Synthesis of novel dipyrazolo[3,4-b:3,4-d]pyridines and study of their fluorescence behavior

Article abstract of DOI:10.1016/j.tet.2007.08.052

A convenient route was successfully developed for the synthesis of novel heterocycles such as pyrazolo[3,4-h][1,6]naphthyridine and dipyrazolo[3,4-b:3,4-d]pyridine (DPP) from pyrazolo[3,4-b]pyridine in good yield. The DPP derivatives synthesized were furt

Full text of DOI:10.1016/j.tet.2007.08.052

Tetrahedron 63 (2007) 11000–11004
Synthesis of novel dipyrazolo[3,4-b:3,4-d]pyridines and
study of their fluorescence behavior
*
Dhananjay B. Kendre, Raghunath B. Toche and Madhukar N. Jachak
Organic Chemistry Research Center, Department of Chemistry, K.T.H.M. College, Gangapur road, Nashik 422002, Maharashtra, India
Received 21 May 2007; revised 28 July 2007; accepted 16 August 2007
Available online 22 August 2007
Abstract—A convenient route was successfully developed for the synthesis of novel heterocycles such as pyrazolo[3,4-h][1,6]naphthyridine
and dipyrazolo[3,4-b:3,4-d]pyridine (DPP) from pyrazolo[3,4-b]pyridine in good yield. The DPP derivatives synthesized were further studied
for their fluorescence properties.
Ó 2007 Elsevier Ltd. All rights reserved.
X
N
1. Introduction
Since the ground-breaking work1 of Tang and VanSlyke in
electroluminescence (EL) devices that use organic molecu-
lar materials, the research activity on organic light emitting
diodes (OLEDs) has been expanding rapidly and progressed
considerably in recent years. The LEDs of this category are
of great interest because of their potential applications for
making low-cost display products. The continuing efforts
include the development of new efficient materials and inge-
nious device fabrications.2 There are many activities focused
on blue-light emitting OLEDs and a wide variety of organic
and organometallic compounds have been utilized for this
purpose. Only few compounds like distyrylarylene3 and silyl
substituted ter-(phenylene-vinylene)4 are significant since
the blue emission required is over 10 000 cd/m2. Thus a suit-
able blue-light emitting material with high brightness and
good thermal stability still remains to be developed.
CH3
N
H3C
N
N
N
X-DMPP
X = N(CH3)2, H, NO2, OCH3
Figure 1.
solvents. The quantum yield decreases in polar solvents,
and the emitting state changes its character from a weakly
polar to a CT one, confirmed by experimental results.6–9 In
protic solvents dual fluorescence is observed, a phenomenon
not often occurring in the case of noncoplanar large donar–
acceptor systems.
Derivatives of 3,5-dimethyl-1,7-diphenyl-bis-pyrazolo[3,4-
b:3,4-e]pyridine (DMA-DMPP) with different substituents
in position 4 (Fig. 1) show intense fluorescence in the blue-
green region and have been considered for applications as
fluorescence standards and luminophores in organic light
emitting diodes.5 The derivatives with phenyl and
4-methoxyphenyl substituent (H-DMPP and CH3O-DMPP,
respectively) are characterized by a very intense, solvent
independent fluorescence. The nitro derivative (NO2-DMPP)
shows an unexpected photophysical behavior. DMA-
DMPP fluoresces with a large quantum yield in nonpolar
Apart from this, the dipyrazolo[3,4-b:3,4-e]pyridines are
examples of condensed heterocyclic compounds with nota-
ble pharmacological activity, e.g., as sedative10 or anti-
asthmatic compounds.11 Pyrazolopyridines are attractive
targets in organic synthesis due to their significant biological
and pharmacological activities, such as hypotensive,12 cyto-
toxic,13 and anti-bacterial activity,14 and found to be poten-
tial purine antagonists.15
As a part of our ongoing interest in this area 16–18 we have
reported the synthesis of pyrazolo[3,4-b]pyridines, pyr-
azolo[3,4-b]quinolines, pyrazolonaphthyridines, and pyr-
azolopyridopyrimidines by Friedlander condensation of
reactive methylene compounds with 5-aminopyrazole. In
our recent communications19 we reported the synthesis
Keywords: Pyrazolo[3,4-b]pyridine; Dipyrazolo[3,4-b:3,4-d]pyridine; Pyr-
azolo[3,4-h][1,6]naphthyridine; Absorption; Emission.
* Corresponding author. Fax: +91 0253 2577341; e-mail: dken10@gmail.
com
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.052

D. B. Kendre et al. / Tetrahedron 63 (2007) 11000–11004
11001
Cl
N
O
Ar
N3
O
NH2
O
Ar
Ar
NaN3
OEt
Na2S2O4
OEt
OEt
N
N
N
DMF, 10-15 °C
N
MeOH, reflux
N
N
N
N
Ph
Ph
Ph
1a-b
4a-b
2a-b
1-5 Ar
CH2(CN)2
+
a p-Cl-C6H4
b p-Br-C6H4
EtOH, reflux
N
NH2
CN
N
N
Ar
N
Ar
OH
N
OH
N
N
N
Ph
N
N
5a-b
3a-b
Ph
Scheme 1.
H
N
H
H
O
N
CH3
H
O
O
N
N
O
Ar
N
N
N
N
Urea
EtOH, reflux
OEt
6a-b
R1
N
Ph
Cl
O
Ar
Figure 2.
OEt
N
N
Ph
H
R
In continuation of our research on 1 we carried out the reac-
tion with urea and different hydrazines. Thus the reaction of
urea with 1 in ethanol containing a catalytic amount of potas-
sium hydroxide furnished an open chain derivative 6 in good
yield. Further the reaction of phenylhydrazine or hydrazine
hydrate in xylene containing catalytic amount of triethyl-
amine at reflux for 5 h yielded the titled dipyrazolo[3,4-
b:3,4-d]pyridine (DPP) 7 in 60% yield. The structure of all
N
1a-b
N
N
Ar
O
R-NH-NH2
1,6,7 Ar
R
N
a p-Cl-C6H4 C6H5
b p-Br-C6H4 C6H5
c p-Cl-C6H4
d p-Br-C6H4
Xylene, reflux
N
N
Ph
7a-d
H
H
Scheme 2.
1
these compounds was confirmed by IR and H NMR spec-
troscopies, and elemental analysis.
of fused pyrimidines. These literature reports and our
ongoing research in this area prompted us to synthesize
DPP and to study their fluorescence behavior (Schemes 1
and 2).
3. Conclusion
It was observed that the dipyrazolo[3,4-b:3,4-d]pyridine
(DPP) 7 showed strong fluorescence, so we further studied
the photophysical properties of these compounds. It was
noted that DPP 7 showed similar absorption and emission
spectra. The DPP 7a,b prepared using phenylhydrazine
showed a small peak at the base of strong absorption (a)
and emission (b) peaks as shown in (Fig. 3). The appearance
of this small characteristic peak might be because of the dual
2. Results and discussion
Compounds 1 containing bifunctional groups were used as
precursors for the synthesis of tricyclic heterocycles such
as dipyrazolo[3,4-b:3,4-d]pyridine. Thus compound 1 on
treatment with sodium azide in DMF at 10–15 ꢀC furnished
a mixture of azido pyrazolopyridine derivatives 2 and
pyrazolopyridotriazine 3 in 60:20% yield, respectively.
The mixture of 2 and 3 were separated by column chromato-
graphy using 4:1 toluene/acetone as the eluant. The reduction
of N3 was achieved successfully by refluxing in methanol,
containing a catalytic amount of sodium dithionate, for 3 h
that yielded the expected 4-aminopyrazolo[3,4-b]pyridine
derivatives 4 in 60% yield. Despite the proximity of an
amine and ester group ortho to each other in compounds 4
were unable to form the amide. Moreover, the reaction of
4 with active methylene compounds also proved to be diffi-
cult. This might be due to the strong intramolecular hydro-
gen bond between ester carbonyl and the 4-amino group as
reported earlier by Bare et al.20 in the case pyrazolopyridine
(Fig. 2). Only the reaction of 4 with malononitrile in ethanol
at reflux for 18 h was successfully carried out to yield the
pyrazolonaptharidines 5 in 50% yield.
Figure 3. The absorption (a) and emission (b) spectra of 7a in DMSO.

11002
D. B. Kendre et al. / Tetrahedron 63 (2007) 11000–11004
fluorescence of DPP due to the presence of phenyl ring as it
is observed in case of DMA-DMPP. While the absorption
and emission spectra of the DPP 7c,d synthesized using
hydrazine hydrate does not show any small peak at the
base of strong peak (Fig. 4). The DPP 7 showed absorption
peaks at 369, 370, 384, and 384.5 nm and emission peaks
at 410, 407, 419, and 417 nm.
theoretical percentage. All reactions were monitored by
thin layer chromatography, carried out on 0.2 mm silica gel
60 F254 (Merk) plates using UV light (254 and 366 nm) for
detection. Common reagents grade chemicals are either
commercially available and were used without further
purification or prepared by standard literature procedures.
4.2. General procedure for the synthesis of (2a–b),
(3a–b)
The spectroscopic data are compiled in Table 1 and the quan-
tum yields calculated are impressive. All these findings re-
veal that DPP are very useful because of their stability and
their photophysical properties. The structures of 7c–d were
also characterized by IR and 1H NMR spectroscopies.
A solution of 1 (0.01 mol) and sodium azide (0.01 mol) in
DMF (15 mL) was stirred at 10–20 ꢀC until the starting
material had disappeared (3 h, checked by TLC monitoring).
Then the solution was poured into cold water (50 mL) and
stirred for 30 min. The obtained solid was filtered, washed
with cold water (100 mL), and dried, to afford a mixture
of compounds 2 and 3, which was separated by column chro-
matography using 4:1 toluene/acetone as the eluant to afford
2 and 3 in 60:20% yield, respectively.
4.3. Synthesis of ethyl 4-amino-3-aryl-1-phenyl-1H-
pyrazolo[3,4-b]pyridine-5-carboxylate (4a–b)
A solution of 2 (0.01 mol) and sodium dithionate (0.01 mol)
in methanol (15 mL) was refluxed for 3 h. Then the solution
was allowed to cool, and poured into cold water (30 mL) and
stirred for 30 min, the solid separated out was filtered, dried,
and recrystallized from the proper solvent to afford 4 in good
yield.
Figure 4. The absorption (a) and emission (b) spectra of 7c in DMSO.
4.4. Synthesis of 2-amino-9-aryl-4-hydroxy-7-phenyl-
7H-pyrazolo[3,4-h][1,6]naphthyridine-3-carbonitrile
(5a–b)
Table 1. Photophysical data for electronic absorption (abs) and fluorescence
(flu) of DPP 7 in DMSO
Compound
labs
(DMSO)
lflu
(DMSO)
3
(DMSO)
FF
(DMSO)
A solution of 4 (0.01 mol) and malononitrile (0.01 mol) in
ethanol (15 mL) containing catalytic amount of piperidine
was refluxed for 18 h. Then the solution was allowed
to cool and the solid separated out was filtered, dried,
and recrystallized from proper solvent to afford 5 in good
yield.
7a
7b
7c
7d
369
370
384
384.5
410
407
419
417
7325
6411
5402
6262
0.172
0.173
0.168
0.166
4.5. Synthesis of ethyl 3-aryl-4-{[(ethylamino)-
carbonyl]amino}-1-phenyl-1H-pyrazolo[3,4-b]pyridine-
5-carboxylate (6a–b)
4. Experimental
4.1. General
A solution of compound 1 (0.01 mol) and ethyl urea
(0.02 mol) in ethanol (15 mL) containing catalytic amount
of potassium hydroxide was refluxed for 5 h. Then the solu-
tion was allowed to cool, and poured into cold water (25 mL)
and stirred for 20 min. The solid separated was filtered,
washed with water (100 mL), and dried to afford 6 in good
yield.
Melting points were determined on a Gallenkamp Melting
Point Apparatus, Mod. MFB-595 in open capillary tubes
1
and are uncorrected. The H and 13C NMR spectra were
recorded on a Varian XL-300 spectrometer (300 MHz).
Chemical shifts are reported in parts per million using tetra-
methylsilane as internal standard and are given in d units.
The solvent for NMR spectra was deuteriochloroform unless
otherwise stated. Infrared spectra were taken on Shimadzu
IR-408, a Shimadzu FTIR instrument in potassium bromide
pellets unless otherwise stated. UV spectra were recorded on
a Shimadzu UV-1601 UV–vis Spectrophotometer. Com-
pounds for UV scan were dissolved in DMSO. Fluorescence
spectra were recorded using RF-5301 PC Spectrofluoro-
photometer. Compounds for fluorescence measurements
were dissolved in DMSO. UV and fluorescence scans were
recorded from 200 to 600 nm. Elemental analysis was per-
formed on a Hosli CH-Analyzer and is within ꢁ0.4 of the
4.6. Synthesis of 8-aryl-1,6-diphenyl-1,6-dihydrodi-
pyrazolo[3,4-b:30,40-d]pyridin-3(2H)-one (7a–d)
A solution of compound 1 (0.01 mol) and phenylhydrazine
or hydrazine hydrate (0.01 mol) in xylene (15 mL) con-
taining a catalytic amount of triethylamine (0.5 mL) was
refluxed for 3–5 h. The excess solvent was removed by
reduced pressure. The solid obtained was stirred in ethanol
(20 mL), filtered, dried, and recrystallized from proper
solvent to afford 7 in good yield.

D. B. Kendre et al. / Tetrahedron 63 (2007) 11000–11004
11003
4.6.1. Ethyl 4-azido-3-(4-chlorophenyl)-1-phenyl-1H-
pyrazolo[3,4-b]pyridine-5-carboxylate (2a). Recrystal-
lized from ethanol to afford colorless needles; mp
187–188 ꢀC. IR (KBr): 2991, 2922, 2854, 2144, 1706, 1585,
172–173 ꢀC. IR (KBr): 3101, 2948, 1688, 1598, 1525,
1
1368, 1406, 1155, 769 cmꢂ1. H NMR (CDCl3): d 1.39 (t,
J¼6.9 Hz, 3H, CH3), 4.35 (q, J¼7.2 Hz, 2H, –OCH2), 5.53
(br s, 1H, NH), 7.26–8.01 (m, 9H, Ar-H) 8.45 (br s, 1H,
NH), 8.97 (s, 1H, C6-H). 13C NMR (CDCl3): d 14.4, 60,
106.5, 107.2, 121.6, 126, 128, 128.8, 129, 130, 131.6,
133.1, 144.5, 147, 152.4, 154.3, 169. Anal. Calcd for
C21H17BrN4O2: C, 57.68; H, 3.92; N, 12.81. Found: C,
57.67; H, 3.99; N, 12.90.
1
1498, 1269, 1134, 910 cmꢂ1. H NMR (CDCl3): d 1.43 (t,
J¼6.9 Hz, 3H, CH3), 4.45 (q, J¼7.5 Hz, 2H, OCH2), 7.23–
7.55 (m, 5H, Ar-H), 7.80 (d, J¼8.4 Hz, 2H, Ar-H), 8.21
(d, J¼8.4 Hz, 2H, Ar-H), 9.07 (s, 1H, C6-H). 13C NMR
(CDCl3): d 14.1, 60.8, 105.3, 120.2, 125.4, 126.2, 128.4,
128.7, 129.3, 129.4, 134.2, 135.7, 139.7, 144.2, 148.9,
150.2, 167.6. Anal. Calcd for C21H15ClN6O2: C, 60.22; H,
3.61; N, 20.07. Found: C, 60.40; H, 3.44; N, 20.30.
4.6.7. 2-Amino-9-(4-chlorophenyl)-4-hydroxy-7-phenyl-
7H-pyrazolo[3,4-h][1,6]naphthyridine-3-carbonitrile
(5a). Recrystallized from ethanol to afford colorless needles;
mp 215–216 ꢀC. IR (KBr): 3435, 3315, 3126, 2234, 1470,
1160, 945 cmꢂ1. 1H NMR (CDCl3): d 4.74 (br s, 2H, NH2),
7.18–8.35 (m, 9H, Ar-H), 8.63 (s, 1H, C6-H). 13C NMR
(CDCl3): d 82.4, 100.8, 106.3, 117.0, 120.2, 120.4, 128.3,
128.6, 129.2, 129.4, 134.3, 134.4, 145.9, 148.1, 148.3,
149.1, 162.8, 171.2. Anal. Calcd for C22H13ClN6O: C,
64.01; H, 3.17; N, 20.36. Found: C, 64.07; H, 3.19; N, 20.40.
4.6.2. Ethyl 4-azido-3-(4-bromophenyl)-1-phenyl-1H-
pyrazolo[3,4-b]pyridine-5-carboxylate (2b). Recrystal-
lized from ethanol to afford colorless needles; mp
191–192 ꢀC. IR (KBr): 2958, 2912, 2314, 1700, 1515,
1445, 1134, 912 cmꢂ1 1H NMR (CDCl3): d 1.42 (t,
.
J¼6.9 Hz, 3H, CH3), 4.43 (q, J¼7.2 Hz, 2H, OCH2), 7.21–
7.51 (m, 5H, Ar-H), 7.81 (d, J¼8.4 Hz, 2H, Ar-H), 8.22
(d, J¼8.4 Hz, 2H, Ar-H), 9.07 (s, 1H, C6-H). 13C NMR
(CDCl3): d 14.2, 60.0, 106.3, 120, 125, 126.2, 128, 128.4,
129, 129.1, 133.6, 134.3, 138.5, 144.1, 147.5, 152, 168.6.
Anal. Calcd for C21H15BrN6O2: C, 54.44; H, 3.26; N,
18.14. Found: C, 54.40; H, 3.22; N, 18.30.
4.6.8. 2-Amino-9-(4-bromophenyl)-4-hydroxy-7-phenyl-
7H-pyrazolo[3,4-h][1,6]naphthyridine-3-carbonitrile
(5b). Recrystallized from ethanol to afford colorless needles;
mp 221–222 ꢀC. IR (KBr): 3456, 3341, 3221, 2244, 1461,
1162, 948 cmꢂ1 1H NMR (CDCl3): d 4.73 (br s, 2H,
.
4.6.3. 9-(4-Chlorophenyl)-7-phenyl-7H-pyrazolo[40,30:5,6]-
pyrido[4,3-d][1,2,3]triazin-4-ol (3a). Recrystallized from
ethanol to afford colorless needles; mp 201–203 ꢀC. IR
(KBr): 3416, 3044, 2926, 2855, 2762, 1538, 1456, 1287,
NH2), 7.17–8.36 (m, 9H, Ar-H), 8.65 (s, 1H, C6-H). 13C
NMR (CDCl3): d 83, 101.4, 105.2, 116.1, 120.3, 120.4,
128, 128.5, 129, 129.9, 133.8, 135.9, 145, 148.3, 148.8,
149.5, 162.6, 171. Anal. Calcd for C22H13BrN6O: C,
57.78; H, 2.87; N, 18.38. Found: C, 57.70; H, 2.89; N, 18.40.
1
1136, 922 cmꢂ1. H NMR (CDCl3): d 7.24 (m, 5H, Ar-H),
7.67 (d, J¼8.4 Hz, 2H, Ar-H), 8.18 (d, J¼8.4 Hz, 2H, Ar-
H), 9.24 (s, 1H, Ar-H). 13C NMR (CDCl3): d 108, 119,
123.6, 124.8, 125.4, 127.5, 129.9, 130, 132.8, 135, 139,
145, 148.2, 149.1, 155. Anal. Calcd for C19H11ClN6O: C,
60.89; H, 2.96; N, 22.42. Found: C, 60.90; H, 2.92; N, 22.49.
4.6.9. Ethyl 3-(4-chlorophenyl)-4-{[(ethylamino)carbonyl]-
amino}-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carb-
oxylate (6a). Recrystallized from ethanol to afford colorless
needles; mp 235–236 ꢀC. IR (KBr): 3315, 3245, 2966, 1738,
1
1618, 1455, 1136, 915 cmꢂ1. H NMR (CDCl3): d 1.00 (t,
4.6.4. 9-(4-Bromophenyl)-7-phenyl-7H-pyrazolo[40,30:
5,6]pyrido[4,3-d][1,2,3]triazin-4-ol (3b). Recrystallized
from ethanol to afford colorless needles; mp 211–212 ꢀC.
IR (KBr): 3452, 3125, 3012, 2906, 2812, 2760, 1507,
J¼6.9 Hz, 3H, CH3), 1.39 (t, J¼6.8 Hz, 3H, CH3), 2.83 (q,
J¼7.2 Hz, 2H, CH2), 4.33 (q, J¼7.2 Hz, 2H, OCH2), 7.24
(m, 9H, Ar-H), 8.72 (br s, 1H, –NH), 8.95 (s, 1H, C6-H).
13C NMR (CDCl3): d 14.1, 14.5, 36.5, 60.4, 104.3, 105.8, 120,
126, 128.3, 129.4, 129.6, 131.8, 134.6, 139.8, 145.9, 149.3,
151.3, 154, 155, 166. Anal. Calcd for C24H22ClN5O3: C,
62.14; H, 4.78; N, 15.10. Found: C, 62.20; H, 4.84; N, 15.30.
1
1344, 1227, 1134, 920 cmꢂ1. H NMR (CDCl3): d 7.23
(m, 5H, Ar-H) 7.68 (d, J¼8.4 Hz, 2H, Ar-H), 8.19 (d,
J¼8.4 Hz, 2H, Ar-H), 9.23 (s, 1H, Ar-H). Anal. Calcd for
C19H11BrN6O: C, 54.43; H, 2.64; N, 20.05. Found: C,
54.47; H, 2.70; N, 20.09.
4.6.10. Ethyl 3-(4-bromophenyl)-4-{[(ethylamino)carbo-
nyl]amino}-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carb-
oxylate (6b). Recrystallized from ethanol to afford colorless
needles; mp 239–240 ꢀC. IR (KBr): 3328, 3215, 2926, 1734,
4.6.5. Ethyl 4-amino-3-(4-chlorophenyl)-1-phenyl-1H-
pyrazolo[3,4-b]pyridine-5-carboxylate (4a). Recrystal-
lized from ethanol to afford colorless needles; mp
161–162 ꢀC. IR (KBr): 2916, 2848, 1678, 1598, 1552,
1
1628, 1465, 1160, 930 cmꢂ1. H NMR (CDCl3): d 1.00 (t,
J¼6.9 Hz, 3H, CH3), 1.37 (t, J¼6.8 Hz, 3H, CH3), 2.82 (q,
J¼7.2 Hz, 2H, CH2), 4.34 (q, J¼7.2 Hz, 2H, OCH2), 7.23
(m, 9H, Ar-H), 8.71 (br s, 1H, –NH), 8.95 (s, 1H, C6-H).
13C NMR (CDCl3): d 14.1, 14.6, 36.3, 60, 103.8, 106.5,
121, 125.2, 128.3, 129, 129.7, 131, 133.4, 138.9, 145, 149,
151.6, 155, 155.8, 167. Anal. Calcd for C24H22BrN5O3: C,
56.70; H, 4.36; N, 13.78. Found: C, 56.75; H, 4.34; N, 13.80.
1
1468, 1406, 1163, 723.3 cmꢂ1. H NMR (CDCl3): d 1.38
(t, J¼6.9 Hz, 3H, CH3), 4.33 (q, J¼7.2 Hz, 2H, OCH2),
5.50 (br s, 1H, NH), 7.24–8.14 (m, 9H, Ar-H) 8.41 (br s,
1H, NH), 8.97 (s, 1H, C6-H). 13C NMR (CDCl3): d 14.1,
60.9, 104.6, 105.0, 120.2, 126.3, 128.8, 128.9, 129.4,
130.2, 131.3, 134.3, 145.9, 149.1, 151.3, 155.0, 166.0.
Anal. Calcd for C21H17ClN4O2: C, 64.21; H, 4.36; N,
14.26. Found: C, 64.37; H, 4.40; N, 14.09.
4.6.11. 8-(4-Chlorophenyl)-1,6-diphenyl-1,6-dihydrodi-
pyrazolo[3,4-b:30,40-d]pyridin-3(2H)-one (7a). Recrystal-
lized from DMF/ethanol (2:8) to afford yellow needles;
mp 220–221 ꢀC. IR (KBr): 3216, 2912, 1632, 1553, 1435,
4.6.6. Ethyl 4-amino-3-(4-bromophenyl)-1-phenyl-1H-
pyrazolo[3,4-b]pyridine-5-carboxylate (4b). Recrys-
tallized from ethanol to afford colorless needles; mp
1
1162, 936 cmꢂ1. H NMR (DMSO-d6): d 7.19–7.65 (m,

11004
D. B. Kendre et al. / Tetrahedron 63 (2007) 11000–11004
10H, Ar-H), 7.95 (d, J¼8.4 Hz, 2H, Ar-H), 8.18 (d,
J¼8.4 Hz, 2H, Ar-H), 8.50 (s, 1H, C6-H), 8.62 (br s, 1H,
NH). 13C NMR (DMSO-d6): d 104.6, 115.8, 120.1, 121.2,
123.4, 125.6, 125.7, 126.1, 126.2, 129.1, 129.2, 130.1,
134.2, 134.3, 145.9, 149.1, 154.6, 156.6, 167.3. Anal. Calcd
for C25H16ClN5O: C, 68.57; H, 3.66; N, 15.99. Found: C,
68.67; H, 3.69; N, 15.80.
Department of Chemistry, University of Pune, India for his
valuable co-operation for the measurement of fluorescence
properties.
References and notes
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Phys. Lett. 1995, 67, 3853.
4. Gao, Z.; Lee, C.; Bello, I.; Lee, S.; Chen, R.-M.; Luh, T.-Y.;
Shi, J.; Tang, C. Appl. Phys. Lett. 1999, 74, 865.
5. Piorun, D.; Parusel, A.; Rechthaler, K.; Rotkiewicz, K.; Kohler,
G. J. Photochem. Photobiol., A: Chem. 1999, 129, 33.
6. Parusel, A.; Schamschule, R.; Kohler, G. Ber. Bunsenges, Phys.
Chem. 1997, 101, 1836.
4.6.12. 8-(4-Bromophenyl)-1,6-diphenyl-1,6-dihydrodi-
pyrazolo[3,4-b:30,40-d]pyridin-3(2H)-one (7b). Recrystal-
lized from DMF/ethanol (2:8) to afford yellow needles;
mp 226–227 ꢀC. IR (KBr): 3217, 2933, 1622, 1511, 1415,
1
1162, 935 cmꢂ1. H NMR (DMSO-d6): d 7.18–7.64 (m,
10H, Ar-H), 7.91 (d, J¼8.4 Hz, 2H, Ar-H), 8.19 (d,
J¼8.4 Hz, 2H, Ar-H), 8.51 (s, 1H, C6-H), 8.63 (br s, 1H,
NH). 13C NMR (DMSO-d6): d 106, 114, 121.5, 121.8,
123, 124, 125.9, 126.8, 126.9, 129, 129.8, 130, 133.2,
134.5, 141, 146, 152.6, 158.6, 169.2. Anal. Calcd for
C25H16BrN5O: C, 62.25; H, 3.34; N, 14.52. Found: C,
62.27; H, 3.39; N, 14.66.
7. Parusel, A.; Schamschule, R.; Kohler, G. J. Comput. Chem.
1998, 19, 1584.
8. Miyasaka, H.; Itaya, A.; Rotkiewicz, K.; Rechthaler, K. Chem.
Phys. Lett. 1999, 307, 121.
9. Rotkiewicz, K.; Rechthaler, K.; Puchala, A.; Rasala, D.;
Styrez, S.; Kohler, G. J. Photochem. Photobiol., A: Chem.
1996, 98, 15.
10. Hoehn, H.; Denzel, T. Patent BRD 2159600; Chem. Abstr.
1972, 77, 114401.
11. Hoehn, H.; Schulze, E. Patent BRD 2333603; Chem. Abstr.
1974, 77, 108514.
4.6.13. 8-(4-Chlorophenyl)-6-phenyl-1,6-dihydrodipyr-
azolo[3,4-b:30,40-d]pyridin-3(2H)-one (7c). Recrystallized
from DMF/ethanol (2:8) to afford yellow needles; mp
242–243 ꢀC. IR (KBr): 3315, 3128, 2926, 1612, 1535,
1
1456, 1228, 936 cmꢂ1. H NMR (DMSO-d6): d 7.22–8.16
(m, 9H, Ar-H), 8.53 (s, 1H, C6-H), 8.62 (br s, 1H, NH).
13C NMR (DMSO-d6): d 105.2, 115, 121.6, 124, 126.7,
128.5, 129, 129.3, 130, 130.2, 145, 149, 154, 156, 167.3.
Anal. Calcd for C19H12ClN5O: C, 63.08; H, 3.34; N,
19.36. Found: C, 63.17; H, 3.44; N 19.56.
12. Hoehn, H.; Denzel, T. U.S. Patent 3,840,546, 1974; Chem.
Abstr. 1975, 82, 43413.
13. Sanghvi, Y.; Larson, S.; Willis, R.; Robins, R.; Revankar, G.
J. Med. Chem. 1989, 32, 945.
14. Joshi, K.; Dubey, K.; Dandia, A. Pharmazie 1981, 36, 336.
15. Robins, R.; Holum, L.; Furcht, F. J. Org. Chem. 1956, 21,
833.
16. Jachak, M.; Avhale, A.; Tantak, C.; Toche, R.; Reidlinger, C.;
Stadlbauer, W. J. Heterocycl. Chem. 2005, 42, 311.
17. Jachak, M.; Avhale, A.; Medhane, V.; Toche, R. J. Heterocycl.
Chem. 2006, 43, 1169.
18. Jachak, M.; Avhale, A.; Toche, R.; Sabnis, R. J. Heterocycl.
Chem. 2007, 44, 343.
4.6.14. 8-(4-Bromophenyl)-6-phenyl-1,6-dihydrodipyr-
azolo[3,4-b:30,40-d]pyridin-3(2H)-one (7d). Recrystallized
from DMF/ethanol (2:8) to afford yellow needles; mp
248–249 ꢀC. IR (KBr): 3328, 3216, 2927, 1624, 1545,
1
1416, 1229, 912 cmꢂ1. H NMR (DMSO-d6): d 7.21–8.14
(m, 9H, Ar-H), 8.54 (s, 1H, C6-H), 8.61 (br s, 1H, NH).
13C NMR (DMSO-d6): d 107.2, 117, 121, 124.8, 126.3,
128.4, 129.5, 129.9, 130.2, 130.3, 142, 148, 151, 154, 168.
Anal. Calcd for C19H12BrN5O: C, 56.18; H, 2.98; N,
17.24. Found: C, 56.27; H, 2.77; N, 17.36.
19. Toche, R.; Ghotekar, B.; Kazi, M.; Kendre, D.; Jachak, M.
Tetrahedron 2007, 63, 8157.
Acknowledgements
20. Bare, T.; McLaren, C.; Campbell, J.; Firor, J.; Resch, J.;
Walters, C.; Salama, A.; Meiners, B.; Patel, J. J. Med. Chem.
1989, 32, 2561.
The authors thank to UGC, New Delhi, India for financial
support to this research project. We thank Prof. D. D. Dhavale,