An efficient one-pot synthesis of pyrazolo[3,4-b]pyridinone derivatives catalyzed by L -proline

Article abstract of DOI:10.1002/jhet.573

A series of 3-methyl-1,4-disubstituted-4,5-dihydro-1H-pyrazolo[3,4-b] pyridine-6(7H)-ones was synthesized via the three-component reaction of aldehyde, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and Meldrum's acid catalyzed by L-proline. This protocol has the

Full text of DOI:10.1002/jhet.573

March 2011
An Efficient One-Pot Synthesis of Pyrazolo[3,4-b]pyridinone
Derivatives Catalyzed by L-Proline
351
Chun-Ling Shi, Hui Chen, and Da-Qing Shi*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical and
Materials Science, Soochow University, Suzhou 215123, People’s Republic of China
*E-mail: dqshi@suda.edu.cn
Received September 1, 2009
DOI 10.1002/jhet.573
Published online 16 December 2010 in Wiley Online Library (wileyonlinelibrary.com).
A series of 3-methyl-1,4-disubstituted-4,5-dihydro-1H-pyrazolo[3,4-b]pyridine-6(7H)-ones was synthe-
sized via the three-component reaction of aldehyde, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and Mel-
drum’s acid catalyzed by L-proline. This protocol has the advantages of easier work-up, milder reaction
conditions, and high yields.
J. Heterocyclic Chem., 48, 351 (2011).
INTRODUCTION
been studied more and more extensively. A lot of small
organic molecules, for instance, cinchona alkaloids,
L-proline, and its derivatives have been used in various
transformations with excellent yields [12,13]. Direct cat-
alytic asymmetric aldol [14], Mannich [15,16], Michael
[17–19], Diels–Alder [20], a-amination reactions [21],
and Knoevenagel type reaction [22] using L-proline as
catalyst have also been reported. Recently, L-proline and
its derivatives have been used in multicomponent
unsymmetric Biginelli [23,24] and Hantzsch reactions
[25] and other MCR [26,27]. As a consequence of our
interest in organic synthesis catalyzed by L-proline, we
would like to describe a mild and highly efficient proto-
col for the synthesis of pyrazolo[3,4-b]pyridinone deriv-
atives catalyzed by L-proline.
Pyrazole derivatives exhibit pharmacological activities
such as hypotensive, antibacterial, anti-inflammatory, and
antitumor properties [1–4]. In particular, condensed pyra-
zoles are known for various biological activities, e.g., pyr-
azolo[3,4-b]pyridines are useful for treatment of a wide
variety of stress-related illnesses, such as depression, Alz-
heimer’s disease, gastrointestinal disease, anorexia nerv-
osa, hemorrhaged stress, drug and alcohol withdrawal
symptoms, drug addition, and infertility [5]. Pyrazolo[3,4-
b]pyridine derivatives are generally prepared by reaction
of 5-aminopyrazole and substituted a,b-unsaturated nitriles
or benzylidene derivatives of Meldrum’s acid in organic
solvent (i.e., ethanol) using triethylamine as catalyst [6–8],
but most of them suffer from drawbacks such as lower
yields, and using organic solvent.
Multicomponent reactions (MCRs), in which multiple
reactions are combined into one synthetic operation,
have been used extensively to form carbon–carbon
bonds in synthetic chemistry [9]. Such reactions offer a
wide range of possibilities for the efficient construction
of highly complex molecules in a single procedural step,
thus, avoiding the complicate purification operations and
allowing savings of both solvents and reagents. In the
past decade, there have been tremendous development
in three- and four-component reactions and great efforts
continue to be made to develop new MCRs [10,11].
The replacement of current chemical process with
more environmentally benign alternatives is an increas-
ingly attractive goal in organic synthesis. Recently, or-
ganic reaction catalyzed by small organic molecules has
RESULTS AND DISCUSSION
When the mixture of aldehyde 1, 3-methyl-1-phenyl-
1H-pyrazol-5-amine 2, Meldrum’s acid 3, and catalytic
amount of L-proline were stirred for 1–3 h at 80ꢀC in
ethanol solution, the desired products 4 were obtained in
good yields (Scheme 1), and the results are summarized
in Table 1.
As shown in Table 1, this protocol could be applied
not only to the aromatic aldehydes with electron-with-
drawing groups (such as halide and nitro groups) but
also to aromatic aldehydes with electron-donating
groups (such as alkyl and alkoxyl groups). Therefore,
we concluded that the electronic nature of the
C
V
2010 HeteroCorporation

352
C.-L. Shi, H. Chen, and D.-Q. Shi
Vol 48
Scheme 1
Scheme 2
substituents of aromatic aldehydes has no significant
effect on this reaction.
The structures of the compounds 4 were identified by
their spectroscopy analysis. Thus, the infrared (IR) spec-
tra of compounds 4 measured in potassium bromide pel-
lets show one band of the elongation vibrations of the
C¼¼O group at 1678–1692 cmꢁ1 and NH groups at
1
3112–3356 cmꢁ1. In the H NMR spectra of compounds
by the cycloaddition and losing of acetone and carbon
dioxide to form the desired products 4.
4 measured in dimethyl-d6 sulfoxide, the CH3 proton
signals at 1.76–2.07 ppm, the CH2 proton signals at
2.58–2.75 and 2.96–3.43 ppm, the CH proton signals at
4.10–4.61 ppm, the NH proton signals at 10.30–10.69
ppm, and the aromatic proton signals at 6.64–8.22 ppm
were observed.
In conclusion, we have developed an efficient synthe-
sis of 3-methyl-1,4-disubstituted-4,5-dihydro-1H-pyra-
zolo [3,4-b]pyridine-6(7H)-ones via the three-component
reaction of aldehyde, 3-methyl-1-phenyl-1H-pyrazol-5-
amine, and Meldrum’s acid catalyzed by L-proline. This
protocol has the advantages of easier work up, milder
reaction conditions, and high yields.
Although the detailed mechanism of above reaction
remains not to be fully clarified, the formation of com-
pounds 4 could be explained by a reaction sequence pre-
sented in Scheme 2. We proposed that the reaction pro-
ceeded via a reaction sequence of condensation, addi-
tion, cyclization, and elimination. We suggest that L-pro-
line catalyzes the formation of iminium ion 5 in a re-
versible reaction with aldehydes 1. The higher reactivity
of the iminium ion compared with the carbonyl species
could facilitate Knoevenagel condensation between alde-
hydes 1 and Meldrum’s acid 3 via intermediate 6, and
after the elimination of L-proline, 7 might be produced
as an intermediate. Then, intermediate 7 is attacked via
Michael addition of 3-methyl-1-phenyl-1H-pyrazol-5-
amine 2 to give the intermediate 8, which is followed
EXPERIMENTAL
Commercial solvents and reagents were used as received.
Melting points are uncorrected. IR spectra were recorded on
Varian F-1000 spectrometer in KBr with absorptions in cmꢁ1
.
1H NMR was determined on Varian-400 MHz spectrometer in
dimethyl sulfoxide (DMSO)-d6 solution. J values are in Hz.
Chemical shifts are expressed in ppm downfield from internal
standard tetramethylsilane (TMS). High resolution mass spec-
tra (HRMS) data were obtained using time-of-flight mass spec-
trometry (TOF-MS) instrument.
General Procedure for the Synthesis of 3-methyl-1,4-disubsti-
tuted-4,5-dihydro-1H-pyrazolo[3,4-b]pyridine-6(7H)-ones
3. A
dry 50 mL flask was charged with aldehyde 1 (1 mmol),
3-methyl-1-phenyl-1H-pyrazol-5-amine 2 (1 mmol), Meldrum’s
acid 3 (1 mmol), L-proline (0.1 mmol), and ethanol (2 mL). The
mixture was stirred at 80ꢀC for 1–3 h to complete the reaction
[monitored by thin layer chromatography (TLC)] and then 50
mL H2O was added. The solid was filtered off and washed with
water. The crude product was purified by recrystallization from
ethanol to give pure 4.
Table 1
Synthesis of pyrazolo[3,4-b]pyridinone derivatives 4 catalyzed by
L-proline.
Isolated
yield (%)
Entry
R
Time (h)
Mp (ꢀC)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4-CH3OC6H4
4-ClC6H4
1.5
2
94
91
95
96
92
82
83
93
98
97
88
86
182–184
206–208
217–219
216–218
153–155
148–149
169–171
228–229
127–129
167–168
174–176
140–141
4-(4-Methoxyphenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-
pyrazolo[3,4-b]pyridin-6(7H)-one (4a). Mp: 182–184ꢀC; IR
(potassium bromide): 3135, 3043, 1678, 1596, 1513, 1340,
4-NO2C6H4
4-BrC6H4
2-Thiophenyl
4-(Me)2NC6H4
2-ClC6H4
2
1.5
2
1
1257, 1183, 1024 cmꢁ1; H NMR (DMSO-d6) d: 1.88 (s, 3H,
2
CH3), 2.61 (dd, J1 ¼ 4.8 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 2.97
(dd, J1 ¼ 7.2 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 3.72 (s, 3H,
CH3O), 4.16 (dd, J1 ¼ 4.8 Hz, J2 ¼ 7.2 Hz, 1H, CH), 6.88
(d, J ¼ 8.8 Hz, 2H, ArH), 7.11 (d, J ¼ 8.4 Hz, 2H, ArH),
7.34 (t, J ¼ 7.2 Hz, 1H, ArH), 7.46–7.53 (m, 4H, ArH), 10.51
(s, 1H, NH). HRMS [Found: m/z 333.1476 (Mþ); Calcd for
C20H19N3O2: M 333.1477].
1.5
1.5
2
2-NO2-5-ClC6H3
3-ClC6H4
4j
4k
4l
2,4-Cl2C6H3
2-NO2C6H4
3,4-(MeO)2C6H3
1
1.5
2
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

March 2011
An Efficient One-Pot Synthesis of Pyrazolo[3,4-b]Pyridinone Derivatives
Catalyzed by L-Proline
353
4-(4-Chlorophenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-pyra-
zolo[3,4-b]pyridin-6(7H)-one (4b). Mp: 206–208ꢀC (209–
210ꢀC; ref. [8]); IR (potassium bromide): 3142, 3050, 1684,
;
1595, 1546, 1495, 1385, 1328, 1170, 1085, 1013 cmꢁ1 1H
4-(5-Chloro-2-nitrophenyl)-3-methyl-1-phenyl-4,5-dihydro-
1H-pyrazolo[3,4-b]pyridin-6(7H)-one (4h). Mp: 228–229ꢀC;
IR (potassium bromide): 3356, 3065, 1692, 1598, 1501, 1457,
;
1345, 1202, 1169, 1104, 1068 cmꢁ1 1H NMR (DMSO-d6):
1.79 (s, 3H, CH3), 2.75 (dd, J1 ¼ 6.0 Hz, J2 ¼ 15.6 Hz, 1H,
CH2), 3.12 (dd, J1 ¼ 7.2 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 4.70
(t, J ¼ 6.4 Hz, 1H, CH), 7.33 (d, J ¼ 2.4 Hz, 1H, ArH), 7.37
(t, J ¼ 7.2 Hz, 1H, ArH), 7.50 (d, J ¼ 8.4 Hz, 1H, ArH), 7.55
(t, J ¼ 8.0 Hz, 3H, ArH), 7.65 (dd, J1 ¼ 2.4 Hz, J2 ¼ 8.8 Hz,
1H, ArH), 8.06 (d, J ¼ 8.8 Hz, 1H, ArH), 10.69 (s, 1H, NH).
HRMS [Found: m/z 382.0826 (Mþ); Calcd for C19H1355Cl N4O3:
M 382.0833].
4-(3-Chlorophenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-pyra-
zolo[3,4-b]pyridin-6(7H)-one (4i). Mp: 127–129ꢀC; IR (potas-
sium bromide): 3230, 3154, 3053, 1688, 1598, 1559, 1501,
1479, 1355, 1224, 1161, 1073 cmꢁ1 1H NMR (DMSO-d6):
;
1.91 (s, 3H, CH3), 2.67 (dd, J1 ¼ 4.0 Hz, J2 ¼ 15.6 Hz, 1H,
CH2), 3.05 (dd, J1 ¼ 7.2 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 4.29
(t, J ¼ 6.0 Hz, 1H, CH), 7.19 (d, J ¼ 7.2 Hz, 1H, ArH), 7.27
(s, 1H, ArH), 7.32 (d, J ¼ 8.0 Hz, 1H, ArH), 7.38 (t, J ¼ 7.6
Hz, 2H, ArH), 7.50 (d, J ¼ 7.6 Hz, 2H, ArH), 7.55 (d, J ¼
8.4 Hz, 2H,þArH), 10.60 (s, 1H, NH). HRMS [Found: m/z
337.0983 (M ); Calcd for C19H3165Cl N3O: M 337.0982].
NMR (DMSO-d6): 1.90 (s, 3H, CH3), 2.64 (dd, J1 ¼ 4.8 Hz,
J2 ¼ 15.6 Hz, 1H, CH2), 3.03 (dd, J1 ¼ 7.2 Hz, J2 ¼ 15.6 Hz,
1H, CH2), 4.26 (dd, J1 ¼ 4.8 Hz, J2 ¼ 6.8 Hz, 1H, CH), 7.23
(d, J ¼ 8.4 Hz, 2H, ArH), 7.35 (t, J ¼ 7.2 Hz, 1H, ArH), 7.40
(d, J ¼ 8.4 Hz, 2H, ArH), 7.47–7.54 (m, 4H, ArH), 10.57 (s,
1H, NH).
3-Methyl-4-(4-nitrophenyl)-1-phenyl-4,5-dihydro-1H-pyr-
azolo[3,4-b]pyridin-6(7H)-one (4c). Mp: 217–219ꢀC (223–
224ꢀC; ref. [8]); IR (potassium bromide): 3112, 2998, 1688,
1595, 1516, 1496, 1384, 1352, 1175, 1119 cmꢁ1 1H NMR
;
(DMSO-d6): 1.90 (s, 3H, CH3), 2.69 (dd, J1 ¼ 4.8 Hz, J2
¼
16.0 Hz, 1H, CH2), 3.11 (dd, J1 ¼ 7.6 Hz, J2 ¼ 16.0 Hz, 1H,
CH2), 4.45 (dd, J1 ¼ 4.4 Hz, J2 ¼ 8.0 Hz, 1H, CH), 7.36 (t, J
¼ 6.8 Hz, 1H, ArH), 7.49–7.55 (m, 6H, ArH), 8.22 (d, J ¼
8.4 Hz, 2H, ArH), 10.65 (s, 1H, NH).
4-(4-Bromophenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-pyra-
zolo[3,4-b]pyridin-6(7H)-one (4d). Mp: 216–218ꢀC; IR (potas-
sium bromide): 3143, 3048, 1683, 1596, 1545, 1496, 1457,
;
1327, 1169, 1070 cmꢁ1 1H NMR (DMSO-d6): 1.90 (s, 3H,
4-(2,4-Dichlorophenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-
pyrazolo[3,4-b]pyridin-6(7H)-one (4j). Mp: 167–168ꢀC; IR
(potassium bromide): 3203, 3061, 1692, 1603, 1540, 1500,
CH3), 2.63 (dd, J1 ¼ 4.4 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 3.43
(dd, J1 ¼ 6.8 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 4.25 (dd, J1 ¼ 5.2
Hz, J2 ¼ 6.4 Hz, 1H, CH), 7.17 (d, J ¼ 8.0 Hz, 2H, ArH),
7.35 (t, J ¼ 7.6 Hz, 1H, ArH), 7.47–7.54 (m, 6H, ArH), 10.57
(s, 1H, NH); HRMS [Found: m/z 381.0474 (Mþ); Calcd for
C19H7196BrN3O: M 381.0477].
1
1464, 1380, 1200, 1163, 1103, 1048 cmꢁ1; H NMR (DMSO-
d6): 1.88 (s, 3H, CH3), 2.58 (dd, J1 ¼ 3.6 Hz, J2 ¼ 15.6 Hz,
1H, CH2), 3.12 (dd, J1 ¼ 7.6 Hz, J2 ¼ 16.0 Hz, 1H, CH2),
4.58 (dd, J1 ¼ 4.0 Hz, J2 ¼ 7.6 Hz, 1H, CH), 7.03 (d, J ¼ 8.4
Hz, 1H, ArH), 7.36–7.42 (m, 2H, ArH), 7.50 (d, J ¼ 8.0 Hz,
1H, ArH), 7.55 (t, J ¼ 8.0 Hz, 3H, ArH), 7.70 (s, 1H, ArH),
10.69 (s, 1H, NH). HRMS [Found: m/z 371.0589 (Mþ); Calcd
for C19H3155Cl2N3O: M 371.0592].
3-Methyl-1-phenyl-4-(thiophen-2-yl)-4,5-dihydro-1H-pyra-
zolo[3,4-b]pyridin-6(7H)-one (4e). Mp: 153–155ꢀC; IR (po-
tassium bromide): 3141, 3051, 1692, 1598, 1563, 1500, 1364
1
cmꢁ1; H NMR (DMSO-d6): 2.07 (s, 3H, CH3), 2.73 (dd, J1 ¼
2.8 Hz, J2 ¼ 15.2 Hz, 1H, CH2), 3.11 (dd, J1 ¼ 6.8 Hz, J2 ¼
15.6 Hz, 1H, CH2), 4.52 (dd, J1 ¼ 3.2 Hz, J2 ¼ 6.8 Hz, 1H,
CH), 6.90 (d, J ¼ 2.4 Hz, 1H, ArH), 6.97 (t, J ¼ 4.8 Hz, 1H,
ArH), 7.34–7.38 (m, 2H, ArH), 7.47–7.53 (m, 4H, ArH), 10.60
(s, 1H, NH). HRMS [Found: m/z 309.0937 (Mþ); Calcd for
C17H15N3OS: M 309.0936].
3-Methyl-4-(2-nitrophenyl)-1-phenyl-4,5-dihydro-1H-pyra-
zolo[3,4-b]pyridin-6(7H)-one (4k). Mp: 174–176ꢀC; IR (po-
tassium bromide): 3227, 3051, 1683, 1603, 1528, 1457, 1345,
1
1204, 1070 cmꢁ1; H NMR (DMSO-d6): 1.76 (d, J ¼ 12.4 Hz,
3H, CH3), 2.62–2.70 (m, 1H, CH2), 3.08–3.17 (m, 1H, CH2),
4.60–4.66 (m, 1H, CH), 7.27–7.39 (m, 2H, ArH), 7.47–7.56
(m, 5H, ArH), 7.64–7.70 (m, 1H, ArH), 7.94–7.99 (m, 1H,
ArH), 10.68 (d, J ¼ 11.2 Hz, 1H, NH). HRMS [Found: m/z
348.1224 (Mþ); Calcd for C19H16N4O3: M 348.1222].
4-(4-(Dimethylamino)phenyl)-3-methyl-1-phenyl-4,5-dihy-
dro-1H-pyrazolo[3,4-b]pyridin-6(7H)-one (4f). MP: 148–
149ꢀC; IR (potassium bromide): 3143, 3054, 1687, 1601,
1
1521, 1355, 1226, 1071 cmꢁ1; H NMR (DMSO-d6): 1.90 (s,
4-(3,4-Dimethoxyphenyl)-3-methyl-1-phenyl-4,5-dihydro-
1H-pyrazolo[3,4-b]pyridin-6(7H)-one (4l). Mp: 140–141ꢀC;
IR (potassium bromide): 3220, 3056, 1684, 1598, 1517, 1458,
1383, 1244, 1148, 1026 cmꢁ1; 1H NMR (DMSO-d6): 1.90 (s, 3H,
CH3), 2.68 (dd, J1 ¼ 3.6 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 2.96 (dd, J1
¼ 7.2 Hz, J2 ¼ 16.0 Hz, 1H, CH2), 3.72 (s, 6H, 2 ꢂ OCH3), 4.16
(t, J ¼ 5.2, 1H, CH), 6.64 (d, J ¼ 8.4 Hz, 1H, ArH), 6.87 (d, J ¼
8.8 Hz, 2H, ArH), 7.35 (t, J ¼ 6.8 Hz, 1H, ArH), 7.47–7.54 (m,
4H, ArH), 10.50 (s, 1H, NH). HRMS [Found: m/z 363.1583 (Mþ);
Calcd for C21H21N3O3: M 363.1583].
3H, CH3), 2.60 (dd, J1 ¼ 4.4 Hz, J2 ¼ 15.6 Hz, 1H, CH2),
2.86 (s, 6H, 2 ꢂ CH3), 2.96 (dd, J1 ¼ 7.2 Hz, J2 ¼ 15.6 Hz,
1H, CH2), 4.10 (t, J ¼ 6.0 Hz, 1H, CH), 6.69 (d, J ¼ 8.0 Hz,
2H, ArH), 7.01 (d, J ¼ 8.4 Hz, 2H, ArH), 7.34 (t, J ¼ 6.8 Hz,
1H, ArH), 7.46–7.53 (m, 4H, ArH), 10.48 (s, 1H, NH). HRMS
[Found: m/z 346.1794 (Mþ); Calcd for C21H22N4O:
346.1794].
4-(2-Chlorophenyl)-3-methyl-1-phenyl-4,5-dihydro-1H-
M
pyrazolo[3,4-b]pyridin-6(7H)-one (4g). Mp: 169–171ꢀC; IR
(potassium bromide): 3225, 3161, 3058, 1683, 1602, 1538,
;
1456, 1348, 1264, 1197, 1037 cmꢁ1 1H NMR (DMSO-d6):
1.86 (s, 3H, CH3), 2.61 (dd, J1 ¼ 4.4 Hz, J2 ¼ 16.0 Hz, 1H,
CH2), 3.11 (dd, J1 ¼ 7.6 Hz, J2 ¼ 15.6 Hz, 1H, CH2), 4.61
(dd, J1 ¼ 4.4 Hz, J2 ¼ 7.6 Hz, 1H, CH), 7.03 (dd, J1 ¼ 4.0
Hz, J2 ¼ 6.0 Hz, 1H, ArH), 7.28–7.32 (m, 2H, ArH), 7.37 (t,
J ¼ 7.2 Hz, 1H, ArH), 7.48–7.53 (m, 3H, ArH), 7.56 (d, J ¼
7.6 Hz, 2H,þArH), 10.65 (s, 1H, NH). HRMS [Found: m/z
337.0980 (M ); Calcd for C19H3165Cl N3O: M 337.0982].
Acknowledgments. The authors thank the Key Laboratory of
Organic Synthesis of Jiangsu Province for financial support.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet