Efficient synthesis of 4,4'-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5- ol) derivatives in PEG-400 under catalyst-free conditions

Full text of DOI:10.1080/00304948.2010.526827

This article was downloaded by: [Moskow State Univ Bibliote]
On: 09 January 2014, At: 00:56
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Organic Preparations and Procedures
International: The New Journal for
Organic Synthesis
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/uopp20
Efficient Synthesis of 4,4′-
(Arylmethylene)-bis(3-methyl-1-
phenylpyrazol-5-ol) Derivatives in
PEG-400 under Catalyst-free Conditions
Alireza Hasaninejad a , Abdolkarim Zare b , Mohsen Shekouhy a &
Nooshin Golzar a
a Department of Chemistry, Faculty of Sciences , Persian Gulf
University , Bushehr, 75169, Iran
b Department of Chemistry , Payame Noor University (PNU) , Iran
Published online: 13 Feb 2011.
To cite this article: Alireza Hasaninejad , Abdolkarim Zare , Mohsen Shekouhy & Nooshin Golzar
(2011) Efficient Synthesis of 4,4′-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol) Derivatives in
PEG-400 under Catalyst-free Conditions, Organic Preparations and Procedures International: The New
Journal for Organic Synthesis, 43:1, 131-137, DOI: 10.1080/00304948.2010.526827
To link to this article: http://dx.doi.org/10.1080/00304948.2010.526827
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Organic Preparations and Procedures International, 43:131–137, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print
DOI: 10.1080/00304948.2010.526827
Efficient Synthesis of 4,4ꢀ-(Arylmethylene)-bis(3-
methyl-1-phenylpyrazol-5-ol) Derivatives
in PEG-400 under Catalyst-free Conditions
Alireza Hasaninejad,1 Abdolkarim Zare,2 Mohsen Shekouhy,1
and Nooshin Golzar1
1Department of Chemistry, Faculty of Sciences, Persian Gulf University,
Bushehr 75169, Iran
2Department of Chemistry, Payame Noor University (PNU), Iran
Pollution control demands are a source of inspiration to design and develop new reaction
mediums to achieve high efficiency. Much attention has been directed toward the develop-
ment of environmentally benign syntheses, including the use of solvent-free conditions,1 and
application of solvents such as ionic liquids2 or water.3 These protocols have been success-
fully used to achieve various chemical transformations, but there are some disadvantages
that limit the use of these procedures. For example, in many organic reactions, solvents
play a critical role to promote more efficient molecular interactions, but most organic
compounds are not soluble in water. Moreover, due to the sensitivity of many catalysts to
aqueous conditions, the use of water as solvent is limited to some special reactions. Ionic
liquids also require tedious preparation and their environmental safety is still debatable.
Recently, liquid polymers or low melting point polymers have emerged as alternative
green reaction media with unique properties such as thermal stability, commercial availabil-
ity, non-volatility, immiscibility with a number of organic solvents, and recyclability.4–14
Poly(ethylene glycol)s (PEGs) are preferred to other polymers because they are inexpensive,
completely non-halogenated, easily degradable, and of low toxicity.4,5 Among them, low
molecular weight liquid PEGs can be regarded as protic solvents containing aprotic sites.6
Several organic transformations such as Heck reaction,7 asymmetric dihydroxylation,8
Suzuki cross-coupling reaction,9 oxydehydrogenation of alcohols and cyclic dienes,10 metal
mediated radical polymerization,11 Michael addition of amines to conjugated alkenes,12
Wacker reaction,13 and partial reduction of alkynes14 have been performed using PEGs as
reaction media.
Pyrazolines are important five-membered heterocyclic compounds with different bi-
ological activities and other useful applications.15,16 The conventional chemical approach
Received January 15, 2010; accepted August 13, 2010.
Address correspondence to either Alireza Hasninejad, Department of Chemistry, Faculty of Sci-
ences, Persian Gulf University, Bushehr 75169, Iran, E-mail: ahassaninejad@yahoo.com; or Abdolka-
rim Zare, Department of Chemistry, Payame Noor University (PNU), Iran. E-mail: abdolkarimzare@
yahoo.com
131

132
Hasaninejad et al.
to 4,4ꢀ-(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ols) involves Knoevenagel syn-
thesis of the corresponding arylidenepyrazolones and its base-promoted Michael reaction,
as well as the one-pot tandem Knoevenagel-Michael reaction of arylaldehydes with two
equivalents of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one.17,18 Furthermore, recent
methods such as application of sodium dodecylsulfate (SDS) in aqueous media,19 and elec-
trocatalytic synthesis20 have been reported for the preparation of these compounds. How-
ever, most of the methods suffer from limitations such as low yields, long reaction times,
application of hazardous solvents, tedious work-up procedures, and non-compliance with
green chemistry protocols. Moreover, there is no catalyst-free protocol for the preparation
of 4,4ꢀ-(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ols). Considering the importance
of pyrazoline derivatives, and in continuation of our studies to find green and efficient
methodologies for preparation of organic compounds under catalyst-free conditions,21,22
we have devised a general, efficient, rapid and catalyst-free protocol for the synthesis
of 4,4ꢀ-(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ols) derivatives via the condensa-
tion of 3-methyl-1-phenyl-5-pyrazolone (1) with aromatic and aliphatic aldehydes (2) in
poly(ethylene glycol)-400 (PEG-400) at 110◦C under neutral conditions (Scheme 1).
OH HO
R
O
N
PEG-400, 110 oC
O
N
N
N
N
+
R
H
Catalyst-free
2-3 h
N
1
2
3a-p
R = Aryl, Alkyl
73-94%
Scheme 1
To determine the best conditions, the condensation of 3-methyl-1-phenyl-5-pyrazolone
(1) (2 mmol) with benzaldehyde (1 mmol) was examined in different amounts of PEG-400
at range of 80–120◦C without catalyst. The best result was observed when 1 mL of PEG-400
was applied as reaction medium at 110◦C; in this case, the desired product was produced in
high yield (92%) within 2 h. Increasing the reaction time or the amount of PEG-400 did not
improve the results. The reaction was also performed in the absence of PEG-400 at 110◦C;
however, in these conditions, the product was obtained in 23% after 6 h.
To assess the efficiency and the scope of the catalyst-free protocol, 3-methyl-1-phenyl-
5-pyrazolone was treated with structurally diverse aromatic and aliphatic aldehydes under
the optimized reaction conditions using PEG-400 as solvent. The corresponding results are
displayed in Table 1.
Table 1 indicates that various aromatic aldehydes bearing halogens, electron-
withdrawing or electron-releasing substituents on their aromatic rings as well as aliphatic
aldehydes were efficiently condensed with 3-methyl-1-phenyl-5-pyrazolone to the corre-
sponding 4,4ꢀ-(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol) derivatives in good to
excellent yields and in relatively short reaction times. The results showed that the pres-
ence of halogens as well as electron-releasing substituents CH3 and OCH2CH3 on the

4,4ꢀ-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol)
133
Table 1
Catalyst-free Preparation of 4,4ꢀ-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol)
Derivatives in PEG-400 at 110◦C
OH HO
Ph
Ph
O
PEG-400, 110 oC
Catalyst-free
N
N
N
+
O
N
N
R
H
N
Ph
1
R
2
3a-p
Entry
R
Product
Time (h)
Yield (%)
mp. ◦C (lit.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C6H5
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
2
2.5
2
2
3
3
1
1.5
1
2
1.5
1.5
2
3
2
92
90
89
89
83
90
94
91
91
89
89
84
90
91
73
78
168–170 (171–172)19
213–215 (207–209)19
150–152 (153–154)19
235–236 (236–237)19
149–150 (152–153)19
185–188
229–231 (230–232)19
145–147 (149–150)19
221–223 (224–225)19
190–192
189–191
230–232
172–175
201–203 (203–204)19
225–227 (227–229)19
210–212 (213–214)19
4-ClC6H4
3-ClC6H4
2-ClC6H4
4-HOC6H4
4-EtOC6H4
4-NO2C6H4
3-NO2C6H4
2-NO2C6H4
2-Thienyl
2-Furyl
2-Pyridyl
3-BrC6H4
4-MeC6H4
H
(CH3)2CH
2
aromatic ring of aldehydes had no significant effect on the reaction yields (Table 1, Entries
2–4, 6, 13 and 14); however, a hydroxy group decreased the yield slightly (Table 1, Entry
5). Moreover, electron-withdrawing substituents gave excellent yields in decreased times
(Table 1, Entries 7–9). Interestingly, the catalyst-free method was successfully applied
for the condensation of 3-methyl-1-phenyl-5-pyrazolone with heteroaromatic aldehydes as
well as aliphatic aldehydes (Table 1, Entries 10–12, 15 and 16). Because of the neutral na-
ture of PEG-400, acid-sensitive aldehydes (for example furfural) as well as basic aldehydes
(for example 2-pyridinecarbaldehyde) were successfully applied in the reaction (Table 1,
Entries 11 and 12).
Interestingly, the condensation of 3-methyl-1-phenyl-5-pyrazolone (2 equivalents) with
terephthaldehyde (1 equivalent) in PEG-400 at 110◦C afforded di-4,4ꢀ-(arylmethylene)-
bis(3-methyl-1-phenylpyrazol-5-ol) 5 in 86% yield within 3 h (Scheme 2). It is worth noting
that in nearly none of the reported methods for the preparation of these compounds, the
synthesis of di-4,4ꢀ-(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ols) has been studied.

134
Hasaninejad et al.
OH HO
N
N
N
N
N
N
O
PEG-400, 110 oC
+
OHC
CHO
Catalyst-free
3 h
N
N
N
N
OH HO
1
5
4
86%
Scheme 2
In summary, we have reported the first catalyst-free method for the synthesis of 4,4ꢀ-
(arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ols) in a green recyclable media.23 The
promising points for the presented methodology are efficiency, generality, high yield,
relatively short reaction time, low cost, cleaner reaction profile, ease of product isolation,
simplicity, potential for recycling of the solvent, and finally compliance with the green
chemistry protocols.
Experimental Section
1
All chemicals were purchased from Merck or Fluka Chemical Companies. The H NMR
(500 MHz) and 13C NMR (125 MHz) were run on a Bruker Avance DPX-500, FT-NMR
spectrometer, δ in ppm. Mass spectra were recorded on a Shimadzu GC MS-QP 1000 EX
apparatus. Melting points were recorded on a Bu¨chi B-545 apparatus in open capillary
tubes.
General Procedure for the Synthesis of 4,4ꢀ-(Arylmethylene)-bis(3-methyl-1-
phenylpyrazol-5-ols)
To a mixture of 3-methyl-1-phenyl-5-pyrazolone (0.35 g, 2 mmol) and aldehyde (1 mmol)
in a 10 mL round-bottomed flask connected to a reflux condenser, was added PEG-400
(1 mL), and the resulting mixture was stirred in an oil-bath (110◦C). The progress of the
reaction was monitored by TLC using EtOAc/n-hexane (1/4) as eluent. After completion
of the reaction, the reaction mixture was cooled to room temperature and water (20 mL)
was added. PEG-400 dissolved in the water and the insoluble crude product was isolated
by simple filtration. The crude product was dissolved in warm EtOH or aqueous EtOH (6
mL) and was allowed to stand at room temperature for 5–6 h. The crystalline solids were
collected, washed with ethanol and dried. The filtrate containing PEG-400 was extracted
with Et2O (2 × 20 mL) to remove any organic compounds dissolved in the aqueous phase.

4,4ꢀ-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol)
135
The aqueous layer was separated and the water was evaporated under reduced pressure to
give pure PEG-400 which was used for the next run under similar reaction conditions.
Selected Spectral Data of the Products
Compound 3a: Pale yellow solid (from 3:1 EtOH/H2O), mp. 168–170◦C (lit.27
1
171–172◦C); H NMR (DMSO-d6): δ 2.33 (s, 6H, 2CH3), 4.88 (s, 1H, CH), 7.07 (m,
1H), 7.18 (m, 6H), 7.44 (t, 4H), 7.58 (d, 4H); 13C NMR DMSO-d6): δ 12.0, 33.5, 121.4,
126.2, 126.8, 127.6, 128.2, 129.1, 137.3, 142.9, 146.1.
1
Compound 3b: White solid (from EtOH), mp. 213–215◦C (lit.27 207–209◦C); H
NMR (DMSO-d6): δ 2.32 (s, 6H), 4.97 (s, 1H), 7.26 (d, J = 8.2 Hz, 4H), 7.34 (d, J = 8.0
Hz, 2H), 7.44 (t, J = 7.1 Hz, 4H), 7.71 (d, J = 7.6 Hz, 4H).
Compound 3c: White solid (from EtOH), mp. 150–152◦C (lit.27 153–154◦C).
Compound 3d: White solid (from 5:1 EtOH/H2O), mp. 235–236◦C (lit.27 236–237◦C);
1H NMR (DMSO-d6): δ 2.26 (s, 6H, 2CH3), 5.08 (s, 1H, CH), 7.27–7.29 (m, 2H), 7.41–7.43
(m, 8H), 7.75–7.77 (m, 4H).
Compound 3e: White solid (from 3:1 EtOH/H2O), mp. 149–150◦C (lit.27 152–153◦C);
1H NMR (DMSO-d6): δ 2.31 (s, 6H, 2CH3), 4.86 (s, 1H, CH), 6.66–6.68 (d, J = 8.5 Hz,
2H), 7.05–7.07 (d, J = 8.5 Hz, 2H), 7.23–7.26 (t, J = 7 Hz, 2H), 7.43–7.46 (t, J = 8 Hz,
4H), 7.71–7.73 (d, J = 8 Hz, 4H), 9.16 (s, 1H, OH), 12.40 (s, 1H, OH), 13.95 (s, 1H, OH);
13C NMR (DMSO-d6): δ 12.5, 33.2, 40.9, 115.7, 121.4, 126.4, 128.9, 129.8, 133.2, 143.6,
147.0, 156.4.
1
Compound 3f: White solid (from EtOH), mp. 185–188◦C; H NMR (DMSO-d6): δ
1.06–1.08 (t, J = 7 Hz, 3H, CH3), 2.34 (s, 6H, 2CH3), 3.44–3.48 (q, J = 7 Hz, 2H, CH2),
5.01 (s, 1H, CH) 7.25–7.29 (m, 4H), 7.38–7.46 (m, 6H), 7.71–7.73 (d, J = 8 Hz, 4H), 13.94
(s, 1H, OH); 13C NMR (DMSO-d6): δ 12.4, 19.4, 33.7, 56.9, 121.5, 122.4, 126.5, 127.3,
129.8, 130.8, 131.2, 146.0, 147.2; MS (m/z): 480 (M+).
Anal. Calcd. for C29H28N4O3: C, 72.48; H, 5.87; N, 11.66. Found: C, 72.23; H, 5.98;
N, 11.52.
Compound 3g: Pale yellow solid (from EtOH), mp. 229–231◦C (lit.27 230–232◦C);
1H NMR (DMSO-d6): δ 2.35 (s, 6H, 2CH3), 5.13 (s, 1H, CH), 7.25–7.27 (m, 2H, Arm H),
7.43–7.46 (t, J = 7 Hz, 4H), 7.51–7.53 (d, J = 8 Hz, 2H), 7.70–7.72 (d, J = 8 Hz, 4H),
8.16–8.18 (d, J = 8 Hz, 2H), 12.64 (s, 1H, OH), 13.86 (s, 1H, OH); 13C NMR (DMSO-d6):
δ 12.5, 19.4, 34.0, 56.9, 121.5, 124.2, 126.6, 129.5, 129.8, 146.8, 147.1, 151.2.
Compound 3h: Pale yellow solid (from EtOH), mp. 145–147◦C (lit.27 149–150◦C).
Compound 3i: White solid (from EtOH), mp. 221–223◦C (lit.27 224–225◦C); 1H NMR
(DMSO-d6): δ 2.29 (s, 6H, 2CH3), 5.47 (s, 1H, CH), 7.20–7.26 (m, 2H), 7.40–7.49 (m,
5H), 7.61–7.75 (m, 7H).
Compound 3j: White solid (from 5:1 EtOH/H2O), mp. 190–192◦C; 1H NMR (DMSO-
d6): δ 2.38 (s, 6H, 2CH3), 5.11 (s, 1H, CH), 6.89–6.92 (m, 2H), 7.09–7.48 (m, 7H,),
7.77–7.85 (m, 4H), 13.56 (s, 1H, OH); 13C NMR (DMSO-d6): δ 12.6, 33.3, 121.3, 125.1,
125.3, 128.3, 128.6, 131.4, 131.5, 131.9, 134.5, 139.7, 144.9, 154.8. MS (m/z): 442 (M+).
Anal. Calcd. for C25H22N4O32S: C, 67.85; H 5.01; N 12.66. Found: C, 67.56; H, 5.14; N,
12.57.

136
Hasaninejad et al.
Compound 3k: White solid (from EtOH), mp. 189–191◦C; 1H NMR (DMSO-d6): δ
2.21 (s, 6H, 2CH3), 4.87 (s, 1H, CH), 6.14 (s, 1H), 6.48 (s, 1H), 7.37 (t, 2H), 7.44 (t, 4H),
7.53 (s, 1H), 7.78 (d, 4H); 13C NMR (DMSO-d6): δ 12.2, 28.6, 106.4, 110.2, 121.6, 126.4,
129.9, 142.4, 146.9, 154.4; MS (m/z): 426 (M+).
Anal. Calcd. for C25H22N4O3: C, 70.41; H, 5.20; N, 13.14. Found: C, 70.63; H, 5.29;
N, 13.03.
1
Compound 3l: White solid (from EtOH), mp. 230–232◦C; H NMR (DMSO-d6): δ
2.29 (s, 6H, 2CH3), 5.11 (s, 1H, CH), 7.21 (t, 2H), 7.41 (m, 1H), 7.48 (t, 4H), 7.66 (d, 5H),
8.47 (m, 2H); 13C NMR (DMSO-d6): δ 12.1, 31.6, 104.5, 121.0, 123.7, 126.5, 129.1, 136.3,
137.6, 138.1, 146.5, 147.8, 148.5; MS (m/z): 437 (M+).
Anal. Calcd. for C26H23N5O2: C, 71.38; H, 5.30; N, 16.01. Found: C, 71.21; H, 5.42;
N, 15.93.
1
Compound 3m: White solid (from 5:1 EtOH/H2O), mp. 172–175◦C; H NMR
(DMSO-d6): δ 2.30 (s, 6H, 2CH3), 4.89 (s, 1H, CH), 6.82–7.71 (m, 14H), 12.40 (s, 1H,
OH), 13.92 (s, 1H, OH); 13C NMR (DMSO-d6): δ 10.0, 14.3, 117.9, 123.6, 125.4, 127.2,
127.7, 128.3, 128.7, 129.7, 132.4, 133.6, 140.4, 145.9, 154.4; MS (m/z): 515 (M+).
Anal. Calcd. for C27H23BrN4O2: C, 62.92; H, 4.50; N, 10.87. Found: C, 62.64; H, 4.61;
N, 10.73.
Compound 3n: White solid (from 3:1 EtOH/H2O), mp. 201–203◦C (lit.27 203–204◦C);
1H NMR (DMSO-d6): δ 2.24 (s, 3H, CH3), 2.31 (s, 6H, 2CH3), 4.91 (s, 1H, CH), 7.08–7.71
(m, 14H), 12.40 (s, 1H, OH), 13.92 (s, 1H, OH); 13C NMR (DMSO-d6): δ 12.5, 21.4, 33.6,
40.9, 121.4, 126.4, 127.9, 129.6, 129.8, 135.7, 140.0, 147.1.
Compound 3o: White solid (from 2:1 EtOH/H2O), mp. 225–227◦C (lit.27 227–229◦C);
1H NMR (DMSO-d6): δ 2.15 (s, 6H, 2CH3), 3.31 (s, 2H, CH), 7.28–7.30 (m, 2H), 7.46–7.48
(m, 4H), 7.73–7.75 (m, 4H).
Compound 3p: White solid (from 2:1 EtOH/H2O), mp. 210–212◦C (lit.27 213–214◦C);
1H NMR (DMSO-d6): δ 0.84 (s, 6H, 2CH3), 2.21 (s, 6H, 2CH3), 2.55–2.69 (m, 1H, CH),
2.97–3.08 (d, 1H, CH), 7.25–7.28 (m, 2H), 7.40–7.48 (m, 4H), 7.71–7.73 (m, 4H).
Compound 5: Pale yellow solid (from EtOH), mp. 193–196◦C; 1H NMR (DMSO-d6):
δ 2.16 (s, 12H, 4CH3), 4.71 (s, 2H, CH), 7.00–7.03 (t, J = 7.5 Hz, 4H), 7.06 (s, 4H),
7.17–7.21 (t, J = 8.0 Hz, 8H), 7.55–7.57 (d, J = 8.0 Hz, 8H), 13.40 (s, 4H, OH); 13C NMR
(DMSO-d6): δ 12.2, 33.8, 120.6, 121.5, 125.9, 127.5, 129.0, 131.1, 137.0, 139.2, 146.7;
MS (m/z): 448 (M+-C20H18N4O2), 431, 354.
Anal. Calcd. for C48H42BrN8O4: C, 72.53; H, 5.33; N, 14.10. Found: C, 72.77; H, 5.21;
N, 14.19.
Acknowledgements
The authors appreciate Persian Gulf University and Payame Noor University (PNU)
Research Councils for the financial support of this work.
References
1. K. Tanaka, “Solvent-free Organic Synthesis”, Wiley-VCH, GmbH and KGaA, Weinheim, 2004.

4,4ꢀ-(Arylmethylene)-bis(3-methyl-1-phenylpyrazol-5-ol)
137
2. R. D. Rogers, “Ionic Liquids as Green Solvents: Progress and Prospects”, American Chemical
Society Publication, Washington, 2005.
3. C.-J. Li, Chem. Rev., 105, 3095 (2005).
4. J. Chen, S. K. Spear, J. G. Huddleston and R. D. Rogers, Green Chem., 7, 64 (2005).
5. D. Kumar, V. B. Reddy, B. G. Mishra, R. K. Rana, M. N. Nadagouda and R. S. Varma, Tetrahe-
dron, 63, 3093 (2007).
6. D. Kumar, V. B. Reddy and R. S. Varma, Tetrahedron Lett., 50, 2065 (2009).
7. S. Chandrasekhar, C. Narsihmulu, S. S. Sultana and N. R. K. Reddy, Org. Lett., 4, 4399 (2002).
8. S. Chandrasekhar, C. Narsihmulu, S. S. Sultana and N. R. Reddy, Chem. Commun., 1716 (2003).
9. V. V. Namboodiri and R. S. Varma, Green Chem., 3, 146 (2001).
10. A. Haimov and R. Neumann, Chem. Commun., 876 (2002).
11. S. Perrier, H. Gemici and S. Li, Chem. Commun., 604 (2004).
12. R. Kumar, P. Chaudhary, S. Nimesh and R. Chandra, Green Chem., 8, 356 (2006).
13. A. Haimov and R. Neumann, Chem. Commun., 876 (2002).
14. S. Chandrasekhar, C. Narsihmulu, G. Chandrashekar and T. Shyamsunder, Tetrahedron Lett., 45,
2421 (2004).
15. J. Elguero, A. R. Katritzky, C. W. Rees and E. F. V. Scriven, “Pyrazoles in Comprehensive
Heterocyclic Chemistry II”, Pergamon, Oxford, UK, 1996.
16. L. Yet, A. R. Katritzky, C. A. Ramsden, E. F. V. Scriven and R. J. K. Taylor, “Pyrazoles in
Comprehensive Heterocyclic Chemistry III”, Pergamon, Oxford, UK, 2008.
17. W. S. Hamama, Synth. Commun., 31, 1335 (2001).
18. X.-L. Li, Y.-M. Wang, B. Tian, T. Matsuura and J.-B. Meng, J. Heterocycl. Chem., 35, 129
(1998).
19. W. Wang, S.-X. Wang, X.-Y. Qin and J.-T. Li, Synth. Commun., 35, 1263 (2005).
20. M. N. Elinson, A. S. Dorofeev, R. F. Nasybullin and G. I. Nikishin, Synthesis, 1933 (2008).
21. A. Zare, A. R. Moosavi-Zare, A. Hasaninejad, A. Parhami, A. Khalafi-Nezhad and M. H. Beyzavi,
Synth. Commun., 39, 3156 (2009).
22. A. Zare, A. Parhami, A. R. Moosavi-Zare, A. Hasaninejad, A. Khalafi-Nezhad and M. H. Beyzavi,
Can. J. Chem., 87, 416 (2009).
23. S. Chandrasekhar, N. R. Reddy, S. S. Sultana, C. Narsihmulu and K. V. Reddy, Tetrahedron, 62,
338 (2006).