Three-component, one-pot synthesis of pyrazolo[3,4-b]pyridine derivatives in aqueous media

Article abstract of DOI:10.1080/00397910801929804

6-Amino-4-aryl-5-cyanopyrazolo[3,4-b]pyridines were synthesized by a three-component reaction of aromatic aldehydes, malononitrile, and 5-amino-3-methyl-1-phenylpyrazole using sodium 1-dodecanesulfonic (SDS) as catalyst in aqueous media. The reaction has the advantages of good yields, less pollution, ease of separation, and environmental friendliness. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910801929804

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Three‐Component, One‐Pot Synthesis of
Pyrazolo[3,4‐b]pyridine Derivatives in
Aqueous Media
Da‐Qing Shi a b , Hao Yao b & Jing‐Wen Shi b
a College of Chemistry and Chemical Engineering, Key Laboratory of Organic
Synthesis of Jiangsu Province , Suzhou University , Suzhou, China
b Department of Chemistry , Xuzhou Normal University , Xuzhou, China
Published online: 24 Apr 2008.
To cite this article: Da‐Qing Shi , Hao Yao & Jing‐Wen Shi (2008) Three‐Component, One‐Pot Synthesis of
Pyrazolo[3,4‐b]pyridine Derivatives in Aqueous Media, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 38:10, 1662-1669, DOI: 10.1080/00397910801929804
To link to this article: http://dx.doi.org/10.1080/00397910801929804
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Synthetic Communicationsw, 38: 1662–1669, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801929804
Three-Component, One-Pot Synthesis
of Pyrazolo[3,4-b]pyridine Derivatives
in Aqueous Media
Da-Qing Shi,1,2 Hao Yao,2 and Jing-Wen Shi2
1College of Chemistry and Chemical Engineering, Key Laboratory
of Organic Synthesis of Jiangsu Province, Suzhou University,
Suzhou, China
2Department of Chemistry, Xuzhou Normal University, Xuzhou, China
Abstract: 6-Amino-4-aryl-5-cyanopyrazolo[3,4-b]pyridines were synthesized by a
three-component reaction of aromatic aldehydes, malononitrile, and 5-amino-3-
methyl-1-phenylpyrazole using sodium 1-dodecanesulfonic (SDS) as catalyst in
aqueous media. The reaction has the advantages of good yields, less pollution, ease
of separation, and environmental friendliness.
Keywords: Aqueous media, one-pot synthesis, pyrazolo[3,4-b]pyridine, three-
component reaction
Pyrazole derivatives exhibit pharmacological activities such as hypotensive,
antibacterial, anti-inflammatory, and antitumor properties.[1–4] In particular,
condensed pyrazoles are known for various biological activities; for
example, pyrazolo[3,4-b]pyridines are useful for treatment of a wide variety
of stress-related illnesses, such as depression, Alzheimer’s disease, gastroin-
testinal disease, anorexia nervosa, hemorrhaged stress, drug and alcohol with-
drawal symptoms, drug addition, and infertility.[5] Pyrazolo[3,4-b]pyridine
Received March 5, 2007
Address correspondence to Da-Qing Shi, College of Chemistry and Chemical
Engineering, Key Laboratory of Organic Synthesis of Jiangsu Province, Suzhou
University, Suzhou 215123, China. E-mail: dqshi@suda.edu.cn
1662

Pyrazolo[3,4-b]pyridine Derivatives
1663
derivatives are generally prepared by reaction of 5-aminopyrazole and
substituted a,b-unsaturated nitriles in organic solvent (i.e. ethanol) using
triethylamine as catalyst,[6,7] but most of them suffer drawbacks such as
lower yields and use of organic solvent.
The need to reduce the amount of toxic waste and by-products arising
from chemical processes requires increasing emphasis on the use of less
toxic and environmentally compatible materials in the design of new
synthetic methods. One of the most promising approaches is using water as
reaction media. Breslow et al.,[8] who showed that hydrophobic effects
could strongly enhance the rate of several organic reactions, rediscovered
the use of water as a solvent in organic chemistry in the 1980s. Previously,
the scant solubility of the reactants was the main reason that ruled out this
solvent from studies. Further reasons that make water unique among
solvents are that it is cheap, not flammable, and more importantly, not
toxic. Recently, there has been increasing recognition that water is an attrac-
tive medium for many organic reactions.[9] Based on our previous studies on
the use of water as a solvent for carrying out carbon–carbon bond-forming
reactions under phase-transmitting catalyst,[10] here we like to report one-
pot synthesis of pyrazolo[3,4-b]pyridine derivatives by three-component
reaction in aqueous media (Scheme 1).
Choosing an appropriate solvent is of crucial importance for the success-
ful organic synthesis. To search for the optical solvent, the three-component
reaction of 4-chlorophenyl aldehyde 1a, malononitrile 2, and 5-amino-
3-methyl-1-phenylpyrazole 3 was examined using different solvents, respect-
ively. The results are summarized in Table 1.
As can be seen in Table 1, the best result was obtained when the three-
component reaction was carried out in water in the presence of SDS (entry
1). Indeed, the reaction using SDS proceeded in higher yield and shorter
reaction time than that using triethylbenzylammonium chloride (TEBAC) as
catalyst. Water was chosen as the solvent for all further reactions because it
is environmentally friendly, and the toxic organic reagents can be avoided.
To demonstrate the efficiency and scope of the present method, we
applied water containing SDS to the reaction of a variety of aromatic
aldehydes with malononitrile and 5-amino-3-methyl-1-phenylpyrazole. The
results are summarized in Table 2. Data from Table 2 demonstrated that the
reactions proceeded smoothly to give 4 in high yields under the optimized
conditions. However, other arylamines such as 4-methylaniline and
Scheme 1.

1664
D.-Q. Shi, H. Yao, and J.-W. Shi
Table 1. Solvent optimization for the synthesis of 4a
Reaction
temperature (8C)
Reaction
time (h)
Isolated yield
(%)
Entry
Solvent
1
2
3
4
5
6
7
8
H2O/SDS
H2O/TEBAC
CH3CN
90
90
80
60
80
80
60
100
11
15
39
39
39
15
39
39
97
90
33
0
CH3COCH3
EtOH
0
EtOH/SDS
CHCl3
DMF
0
0
0
1-aminonaphthalene did not undergo the same type of reactions under the
same reaction conditions.
The recovery and reuse of solvent and catalyst are highly preferable in
terms of green synthetic process. Therefore, with the success of these above
reactions, we continued our research by studying the reuse of aqueous
medium containing SDS. It turned out that the recovery and reuse of
aqueous medium is very convenient and highly efficient. Thus, at completion
of the condensation process, precipitated products were collected by suction,
and aqueous medium containing SDS could be recovered easily from the
filtrate. Studies using 1a, 2, and 3 as model substrates showed that the
recovered aqueous medium could be successively recycled in subsequent
reactions without almost any decrease in its efficiency (Table 3). It should
be noted that even in the sixth round, reuse of aqueous medium recovered
from the fifth round still produced the corresponding product with fairly
good yield.
Table 2. The Synthesis of 4 in aqueous media in the presence of SDS
Reaction
time (h)
Isolated yield
(%)
Entry
Ar
4-ClC6H4
4-FC6H4
4a
4b
4c
4d
4e
4f
11
22
17
25
16
18
18
17
10
97
95
85
90
86
94
86
90
92
4-CH3C6H4
4-NO2C6H4
4-BrC6H4
4-CH3OC6H4
3,4-(CH3O)2C6H3
3,4-Cl2C6H3
3,4-(CH3)2C6H3
4g
4h
4i

Pyrazolo[3,4-b]pyridine Derivatives
Table 3. Studies on the reuse of aqueous medium
containing SDS in the preparation of 4a
1665
Round
Yield (%)
1
2
3
4
5
6
97
98
97
96
95
96
The structures of products 4 were conformed by their spectroscopic
analysis. Thus, the IR spectra of compounds 4 measured in potassium
bromide pellets show on bond of the elongation vibrations of the CN group
at 2209–2217 cm21 and two bands for NH2 groups at 3310–3486 cm21. In
1
the H NMR spectra of compound 4 measured in dimethyl-d6 sulfoxide, the
signal of CH3 group at 1.88–1.98 ppm, the aromatic proton signals at
7.09–8.45 ppm, and the signal of 6-NH2 group at 7.22–7.56 ppm were
measured. The structure of 4e was further confirmed by X-ray diffraction
analysis. The molecular structure of 4e is shown in Fig. 1.
In conclusion, with high yields and mild conditions, we think that the
present work provides a useful method for the preparation of 6-amino-4-
aryl-5-cyanopyrazolo[3,4-b]pyridine derivatives. Compared with other
methods, this new method has the advantages of easier workup, milder
reaction conditions, high yields, and an environmentally benign procedure.
EXPERIMENTAL
Melting points were determined in open capillaries and are uncorrected. IR
spectra were recorded on a Tensor 27 spectrometer in KBr with absorptions
Figure 1. ORTEP diagram of 4e.

1666
D.-Q. Shi, H. Yao, and J.-W. Shi
1
in centimeters21. H NMR was measured on a Bruker DPX 400-MHz spec-
trometer in DMSO-d6 with TMS as internal standard. High-resolution mass
spectra (HRMS) were obtained using a time-of-flight mass spectrometry
(TOF-MS) instrument.
General Procedure for the Preparation of 6-Amino-4-aryl-5-cyano-
3-methyl-1-phenylpyrazolo[3,4-b]pyridine (4)
A mixture of an aromatic aldehyde 1 (4 mmol), malononitrile 2 (4 mmol),
5-amino-3-methyl-1-phenylpyrazole 3 (4 mmol), and SDS (0.2 g) in water
(10 ml) was stirred for 10–25 h at 908C, then the reaction mixture was
cooled to room temperature. The crystalline powder formed was collected
by filtration, washed with water, and purified by recrystallization from
ethanol to give pure 4.
Spectral Data
6-Amino-4-(4-chlorophenyl)-5-cyano-3-methyl-1-phenylpyrazolo[3,4-b]
pyridine (4a)
1
Mp 196–198 8C (lit.[6] 195 8C); H NMR (DMSO-d6) d: 1.88 (3H, s, CH3),
7.30–7.34 (1H, m, ArH), 7.40 (2H, s, NH2), 7.51–7.55 (2H, m, ArH), 7.90
(2H, d, J ¼ 8.8 Hz, ArH), 8.18 (2H, d, J ¼ 8.0 Hz, ArH), 8.45 (2H, d,
J ¼ 8.8 Hz, ArH); IR (KBr) n: 3454, 3327, 3054, 2214, 1629, 1580, 1559,
1513, 1497, 1457, 1436, 1409, 1353, 1201, 1148, 1089, 1013, 828, 789,
763, 694 cm21
.
6-Amino-4-(4-fluorophenyl)-5-cyano-3-methyl-1-phenylpyrazolo[3,4-b]
pyridine (4b)
1
Mp 211–213 8C (lit.[11] 216–218 8C); H NMR (DMSO-d6) d: 1.90 (3H, s,
CH3), 7.29 (2H, s, NH2), 7.32 (1H, d, J ¼ 8.0 Hz, ArH), 7.44 (2H, t,
J ¼ 8.8 Hz, ArH), 7.52 (2H, t, J ¼ 8.0 Hz, ArH), 7.62–7.65 (2H, m, ArH),
8.18 (2H, d, J ¼ 8.0 Hz, ArH); IR (KBr) n: 3444, 3321, 2213, 1629, 1602,
1551, 1511, 1438, 1413, 1391, 1352, 1228, 1202, 1156, 1010, 834, 768,
695 cm21
.
6-Amino-4-(4-methylphenyl)-5-cyano-3-methyl-1-phenylpyrazolo[3,4-b]
pyridine (4c)
1
Mp 206–207 8C; H NMR (DMSO-d6) d: 1.90 (3H, s, CH3), 2.44 (3H, s,
CH3), 7.24 (2H, s, NH2), 7.30 (1H, d, J ¼ 7.6 Hz, ArH), 7.40 (2H, d,
J ¼ 8.4 Hz, ArH), 7.44 (2H, d, J ¼ 7.6 Hz, ArH), 7.52 (2H, t, J ¼ 8.0 Hz,

Pyrazolo[3,4-b]pyridine Derivatives
1667
ArH), 8.18 (2H, d, J ¼ 8.4 Hz, ArH); IR (KBr) n: 3449, 3324, 3036, 2921,
2211, 1629, 1582, 1558, 1512, 1496, 1436, 1407, 1389, 1353, 1200, 1182,
1148, 1078, 1008, 889, 819, 789, 762, 731, 694 cm21. HRMS calcd. for
C21H17N5, m/z: 339.1484 (Mþ); found, m/z: 339.1474.
6-Amino-4-(4-nitrophenyl)-5-cyano-3-methyl-1-phenylpyrazolo[3,4-b]
pyridine (4d)
1
Mp 215–217 8C (lit.[6] 215 8C); H NMR (DMSO-d6) d: 1.88 (3H, s, CH3),
7.32 (1H, t, J ¼ 7.2 Hz, ArH), 7.40 (2H, s, NH2), 7.53 (2H, t, J ¼ 8.0 Hz,
ArH), 7.90 (2H, d, J ¼ 8.4 Hz, ArH), 8.18 (2H, d, J ¼ 8.0 Hz, ArH), 8.45
(2H, d, J ¼ 8.8 Hz, ArH); IR (KBr) n: 3486, 3349, 3061, 2214, 1619, 1581,
1518, 1493, 1440, 1412, 1388, 1338, 1201, 1149, 1106, 1004, 853, 769,
711, 695 cm21
.
6-Amino-4-(4-bromophenyl)-5-cyano-3-methyl-1-phenylpyrazolo[3,4-b]
pyridine (4e)
1
Mp 218–220 8C (lit.[11] 222–223 8C); H NMR (DMSO-d6) d: 1.91 (3H, s,
CH3), 7.32 (1H, t, J ¼ 7.2 Hz, ArH), 7.50–7.56 (6H, m, NH2 þ ArH), 7.81
(2H, t, J ¼ 7.6 Hz, ArH), 8.18 (2H, d, J ¼ 7.6 Hz, ArH); IR (KBr) n: 3431,
3346, 2217, 1615, 1585, 1558, 1530, 1489, 1396, 1378, 1344, 1279, 1136,
79
1074, 1011, 918, 817, 764, 738, 696 cm21. HRMS calcd. for C20H14 BrN5,
m/z: 403.0433 (Mþ); found, m/z: 403.0434.
6-Amino-4-(4-methoxyphenyl)-5-cyano-3-methyl-1-phenylpyrazolo
[3,4-b]pyridine (4f)
1
Mp 210–211 8C (lit.[6] 197 8C); H NMR (DMSO-d6) d: 1.94 (3H, s, CH3),
3.87 (3H, s, CH3O), 7.14 (2H, d, J ¼ 8.8 Hz, ArH), 7.22 (2H, s, NH2), 7.30
(1H, t, J ¼ 7.2 Hz, ArH), 7.48–7.53 (4H, m, ArH), 8.19 (2H, d, J ¼ 8.4 Hz,
ArH); IR (KBr) n: 3445, 3351, 2968, 2216, 1629, 1584, 1558, 1509, 1494,
1442, 1406, 1385, 1355, 1297, 1250, 1181, 1115, 1024, 886, 836, 765,
691 cm21
.
6-Amino-4-(3,4-dimethoxyphenyl)-5-cyano-3-methyl-1-phenylpyrazolo
[3,4-b] pyridine (4g)
1
Mp 217–219 8C; H NMR (DMSO-d6) d: 1.98 (3H, s, CH3), 3.81 (3H, s,
CH3O), 3.86 (3H, s, CH3O), 7.09 (1H, d, J ¼ 8.0 Hz, ArH), 7.15 (2H, d,
J ¼ 7.2 Hz, ArH), 7.22 (2H, s, NH2), 7.31 (1H, t, J ¼ 7.2 Hz, ArH), 7.52
(2H, t, J ¼ 7.6 Hz, ArH), 8.19 (2H, d, J ¼ 8.0 Hz, ArH); IR (KBr) n: 3462,
3331, 2918, 2849, 2209, 1626, 1571, 1518, 1492, 1466, 1413, 1381, 1352,
1280, 1258, 1238, 1203, 1171, 1144, 1065, 1026, 800, 764, 694 cm21
HRMS calcd. for C22H19N5O2, m/z: 385.1539 (Mþ); found, m/z: 385.1531.
.

1668
D.-Q. Shi, H. Yao, and J.-W. Shi
6-Amino-4-(3,4-dichlorophenyl)-5-cyano-3-methyl-1-phenylpyrazolo
[3,4-b]pyridine (4h)
1
Mp 192–194 8C (lit.[11] 187–189 8C); H NMR (DMSO-d6) d: 1.93 (3H, s,
CH3), 7.31 (1H, t, J ¼ 7.6 Hz, ArH), 7.36 (2H, s, NH2), 7.52 (2H, t,
J ¼ 8.0 Hz, ArH), 7.60 (1H, d, J ¼ 8.0 Hz, ArH), 7.88 (1H, d, J ¼ 8.4 Hz,
ArH), 7.97 (1H, s, ArH), 8.17 (2H, d, J ¼ 8.0 Hz, ArH); IR (KBr) n: 3466,
3364, 3064, 2210, 1627, 1610, 1583, 1560, 1514, 1492, 1472, 1440, 1409,
1385, 1353, 1250, 1199, 1149, 1131, 1081, 1032, 951, 906, 876, 822, 787,
753, 691 cm21. HRMS calcd. for C20H Cl2N5, m/z: 393.0548 (Mþ);
35
13
found, m/z: 393.0545.
6-Amino-4-(3,4-dimethylphenyl)-5-cyano-3-methyl-1-
phenylpyrazolo[3,4-b]pyridine (4i)
1
Mp 182–184 8C; H NMR (DMSO-d6) d: 1.91 (3H, s, CH3), 2.33 (3H, s,
CH3), 2.34 (3H, s, CH3), 7.23–7.32 (5H, m, NH2 þ ArH), 7.35 (1H, d,
J ¼ 7.6 Hz, ArH), 7.52 (2H, t, J ¼ 7.6 Hz, ArH), 8.19 (2H, d, J ¼ 8.4 Hz,
ArH); IR (KBr) n: 3442, 3310, 3057, 2919, 2850, 2210, 1635, 1580, 1560,
1503, 1442, 1409, 1382, 1349, 1278, 1228, 1206, 1174, 1123, 1065, 1025,
1005, 903, 874, 829, 787, 772, 757, 730, 703, 692 cm21. HRMS calcd. for
C22H19N5, m/z: 353.1640 (Mþ); found, m/z: 353.1647.
Crystal Data for 4e
C20H14BrN5; M ¼ 404.27, colorless block crystals, 0.57 ꢀ 0.48 ꢀ 0.26 mm,
˚
triclinic, space group P-1, a ¼ 11.393 (2), b ¼ 12.396(2), c ¼ 13.718 (3) A,
3
˚
a ¼ 96.528 (3)8, b ¼ 97.374 (3)8, g ¼ 110.171 (3)8, V ¼ 1777.4 (6) A ,
Z ¼ 4, Dc ¼ 1.511 g cm23
.
Intensity data were collected on Smart-1000 diffractometer with graphite
F(000) ¼ 816, m(MoKa) ¼ 2.326 mm21
.
˚
monochromated MoKa radiation (l ¼ 0.71073 A) using v scan mode with
2.108 , u , 25.018. A total of 6191 unique reflections were measured, and
3812 reflections with I . 2s (I) were used in the refinement. The structure
was solved by direct methods and expanded using Fourier techniques. The
final cycle of full-matrix least squares technique to R ¼ 0.0442 and
wR ¼ 0.0985.
ACKNOWLEDGMENTS
We are grateful to the Surpassing Project Foundation of Jiangsu Province
(QL9801) for financial support.

Pyrazolo[3,4-b]pyridine Derivatives
1669
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