.52(m, 3H, ArH), 14.79(b, 1H, -OH); 13C NMR δ
(ppm): 9, 14, 62, 99, 113, 120, 126, 128, 129, 130, 146, 152, 161,167,183; ESI(+)-MS: m/z 309
M+, 331 [(M + Na),+ 35Cl], 333 [(M+Na)+, 37Cl]; anal. calcd. for C15H13O5Cl: C, 58.25; H, 4.21;
found: C, 58.00; H, 4.32.
Bull. Chem. Soc. Ethiop. 2013, 27(1)

Use of transesterified 1,3-diketoesters in the synthesis of trisubstituted pyrazoles
91
Ethyl 4-[5,7-dichloro-3-methylbenzofuran-2-yl)-2,4-dioxobutanoate (3d). Yellow crystals,
0
yield: (45%); m.p.: 125-127 C (from acetone); IR (KBr, ν in cm-1), 3435, 3117 (-OH), 3080,
3007 (ArH), 2987, 2945 (CH3), 1855, 1782, 1728 (C=O, ester), 1683, 1639, 1604, 1577 (C=C);
1H NMR (CDCl3) δ (ppm): 1.41-1.45 (t, J = 7.12 Hz, 3H, OCH2CH3), 4.40-4.45 (q, J = 7.16
Hz, 2H, -OCH2CH3), 2.62 (s, 3H, CH3), 7.17 (s, 1H, =CH) ,7.47 (d, 2H, ArH), 7.5 (d, 1H, ArH),
14.83 (s, 1H, -OH); anal. calcd. for C15H12O5Cl2,: C, 54.71; H, 3.65; found: C, 54.68; H, 3.68.
General procedure for the synthesis of (4a-d)
To a mixture of 2a-d (10 mmol) in CH3COOH (10 mL), phenyl hydrazine (15 mmol) was added
and the reaction mixture was refluxed for 4 h. After that it was concentrated, cooled and poured
in crushed ice, filtered, dried and recrystallized from suitable solvent.
Methyl 5-(benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate (4a). White crystals, yield:
(85%); m.p.: 161-163 0C (from acetic acid); IR (KBr, ν in cm-1), 3061 (ArH), 2955 (CH3), 1618
1
(C=N), 1734 (C=O, ester), 1593, 1500, 1436, 1408 (C=C); H NMR (CDCl3) δ (ppm): 3.97 (s,
3H, -COOCH3), 7.17-7.54 (m, 10H, ArH), 6.22 (s, 1H, pyrazole CH); 13C NMR δ (ppm): 52,
105, 109, 111, 121, 123, 125, 126, 127, 129, 136, 139, 144, 145, 154, 162; ESI(+)-MS: m/z 319
(M+H)+, 341 (M+Na)+; anal. calcd. for C19H14O3N2: C, 71.69; H, 4.40; N, 8.81; found: C,
71.05; H, 4.42; N, 8.42.
Methyl 5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate (4b). White crystals,
yield: (90%); m.p.: 188-190 0C (from acetic acid); IR (KBr, ν in cm-1), 3146, 3001 (ArH), 2953
1
(CH3), 1734 (C=O, ester), 1589 (C=N); H NMR (CDCl3) δ (ppm): 3.97 (s, 3H, -COOCH3),
7.27-7.54 (m, 9H, ArH), 6.12 (s, 1H, pyrazole CH); 13C NMR δ (ppm): 52, 104, 109, 112, 116,
124, 126, 128, 129, 135, 139, 144 , 146, 153, 162; ESI(+)-MS: m/z 397 M+, 419 [(M+Na)+,
79Br], 421 [(M+Na)+, 81Br]; anal. calcd. for C19H13O3N2Br: C, 57.43; H, 3.27; N, 7.05; found: C,
56.98; H, 3.22; N, 6.62.
Methyl 5-(5-chloro-3-methylbenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate (4c). White
0
crystals, yield: (90%); m.p.: 148-150 C (from acetic acid); IR (KBr, ν in cm-1) 3151, 3072
(ArH), 2995, 2951 (CH3), 1720 (C=O, ester), 1689 (C=N), 1595, 1527 (C=C); 1H NMR
(CDCl3) δ (ppm): 2.08 (s, 3H, CH3), 3.99 (s, 3H, -COOCH3), 7.22-7.4 (m, 8H, ArH), 6.22 (s,
1H, pyrazole CH); 13C NMR δ (ppm): 8, 52, 112, 116, 119, 124, 125, 126, 128, 129, 130, 133,
139, 141, 144, 152, 162; ESI(+)-MS: m/z 389 [(M+Na)+, 35Cl], 391 [(M+Na)+, 37Cl]; anal. calcd.
for C20H15O3N2Cl: C, 65.39; H, 4.08; N, 7.63; found: C, 65.00; H, 4.13; N, 7.34.
Methyl 5-(5,7-dichloro-3-methylbenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate (4d).
0
White crystals, yield: (80%); m.p.: 149-151 C (from acetic acid); IR (KBr, ν in cm-1), 3082
1
(ArH), 2993, 2953 (CH3), 1724, 1749 (C=O, ester), 1600 (C=N), 1579, 1552, 1523 (C=C); H
NMR (CDCl3) δ (ppm): 2.06 (s, 3H, CH3), 3.99 (s, 3H, -COOCH3), 7.26-7.46 (m, 8H, ArH +
pyrazole CH); 13C NMR δ (ppm): 8, 52, 111, 112, 113, 116, 117, 118, 120, 123, 124, 125, 128,
129, 131, 133, 135, 139, 142, 144, 148, 162; ESI(+)-MS: m/z 401 M+, 423 [(M+Na)+, 35Cl], 425
[(M+Na)+, 37Cl]; anal. calcd. for C20H14O3N2Cl2: C, 59.85; H, 3.49; N, 6.98; found: C, 59.80; H,
3.50; N, 6.45.
Bull. Chem. Soc. Ethiop. 2013, 27(1)

92
Naqui-Jahan Siddiqui et al.
General procedure for the synthesis of (5a-d)
To a mixture of 4a-d (10 mmol) in ethanol (100 mL), hydrazine hydrate (100%, 1.7 mL) was
added and refluxed for 8 h. Then it was concentrated, cooled, filtered, washed and recrystallized
from suitable solvent.
5-(Benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide (5a) [35]. White crystals, yield:
0
(88%); m.p.: 145-146 C (from ethanol). IR(KBr, ν in cm-1) 3429, 3317, 3225, 3159 (-NH-
1
NH2), 3066 (ArH), 1683 (C=O), 1649 (C=N), 1531, 1597 (C=C); H NMR (CDCl3) δ (ppm):
3.69-3.71 (s, 2H, -CONHNH2), 8.49 (b, 1H, -CONHNH2), 7.17-7.54 (m, 10H, ArH), 6.22 (s,
1H, pyrazole CH); 13C NMR δ (ppm): 105, 107, 111, 121,123, 125, 126, 127, 129, 136, 139,
145, 145, 154, 162; ESI(+)-MS: m/z 319 (M+H)+, 341 (M+Na)+; anal. calcd. for C18H14O2N4,:
C, 67.92; H, 4.40; N, 17.61; found: C, 67.50; H, 4.35; N, 16.88.
5-(5-Bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide (5b). White crystals,
0
yield: (90%); m.p.: 174-176 C (from ethanol); IR (KBr, ν in cm-1), 3323 (-NHNH2), 3068
1
(ArH), 1683 (C=O, ester), 1664 (C=N), 1620, 1541, 1599 (C=C); H NMR (CDCl3) δ (ppm):
3.70-3.72 (b, 2H, -CONHNH2), 8.29 (b, 1H, -CONHNH2), 7.27-7.56 (m, 9H, ArH), 6.16 (s, 1H,
pyrazole CH); 13C NMR δ (ppm): 104, 108, 112, 116, 123, 128, 129, 135, 139, 145, 146, 153,
162; ESI(+)-MS: m/z 397 M+, 399 (M+2)+ , 421 [(M+Na)+, 79Br], 422 [(M+Na)+, 81Br]; anal.
calcd. for C18H13O2N4Br: C, 54.40; H, 3.27; N, 14.11; found: C, 53.51; H, 3.48; N, 13.54.
5-(5-Chloro-3-methylbenzofuran-2-yl)-1-phenyl-1H-pyrazole-3–carbohydrazide (5c). White
crystals, yield: (90%); m.p.: 159-160 0C (from ethanol); IR (KBr, ν in cm-1) 3313, 3279
1
(-NHNH2), 3068 (ArH), 1678 (C=O, ester), 1618 (C=N), 1541, 1518 (C=C); H NMR (CDCl3)
δ (ppm): 2.10 (s, 3H, CH3), 3.86 (b, 2H, -CONHNH2), 8.33 (b, 1H, -CONHNH2), 7.17-7.46 (m,
9H, ArH); 13C NMR δ (ppm): 8, 110, 112, 116, 119, 124, 125, 128, 129, 130, 133, 139, 141,
145, 152, 162; ESI(+)-MS: m/z 367 M+, 389 [(M +Na)+, 35Cl], 391 [(M+Na)+, 37Cl]; anal. calcd.
for C19H15O2N4Cl: C, 62.12; H, 4.08; N, 15.25; found: C, 62.28; H, 4.00; N, 14.84.
5-(5,7-Dichloro-3-methylbenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide (5d). White
0
crystals, yield: (85%); m.p.: 199-200 C (from acetic acid); IR (KBr, ν in cm-1), 3313, 3140
(-NHNH2), 3006 (ArH), 2924 (CH3), 1714 (C=O, ester), 1660 (C=N), 1604, 1575, 1500 (C=C);
1H NMR (CDCl3) δ (ppm): 2.10 (s, 3H, CH3), 3.24 (b, 2H, -CONHNH2), 8.17 (b, 1H, -
CONHNH2), 7.2-7.42 (m, 8H, ArH); 13C NMR δ (ppm): 8, 109, 116, 117, 124, 128, 131, 132,
139, 142, 145,148, 159, 162; ESI(+)-MS: m/z 401 M+, 403 (M+2)+; anal. calcd. for
C19H14O2N4Cl2: C, 56.85; H, 3.49; N,13.96; found: C, 55.65; H, 3.45; N, 12.74.
Antifungal activity
Test solution was prepared by dissolving known weight of each compound 2a-d, 3a-d, 4a-d
and 5a-d in dimethyl sulphoxide (DMSO) as solvent and diluted suitably to give the resultant
concentration of 100, 200, 300, 400, 500 µg/mL. Whatmann No. 1 sterile paper discs (6 mm)
were impregnated with solution and allowed to dry at room temperature. In vitro antifungal
activity was determined by using Sabouraud Dextrose Agar obtained from Himedia
Ltd/Mumbai. Twenty four hours old culture of selected fungi, Aspergillus niger was mixed with
physiological saline and the turbidity was corrected by adding sterile physiological saline and
sub cultured on Sabouraud Dextrose and suspended in sterile distilled water to an absorbance of
0.6 at 450 nm. Petri plates were prepared by pouring 10 mL Sabouraud Dextrose Agar for fungi
containing microbial culture and was allowed to solidify. The discs were then applied and the
Bull. Chem. Soc. Ethiop. 2013, 27(1)

Use of transesterified 1,3-diketoesters in the synthesis of trisubstituted pyrazoles
93
0
plates were incubated at 28 C for 72-96 h (fungi) and the inhibition zone was measured in four
directions and expressed as mean and the results were compared by using Kanamycin as
antifungal standard.
Antibacterial study
As the sensitivity was not observed at conc. < 500 µg/mL, the antibacterial activity of the test
compounds has been screened at concentration of 1 mg/mL using dimethyl sulphoxide (DMSO)
as solvent and chloramphenicol (100 µg/mL) as standard for antibacterial activity against
Staphylococcus aureus and Escherichia coli in Mueller Hinton Agar by using cup plate agar
diffusion method [36, 37]. 10 mL of this sterilized agar media were poured into petridishes and
allowed to solidify. On the surface of media microbial suspension were spread with the help of
sterilized triangular loop. A stainless steel cylinder of 10 mm diameter (pre-sterilized) was used
to bore the cavity. Into these wells were added 0.1 mL portion of the test compound in the
solvent. The drug solution was allowed to diffuse for about an hour into the medium. The plates
0
were incubated at 37 C for 24 h. Zone of inhibition observed around the cup after respective
incubation was measured with the help of Vernier Calipers. The results of antifungal and
antibacterial activity are given in the Table 1.
CONCLUSION
In summary, we have demonstrated in the present study that transesterification reaction was
succeeded for the conversion of 1a-d to methyl 4-substituted/unsubstituted benzofuran-2-yl)-
2,4-dioxobutanoate 2a-d; which upon condensation with phenyl hydrazine yielded methyl 5-
(substituted/unsubstituted benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carboxylate 4a-d. This
method provides an easy and versatile access to cyclize 1,3-diketoester for synthesizing
pyrazoles of significant biological interest. 4a-d were easily converted to 5-(substituted/
unsubstituted benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide 5a-d by reaction with
hydrazine hydrate. The structures of synthesized compounds were confirmed by spectroscopic
investigation and elemental analysis. The biological screenings of the newly synthesized
derivatives were carried out against two bacteria and one fungus and it was concluded that the
test compounds revealed the antifungal activity much better than their antibacterial activities at
lower concentrations.
ACKNOWLEDGEMENTS
The authors are thankful to the Principal, Priyadarshini College of Engineering, Nagpur for
providing Laboratory facilities and to the Director, SAIF, Punjab University, Chandigarh for
1
providing H NMR, 13C NMR and mass spectra, RSIC, CDRI, Lucknow, India for providing
CHN analysis. The authors are also thankful to Dr. Ugale, Head, Department of Pharmacology,
College of Pharmacy, Kamptee for antimicrobial screening of the compound.
REFERENCES
1. Hassan, M.M.; Wojtamis. J. Indian J. Chem. 1985, 24B, 188.
2. Hassan, M.A.; Mohammad, S.I.M.; Hassan, M.F. Indian J. Chem. 1996, 35B, 22.
3. Saleh, R.M. Indian J. Chem. 1991, 30B, 313.
4. Holla, B.S.; Akberali, P.M.; Shivananda, M.K. IL Farmaco 2000, 55, 256.
5. Liu, X.-H.; Zhi, L.-P.; Song, B.-A.; Xu, H.-L. Chem. Res. 2008, 24, 454.
6. Abid, M.; Bhat, A.R.; Athar, F.; Azam, A. Eur. J. Med Chem. 2009, 44, 417.
Bull. Chem. Soc. Ethiop. 2013, 27(1)

94
Naqui-Jahan Siddiqui et al.
7. Mustafa, A.; Hismat, C.A.; Yannis, M.M.J. J. Prakt. Chem. 1970, 312, 1091
8. Elnagdi, M.H.F.; Elmoghayor, M.R.H.; Hatez, E.A.A.; Alnionion, H.H. J. Org. Chem. 1975,
40, 2604.
9. Garg, H.B. J. Med. Chem. 1972, 15, 446.
10. Manna, F.; Chementi, F.; Fioravanti, R.; Bolasco, A. Bioorg. Med. Chem. Lett. 2005, 15,
4632.
11. Ahn, J.H.; Kim, H.M.; Jung, S.H.; Kang, S.K.; Kim, K.R.; Rhea, S.D.; Yong, S.D.; Cheon,
H.G.; Kim, S.S. Bioorg. Med. Chem. Lett. 2004, 14, 4461.
12. Ragavan, R.V.; Vijayakumar, V.; Kumari, N.S. Eur. J. Med. Chem. 2010, 45, 1173.
13. Jung, J.C.; Watkins, E.B.; Avery, M.A. Heterocycles 2005, 65, 71.
14. Rashad, A.E.; Hegab, M.I.; Abdel-Megeid, R.E.; Micky, J.A.; Abdel- Megeid, F.M.E.
Bioorg. Med. Chem. 2008, 16, 7102.
15. Farag, A.M.; Mayhoub, A.S.; Barakat, S.E.; Bayomi, A.H. Bioorg. Med. Chem. 2008, 16,
881.
16. Farag, A.M.; Mayhoub, A.S.; Barakat, S.E.; Bayomi, A.H. Bioorg. Med. Chem. 2008, 16,
4569.
17. Hui, Y.; Ptak, R.; Paulman, R.; Pallansch, M.; TomChanger, C.W. Tetrahedron Lett. 2002,
43, 9255.
18. Ezawa, M.; Garvey D.S.; Janero D.R.; Khamapure S.P.; Letts L.G.; Martino, A.; Ranetunge,
R.R.; Schwalb, D.J.; Young, D.V. Lett. Drug Design. Discov. 2005, 2, 40.
19. Ranetunge, R.R.; Augustyniak, M.; Bandarage, U.K.; Earl, R.F.; Murty, M.G.; Richardson,
S.R.; Schrodar, J.D.; Shamway, M.J.; Tann, S.W.; Troche A.M.; Young, D.V. J. Med.
Chem. 2004, 47, 2180.
20. Vicini, P.; Zani, F.; Cozzini, P.; Doytchinova, I. Eur. J. Med. Chem. 2002, 37, 553.
21. Loncle, C.; Brunel, J.M.; Vidal, N.; Dherbomez, M.; Letourneux, Y. Eur. J. Med. Chem.
2004, 39, 1067.
22. Todeschini, A.R.; Miranda, A.L.P.; Silva, K.C.M.; Parrini, S.C.; Barreiro, E.J. Eur. J. Med.
Chem. 1998, 33, 189.
23. Melnyk, P.; Leroux, V.; Sergheraert, C.; Grellier, P. Bioorg. Med. Chem. Lett. 2006, 16, 31.
24. Sridhar, S.K.; Pandeya, S.N.; Stables, J.P.; Atmakuru, R. Eur. J. Pharm. Sci. 2002, 16, 129.
25. Kaymakçloglu, B.K.; Rollas, S. IL Farmaco 2002, 57, 595.
26. Patole, J.; Sandbhor U.; Padhye, S.; Deobagkar, D.N.; Anson, C.E.; Powell, A. Bioorg. Med.
Chem. Lett. 2003, 13, 51.
27. Chalina, E.G.; Chakarova, L. Eur. J. Med .Chem. 1998, 33, 975.
28. Delawar, D.L.; Sharma, M.S.; Iyengar, B.S.; Remers, W. A. Antibiot. 1986, 39, 201.
29. Wang, C.L.; Yang, J.F.; Chen, S.Y.; Li, B.Q. Chin. J. Appl. Chem. 2009, 26, 251 and 962.
30. Farghaly, A.R.; El-Kashef, H. ARKIVOK, 2006, 9, 76.
31. Elliot, E.D. J. Amer. Chem. Soc. 1951, 73, 754.
32. Silverstein, R.M.; Webster, F.X. Spectrometric Identification of Organic Compounds, 6th
ed., John Wiley and Sons: New Delhi; 2010.
33. Karpenko, A.V.; Kovelenko, S.I.; Shishkin, O.V. Tetrahedron 2009, 65, 5964.
34. Payard, M.; Paris, J.; Couquelet, J. Trav. Soc. Pharm. Montp. 1976, 36, 115; Chem. Abstr.
1977, 85, 152.
35. Abdel-Wahab, B.F.; Abdel-Aziz, H.A.; Ahmed, E.M. Arch. Pharm. Chem. Life Sci. 2008,
341, 734.
36. Kawangh, F. Analytical Microbiology, Academic Press: New York; 1963.
37. British Pharmacopaeia - II, Biological Assay and Tests, The Stationary Office Ltd.: London;
1998; p A-205.
Bull. Chem. Soc. Ethiop. 2013, 27(1)