Ionic Liquid Catalyzed One-Pot Synthesis of 2H-Pyridazino[1,2-a]indazole-1,6,9(11H)-triones Via Three-Component Reaction under Solvent-Free Conditions

Article abstract of DOI:10.1002/jhet.1736

2H-Pyridazino[1,2-a]indazole-1,6,9(11H)-triones were synthesized through one-pot, three-component condesation of aldehydes, maleic hydrazide, and dimedone using a green and inexpensive Br?nsted acidic ionic liquid 1-methyl-2-pyrrolidinone hydrosulfate ([Hnmp]HSO₄) as catalyst under solvent-free conditions. The method provided several advantages such as milder conditions, shorter reaction time, high yields, and environmentally benign procedure.

Full text of DOI:10.1002/jhet.1736

Month 2016
Ionic Liquid Catalyzed One-Pot Synthesis of 2H-Pyridazino[1,2-a]
indazole-1,6,9(11H)-triones Via Three-Component Reaction under
Solvent-Free Conditions
*
Maohua Ding and Hongyun Guo
College of Chemical Engineering and Materials, Zhejiang University of Technology, Zhejiang, People’s Republic of China
*
E-mail: guohy63@163.com
Received August 13, 2011
DOI 10.1002/jhet.1736
Published online 00 Month 2016 in Wiley Online Library (wileyonlinelibrary.com).
O
O
O
R
O
[Hnmp]HSO
NH
NH
N
N
4
RCHO
+
+
o
Solvent-free, 85 C
O
O
O
1
2
3
4
2H-Pyridazino[1,2-a]indazole-1,6,9(11H)-triones were synthesized through one-pot, three-component
condesation of aldehydes, maleic hydrazide, and dimedone using a green and inexpensive Brönsted acidic
ionic liquid 1-methyl-2-pyrrolidinone hydrosulfate ([Hnmp]HSO4) as catalyst under solvent-free conditions.
The method provided several advantages such as milder conditions, shorter reaction time, high yields, and
environmentally benign procedure.
J. Heterocyclic Chem., 00, 00 (2016).
INTRODUCTION
Recently the synthesis of 2H-pyridazino[1,2-a]indazole-
1,6,9(11H)-triones has been reported by Bazgir and
Teimouri using p-TSA as catalyst [18,19]. However, the
method has various drawbacks: low yields, the use of
expensive catalyst and non-recyclability. Now we
reported an efficient method for the preparation of 2H-
pyridazino[1,2-a]indazole-1,6,9(11H)-trione derivatives
using task-specific Brönsted acidic ionic liquid [Hnmp]
HSO4 as recyclable catalyst under solvent-free conditions
(Scheme 1).
Multicomponent reactions (MCRs) have been designed to
produce elaborate biologically active compounds and have
become an important area of research in organic, combinato-
rial, and medicinal chemistry [1]. The MCR strategy offers
significant advantages over conventional linear-type synthe-
sis because of its flexible, convergent, and atom efficient
nature [2]. In recent years, the synthesis of combinatorial
small-molecule heterocyclic libraries has emerged as a
valuable tool in the search for novel lead structures [3]. Thus,
the success of combinatorial chemistry in the drug discovery
process considerably depends on further advances in the
heterocyclic MCR methodology and also the environmen-
tally benign multicomponent procedures.
The indazole nucleus is a pharmaceutically important
and emerging heterocycle with a broad spectrum of
activities, including anti-inflammatory [4], antitumor [5],
anti-HIV [6], antimicrobial [7], contraceptive [8], and have
also been used as nNOS inhibitors [9]. Therefore, a number
of methods have been reported for the synthesis of indazole
derivatives [10–12]. Nevertheless, the development of new
synthetic methods for the efficient preparation of hetero-
cycles containing indazole ring fragment is therefore an
interesting challenge.
RESULTS AND DISCUSSION
Initially, the three-component reaction of benzaldehyde
(1a, 1 mmol), maleic hydrazide (2, 1 mmol), and dimedone
(3, 1 mmol) was carried out in different solvents in the
presence of [Hnmp]HSO4 and the influence of the amount
of ionic liquid. As shown in Table 1, different solvents
affected the efficiency of the reaction. Organic solvents and
water were used; no expected product was obtained. Espe-
cially, when the reaction was carried out under solvent-free
condition, the reaction proceeded fast and excellent yield
was obtained. In addition, no expected product could be
detected in the absence of ionic liquid [Hnmp]HSO4. There-
fore, the best results were obtained with 10% mol catalyst
amount of ionic liquid under solvent-free conditions.
The reaction temperature has a great influence on the
model reaction. The reactions were carried out at different
temperatures ranging from 70 to 100ꢀC under solvent-free
conditions. The results are presented in Table 2. The yield
of product 4a was increased, and the reaction time was
shortened as the temperature was increased from 70 to
In recent years, the room temperature ionic liquids are
attracting increasing interest as a “green” recyclable alter-
native to classical molecular solvents for synthetic organic
chemistry [13–15]. To date, some important reactions have
been carried out and investigated. Meanwhile, ionic liquids
are able to generate an internal pressure and promote the
association of reactants in the solvent cavity during the
activation process [16,17].
© 2016 Wiley Periodicals, Inc.

M. Ding and H. Guo
Vol 000
Scheme 1. Synthesis of 2H-pyridazino[1,2-a]indazole-1,6,9(11H)-trione derivatives catalyzed by ionic liquid [Hnmp]HSO4.
nature of the substituents on aromatic aldehydes has
some effect on this reaction. However, when the ali-
phatic ketones or aromatic ketones were applied to this
reaction, no expected product was obtained. In this
study, all the products were characterized by mp, IR,
1H NMR, and elemental analyses.
Table 1
Solvent effect and amount of catalyst on the reaction of benzaldehyde,
maleic hydrazide, and dimedone catalyzed by ionic liquid [Hnmp]HSO4.
Catalyst
Yield of
Entry Solventa Temperature (mol%) Time (h) 4a (%)b
As a green solvent or catalyst, the recovery and reuse of
ionic liquids are very important in green synthetic process.
Therefore, we also studied on the reuse of [Hnmp]HSO4.
As shown in Table 4, the ionic liquid [Hnmp]HSO4
could be successively reused in subsequent reactions and
had not decreased obviously in its catalytic activity. The
corresponding product still could be obtained in good yield
when [Hnmp]HSO4 was reused in the fourth round.
A reasonable mechanism for the formation of the product
4 is outlined in Scheme 2. The reaction occurs via initial
formation of intermediate 5 in quantitative yield by the
Knoevenagel addition of dimedone 3 to the aldehyde 1 and
followed by loss of water molecules. Subsequently,
Michael-type addition of the maleic hydrazide 2 to the inter-
mediate 5, followed by cyclization and tautomerization
affords the corresponding products 4.
1
2
3
4
5
6
7
8
9
EtOH
CH3CN
DMF
THF
Reflux
Reflux
100ꢀC
Reflux
Reflux
80ꢀC
10
10
10
10
10
10
0
12
12
12
12
12
0.2
12
0.5
0.5
Trace
Trace
Trace
Trace
Trace
90
Trace
82
88
Water
Solvent-free
Solvent-free
Solvent-free
Solvent-free
80ꢀC
80ꢀC
5
15
80ꢀC
aSolvent (5 mL) was used.
bIsolated yield.
Table 2
Effect of temperature on the solvent-free synthesis of 4a.
Entry
Temperature (ꢀC)
Time (min)
Yield of 4a (%)a
1
2
3
4
5
6
70
80
85
90
95
30
12
6
6
6
75
90
91
85
81
78
CONCLUSION
100
6
In conclusion, we have successfully developed a green and
highly efficient procedure for one-pot three-component
synthesis of 2H-pyridazino[1,2-a]indazole-1,6,9(11H)-trione
derivatives by using a novel Brönsted acidic ionic liquid
[Hnmp]HSO4 under solvent-free conditions. The reasonable
reaction times, very good yields, simple work-up procedure,
and environmentally friendly conditions are the merits of
this method.
All reaction were run with benzaldehyde (1 mmol), maleic hydrazide
(1 mmol), and dimedone (1 mmol) and [Hnmp]HSO4 (0.1 mmol).
aIsolated yield.
85ꢀC (Table 2, entries 1–3). However, further increase of
the temperature to 90À100ꢀC failed to improve the yield
of product 4a (Table 2, entries 4–6). Therefore, the best
temperature for the reaction was 85ꢀC.
On the basis of the optimized reaction conditions, a
series of 2H-pyridazino[1,2-a]indazole-1,6,9-(11H)-triones
were synthesized. The results summarized in Table 3 show
that the three-component reaction in the presence of 10 mol
% [Hnmp]HSO4 at 85ꢀC gave the corresponding products
in moderate to good yields. It is obvious that protocol
could be applied to various aldehydes. Besides, the results
suggest that the aromatic aldehydes bearing electron-
withdrawing groups have higher reactivity (higher yields
and shorter reaction time) than those bearing electron-
donating groups. So, it is concluded that the electronic
EXPERIMENTAL
Melting points were determined with an X-4 microscopic
melting-point apparatus (Tech, Peking, China) and were uncor-
rected. IR spectra were recorded on a NEXUS 670 spectrometer
1
(ThermoNicolet, WI) in KBr. H NMR spectra were measured
on a BRUKER AVANCE-II 500 MHz spectrometer (Bruker,
Fällanden, Switzerland) using TMS as internal standard and
DMSO-d6 as solvent. Elemental analyses were performed on
FLASH EA 1112 elemental analyzer (Thermo Electron SpA,
Milan, Italy).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2016
Ionic Liquid Catalyzed Three-Component Reaction under Solvent-Free Conditions
Table 3
Synthesis of 2H-pyridazino[1,2-a]indazole-1,6,9(11H)-trione derivatives 4.
Entry
R
Products
Time (min)
Yield (%)a
Mp (ꢀC) [Ref]
1
2
3
4
5
6
7
8
C6H5
4-Cl-C6H4
4-MeO-C6H4
4-F-C6H4
4-CH3-C6H4
4-NO2-C6H4
3-Br-C6H4
2-NO2-C6H4
2-Cl-C6H4
2-Naphthyl
–CH2CH3
–CH2CH2CH3
4a
4b
4c
4d
4e
4f
4g
4h
4i
6
5
10
3
10
3
6
5
5
6
10
10
91
93
88
94
86
93
91
92
92
90
77
82
230À231 [18]
214À216 [18]
192À194
186À188
248À250 [18]
210À212 [18]
180À181 [18]
207À209
9
220À222 [18]
234À235
10
11
12
4j
4k
4l
169À171
171À173 [19]
aIsolated yield.
Table 4
Studies on the reuse of [Hnmp]HSO4 in the preparation of 4a.
materials and other organic contaminations. Then the water was
evaporated under reduced pressure and dried to recover the ionic
liquid for subsequent use.
3,4-dihydro-3,3-dimethyl-11-phenyl-2H-pyridazino[1,2-a]indazole-
Round
1
2
3
4
5
1,6,9(11H)-trione(4a).
This compound was obtained as yellow
Yield (%)a
91
89
90
88
75
powder. 1H NMR (500 MHz, DMSO-d6): d=1.07 (s, 3H, CH3), 1.10
(s, 3H, CH3), 2.23 (s, 2H, CH2), 3.05 (dd, J1 =2.5Hz,
J2 = 16.5 Hz, 1H, CH2), 3.18 (dd, J1 =1.5Hz, J2 = 17.5 Hz, 1H, CH2),
6.15 (s, 1H, CH), 6.99 (d, J= 10.5 Hz, 1H, CHCO), 7.06
(d, J= 10.0 Hz, 1H, CHCO), 7.25À7.38 (m, 5H, Ar-H); IR (KBr):
3045, 2966, 1664, 1649, 1586, 1442, 1362, 1316, 1274 cmÀ1; Anal.
Calcd for C19H18N2O3: C, 70.79; H, 5.63; N, 8.69. Found: C, 70.68;
H, 5.59; N, 8.73.
aIsolated yield.
The synthesis of this task-specific ionic liquid has been carried
out from a similar method in the literature [20]. The ionic liquid
was formed quantitatively and in high purity as assessed by
1H NMR. All other chemicals (AR grade) were commercially
available and used without further purification.
11-(4-chlorophenyl)-3,4-dihydro-3,3-dimethyl-2H-pyridazino
[1,2-a]indazole-1,6,9(11H)-trione (4b).
This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.06 (s, 3H, CH3), 1.09 (s, 3H, CH3), 2.22 (s, 2H, CH2), 3.04
(dd, J1 = 2.5 Hz, J2 = 16.5 Hz, 1H, CH2), 3.16 (dd, J1 = 1.5 Hz,
J2 = 17.5 Hz, 1H, CH2), 6.16 (s, 1H, CH), 6.98 (d, J = 10.0 Hz,
1H, CHCO), 7.06 (d, J = 10.0 Hz, 1H, CHCO), 7.36À7.43
(m, 4H, Ar-H); IR (KBr): 3054, 2962, 1659, 1624, 1589, 1439,
1363, 1312, 1269 cmÀ1; Anal. Calcd for C19H17ClN2O3: C,
63.96; H, 4.80; N, 7.85. Found: C, 63.80; H, 4.75; N, 7.88.
3,4-dihydro-11-(4-methoxyphenyl)-3,3-dimethyl-2H-pyridazino
General procedure for the synthesis of 2H-pyridazino[1,2-a]
indazole-1,6,9(11H)-trione derivatives 4. The mixture of the
aldehyde 1 (1 mmol), maleic hydrazide 2 (1mmol), dimedone 3
(1mmol), [Hnmp]HSO4 (0.1 mmol) was stirred at 85ꢀC for the
appropriate time (monitored by thin-layer chromatography
[TLC]). After completion of the reaction, the result mixture was
cooled to room temperature and poured into 10 mL of water. The
solid product was collected by filtration and recrystallized from
ethanol to give the pure compound 4. The filtrate was extracted
with diethyl ether several times to remove unreacted starting
[1,2-a]indazole-1,6,9(11H)-trione (4c).
This compound was
Scheme 2. The possible mechanism for the synthesis of 2H-pyridazino[1,2-a]indazole-1,6,9(11H)-trione derivatives.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. Ding and H. Guo
Vol 000
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.08 (s, 3H, CH3), 1.10 (s, 3H, CH3), 2.23 (s, 2H, CH2), 3.07
(dd, J1 =2.5Hz, J2 = 16.5 Hz, 1H, CH2), 3.21 (dd, J1 = 1.5 Hz,
J2 = 17.5 Hz, 1H, CH2), 3.72 (s, 3H, OCH3), 6.10 (s, 1H, CH),
6.84 (m, 2H, Ar-H), 6.96 (d, J = 10.5 Hz, 1H, CHCO), 7.03
(d, J = 10.5 Hz, 1H, CHCO), 7.26 (m, 2H, Ar-H); IR (KBr): 2959,
1663, 1586, 1512, 1442, 1391, 1363, 1248 cmÀ1; MS (EI, 70 eV)
m/z (%): 352 (M+, 59.5), 308 (49.5), 270 (100), 245 (81.3), 217
(38.2). Anal. Calcd for C20H20N2O4: C, 68.17; H, 5.72; N, 7.95.
Found: C, 68.10; H, 5.68; N, 7.99.
11-(2-chlorophenyl)-3,4-dihydro-3,3-dimethyl-2H-pyridazino
[1,2-a]indazole-1,6,9(11H)-trione (4i). This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.07 (s, 3H, CH3), 1.11 (s, 3H, CH3), 2.19 (s, 2H, CH2), 3.06
(dd, J1 = 2.5 Hz, J2 = 16.5 Hz, 1H, CH2), 3.17 (dd, J1 = 1.5 Hz,
J2 = 17.5 Hz, 1H, CH2), 6.49 (s, 1H, CH), 6.99 (d, J = 10.0 Hz,
1H, CHCO), 7.09 (d, J = 10.0 Hz, 1H, CHCO), 7.28À7.46
(m, 4H, Ar-H); IR (KBr): 3051, 2963, 1658, 1628, 1589, 1440,
1364, 1314, 1270 cmÀ1; Anal. Calcd for C19H17ClN2O3: C,
63.96; H, 4.80; N, 7.85. Found: C, 63.82; H, 4.74; N, 7.86.
3,4-dihydro-3,3-dimethyl-11-(naphthalen-3-yl)-2H-pyridazino
11-(4-fluorophenyl)-3,4-dihydro-3,3-dimethyl-2H-pyridazino
[1,2-a]indazole-1,6,9(11H)-trione (4d).
This compound was
[1,2-a]indazole-1,6,9(11H)-trione (4j).
This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.07 (s, 3H, CH3), 1.10 (s, 3H, CH3), 2.23 (s, 2H, CH2), 3.04
(dd, J1 =2.0Hz, J2 = 16.5 Hz, 1H, CH2), 3.17 (dd, J1 =1.0Hz,
J2 = 17.5 Hz, 1H, CH2), 6.17 (s, 1H, CH), 6.97 (d, J= 10.0 Hz, 1H,
CHCO), 7.05 (d, J= 10.0 Hz, 1H, CHCO), 7.11À7.44 (m, 4H,
Ar-H); IR (KBr): 3053, 2963, 1659, 1625, 1589, 1507, 1439, 1365,
1313, 1271 cmÀ1; MS (EI, 70 eV) m/z (%): 340 (M+, 34.7), 259
(36.5), 245 (100), 217 (37.3). Anal. Calcd for C19H17FN2O3:
C, 67.05; H, 5.03; N, 8.23. Found: C, 66.93; H, 5.01; N, 8.28.
3,4-dihydro-3,3-dimethyl-11-p-tolyl-2H-pyridazino[1,2-a]indazole-
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.05 (s, 3H, CH3), 1.12 (s, 3H, CH3), 2.16 (s, 2H, CH2), 3.11
(dd, J1 = 2.5 Hz, J2 = 16.5 Hz, 1H, CH2), 3.24 (dd, J1 = 1.5 Hz,
J2 = 17.5 Hz, 1H, CH2), 6.97 (s, 1H, CH), 6.99 (d, J = 10.0 Hz,
1H, CHCO), 7.09 (d, J = 10.0 Hz, 1H, CHCO), 7.41À7.94
(m, 7H, Ar-H); IR (KBr): 3051, 2960, 1655, 1627, 1589, 1437,
1362, 1314, 1269 cmÀ1; MS (EI, 70 eV) m/z (%): 372 (M+,
38.7), 291 (20.7), 245 (100), 217 (27.4). Anal. Calcd for
C23H20N2O3: C, 74.18; H, 5.41; N, 7.52. Found: C, 74.25; H,
5.44; N, 7.48.
1,6,9(11H)-trione(4e).
This compound was obtained as
11-Ethyl-3,3-dimethyl-2,3,4,11-tetrahydro-pyridazino[1,2-a]
yellow powder. 1H NMR (500 MHz, DMSO-d6): d=1.06 (s, 3H,
CH3), 1.09 (s, 3H, CH3), 2.22 (s, 2H, CH2), 2.25 (s, 3H, CH3), 3.03
(dd, J1 =2.5Hz, J2 = 16.5 Hz, 1H, CH2), 3.17 (dd, J1 =1.5Hz,
J2 = 17.5 Hz, 1H, CH2), 6.10 (s, 1H, CH), 6.96 (d, J= 10.5 Hz, 1H,
CHCO), 7.04 (d, J= 10.5 Hz, 1H, CHCO), 7.09À7.24 (m, 4H,
Ar-H); IR (KBr): 3017, 2960, 2873, 1666, 1652, 1587, 1512, 1442,
1392, 1315, 1272 cmÀ1; Anal. Calcd for C20H20N2O3: C, 71.41; H,
5.99; N, 8.33. Found: C, 71.33; H, 5.91; N, 8.38.
indazole-1,6,9-trione (4k).
This compound was obtained as
yellow powder. 1H NMR (500 MHz, DMSO-d6): d=0.63
(t, J = 7.5 Hz, 3H, CH3), 1.10 (d, J = 4.9 Hz, 6H, (CH3)2), 1.90
(dqd, J = 14.9, 7.5, 2.8 Hz, 1H), 2.37–2.27 (m, 3H), 2.99 (dd,
J = 18.9, 2.5 Hz, 1H), 3.12 (d, J = 19.1 Hz, 1H,), 5.44–5.32
(m, 1H, CH),7.08–7.03 (m, 2H, CHCO) ppm; 13C NMR
(500 MHz, DMSO-d6): 192.7, 154.8, 153.7, 151.6, 135.2,
134.9, 115.6, 63.0, 50.3, 36.8, 34.1, 28.1, 27.7, 20.8, 6.9 ppm.
IR (KBr): 1700, 1662, 1658, 1589 cmÀ1; MS (EI, 70 eV) m/z
(%): 274 (M+, 2.2), 246 (15.7), 245 (100), 217 (18.1). Anal.
Calcd for C14H16N2O3: C, 65.68; H, 6.61; N, 10.21. Found: C,
65.54; H, 6.52;N, 9.90.
3,4-dihydro-3,3-dimethyl-11-(4-nitrophenyl)-2H-pyridazino
[1,2-a]indazole-1,6,9(11H)-trione (4f).
This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.06 (s, 3H, CH3), 1.11 (s, 3H, CH3), 2.23 (s, 2H, CH2), 3.07
(dd, J1 = 2.0 Hz, J2 = 16.5 Hz, 1H, CH2), 3.17 (dd, J1 = 1.0 Hz,
J2 = 17.5Hz, 1H, CH2), 6.32 (s, 1H, CH), 7.02 (d, J = 10.0Hz,
1H, CHCO), 7.11 (d, J = 10.0Hz, 1H, CHCO), 7.72À8.18
(m, 4H, Ar-H); IR (KBr): 3061, 2968, 1661, 1624, 1589, 1522,
1435, 1347, 1311, 1269 cmÀ1; Anal. Calcd for C19H17N3O5: C,
62.12; H, 4.66; N, 11.44. Found: C, 62.17; H, 4.70; N, 11.38.
11-(3-bromophenyl)-3,4-dihydro-3,3-dimethyl-2H-pyridazino
3,3-Dimethyl-11-propyl-2,3,4,11-tetrahydro-1H-pyridazino
[1,2-a]-indazole-1,6,9-trione (4l). This compound was obtained
as yellow powder. 1H NMR (500 MHz, DMSO-d6) d = 0.79
(t, J = 7.3 Hz, 3H,CH3), 1.05 (dd, J = 15.0, 7.0 Hz, 2H,CH2), 1.09
(s, 6H, (CH3)2), 1.88 (ddd, J = 11.6, 5.7, 2.9 Hz, 1H), 2.22 (dd,
J = 11.9, 3.6 Hz, 1H), 2.31 (q, J = 16.0Hz, 2H), 2.54–2.48
(m, 1H), 2.98 (dd, J =18.9, 2.4 Hz, 1H, CH2), 3.11 (d, J = 18.9 Hz,
1H, CH2), 5.35 (t, J = 8.1 Hz, 1H, CH), 7.02–7.07 (m, 2H, CHCO);
13C NMR (500 MHz, DMSO-d6): 192.7, 154.9, 153.7, 151.3,
135.6, 134.9, 116.2, 62.3, 50.3, 36.8, 34.1, 30.2, 28.1, 27.8, 16.0,
13.7 ppm. IR (KBr): n= 1685, 1654, 1650, 1582 cmÀ1; Anal.
Calcd for C16H20N2O3: C, 66.65; H, 6.99; N, 9.72. Found: C,
64.73; H, 6.62; N, 9.50.
[1,2-a]indazole-1,6,9(11H)-trione (4g).
This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.07 (s, 3H, CH3), 1.10 (s, 3H, CH3), 2.22 (s, 2H, CH2), 3.05
(dd, J1 = 2.0 Hz, J2 = 16.5 Hz, 1H, CH2), 3.16 (dd, J1 = 1.0 Hz,
J2 = 17.5 Hz, 1H, CH2), 6.18 (s, 1H, CH), 6.97 (d, J = 10.0 Hz,
1H, CHCO), 7.05 (d, J = 10.0 Hz, 1H, CHCO), 7.15À7.44
(m, 4H, Ar-H); IR (KBr): 3063, 2958, 1663, 1614, 1588, 1521,
1445, 1346, 1313, 1269 cmÀ1; Anal. Calcd for C19H17BrN2O3:
C, 56.87; H, 4.27; N, 6.98. Found: C, 56.77; H, 4.23; N, 7.02.
3,4-dihydro-3,3-dimethyl-11-(2-nitrophenyl)-2H-pyridazino
Acknowledgments. This work was financially supported by the
Research Foundation of Zhejiang Provincial Education Department
(20060811).
[1,2-a]indazole-1,6,9(11H)-trione (4h).
This compound was
obtained as yellow powder. 1H NMR (500 MHz, DMSO-d6):
d=1.05 (s, 3H, CH3), 1.10 (s, 3H, CH3), 2.22 (s, 2H, CH2), 3.05
(dd, J1 =2.5Hz, J2 = 16.5 Hz, 1H, CH2), 3.14 (dd, J1 =1.0Hz,
J2 = 17.5 Hz, 1H, CH2), 7.00 (s, 1H, CH), 6.98 (d, J= 10.0 Hz, 1H,
CHCO), 7.08 (d, J= 10.0 Hz, 1H, CHCO), 7.52À7.97 (m, 4H,
Ar-H); IR (KBr): 2961, 2933, 1659, 1627, 1590, 1531, 1440, 1391,
1360, 1312, 1271 cmÀ1; MS (EI, 70 eV) m/z (%): 367 (M+, 31.7),
350 (100), 264 (30.3), 233 (29.0). Anal. Calcd for C19H17N3O5:
C, 62.12; H, 4.66; N, 11.44. Found: C, 62.18; H, 4.71; N, 11.36.
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