Green synthesis of pyrazolopyranopyrimidinone and pyranopyrazole derivatives using porphyrin-initiated amine-functionalized PolyBCMO dendritic polymer as sonocatalyst

Article abstract of DOI:10.1002/jhet.3765

A novel porphyrin-initiated amine-functionalized poly-3,3-bis(chloromethyl)oxetane (PBCMO-amine) dendritic polymer was effectively synthesized. Characterization using the UV-vis, IR, NMR, PXRD, TG, and FE-SEM spectroscopy and microscopy enabled one to ass

Full text of DOI:10.1002/jhet.3765

Received: 31 July 2019
DOI: 10.1002/jhet.3765
Revised: 6 September 2019
Accepted: 6 September 2019
A R T I C L E
Green synthesis of pyrazolopyranopyrimidinone and
pyranopyrazole derivatives using porphyrin‐initiated
amine‐functionalized PolyBCMO dendritic polymer as
sonocatalyst
Avudaiappan Govindan | Unnimaya T. Jayaprakash | Asha Pallikkattil |
Unnikrishnan Vettukattil | Sreekumar Krishnapillai
Department of Applied Chemistry, Cochin
Abstract
University of Science and Technology,
A novel porphyrin‐initiated amine‐functionalized poly‐3,3‐bis(chloromethyl)
Kochi, India
oxetane (PBCMO‐amine) dendritic polymer was effectively synthesized. Char-
Correspondence
Sreekumar K., Department of Applied
acterization using the UV‐vis, IR, NMR, PXRD, TG, and FE‐SEM spectroscopy
Chemistry, Cochin University of Science
and Technology, Kochi 682022, Kerala,
India.
and microscopy enabled one to assess the structural and morphological stabil-
ity of the PBCMO‐amine. Its catalytic activity was studied in one‐pot four‐
component solvent‐free synthesis of pyrazolopyranopyrimidinone and
pyranopyrazole using aldehyde, ethylacetoacetate, hydrazine hydrate, and
barbituric acid/malononitrile by simple ultrasonic irradiation. Because of the
water‐soluble nature of PBCMO‐amine, the catalyst could be separated and
reused without the loss of its activity.
Email: kskpolymer.cusat@gmail.com
Funding information
University Grants Commission, Grant/
Award Number: UGC‐JRF
1 | INTRODUCTION
are found to be effective as antiplatelet molecules[17]
(Figure 1).
Multicomponent reactions play an important role in
forming highly functionalized organic molecules in a
single step from readily accessible starting materials.[1–3]
The main advantages of such kind of reactions are eco‐
compatibility,[4] cost‐effectiveness,[5] effective formation
of multiple bonds,[6] low waste production,[7] and
negative activation volume.[8] Hence, the synthesis of het-
erocyclic compounds through multicomponent reactions
has great significance in the field of organic chemistry.[9]
Pyrazolopyranopirimidinones and pyranopyrazoles are
important classes of oxygen‐nitrogen heterocyclic com-
pounds.[10,11] They find wide applications in the pharma-
cological field, which include anticancerous,[12]
antimicrobial,[13] anti‐inflammatory,[14] and insecticidal
activities.[15] They also find application as pharmaceutical
ingredients and biological agrochemicals.[16] Also,
pyranopyrazoles act as potential inhibitors of human
chk l kinase.[16] Some of the substituted pyranopyrazoles
Only
a
few methods for the synthesis of
pyrazolopyranopyrimidinones using base catalysts were
reported in the literature, including the four‐component
reaction between ethyl acetoacetate, hydrazine hydrate,
aromatic aldehyde, and barbituric acid.[18] This procedure
has many limitations including toxic solvent,[19] long reac-
tion time,[20] and low product yield. So a green protocol for
the efficient synthesis of pyrazolopyranopyrimidinone and
pyranopyrazole derivatives is still in demand.
Because of their extraordinary properties,[21] dendritic
polymers are widely used in catalysis.[22] Here, a newly
synthesized porphyrin initiated poly3,3‐bis(chloromethyl)
oxetane (PBCMO) cored amine functionalized dendritic
polymer was used as an effective and reusable catalyst for
the solvent‐free synthesis of pyrazolopyranopyrimidinones
and pyranopyrazoles by simple sonication method. The
high thermal, mechanical stability[23] and the presence of
easily functionalizable chloro groups make PBCMO an
J Heterocyclic Chem. 2019;1–13.
wileyonlinelibrary.com/journal/jhet
© 2019 Wiley Periodicals, Inc.
1

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AVUDAIAPPAN ET AL.
FIGURE 1 Substituted pyranopyrazoles
efficient material in the field of catalysis.[24] Here, we have
used ultrasonic irradiation as an energy source, because it
has been established as a major technique in synthetic
organic chemistry.[25] Short response time is the main
advantage of ultrasound‐assisted reactions.[26] The simple
experimental method, very high yields, improved selectiv-
ity and clean reactions of many ultrasound‐induced
organic transformations present extra facilities in the field
of synthetic organic chemistry.[27,28] The beneficial effects
of ultrasound irradiation have gained an important role
in flow chemistry, particularly in cases where classical
procedures need drastic conditions for prolonged reaction
times.[29,30]
dendritic polymer. The complete disappearance of the
band at 2100 cm−1 and the origin of new band near
3451 cm−1 confirmed the completeness of the reduction
process. Further, the structure of the amine‐
functionalized POR‐polyBCMO was confirmed by 1H
and 13C NMR spectroscopy (Figure 5). The peaks near
7.9 and 6.8 ppm in 1H NMR spectrum confirmed the por-
phyrin nucleus, and the peaks at 2.5 to 5 ppm confirmed
the alkoxy dendritic chains. The increase in mass (Mw) of
the amine‐functionalized POR‐BCMO was confirmed by
GPC analysis, which turned out to be 29132 with PDI of
1.01.
The PXRD analysis of the amine‐functionalized
PBCMO gave broad peaks, which confirmed the semicrys-
talline nature of the dendritic polymer. The spherical mor-
phology of the PBCMO‐amine was confirmed by the FE‐
SEM image (Figure 6). The thermal stability of the den-
dritic polymer was analyzed using thermogravimetric
analysis, which is shown in Figure 7. From the TG traces,
it was inferred that the dendritic polymer was stable up
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization of
PBCMO‐amine
The cationic ring opening polymerization of 3,3‐bis(-
chloromethyl)oxetane initiated by hydroxyphenyl
porphyrin has led to the formation of dendritic polymer
to 200 ̊C. The amine capacity of PBCMO‐amine was esti-
mated by titration method and found to be 621.03 mmol/g.
Because of the presence of numerous amino groups
on the surface of PBCMO‐amine, it was identified as a
good base catalyst for the effective synthesis of
pyrazolopyranopyrimidinone and pyranopyrazole deriva-
tives. These reactions are given in Scheme 2. For this,
the condensation of benzaldehyde, ethyl acetoacetate,
hydrazine hydrate, and barbituric acid/malononitrile
was selected as the model reaction.
POR‐polyBCMO (Scheme
1
and Figure 2). The
effective polymerization was confirmed by the GPC
analysis, which showed high weight average molecular
mass (Mw) of 26884 and low PDI value of 1.06. An
intense peak around 430 nm in UV‐vis spectrum
(Figure 3) confirmed the presence of porphyrin moiety
in the dendritic polymer system.[31] The structure of
the synthesized POR‐polyBCMO was identified by 1H
and 13C NMR spectroscopy (Figure 4). The peak near
1
3.7 ppm in H NMR spectrum confirmed the ether link-
2.2 | Synthesis of
pyrazolopyranopyrimidinone and
pyranopyrazole derivatives
age of POR‐polyBCMO.
The chloro substituents of POR‐polyBCMO were con-
verted to azide group by the reaction with sodium azide.
The completeness of the reaction was monitored by FTIR
spectroscopy. A strong band near 2100 cm−1 indicated the
presence of azide functionality of the POR‐polyBAMO
(poly3,3‐bis(azidomethyl)oxetane). Finally, the reduction
of azide group resulted in the formation of amine‐
The reaction was conducted at different temperatures. The
results are tabulated in Table 1. The results showed that
compared with heating of the substrates, ultrasonication
gave better yield. This is due to the high agitation of
the reactants by sound wave. So ultrasonication of the
reaction mixture for 15 minutes at room temperature
functionalized
POR‐polyBCMO
(PBCMO‐amine)

AVUDAIAPPAN ET AL.
3
SCHEME 1 Synthesis of PBCMO‐amine dendritic polymer [Color figure can be viewed at wileyonlinelibrary.com]

4
AVUDAIAPPAN ET AL.
FIGURE 2 Structure of PBCMO‐amine
dendritic polymer [Color figure can be
viewed at wileyonlinelibrary.com]
FIGURE 3 UV‐vis and IR spectrum of POR‐polyBCMO [Color figure can be viewed at wileyonlinelibrary.com]
was selected as the optimum condition for the synthesis of
pyrazolopyranopyrimidinone derivatives. Similarly,
effective synthesis of pyrazolopyranopyrimidinone deriva-
tives. Correspondingly, the sonication of the reaction mix-
ture for 10 minutes was the optimized condition for the
synthesis of pyranopyrazole derivatives. An increase of
reaction time did not alter the product yield.
The optimized conditions were applied to different
aldehydes to analyze the generality of the synthesis of
pyrazolopyranopyrimidinone and pyranopyrazole deriva-
tives. All aldehydes gave good yield within 15 minutes
of reaction time. The results are tabulated in Tables 3
and 4.
ultrasonication of 10 minutes at room temperature was
fixed for the synthesis of pyranopyrazole derivatives.
For optimizing the solvent for the efficient synthesis of
pyrazolopyranopyrimidinone, the reaction mixture was
sonicated in the presence of different solvents and inferred
that the solvent free synthesis promoted high yield com-
pared with others. The results are tabulated in Table 2. So
sonication of the reaction mixture for 15 minutes without
any solvent was taken as the optimized condition for the

AVUDAIAPPAN ET AL.
5
2.3 | Synthesized
pyrazolopyranopyrimidinone derivatives
FIGURE 4 1H NMR spectrum of POR‐polyBCMO [Color figure
can be viewed at wileyonlinelibrary.com]
2.4 | Synthesized pyranopyrazole
derivatives
FIGURE 5 1H NMR spectrum of PBCMO‐amine [Color figure
can be viewed at wileyonlinelibrary.com]
FIGURE 6 FE‐SEM image of PBCMO‐amine
PBCMO‐amine abstracted acidic proton of 3b to form an
intermediate 3c, which attacked the Knoevenagel product
3a to form an intermediate 3d; 3d underwent intramolec-
ular cyclization to form the preferred product 3e.
2.5 | Proposed mechanism for the
synthesis of pyrazolopyranopyrimidinone
derivatives
2.6 | Proposed mechanism for the
synthesis of pyranopyrazole derivatives
According to the previously reported works,[32–34] the fol-
lowing mechanism (Scheme 3) was proposed. In the pres-
ence of PBCMO‐amine catalyst, the aldehyde reacted with
barbituric acid to form a Knoevenagel product 3a. The
From the previously reported works,[35–37] the following
mechanism (Scheme 4) was proposed. In the presence
of PBCMO‐amine catalyst, the aldehyde reacted with
malononitrile to form a Knoevenagel product 4a. The

6
AVUDAIAPPAN ET AL.
the high water soluble nature of the PBCMO‐amine cat-
alyst, it could be easily separated from the product by
simple water washing. Centrifugation of washed water
can regenerate the catalyst. It was reused up to six reac-
tion cycles without the loss of its activity (Figure 8).
2.8 | Comparative study
Tables 5 and 6 represent the previously reported methods
for the synthesis of pyrazolopyranopyrimidinone and
pyranopyrazole derivatives by different catalysts compared
with the current method of ultrasonic irradiation by
PBCMO‐amine. In the absence of catalyst, the reaction
sluggishly proceeded and resulted to poor yield. From
Tables 5 and 6, it could be noted that the methodology by
PBCMO‐amine is quite better than any other as it is a
solvent‐free synthesis with less time requirement, only very
low catalyst loading, energy saving, and excellent yield.
FIGURE 7 TG‐DTA Trace of PBCMO‐amine [Color figure can be
viewed at wileyonlinelibrary.com]
PBCMO‐amine abstracted acidic proton of 3b to form an
intermediate 3c, which attacked the Knoevenagel product
4a to form an intermediate 4b; 4b underwent intramolec-
ular cyclization to form the preferred product 4c.
3 | CONCLUSION
In this study, the successful green protocol for the synthesis
of pyrazolopyranopyrimidinone and pyranopyrazole
derivatives using a simple, mild, and effective porphyrin‐
cored polyBCMO‐amine dendritic polymer as an efficient
2.7 | Reusability of the catalyst
When the reaction was completed, the product was
washed with deionised water three times. Because of
SCHEME 2 Four‐component one‐pot
synthesis of pyrazolopyranopyrimidinones
[Color figure can be viewed at
wileyonlinelibrary.com]
TABLE 1 Optimization of temperature for the synthesis of pyrazolopyranopyrimidinone and pyranopyrazole derivatives
Pyrazolopyranopyrimidinone
Pyranopyrazole*
Time, h
Sl.
No
Temperature,
°C
Time, h
Yield, %
Yield, %
1
2
3
4
5
6
7
8
9
30
12
80
80
83
83
85
85
90
90
82
12
70
70
72
75
89
89
91
91
80
40
12
12
50
12
12
60
12
12
80
3
3
80
5
5
Sonication
Sonication
Sonication
1
1
15 min
10 min
10 min
5 min
Note. Conditions: benzaldehyde (3 mmol), ethyl acetoacetate (3 mmol), barbituric acid/malononitrile* (3 mmol), hydrazine hydrate, PBCMO‐amine (0.3 mol%)
in ethanol medium.

AVUDAIAPPAN ET AL.
7
TABLE 2 Optimization of solvent for the synthesis of pyrazolopyranopyrimidinone and pyranopyrazole derivatives
Pyrazolopyranopyrimidinone
Pyranopyrazole*
Sl.
No
Solvent Used
Time, min
Yield, %
Time, min
Yield, %
1
Acetonitrile
Dichloromethane
DMF
60
60
60
60
60
60
60
60
15
20
90
83
70
82
88
90
87
65
99
99
60
60
60
60
60
60
60
60
30
10
85
80
75
80
85
91
85
35
99
99
2
3
4
Chloroform
Methanol
5
6
Ethanol
7
Water
8
Toluene
9
Without solvent
Without solvent
10
Note. Conditions: benzaldehyde (3 mmol), ethyl acetoacetate (3 mmol), barbituric acid/malononitrile* (3 mmol), hydrazine hydrate, PBCMO‐amine (0.3 mol%),
ultrasonication.
TABLE 3 Synthesis of pyrazolopyranopyrimidinone derivatives
TABLE 4 Synthesis of pyranopyrazole derivatives using different
using different aldehydes
aldehydes
Sl. Compound
No. ID
Time, Yield,
Sl. Compound
No. ID
Time, Yield,
Aldehyde
min
%
Aldehyde
min
%
1
2
3
4
5
6
7
8
9
PPP1
PPP2
PPP3
PPP4
PPP5
PPP6
PPP7
PPP8
PPP9
Benzaldehyde
15
15
15
15
15
15
99
98
99
98
99
93
97
92
96
97
85
96
1
2
3
4
5
6
7
8
9
PP1
PP2
PP3
PP4
PP5
PP6
PP7
PP8
PP9
Benzaldehyde
10
10
10
10
10
10
99
98
97
99
99
90
96
92
96
97
88
96
4‐Bromobenzaldehyde
Naphthaldehyde
4‐Bromobenzaldehyde
Naphthaldehyde
4‐Chlorobenzaldehyde
4‐Nitrobenzaldehyde
Veratraldehyde
4‐Chlorobenzaldehyde
4‐Nitrobenzaldehyde
Veratraldehyde
Dimethylaminobenzaldehyde 15
Dimethylaminobenzaldehyde 10
Furfuraldehyde
15
15
15
15
15
Furfuraldehyde
10
10
10
15
10
4‐Methoxybenzaldehyde
2‐Thiophenaldehyde
Cinnamaldehyde
Anthraldehyde
4‐Methoxybenzaldehyde
2‐Thiophenaldehyde
Cinnamaldehyde
Anthraldehyde
10 PPP10
11 PPP11
12 PPP12
10 PP10
11 PP11
12 PP12
Note. Conditions: benzaldehyde (3 mmol), ethyl acetoacetate (3 mmol),
barbituric acid (3 mmol), hydrazine hydrate, PBCMO‐amine (0.3 mol%),
ultrasonication.
More interestingly, the PBCMO‐amine can be recycled
and reused without any significant loss of its activity.
reusable sonocatalyst was presented. The catalyst was
characterized by different spectral techniques including
UV‐vis, IR, 1H and 13C NMR, and GPC. The catalytic activ-
ity of PBCMO‐amine was studied in the ultrasound
promoted synthesis of pyrazolopyranopyrimidinones and
pyranopyrazoles in a one‐pot fashion. This method was
efficient, solvent free, metal free, having low reaction time,
minimization of waste, no tedious work up and required
only mild reaction conditions, which made this an
improved protocol than existing methods. The products
were obtained in high yields and within a short period.
4 | EXPERIMENTS AND METHODS
4.1 | Experimental techniques
All the solvents were purified according to the standard
procedures. All other chemicals were used as received.
TLC was done on silica‐coated alumina plates. FTIR spec-
tra were recorded on JASCO model 4100 FTIR spectrome-
ter as KBr pellets.¹H NMR spectra were recorded on
Bruker 400‐MHz instrument with TMS as internal

8
AVUDAIAPPAN ET AL.
SCHEME 3 Proposed mechanism for the synthesis of pyrazolopyranopyrimidinone derivatives [Color figure can be viewed at
wileyonlinelibrary.com]
SCHEME 4 Proposed mechanism for the synthesis of pyranopyrazole derivatives [Color figure can be viewed at wileyonlinelibrary.com]
standard in DMSO‐d6/CDCl3. 13C NMR spectra were
recorded with the 100‐MHz NMR spectrometer in
DMSO‐d6/CDCl3.
5,10,15,20‐tetrakis(3,4,5‐trihydroxyphenyl) porphyrin dis-
solved in a 20 mL of dry THF was added. The reaction
mixture was stirred for about 15 minutes in order to
ensure homogeneity of the mixture; 4.4‐mL boron
trifluoride etherate (36 mmol) was added, using a
dropping funnel. The reaction mixture changed from a
clear, colorless liquid to a cloudy, dark liquid. The reac-
tion mixture was stirred for another 1 hour. To this mix-
ture, 46.5 g of BCMO (300 mmol) dissolved in 20 mL of
dry THF was added dropwise over a period of 1 hour
using a dropping funnel. The reaction was carried out at
room temperature for 3 hours. The polymerization was
4.2 | Synthesis of polyBCMO with
porphyrin core (POR‐PBCMO)
To a dry 250‐mL three necked, round bottom flask,
placed in a temperature‐controlled water bath, fitted with
a condenser and a calcium chloride guard tube in the top,
and an efficient magnetic stirrer bar, 2.42 g (3 mmol) of

AVUDAIAPPAN ET AL.
9
by vacuum distillation. Yield = 90%, (Mw) = 26 884, Spec-
1
tral data: IR (cm−1): 3400, 2800, 2900, 1580, 1124; H
NMR: (400 MHz, DMSO‐d6): δ = 7.9‐8.6 (m, 16H), 4.45‐
4.13 (m, 8H), 3.84 (s, 32 H), 3.65 (d, 16H), 3.38(d, 40 H),
3.22 (s, 8H), 3.14 (s, 8H), 2.89 (s, 8H), 2.75‐2.42 (m,
88H). 13C NMR (100 MHz, DMSO‐d6): δ = 162.3, 77.83,
75.96, 74.91, 68.09, 63.25, 50.
4.3 | Conversion of POR‐PBCMO to
polyazide
A slurry of sodium azide (1.52 g) in DMSO (5 mL) was
added to LiCl (0.011 g) taken in an RB flask, and the reac-
tion mixture was heated to 100°C. A solution of POR‐
PBCMO (2.01 g) in DMSO (1 mL) was heated to 100°C
FIGURE 8 Reusability of catalyst [Color figure can be viewed at
wileyonlinelibrary.com]
TABLE 5 Comparative study of PPBCMO‐amine catalyst with reported catalysts for the synthesis of pyrazolopyranopyrimidines
derivatives
Sl. No
Catalyst
Temperature
Solvent
Time (min)
Yield (%)
Reference
[19]
1
2
3
4
5
6
7
DABCO
Reflux
Water
45
>90
90
[38]
[39]
[32]
[40]
PEG‐400
R. T.
PEG‐400
Water
30
SBA‐Pr‐SO3H
Meglumine
Reflux
10
92
Stir. (R. T.)
80°C
Water
15–60
60
90
DES (choline chloride:urea)
Without catalyst
PPBCMO‐amine
Ethanol
Solvent free
Solvent free
92
Ultrasonic irradiation
Ultrasonic irradiation
60
40
15
99
This work
TABLE 6 Comparative study of PPBCMO‐amine catalyst with the reported catalyst for the synthesis of pyranopyrazole derivative
Sl. No
Catalyst
Temperature
Solvent
Time, min
Yield, %
Reference
[41]
1
2
3
4
5
6
7
8
Glycine
25°C
Water
20
60
30
10
60
30
60
10
95
86
86
90
94
85
49
99
[42]
[43]
[44]
[20]
[45]
MS 4
Reflux
Ethanol
Fe3O4@ D‐NH2‐HPA
Iodine
Reflux
Ethanol
Ultrasonic irradiation
70°C
Water
BS‐2G‐Ti
Water
[(CH2)4 SO3HMIM][HSO4]
Without catalyst
PPBCMO‐amine
30°C
Solvent free
Solvent free
Solvent free
Ultrasonic irradiation
Ultrasonic irradiation
This work
terminated by adding distilled water and vigorously stir-
ring for about 30 minutes.
in a beaker. This second hot solution was rapidly added
to the first reaction mixture with stirring. The resulting
mixture was maintained at 100°C for 3 days with constant
stirring. After the completion of the reaction, excess
reagents were removed by washing with hot water in a sep-
arating funnel. The organic layer was separated. The sol-
vent DMSO was removed under vacuum to obtain the
polymer. Yield = 85%; (Mw) = 27 492, Spectral data: IR
(cm−1): 3419, 2941, 2889, 2101, 1644, 1437, 1209, 1110, 954.
The crude reaction product was transferred to a sepa-
rating funnel, and the organic layer was washed three
times with distilled water in order to remove all
unreacted monomers and boron trifluoride. The organic
layer was transferred to a round bottom flask and dried
over magnesium sulphate. Finally, the organic layer and
the product were filtered, and the solvent was removed

10
AVUDAIAPPAN ET AL.
ppm): 2.27 (s, 3H), 5.42 (s, 1H), 6.05 (s, 1H), 7.32‐7.92
(m, 4H), 11.31 (s, 2H). 13C NMR (100 MHz,
DMSO‐d6): 173.3, 164.5, 153.2, 146.8, 142.7, 131.4,
129.1, 118.6, 106.1, 94.2, 31.6, 10.4. LC‐MS: 372.20
(M − 2).
4.4 | Reduction of polyazide to polyamine
dendrimer (PBCMO‐amine)
About 3 g of polyazide was dissolved in anhydrous
THF (40 mL) taken in 250‐mL double necked RB flask.
The reaction mixture was cooled in an ice bath. A
solution of powdered LiAlH4 (0.76 g) in dry THF was
added dropwise with constant stirring to the polyazide
solution using dropping funnel. The reaction mixture
was stirred at 0°C for 4 hours and allowed to attain
room temperature for 1 hour. The reaction mixture
was filtered using methanol, and excess solvent was
removed by vacuum evoperation. Yield = 80%, ( M
w) = 29 132, Spectral data: IR (cm−1): 3423, 2931,
2858, 1614, 1110; 1H NMR (400 MHz, DMSO‐d6):
δ = 7.9(d, 4H), 6.8 (s, 4H), 6.6 (s, 8H), 4.8 (s, 16H),
4.25 (t, 16H), 3.5 (t, 24H), 3.36 (d, 48H), 3.32 (s, 8H),
3.27 (d, 8H), 2.9‐2.3 (m, 32H), 1.21 (t, 8H). 13C NMR
(100 MHz, DMSO‐d6): δ = 75.02, 62.60, 59.78, 59.37,
53.18, 51.07, 50.84, 45.66, 45.36, 45.24, 44.86, 44.09,
42.99, 42.01, 40.01.
PPP3
3‐Methyl‐4‐(naphthalen‐1‐yl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]‐pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP3)
Yellow solid, mp 222‐223°C,IR (KBr): 3061, 1641, 1610,
1
1512, 1473, 1390 cm−1; H NMR (400 MHz, DMSO‐d6, δ
ppm): 2.19 (s, 3H), 5.70 (s, 1H), 7.30 (t, J ¼ 8.0 Hz, 1H),
7.39‐7.48 (m, 3H), 7.69 (d, J ¼ 8.0 Hz, 1H), 7.85 (t, J ¼
6.5 Hz, 1H), 8.21 (d, J ¼ 7.5 Hz, 1H), 10.12 (s, 2H),
13.04 (br s, 1H). 13C NMR (100 MHz, DMSO‐d6): 10.4,
29.2, 80.9, 124.1, 125.2, 125.3, 125.4, 126.3, 126.4, 126.7,
127.1, 129.4, 131.3, 131.9, 134.2, 139.4, 151.6, 161.2. LC‐
MS: 346.19.
3‐Methyl‐4‐(4‐chlorophenyl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP4)
4.5 | General procedure for the synthesis
of pyrazolopyranopyrimidinone derivatives
White solid, mp 223‐224°C. IR (KBr): 1215, 1535, 1685,
3012, 3145 cm−1 1H NMR (400 MHz, DMSO‐d6, δ
.
ppm): 2.22 (s, 3H), 5.43 (s, 1H), 6.24 (s, 1H), 7.26‐7.92
(m, 4H), 11.31 (s, 2H). 13C NMR (100 MHz, DMSO‐d6):
172.1, 162.4, 159.1, 146.3, 142.5, 132.0, 129.1, 128.2,
128.3, 30.5, 10.6. LC‐MS: 328.97 (M + 2).
A 50‐mL conical flask was charged with aldehyde
(3 mmol), barbituric acid (3 mmol), hydrazine hydrate
(3 mmol), ethyl acetoacetate (3 mmol), and catalyst
(0.3 mol%). The reaction mixture was sonicated for
15 minutes. The precipitate formed was filtered and
washed with water and dried. All the compounds were
characterized using melting point, LC‐MS, FTIR, 1H
NMR, and 13C NMR spectroscopy.
3‐Methyl‐4‐(4‐nitroyphenyl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP5)
White solid, mp 230‐232°C. IR (KBr): 1243, 1341, 1461,
1
1520, 1590, 1673, 3041, 3156 cm−1. H NMR (400 MHz,
DMSO‐d6, δ ppm): 2.24 (s, 3H), 5.51 (s, 1H), 6.01 (s,
1H), 7.35‐8.07 (m, 4H), 11.20 (s, 2H). 13C NMR
(100 MHz, DMSO‐d6): 172.9, 160.4, 151.5, 151.3, 146.2,
144.5, 131.9, 129.1, 123.4, 106.1, 91.4, 30.9, 10.2. LC‐MS:
339.96 (M + 1).
4.5.1 | Characterization of
pyrazolopyranopyrimidinone derivatives
3‐Methyl‐4‐phenyl‐6,8‐dihydropyrazolo[4′,3′:5,6]
pyrano[2,3‐d]pyrimidine‐5,7(1H,4H)‐dione (PPP1)
White solid, mp 217‐218°C. IR (KBr): 1321, 1452, 1642,
3230, 3414 cm−1 1H NMR (400 MHz, DMSO‐d6, δ
.
3‐Methyl‐4‐(3,4‐dimethoxyphenyl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP6)
ppm): 2.32 (s, 3H), 5.24 (s, 1H), 6.05 (s, 1H), 7.42‐7.56
(m, 5H), 10.85 (s, 2H). 13C NMR (100 MHz, DMSO‐d6):
173.6, 160.5, 152.3, 148.2, 144.3, 134.3, 131.7, 131.2,
130.7, 121.5, 104.2, 31.7, 10.3. LC‐MS: 296.10.
White solid, mp 276‐277°C; IR (KBr): 3139,3054,
1720,1660,1535,1421,1380, cm−1 1H NMR (400 MHz,
.
DMSO‐d6, δ ppm): 2.25 (s, 3H), 3.63 (s, 3H), 3.68 (s,
3H), 7.07 (d, J = 8.4 Hz, 1H), 7.38 (d, J = 8.8 Hz, 1H),
7.49 (s, 2H), 8.53 (s, 1H). 13C NMR (100 MHz,
DMSO‐d6): 164.2, 163.1, 161.7, 161.1, 155.4, 151.2, 149.1,
148.2, 132.6, 124.7, 117.8, 114.9, 111.0, 56.8, 55.9, 55.8,
10.7. LC‐MS: 358.17 (M + 2).
3‐Methyl‐4‐(4‐bromoyphenyl)‐6,8‐dihydropyrazolo
[4′,3′:5,6]pyrano
[2,3‐d]pyrimidine‐5,7(1H,4H)‐dione
(PPP2)
White solid, mp 211‐212°C. IR (KBr): 1210, 1601, 1680,
2990, 3160 cm−1 1H NMR (400 MHz, DMSO‐d6, δ
.

AVUDAIAPPAN ET AL.
11
1
3‐Methyl‐4‐(4‐N,N‐dimethylphenyl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP7)
1H H NMR (400 MHz, DMSO‐d6, δ ppm): 2.21 (s, 3H),
4.37 (s, 1H), 6.52‐7.49 (m, 9H), 11.47 (s, 2H), 12.24 (s,
1H). 13C NMR (100 MHz, DMSO‐d6): 159.1, 153.7, 141.6,
137.8, 125.3, 124.7, 113.1, 105.6, 92.8, 53.7, 32.9, 23.1,
17.8, 10.1. LC‐MS: 396.21.
White solid, mp 276‐277°C. IR (KBr): 1240, 1571, 1683,
1
2939, 3152, 3454 cm−1. H NMR (400 MHz, DMSO‐d6, δ
ppm): 2.18 (s, 3H), 2.39 (s, 6H), 5.29 (s, 1H), 6.71 (s, 1H),
7.12‐7.54 (m, 4H), 11.04 (s, 2H). 13C NMR (100 MHz,
DMSO‐d6): 172.7, 165.0, 159.7, 152.1, 147.3, 135.9, 132.2,
129.6, 117.9, 108.2, 98.3, 31.7, 10.5. LC‐MS: 339.25.
4.6 | General procedure for the synthesis
of pyranopyrazole derivatives
4‐(Furan‐2‐yl)‐3‐methyl‐6,8‐dihydropyrazolo[4′,3′:5,6]
pyrano[2,3‐d]pyrimidine‐5,7(1H,4H)‐dione (PPP8)
White solid, mp 246‐247°C. IR (KBr): 1242, 1585, 1672,
A 50‐mL conical flask was charged with aldehyde
(3 mmol), malononitrile (3 mmol), hydrazine hydrate
(3 mmol), ethyl acetoacetate (3 mmol), and catalyst
(0.3 mol%). The reaction mixture was sonicated for
10 minutes. The precipitate formed was filtered and
washed with water and then dried. All the compounds
were characterized using melting point, LC‐MS, FTIR,
1H NMR, and 13C NMR spectroscopy.
1
2951, 3157 cm−1. H NMR (400 MHz, DMSO‐d6, δ ppm):
2.15 (s, 3H), 5.20 (s, 1H), 6.12 (s, 1H), 6.23 (d, 1H), 6.73 (d,
1H), 7.09‐7.17 (m, 1H), 11.26 (s, 2H). 13C NMR (100 MHz,
DMSO‐d6): 174.3, 169.5, 157.8, 154.69, 143.1, 137.7, 125.1,
115.4, 114.9, 108.7, 95.5, 30.1, 10.7. LC‐MS: 285.13 (M + 1).
3‐Methyl‐4‐(4‐methoxyphenyl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP9)
4.6.1 | Characterization of
pyrazolopyranopyrimidinone derivatives
White solid, mp 190‐191°C. IR IR (KBr): 1395, 1459, 1470,
1
1659, 1681, 3479 cm−1. H NMR (400 MHz, DMSO‐d6, δ
6‐Amino‐2,4‐dihydro‐3‐methyl‐4‐phenylpyrano[2,3‐c]
pyrazole‐5‐carbonitrile (PP1)
ppm): 2.21 (s, 3H), 3.59 (s, 3H), 5.13 (s, 1H), 6.09 (s, 1H),
7.15‐7.71 (m, 4H), 11.17 (s, 2H). 13C NMR (100 MHz,
DMSO‐d6): 174.5, 161.7, 159.0, 147.9, 143.2, 132.7, 131.1,
117.9,105.2,104.7,96.5,59.7,30.9,10.3.LC‐MS:325.16(M‐1).
White solid, mp 244‐245
̊C. FT‐IR (KBr) 3425, 3356, 3172,
2165, 1630, 1521, 1470, 1350, 1226, 1182, 956, 823 cm−1
.
1H NMR (400 MHz, DMSO‐d6, δ ppm): 11.91 (s, 1H),
7.17‐7.60 (m, 5H), 6.89 (s, 2H), 4.57 (s, 1H), 1.82 (s, 3H).
13C NMR (100 MHz, DMSO‐d6): 159.1, 153.1, 145.6,
134.6, 123.8, 123.1, 122.9, 120.7, 96.3, 54.6, 50.8. LC‐MS:
252.10.
3‐Methyl‐4‐(thiophen‐2‐yl)‐6,8‐
dihydropyrazolo[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐
5,7(1H,4H)‐dione (PPP10)
Red solid, mp 252‐254°C. IR (KBr): 1291, 1352, 1469, 1530,
1572, 1657, 3031, 3491 cm−1 1H NMR (400 MHz,
.
6‐Amino‐4‐(4‐bromophenyl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP2)
White solid, mp 178‐179°C. FT‐IR (KBr): 1052, 1421,
DMSO‐d6, δ ppm): 2.21 (s, 3H), 5.47 (s, 1H), 6.71 (s, 1H),
6.81‐6.84 (m, 3H), 11.25 (s, 2H). 13C NMR (100 MHz,
DMSO‐d6): 173.1, 165.3, 162.1, 160.5, 159.7, 137.4, 130.7,
125.3, 116.7, 113.2, 113, 29.7, 10.1. LC‐MS: 303.10.
1
1480, 1621, 1654, 2182, 2932, 3250, 3385, 3426 cm−1. H
NMR (400 MHz, DMSO‐d6, δ ppm): 1.80 (s, 3H), 4.53 (s,
1H), 6.82 (s, 2H), 7.21 (d, 2H, J = 8.8 Hz), 7.42 (d, 2H,
J = 8.8 Hz), 12.21 (s, 1H). 13C NMR (100 MHz,
DMSO‐d6): 9.9, 17.2, 57.3, 114.6, 122.6, 129.6, 129.7,
131.5, 136.1, 142.9, 154.2, 161.1. LC‐MS: 331.17.
3‐Methyl‐4‐styryl‐1,4‐dihydropyrazolo[4′,3′:5,6]pyrano
[2,3‐d]pyrimidine‐5,7(6H,8H)‐diones (PPP11)
White solid, mp 252‐254°C. IR (KBr): 1590, 1672, 2946,
3138. 1H NMR (400 MHz, DMSO‐d6, δ ppm): 1.82 (s,
1H), 2.33 (s, 3H), 5.02 (s, 1H), 6.28 (s, 1H), 7.12‐7.78 (m,
5H), 11.12 (s, 1H), 11.41 (s, 1H). 13C NMR (100 MHz,
DMSO‐d6): 10.28, 58.7, 98.2, 103.5, 107.8, 118.6, 121.8,
131.1, 143.8, 149.3, 159.1, 164.8, 174.5. LC‐MS‐ 323.51.
6‐Amino‐3‐methyl‐4‐(naphthalen‐2‐yl)‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP3)
Yellow solid, mp 201‐203°C. FT‐IR (KBr, cm−1): 1401,
1
1480, 1585, 1621, 1666, 2180, 3160, 3310, 3380. H NMR
(400 MHz, DMSO‐d6, δ ppm): 1.73(s, 3H),4.81(s, 1H), 6.92
(s, 2H), 4.51 (s, 1H), 6.86 (s, 1H), 7.21 (d, J = 8.4 Hz, 1H),
7.48 (m,2H),7.77 (s, 1H),7.86 (m,3H), 12.12 (s,1H). 13C
NMR (100 MHz, DMSO‐d6): 9.8, 36.3, 57.1, 97.4, 125.7,
125.8, 125.9, 126.3, 127.6, 127.7, 128.4, 132.2, 132.9, 135.7,
135.8, 141.5, 154.1, 160.8. LC‐MS: 303.12.
3‐Methyl‐4‐(4‐anthracene‐9‐yl)‐6,8‐dihydropyrazolo‐
[4′,3′:5,6]pyrano[2,3‐d]pyrimidine‐5,7(1H,4H)‐dione
(PPP12)
Orange solid, mp 223‐225°C. IR (KBr): 3342, 3320, 3258,
1420, 1401, 1357, 1223, 1040, 1021, 847, 721, 512 cm−1
.

12
AVUDAIAPPAN ET AL.
6‐Amino‐4‐(4‐chlorophenyl)‐3‐methyl‐2,4‐
6‐Amino‐4‐(4‐methoxyphenyl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP4)
White solid, mp 233‐234°C). FT‐IR (KBr, cm−1): 3520,
3398, 3120, 2165, 1672, 1567, 1430, 1235, 1165, 1003,
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP9)
White solid, mp 211‐212°C. FT‐IR (KBr, cm−1): 1040,
1
1420, 1501, 1622, 2190, 3260, 3487. H NMR (400 MHz,
1
828. H NMR (400 MHz, DMSO‐d6, δ ppm): 12.05 (s,
DMSO‐d6, δ ppm): 1.68 (s, 3H), 3.42 (s, 3H), 4.14 (s,1H),
6.88 (d, 2H, J = 8.2 Hz), 6.62 (d, 2H, J = 8.2 Hz), 7.17
(s, 2H), 12.47 (s, 1H). 13C NMR (100 MHz, DMSO‐d6):
9.1, 36.2, 52.9, 54.6, 112.8, 109.4, 110.7, 115.1, 137.8,
142.8, 153.2, 153.7, 161.6. LC‐MS: 282.60.
1H), 7.32‐7.39 (d, 2H, J = 8.29 Hz), 7.27‐7.08 (d, 2H,
J = 8.40 Hz), 1.93 (s, 3H). 13C NMR (100 MHz,
DMSO‐d6): 159.2, 153.5, 144.1, 132.5, 130.8, 128.6, 128.4,
120.7, 97.5, 56.3, 9.8. LC‐MS: 287.30.
6‐Amino‐4‐(4‐nitrophenyl)‐3‐methyl‐2,4‐
6‐Amino‐4‐(thiophen‐2‐yl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP5)
White solid, mp 250‐251°C. FT‐IR (KBr, cm−1): 3405,
3210, 3075, 2210, 1668, 1610, 1575, 1520, 1445, 1390,
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP10)
Red solid, mp 211‐212°C. FT‐IR (KBr, cm−1): 925, 1084,
1
1140, 1235, 1605, 1672, 2194, 3335. H NMR (400 MHz,
1315,1240, 1190, 770 cm−1
.
1H NMR (400 MHz,
DMSO‐d6: 1.90 (s, 3H), 4.88 (s, 1H), 6.42‐7.35 (m, 3H),
8.48 (s, 2H), 12.08 (s, 1H). 13C NMR (100 MHz,
DMSO‐d6): 8.8, 29.4, 54.4, 93.9, 117.2, 122.1, 124.4,
132.5, 147.0, 153.9, 155.2. LC‐MS: 259.76.
DMSO‐d6, δ ppm): 1.72 (s, 3H), 4.81 (s, 1H), 6.95 (s, br,
2H), 7.52 (d, 2H, J = 8.4 Hz), 8.10 (d, 2H, J = 8.6 Hz),
12.15 (s, 1H). 13C NMR (100 MHz, DMSO‐d6): 160.7,
151.8, 148.2, 147.5, 134.9, 128.2, 124.9, 121.6, 99.6, 62.0,
36.1, 10.8. LC‐MS: 298.09 (M + 1).
6‐Amino‐2,4‐dihydro‐3‐methyl‐4‐styryl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP11)
6‐Amino‐4‐(3,4‐dimethoxyphenyl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP6)
White solid, mp 250‐251°C. FT‐IR (KBr, cm−1): 3375,
3282, 3160, 2901, 2117, 1652, 1631, 1527, 1432,
White solid, mp 201‐202°C. FT‐IR (KBr, cm−1): 1025,
1130, 1284, 1530, 2190, 3421, 3430. H NMR (400 MHz,
DMSO‐d6): 2.08 (s, 3H), 4.56 (s, 1H), 6.72 (br, s, 2H),
6.32‐7.10 (m, 7H). 13C NMR (100 MHz, DMSO‐d6): 12.4,
50.1, 96.5, 127.4, 127.3, 127.2, 135.6, 146.9, 152.8, 158.3.
LC‐MS: 279.61.
1
1
1011 cm−1. H NMR (400 MHz, DMSO‐d6, δ ppm): 1.69
(s, 3H), 3.52 (s, 3H), 3.58 (s, 3H), 4.29 (s, 1H), 5.82 (s,
2H), 6.53 (d, 1H, J = 6.8 Hz), 6.59 (s, 1H), 6.67 (d, 1H,
J = 8.4 Hz), 11.22 (s, 1H); 9.6, 35.6, 56.3, 55.1, 60.0, 96.4,
104.0, 104.2, 104.6, 121.6, 134.8, 139.7, 153.5, 153.8,
154.6, 161.4. LC‐MS: 312.85.
6‐Amino‐4‐(anthracen‐9‐yl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP12)
Yellow solid, mp 207‐208°C. FT‐IR (KBr, cm−1): 1031,
1401, 1472, 1590, 1628, 2133, 2952, 3062, 3127, 3111,
1
3385 cm−1. H NMR (400 MHz, DMSO‐d6, δ ppm): 1.52
6‐Amino‐4‐(4‐(dimethylamino)phenyl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP7)
Brown solid, mp 233‐235°C. FT‐IR (KBr, cm−1): 868,
1059, 1410, 1484, 1610, 1636, 2192, 2930, 3175,
(s, 3H), 5.82 (s, 2H), 6.31 (s, 1H), 7.47‐7.51 (m, 3H), 7.91‐
8.12 (m, 3H), 8.43‐8.52 (m, 2H), 8.58 (s, 1H). 13C NMR
(100 MHz, DMSO‐d6): 10.1, 30.3, 59.8, 97.6, 115.9, 121.2,
122.7, 123.9, 124.0, 124.1, 124.3, 126.8, 127.1, 129.1, 129.2,
131.9, 131.6, 135.7, 155.5, 159.9. LC‐MS: 351.32.
1
3379 cm−1. H NMR (400 MHz, DMSO‐d6, δ ppm): 1.72
(s, 3H), 2.69 (s, 6H), 4.41 (s, 1H), 6.03 (s, 2H), 6.60 (d,
2H, J = 8.4 Hz), 6.96 (d, 2H, J = 7.6 Hz). 13C NMR
(100 MHz, DMSO‐d6): 14.0, 35.4, 41.7, 69.3, 102.3, 120.1,
124.9, 135.3, 131.5, 133.6, 142.9, 160.0, 163.5. LC‐MS:
295.05.
Acknowledgments
The authors gratefully acknowledge University Grants
commission (UGC), New Delhi, India, Kerala State Coun-
cil for Science, Technology and Environment, Kerala,
India and Cochin University of Science and Technology,
Kerala, India for the financial support.
6‐Amino‐4‐(furan‐2‐yl)‐3‐methyl‐2,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile (PP8)
White solid, mp 218‐219°C. FT‐IR (KBr, cm−1): 921, 1125,
1211, 1638, 2187, 2956, 3138, 3378 cm−1 1H NMR
.
(400 MHz, DMSO‐d6, δ ppm): 1.90 (s, 3H), 4.63 (s, 1H),
5.89 (s, 2H), 6.12 (d, 1H, J = 1.6 Hz), 6.28 (dd, 1H,
J = 1.6, J = 3.2 Hz), 7.49 (d, 1H,J = 3.2 Hz), 12.09 (s,
1H, NH). 13C NMR (100 MHz, DMSO‐d6): 10.3, 28.1,
53.96, 96.2, 106.4, 111.4, 122.6, 137.8, 143.8, 155.1, 155.7,
163.8. LC‐MS: 242.69.
Supporting Information Summary
Details of experimental procedure, catalyst characterization
1
data, and copies of LCMS, H, and 13CNMR spectra of
selectedpyrazolopyranopirimidinonesandpyranopyrazoles
are available in the supporting information.

AVUDAIAPPAN ET AL.
13
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
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How to cite this article: Avudaiappan G,
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