Dibromination of 5-pyrazolones and 5-hydroxypyrazoles via dibromoisocyanuric acid

Article abstract of DOI:10.1002/jhet.442

(Chemical Equation Presented) A safe and efficient method was developed for the dibromination of pyrazolones and 5-hydroxypyrazoles by use of dibromoisocyanuric acid (DBI). The reaction gave the corresponding dibrominated pyrazolones in excellent yields (≥91%).

Full text of DOI:10.1002/jhet.442

September 2010
Dibromination of 5-Pyrazolones and 5-Hydroxypyrazoles
via Dibromoisocyanuric Acid
1153
Kaung-Min Cheng,a Jin Bin Wu,a Hui-Chang Lin,a Jiann-Jyh Huang,b
Yu-Ying Huang,a Shao-Kai Lin,c Tsung-Ping Lin,a and Fung Fuh Wonga*
aGraduate Institute of Pharmaceutical Chemistry, China Medical University, Taichung,
Taiwan 40402, Republic of China
bDevelopment Center for Biotechnology, Xizhi City, Taipei County, Taiwan 221,
Republic of China
cSustainable Environment Research Center, National Cheng Kung University,
Tainan City, Taiwan 709, Republic of China
*E-mail: ffwong@mail.cmu.edu.tw
Received November 10, 2009
DOI 10.1002/jhet.442
Published online 26 July 2010 in Wiley Online Library (wileyonlinelibrary.com).
A safe and efficient method was developed for the dibromination of pyrazolones and 5-hydroxypyra-
zoles by use of dibromoisocyanuric acid (DBI). The reaction gave the corresponding dibrominated pyra-
zolones in excellent yields (ꢀ91%).
J. Heterocyclic Chem., 47, 1153 (2010).
INTRODUCTION
and 5-hydroxypyrazoles by using DBI. A series of 4,4-
dibromo-5-pyrazolones could be obtained in excellent
yields (ꢀ91%) by this method. Comparison with the use
of NBS as the brominating agent, we found the use of
DBI toward pyrazolones was more efficient.
Halogenated pyrazolone compounds attracted atten-
tions for some of them displaying interesting biological
activities [1]. Among the compounds, 4,4-dibromo-5-py-
razolone have been reported as fungicides against Hel-
minthosporium oryzae [2], a-glucosidase inhibitors, and
used for the treatment of tumor metastasis, AIDS, diabe-
tes, hyperlipidemia, autoimmune disease, allergy, and
rejection in organ transplant [3]. They are also useful
synthetic intermediates for the preparation of diazo-dyes
[4], and fused- [5] and spiro-hetercyclic compounds [6].
Traditional method for the synthesis of brominated
pyrazolone is the use of Br2 in acetic acid [7]. However,
harsher conditions and manipulations with care are
required. Use of the mild brominating reagent N-bromo-
succinimide (NBS) [8b] or 1,3-dibromo-5,5-dimethylhy-
dantoin [8c] does not also provide the corresponding
dibrominated products in satisfactory yields as the
monobrominated and coupling by-products were accom-
panied to form. As a mild brominating agent, dibromoi-
socyanuric acid (DBI) has been reported to brominates
primary amides [9] and N,N-dimethylanilines [10]. For
the structural similarity of the substrates, it is possible
to extend the reagent to pyrazolones. Herein, we report
an efficient method for the dibromination of pyrazolones
RESULTS AND DISCUSSION
5-Pyrazolones were prepared as the substrates for the
investigation of dibromination by DBI through tandem
condensation and thermal cyclization following the
reported procedure [11]. a-Keto esters 1 were heated at
reflux in AcOH with equal equivalent of arylhydrazines
2a–2h possessing various substituents including m-Me,
p-OMe, o, p-di-NO2, and 2,4,6,-trichloro at the phenyl
ring for 4.0 h. The corresponding 5-pyrazolones (keto
form) were obtained in good to excellent yields (>75%,
see Scheme 1 and Chart 1) [11]. Use of hydrazine, and
pyridyl and isoquinolinyl hydrazines as the starting ma-
terial provided the corresponding 5-hydroxypyrazoles
3i–3k (enol form) in >86% yields (see Scheme 1, and
Chart 1). The experiment results were consistent with
the literature reported [12].
To search an efficient and reproducible procedure, we
carried out a model study by treating 5-pyrazolone (3a)
C
V
2010 HeteroCorporation

1154
K.-M. Cheng, J. B. Wu, H.-C. Lin, J.-J. Huang, Y.-Y. Huang,
S.-K. Lin, T.-P. Lin, and F. F. Wong
Vol 47
Scheme 1
Scheme 2
nucleophilic substitution reaction to generate the corre-
sponding mono-bromo-5-pyrazolone intermediates
with DBI [13] in THF at room temperature for 30 min
(see Chart 1 and Scheme 2). The reaction afforded the
desired 4,4-dibromo-5-pyrazolone (4a) in 95% yield.
Compound 4a was fully characterized by spectroscopic
method and the results were consistent with the reported
data from literature [14]. In a control experiment by
reacting 3a with NBS, the reaction was less efficient
which provided 4a in 78% yield.
6
with N-monobromoisocyanuric acid 5. Application of 5-
hydroxy-3-phenyl-1H-pyrazole (3i), 5-hydroxy-3-phenyl-
1-(pyrid-2-yl)-1H-pyrazole (3j), and 5-hydroxy-3-phe-
nyl-1-(3-isoquinolinyl)-1H-pyrazole (3k) as the model
demonstrated that the enol species could also proceeded
the nucleophilic substitution in the same reaction condi-
tion. For the further conjunction conversion, mono-
bromo-5-pyrazolones 6 were converted to the mono-
bromo-5-hydroxypyrazoles 7 under the reaction mixture.
Finally, mono-bromo-5-hydroxypyrazole intermediates 7
consequential trapped the secondary equivalent bromine
from the N-monobromoisocyanuric acid 5 to generate
final dibrominated products 4a–4k and cyanuric acid 8.
Cyanuiric acid 8 can be isolated by column chromatog-
raphy and identified by IR and 13C NMR spectroscopic
methods to demonstrate the plausible mechanism.
By using the newly developed method shown in
Scheme 2, we successful applied this synthetic strategy
to 5-pyrazolones 3b–3h with N-substituted group,
including m-Me, p-OMe, o,p-di-NO2, and 2,4,6-tri-
chloro. The corresponding products 4b–4h were
obtained in the ꢀ91% yields (see Table 1). This syn-
thetic strategy is applicable to 5-hydroxypyrazole (enol
form of 5-pyrazolone) that bear N-substituted group,
such as H, pyridyl, and isoquinolinyl (3i–3k). The
desired compounds 4i–4k were afforded in 91–95%
yields and fully characterized by spectroscopic methods.
For example, compound 4k possessed characterization
absorptions at d 42.5 ppm for O¼¼CA13C(Br)2 in pyraz-
olone ring and IR absorptions showed peaks at 1751
cm–1 for stretching of the AC¼¼O group.
In conclusion, we have successfully developed a
dibrominating method for the conversion of the keto
form pyrazolone and the enol form 5-hydroxypyrazole
substrates by use of DBI as the reagent. The reaction
provided 4,4-dibromo-pyrazolones 4a–4k in excellent
yields (ꢀ91%). This newly developed bromination
method was a safe and efficient would be useful in the
large-scale preparation of the dibrominated pyrazolones.
We proposed a plausible mechanism for the dibromi-
nation of 5-pyrazolones by use of DBI as shown in
Scheme 3. When 5-hydroxypyrazoles 3a–3h were
treated with DBI, the compounds favored the enol form
in the acidic condition and underwent the smoothly
Table 1
The results of bromination by using dibromoisocyanuric acid (DBI).
5-Pyrazolones (3a–3h) or
5-hydroxypyrazoles (3i–3k)
Dibromination
(4a–4k)
Compounds
X
R
Products Yields (%)
3a
3b
3c
3d
3e
3f
3g
3h
3i
Ph
Ph
Me
CF3
i-Pr
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
95
94
98
96
94
93
97
92
93
95
91
Ph
Ph
m-Me-Ph
p-OMe-Ph
o,p-di-NO2-Ph
Ph
Ph
Ph
2,4,6,-tri-Chloro-Ph Ph
H
Pyridyl
Isoquinolinyl
Ph
Ph
Ph
3j
3k
4j
4k
Chart 1
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

September 2010
Dibromination of 5-Pyrazolones and 5-Hydroxypyrazoles
via Dibromoisocyanuric Acid
1155
Scheme 3
(20 mL ꢃ 2), brine (20 mL ꢃ 2), and concentrated under
reduced pressure. The residue was purified by column chroma-
tography on silica gel (30% EtOAc in hexanes as eluant) to give
4,4-dibromo-5-pyrazolones 4a–4k as solids in 91–98% yields.
4,4-Dibromo-3-methyl-1-phenyl-2-pyrazolin-5-one (4a). To
a solution of pyrazolones 3a (20 g, 0.114 mol, 1.0 equiv) in
THF (150 mL) was added DBI (69.2 g, 0.242 mol, 2.1 equiv).
The reaction mixture was stirred at room temperature for ꢂ1 h.
The solution was concentrated under reduced pressure and the
resultant oil was redissolved in CH2Cl2 (200 mL). The solution
was washed with H2O (80 mL ꢃ 2), brine (80 mL ꢃ 2), and
concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel (30% EtOAc in hex-
anes as eluant) to give 4,4-dibromo-5-pyrazolones 4a as solids
in 95 % yields. mp 80–82ꢄC; 1H NMR (CDCl3, 200 MHz) d
2.42 (s, 3 H, CH3), 7.21 (d, 1 H, J ¼ 2.6 Hz, ArH), 7.39 (dd, 2
H, J ¼ 7.4, 2.6 Hz, ArH), 7.84 (d, 2 H, J ¼ 7.4 Hz, ArH); 13C
NMR (CDCl3, 50 MHz) d 20.0, 41.7, 118.9, 125.0, 128.8,
138.1, 159.9, 170.6; IR (KBr) 3199 (m), 2960 (m), 1706 (s,
C¼¼O), 1508 (s, C¼¼N), 1348 (m), 1227 (m), 972 (m), 754 (m)
cm–1; EIMS m/z (relative intensity) 362 (M þ 2, 7), 360 (Mþ,
14), 358 (M – 2, 7), 281 (84), 279 (84), 265 (3), 201 (20), 200
(13), 184 (3), 171 (4), 131 (3), 105 (11), 95 (7), 92 (4), 77
(100), 65 (8), 51 (13). Anal. Calcd for C10H8Br2N2O; C: 36.18;
H: 2.43; N: 8.44, Found: C: 36.22; H: 2.47; N: 8.46.
EXPERIMENTAL
General procedure. All chemicals were reagent grade and
used as purchased. All reactions were carried out under nitrogen
atmosphere and monitored by TLC analysis. Flash column chro-
matography was carried out on silica gel (230–400 mesh). Com-
mercially available reagents were used without further purifica-
tion unless otherwise noted. Dichloromethane, ethyl acetate,
hexanes, and methanol were purchased from Mallinckrodt
Chemical Co. Dry tetrahydrofuran (reagent grade) was used.
The following compounds were purchased from Acoros Chemi-
cal Co: o-tolyhydrazine hydrochoide, tert-butyl acetoacetate,
ethyl isobutylacetate, phenylhydrazine 4-methoxyphenylhydra-
zine hydrochloride, and 2,4-dinitrophenyl hydrazine. 2,4,6-Tri-
chlorophenyl hydrazine, 2-hydrazinopyridine, and isonicotinic
acid hydrazide were purchased from TCI Chemical Co. Ethyl
trifluoroacetoacetate and tert-butyl acietoacetate from Alfa
Chemical Co. Purification by gravity column chromatography
was carried out by use of Merck Reagents Silica Gel 60 (particle
size 0.063–0.200 mm, 70–230 mesh ASTM). Infrared (IR) spec-
tra were measured on a Bomem Michelson Series FTIR spec-
trometer. The wavenumbers reported are referenced to the poly-
styrene 1601 cmꢁ1 absortion. Absorption intensities are
recorded by the following abbreviations: s, strong; m, medium;
w, weak. Proton NMR spectra were obtained on a Bruker (200
MHz) spectrometer by use of CDCl3, CH3OD, and d6-DMSO as
solvent. Carbon-13 NMR spectra were obtained on a Bruker (50
MHz) spectrometer by used of CDCl3, CH3OD, and d6-DMSO
as solvent. Carbon-13 chemical shifts are referenced to the cen-
ter of the CDCl3 triplet (d 77.0 ppm). Multiplicities are recorded
by the following abbreviations: s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet; J, coupling constant (Hz). Elemental anal-
yses were carried out on a Heraeus CHN–O RAPID element
analyzer.
4,4-Dibromo-1-phenyl-3-trifluoro-2-pyrazolin-5-one (4b). mp
119–121ꢄC; 1H NMR (CDCl3, 200 MHz) d 7.24–7.52 (m, 3
H, ArH), 7.81 (d, 2 H, J ¼ 7.8 Hz, ArH); IR (KBr) 3391 (s),
3184 (m), 1631 (s, C¼¼O), 1576 (s, C¼¼N), 1404 (m), 1113
(m), 773 (m), 704 (m), 633 (m) cm–1. Anal. Calcd for
C10H5Br2F3N2O; C: 31.12; H: 1.31; N: 7.26, Found: C: 31.46;
H: 1.65; N: 6.94.
4,4-Dibromo-3-isopropyl-1-phenyl-2-pyrazolin-5-one (4c). mp
1
77–79ꢄC; H NMR (CDCl3, 200 MHz) d 1.44 (d, 6 H, J ¼ 7.2
Hz, 2 ꢃ CH3), 3.06 (m, 1 H, CHMe2), 7.23 (d, 1 H, J ¼ 7.9
Hz, ArH), 7.41 (dd, 2 H, J ¼ 7.9, 3.2 Hz, ArH), 7.86 (d, 2 H,
J ¼ 3.2 Hz, ArH); 13C NMR (CDCl3, 50 MHz) d 22.2 (2 ꢃ
CH3), 28.6, 45.8, 118.8 (2 ꢃ CH), 125.9, 129.0 (2 ꢃ CH),
137.1, 163.1, 165.0; IR (KBr) 3193 (m), 2935 (m), 1717 (s,
C¼¼O), 1575 (s, C¼¼N), 1489 (m), 1283 (m), 979 (m), 802
(m), 763 (m) cm–1; EIMS m/z (relative intensity) 359 (Mþ2,
4), 358 (Mþ, 8), 357 (M–2, 4), 344 (9), 315 (4), 278 (6), 254
(8), 253 (14), 252 (8), 201 (9), 184 (5), 174 (28), 173 (32),
171 (4), 145 (3), 130 (6), 119 (4), 105 (19), 91 (32), 78 (10),
77 (100), 67 (11), 64 (10), 51 (24). Anal. Calcd for
C12H12Br2N2O; C: 40.03; H: 3.36; N: 7.78, Found: C: 40.06;
H: 3.32; N: 7.81.
4,4-Dibromo-1,3-diphenyl-2-pyrazolin-5-one (4d). mp 128–
130ꢄC; 1H NMR (CDCl3, 200 MHz) d 7.27 (d, 1 H, J ¼ 7.6
Hz, ArH), 7.42–7.54 (m, 5 H, ArH), 7.99 (d, 2 H, J ¼ 7.8 Hz,
ArH), 8.23 (d, 2 H, J ¼ 7.8 Hz, ArH); 13C NMR (CDCl3, 50
MHz) d 42.7, 119.1 (2 ꢃ CH), 126.4, 127.2 (2 ꢃ CH), 128.9
(2 ꢃ CH), 129.2 (2 ꢃ CH), 131.7, 137.0, 137.1, 153.5, 165.7;
IR (KBr) 3391 (s), 3184 (m), 1632 (s, C¼¼O), 1575 (s, C¼¼N),
1404 (m),1112 (m), 773 (m), 704 (m) cm–1; EIMS m/z (rela-
tive intensity) 397 (Mþ2, 18), 395 (Mþ, 30), 393 (M–2, 18),
338 (14), 315 (45), 263 (9), 219 (66), 241 (15), 165 (19), 154
(39), 119 (52), 95 (93), 69 (99), 55 (100); HRMS calcd for
C15H10Br2N2O 391.9160, found 391.9157. Anal. Calcd for
C15H10Br2N2O; C: 45.72; H: 2.56; N: 7.11, Found: C: 45.76;
H: 2.59; N: 7.15.
Standard procedure for dibromination to prepare 4,4-
dibromo-5-pyrazolone derivatives 4a–4k. To a solution of
pyrazolones 3a–3h or 5-hydroxypyrazoles 3i–3k (1.0 equiv) in
THF (20 mL) was added DBI (2.1 equiv). The reaction mixture
was stirred at room temperature for ꢂ1 h. The solution was con-
centrated under reduced pressure and the resultant oil was redis-
solved in CH2Cl2 (50 mL). The solution was washed with H2O
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1156
K.-M. Cheng, J. B. Wu, H.-C. Lin, J.-J. Huang, Y.-Y. Huang,
S.-K. Lin, T.-P. Lin, and F. F. Wong
Vol 47
4,4-Dibromo-1-(2-methyl)-phenyl-3-phenyl-2-pyrazolin-5-one
4,4-Dibromo-3-phenyl-1-(pyrid-2-yl)-2-pyrazolin-5-one (4j). mp
1
(4e). mp 104–106ꢄC; 1H NMR (CD3OD, 200 MHz) d 2.23 (s, 3
H, CH3), 7.47–7.52 (m, 7 H, ArH), 7.96–8.01 (m, 2 H, ArH);
13C NMR (CD3OD, 50 MHz) d 16.0, 126.1 (2 ꢃ CH), 127.0,
127.6, 128.0, 128.5, 129.0 (2 ꢃ CH), 130.6, 131.0, 131.1,
132.5, 136.6, 149.8, 157.5; IR (KBr) 3198 (s), 2959 (m), 1717
(s, C¼¼O), 1542 (s, C¼¼N), 1319 (m), 1194 (m), 980 (m), 761
(m) cm–1; MS m/z (relative intensity) 410 (M þ 2, 6), 408 (Mþ,
12), 406 (M – 2, 6), 365 (2), 327 (74), 311 (3), 283 (7), 249
(53), 219 (10), 191 (6), 171 (6), 145 (12), 129 (36), 105 (24),
91 (100), 65 (26), 51 (16). Anal. Calcd for C16H12Br2N2O; C:
47.09; H: 2.96; N: 6.86, Found: C: 47.13; H: 2.92; N: 6.90.
4,4-Dibromo-1-(4-methoxy)-phenyl-3-phenyl-2-pyrazolin-5-
180–182ꢄC; H NMR (CDCl3, 200 MHz) d 7.16–7.27 (m, 1 H,
ArH), 7.43–7.50 (m, 3 H, ArH), 7.79–7.87 (m, 1 H, ArH), 7.90–
7.99 (m, 1 H, ArH), 8.21–8.26 (m, 2 H, ArH), 8.55–8.58 (m, 1 H,
ArH); 13C NMR (CDCl3, 50 MHz) d 42.4, 114.9, 122.0, 127.0,
127.5 (2 ꢃ CH), 127.8, 128.7 (2 ꢃ CH), 131.8, 138.5, 148.9,
154.2, 165.9; IR (KBr) 3200 (s), 2929 (m), 1718 (s, C¼¼O), 1558
(s, C¼¼N), 1409 (m), 1311 (m), 1268 (m), 974 (m), 864 (m), 828
(m), 812 (m), 739 (m), 690 (m) cm–1; EIMS m/z (relative inten-
sity) 395 (Mþ, 2), 320 (8), 318 (16), 316 (8), 237 (46), 209 (7),
182 (12), 160 (12), 129 (100), 102 (69), 75 (32), 51 (21); HRMS
calcd for C14H9Br2N3O 392.9112, found 392.9109.
4,4-Dibromo-3-phenyl-1-(3-isoquinolinyl)-2-pyrazolin-5-one
1
(4k). mp 131–133ꢄC; H NMR (CDCl3, 200 MHz) d 7.38–7.58
1
one (4f). mp 108–110ꢄC; H NMR (CDCl3, 200 MHz) d 3.81
(m, 5 H, ArH) 7.70–7.85 (m, 3 H, ArH) 8.09–8.16 (m, 1 H,
ArH) 8.27–8.34 (m, 2 H, ArH); 13C NMR (CDCl3, 50 MHz) d
42.5, 113.7, 126.7, 126.9, 127.1, 127.5, 127.6 (2 ꢃ CH), 128.7
(2 ꢃ CH), 129.1, 130.4, 131.9, 138.9, 146.8, 148.0, 154.3,
166.2; IR (KBr) 3045 (m), 2884 (m), 1751 (s, C¼¼O), 1645 (m,
C¼¼N), 1503 (m), 1429 (m), 1383 (m), 1290 (m), 899 (m), 823
(m), 686 (m) cm–1. Anal. Calcd for C18H11Br2N3O; C: 48.57;
H: 2.49; N: 9.44, Found: C: 48.24; H: 2.64; N: 9.31.
(s, 3 H, CH3), 6.97 (d, 2 H, J ¼ 7.2 Hz, ArH), 7.48–7.51 (m,
3 H, ArH), 7.85 (d, 2 H, J ¼ 7.2 Hz, ArH), 8.19 (d, 2 H, J ¼
7.8 Hz, ArH); 13C NMR (CDCl3, 50 MHz) d 42.6, 55.6, 114.2
(2 ꢃ CH), 121.0 (2 ꢃ CH), 127.1 (2 ꢃ CH), 127.3, 128.8 (2
ꢃ CH), 130.2, 131.5, 153.4, 157.9, 165.4; IR (KBr) 3194 (s),
2959 (m), 1717 (s, C¼¼O), 1508 (s, C¼¼N), 1251 (m), 1006
(m) cm–1; MS m/z (relative intensity) 427 (Mþ2, 2), 425 (Mþ,
4), 423 (M–2, 2), 345 (99), 343 (97), 266 (82), 265 (53), 235
(14), 221 (17), 209 (6), 162 (8), 160 (15), 158 (8), 135 (48),
129 (39), 121 (30), 107 (100), 102 (17), 92 (38), 77 (66), 64
(19). Anal. Calcd for C16H12Br2N2O2; C: 45.31; H: 2.85; N:
6.61, Found: C: 45.27; H: 2.89; N: 6.57.
Acknowledgments. The authors are grateful to the China Medi-
cal University (CMU97–225 & CMU97–251) and the National
Science Council of Republic of China for financial support.
4,4-Dibromo-1-(2,4-dinitro)-phenyl-3-phenyl-2-pyrazolin-5-
one (4g). mp 182–184ꢄC; 1H NMR (CDCl3, 200 MHz) d
7.22–7.28 (m, 1 H, ArH), 7.45–7.52 (m, 2 H, ArH), 7.86 (dd,
1 H, J ¼ 7.8, 3.7 Hz, ArH), 7.97 (d, 1 H, J ¼ 7.8 Hz, ArH),
8.22–8.27 (m, 2 H, ArH), 8.61 (d, 1 H, J ¼ 3.7 Hz, ArH); 13C
NMR (CDCl3, 50 MHz) d 38.4, 121.2, 124.9, 126.3 (2 ꢃ CH),
127.5, 129.2 (2 ꢃ CH), 129.8, 131.7, 134.3, 141.9, 144.6,
157.2, 169.9; IR (KBr) 3195 (m), 2926 (s), 1749 (s, C¼¼O),
1510 (s, C¼¼N), 1339 (m), 1169 (m), 1079 (m), 892 (m), 685
(m) cm–1; EIMS m/z (relative intensity) 486 (Mþ2, 9), 484
(Mþ, 17), 482 (M–2, 9), 405 (98), 325 (89), 279 (11), 205
(17), 147 (19), 129 (100), 103 (88), 93 (29), 77 (80), 63 (22-),
51 (31); HRMS calcd for C15H8Br2N4O5 481.8861, found
481.8857. Anal. Calcd for C15H8Br2N4O5; C: 37.22; H: 1.67;
N: 11.57, Found: C: 37.26; H: 1.71; N: 11.61.
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5-one (4h). mp 90–91ꢄC; H NMR (CDCl3, 200 MHz) d 7.46–
7.52 (m, 5 H, ArH), 8.11–8.16 (m, 2 H, ArH); IR (KBr) 3198
(m), 1749 (s, C¼¼O), 1557 (s, C¼¼N), 1470 (m), 1183 (m),
1064 (m), 815 (m) cm–1; EIMS m/z (relative intensity) 502 (M
þ 2, 4), 500 (Mþ, 8), 498 (M ꢁ 2, 4), 419 (67), 416 (100),
391 (14), 389 (21), 387 (11), 339 (46), 303 (20), 273 (21), 221
(4), 207 (27), 179 (57), 158 (29), 129 (63), 103 (68), 75 (33),
51 (25). Anal. Calcd for C15H7Br2Cl3N2O; C: 36.22; H: 1.42;
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las, A.; Ovalles, A. G.; Lopez, B.; Acero, N.; Llinares, F.; Mingarro,
4,4-Dibromo-3-phenyl-2-pyrazolin-5-one (4i). mp 147–149ꢄC;
1H NMR (DMSO-d6, 200 MHz) d 7.49–7.54 (m, 3 H, ArH),
8.11–8.16 (m, 2 H, ArH); 13C NMR (DMSO-d6, 50 MHz) d
40.5, 126.3 (2 ꢃ CH), 127.9, 128.3 (2 ꢃ CH), 130.7, 154.3,
170.5; IR (KBr) 3156 (m), 1742 (s, C¼¼O), 1541 (m, C¼¼N),
1271 (m), 865 (m), 742 (m), 692 (m) cm–1; EIMS m/z (rela-
tive intensity) 320 (M þ 2, 8), 318 (Mþ, 16), 316 (M – 2, 8),
240 (61), 209 (7), 182 (13), 160 (41), 129 (100), 102 (86), 77
(44), 75 (46), 63 (12), 51 (39). Anal. Calcd for C9H6Br2N2O;
C: 34.00; H: 1.90; N: 8.81, Found: C: 33.97; H: 1.94; N: 8.78.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet