Synthesis of pyrazolopyridine annulated heterocycles and study the effect of substituents on photophysical properties

Article abstract of DOI:10.1007/s10895-011-0960-x

Pyrazolo[3,4-b]pyridines having 4-chloro-5- chloroethyl side chain are synthesized by the reaction of 5-aminopyrazole and cyclic β-formylester gave aminopyrazolodihydrofuranone intermediate, which on cyclization in phosphorous oxychloride exclusively converted in to 4-chloro-5-chloroethyl pyrazolo[3,4-b]pyridines 4(a-b) in major amount. The side chain with acetic acid, thiourea and aromatic amines are used to form angular ring leads to formation of tricyclic Furo[2,3-d]pyrazolo[2,3-b]pyridines 5(a-b), pyrazolo[3,4-b]thieno[2,3-d]pyridines 6(a-b) and pyrazolo[3,4-b]pyrrolo[2,3-d] pyridines 7(a-n) respectively. The substituents effect at C₄ position on fluorescence properties of pyrazolopyridines has been studied. Moreover the effect of electron donor and halogen substituents on fluorescence properties of pyrazolopyrrolopyridines 7(a-n) has been investigated along with their fluorescent quantum yield.

Full text of DOI:10.1007/s10895-011-0960-x

J Fluoresc (2012) 22:31–41
DOI 10.1007/s10895-011-0960-x
RAPID COMMUNICATION
Synthesis of Pyrazolopyridine Annulated Heterocycles
and Study the Effect of Substituents
on Photophysical Properties
Shivaraj P. Patil & Deepak P. Shelar &
Raghunath B. Toche
Received: 22 June 2011 /Accepted: 30 August 2011 /Published online: 14 September 2011
#
Springer Science+Business Media, LLC 2011
Abstract Pyrazolo[3,4-b]pyridines having 4-chloro-5-
chloroethyl side chain are synthesized by the reaction of
5-aminopyrazole and cyclic β-formylester gave amino-
pyrazolodihydrofuranone intermediate, which on cycliza-
tion in phosphorous oxychloride exclusively converted in to
4-chloro-5-chloroethyl pyrazolo[3,4-b]pyridines 4(a-b) in
major amount. The side chain with acetic acid, thiourea and
aromatic amines are used to form angular ring leads to
formation of tricyclic Furo[2,3-d]pyrazolo[2,3-b]pyridines
5(a-b), pyrazolo[3,4-b]thieno[2,3-d]pyridines 6(a-b) and
pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines 7(a-n) respectively.
The substituents effect at C4 position on fluorescence
properties of pyrazolopyridines has been studied. Moreover
the effect of electron donor and halogen substituents on
fluorescence properties of pyrazolopyrrolopyridines 7(a-n)
has been investigated along with their fluorescent quantum
yield.
years and have great potential especially for use in optical
communication, information processing, frequency dou-
bling and integrated optics [1–4]. One commonly used
strategy to design π-electron chromophores for second
order NLO application is to end-cap a suitably conjugated
bridge with donor (D) and acceptor (A) substituents. In the
90s several authors pointed out that the strength of electron
donor and acceptor substituents must be optimized for the
specific π-conjugated system and the loss of aromaticity
between the neutral form and the charge separated
zwitterionic form of the chromophores is believed to be
responsible for the reduced or saturated β values [5–9]. The
electron excessive/deficient heterocycles act as an auxiliary
donors/acceptors while connected to donating/withdrawing
groups, and the increase of donor/acceptors ability leads to
substantial increases in β values [10, 11]. Having in mind
this idea, several investigators reported on the synthesis and
characterization of conjugated heterocyclic system in which
the donor moiety was represented by a π-excessive five
membered heterocycle (pyrrolo or thiophene) and the
acceptor group was a deficient heterocyclic azine ring.
These new heterocyclic derivatives exhibited improved
solvatochromic, electrochromic, photochromic, fluorescent,
and nonlinear optical properties [12–21].
.
.
Keywords Pyrazolo[3,4-b]pyridine Fluorescence
.
HOMO-LUMO Quantum yield
Introduction
The design and synthesis of organic chromophores as non-
linear optical (NLO) materials has much attention in recent
Despite the growing interest in NLO heteroaromatic
chromophores, relevant information concerning the relation
between molecular structure and effective material proper-
ties for these NLO systems is still scarce. Derivatives with
various other substituents in position C4 showed intense
fluorescence can be used as fluorescence standard and
found application as blue-green organic light-emitting
diode. Thus, pyrazolopyridine having different substituents
at C4 position with blue-emission, high brightness, high
quantum yield and good thermal stability remain to be
developed [22–25].
:
:
S. P. Patil D. P. Shelar R. B. Toche (*)
Organic Chemistry Research Center, Department of Chemistry,
K. H. T. M. College,
Gangapur Road,
Nashik 422002 M.S., India
e-mail: raghunath_toche@rediffmail.com
:
:
S. P. Patil D. P. Shelar R. B. Toche
University of Pune,
Pune-07, M. S., India

32
J Fluoresc (2012) 22:31–41
Apart from this, the pyrazolo annelated heterocycles
sodium salt of α-formyl-γ-butyrolactone 2 in AcOH and
MeOH at reflux temperature. The in situ formation of free
formyl ester generated by weak acid catalyst undergoes
attack of amino group yielding the Z-enamine 3. Compounds
1 and 2 on refluxing in presence of AcOH or NH4OAc
furnished into fused tricyclic dihydrofuropyrazolopyridines 5
in 85% yield. Similar reactions with intermediate 3 in POCl3
at refluxed temperature furnished mixture of compounds 4
and 5 (TLC check), are separated by column chromatogra-
phy (chloroform-methanol/v:v 9:1) and obtained in 70% and
30% yields respectively. We assighned structure 4 and 5 on
the basis of spectral and analytical data.
have demonstrated wide spectrum of agriculture and
pharmacological activity [26, 27]. Pyrazolo[3,4-b]pyridine
are promising candidates in organic synthesis due to their
significant application in medicinal chemistry, such as
diagnosis of brain disorder [28], treatment of coronary
heart disease [29], viral disease [30] and the pyrazolothie-
nopyridine showed the anti-inflammatory and anti-platelet
agents [31].
Our recent report on the effect of C4 substituent on the
fluorescence properties of pyrazolo[3,4-b]pyrrolo[2,3-d]
pyridine [32], dipyrazolo[3,4-b:3,4-d]pyridines [33] and
this reports have attracted us to synthesize this particular
family of compounds. Encouraged by this study and hunt
for new fluorescent pyrazolo-annelated heterocycles herein
we synthesized pyrazolo[3,4-b] pyridine 4(a-b), dihydro-
2H-furo[2,3-d]pyrazolo[3,4-b]pyridine 5(a-b), pyrazolo
[3,4-b]thieno [2,3-d]pyridine 6(a-b) and pyrazolo[3,4-b]
pyrrolo[2,3-d]pyridines 7(a-n) and studied the effect of Cl,
O, S and N at C4 position of pyrazolo pyridines ring on
fluorescent behavior. Photophysical properties of 7(a-n) are
also studied and compared absorption and fluorescence
emission maxima with reference to donor and halogen
substituent on D ring (Fig. 2). Moreover, substituents effect
on the performance of 7(a-n) are studied by calculating
HOMO, LUMO energies and electron hole gap by using
MOPAC-2009 to investigate the fluorescence properties.
For instance IR of 3b shows lactone carbonyl stretching
at 1,722 cm−1, NH at 3,230 cm−1 and (C=C) at 1,640 cm−1.
1
The H NMR of this compound in CDCl3 shows doublet
for broad exchangeable with D2O NH proton at 6.05 δ with
J=9.3 Hz, 2H showed multiplet at 2.81 δ, 2H shows triplet
at 4.21 δ with J=8.4 Hz. All aromatic proton shows
expected chemical shifts and splitting pattern which
resemble with structure of 3b. The 13C NMR spectrum of
this compound with the structure proposed. The mass
spectrum 3b revealed a molecular ion peak m/z at 345. The
structure of 4 and 5 are established by spectral and
analytical data, the compound 4a shows absences of
carbonyl and NH streching frequency in IR, while
compound 5a showed absences of carbonyl and NH
streching frequency but shows CH2-O-C, stretching
frquency at 1,280 cm−1. The 1H NMR of 5a in CDCl3
clearly showed (O-CH2) at 4.27 δ as a triplet with J=
6.6 Hz, and (CH2-CH2) at 2.88 δ as triplet with J=6.6 Hz.
Advantage of C4-Cl and C3-chloroethyl is also taken to
annelated five member tetrahydrofuran rings on pyridine
nucleus to yield compounds 5a-b (Scheme 1).
Experimental
Synthesis and Compound Identification
Intermediate pyrazoloaminodihydrofuranones 3, (Scheme 1)
were obtained by condensation of 5-aminopyrazole 1 with
Reaction of compounds 4(a-b) with thiourea in acetic
acid under reflux condition furnished thienopyrazolopyr-
Method II
AcOH
reflux
2-3 h
25%
Cl
Cl
O
O
Method I
POCl3
Ar
Ar
MeOH/
AcOH
Ar
O
+
N
N
N
reflux
3 h
N
H
N
H
N
reflux
10-12 h
N
N
N
H
Ph
4 a-b
Ar
Ph
3 a-b
65%
Ph
5 a-b
30%
ONa
70%
N
+
NH2
N
O
O
Ph
Method III
2
1 a-b
i)
or
NH4OAc
AcOH
reflux
10-15 h
80-85%
ii)
1, 3, 4, 5 Ar, a = p-ClC6H4; b = p-MeC6H4
Scheme 1 Synthesis of 4-chloro-5-(2-chloroethyl)-pyrazolo[3,4-b]pyridines 4 and furo[2,3-d]pyrazolo[3,4-b]pyridine 5 derivatives

J Fluoresc (2012) 22:31–41
33
idines 6(a-b) in good yields. The targeted new fused
heterocyclic compound pyrazolo[3,4-b]pyrrolo[2,3-d]pyri-
dine 7(a-n) are successfully synthesized in 65–85% yield,
from pyrazolo[3,4-b]pyridine 4 by neat heat with primary
aromatic amines. The compound 7 are characterized by IR,
1H NMR, 13C NMR, Mass and elemental analysis given in
experimental part (Scheme 2). Synthesized pyrazolopyri-
dine are further studied for their photophysical properties.
Photophysical Properties
UV-visible and fluorescence spectra of compounds 4(a-b),
5(a-b), 6(a-b) and 7(a-n) are taken in DMF as a solvent at
same concentration i.e. 1.0×10-3 M. The UV−visible and
fluorescence spectral data of pyrazolopyridine are summa-
rized in Tables 2 and 3. Fluorescence quantum yield of all
synthesized compounds are determined by standard litera-
ture procedure using quinine sulfate as an a reference
standard [36, 37] and are given Tables 2 and 3. We
observed effect of substituents at C4 position on UV–vis
and fluorescence emission. Among Cl, O, S and N
substituent at C4 position, N-substituted pyrazolopyridine
shows red shift in its fluorescence emission and higher
quantum yields (Φf) as compare to Cl, O and S substituents
at C4 position. Thus, C4-N pyrazolopyridine (7a-n) shows
greater fluorescence emission as compare to C4-Cl, C4-O,
C4-S and it shown by above sequence: C4-N(lf max) > C4-S
(lf max) > C4-O(lf max) > C4-Cl(λf max) (Tables 2 and 3).
The comparative absorption and emission spectra of com-
pound 4b, 5b, 6b and 7j are graphically presented in Fig. 2.
From Table 2, we observed the moderate shift in absorption
maxima for 5(a-b) and 6(a-b) but on the other hand
fluorescence maxima shift to red from C4-O to C4-S (i.e.
from 5a-b to 6a-b), may be because of oxygen is more
electronegative as compare to sulfur. It also observed that 4a-
b shows blue shifted fluorescence maxima as compare to 5
(a-b) and 6(a-b), may be because of Cl at C4 position shows
quenching of fluorescence as a substituents. From Table 3, it
observed that substituents on D ring exhibit moderate shift
Semi-empirical Study
As a keen interest into the atomic contribution on the
frontier orbital, we have analyzed three-dimensional HOMO
and LUMO coefficient contribution by the MOPAC-2009
(Version 8.331) [34, 35] and are given in Table 1. From
Table 1, we observed that, among 4(a-b), 5(a-b) and 6(a-b),
4b, 5b and 6b bears electron donating group through +I
effect i.e. methyl group at para-position of aromatic ring,
shows low electron hole gap and fluorescent at longer
wavelength with high quantum yield as compare to 4a, 5a
and 6a. For 7(a-n), it observed that, charge is more
concentrated on ring D as compared to A, B, C and E
(Fig. 1). The donor chromophores i.e. OCH3 (+R effect) and
CH3 (+I effect) on ring D plays an important role in
increasing the electron density and lowering electron hole
gap. Among 7(a-n), compounds 7b, 7c, 7e, 7f, 7h, 7i, 7j, 7l
and 7m shows low GAP values indicates higher overlapping
of HOMO or LUMO orbitals which shows red shift in its
fluorescence emission and high quantum yields as compare
to others (Table 1 and Fig. 2).
Scheme 2 Synthesis of pyra-
zolo[3,4-b]thieno[2,3-d]pyridine
6 and pyrazole[3,4-b] pyrrolo
[2,3-d]pyridine 7 derivatives
R
N
Cl
Cl
S
Ar
Ar
Ar
RNH2
Thiourea/AcOH
reflux, 2-3 h
N
N
N
N
heat, 110-150 °C
2-4 h
N
N
N
N
N
Ph
7 a-n
Ph
4 a-b
Ph
6 a-b
75-90%
80-90%
6, 4 Ar, a = p-ClC6H4; b = p-MeC6H4
4a, 7
Ar
R
4b, 7
Ar
R
p-ClC6H4 m-ClC6H4
p-ClC6H4 p-MeC6H4
p-ClC6H4 p-OMeC6H4
p-ClC6H4 p-ClC6H4
p-ClC6H4 C6H5
p-Me-C6H4 m-ClC6H4
p-Me-C6H4 p-MeC6H4
a
b
c
d
e
f
h
i
p-Me-C6H4 p-OMeC6H4
p-Me-C6H4 p-ClC6H4
p-Me-C6H4 C6H5
j
k
l
p-ClC6H4 m-MeC6H4
p-ClC6H4 4-Cl 3-FC6H4
p-Me-C6H4 m-MeC6H4
p-Me-C6H4 4-Cl 3-FC6H4
m
n
g

34
J Fluoresc (2012) 22:31–41
Table 1 The molecular electron-
ic properties, (HOMO-LUMO
energy, Gap) of Pyrazolo[3,4-b]
pyridine 4(a-b), 5(a-b), 6(a-b)
and 7(a-n)
Comp.
Ar
R
HOMO (eV)
LUMO (eV)
GAP (eV)
4a
4b
5a
5b
6a
6b
7a
7b
7c
7d
7e
7f
p-ClC6H4
p-MeC6H4
p-ClC6H4
p-MeC6H4
p-ClC6H4
p-MeC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
–
−8.4515
−8.1693
−8.3551
−8.0999
−8.8961
−8.1554
−8.3736
−8.2599
−8.2871
−8.3802
−8.2792
−8.2621
−8.4446
−6.4010
−8.0304
−8.0629
−8.1603
−8.0501
−8.0308
−8.2310
−1.5793
−1.8095
−1.8988
−2.1570
−1.8961
−2.1715
−1.7823
−1.9540
−1.9078
−1.7739
−1.9236
−1.9481
−1.6825
−1.7954
−2.2360
−2.1881
−2.0496
−2.2058
−2.2259
−1.9581
6.8722
6.3598
6.4563
5.9429
7.0000
5.9839
6.5913
6.3059
6.3778
6.6063
6.3556
6.3140
6.7621
4.6056
5.7944
5.8748
6.1107
5.8443
5.8049
6.2729
–
–
–
–
–
m-ClC6H4
p-MeC6H4
p-OMeC6H4
p-ClC6H4
C6H5
m-MeC6H4
4-Cl-3-FC6H4
m-ClC6H4
p-MeC6H4
p-OMeC6H4
p-ClC6H4
C6H5
7g
7h
7i
7j
7k
7l
7m
7n
m-MeC6H4
4-Cl-3-FC6H4
GAP = ELUMO-EHOMO
on the absorption maximum and on the other hand there
is marked influence of substituents on the fluorescence
emission behavior of pyrazolopyridnes 7(a-n). Com-
pound 7b, 7c, 7f, 7i, 7j, 7m shows fluorescence band
appearing at longest wavelength was substantially bath-
ochromically shifted, we ascribed to the increased
π-electron density on the D ring arising from the electron
donating nature of OCH3 and CH3 group. Another
interesting feature is that halo-substituted molecule (7a,
7b, 7g, 7h, 7k and 7n) has less fluorescence emission (λf
max) and fluorescence quantum yield (Φf) than methoxy
and methyl substituted compounds. This may be due to the
quenching of fluorescence with halogen atoms as the
substitution. From Tables 1, 3 and Fig. 2, we reveal that
charge is more concentrate on ring D and substituents on
ring D plays important role to decide the fluorescence
wavelength of 7(a-n). It observed that Cl or CH3
substituent on ring E, much not play a role to decide the
absorption maxima and fluorescence emission of 7(a-n).
We observed that, on replace CH3 group by H at C6 in
pyrazolopyrrolopyridines which reported previously [32]
resulting increase in absorption, emission and quantum
yields. This may be due to disturbance in planarity of
pyrazolopyrrolopyridines by replacement of in CH3 by H.
Conclusion
In summary, fluorescent pyrazolopyridines have been
synthesized in good yields, in which C4 position of pyridine
ring is substituted by Cl, S, O and N with different
substituent’s on phenyl rings. These compounds show
considerable absorption (labs max) and fluorescence emis-
sion (lf max). Among Cl (4a-b), S (5a-b), O (6a-b) and N
Fig. 1 3D picture of furo[2,3-d]
pyrazolo[3,4-b]pyridine 5(a-b),
R'
R''
pyrazolo[3,4-b]thieno [2,3-d]
pyridine 6(a-b) and pyrazolo
[3,4-b]pyrrolo[2,3-d]pyridine 7
(a-n)
X
Cl
A
N
N
N
N
N
N
N
A = O and S
X = Cl, Me
X = Cl, Me
5(a-b) and 6(a-b)
7 (a-n)

J Fluoresc (2012) 22:31–41
35
Fig. 2 The comparative absorption (labs max) and fluorescence emission (lf max) spectra of compounds 4b, 5b, 6b and 7j respectively
(7a-n) substituents at C4 position of pyrazolopyridine, C4-N
i.e. 7(a-n) shows maximum fluorescence emission as
compare to others. The fluorescence emission maxima of
7(a-n) depend upon the nature of substituents on D ring
(Table 3). Thus, donor chromophores on ring D such as
OCH3, CH3 (compound 7b, 7c, 7f, 7i, 7j and 7m) are
shows red shifted fluorescence emission (bathochromic
shift). From empirical calculations, we reveals that pyrazo-
lopyridines which shows low electron hole gap values (5b,
6b, 7b, 7c, 7f, 7i, 7j, 7l and 7m) have high fluorescence
emission as well as high quantum yields (except 7h and
7k). While compound have high electron–hole gap (4a, 5a,
6a, 7a, 7d and 7g) shows low fluorescence emission and
low quantum yields and are in agreement with theoretical
observation. Quantum yield of all synthesized compound
are calculated. This study has brought out interesting
substituents dependent fluorescence properties of pyrazolo-
pyridine can be used as NLO materials. These pyrazolopyr-
idine synthesized compounds are addition to library of
heterocyclic compounds.
Instrumentation
Quinine sulphate [for determination of Φf] was purchased
from Research-Lab Fine Chem Industries, Mumbai (India)
respectively. All other chemicals, reagents and solvents
[such as acetonitrile, dimethylformamide (DMF), dioxane,
ethanol, ethyl acetate, n-hexane, pet-ether methanol and
tetrahydrofuran (THF)] used in spectroscopic and other
studies were obtained from LOBA Chemie. Pvt. Ltd.,
Mumbai (India), Spectrochem, Mumbai (India) and E.
Merck (India). All AR-grade organic solvents were dried
and freshly distilled prior to use. The UV-grade solvents
were used for spectral studies. Melting points were
Table 3 The photophysical data for electronic absorption (labs max)
and fluorescence (lf max) of Pyrazolo[3,4-b]pyrrolo[2,3-d]pyridine 7
in DMF as the solvent (ca. 10−3) at room temperature
Comp.
Ar
R
labs
lflu
ФF
7a
7b
7c
7d
7e
7f
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
m-ClC6H4
p-MeC6H4
p-OMeC6H4
p-ClC6H4
C6H5
364.20
366.50
369.00
364.80
364.50
367.60
346.00
364.70
369.50
370.50
363.50
363.60
365.00
356.00
416
437
452
423
419
431
408
413
444
461
418
429
430
412
0.182
0.271
0.284
0.196
0.192
0.261
0.179
0.187
0.282
0.291
0.192
0.258
0.231
0.195
Table 2 The photophysical data for electronic absorption (labs max)
and fluorescence (lf max) of Pyrazolo[3,4-b]pyridine 4(a-b), 5(a-b)
and 6(a-b) in DMF as the solvent (ca. 10–3) at room temperature
m-MeC6H4
4-Cl,3-FC6H4
m-ClC6H4
p-MeC6H4
p-OMeC6H4
p-ClC6H4
C6H5
7g
7h
7i
Comp.
Ar
labs
lf
Фf
4a
4b
5a
5b
6a
6b
p-ClC6H4
p-Me-C6H4
p-ClC6H4
p-Me-C6H4
p-ClC6H4
p-Me-C6H4
335
336
318
325
324
327
414
424
414
429
421
436
0.177
0.185
0.188
0.213
0.211
0.234
7j
7k
7l
7m
7n
m-MeC6H4
4-Cl,3-FC6H4

36
J Fluoresc (2012) 22:31–41
determined on a Gallenkamp melting point apparatus, Mod.
MFB595 in open capillary tubes and are uncorrected.
Fourier transform infrared (FTIR) spectra in KBr disk were
121.8, 125.7, 126.7, 128.2, 129.1, 131.9, 135.1, 137.4,
138.7, 144.0, 151.5, 168.9. MS (70 eV) m/z: 365 (M+), 367
(M+2). Anal. Calcd for C20H16ClN3O2 (365.81): C, 65.67;
H, 4.41; N, 11.49% Found: C, 65.74; H, 4.33; N, 11.27%.
1
measured on a Shimadzu FTIR-408 spectrophotometer. H
NMR and 13C NMR spectra were recorded on a Varian XL-
300 MHz spectrometer using tetramethylsilane (TMS) as
internal standard and solvents are deuterio-chloroform
(CDCl3) and deuterio-dimethylsulphoxide (DMSO-d6).
Chemical shifts were reported in ppm from internal
tetramethylsilane standard and were given in δ-units.
High-resolution mass spectra are obtained with a Mat 112
Varian Mat Bremen (70 eV) mass spectrometer. Elemental
analyses were performed on a Hosli CH-Analyzer and
within 0.3 of the theoretical percentage. The absorption
spectra were measured using a Shimadzu UV-1601 UV–VIS
spectrophotometer. The fluorescence spectra were recorded
on a RF-5301 PC spectrofluorophotometer by exciting the
samples at their absorption maximum (labs. max.). Compounds
for UV and fluorescence measurements were dissolved in
DMF, UV and fluorescence scan were recorded from 200 to
700 nm. Both samples and standard were excited at the same
excitation wavelength and the optical density (OD) of the
standard and the sample was adjusted to be nearly equal. For
all electronic spectroscopic studies (absorption, fluorescence
excitation and emission) 1.0×10−3 mol L−1 solutions of the
compounds were used. All reactions are monitored by thin
layer chromatography, carried out on 0.2 mm silica gel
60 F254 (Merck) plates using UV light (250 and 400 nm) and
Fluorescence light (400 and 600 nm) for detection.
(Z)-3-((1-phenyl-3-p-tolyl-1H-pyrazol-5-ylamino)meth-
ylene)-dihydrofuran-2(3H)-one (3b)
Yield: 24.1 g (70%), recrystallized from toluene to afford
white crystalline solid. M.p.178–180 °C. IR (KBr): 3,230,
1
2,938, 2,723, 1,722, 1,640, 1,578, 1,048 cm−1. H NMR
(300 MHz CDCl3) δ: 2.41 (s, 3H, CH3), 2.81 (dt, J=2 Hz,
CH2), 4.21 (t, J=8.4 Hz, 2H, CH2), 6.05 (d, J=9.3 Hz, 1H,
NH), 6.20 (s, 1H, ArH), 7.22 (d, J=6 Hz, 2H, ArH), 7.39–
7.42 (m, 1H, ArH), 7.44–7.53 (m, 5H, ArH), 7.73 (d, J=
6 Hz, 2H, ArH). 13C NMR (75 MHz CDCl3) δ: 20.8, 24.4,
64.8, 94.8, 97.2, 123.5, 125.1, 127.2, 129.2, 129.9, 137.3,
138.0, 138.7, 142.4, 150.4, 172.7. MS (70 eV) m/z: 345 (M+).
Anal. Calcd for C21H19N3O2 (345.39): C, 73.03; H, 5.54; N,
12.17% Found: C, 73.22; H, 5.66; N, 12.12%.
General procedure for the synthesis of 4-Chloro-5-(2-
chloroethyl)-3-(aryl)-1-phenyl-1H-pyrazolo [3,4-b]pyr-
idine (4) and 8-(aryl)-6-phenyl-3,6-dihydro-2H-furo
[2,3-d]pyrazolo[3,4-b] pyridine (5)
Method-I
Aminopyrazolyldihydrofuranone 3 (0.01 mol) was stirred at
room temperature in phosphorus oxychloride (20 mL) until
the end of the exothermic reaction, which usually starts
about 80–90 °C. The mixture was then refluxed further for
3–4 h. The excess POCl3 was removed under vacuum. The
residue obtained was stirred in ice-cold water for 2 h and
then the resulting solution was neutralizing by addition of
solid sodium carbonate (2–3 g). The solid separated was
isolated by filtration and dried. The TLC analysis showed
two products. These two solid were separated by column
chromatography, using chloroform : methanol, (9:1) as
eluent, afforded pyrazolo[3,4-b]pyridine 4 in 70% and 3,6-
dihydro-2H-furo[2,3-d]pyrazolo[3,4-b]pyridine 5 in 30%
yield respectively.
Synthesis
Synthesis of (Z)-3-((3-Aryl)-1-phenyl-1H-pyrazol-5-
ylamino)methylene)-dihydrofuran-2-(3H)-one (3a-b)
A mixture of 5-aminopyrazole (0.1 mol) and Na-salt of
α-formyl-γ-butyrolactone (13.6 g, 0.1 mol) in 80 mL
MeOH and 70 mL AcOH was refluxed in an oil bath for
10–12 h. (TLC check (hexane: ethyl acetate, 1:1v/v).
Reaction mixture was cooled to room temperature and
poured in ice cold water. The solid separated was isolated
by filtration, dried and recrystallized from toluene.
Method-II
(Z)-3-((3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-5-yla-
mino)methylene)-dihydrofuran-2(3H)-one (3a)
General procedure for the synthesis of and 8-(Aryl)-6-
phenyl-3,6-dihydro-2H-furo[2,3-d] pyrazolo[3,4-b]
pyridine (5)
Yield: 23.7 g (65%), recrystallized from toluene to afford
white crystalline solid; M.p. 190–192 °C. IR (KBr): 3246
(NH), 2,959, 1,718, 1,647, 1,593, 1,564, 1,055, 1,026 cm−1.
1H NMR (300 MHz CDCl3) δ: 2.72 (dt, 2H, CH2), 4.19 (t,
J=8.2 Hz, 2H, CH2), 5.56 (d, J=9.1 Hz, 1H, NH), 6.16 (s,
1H, ArH), 7.15 (d, J=6.2 Hz, 2H, ArH), 7.40 (m, 1H,
ArH), 7.48–7.54 (m, 5H, ArH), 7.58–7.60 (d, J=6 Hz, 2H,
ArH). 13C NMR (75 MHz CDCl3) δ: 33.5, 43.1, 96.4, 99.2,
4-Chloro-5-(2-chloroethyl)-3-(4-aryl)-1-phenyl-1H-pyra-
zolo[3,4-b]pyridine 4 (0.001 mol) was refluxed in acetic acid
(5 mL) for 2–3 h (TLC check hexane: ethyl acetate, 1:1v/v).
After completion of the reaction cooled reaction mixture and
poured on ice cold, water upon which a solid separated.

J Fluoresc (2012) 22:31–41
37
Obtained solid was isolated by filtration, dried and recrystal-
lized from ethanol to furnish compound 5 in 25% yield.
(KBr): 2,955, 1,602, 1,593, 1,280 cm−1. 1H NMR (300 MHz
CDCl3) δ: 2.88 (t, J=6.6 Hz, 2H, CH2), 4.27 (t, J=6.6 Hz,
2H, CH2), 7.39–7.57 (m, 5H, ArH), 7.20 (d, J=7.5 Hz, 2H,
ArH), 7.80 (d, J=7.5 Hz, 2H, ArH) 7.89 (s, 1H, ArH). 13C
NMR (75 MHz CDCl3) δ: 27.3, 70.8, 110.4, 116.6, 121.0,
125.7, 126.5, 128.2, 128.8, 128.9, 131.5, 134.2, 139.2,
142.8, 150.3, 168.5. MS (70 eV) m/z: 347 (M+), 349 (M+2).
Anal. Calcd for C20H14ClN3O (347.8): C, 69.00; H, 4.06; N,
12.08% Found: C, 68.88; H, 4.06; N, 11.98%.
Method-III
General procedure for the synthesis of and 8-(Aryl)-6-
phenyl-3,6-dihydro-2H-furo[2,3-d] pyrazolo[3,4-b]
pyridine (5)
A mixture of 5-aminopyrazole 1 (0.001 mol) and Na-salt
of α-formyl-γ-butyrolactone 2 (0.136 g, 0.001 mol) in
NH4OAc (5 g) or AcOH (5 mL) was refluxed for 10–15 h
(TLC check hexane: ethyl acetate, 1:1v/v). Reaction
mixture was cooled to room temperature and poured in
ice cold water. The solid separated was filter dried and
recrystallized from ethanol: DMF (9:1), to furnish com-
pound 5 in 80–85% yield.
8-(4-Methylphenyl)-6-phenyl-3,6-dihydro-2H-furo[2,3-
d]pyrazolo[3,4-b]pyridine (5b)
Yield: Method-I 0.098 g (30%), Method-II 0.081 g (25%),
Method-III 0.278 g (85%), recrystallized from ethanol to
afford cream colored crystalline solid; M.p. 197–199 °C. IR
(KBr): 2,955, 1,602, 1,593, 1,280 cm−1; 1H NMR (300 MHz
CDCl3) δ: 2.39 (s, 3H, CH3) 2.78 (t, J=6.9 Hz, 2H, CH2),
4.32 (t, J=6.9 Hz, 2H, CH2), 7.09–7.46 (m, 5H, ArH), 7.29
(d, J=8.1 Hz, 2H, ArH), 7.74 (d, J=8.1 Hz, 2H, ArH) 8.01
(s, 1H, ArH). 13C NMR (75 MHz CDCl3) δ: 21.1, 27.3,
70.7, 110.4, 116.7, 120.9, 126.1, 126.5, 128.7, 128.9, 129.0,
131.5, 134.2, 141.4, 143.0, 150.2, 168.7. MS (70 eV) m/z:
327 (M+). Anal. Calcd for C21H17N3O (327.38): C, 77.04;
H, 5.23; N, 12.84% Found: C, 77.18; H, 5.16; N, 12.98%.
4-Chloro-5-(2-chloroethyl)-3-(4-chlorophenyl)-1-phe-
nyl-1H-pyrazolo[3,4-b]pyridine (4a)
Yield: 0.241 g (60%), recrystallized from ethanol to afford
colorless crystalline solid; M.p. 185–187 °C. IR (KBr): 2,930,
1
1,601, 1,590, 1,290 cm−1. H NMR (300 MHz CDCl3) δ:
3.37 (t, J=6.9 Hz, 2H, CH2), 3.80 (t, J=6.9 Hz, 2H, CH2),
7.33–7.57 (m, 5H, ArH), 7.71 (d, J=8.4 Hz, 2H, ArH), 8.24
(d, J=8.4 Hz, 2H, ArH) 8.52 (s, 1H, ArH). 13C NMR
(75 MHz CDCl3) δ: 33.4, 43.1, 121.8, 125.7, 126.1, 126.7,
128.2, 128.4, 129.0, 129.1, 130.7, 131.7, 135.0, 137.4,
138.7, 144.0, 151.0, 151.5. MS (70 eV) m/z: 403 (M+), 405
(M+2), 407 (M+4), 409 (M+6). Anal. Calcd for
C20H14Cl3N3 (402.7): C, 59.65; H, 3.50; N, 10.43% Found:
C, 59.54; H, 3.42; N, 10.48%.
General procedure for the synthesis of Pyrazolo[3,4-b]
thieno[2,3-d]pyridine (6)
A solution of 4 (0.01 mol) in acetic acid (10 mL) and
thiourea (2.28 g, 0.01 mol) was refluxed for about 2–3 h
(TLC check chloroform/methanol, 9:1). The excess of acetic
acid was removed under pressure. The obtained residue was
stirred in cold water (15 mL). The resulting precipitated solid
was isolated by filtration, washed with water and dried to get
analytical pure solid 9 in good yield, This solid product did
not need further purification.
4-Chloro-5-(2-chloroethyl)-1-phenyl-3-p-tolyl-1H-pyr-
azolo[3,4-b]pyridine (4b)
Yield: 0.248 g (65%), recrystallized from ethanol to
afford white crystalline solid; M.p. 140–142 °C. IR (KBr):
2,942, 1,610, 1,599, 1,254 cm−1; 1H NMR (300 MHz
CDCl3) δ: 2.45 (s, 3H, CH3) 3.63 (t, J=5.4 Hz, 2H, CH2),
3.79 (t, J=5.4 Hz, 2H, CH2), 7.30–7.55 (m, 5H, ArH), 7.60
(d, J=6 Hz, 2H, ArH), 8.39 (d, J=6 Hz, 2H, ArH) 8.52 (s,
1H, ArH). 13C NMR (75 MHz CDCl3) δ: 20.9, 33.3, 43.1,
121.1, 126.1, 126.5, 126.8, 128.2, 128.8, 129.0, 129.1,
130.7, 131.6, 135.3, 137.4, 140.1, 143.0, 150.9, 151.4. MS
(70 eV) m/z: 381 (M+), 383 (M+2), 385 (M+4).
8-(4-Chlorophenyl)-6-phenyl-3,6-dihydro-2H-pyrazolo
[3,4-b]thieno[2,3-d]pyridine (6a)
Yield: 2.91 g (80%), recrystallized from ethanol to afford
white amorphous solid; M.p. 268–270 °C; IR (KBr): 2,921,
1
1,616, 1,545, 1,210 cm−1. H NMR (300 MHz CDCl3) δ:
3.30 (t, J=6.7 Hz, 2H), 3.78 (t, J=6.7 Hz, 2H), 7.20–7.54
(m, 5H, ArH), 7.80 (d, J=8.5 Hz, 2H, ArH), 8.24 (d, J=
8.5 Hz, 2H, ArH), 8.30 (s, 1H, ArH). 13C NMR (75 MHz
CDCl3) δ: 29.6, 34.4, 121.6, 126.7, 128.7, 129.0, 130.1,
130.3, 134.9, 139.3, 143.4. MS (70 eV) m/z: 363(M+) 365
(M+2); Anal. Calcd for C20H14ClN3S (363.83): C, 66.02;
H, 3.88; N, 11.55% Found: C, 66.18; H, 3.79; N, 11.60%.
Anal. Calcd for C21H17Cl2N3 (382.29): C, 65.98; H,
4.48; N, 10.99% Found: C, 65.80; H, 4.42; N, 11.08%.
8-(4-Chlorophenyl)-6-phenyl-3,6-dihydro-2H-furo[2,3-d]
pyrazolo[3,4-b]pyridine (5a)
8-(4-Methylphenyl)-6-phenyl-3,6-dihydro-2H-pyrazolo
[3,4-b]thieno[2,3-d]pyridine (6b)
Yield: Method-I 0.104 g (30%), Method-II 0.087 g (25%),
Method-III 0.277 g (80%) recrystallized from ethanol to
afford crystalline cream colored solid; M.p. 189–191 °C. IR
Yield: 3.10 g (90%), recrystallized from ethanol to afford
white amorphous solid; M.p.177–180 °C; IR (KBr): 2,934,

38
J Fluoresc (2012) 22:31–41
2,730, 1,599, 1,545, 1,234 cm−1; 1H NMR (300 MHz
CDCl3) δ: 2.45 (s, 3H CH3), 3.34 (t, J=6.8 Hz, 2H), 3.86 (t,
J=6.8 Hz, 2H), 7.29–7.38 (m, 3H, ArH), 7.50–7.57 (m, 2H,
ArH), 7.89 (d, J=8.3 Hz, 2H, ArH), 8.26 (s, 1H, ArH), 8.30
(d, J=8.3 Hz, 2H, ArH). 13C NMR (75 MHz CDCl3) δ:
21.0, 29.6, 34.3, 121.6, 126.7, 128.6, 130.2, 130.3, 131.1,
135.0, 139.4, 143.4. MS (70 eV) m/z: 343 (M+). Anal.
Calcd for C21H17N3S (345.44): C, 73.44; H, 4.99; N,
12.23% Found: C, 73.32; H, 4.93; N, 12.29%.
8-(4-Chlorophenyl)-1-(4-methoxyphenyl)-6-phenyl-
1,2,3,6-tetrahydropyrazole[3,4-b]pyrrolo [2,3-d]pyridine
(7c)
Yield: 4.07 g (90%), recrystallized from ethanol: DMF
(9:1) to afford grey crystalline solid, M.p.199–200 °C. IR
(KBr): 2,945, 1,598, 1,350, 1,120 cm−1. 1H NMR (300 MHz
CDCl3) δ: 3.33 (t, J=8.7 Hz, 2H), 3.69 (s, 3H, OCH3) 4.12
(t, J=8.7 Hz, 2H), 6.41 (d, J=8 Hz, 2H, ArH), 6.73 (d, J=
8.3 Hz, 2H, ArH), 6.83 (d, J=8.3 Hz, 2H, ArH), 7.06 (m,
3H, ArH), 7.10–7.34 (m, 2H, ArH) 8.20 (d, J=8 Hz, 2H,
ArH), 8.26 (s, 1H, ArH). MS (70 eV) m/z: 452 (M+), 454
(M+2). Anal. Calcd for C27H21ClN4O (452.93): C, 71.60;
H, 4.67; N, 12.37% Found: C, 71.86; H, 4.74; N, 12.42%.
General procedure for the synthesis of 1-Phenyl-8-(4-
aryl)-6-phenyl-1,2,3,6-tetrahydro pyrazole[3,4-b]pyr-
rolo[2,3-d]pyridine (7)
A mixture of 4 (0.01 mol) and primary aliphatic or
aromatic amines (0.04 mol) was heated at 110–120 °C for
about 2–3 h, until TLC showed no more starting material.
Then the mixture was cooled at 20 °C, after cold methanol
5 °C (20 mL) was added. The resulting solid was filtered by
suction, washed with methanol, dried and recrystallized
from the ethanol:DMF to furnish compound 10 in good
yield.
1,8-Bis(4-chlorophenyl)-6-phenyl-1,2,3,6-tetrahydro-
pyrazolo[3,4-b]pyrrolo[2,3-d]pyridine (7d)
Yield: 3.75 g 82%, recrystallized from ethanol:DMF 9:1
to afford grey amorphous solid, M.p. 190–192 °C. IR
(KBr): 2,980, 2,940, 1,610, 1,580 cm−1 1H NMR
.
(300 MHz CDCl3) δ: 3.36 (t, J=8.5 Hz, 2H, ArH), 4.20
(t, J=8.5 Hz, 2H, ArH), 6.53 (d, J=7.9, 2H, ArH), 7.01 (d,
J=7.9, 2H, ArH), 7.08–7.47 (m, 5H, ArH), 7.48 (d, J=8.3,
2H, ArH), 7.78 (d, J=8.3, 2H, ArH), 8.22 (s, 1H, ArH). MS
(70 eV) m/z: 456 (M+), 458 (M+2), 460 (M+4). Anal.
Calcd for C26H18Cl2N4 (457.35): C, 68.28; H, 3.97; N,
12.25% Found: C, 68.16; H, 4.01; N, 12.34%.
8-(4-Chlorophenyl)-1-(3-chlorophenyl)-6-phenyl-
1,2,3,6-tetrahydropyrazole[3,4-b]pyrrolo[2,3-d]pyri-
dine (7a)
Yield: 3.43 g (75%), recrystallized from ethanol: DMF
(9:1) to afford colorless crystalline solid, M.p. 176–178 °C.
IR (KBr): 2,930, 1,595, 1,588, 1,228 cm−1; 1H NMR
(300 MHz CDCl3) δ: 3.35 (t, J=8.7 Hz, 2H), 4.22 (t, J=
8.7 Hz, 2H), 6.81 (m, 1H, ArH), 6.85 (m, 3H, ArH), 7.08–
7.14 (m, 5H, ArH) 7.52 (t, J=7.8 Hz, 2H, ArH), 8.26 (d, J=
8.4 Hz, 2H, ArH), 8.30 (s, 1H, ArH). MS (70 eV) m/z: 456
(M+), 458 (M+2), 460 (M+4). Anal. Calcd for C26H18
Cl2N4 (457.35): C, 68.28; H, 3.97; N, 12.25% Found: C,
68.14; H, 3.88; N, 12.29%.
8-(4-Chlorophenyl)-1,6-diphenyl-1,2,3,6-tetrahydro-
pyrazolo[3,4-b]pyrrolo[2,3-d]pyridine (7e)
Yield: 3.29 g (78%), recrystallized from ethanol: DMF
(9:1) to afford white amorphous solid; M.p. 207–209 °C. IR
(KBr): 2,908, 1,616, 1,598, 1,238 cm−1 1H NMR
.
(300 MHz CDCl3) δ: 3.34 (t, J=6.9 Hz, 2H), 4.23 (t, J=
6.9 Hz, 2H), 6.78–6.84 (m, 2H, ArH), 6.88–6.92 (m, 5H,
ArH), 7.32–7.34 (m, 3H, ArH), 7.52 (d, J=8.7 Hz, 2H,
8-(4-Chlorophenyl)-6-phenyl-1-p-tolyl-1,2,3,6-tetrahy-
dropyrazole[3,4-b]pyrrolo[2,3-d]pyridine (7b)
ArH), 8.25 (d, J=8.7 Hz, 2H, ArH), 8.25 (s, 1H, ArH). 13
C
NMR (75 MHz CDCl3) δ: 31.3, 43.9, 119.8, 120.6, 121.0,
122.2, 126.4, 126.7, 127.1, 128.1, 128.5, 129.1, 129.5,
130.1, 131.1, 138.5, 143.2, 144.4, 151.3. MS (70 eV) m/z:
422 (M+), 424 (M+2). Anal. Calcd for C26H19ClN4
(422.91): C, 73.84; H, 4.53; N, 13.25% Found: C, 73.64;
H, 4.58; N, 13.18%.
Yield: 3.05 g (70%), recrystallized from ethanol: DMF
(9:1) to afford off white solid; M.p. 192–194 °C; IR (KBr):
2,950, 2,717, 1,610, 1,202 cm−1; 1H NMR (300 MHz
CDCl3) δ: 2.23 (s, 3H, CH3), 3.33 (t, J=9 Hz, 2H), 4.18 (t,
J=9 Hz, 2H), 6.50 (d, J=8.1 Hz, 2H, ArH), 6.80 (d, J=
8.4 Hz, 2H, ArH), 6.92 (d, J=8.4 Hz, 2H, ArH), 7.26 (m,
2H, ArH), 7.30 (d, J=7.5 Hz, 2H, ArH), 7.51 (t, J=7.5 Hz,
2H, ArH), 8.22 (d, J=8.1 Hz, 2H), 8.24 (s, 1H, ArH). 13C
NMR (75 MHz CDCl3) δ: 21.1, 31.2, 43.6, 120.1, 120.8,
121.9, 126.5, 126.7, 127.5, 128.2, 128.3, 128.7, 129.0,
129.5, 130.1, 132.5, 134.3, 140.3, 143.7, 150.8. MS
(70 eV) m/z: 434 (M+), 436 (M+2).
8-(4-Chlorophenyl)-6-phenyl-1-m-tolyl-1,2,3,6-tetrahy-
dropyrazolo[3,4-b]pyrrolo[2,3-d]pyridine (7f)
Yield: 3.71 g (75%), recrystallized from ethanol: DMF
(9:1) to afford off white amorphous solid, M.p. 148–150 °C;
IR (KBr): 2,930, 2,728, 1,600, 1,588 cm−1; 1H NMR
(300 MHz CDCl3) δ: 2.18 (s, 3H, CH3), 3.27 (t, J=7.2 Hz,
2H), 4.22 (t, J=7.2 Hz, 2H), 6.56 (d, J=8.2 Hz, 2H, ArH),
6.78 (s, 1H, ArH), 6.95–7.18 (m, 5H, ArH), 7.30–7.38 (m,
Anal. Calcd for C27H21ClN4 (434.36): C, 74.22; H, 4.84;
N, 12.82% Found: C, 74.08; H, 4.90; N, 12.96%.

J Fluoresc (2012) 22:31–41
39
3H, ArH), 8.10 (d, J=8.2 Hz, 2H, ArH), 8.22 (s, 1H, ArH).
MS (70 eV) m/z: 436 (M+), 438 (M+2). Anal. Calcd for
C27H21ClN4 (436.94): C, 74.22; H, 4.84; N, 12.82% Found:
C, 74.35; H, 4.80; N, 12.78%.
8.1 Hz, 2H), 3.74 (s, 3H, OCH3), 4.13 (t, J=8.1 Hz, 2H),
6.77 (d, J=8.6 Hz, 2H, ArH), 6.84 (d, J=6.9 Hz, 2H, ArH),
6.89–6.92 (m, 4H, ArH), 7.10–7.34 (m, 3H, ArH), 8.01 (s,
1H, ArH), 8.10 (d, J=6.9 Hz, 2H, ArH). MS (70 eV) m/z:
432 (M+). Anal. Calcd for C28H24ON4 (432.52): C, 77.75;
H, 5.59; N, 12.95% Found: C, 77.62 H, 5.55; N, 12.99%.
1-(3-Chloro-4-fluoro)-8-(4-chlorophenyl)-6-phenyl-
1,2,3,6-tetrahydropyrazolo[3,4-b]pyrrolo [2,3-d]pyridine
(7g)
1-(4-Chlorophenyl)-6-phenyl-8-p-tolyl-1,2,3,6-tetrahy-
dropyrazolo[3,4-b]pyrrolo[2,3-d]pyridine (7k)
Yield: 3.56 g (75%), recrystallized from ethanol: DMF (9:1)
to afford orange amorphous solid, M.p. 158–160 °C; IR (KBr):
2,900, 1,616, 1,585, 1,240 cm−1. 1H NMR (300 MHz CDCl3)
δ: 3.20 (t, J=8 Hz, 2H), 4.26 (t, J=8 Hz, 2H), 6.72 (s, 1H),
6.80–6.82 (m, 2H, ArH), 7.01 (d, J=6 Hz, 2H, ArH), 7.26–
7.45 (m, 5H, ArH), 7.89 (d, J=6 Hz, 2H, ArH), 8.02 (s, 1H,
ArH). MS (70 eV) m/z: 474 (M+), 476 (M+2), 478 (M+4).
Anal. Calcd for C26H17Cl2FN4 (475.34): C, 65.70; H, 3.60; N,
11.79% Found: C, 65.47; H, 3.72; N, 11.89%.
Yield: 3.05 g (73%), recrystallized from ethanol: DMF (9:1)
to afford off white amorphous solid, M.p. 167–169 °C; IR
1
(KBr): 2,920, 2,736, 1,596, 1,580 cm−1. H NMR (300 MHz
CDCl3) δ: 2.32 (s, 3H, CH3), 3.33 (t, J=8.7 Hz, 2H), 4.19 (t,
J=8.7 Hz, 2H), 6.79 (d, J=7 Hz, 2H, ArH), 6.98–7.02 (m,
3H, ArH), 7.12–7.34 (m, 4H, ArH), 7.54 (d, J=6.9 Hz,
2H, ArH), 8.20 (d, J=6.9 Hz, 2H, ArH), 8.28 (s, 1H, ArH).
13C NMR (75 MHz CDCl3) δ: 20.8, 32.4, 43.6, 120.7,
121.2, 122.1, 126.0, 126.5, 128.1, 128.5, 128.8, 129.1,
130.1, 138.3, 144.6, 151.9. MS (70 eV) m/z: 436 (M+), 438
(M+2). Anal. Calcd for C27H21ClN4 (436.94): C, 74.22;
H, 4.84; N, 12.82% Found: C, 74.06; H, 4.90; N, 12.80%.
1-(3-Chlorophenyl)-6-phenyl-8-p-tolyl-1,2,3,6-tetrahy-
dropyrazolo[3,4-b]pyrrolo[2,3-d]pyridine (7h)
Yield; 2.84 g (65%), recrystallized from ethanol: DMF
(9:1) to afford grey crystalline solid, M.p. 162–164 °C; IR
(KBr): 2,919, 2,726, 1,605, 1,267 cm−1 1H NMR
.
1,6-Diphenyl-8-p-tolyl-1,2,3,6-tetrahydropyrazolo[3,4-b]
pyrrolo[2,3-d]pyridine (7l)
(300 MHz CDCl3) δ: 2.22 (s, 3H, CH3), 3.22 (t, J=
8.4 Hz, 2H), 4.17 (t, J=8.4 Hz, 2H), 6.43–6.72 (m, 3H,
ArH), 6.80 (s, 1H, ArH), 6.98–7.33 (m, 5H, ArH), 7.43 (d,
J=7.7 Hz, 2H, ArH), 8.03 (s, 1H, ArH), 8.33 (d, J=7.7 Hz,
2H, ArH). 13C NMR (75 MHz CDCl3) δ: 21.0, 26.0, 56.9,
118.8, 119.8,121.2, 122.6, 123.4, 125.7, 128.0, 128.2,
128.3, 128.5, 128.9, 129.3, 130.8, 133.9, 137.3, 139.7,
144.2, 146.7, 148.5. MS (70 eV) m/z: 436 (M+), 438 (M+
2). Anal. Calcd for C27H21ClN4 (436.94): C, 74.22; H,
4.84; N, 12.82% Found: C, 74.38; H, 4.80; N, 12.76%.
Yield: 3.17 g (79%), recrystallized from ethanol: DMF
(9:1) to afford off white crystalline solid, M.p. 175–177 °C.
IR (KBr): 2,920, 2,736, 1,596, 1,580 cm−1. 1H NMR
(300 MHz CDCl3) δ: 2.34 (s, 3H CH3), 3.28 (t, J=8.0 Hz,
2H), 4.22 (t, J=8.0 Hz, 2H), 6.60–6.64 (m, 3H, ArH), 6.70
(d, J=7.8 Hz, 2H, ArH), 7.05–7.27 (m, 5H, ArH), 7.30–
7.38 (m, 2H, ArH), 8.08 (s, 1H, ArH), 8.12 (d, J=7.1 Hz,
2H, ArH). MS (70 eV) m/z: 402 (M+). Anal. Calcd for
C27H22N4 (402.49): C, 80.57; H, 5.51; N, 13.92% Found:
C, 80.46; H, 5.56; N, 13.82%.
6-Phenyl-1,8-bis-p-tolyl-1,2,3,6-tetrahydropyrazolo
[3,4-b]pyrrolo[2,3-d]pyridine (7i)
6-Phenyl-1-m-tolyl-8-p-tolyl-1,2,3,6-tetrahydropyrazolo
[3,4-b]pyrrolo[2,3-d]pyridine (7m)
Yield: 3.33 g (80%), recrystallized from ethanol: DMF
(9:1) to afford yellow solid, M.p. 206–208 °C. IR (KBr):
3,065, 2,918, 2,864, 1,593, 1,494 cm−1
.
1H NMR
Yield: 2.83 g (68%), recrystallized from ethanol: DMF
(9:1) to afford off white solid, M.p. 179–181 °C. IR (KBr):
2,916, 2,727, 1,600, 1,589 cm−1. 1H NMR (300 MHz
CDCl3) δ: 2.30 (s, 3H, CH3), 2.35 (s, 3H, CH3), 3.34 (t, J=
8.4 Hz, 2H), 4.22 (t, J=8.4 Hz, 2H), 6.49–6.54 (m, 1H,
ArH), 6.69 (s, 1H, ArH), 6.89 (d, J=7.8 Hz, 2H, ArH),
6.91–6.98 (m, 2H, ArH), 7.08–732 (m, 5H, ArH), 8.04 (d,
J=7.8 Hz, 2H, ArH), 8.11 (s,1H, ArH). MS (70 eV) m/z:
416 (M+). Anal. Calcd for C28H24N4 (416.52): C, 80.74; H,
5.81; N, 13.45% Found: C, 80.61; H, 5.75; N, 13.53%.
(300 MHz CDCl3) δ: 2.35 (s, 3H, CH3), 2.38 (s, 3H,
CH3), 3.27 (t, J=8.3 Hz, 2H), 4.20 (t, J=8.3, 2H), 6.49 (d,
J=7.3 Hz, 2H, ArH), 6.89–7.04 (m, 4H, ArH), 7.29 (t, J=
6.9 Hz, 2H, ArH), 7.37–7.40 (m, 3H, ArH), 8.14 (d, J=
8.7 Hz, 2H, ArH), 8.20 (s, 1H, ArH). MS (70 eV) m/z: 416
(M+), Anal. Calcd for C28H24ClN4 (416.52): C, 80.74; H,
5.81; N, 13.45% Found: C, 80.60; H, 5.77; N, 13.53%.
1-(4-Methoxyphenyl)-6-phenyl-8-p-tolyl-1,2,3,6-tetra-
hydropyrazolo[3,4-b]pyrrolo[2,3-d] pyridine (7j)
1-(4-Chloro-3-fluorophenyl)-6-phenyl-8-p-tolyl-1,2,3,6-
tetrahydropyrazolo[3,4-b]pyrrolo[2,3-d] pyridine (7n)
Yield: 3.67 g (85%), recrystallized from ethanol: DMF
(9:1) to afford grey solid, M.p. 224–226 °C; IR (KBr):
2,937, 2,720, 1,589, 1,357, 1,267 cm−1
.
1H NMR
Yield: 3.41 g (75%), recrystallized from ethanol: DMF
(300 MHz CDCl3) δ: 2.34 (s, 3H, CH3), 3.18 (t, J=
(9:1) to afford colorless solid, M.p. 160–162 °C. IR (KBr):

40
J Fluoresc (2012) 22:31–41
2,949, 2,716, 1,608, 1,588 cm−1. 1H NMR (300 MHz
CDCl3) δ: 2.32 (s, 3H, CH3), 3.28 (t, J=8.8 Hz, 2H), 4.17
(t, J=8.8 Hz, 2H), 6.62 (s, 1H, ArH), 6.78 (d, J=7.2 Hz,
1H, ArH), 6.83 (d, J=7.2 Hz, 1H, ArH), 7.02 (d, J=6.9 Hz,
2H, ArH), 7.08–7.34 (m, 5H, ArH), 8.02 (s, 1H, ArH),
8.12 (d, J=6.9 Hz, 2H, ArH). MS (70 eV) m/z: 454 (M+),
456 (M+2); Anal. Calcd for C27H20ClFN4 (454.93): C,
80.74; H, 5.81; N, 13.45% Found: C, 80.89; H, 5.74; N,
13.38%.
14. Bradamante S, Facchetti A, Pagani GA (1997) Heterocycles as
donor and acceptor units in push–pull conjugated molecules Part
1. J Phy Org Chem 10:514
15. Facchetti A, Abbotto A, Beverina L, Ven Der Boom ME, Dutta P,
Evemenenko G, Marks TJ, Pagani GA (2002) Azinium–(π-
bridge)–pyrrole NLO-phores: influence of heterocycles acceptors
on chromophoric and self-assembled thin-film properties. Chem
Mater 14:4996
16. Abbotto A, Beverina L, Bradamante S, Facchetti A, Klein C,
Pagani GA, Rediabshiro M, Wortmann R (2003) A distinctive
example of the cooperative interplay of structure and environment
in tuning of intramolecular charge transfer in second-order
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Signoroni R (2003) Novel heteroaromatic-based multi-branched
dyes with enhanced two-photon absorption activity. Chem
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18. Facchetti A, Abbotto A, Beverina L, van der Boom ME, Dutta P,
Evmenenko G, Pagani GA, Marks TJ (2003) Layer-by-layer self-
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(2005) Electrochromic conjugated N-salicylidene-aniline (anil)
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Acknowledgements The authors thank to CSIR New Delhi and
BCUD University of Pune, India for financial support to this research
project. Authors also thanks to Department of Chemistry University of
Pune, IIT-Powai Mumbai and Principal KTHM College Nashik, for
spectral and analytical facilities.
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