Four-Component Domino Synthesis of Pyrazolo[3,4- h]quinoline-3-carbonitriles: "turn-Off" Fluorescent Chemosensor for Fe3+ Ions

Article abstract of DOI:10.1021/acs.joc.8b01991

The synthesis of novel pyrazolo[3,4-h]quinoline-3-carbonitriles has been achieved through a one-pot, four-component domino strategy under solvent-free microwave conditions. One of these compounds exhibited fluorescence under UV lamp and was found to be hi

Full text of DOI:10.1021/acs.joc.8b01991

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Note
Four-component Domino Synthesis of Pyrazolo[3,4-h]quinoline-3-
3+
carbonitriles: ‘Turn-off’ Fluorescent Chemosensor for Fe Ions
Adaikalam Shylaja, Somi Santharam Roja, Rakkappan Vishnu Priya, and Raju Ranjith Kumar
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01991 • Publication Date (Web): 25 Oct 2018
Downloaded from http://pubs.acs.org on October 26, 2018
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Four-component Domino Synthesis of Pyrazolo[3,4-h]quinoline-3-carbonitriles: ‘Turn-off’
Fluorescent Chemosensor for Fe3+ Ions
7
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Adaikalam Shylaja,† Somi Santharam Roja,† Rakkappan Vishnu Priya‡ and Raju Ranjith
Kumar*,†
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†Department of Organic Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai
625021, Tamil Nadu, INDIA.
‡Department of Physics, Madura College, Madurai 625011, Tamil Nadu, INDIA.
Abstract
The synthesis of novel pyrazolo[3,4-h]quinoline-3-carbonitriles has been achieved
through a one-pot, four-component domino strategy under solvent-free microwave conditions.
One of these compounds exhibited fluorescence under UV lamp and was found to be highly
sensitive towards Fe3+ ions in DMSO against various metal ions with a detection limit of 8.6 ×
10–7 M.
Keywords: Domino reaction; pyrazolo[3,4-h]quinolone; Microwave-assisted; Fluorescence;
Chemosensor; Iron.
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Iron is one of the most abundant and multifaceted elements and an integral part of all the living
systems. It is an essential trace element in the biological processes like oxygen metabolism,
electron transfer and transcriptional regulation.1,2 Deficiency of iron results in anemia, whereas
an excess in the level may lead to hepatitis, certain cancers and deterioration of vital organs3–6
apart from causing Alzheimer’s and Parkinson’s diseases.7 Hence proper attention in monitoring
the level of iron is imperative. Complexity in the operation of existing techniques mandates the
development of simple and cost effective methodologies for detecting iron.6–8 The
spectrofluorometric technique employing fluorescence materials is one of the versatile methods
for the detection of heavy metal ions including iron.9 This methodology has been widely used for
sensing and imaging in chemical and medical fields.10–13 Several Fe3+ based fluorescence
chemosensors exhibiting both “turn-off” and “turn-on” mechanisms have been reported.13–22
However, incessant effort is being continually put towards the design and development of cost-
effective, highly selective and sensitive fluorescent probes for the detection of Fe3+ ions.
Pyrazoloquinolines are privileged class of organic heterocycles possessing broad array of
applications,23 for example, in materials chemistry as electroluminescent materials, light emitting
diodes and fluorescent chemosensors.24 In addition pyrazoloquinolines display antiviral,
antibacterial, anti-proliferative and immunosuppressant activities apart from exhibiting oral
antipsychotic activity in the MK-801 induced hyperactive rat model.25 Among the
pyrazoloquinolines, the syntheses and applications of pyrazolo[3,4-b]quinolone derivatives have
been investigated extensively.23–26 However, the syntheses of pyrazolo[3,4-h]quinolines have
received less attention.27 In the present work novel pyrazolo[3,4-h]quinoline-3-carbonitriles have
been synthesized through a one-pot, four-component domino strategy under microwave
conditions. Incidentally, multi-component domino reactions (MDRs) are environmentally benign
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protocols widely employed to synthesize natural and unnatural compounds of biological
importance.28 On the other hand microwave-assisted reactions are energy efficient process that
offers a simple and rapid access to complex molecules.29 Microwave-assisted MDRs further
augment the greenness of the reaction towards sustainable chemical synthesis.30
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Initially, the precursor 1-aryl-1,5,6,7-tetrahydro-4H-indazol-4-ones 1 were synthesized
following literature procedure (Table 1).31 Subsequently the reaction of 1-phenyl-1,5,6,7-
tetrahydro-4H-indazol-4-one 1, 4-chlorobenzaldehyde 2a, malononitrile 3 and ammonium
acetate 4 presumably affording pyrazolo[3,4-h]quinoline-3-carbonitrile 5a was taken as a model
in order to find out the optimized reaction condition (Table 1). To begin with an equimolar
mixture of the above reactants was refluxed in ethanol, which afforded 5a in 50% after 6 h. The
yield of 5a increased to 70% when two equivalent of ammonium acetate was employed. This
reaction in refluxing acetic acid afforded 80% of 5a, whereas a neat mixture of the above
reactants at 100oC yielded 75% of 5a after 6h.
Table 1. Optimization of the reaction condition
O
NH2
CHO
2
NC
N1
9b
N
3
N
9
conditions
9a
Cl
4
4a
5
1
Ph
CN
2a
NH4OAc
4
8
N
NC
6a N7
Cl
6
5a
Ph
3
Entry Condition
Yield of 5a (%)a
1
2
Ethanol, reflux, 6h
Ethanol, reflux, 6h
(with 2 equiv. of 4)
Acetic acid, reflux, 6h
50
70
3
4
5
80
Solvent-free, 100oC, 6h 75
Microwave, 2–3 min
96
aIsolated yield
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Gratified with the yield of 5a obtained under solvent-free conditions, we explored to
perform the above reaction under solvent-free microwave heating. Accordingly, a 1:1:1:2
mixture of 1, 2a, 3 and 4 was taken in a microwave vial and mixed thoroughly. Then the closed
vail was irradiated at 110oC in a microwave synthesizer. The progress of the reaction was
monitored by TLC after every 1 min of irradiation, which revealed the reaction completed within
2–3 min. The mixture was then cooled to room temperature and 2 mL of ethanol was added. The
precipitate formed was filtered, washed with ethanol (2 mL) and dried under vacuum to obtain
pyrazolo[3,4-h]quinoline-3-carbonitrile 5a in 96% yield. The structure of 5a was elucidated
unambiguously using NMR spectroscopy and further confirmed from single crystal X-ray studies
(Figure S9, SI).32 The optimized condition was then employed to synthesize nine novel
pyrazolo[3,4-h]quinoline-3-carbonitriles 5a–i in 88–96% yields (Scheme 1). In addition, two
isomeric products 5j and 5k were isolated when the reaction was performed with ethyl
cyanoacetate instead of malononitrile.
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NH2
N
NH2
N
NH2
N
NH2
N
NC
NC
NC
NC
N
N
N
N
N
N
N
N
Cl
MeO
NC
Cl
5c
Ph
Ph
Ph
Ph
5a
5b
5d
, 96%
, 94%
, 96%
, 90%
NO2
NC
NH2
NH2
NH2
N
NH2
NC
NC
N
N
N
N
N
N
N
N
N
N
N
Cl
Cl
5f
Cl
MeO
Ph
Ph
5e
5g
5h
, 90%
, 88%
, 90%
EtO2
, 95%
H2
N
H2
N
O
N
Cl
Cl
N
NH
NC
C
NC
N
N
N
N
N
N
MeO
Cl
Cl
5i
5j
5k
, 50%
, 92%
, 46%
Scheme 1. Pyrazolo[3,4-h]quinoline derivatives 5a–k
The plausible mechanism for the formation of pyrazolo[3,4-h]quinoline-3-carbonitriles 5
is given in Scheme 2. The Knoevenagel condensation of aromatic aldehyde 2 and malononitrile
3 affords 2-arylidenemalononitrile 6, which undergoes Michael addition with tetrahydro-4H-
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indazol-4-one 1 to form the ketenimine intermediate 7. The nucleophilic addition of ammonium
acetate 4 to the carbonyl of 7 leads to the formation of enamine 8. The enamine intermediate 8
undergoes intramolecular N-cyclization to afford the pyrazolo[3,4-h]quinoline-3-carbonitrile 9,
which upon oxidative aromatization by molecular oxygen as the sole oxidant affords the
pyrazolo[3,4-h]quinoline-3-carbonitriles 5. This multi-step domino reaction leads to the
formation of two new C–C and C–N bonds in a single transformation affording the products 5a–i
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in excellent yields.
NH
N
O
C
O
NC
NC
CN
Knoevenagel
3
N
NH4OAc
-H2O
N
Michael Ar
NC
Ar
ArCHO
N
N
6
1
2
7
Ph
Ph
addition
to C=O
NH4OAc
4
NH2
N
NH2
NH
oxidative
aromatization
NC
Ar
NC
Ar
C
NH
NH2
NC
N-cyclization
air
N
N
N
Ar
N
N
N
5
New bonds formed
9
8
Ph
Ph
Ph
Scheme 2. Plausible mechanism for the formation of 5
Among the pyrazolo[3,4-h]quinoline-3-carbonitriles, compounds 5a–c, 5e and 5g
exhibited blue fluorescence under UV lamp. The relative quantum yield of 5 was measured using
anthracene in ethanol as standard (Table S2, SI).33 The pyrazolo[3,4-h]quinoline-3-carbonitrile
5b was chosen for further studies in view of its higher quantum yield of 0.60. The initial
solvatochromism studies of 5b in chloroform, methanol, ethyl acetate, DMSO, DCM and THF
(20 M each) revealed notable red shift in the UV absorption of 5b in DMSO and methanol
(Table S3, SI). The maximum absorption of 5b in DMSO (20 M) was found to be around 370
nm, which may be attributed to the π–π* or n–π* transitions. The fluorescence emission
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spectrum of 5b was recorded in DMSO (20 M) with an excitation wavelength of 370 nm and
maximum fluorescence emission intensity was observed at 415 nm (Figures S33–S36, SI).
Subsequently, changes in the absorption and fluorescence response of the probe 5b in
DMSO (20 M) at an excitation/emission wavelengths of 370/415 nm towards thirteen different
metal ions namely Ag+, Al3+, Ba2+, Co2+, Cr3+, Cu2+, Fe2+, Fe3+, Hg2+, Na+, Ni2+, Pb2+ and Zn2+
(in water, 2 × 10–4 M) at room temperature was investigated. No major changes in the UV
absorption was noted upon the addition of Ag+, Al3+, Ba2+, Co2+, Cr3+, Fe2+, Hg2+, Na+, Ni2+, Pb2+
or Zn2+ to the probe solution. However, significant blue shift to 356 and 283 nm was observed
upon addition of Fe3+and Cu2+, respectively (Figure 1). Similarly the changes in the fluorescence
spectra of 5b were observed upon addition of the above metal ions to the probe solution. It is
pertinent to note that the fluorescence intensity of the probe 5b significantly quenched upon
adding Fe3+ (Figure 2).
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Further, the UV and emission spectra of probe 5b with various concentration of Fe3+
ranging from 0 to 500 M showed linear relationships while plotting absorbance/fluorescence vs
concentration of Fe3+. These observations reveal that probe 5b is suitable for detecting Fe3+.
From the Stern-Volmer plot the Stern-Volmer constant (Ksv) was found to be 1.5 × 104 M–1,
which linearly decreased with a regression coefficient of 0.983. The lower limit of detection
(LOD) was found to be 8.6 × 10–7 M. In addition, the stoichiometry binding ratio of probe 5b
with Fe3+ ion was calculated as 1:1 from the Job’s plot (Figures S37–S40, SI).
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Figure 1. UV spectra of 5b in the presence of various metal ions
Figure 2. Emission spectra of 5b in the presence of various metal ions
To establish the selectivity of probe 5b towards Fe3+ over a range of metal ions,
competitive experiments were carried out with high concentration of other metal ions viz. Ag+,
Al3+, Ba2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Na+, Ni2+, Pb2+ and Zn2+ (10 equiv.). The presence of
other metal ions had no effect on the quenching intensity and hence it is clear that the probe 5b is
selective towards Fe3+. However, interference was observed in the case of Cr3+.34–38
The probe 5b was compared with various other probes from the literature (Table S4, SI)
for relative quantum yield and LOD. From the table it is clear that the probe 5b has high
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quantum yield of 0.60 when compared to the probes listed and highly sensitive towards Fe3+ with
LOD of 8.6 × 10–7 M, which is in good agreement with the probes already reported.
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In order to gain insight into the quenching mechanism, theoretical calculations of 5b and
5b+Fe3+ were performed at DFT using Gaussian 09 program. The structure of 5b and 5b+Fe3+
was optimized using B3LYP and B3LYP/LanL2DZ basis set, respectively (Figure 3).39 The
frontier molecular orbital analysis reveals that in probe 5b HOMO is located over pyrazolo[3,4-
h]quinoline unit, the amino and cyano groups, whereas the LUMO is spread over the whole
molecule. However, in 5b+Fe3+ HOMO appears mainly over the pyridine ring and the amino
group, whereas the LUMO is located over Iron (Figure 3). Further, the calculated HOMO-
LUMO energy gap difference for 5b+Fe3+ (3.0453 eV) is lesser than that of the probe 5b (4.0379
eV), which also indicates favorable coordination between the probe 5b and Fe3+. From the above
observations it can be concluded that an internal charge transfer (ICT) occurs between the
electron-releasing methoxy group in the phenyl ring and the electron withdrawing CN group in
the pyrazolo[3,4-h]quinoline ring, which induces fluorescence turn on in the probe 5b. The
complexation of the probe 5b with Fe3+ inhibits the ICT and hence results in fluorescence turn
off.
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Figure 3. Optimized structure of (A) 5b and (B) 5b+Fe3+. Frontier molecular orbital of (C)
probe 5b and (D) 5b+Fe3+
To further vindicate the quenching mechanism, the fluorescence lifetime measurements
were recorded for the probe 5b (20 M) and 5b+Fe3+ (20 M 5b + 200 M Fe3+) using time-
correlated single photon counting spectrometer (Figure S60 and Table S5, SI). The average
fluorescence lifetime () of the probe 5b and the complex 5b+Fe3+ was found to be 0.24 and 0.23
ns, respectively. The results indicate that the fluorescence decay profiles of 5b and 5b+Fe3+
remain unchanged and hence the quenching mode is static.
With a view to study the practical applicability of probe 5b, real sample analyses was
performed to determine the concentration of Fe3+ in three different water samples. Drinking
water (reverse osmosis treated) from the authors department, river water from Thamirabarani at
Tirunelveli and tap water from Velachery, Chennai was collected, filtered and used for the
analysis (Table S6 and Figures S61, SI). The water samples were spiked with standard Fe3+ at
three different concentrations and determined by standard addition method using the probe 5b.
Emission studies were performed by taking 40 l of 5b from 10–3 M stock solution in 2 mL
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DMSO with corresponding 30, 40 and 50 l Fe3+ spiked water samples from 10–2 M solution
(0.0162 g in 10 mL of water sample). The average recovery of the spiked samples was found to
be 109, 94 and 117 respectively for drinking, tap and river water samples. The results show that
the probe 5b successfully quantifies the amount of Fe3+ in the water samples.
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Conclusions
In conclusion, novel pyrazolo[3,4-h]quinoline-3-carbonitriles 5a–i were synthesized
through a facile one-pot, four-component reaction of 1-aryl-1,5,6,7-tetrahydro-4H-indazol-4-
ones, aromatic aldehydes, malononitrile and ammonium acetate under environmentally benign
solvent-free microwave conditions. The reaction presumably occurred via domino Knoevenagel
condensation–nucleophilic addition–Michael addition–intramolecular N-cyclization–oxidative
aromatization sequence of reactions in a single transformation affording the pyrazolo[3,4-
h]quinoline-3-carbonitriles 5a–i in excellent yields. Among the synthesized compounds the
pyrazolo[3,4-h]quinoline-3-carbonitrile 5b exhibited fluorescence in UV and was able to sense
Fe3+ ions through “turn off” mechanism with a detection limit of 8.6 × 10–7 M in DMSO.
EXPERIMENTAL SECTION
General information
The melting points were measured in open capillary tubes and are uncorrected. The
microwave reactions were performed in CEM DISCOVER, Benchmate model single-mode
design. The reaction temperature was monitored with an inbuilt floor mounted IR sensor. The
13
1H, C{1H} and 2D NMR spectra were recorded on Bruker (Avance) 300 MHz or (Avance III
HD Nanobay) 400 MHz NMR instruments using TMS as internal standard and CDCl3 or
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CDCl3+DMSO mixture as solvents. Standard Bruker software was used throughout. Chemical
shifts are given in parts per million (-scale) and the coupling constants are given in Hertz. The
UV–vis spectrum of the sample was measured using JASCO (v-630) spectrophotometer. The
Photoluminescence (PL) spectra were acquired using JASCO (F-8500) fluorescence
spectrophotometer. Sample was placed in a 3 mL quartz cuvette to get PL spectra. The PL
experiments were run in proper wavelength window with 0.2 nm steps. The PMT voltage was set
to auto. The time-resolved fluorescence life time measurements were carried out using time-
correlated single photon counting (TCSPC) spectrometer, Edinburgh instrument FLS 980 model
(UK). HR-Mass data were recorded on Agilent Accurate-Mass Q-TOF (model HAB 273). The
IR data were recorded in NICOLET 6700 ATR-FT-IR instrument. The single crystal X-ray data
were collected on Enraf–Nonius (CAD4) diffractometer with Mo K (0.71073 Å) radiation.
Scan range was 2.02o ≤ θ ≤ 24.97o. SHELXTL software was used for structure solution and
refinement. Silica gel-G plates (Merck) were used for TLC analysis with a mixture of petroleum
ether (60–80oC) and ethyl acetate as eluent. All the chemicals were purchased from Sigma-
Aldrich and used without any further purification. The ground-state geometries were optimized
using density functional theory with B3LYP and LANL2DZ hybrid functional at the basis set
level of 6-31/6-311G*. All the calculations were performed using Gaussian 09 package.
UV-vis and Photoluminescence (PL) experiments
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The stock solution (10–3 M) of the probe was prepared by taking 0.0012 g of 5b in 3 mL
DMSO. The stock solution of the Fe3+ ions was prepared by taking 0.016 g of Iron (III) chloride
in 10 mL double distilled water. Then 20 M of sample 5b from the stock solution was placed
in a quartz cuvette to get absorbance and PL spectra using the respective instruments. The PL
experiments of Fe3+ ions determination was carried out by adding 2 × 10–4 M of Fe3+ from 10–2
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M stock solution added to the probe. The excitation wavelength for this experiment is 370 nm.
The PL experiments for interference studies were run in the same excitation wavelength and
emission intensities recorded at wavelength of 415 nm. All metal ion solutions were prepared in
Double Distilled (DD) Water from the corresponding metal chloride salts and used for metal
interference studies. For all the fluorescence measurements, the excitation/emission wavelengths
are set to 370/415 nm under room temperature.
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General procedure for the synthesis of 1-aryl-1,5,6,7-tetrahydro-4H-indazol-4-ones 1
2-((Dimethylamino)methylene)cyclohexane-1,3-dione (1 mmol) and aryl hydrazine (1
mmol) in water (1 mL) were mixed thoroughly in a microwave vial followed by addition of
glacial acetic acid (1 mmol). The closed vial was subjected to irradiation in a microwave
synthesizer (CEM DISCOVER, Benchmate model, single-mode design with inbuilt IR
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temperature sensor) for 2 minutes at 200 C. Then the microwave vial was cooled to room
temperature and 6–7 mL of water was added. The resultant precipitate was filtered and dried to
obtain the 1-aryl-1,5,6,7-tetrahydro-4H-indazol-4-ones 1, which was used for subsequent reactions.
General procedure for the synthesis of pyrazolo[3,4-h]quinoline derivatives 5a–k
A mixture of 1-aryl-1,5,6,7-tetrahydro-4H-indazol-4-ones 1, (1 mmol), aromatic
aldehydes 2, (1 mmol), malononitrile/ethyl cyanoacetate 3, (1 mmol) and ammonium acetate 4,
(2 mmol) was taken in a microwave vail and mixed thoroughly. The closed vial was then
irradiated at 110oC in a microwave synthesizer (CEM DISCOVER, Benchmate model, single-
mode design with inbuilt IR temperature sensor). The progress of the reaction was monitored by
TLC after every 1 min of irradiation, which revealed the reaction completed within 2–3 min. The
mixture was cooled to room temperature and 2 mL of ethanol was added. The precipitate formed
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was filtered, washed with ethanol (2 mL) and dried under vacuum to obtain pyrazolo[3,4-
h]quinoline derivatives 5.
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carbonitrile 5a. Obtained as yellow solid; Yield: 0.179g, 96%; m.p.: 250–253 C; IR : 3323,
2199, 1740, 1549, 1505 cm–1; H NMR (300 MHz, CDCl3) δ 8.21 (s, 1H), 7.25–7.50 (m, 9H),
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5.25 (s, 2H), 2.94 (t, J=6.0 Hz, 2H), 2.73 (t, J=6.0 Hz, 2H); C{1H} NMR (75 MHz, CDCl3) δ
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159.1, 153.8, 151.6, 143.1, 139.3, 138.1, 135.7, 135.0, 130.2, 129.7, 129.5, 128.2, 123.7,
120.3,117.3, 116.6, 88.4, 25.7, 21.9. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C23H17ClN5
398.1172; Found 398.1162.
2-Amino-4-(4-methoxyphenyl)-7-diphenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5b. Obtained as yellow solid; Yield: 0.174 g, 94%; m.p.: 260–263 C; IR : 3331,
2202, 1739, 1554, 1502 cm–1; H NMR (300 MHz, CDCl3) δ 8.20 (s, 1H), 7.38–7.50 (m, 4H),
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7.37–7.43 (m, 1H), 7.23–7.32 (m, 3H), 7.02 (d, J=9.0 Hz, 2H), 5.19 (s, 2H), 3.87 (s, 3H), 2.90 (t,
J=6.0 Hz, 2H), 2.70 (t, J=6.0 Hz, 2H); C{1H} NMR (75 MHz, CDCl3) δ 160.5, 159.2, 153.5,
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152.8, 143.2, 139.3, 138.1, 130.2, 129.8, 128.7, 128.1, 123.7, 120.5, 117.9, 116.9, 114.5, 89.0,
55.8, 25.7, 21.9. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C24H20N5O 394.1668; Found
394.1661.
2-Amino-4-(2-cholorophenyl)-7-diphenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5c. Obtained as yellow solid; Yield: 0.179 g, 96%; m.p.: 275–278 C; IR : 3353,
2209, 1740, 1557, 1505 cm–1; H NMR (300 MHz, CDCl3) δ 8.24 (s, 1H), 7.48–7.56 (m, 5H),
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7.39–7.44 (m, 3H), 7.26–7.29 (m, 1H), 5.32 (s, 2H), 2.92–3.05 (m, 2H), 2.52–2.77 (m, 2H);
13C{1H} NMR (75 MHz, CDCl3+DMSO-d6) δ 158.1, 152.1, 148.8, 144.1, 142.1, 137.9, 135.4,
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131.0, 130.7, 128.8, 128.4, 126.8, 126.2, 122.3, 118.8, 118.3, 115.7, 112.2, 23.9, 20.3. HRMS
(ESI-TOF) m/z: [M + H]+ Calcd for C23H17ClN5 398.1172; Found 398.1161.
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2-Amino-4-(3-nitrophenyl)-7-diphenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-carbonitrile
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5d. Obtained as yellow solid; Yield: 0.173 g, 90%; m.p.: 179–181 C; IR : 3316, 2203, 1737,
1524, 1502 cm–1; 1H NMR (300 MHz, CDCl3) δ 8.34–8.38 (m, 1H), 8.21 (s, 1H), 7.63–7.88 (m,
2H), 7.45–7.59 (m, 5H), 7.40–7.44 (m, 1H), 5.25 (s, 2H), 2.94–3.00 (m, 2H), 2.65–2.80 (m, 2H);
13C{1H} NMR (75 MHz, CDCl3+DMSO-d6) δ 164.6, 158.6, 154.8, 153.4, 148.2, 144.1, 143.3,
142.6, 140.2, 135.5, 134.6, 133.0, 129.0, 128.6, 128.4 125.1, 122.1, 120.4, 92.0, 30.3, 26.5.
HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C23H17N6O2 409.1413; Found 409.1418.
2-Amino-4-(naphthyl)-7-diphenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-carbonitrile 5e.
Obtained as yellow solid; Yield: 0.171 g, 88%; m.p.: 190–193 oC; IR : 3342, 2212, 1738, 1556,
1503 cm–1; 1H NMR (300 MHz, CDCl3) δ 8.27 (s, 1H), 7.96 (m, 2H), 7.31–7.78 (m, 10H), 5.31
(s, 2H), 2.84 (t, J=6.0 Hz, 2H), 2.50 (t, J=6.0 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3+ DMSO-
d6) δ 158.0, 151.3, 149.4, 141.5, 137.4, 135.9, 132.7, 131.9, 129.0, 127.7, 127.1, 126.6, 125.5,
124.9, 124.1, 123.2, 121.7, 118.5, 115.5, 115.1, 86.8, 23.52, 19.76. HRMS (ESI-TOF) m/z: [M +
H]+ Calcd for C27H20N5 414.1719; Found 414.1719.
2-Amino-4-(2,4-dicholorophenyl)-7-diphenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5f. Obtained as yellow solid; Yield: 0.183 g, 90%; m.p.: 266–269 C; IR : 3222,
2923, 2213, 1738, 1550, 1503 cm–1; H NMR (300 MHz, CDCl3) δ 8.19 (s, 1H), 7.40–7.57 (m,
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6H), 7.22–7.27 (m, 3H), 5.20 (s, 2H), 2.90–3.03 (m, 2H), 2.65–2.70 (m,1H), 2.54–2.61 (m,1H);
13C{1H} NMR (75 MHz, DMSO) δ 160.1, 153.7, 149.2, 144.3, 139.5, 137.8, 135.4, 135.1, 133.5,
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132.5, 130.2, 130.1, 128.9, 128.5, 124.0, 120.2, 117.3, 116.0, 87.0, 80.2, 79.8, 79.4, 25.3, 21.5.
HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C23H16Cl2N5 432.0783; Found 432.0801.
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2-Amino-4,7-bis-(4-cholorophenyl)-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-carbonitrile 5g.
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Obtained as pale yellow solid; Yield: 0.193 g, 95%; m.p.: 201–203 C; IR : 3318, 2203, 1735,
1550, 1495 cm–1; 1H NMR (300 MHz, CDCl3) δ 8.19 (s, 1H), 7.36–7.57 (m, 6H), 7.18–7.33 (m,
3H), 5.21 (s, 2H), 2.92 (t, J =6.0 Hz, 2H), 2.75 (t, J = 6.0 Hz, 2H); C{1H} NMR (75 MHz,
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CDCl3+DMSO-d6) δ170.0, 165.0, 164.9, 159.1, 158.0, 156.7, 156.3, 150.0, 148.3, 147.3, 142.8,
135.5, 134.7, 134.1, 129.8, 120.3, 92.4, 30.2, 26.5. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for
C23H16Cl2N5 432.0783; Found 432.0790.
2-Amino-7-(4-chlorophenyl)-4-(4-methoxyphenyl)-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5h. Obtained as brown solid; Yield: 0.156 g, 90%; m.p.: 200–203 C; IR : 3331,
2205, 1609, 1555, 1514 cm–1; 1H NMR (400 MHz, DMSO) δ 8.12 (s, 1H), 7.57 (d, J = 12.0 Hz,
2H), 7.48 (s, 3H), 7.26 (d, J = 8.0 Hz, 2H), 7.02 (d, J = 8.0 Hz, 2H), 5.70 (s, 2H), 3.87 (s, 3H),
2.80–2.77 (m, 2H), 2.61 (d, J = 12.0 Hz, 2H); 13C{1H} NMR (100 MHz, DMSO) δ 152.7, 152.4,
142.8, 137.8, 137.5, 133.2, 129.8, 129.4, 128.4, 124.4, 120.4, 117.5, 115.9, 114.1, 88.3, 55.3,
25.1, 21.4. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C24H19ClN5O 428.1200; Found 428.2500.
2-Amino-4-(4-methoxyphenyl)-7-(p-tolyl)-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5i. Obtained as brown solid; Yield: 0.165 g, 92%; m.p.: 195–198 C IR : 3323,
3214, 2202, 1625, 1609 cm–1; H NMR (400 MHz, CDCl3) δ 8.14 (s, 1H), 7.35 (s, 3H), 7.30–
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7.25 (m, 4H), 7.02 (d, J = 8.0 Hz, 2H), 5.36 (s, 2H), 3.87 (s, 3H), 2.92–2.88 (m, 2H), 2.78 (d, J =
8.0 Hz, 2H), 2.41 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 159.7, 158.6, 152.1, 142.1, 137.5,
137.1, 136.2, 129.6, 129.5, 128.1, 122.9, 119.6, 117.30, 116.1, 113.8, 88.0, 55.1, 25.0, 21.1, 20.8.
HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C25H22N5O 408.1746; Found 408.2177.
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Ethyl-2-amino-4-(4-cholorophenyl)-7-phenyl-6,7-dihydro-5H-pyrazolo[3,4-h]quinoline-3-
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carboxalate 5j. Obtained as yellow solid; Yield: 0.096 g, 46%; m.p.: 214–217 C; IR : 3321,
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3213, 2921, 2202, 1736 cm–1; H NMR (400 MHz, CDCl3) δ 8.20 (s, 1H), 7.49 (d, J = 4.0 Hz,
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4H), 7.38 (d, J = 8.0 Hz, 3H), 7.08 (d, J = 8.0 Hz, 2H), 6.14 (s, 2H), 3.89–3.85 (m, 2H), 2.90 (t, J
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= 8.0 Hz, 21H), 2.57 (t, J = 8.0 Hz, 2H), 0.76 (t, J = 8.0 Hz, 3H); C{1H} NMR (100 MHz,
CDCl3) δ 168.1, 158.1, 152.2, 150.0, 142.5, 139.0, 137.5, 133.0, 129.2, 129.1, 128.2, 127.5,
123.2, 120.1, 116.4, 104.4, 60.4, 29.7, 25.4, 21.6, 13.2. HRMS (ESI-TOF) m/z: [M + H]+ Calcd
for C25H22ClN2O2 445.1353; Found 445.2898.
4-(4-Chlorophenyl)-2-oxo-7-phenyl-2,5,6,7-tetrahydro-1H-pyrazolo[3,4-h]quinoline-3-
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carbonitrile 5k. Obtained as yellow solid; Yield: 0.094 g, 50%; m.p.: 203–206 C; IR : 3327,
2921, 2205, 1625, 1610 cm–1; 1H NMR (400 MHz, CDCl3) δ 14.71 (s, 1H), 8.67 (s, 1H), 7.50 (d,
J = 8.0 Hz, 3H), 7.41 (d, J = 8.0 Hz, 2H), 7.17 (d, J = 8.0 Hz, 2H), 6.95 (s, 2H), 3.00 (s, 2H),
2.56 (s, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ 162.9, 159.5, 144.6, 143.8, 138.5, 137.8,
135.0, 133.6, 129.5, 129.4, 128.6, 128.2, 123.8, 113.6, 110.1, 97.7, 24.6, 21.1. HRMS (ESI-TOF)
m/z: [M + H]+ Calcd for C23H16ClN4O 399.0934; Found 397.2457
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
NMR, IR and HRMS of all the new products, log file of theoretical calculations and X-ray data
for 5a (CIF).
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AUTHOR INFORMATION
Corresponding Author
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*E-mail: raju.ranjithkumar@gmail.com
ORCID
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Raju Ranjith Kumar: 0000-0002-9926-7770
ACKNOWLEDGEMENTS
RRK, AS and SSR thank the DST, New Delhi for funds under IRHPA program for the
high resolution NMR facility in the Department and the DST-PURSE program, MKU. AS thanks
DST, New Delhi for the INSPIRE fellowship (IF160126). The authors thank Prof. S. Murugesan
and Dr. A. Siva, Department of Inorganic Chemistry, School of Chemistry, Madurai Kamaraj
University for UV and emission studies and the theoretical calculations. The authors thank Dr. S.
Easwaramoorthi, CLRI, Chennai, for the fluorescence lifetime measurements.
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S = ST (GradS/GradST)(2 /2
)
ST
S
where S and ST denotes quantum yield of sample and standard respectively, Grad
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