Synthesis of 7-aryl-9-methyl-3h- pyrazolo[4,3-f]quinoline derivatives catalysed by iodine

Article abstract of DOI:10.3184/174751911X13148095775284

A mild and efficient method for the synthesis of 7-aryl-9-methyl-3H- pyrazolo[4,3-f]quinoline derivatives via a threecomponent reaction of an aromatic aldehyde, 1H-indazol-5-amine and acetone catalysed by iodine is described. This new procedure has the ad

Full text of DOI:10.3184/174751911X13148095775284

JOURNAL OF CHEMICAL RESEARCH 2011
RESEARCH PAPER 513
SEPTEMBER, 513–515
Synthesis of 7-aryl-9-methyl-3h- pyrazolo[4,3-f]quinoline derivatives
catalysed by iodine
Ming-Yue Yina,b, Wei Wanga,b, Mei-Mei Zhanga,b and Xiang-Shan Wanga,b*
aSchool of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Xuzhou
Normal University, Xuzhou Jiangsu 221116, P. R. China
b The Key Laboratory of Biotechnology on Medical Plant of Jiangsu Province, Xuzhou Normal University, Xuzhou Jiangsu 221116, P. R. China
A mild and efficient method for the synthesis of 7-aryl-9-methyl-3H- pyrazolo[4,3-f]quinoline derivatives via a three-
component reaction of an aromatic aldehyde, 1H-indazol-5-amine and acetone catalysed by iodine is described. This
new procedure has the advantages of mild reaction conditions, high yields and a metal-free catalyst.
Keywords: pyrazolo[4,3-f]quinoline, 1H-indazol-5-amine, iodine
Pyrazoloquinoline derivatives are an important class of hetero-
cycles because they are promising materials for optoelectronic
applications.1–5 In addition, they possess antileishmanial6 and
antimicrobial activities.7 Some of them are used as modulators
of cytokine biosynthesis for treatment of viral and neoplastic
diseases,8 and immune-modulators for inducing cytokine
biosynthesis in animals, and in the treatment of diseases,
including viral and neoplastic disorders.9 They are also human
A3 adenosine receptor (AR) antagonists.10,11
Although a number of useful synthetic procedures to pre-
pare pyrazoloquinolines has been developed,12–16 several limi-
tations remain. For example, most reported procedures involve
several steps, or give low yields. Moreover, the starting materi-
als are not often readily available. Thus, simple and efficient
method to synthesise pyrazoloquinolines would be attractive.
Over the past few years, molecular iodine (I2) has emerged
as a powerful catalyst for various organic transformations
because of its inexpensive, nontoxic, and eco-friendly nature.17–22
In view of the importance of pyrazoloquinoline derivatives and
as a continuation of our research devoted to the development
of new methods for the preparation of heterocycles via multi-
component reactions catalysed by iodine,23,24 we now report
the synthesis of 7-aryl-9-methyl-3H-pyrazolo[4,3-f]quinoline
derivatives by the reaction of an aromatic aldehyde, 1H-
indazol-5-amine and acetone in THF catalysed by iodine.
Table 1 (entries 5−7) show that 5 mol% I2 at reflux in THF is
sufficient to initiate the reaction. Higher loading of the catalyst
had no significant influence on the reaction yield. To find the
optimum reaction temperature, the reaction was carried out
with 5 mol% of I2 at room temperature, at 50 °C and at reflux
temperature, resulting in the isolation of 4a in trace amounts,
72% and 90% yields (Table 1, entries 3−5), respectively. Thus,
5 mol% of I2 and a reaction temperature at reflux were optimal
conditions. In addition, CH3CN, benzene, DMF and CHCl3
(Table 1, entries 8−11) were also tested as the solvents. In
these cases, product 4a was formed in slightly lower yields
(Table 1, entries 8−11).
According to the optimised conditions, various aromatic
aldehydes 1 were then subjected to reaction with 2 and 3
to generate a library of 7-aryl-9-methyl-3H- pyrazolo[4,3-
f]quinoline derivatives 4 (Table 2). For aldehyde 1, the yields
of 4 were not sensitive to the electronic properties of the aro-
matic ring in the presence of electron-withdrawing groups
(such as halide) or electron-donating groups (such as alkyl or
alkoxy group) (Table 2). The structures of the products 4 were
characterised by 1H NMR, IR and HRMS, the spectra were all
in full agreement with their constitution.
Table 1 Yield optimisation for 4a under different conditions a
Entry Temp. /°C) Catalyst /mol % Solvent
Yields /%b
1
2
r.t.
0
0
THF
0
0
Results and discussion
Reflux
r.t.
THF
Treatment of aromatic aldehyde 1, 1H-indazol-5-amine 2
and acetone 3 in THF in the presence of 5 mol% iodine at
reflux condition afforded the corresponding 7-aryl-9-methyl-
3H-pyrazolo[4,3-f]quinoline derivatives 4 in high yields
(Scheme 1).
In our initial study, the reaction of 2-chlorobenzaldehyde
1a, 1H-indazol-5-amine 2 and acetone 3 was used as a model
reaction to optimise the reaction conditions. The reaction was
firstly carried out in THF in the absence of I2. It was found that
no reaction occurred either at room temperature or under reflux
(Table 1, entries 1 and 2). Similar reactions were attempted
in the presence of 5, 10 and 20 mol% of I2. The results from
3
5
THF
trace
72
4
50
5
5
THF
5
Reflux
Reflux
Reflux
Reflux
Reflux
80
THF
90
6
10
20
5
THF
89
7
THF
90
8
CH3CN
Benzene
DMF
CHCl3
86
9
5
78
10
11
5
82
Reflux
5
80
a Reagents and conditions: 2-chlorobenzaldehyde 1a (0.281 g,
2.0 mmol), 2 (0.266 g, 2.0 mmol), 3 (0.232 g, 4 mmol), solvent
(10 mL).
b Isolated yields.
Scheme 1
* Correspondent. E-mail: xswang1974@yahoo.com

514 JOURNAL OF CHEMICAL RESEARCH 2011
Table 2 Synthetic results of 4a–l catalysed by iodine in THFa
indicated by TLC, a little DMF was added to the mixture until all the
yellow solid was dissolved. The generated powder was collected
by filtration to give 4 when the mixture was cooled to room
temperature.
Entry
Ar
Products
Time /h
Yields /%b
1
2
2-ClC6H4
4a
4b
4c
4d
4e
4f
4g
4h
4i
12
10
13
14
12
14
14
16
16
16
10
16
90
92
87
83
88
92
94
88
82
89
90
90
7-(2-Chlorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4a):
2-FC6H4
1
Pale yellow powder from DMF-THF, m.p. 250–252 °C; H NMR
3
3-ClC6H4
(DMSO-d6, δH, ppm): 2.95 (s, 3H, CH3), 7.48–7.52 (m, 2H, ArH),
7.60–7.64 (m, 1H, ArH), 7.66–7.69 (m, 1H, ArH), 7.76 (s, 1H, ArH),
7.94–7.99 (m, 2H, ArH), 8.62 (s, 1H, CH), 13.75 (s, 1H, NH). IR
(KBr, ν, cm−1): 3193, 3158, 3120, 3002, 2954, 1661, 1576, 1538,
1475, 1442, 1376, 1353, 1334, 1291, 1263, 1179, 1096, 1049, 1010,
940, 875, 845, 792, 756, 730. HRMS (ESI, m/z): Calcd for C17H1335ClN3
(M + H+): 294.0798. Found: 294.0811.
4
3-BrC6H4
5
4-FC6H4
6
4-ClC6H4
7
4-BrC6H4
8
4-MeC6H4
4-MeOC6H4
3,4-OCH2OC6H3
3,4-Cl2C6H3
3,4-Me2C6H3
9
10
11
12
4j
4k
4l
7-(2-Fluorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4b):
1
Pale yellow powder from DMF-THF, m.p. 221–223 °C; H NMR
(DMSO-d6, δH, ppm): 2.96 (s, 3H, CH3), 7.36–7.41 (m, 2H, ArH),
7.51–7.56 (m, 1H, ArH), 7.90 (s, 1H, ArH), 7.95–7.98 (m, 2H, ArH),
8.03–8.07 (m, 1H, ArH), 8.61 (s, 1H, CH), 13.76 (s, 1H, NH). IR
(KBr, ν, cm−1): 3199, 3153, 3107, 3000, 2955, 2919, 1619, 1575,
1542, 1494, 1462, 1447, 1376, 1353, 1333, 1213, 1177, 1106, 1086,
942, 875, 839, 820, 787, 756, 734. HRMS (ESI, m/z): Calcd for
C17H13FN3 (M + H+): 278.1094. Found: 278.1082.
7-(3-Chlorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4c):
White powder from DMF-THF, m.p. 240–242 °C; 1H NMR (DMSO-
d6, δH, ppm): 2.98 (s, 3H, CH3), 7.52–7.60 (m, 2H, ArH), 7.96–7.80
(m, 2H, ArH), 8.21 (s, 1H, ArH), 8.25 (d, J = 7.6 Hz, 1H, ArH), 8.34
(s, 1H, ArH), 8.59 (s, 1H, CH), 13.73 (s, 1H, NH). IR (KBr, ν, cm−1):
3206, 3158, 3116, 3062, 2968, 2918, 1662, 1578, 1568, 1542, 1483,
1448, 1408, 1373, 1350, 1271, 1178, 1097, 1079, 1052, 1009, 946,
908, 840, 808, 735, 692. HRMS (ESI, m/z): Calcd for C17H1335ClN3
(M + H+): 294.0798. Found: 294.0800.
7-(3-Bromophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4d):
White powder from DMF-THF, m.p. 259–261 °C; 1H NMR (DMSO-
d6, δH, ppm): 2.97 (s, 3H, CH3), 7.50–7.53 (m, 1H, ArH), 7.67 (d, J =
8.8 Hz, 1H, ArH). 7.96–8.00 (m, 2H, ArH), 8.21 (s, 1H, ArH), 8.29
(d, J = 7.6 Hz, 1H, ArH), 8.48 (s, 1H, ArH), 8.59 (s, 1H, CH), 13.73
(s, 1H, NH). IR (KBr, ν, cm−1): 3198. 3124, 3009, 2954, 1593, 1566,
1540, 1475, 1451, 1377, 1348, 1289, 1175, 1095, 940, 899, 839, 818,
789, 709, 681. HRMS (ESI, m/z): Calcd for C17H1379BrN3 (M + H+)
338.0293. Found: 338.0301.
a Reagents and conditions: 1 (2.0 mmol), 2 (0.266 g, 2.0 mmol),
3 (0.232 g, 4.0 mmol), I2 (0.1 mmol, 0.026 g), THF (10 mL).
b Isolated yields.
Formation of 4 can be considered as an example of the
Povarov reaction,25 which is usually catalysed by various
Lewis acids, as documented by Kouznetsov.26 According to our
previous study,23,24 we suggest that iodine catalyses the reac-
tion as a mild Lewis acid. The mechanism proposed is shown
in Scheme 2. In the presence of iodine, acetone is in equilib-
rium with the enol form I.27 The Schiff base II may be formed
by the reaction of aromatic aldehyde and 1H-indazol-5-amine
initially. An imino-Diels–Alder reaction takes place between
the iodine-activated Schiff base III and enol form II to
give IV. The subsequent dehydration of IV results in dihydro-
quinoline V, which is further oxidised by air to give the final
aromatised products 4.
Experimental
Melting points were determined in open capillaries and are uncor-
rected. IR spectra were recorded on a Tensor 27 spectrometer in KBr
1
pellet. H NMR spectra were obtained from a solution in DMSO-d6
7-(4-Fluorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4e):
White powder from DMF-THF, m.p. 258–259 °C; 1H NMR (DMSO-
d6, δH, ppm): 2.96 (s, 3H, CH3), 7.37 (t, J = 8.8 Hz, 2H, ArH), 7.95
(s, 2H, ArH), 8.13 (s, 1H, ArH), 8.30–8.34 (m, 2H, ArH), 8.58 (s, 1H,
CH), 13.73 (s, 1H, NH). IR (KBr, ν, cm−1): 3190, 3155, 3123, 3006,
1605, 1573, 1512, 1443, 1411, 1378, 1351, 1290, 1229, 1176, 1158,
1093, 1011, 940, 822, 788, 727. HRMS (ESI, m/z): Calcd for
C17H13FN3 (M + H+): 278.1094. Found: 278.1095.
with Me4Si as internal standard using a Bruker-400 spectrometer.
HRMS analyses were carried out using a Bruker-micro-TOF-Q-MS
analyser.
Syntheses of pyrazolo[4,3-f]quinoline derivatives 4a–l; general pro-
cedure
A dry 50-mL flask was charged with aromatic aldehyde (2.0 mmol),
1H-indazol-5-amine (0.266 g, 2.0 mmol), acetone (0.232 g, 4.0 mmol),
I2 (0.026 g, 0.1 mmol) and THF (10 mL). The reaction mixture was
stirred at reflux for 10–16 h. After completion of the reaction as
7-(4-Chlorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4f):
1
Pale yellow powder from DMF-THF, m.p. 282–284 °C; H NMR
Scheme 2

JOURNAL OF CHEMICAL RESEARCH 2011 515
(DMSO-d6, δH, ppm): 2.97 (s, 3H, CH3), 7.61 (d, J = 8.4 Hz, 2H, ArH),
7.96 (s, 2H, ArH), 8.17 (s, 1H, ArH), 8.32 (d, J = 8.8 Hz, 2H, ArH),
8.59 (s, 1H, CH), 13.72 (s, 1H, NH). IR (KBr, ν, cm−1): 3152, 3116,
3066, 3001, 1581, 1569, 1541, 1493, 1452, 1403, 1375, 1350, 1272,
1174, 1091, 1012, 940, 849, 821, 788, 722. HRMS (ESI, m/z): Calcd
for C17H1335ClN3 (M + H+): 294.0798. Found: 294.0814.
quinoline derivatives via a three-component reaction of an aro-
matic aldehyde, 1H-indazol-5-amine and acetone catalysed by
iodine. The features of this procedure are mild reaction con-
ditions, high yields, operational simplicity and a metal-free
catalyst.
7-(4-Bromophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4g):
Pale yellow powder from DMF-THF, m.p. 295–296 °C; H NMR
1
We are grateful to the National Natural Science foundation of
China (20802061), A Project Funded by the Priority Academic
Program Development of Jiangsu Higher Education Institu-
tions and Qing Lan Project (08QLT001, 10QLD008) of Jiangsu
Education Committee for financial support.
(DMSO-d6, δH, ppm): 2.97 (s, 3H, CH3), 7.74 (d, J = 8.4 Hz, 2H, ArH),
7.96 (s, 2H, ArH), 8.17 (s, 1H, ArH), 8.25 (d, J = 8.4 Hz, 2H, ArH),
8.59 (s, 1H, CH), 13.72 (s, 1H, NH). IR (KBr, ν, cm−1): 3148, 3105,
2983, 2953, 1579, 1567, 1541, 1490, 1443, 1400, 1349, 1331, 1273,
1174, 1092, 1073, 1008, 941, 848, 820, 788, 721. HRMS (ESI, m/z):
Calcd for C17H1379BrN3 (M + H+): 338.0293. Found: 338.0326.
9-Methyl-7-p-tolyl-3H-pyrazolo[4,3-f]quinoline (4h): Pale yellow
powder from DMF-THF, m.p. 260–261 °C; 1H NMR (DMSO-d6, δH,
ppm): 2.39 (s, 3H, CH3), 2.96 (s, 3H, CH3), 7.35 (d, J = 8.0 Hz, 2H,
ArH), 7.94 (s, 2H, ArH), 8.10 (s, 1H, ArH), 8.17 (d, J = 8.0 Hz, 2H,
ArH), 8.57 (s, 1H, CH), 13.70 (s, 1H, NH). IR (KBr, ν, cm−1): 3144,
3097, 3062, 2983, 2866, 1607, 1572, 1543, 1511, 1447, 1376, 1352,
1339, 1271, 1177, 1094, 1012, 980, 933, 824, 792, 730. HRMS (ESI,
m/z): Calcd for C18H16N3 (M + H+): 274.1344. Found: 274.1346.
7-(4-Methoxyphenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline (4i):
Received 25 July 2011; accepted 26 August 2011
Paper 1100810 doi: 10.3184/174751911X13148095775284
Published online: 30 September 2011
References
1
2
A. Danel, E. Gondek and I. Kityk, Opt. Mater., 2009, 32, 267.
K. Khachatryan, W. Boszczyk and P. Tomasik, Polish J. Chem., 2005, 79,
1645.
3
4
5
6
7
8
9
B. Luszczynska, E. Dobruchowska, I. Glowacki, J. Ulanski, F. Jaiser,
X. Yang, D. Neher and A. Danel, J. Appl. Phy., 2006, 99, 024505/1.
E. Gondek, I.V. Kityk, J. Sanetra, P. Szlachcic, P. Armatys, A. Wisla and
A. Danel, Opt. Laser Technol., 2006, 38, 487.
E. Gondek, I.V. Kityk, A. Danel, A. Wisla and J. Sanetra, Synth. Metals,
2006, 156, 1348.
A. Al-Qahtani, Y.M. Siddiqui, A.A. Bekhit, O.A. El-Sayed, H.Y. Aboul-
Enein and M.N. Al-Ahdal, Arch. Pharm. 2005, 338, 484.
S.P.Vartale, J.S. Jadhav, M.A. Kale and S.V. Kuberkar, Indian J. Heterocycl.
Chem., 2006, 16, 163.
D.S. Hays, R.B. Prince, C.A. Haraldson and J.D. Bonk, PCT Int. Appl. WO
2006107851 A1 12 Oct 2006, 152pp. Chem. Abstr., 2006, 145, 419133.
B.A. Merrill, M.E. Danielson, D.S. Hays, D.T. Amos, P.D. Heppner, T.A.
Kshirsagar, G.D. Lundquist and W.H. Moser, PCT Int. Appl. WO
2006107771 A2 12 Oct 2006, 135pp. Chem. Abstr., 2006, 145, 419140.
1
Pale yellow powder from DMF-THF, m.p. 217–218 °C; H NMR
(DMSO-d6, δH, ppm): 2.95 (s, 3H, CH3), 3.85 (s, 3H, OCH3), 7.10
(d, J = 8.8 Hz, 2H, ArH), 7.94 (s, 2H, ArH), 8.09 (s, 1H, ArH), 8.23 (d,
J = 8.8 Hz, 2H, ArH), 8.59 (s, 1H, CH), 13.69 (s, 1H, NH). IR (KBr,
ν, cm−1): 3142, 3096, 3096, 2970, 1607, 1571, 1510, 1458, 1417,
1377, 1353, 1306, 1253, 1174, 1135, 1099, 1027, 979, 931, 836, 815,
788, 738. HRMS (ESI, m/z): Calcd for C18H16N3O (M + H+): 290.1293.
Found: 290.1317.
9-Methyl-7-piperonyl-3H-pyrazolo[4,3-f]quinoline ( 4j): Pale
yellow powder from DMF-THF, m.p. 247–248 °C; 1H NMR (DMSO-
d6, δH, ppm): 2.95 (s, 3H, CH3), 6.12 (s, 2H, CH2), 7.08 (d. J = 8.0 Hz,
1H, ArH), 7.83–7.86 (m, 2H, ArH), 7.93 (s, 2H, ArH), 8.09 (s, 1H,
ArH), 8.56 (s, 1H, CH), 13.67 (s, 1H, NH). IR (KBr, ν, cm−1): 3151,
3106, 3062, 2994, 1573, 1543, 1503, 1459, 1436, 1344, 1326, 1241,
1211, 1171, 1114, 1042, 942, 872, 858, 818, 769, 725. HRMS (ESI,
m/z): Calcd for C18H13N3O2 (M + H+) 304.1086. Found: 304.1133.
7-(3,4-Dichlorophenyl)-9-methyl-3H-pyrazolo[4,3-f]quinoline
10 V. Colotta, D. Catarzi, F. Varano, F. Capelli, O. Lenzi, G. Filacchioni, C.
Martini, L. Trincavelli, O. Ciampi, A.M. Pugliese, F. Pedata, A. Schiesaro,
E. Morizzo and S. Moro, J. Med. Chem., 2007, 50, 4061.
11 V. Colotta, F. Capelli, O. Lenzi, D. Catarzi, F. Varano, D. Poli, F. Vincenzi,
K. Varani, P.A. Borea, D. Dal Ben, R. Volpini, G. Cristalli and G.
Filacchioni, Bioorg. Med. Chem., 2009, 17, 401.
12 D. Malleshwar, K. Gautami and A. Jayashree, Org. Chem: An Indian J.,
2009, 5, 344.
13 J.R. Mali, U.R. Pratap, D.V. Jawale and R.A. Mane, Tetrahedron Lett.,
2010, 51, 3980.
14 S.-J. Tu, S.-S. Wu, X.-H. Zhang, Z.-G. Han, X.-D. Cao and W.-J. Hao,
Synth. Commun., 2010, 40, 1057.
15 S. Duggineni, D. Sawant, B. Saha and B. Kundu, Tetrahedron, 2006, 62,
3228.
16 M.N. Jachak, A.B. Avhale, V.J. Medhane and R.B. Toche, J. Heterocycl.
Chem., 2006, 43, 1169.
17 C.-H. Cho, B. Neuenswander, G.H. Lushington and R.C. Larock, J. Comb.
Chem., 2009, 11, 900.
1
(4k): White powder from DMF-THF, m.p. 279–280 °C; H NMR
(DMSO-d6, δH, ppm): 2.97 (s, 3H, CH3), 7.80 (d, J = 8.4 Hz, 1H, ArH),
7.96 (d, J = 5.6 Hz, 2H, ArH), 8.24 (s, 1H, ArH), 8.29 (d, J = 8.8 Hz,
1H, ArH), 8.53 (s, 1H, ArH), 8.59 (s, 1H, CH), 13.74 (s, 1H, NH).
IR (KBr, ν, cm−1): 3192, 2993, 2959, 2920, 1578, 1560, 1537, 1475,
1456, 1440, 1398. 1373, 1327, 1262, 1178, 1102, 1028, 941, 912, 847,
818, 788, 717. HRMS (ESI, m/z): Calcd for C17H1235Cl2N3 (M + H+):
328.0448. Found: 328.0425.
9-Methyl-7-(3,4-dimethylphenyl)-3H-pyrazolo[4,3-f]quinoline
(4l): Pale yellow powder from DMF-THF, m.p. 256–258 °C; 1H NMR
(DMSO-d6, δH, ppm): 2.30 (s, 3H, CH3), 2.36 (s, 3H, CH3), 2.96 (s,
3H, CH3),7.30 (d, J = 8.0 Hz, 1H, ArH), 7.93 (d, J = 8.8 Hz, 2H, ArH),
7.99 (d, J = 8.0 Hz, 1H, ArH), 8.09 (d, J = 10.8 Hz, 2H, ArH), 8.57
(s, 1H, CH), 13.68 (s, 1H, NH). IR (KBr, ν, cm−1): 3146, 2104, 2972,
2917, 1665, 1576, 1536, 1504, 1446, 1376, 1357, 1336, 1267, 1184,
1094, 1009, 927, 875, 827, 786, 726. HRMS (ESI, m/z): Calcd for
C19H18N3 (M + H+) 288.1501. Found: 288.1520.
18 L-H. Zeng and C. Cai, J. Comb. Chem., 2010, 12, 35.
19 B. Das, P. Balasubramanyam, M. Krishnaiah, B. Veeranjaneyulu and G.C.
Reddy, J. Org. Chem., 2009, 74, 4393.
20 G.-W. Wang and J. Gao, Org. Lett., 2009, 11, 2385.
21 D. Mal and S.R. De, Org. Lett., 2009, 11, 4398.
22 P.T. Parvatkar, P.S. Parameswaran and S.G. Tilve, J. Org. Chem., 2009, 74,
8369.
23 X.S. Wang, Q. Li, J.R. Wu and S.J. Tu, J. Comb. Chem., 2009, 11, 433.
24 X.S. Wang, Q. Li, C.S. Yao and S.J. Tu, Eur. J. Org. Chem., 2008, 3513.
25 L.S. Povarov, Russ. Chem. Rev., 1967, 36, 656.
26 V.V. Kouznetsov, Tetrahedron, 2009, 65, 2721.
Conclusion
In conclusion, we have developed a mild and efficient method
for the synthesis of 7-aryl-9-methyl-3H-pyrazolo[4,3-f]
27 X.F. Lin, S.L. Cui and Y.G. Wang, Tetrahedron Lett., 2006, 47, 3127.

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