Preparation, characterization and catalytic activity of dendrimer-encapsulated phosphotungstic acid nanoparticles immobilized on nanosilica for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones under solvent-free or sonochemical conditions

Article abstract of DOI:10.1007/s13738-015-0782-x

In this paper, we adopt a facile method to prepare a type of porous silica nanoparticles (n-SiO₂) from tetraethyl orthosilicate as the source of silica. Then, dendritic polymer supported on nanosilica with surface amino groups was fabricated. Finally, H₃PW₁₂O₄₀ nanoparticles (PWAⁿ) were synthesized by the treatment of H₃PW₁₂O₄₀ powder with n-Octane as solvent by a solvothermal method and then immobilized onto the dendrimer polymer functionalized nanosilica. The synthesized nanostructures were characterized by fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), N₂ adsorption-desorption isotherm analysis, UV-Vis and elemental analysis. The morphology of the catalyst was characterized using transmission electron microscopes (TEM). The acidity of the catalyst was determined by FTIR pyridine adsorption spectroscopy. Then, this catalytic system was used as an efficient catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones via multi-component and one-pot reactions of various aldehydes, phthalic anhydride, hydrazinium hydroxide, and dimedone under thermal solvent-free conditions or ultrasound irradiation at room temperature. Also, the catalyst can be easily recovered and reused for six consecutive reaction cycles without significant loss of activity.

Full text of DOI:10.1007/s13738-015-0782-x

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0782-x
ORIGINAL PAPER
Preparation, characterization and catalytic activity
of dendrimer‑encapsulated phosphotungstic acid nanoparticles
immobilized on nanosilica for the synthesis of 2H‑indazolo[2,1‑b]
phthalazine‑triones under solvent‑free or sonochemical conditions
Mohsen Esmaeilpour1 · Jaber Javidi2,3 · Farzaneh Dehghani1
Received: 15 July 2015 / Accepted: 7 November 2015
© Iranian Chemical Society 2015
Abstract In this paper, we adopt a facile method to pre-
pare a type of porous silica nanoparticles (n-SiO2) from
tetraethyl orthosilicate as the source of silica. Then, dendritic
polymer supported on nanosilica with surface amino groups
was fabricated. Finally, H3PW12O40 nanoparticles (PWAn)
were synthesized by the treatment of H3PW12O40 powder
with n-Octane as solvent by a solvothermal method and then
immobilized onto the dendrimer polymer functionalized
nanosilica. The synthesized nanostructures were character-
ized by fourier transform infrared (FT-IR), X-ray diffraction
(XRD), thermogravimetric analysis (TGA), dynamic light
scattering (DLS), N2 adsorption–desorption isotherm analy-
sis, UV–Vis and elemental analysis. The morphology of the
catalyst was characterized using transmission electron micro-
scopes (TEM). The acidity of the catalyst was determined by
FTIR pyridine adsorption spectroscopy. Then, this catalytic
system was used as an efficient catalyst for the synthesis of
2H-indazolo[2,1-b]phthalazine-triones via multi-component
and one-pot reactions of various aldehydes, phthalic anhy-
dride, hydrazinium hydroxide, and dimedone under thermal
solvent-free conditions or ultrasound irradiation at room
temperature. Also, the catalyst can be easily recovered and
reused for six consecutive reaction cycles without significant
loss of activity.
Keywords Dendrimer-PWAn · Reusable catalyst ·
One-pot four-component reaction · 2H-indazolo[2,1-b]
phthalazine-1,6,11-triones · Ultrasound irradiation ·
Solvent-free conditions
Introduction
The development of simple synthetic routes for com-
plex organic molecules from readily available reagents is
an important task in organic synthesis. Multicomponent
(MCRs) protocol emphasizes as one-pot reaction in which
three or more reactants are combined together to generate a
single product with greater efficiency [1]. Multicomponent
reactions enable multiple reactions leading to interesting
heterocyclic scaffolds which are useful for the construction
of poly-functionalized heterocyclic ‘drug like’ libraries [2].
Nitrogen-containing heterocyclic compounds are well
known in nature, and their applications to pharmaceuti-
cals, agrochemicals, and functional materials are becom-
ing more and more important [3]. Among a large variety of
heterocyclic compounds, bridgehead nitrogen heterocycles
containing a phthalazine moiety are of interest because they
exhibit pharmacological and biological activities including,
antimicrobial [4] and anticonvulsant [5]. Nevertheless, the
development of new synthetic methods for the efficient
preparation of heterocycles containing phthalazine ring
fragment is an interesting challenge. A number of methods
have been reported for the synthesis of phthalazine deriva-
tives such as three-component condensation of phthalhy-
drazide, dimedone, and aromatic aldehydes [6–8] or four-
component reaction of phthalic anhydride, hydrazinium
hydroxide, dimedone and aromatic aldehydes in the pres-
ence of various catalysts such as heteropoly acids (HPAs)
[9], ZnO nanoparticles [10] and etc.
* Mohsen Esmaeilpour
m1250m551085@yahoo.com
* Jaber Javidi
jaberjavidi@gmail.com; jaberjavidi@sbmu.ac.ir
1
Chemistry Department, College of Science, Shiraz
University, 71454 Shiraz, Iran
2
Department of Pharmaceutics, School of Pharmacy, Shahid
Beheshti University of Medical Sciences, Tehran, Iran
3
Students Research Committee, School of Pharmacy, Shahid
Beheshti University of Medical Sciences, Tehran, Iran
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J IRAN CHEM SOC
Heteropolyacids (HPAs) have been used as efficient cat-
alysts for a variety of organic reactions [11–17]. Although
HPAs in their acidic form are versatile compounds, their
main disadvantages are high solubility in polar solvents
and low surface area. In previous study [18] we find that
by reducing the particle size of PWA from bulk powder
to nanometer scale, the surface area increased from 12 to
242 m2/g. Furthermore, acidity and catalytic activity of
HPAs rising by declining particle size or increasing of sur-
face area [19]. The use of support is another approach, that
allows the heteropolyacids to be dispersed over a large sur-
face area and increases theirs catalytic activity. Silica is a
very important industrial material and is extensively used
for a wide range of commercial applications such as cata-
lyst supports, molecular sieves, resins, fillers in polymers,
as well as in biomedical applications [20]. In particular, sil-
ica nanoparticles with high surface area are of high interest
to many key chemical applications [21].
Dendrimers are a well-recognized class of precise
macromolecules that should find multiple applications in
molecular electronics [22], catalysis [23] and biomedical
applications [24, 26, 27].
The use of ultrasonic irradiation accelerates an organic
transformation at ambient conditions which otherwise
require harsh conditions of temperature and pressure [28].
The interaction between molecules and ultrasound is not
direct but the energy of theses long wavelength can cause
cavitation which makes the reaction faster [29].
X-ray diffractometer using Cu Kα radiation (λ = 1.5418).
Transmission electron microscopy (Philips EM208) with an
accelerating voltage of 100 kV was used to examine mor-
phology and size of the nanoparticles and dynamic light
scattering (DLS) was recorded on a HORIBA-LB550. The
n-SiO2 and Dendrimer-PWAn were dispersed on ethanol
solution under ultrasonic vibration for 10 min and one drop
of the suspension evaporated onto a carbon-coated cop-
per grid for TEM measurement. TGA thermograms were
recorded on an instrument of Perkin Elmer with N2 carrier
gas and the rate of temperature change of 20 °C min−1. BET
surface area and porosity of catalysts were determined from
nitrogen adsorption isotherm by the Brunauer-Emmett-
Teller (BET) method and determination of the pore size
distribution from adsorption branch by the Barrett-Joyner-
Halenda (BJH) method. Diffuse reflectance UV–visible
measurements were recorded at room temperature on a Per-
kin-Elmer Lambda 650 spectrometer. Tungsten contents in
the Dendrimer-PWAn sample were estimated by inductively
coupled plasma-atomic emission spectroscopy (ICP-AES).
The C, H, N and S elemental analyses were carried out by
the using a Thermofinigan Flash EA-1112 CHNSO rapid
elemental analyzer. Melting points were determined with a
Buchi 510 instrument in open capillary tubes and are uncor-
rected. Determination of the purity of the substrate and
monitoring of the reaction were accomplished by thinlayer
chromatography (TLC) on a silica gel polygram SILG/UV
254 plates. Therefore, all of the products were characterized
by FT-IR, 1H NMR and 13C NMR, and also by comparison
with authentic samples.
Therefore, as part of our continuing interest in devel-
oping of recyclable nanocatalyst in synthesis of useful
compounds [30], we report on the preparation of den-
drimer-encapsulated phosphotungstic acid nanoparticles
immobilized on nanosilica (Dendrimer-PWAn) as recy-
clable catalyst (Scheme 1) for the one-pot synthesis of
2H-indazolo [2,1-b] phthalazine-triones via a one-pot four-
component reaction from simple and easily available start-
ing materials under much milder reaction conditions.
Synthesis of dendrimer‑encapsulated phosphotungstic
acid nanoparticles immobilized on nanosilica
Synthesis of silica nanoparticles
0.5 ml TEOS was added into the mixture of 50 ml ethanol,
20 ml water and 0.5 ml ethylenediamine under ultrasonic
irradiation [25]. After 30 min, the precipitate was isolated
by centrifuging and washed with ethanol and water several
times. The as-obtained products were dried at 80 °C under
vacuum for 2 h and then were calcined at 650 °C for 2 h.
Experimental
General
Chemicals were purchased from Merck and Aldrich Chemi-
cal Companies. All other chemicals are analytical grade and
used without further purification. Fourier transform infrared
spectroscopy (FT-IR) analysis of the samples was taken on
a Shimadzu FT-IR 8300 spectrophotometer and the sample
and KBr were pressed to form a tablet. The NMR spectra
were recorded on a Bruker avance DPX 500 MHz spectrom-
eter in chloroform (CDCl3) using tetramethylsilane (TMS)
as an internal reference. X-ray powder diffraction (XRD)
analysis was conducted on a Bruker AXS D8-advance
Preparation of functionalized SiO2 nanoparticle
with 3‑chloro triethoxy propyl silane (nSiO2‑Cl)
Nano SiO2 (1 g) was added to the solution of 3-chloro tri-
ethoxy propylsilane (10 mmol, 2.4 mL) in ethanol (10 mL)
and the resultant mixture was under reflux for 10 h under
nitrogen atmosphere [27]. After refluxing, the mixture was
cooled to room temperature and the solid product was fil-
tered off, washed with ethanol and water to remove unre-
acted species and dried at 60 °C for 8 h.
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J IRAN CHEM SOC
Scheme 1 Process for prepara-
tion of nanosilica supported
dendritic polymer
Preparation of nSiO2‑NH2
sufficient amount of distilled water, and dried at 60 °C for
12 h to afford nSiO2-NH2 nanoparticles.
In a typical synthetic procedure [30], 1.2 mL (10 mmol)
of bis(3-aminopropyl) amine was added to a suspension of
nSiO2-Cl (1.0 g) in 10 mL acetonitrile, potassium iodide
(10 mmol, 1.66 g) and potassium carbonate (10 mmol,
1.38 g). The reaction mixture was refluxed in an oil bath
for 10 h. The solid product was filtered off, washed with
Preparation of P0
nSiO2-NH2 (1 g) was added to the stirred solution of
methyl acrylate (20 mmol, 1.7 mL) in methanol (10 mL).
The final mixture was stirred at room temperature for 24 h.
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J IRAN CHEM SOC
Then, the solid material was separated by filtration, washed
with hot methanol for 6 h in a Soxhlet apparatus to remove
the unreacted starting materials and then finally dried in a
vacuum oven at 60 °C.
Preparation of dendrimer‑encapsulated phosphotungstic
acid nanoparticles immobilized on nanosilica (Den‑
drimer‑PWAn)
For the anchoring of PWAn on to P1.5. 2 g of P1.5 was
dispersed in 40 mL of n-Hexane and ultrasonicated for
30 min. Then, PWAn (0.5 mmol, 1.48 g) was added into the
solution and ultrasonicated for 30 min and the mixture was
stirred for 24 h at room temperature. Finally, the formed
Dendrimer-PWAn was washed with distilled water for sev-
eral times and then dried in a desiccator for 6 h. The sam-
ple thus prepared was designated as Dendrimer-PWAn and
stored in airtight bottle for further use.
Preparation of nanosilica supported dendritic polymer
(P0.5)
To a slurry of P0 (1 g) in methanol (10 mL) was added
bis(3-aminopropyl) amine (20 mmol, 2.4 mL). The reac-
tion mixture was refluxed with continuous stirring under
inert atmosphere for 4 h. Final product was filtered, washed
with hot methanol for 6 h in a Soxhlet apparatus to remove
the unreacted starting materials and then dried in a vacuum
oven at 60 °C [23].
General procedure for the synthesis
of 2H‑indazolo[2,1‑b] phthalazine‑triones
under solvent‑free conditions
Preparation of nanosilica supported dendritic polymer
(P1.5)
A mixture of dimedone (1 mmol), aldehyde (1 mmol),
hydrazinium hydroxide (1.2 mmol), phthalic anhy-
dride (1 mmol) and Dendrimer-PWAn catalyst (0.01 g,
0.14 mol %) was heated at 80 °C for the time indicated in
Table 2. The reactions were followed by thin layer chroma-
tography (TLC) using hexane/ethyl acetate (3:1) as an elu-
ent. After completion of the reaction as indicated by TLC,
the reaction mixture was cooled, the solid residue was dis-
solved in hot EtOH and the catalyst was filtered off. The fil-
trate solution was evaporated under vacuum, and the solid
crude product was purified by recrystallized from ethanol
for more purification.
A well stirred solution of methyl acrylate (40 mmol,
3.4 mL) in methanol (15 ml) was added to the stirred solu-
tion of P0.5 (1 g). The final mixture was stirred at room
temperature for 24 h. Then, the solid material (P1) was sep-
arated by filtration, washed with hot methanol for 6 h in a
Soxhlet apparatus to remove the unreacted starting materi-
als and then finally dried in a vacuum oven at 60 °C. Then,
bis(3-aminopropyl) amine (40 mmol, 4.8 mL) was added to
a stirred solution of P1 (1 g) in 15 mL methanol. The final
mixture was refluxed with continuous stirring under inert
atmosphere for 6 h Final product (P1.5) was filtered, washed
with hot methanol for 6 h in a Soxhlet apparatus to remove
the unreacted starting materials and then dried in a vacuum
oven at 60 °C [23].
General procedure for the synthesis
of 2H‑indazolo[2,1‑b]phthalazine‑triones by ultrasound
irradiation
Synthesis of H3PW12O40 nanoparticles (PWAn)
Dimedone (1 mmol), aldehyde (1 mmol), hydrazinium
hydroxide (1.2 mmol) and phthalic anhydride (1 mmol)
were added to Dendrimer-PWAn catalyst (0.015 g,
0.21 mol %) in a 25 mL Pyrex flask. The mixture was con-
tinuously irradiated for the appropriate time (Table 2) at
room temperature (solid paste using a drop of acetonitrile
was prepared in case of solid aldehydes). The reactions
were followed by thin layer chromatography (TLC) using
hexane/ethyl acetate (3:1). The temperature was controlled
and fixed at room temperature by pouring cold water in the
bath in the case of any elevation of temperature. After com-
pletion of the reaction as indicated by TLC, the solid resi-
due was dissolved in hot EtOH and the catalyst was filtered
off. The filtrate solution was evaporated under vacuum, and
the solid crude product was purified by recrystallized from
ethanol for more purification.
PWAn nanoparticles were prepared in our previous work
[18]. H3PW12O40 nanoparticles (which were labeled as
PWAn) were composed by heat treatment of their bulky
forms in an autoclave. HPAs are soluble in polar solvents
such as methanol and water but are insoluble in non-polar
solvent such as hexane. In a typical procedure, 0.3 mmol
of bulk H3PW12O40.14H2O (PWAb) was dispersed in 50 ml
hexane and the obtained mixture was stirred vigorously for
30 min at room temperature in order to forming a homo-
geneous dispersion. This dispersion was transferred into
a Teflon-lined stainless autoclave and filled 80 % of its
total volume. The autoclave was sealed and maintained at
150 °C for 12 h and then was cooled to room temperature.
Finally, the produced powder was filtered and dried in a
vacuum at 60 °C for 12 h.
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J IRAN CHEM SOC
Fig. 2 XRD patterns of a nSiO2, b P1.5, c PWAn and d Dendrimer-
PWAn nanoparticles
The presence of bands in the FT-IR spectra at 696 (C–Cl),
1000–1150 (Si–O–Si), 1472 (CH2 bending) and 2845–
2915 cm−1 (C–Haliph) confirms the synthesis of nSiO2–Cl
(Fig. 1b) [31]. Figure 1c shows the FT-IR spectrum of
n-SiO2–NH2 nanoparticles; the peaks at 1000–1150, 1271
and 1589 cm−1 are attributed to Si–O–Si (asymmetric
stretching), C–N (stretching vibration) and N–H (bend-
ing), respectively [27]. Also, the absorption peaks in the
regions 2854–2916 and 3100–3300 cm−1 are associated to
C–H stretching of the methylene groups and N–H stretch-
ing (Fig. 1c). Complete conversion of amine (n–SiO2–
NH2) to ester (P0) and ester to amide (P0.5) was proven by
FT-IR spectra. Figure 1d shows the FT-IR spectrum of P0
nanoparticles, the presence of absorbances at 2808–2924,
1735, 1288, 1234 and 1000–1150 are attributed to CH
(stretching), C=O (ester stretching), C–O (stretching),
C–N (stretching) and Si–O–Si, respectively [32]. From
the IR spectra presented in Fig. 1e, the absorption peaks
at 1642 cm−1 belonged to the stretching vibration mode
of amide peaks in P0.5 nanoparticles. Also, the presence
of vibration bands in 3400 (O–H stretching), 3100–3300
(N–H stretching), 2841–2920 (C–H stretching), 1471 (CH2
bending), 1241 (C–N) and 1000–1150 (Si–O–Si stretching)
demonstrates the existence of P0.5 nanoparticles in the spec-
trum (Fig. 1e) [32].
Fig. 1 FT-IR spectra a nSiO2, b nSiO2–Cl, c nSiO2–NH2, d P0, e P0.5
,
f PWAn and g Dendrimer-PWAn nanoparticles
Results and discussion
Catalyst characterization
FT-IR spectra of nSiO2, nSiO2–Cl, nSiO2–NH2, P0, P0.5
,
PWAn and Dendrimer-PWAn nanoparticles are shown in
Fig. 1a–g. The bands centered around 3400 and 1620 cm−1
are, respectively, assigned to the O–H stretching and
deforming vibrations of adsorbed water. The adsorption
peaks at 1103 and 794 cm−1 corresponds to the antisym-
metric and symmetric stretching vibration of Si–O–Si bond
in oxygen-silica tetrahedron, respectively (Fig. 1a) [27].
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J IRAN CHEM SOC
FT-IR spectroscopy, as a means of providing the struc-
ture of the HPAs, is convenient and widely is used for
the characterization of heteropolyacids [18]. The FT-IR
spectrum for PWAn shows four bands in the range 500–
1200 cm−1 that these bands are assigned at 764, 872, 972
and 1080 cm−1, which are correspond to νas(W-Oe-W),
νas(W-Oc-W), νas(W-Ot) and νas(P-O*), respectively [18].
It also shows a weak band in the region of 586 cm−1 that
corresponds to the δ(P–O) vibration [18]. In the case of
Dendrimer-PWAn nanoparticles, the peak at 1080 cm−1
overlap with Si–O–Si stretching vibration, however, new
peaks and non-overlapped bands at 977, 881 and 769 cm−1
are observed on FT-IR spectra of Dendrimer-PWAn, indi-
cating that PWAn was anchored to P1.5 successfully.
The hydrodynamic diameter of nanoparticles is deter-
mined by the DLS technique. This size distribution is cen-
tered at a value of 25, 30, 40 and 55 nm for nSiO2, PWAn,
Dendrimer-PWAn and Dendrimer-PWAn after six cycles,
respectively (Fig. 3e–h).
The presence of PWAn species anchored on the sup-
port was also confirmed by UV–vis spectroscopy. Diffuse
reflectance UV–visible spectra of nSiO2, PWAn and Den-
drimer-PWAn are shown in Fig. 4A. Nanosilica shows no
absorption in the UV–vis region. PWAn shows absorption
band at 257 nm which is attributed to oxygen-tungsten
charge transfer absorption bands for the Keggin anion
[34]. On anchoring with P1.5 nanoparticles, the 257 nm
band is shifted to 263 nm reconforming the presence of
PWAn in P1.5. According to the UV–vis analysis, PWAn
species indeed have been immobilized onto the support of
P1.5.
XRD analysis of the nSiO2, P1.5, PWAn and Dendrimer-
PWAn nanoparticles is shown in Fig. 2. The diffraction peak
which appeared at about 2Ɵ = 10–20° in the structures is
attributed to the amorphous silica gel (Fig. 2a, b, d) [33].
For P1.5 and Dendrimer-PWAn nanoparticles, the broad
peak was transferred to lower angles due to the synergetic
effect of amorphous silica and dendritic polymer (Fig. 2b,
d). The strong characteristic peaks at 2Ɵ = 10.55o, 21.10o,
25.95o, 30.33o and 35.30o in Fig. 2c, are assigned to Keggin
structure of PWAn [JCPDS File 50-0657] [18]. Also, the
XRD pattern of Dendrimer-PWAn nanoparticles, showing
the peaks of both amorphous silica and PWAn and the dif-
fraction peak at 25.95o and 35.30o indicates that PWAn was
anchored to P1.5 successfully.
Morphology and structure of the synthesized materials
were firstly investigated by TEM images. It is clear that the
synthesized SiO2 nanoparticles are well dispersed, but also
in some areas bigger structures with non-spherical mor-
phology are observed, more likely coming from aggrega-
tion of individual nanoparticles. The size distribution of
these spheres is relatively uniform and their average diam-
eter is 25 nm. Figure 3b displays the TEM image of PWAn
nanoparticles. The size of nanoparticles obtained from the
TEM image, turned out to be approximately 30 nm for
PWAn, and their shape is nearly spherical. Figure 3c repre-
sented of TEM of Dendrimer-PWAn nanoparticles. As illus-
trated, surface fictionalization of nanosilicate with dendritic
polymer supported nano H3PW12O40 caused nanoparticle
aggregated and size of them arise to about 40 nm. In TEM
image of these particles PWAn nanoparticles clearly were
seen (Fig. 3c). Also, to confirm if any aggregation of the
PWAn nanoparticles occurs, TEM analysis of the reused
catalyst was performed (Fig. 3d). After six repeated reac-
tion cycles, we did not observe significant change in the
morphology of the catalyst, but some PWAn particles might
have aggregated onto the surfaces of the matrices. This may
take place through the leaching/re-deposition processes
during the catalytic reactions.
Figure 4B depicts the TGA results of nSiO2-Cl, nSiO2-
NH2, P0, P0.5 and Dendrimer-PWAn.
TGA with heating from room temperature to 700 °C
under a nitrogen atmosphere were conducted to determine
the amount of organic composition in the modified silica
nanoparticles. The TGA plots of samples depicted a two-
step thermal decomposition.
According to Fig. 4B, the nanoparticles exhibit a weight
loss in the range of 50–200 °C corresponding to the loss
of physically adsorbed water and residual solvent from
the surface of the silica nanoparticles, while weight loss
between 200 and 430 °C was due to the removal of organic
moieties on the surface [35].
The weight loss of Dendrimer-PWAn NPs was 49.4 %,
while only 5.7, 12.1, 21.4 and 31.6 % for nSiO2-Cl, nSiO2-
NH2, P0 and P0.5 NPs over the whole temperature range
(Fig. 4B a–e).
The textural properties of n-SiO2 and Dendrimer-PWAn
were evaluated from the nitrogen adsorption–desorption
isotherms (Fig. 4C) and the respective specific surface area
(BET method), pore volume (BJH method) and average
pore radius were calculated.
It can be clearly seen that N2 adsorption–desorption
isotherms of n-SiO2 and Dendrimer-PWAn all show rep-
resentative type-IV curves with type H1 hysteresis loops,
indicating the presence of textual mesopores. The average
pore radius of n-SiO2 is 10.2 nm, and its BET surface area
and pore volume are calculated to be 531 and 1.3 cm3 g−1
,
respectively. After dendrimer encapsulated PWAn func-
tionalization, the average pore radius, BET surface area,
and pore volume of Dendrimer-PWAn decrease to 6.1 nm,
479 m2 g−1, and 0.6 cm3 g−1, respectively. This indicates
that pore volume decreases upon grafting of dendritic poly-
mer molecules within the pore structure or in other words
thickness of pore wall increases.
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J IRAN CHEM SOC
Fig. 3 TEM images of: a
nSiO2, b PWAn, c Dendrimer-
PWAn and d Dendrimer-PWAn
after six cycles; particle size
distribution results for e nSiO2,
f PWAn, g Dendrimer-PWAn
and h Dendrimer-PWAn after
six cycles
Brönsted or Lewis acidity of the Dendrimer-PWAn
catalyst was distinguished by studying the FTIR spec-
trum of the catalyst after reaction with pyridine (Fig. 4D).
Pyridine molecules were adsorbed on Lewis acid sites
(1610 and 1450 cm−1) and formed the pyridinium ion by
interaction with Brönsted acid sites (1640 and 1540 cm−1
)
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Fig. 4 A UV–Vis spectra of nSiO2, PWAn and Dendrimer-PWAn; B
Thermogravimetric analysis of a n-SiO2–Cl, b n-SiO2–NH2, c P0, P0.5
and Dendrimer-PWAn nanoparticles; C Nitrogen adsorption–desorp-
tion isotherms of nSiO2, and Dendrimer-PWAn; D FT-IR spectra a
Dendrimer-PWAn, and pyridine adsorption of b Dendrimer-PWAn, E
TGA and F elemental analysis (EA) results for the synthesis of Den-
drimer-PWAn nanoparticles
[18]. Both types of adsorbed species contribute to the
band at 1490 cm−1. The formation of pyridinium ion was
observed by absorptions at 1485, 1544 and 1643 cm−1
(Fig. 4D b). It should be mentioned that absorption band
at 1643 cm−1 is not totally conclusive although considered
as pyridinium ion because of contributions of pyridinium
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J IRAN CHEM SOC
ion and moisture, since the spectrum was taken at ambient
conditions.
A summary of the TGA and elemental analysis data
is included in Fig. 4. A good agreement was observed
between elemental analysis and TGA data for these
conversions.
reaction was refluxed in the presence of 0.14 mol % of
Dendrimer-PWAn and a variety of solvents such as H2O,
EtOH, EtOH:H2O [1/1(v/v)], DMF, CH2Cl2 and CH3CN.
The represented data in Table 1 showed the correspond-
ing products were obtained in 66, 68, 51, 62, 33, and 56 %
yield, respectively, after 1 h (Table 1, entries 1–5 and 7).
We also checked the model reaction in refluxing toluene
as a solvent in the presence of 0.14 mol % of Dendrimer-
PWAn and the corresponding products were obtained in
44 % yield (Table 1, entry 6). As it was shown in Table 1
the best result was obtained when the model reaction was
carried out under solvent-free condition in the presence of
0.14 mol % of Dendrimer-PWAn at 80 °C and the desired
product was obtained in high yields after 10 min (Table 1,
entry 8). The model reaction was also examined in absent
of catalyst under solvent‐free conditions at 100 °C and the
reaction did not proceed even after 3 h (Table 1, entry 9).
Then we decided to check the model reaction under sol-
vent-free condition at 80 °C and various amount of cata-
lyst. As it was shown in Table 1 the best result was obtained
when we carried out the model reaction in the presence
of 0.14 mol % of catalyst. This condensation was carried
out with low amounts of Dendrimer-PWAn of 0.07 and
Also, in this article, determination of PWAn content was
performed by inductively coupled plasma-atomic emis-
sion spectroscopy (ICP-AES). According to the ICP-AES
analysis, the amounts of PWAn immobilized on nanosilica
supported dendritic polymer was found to be 39.7 wt %
(0.14 mmol/g).
Synthesis of 2H‑indazolo[2,1‑b]phthalazine‑triones
in the presence of Dendrimer‑PWAn catalyst
Due to ability of Dendrimer-PWAn as a mild and efficient
acid catalyst, we decided to apply this catalyst for synthesis
of 2H-indazolo[1,2-b] phthalazine-triones.
Initially to obtain the best reaction conditions, the reac-
tion of benzaldehyde (1 mmol), dimedone (1 mmol),
hydrazinium hydroxide (1.2 mmol) and phthalic anhy-
dride (1 mmol) was chosen as a model reaction. The model
Table 1 Optimization of the
Entry
Catalyst amount (mol %)
Solvent
Condition
Time (min)
Yield (%)a
amount of catalyst, solvent
and temperature in a one-pot
four-component synthesis of the
model reaction
1
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
None
0.07
0.11
0.17
0.20
0.14
0.14
0.14
0.14
None
0.07
0.14
0.18
0.21
0.25
EtOH
Reflux
Reflux
120 °C
Reflux
Reflux
Reflux
Reflux
80 °C
100 °C
80 °C
80 °C
80 °C
80 °C
rt
60
60
60
60
60
120
60
10
180
30
15
10
10
60
30
20
10
60
60
20
10
10
15
68
51
62
56
33
44
66
93
–
2
EtOH-H2O [50/50(v/v)]
DMF
3
4
CH3CN
5
CH2Cl2
6
Toluene
7
H2O
8
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
77
88
92
90
34
83
90
92
–
50 °C
70 °C
90 °C
)))), rt
)))), rt
)))), rt
)))), rt
)))), rt
)))), rt
56
74
87
94
94
Reaction conditions benzaldehyde (1 mmol), dimedone (1 mmol), hydrazinium hydroxide (1.2 mmol),
phthalic anhydride (1 mmol), Dendrimer-PWAn catalyst and solvent (3 mL)
a
Isolated yield
1 3

J IRAN CHEM SOC
0.11 mol % and the corresponding products were obtained
in longer reaction times and lower yields (Table 1, entries
10 and 11). On the other hand, higher amounts of catalyst
did not improve the yield or reaction time (Table 1, entries
12, 13). The effect of temperature was also studied by car-
rying out the model reaction in the presence of 0.14 mol %
of catalyst at RT, 50, 70 and 90 °C under solvent-free con-
dition. It was observed that the corresponding products
were obtained in 34, 83, 90 and 92 % yield, respectively
(Table 1, entries 14–17).
Considering the ability of ultrasonic irradiation for the
acceleration of organic reactions, we examined the model
reaction under ultrasonic irradiation and solvent-free condi-
tion at room temperature in presence of various amount of
catalyst. As it is clear from Table 1, the best results were
obtained in the presence of 0.21 mol % of catalyst (Table 1,
entry 22).
However, synthesis of organic compounds under ultra-
sound irradiation has been limited by the need for a spe-
cialized apparatus that may not be available in many
laboratories. Because of this limitation, herein we report
both ultrasonic irradiation in presence of 0.21 mol % of
catalyst at room temperature and solvent-free condition in
the presence of 0.14 mol % of catalyst at 80 °C (Table 1,
entries 22 and 8) for the synthesis of 2H-indazolo[1,2-b]
phthalazine-triones.
time, probably due to the low reactivity of aliphatic alde-
hydes in compare with aromatics.
A proposed mechanism for the synthesis of 2H-indazolo
[2,1-b] phthalazine-triones outlined in Scheme 2. Based
on this mechanism, as shown in Scheme 2, the reaction
occurs in step 1 via initial formation of the phthalhydrazide
by nucleophilic addition of hydrazinium hydroxide to
phthalic anhydride followed by dehydration. The second
step involves initial formation of heterodyne by standard
Knoevenagel condensation of dimedone and aldehyde.
Subsequent Michael-type addition of the phthalhydrazide
followed by cyclization affords the corresponding product
[41] (Scheme 2).
To compare the reactivity of the Dendrimer-PWAn
with previously reported catalysts, a comparative chart is
presented in Table 3. Although, all the catalysts listed in
Table 3 were able to produce good yields of corresponding
products, however some of these reactions were carried out
under harsh reaction conditions such as toxic solvents and
high temperature (Table 3, entries 5 and 9). Some of these
need very long reaction time (Table 3, entry 12). Moreo-
ver, some of the catalysts listed in Table 3 are not reus-
able. Thus, our reusable catalyst and green methodologies
have been established as a better alternative compared to
the reported methods for the fabrication of corresponding
products.
After optimizing the reaction conditions, the generality
of this catalytic system was confirmed by the employment
of a series of aldehydes, dimedone, hydrazinium hydrox-
ide and phthalic anhydride to obtain desired products under
the optimized conditions. The results are summarized in
Table 2.
As it is shown in Table 2, based on the optimized reac-
tion conditions, we studied the reaction with a wide range
of aromatic aldehydes with electron donating and electron
withdrawing groups. Both electron-rich and electron-defi-
cient aldehydes worked well and give high yields of prod-
ucts under both solvent-free and ultrasonic irradiation in
short reaction times. Thus, the nature and position of sub-
stitution in the aromatic ring did not affect the reactions
much (Table 2, entries 2–19).
The reusability and recovery of the catalyst are impor-
tant issues, especially when the reactions use solid cata-
lysts. Thus, the recovery and reusability of catalyst
were investigated for the preparation of 3,4-dihydro-
3,3-dimethyl-13-phenyl-2H-indazolo[2,1-b]phthalazine-
1,6,11(13H)-trione (5a) under ultrasound irradiation at
room temperature and solvent-free conditions at 80 °C
(Fig. 5). The catalyst was recovered after each run, washed
with hot ethanol (2 × 10 mL), dried in an oven at 60 °C
for 180 min prior to use and tested for its activity in the
subsequent run. The performance of the recycled catalyst
in reaction up to six successive runs was shown in Fig. 5.
These bar diagrams clearly suggest that the desired prod-
ucts were obtained in high yields without distinct deteriora-
tion in catalytic activity.
Also both of our methodologies have been successfully
used for heteroaromatic aldehydes that are acid sensitive
species such as thiophene-2-carbaldehyde, 5-bromothio-
phene-2-carbaldehyde, indole-3-carbaldehyde and pyri-
dyne-2-carbaldehyde and the corresponding products were
obtained in excellent yields without the formation of any
byproduct (Table 2, entries 21–24). We also checked ali-
phatic aldehydes (Table 2, entries 25–27), the yields were
quite reasonable. Aliphatic aldehydes gave the correspond-
ing product in moderate yield and required more reaction
To determine the degree of leaching of the metal from
the heterogeneous catalyst, the catalyst was removed by
using a magnetic field and the Tungsten (W) amount in
reaction medium after each reaction cycle was measured
through Inductively Coupled Plasma (ICP) analyzer. The
amount of W leaching after the first run was determined by
ICP analysis to be only 0.28 %, and after six repeated recy-
cling was 4.34 %. Therefore, the analysis of the reaction
mixture by the ICP technique showed that the leaching of
H3PW12O40 was negligible.
1 3

J IRAN CHEM SOC
Table 2 One-pot four-component synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives catalyzed by Dendrimer-PWAn
Solvent-free/80oC
Ultrasonic/r.t
Aldehyde
Product
M.p. oC (Lit.)
Time
(min)
Yield
Time
(min)
Yield
(%)b
(%)b
O
O
CHO
1
204-205 (206-208)[36]
N
10
93
10
94
N
O
O
5a
Cl
CHO
O
2
10
15
92
89
260-261 (260-262)[37]
10
15
91
90
N
N
Cl
O
O
5b
Cl
Cl
O
CHO
267-268 (266-267)[36]
N
N
3
4
O
O
5c
Br
CHO
O
N
N
18
15
10
91
94
95
10
88
264-265 (265-267)[10]
Br
O
O
5d
Cl
Cl
Cl
O
CHO
5
218-220 (219-221)[9]
8
95
N
Cl
N
O
O
5e
NO2
CHO
O
217-218 (215-217)[36]
10
94
N
N
6
O2N
O
O
5f
NO2
O
O2N
CHO
N
N
7
15
87
10
90
268-270 (269-272)[38]
O
5g
1 3

J IRAN CHEM SOC
Table 2 continued
Solvent-free/80oC
Ultrasonic/r.t
Aldehyde
Product
M.p. oC (Lit.)
Time
(min)
Yield
Time
(min)
Yield
(%)b
(%)b
CF3
CHO
O
O
8
216 (214-216)[36]
10
90
12
88
N
N
F3C
O
O
5h
F
CHO
O
9
12
10
89
88
15
15
92
86
219-221 (221-222)[37]
N
N
F
O
O
5i
F
O
CHO
268-269 (270-272)[39]
10
N
N
F
O
O
5j
F
NO2
O
O2N
F
CHO
10
94
10
93
226-228 (225-227)[11]
N
N
11
12
O
O
5k
OMe
CHO
O
12
87
15
90
220-222 (218-220)[36]
N
N
MeO
O
5l
Me
CHO
O
O
13
229-230 (227-229)[36]
20
89
20
91
N
N
Me
O
5m
1 3

J IRAN CHEM SOC
Table 2 continued
Solvent-free/80oC
Ultrasonic/r.t
Aldehyde
Product
M.p. oC (Lit.)
Time
(min)
Yield
Time
(min)
Yield
(%)b
(%)b
Me
O
O
CHO
N
N
14
15
20
12
91
93
25
10
88
91
238-240 (239-241)[36]
Me
O
O
5n
SMe
CHO
O
230-232 (230-231)[37]
N
N
MeS
PhO
O
O
5o
5p
OPh
O
CHO
N
N
16
10
91
185-186 (183-185)[36]
15
93
O
CHO
O
O
O
17
229-230 (230-232)[36]
15
85
12
87
N
N
5q
OMe
OMe
OMe
OMe
O
O
O
MeO
MeO
CHO
18
15
89
20
86
185-187
N
N
5r
O
CHO
19
10
90
15
92
160-162
O
O
O
O
N
N
5s
1 3

J IRAN CHEM SOC
Table 2 continued
Solvent-free/80oC
Ultrasonic/r.t
Aldehyde
Product
M.p. oC (Lit.)
Time
(min)
Yield
Time
(min)
Yield
(%)b
(%)b
CHO
10
92
249-251 (250-252)[40]
12
91
20
O
O
N
N
O
O
5t
CHO
N
O
231-232 (230-232)[37]
8
92
90
10
15
89
93
N
21
N
N
O
O
5u
5v
S
O
10
219-220
CHO
N
N
22
23
S
O
S
Br
O
O
12
91
CHO
10
88
205-207
N
S
N
Br
O
5w
NH
CHO
O
O
O
250-251 (248-250)[36]
20
93
18
91
N
N
24
N
H
5x
O
O
CHO
N
25
26
20
20
87
78
25
30
86
74
219-221 (220-222)[37]
N
O
O
5y
O
N
N
145-147 (146-148)[40]
CHO
O
5z
O
O
O
27
84-86 (82-85)[9]
CH3(CH2)5CHO
30
77
25
73
N
N
5aa
Reaction conditions aldehyde (1 mmol), dimedone (1 mmol), hydrazinium hydroxide (1.2 mmol), phthalic anhydride (1 mmol), Dendrimer-
PWAn catalyst (0.14 mol %/solvent-free/80 °C, 0.21 mol %/ultrasonic/r.t)
a
Isolated yield
1 3

J IRAN CHEM SOC
Scheme 2 Suggested mechanism for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones in the presence of Dendrimer-PWAn catalyst
phthalazine-triones via a one-pot, four-component con-
densation reaction of aldehydes, phthalic anhydride,
hydrazinium hydroxide, and dimedone under solvent-
free ultrasound irradiation at room temperature as well as
solvent-free conditions at 80 °C. The attractive features
of this protocol are high catalytic activity, thermal sta-
bility, heterogeneous nature of the catalyst, operational
simplicity, cleaner reactions, reduced reaction times, eco-
friendly promising strategy, satisfactory yields of prod-
ucts, lower loading of catalyst compared with the other
methods, and avoidance of using hazardous organic sol-
vents that makes this method an instrumental alternative
to the previous methodologies for the scale up of these
one-pot four-component reactions. In addition, the cata-
lyst could be successfully recycled and reused at least for
six runs without significant loss in activity.
Conclusion
In summary, we report for the first time a novel kind of
dendrimer-encapsulated phosphotungstic acid nano-
particles immobilized on nanosilica with surface amino
groups. The catalyst was successfully synthesized and
structural, surface and morphological of these nanopar-
ticles were evaluated. TEM indicate that the silica nano-
particles have been well-coated with dendrimer-encapsu-
lated phosphotungstic acid nanoparticles. The crystallite
size obtained from X-ray line profile fitting is compara-
ble with the particle size obtained from TEM. The FT-IR
and TGA results demonstrated the formation of Dendritic
Polymer in the presence of the SiO2 NPs. Therefore,
the Dendrimer-PWAn is synthesized and can efficiently
catalyze the green synthesis of 2H-indazolo[1,2-b]
1 3

J IRAN CHEM SOC
Table 3 Comparison of our
results with previously reported
methods
Entry
Catalyst
Conditions
Time (min)
Yield (%)a
Ref.
1
2
Mg(HSO4)b2
PMA–SiOb2
Nano-alumina sulfuric acidb
Ce(SO4)2.4H2Oc
PBBSb
[TMG][Ac]c
TMSClb
PEG-OSO3Hc
hexafluoro-2-propanolb
H2SOb4
Solvent-free/100 °C
Solvent-free/80 °C
Solvent-free/110 °C
Solvent-free/125 °C
Solvent-free/100 °C
Solvent-free/80 °C
Reflux/CH3CN/DMF
Solvent-free/80 °C
Solvent-free/55 °C
[bmim]BF4/80 °C
H2O-EtOH/Reflux
Solvent-free/80 °C
Ultrasonic/r.t
10
30
14
6
85
85
85
78
65
92
86
87
92
91
88
90
87
93
93
94
[42]
[39]
3
[43]
4
[41]
5
25
15
30
13
480
35
30
15
20
10
10
10
[9]
6
[40]
7
[38]
8
[44]
9
[45]
10
[46]
[46]
11
(S)-camphorsulfonic acidb
[10]
[10]
12
13
[Bmim]Brc
Dendrimer-PWAn
Ultrasonic/r.t
[47]
Solvent-free/80 °C
Ultrasonic/r.t
This work
This work
a
Yields refer to the isolated pure products
b
c
Based on the reaction of benzaldehyde, dimedone and phthalhydrazide
Based on the reaction of benzaldehyde, dimedone, phthalic anhydride and hydrazinium hydroxide
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑chlorophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5b)
1
White powder, M.P. = 260–261 °C, H NMR (500 MHz,
CDCl3) δ: 1.23 (s, 6H), 2.36 (s, 2H), 3.26 (d, 1H,
AB system, J = 18.90 Hz), 3.43 (d, 1H, AB system,
J = 18.84 Hz), 6.44 (s, 1H), 7.29-7.37 (m, 4H), 7.88–
7.90 (m, 2H), 8.30–8.38 (m, 2H). 13C NMR (125 MHz,
CDCl3) δ: 28.5, 28.7, 34.7, 38.0, 50.9, 64.3, 118.1, 127.7,
128.1, 128.5, 128.8, 128.9, 129.0, 133.7, 134.5, 134.6,
134.9, 151.1, 154.3, 156.0, 192.2; IR (KBr, cm−1): 2960,
1665, 1628, 1361, 1313, 1264, 786; Anal. Calcd for
Fig. 5 Recyclability of Dendrimer-PWAn in the synthesis of 5a
under the optimized conditions
C23H19ClN2O3: C, 67.90; H, 4.71; N, 6.89 %, Found: C,
67.94; H, 4.65; N, 6.81 %.
Selected spectral data
3,4‑Dihydro‑3,3‑dimethyl‑13‑(2‑chlorophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5c)
3,4‑Dihydro‑3,3‑dimethyl‑13‑phenyl‑2H‑indazolo[2,1‑b]
phthalazine‑1,6,11(13H)‑trione (5a)
1
Yellow powder, M.P. = 267–268 °C, H NMR (500 MHz,
1
CDCl3) δ: 1.23 (s, 6H), 2.34 (s, 2H), 3.26 (d, 1H,
AB system, J = 18.98 Hz), 3.42 (d, 1H, AB system,
J = 19.00 Hz), 6.7 (s, 1H), 7.24-7.50 (m, 4H), 7.87-8.39
(m, 4H); 13C NMR (125 MHz, CDCl3) δ: 28.8, 29.2,
35.0, 38.4, 51.3, 64.4, 116.7, 127.6, 128.1, 128.4, 129.1,
129.4, 130.2, 130.9, 132.0, 133.0, 133.9, 134.9, 152.2,
154.6, 156.6, 192.4; IR (KBr, cm−1): 2957, 1661, 1622,
1467, 1472, 1359, 1311, 1267, 791; Anal. Calcd for
C23H19ClN2O3: C, 67.90; H, 4.71; N, 6.89 %, Found: C,
67.83; H, 4.66; N, 6.94 %.
Yellow Powder, M.P. = 204–205 °C, H NMR (500 MHz,
CDCl3) δ: 1.23 (s, 6H), 2.36 (s, 2H), 3.27 (dd,1H,
J = 19.01 Hz and 2.07 Hz), 3.44 (d, 1H, J = 19.01 Hz),
6.4 (s, 1H), 7.29–7.37 (m, 5H), 7.44 (d, 2H, J = 7.2 Hz),
7.86–7.87 (m, 2H), 8.28–8.36 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ: 28.9, 29.1, 35.0, 38.4, 51.3, 95.4, 119.0, 127.5,
128.2, 128.4, 129.1, 129.4, 129.5, 133.9, 134.9, 136.8, 151.2,
154.7, 156.4, 192.5; IR (KBr, cm−1): 2952, 1667, 1578,
1356, 1304, 1271; Anal. Calcd for C23H20N2O3: C, 74.18; H,
5.41; N, 7.52 %, Found: C, 74.11; H, 5.47; N, 7.57 %.
1 3

J IRAN CHEM SOC
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑bromophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5d)
867, 697; Anal. Calcd for C23H19N3O5: C, 66.18; H, 4.59;
N, 10.07 %, Found: C, 66.23; H, 4.66; N, 10.04 %.
1
White powder, M.P. = 264-265 ◦C, H NMR (500 MHz,
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑fluorophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5i)
CDCl3) δ: 1.23 (s, 6H), 2.36 (s, 2H), 3.26 (d, 1H, AB sys-
tem, J = 19.02 Hz), 3.42 (d, 1H, AB system, J = 19.00 Hz),
6.42 (s, 1H), 7.29–7.4 (m, 4H), 7.8–8.3 (m, 4H). 13C NMR
(125 MHz, CDCl3) δ: 28.5, 28.7, 34.7, 38.0, 50.9, 64.4,
118.0, 122.8, 127.8, 128.1, 128.8, 128.9, 129.0, 131.9,
133.7, 134.7, 135.5, 151.1, 154.4, 156.0, 192.1; IR (KBr,
cm−1): 2957, 1656, 1623, 1573, 1471, 1308, 1267; Anal.
Calcd for C23H19BrN2O3: C, 61.21; H, 4.24; N, 6.21 %,
Found: C, 61.13; H, 4.29; N, 6.27 %.
1
Yellow powder, M.P. = 219–221 °C, H NMR (500 MHz,
CDCl3) δ: 1.24 (s, 6H), 2.36 (s, 2H), 3.26 (dd, 1H, AB sys-
tem, J = 19.06 Hz, J = 2.21 Hz), 3.43 (dd, 1H, AB sys-
tem, J = 19.34 Hz, J = 1.20 Hz), 6.46 (s, 1H), 7.02–7.06
(m, 2H), 7.40–7.44 (m, 2H), 7.86-7.89 (m, 2H), 8.27–8.39
(m, 2H); 13C NMR (125 MHz, CDCl3) δ: 28.8, 29.1, 35.1,
38.4, 51.3, 64.7, 116.0, 116.2 (d, JC–F = 276 Hz), 118.6,
128.1, 128.4, 129.3, 129.4, 132.6, 134.0, 135.0, 151.4,
154.8, 156.4, 162.1, 164.1, 192.5; IR (KBr, cm−1): 2958,
2867, 1664, 1655, 1626; 1473, 1309; Anal. Calcd for
C23H19FN2O3: C, 70.76; H, 4.91; N, 7.18 %, Found: C,
70.69; H, 4.85; N, 7.09 %.
4.2.5. 3,4‑Dihydro‑3,3‑dimethyl‑13‑(2,4‑dichlorophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5e):
1
Yellow powder, M.P. = 218–220 °C, H NMR (500 MHz,
CDCl3) δ: 1.21 (s, 3H), 1.23 (s, 3H), 2.33 (s, 2H), 3.20–3.44
(2H, AB system, J = 19.2 Hz), 6.64 (s, 1H), 7.26–8.42 (m,
7H); 13C NMR (125 MHz, CDCl3) δ: 28.4, 28.7, 34.6, 38.0,
50.8, 63.5, 118.1, 127.6, 127.7 (2C), 128.1, 128.6, 129.0,
131.1, 131.7, 133.2, 133.7, 134.6, 135.1, 152.0, 154.3,
156.1, 192.1; IR (KBr, cm−1): 2967, 1664, 1627; 1473,
1369, 1253, 772; Anal. Calcd for C23H18Cl2N2O3: C, 62.60;
H, 4.10; N, 6.35 %, Found: C, 62.71; H, 4.16; N, 6.31 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(2‑fluorophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5j)
Yellow powder, M.P. = 268–269 °C, 1H NMR (500 MHz,
CDCl3) δ: 1.18 (s, 3H), 1.22 (s, 3H), 2.31 (s, 2H), 3.41,
3.22 (2H, AB System, J = 19.06 Hz,), 6.54 (s, 1H), 7.01 (t,
1H, J = 10.36 Hz), 7.14 (t, 1H, J = 7.63 Hz), 7.26–7.31 (q,
1H), 7.44 (t, 1H, J = 7.31 Hz), 7.87–7.89 (m, 2H), 8.19–
8.21 (m, 1H), 8.33–8.35 (m, 1H); 13C NMR (125 MHz,
CDCl3) δ: 27.2, 28.0, 33.8, 37.1, 50.0, 59.7, 114.9, 115.9,
123.5, 126.5, 127.2, 127.9, 128.2, 129.4, 129.5, 132.8,
133.7, 150.8, 153.3, 155.0, 159.2, 191.1; IR (KBr, cm−1):
2951, 2868, 1665, 1621, 1354, 1311.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑nitrophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5f)
1
Yellow powder, M.P. = 217–218 °C, H NMR (500 MHz,
CDCl3) δ: 1.21 (s, 3H), 1.24 (s, 3H), 2.1 (s, 2H), 3.2 (dd, 1H, AB
system, J = 19.10 Hz, J = 2.23 Hz), 3.43 (d, 1H, AB system,
J = 19.21 Hz), 6.53 (s, 1H), 7.61–7.64 (m, 2H), 7.90–7.91 (m,
2H), 8.20–8.41 (m, 4H); 13C NMR (125 MHz, CDCl3) ı: 28.8,
29.1, 31.3, 35.1, 38.4, 51.2, 64.5, 117.7, 128.2, 128.4, 128.6,
129.1, 129.3, 134.3, 135.2, 143.8, 148.3, 152.1, 154.9, 156.3,
192.4. %. IR (KBr, cm−1): 2973, 1697, 1617, 1660, 1525, 1368,
1148, 1102, 858, 701; Anal. Calcd for C23H19N3O5: C, 66.18; H,
4.59; N, 10.07 %, Found: C, 66.23; H, 4.55; N, 10.03 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑fluoro‑3‑nitrophenyl)‑2H‑i
ndazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5k)
Yellow powder, M.P. = 226–228 ◦C, 1H NMR (500 MHz,
CDCl3) δ: 1.22 (s, 6H), 2.35 (s, 2H), 3.42, 3.26 (2H,
AB system, J = 19.25 Hz,), 6.46 (s, 1H), 7.30 (d, 1H,
J = 8.50 Hz), 7.87–7.90 (m, 3H), 8.02 (dd, 1H, J = 9.25,
2.02 Hz,), 8.23–8.26 (m, 1H), 8.36–8.38 (m, 1H); 13C
NMR (125 MHz, CDCl3) δ: 28.4, 28.7, 34.7, 37.9, 50.7,
63.5, 116.7, 118.6, 118.8, 124.3, 127.6, 128.5, 128.9,
133.6, 133.9, 134.8, 135.2, 151.9, 154.7, 155.9, 192.1; IR
(KBr, cm−1): 2956, 2873, 1654, 1321, 1273.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(3‑nitrophenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5 g)
1
Yellow powder, M.P. = 268–270 °C, H NMR (500 MHz,
CDCl3) δ: 1.2 (s, 6H), 2.38 (s, 2H), 3.30 (dd, 1H, AB sys-
tem, J = 19.15 Hz, J = 2.12 Hz), 3.46 (d, 1H, AB sys-
tem, J = 19.20 Hz), 6.5 (s, 1H), 7.59 (t, 1H, J = 7.84 Hz),
7.89–7.93 (m, 3H), 8.19 (d, 2H, J = 8.75 Hz), 8.26–8.42
(m, 2H); 13C NMR (125 MHz, CDCl3) δ: 28.8, 29.1, 35.1,
38.4, 51.2, 64.6, 117.6, 121.9, 124.1, 128.1, 128.7, 129.1,
129.4, 130.1, 134.3, 134.6, 135.2, 139.05, 152.2, 192.5.
(KBr, cm−1): 2926, 1660, 1625, 1516, 1374, 1147, 1107,
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑methoxyphenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5l)
Yellow powder, M.P. = 220–222 °C, 1H NMR (500 MHz,
CDCl3) δ: 1.23 (s, 3 H), 1.24 (s, 3 H), 2.30 (s, 2 H), 3.21,
3.42 (2 H, AB system, J = 18.95), 3.75 (s, 3 H), 6.38 (s,
1 H), 6.35–8.80 (m, 8H); 13C NMR (125 MHz, CDCl3) δ:
1 3

J IRAN CHEM SOC
28.4, 28.7, 34.6, 38.1, 50.9, 55.1, 64.5, 114.1, 118.5, 127.6,
127.9, 128.3, 128.5, 128.9, 129.1, 133.4, 134.9, 1507,
154.2, 156.0, 159.6, 192.2; IR (KBr, cm−1): 2957, 1665,
1627, 1602, 1511, 1467, 1427, 1360, 1314, 1266, 1243,
1170, 1101, 1029, 842, 799, 701.
3H), 6.58 (s, 1H), 6.67 (d, 1H, J = 9.00 Hz), 7.08 (d, 1H,
J = 8.50 Hz), 7.86–7.88 (m, 2H), 8.29–8.31 (m, 1H), 8.38-
8.40 (m, 1H); 13C NMR (125 MHz, CDCl3) δ: 28.4, 28.6,
30.9, 34.7, 38.1, 51.0, 55.8, 56.1, 60.6, 60.9, 62.0, 118.3,
127.6, 127.9, 129.0, 129.2, 133.4, 134.4, 142.1, 151.0,
152.0, 154.0, 154.1, 156.1, 157.2, 192.3; IR (KBr, cm−1):
2963, 2651, 1667, 1366, 1287, 1099, 796; Anal. calcd
for C26H26N2O6: C, 67.52; H, 5.67; N, 6.06 %, Found: C,
67.48; H, 5.63; N, 6.09 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑methylphenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5m)
1
Yellow powder, M.P. = 229–230 ◦C, H NMR (500 MHz,
CDCl3) δ: 1.17 (s, 6H), 2.25 (s, 3H), 2.28 (s, 2H), 3.18,
3.37 (s, 2H, AB system, J = 18.80 Hz), 6.36 (s, 1H),
7.08–7.21 (m, 4H), 7.8 (m, 2H), 8.2–8.3 (m, 2H); 13C
NMR (125 MHz, CDCl3) δ: 21.6, 28.8, 29.1,35.0, 38.4,
51.3, 65.1, 118.9, 127.4, 128.0, 128.3, 129.3, 129.5, 129.7,
133.8, 134.8, 138.8, 151.1, 154.6, 156.3, 192.5; %; IR
(KBr, cm−1): 2898, 1661, 1652, 1602, 1596, 1491, 1085,
825, 788, 685, 624, 493.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑propoxy‑phenyl)‑2H‑indaz
olo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5s)
Yellow, M.P. = 160–162 °C, 1H NMR (500 MHz, CDCl3)
δ: 0.93 (t, 3H, J = 7.00 Hz), 1.23 (s, 3H), 1.25 (s, 3H),
1.73–1.79 (m, 2H), 2.37 (s, 2H), 3.26 (d, 1H, AB system,
J = 19.00 Hz), 3.44 (d, 1H, AB system, J = 19.00 Hz), 3.92
(t, 2H, J = 6.50 Hz), 6.44 (s, 1H), 6.86 (d, 2H, J = 8.5 Hz),
7.34 (d, 2H, J = 8.50 Hz), 7.86–7.88 (m, 2H), 8.29–8.30
(m, 1H), 8.36–8.38 (m, 1H); 13C NMR (125 MHz, CDCl3)
δ: 14.0, 22.4, 28.2, 28.5, 28.7, 28.9, 34.7, 38.1, 51.0, 64.6,
67.9, 114.6, 118.6, 127.7, 127.9, 128.0, 128.5, 129.0, 129.2,
133.5, 134.5, 150.7, 154.3, 156.1, 159.4, 192.3; IR (KBr,
cm−1): 2955, 1669, 1365, 704; Anal. calcd for C26H26N2O4:
C, 72.54; H, 6.09; N, 6.51 %, Found: C, 72.38; H, 5.94; N,
6.66 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑(methylthio)phenyl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5o)
Yellow powder, M.P. = 230–232 °C, 1H NMR (500 MHz,
CDCl3) δ: 1.21 (s, 6H), 2.34 (s, 2H), 2.42 (s, 3H), 3.21–
3.45 (2H, AB system, J = 18.50 Hz), 6.4 (s, 1H), 7.10–7.35
(dd, 4H, J = 8.45 Hz), 7.84–7.88 (2H, m), 8.25–8.37 (m,
2H); 13C NMR (125 MHz, CDCl3) δ: 15.5, 28.4, 28.7, 34.6,
38.0, 50.9, 64.6, 118.3, 126.6 (2C), 127.6 (2C), 127.7,
127.9, 128.9, 129.0, 133.0, 133.5, 134.5, 139.2, 150.9,
154.3, 156.0, 192.1; IR (KBr, cm−1): 2955, 1663, 1629,
1364, 1271, 697; Anal. Calcd for C24H22N2O3S: C, 68.90;
H, 5.30; N, 6.71 %, Found: C, 68.82; H, 5.21; N, 6.78 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(naphthalen‑2‑yl)‑2H‑indazol
o[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5t)
1
M.P. = 249-251 ◦C, H NMR (500 MHz, CDCl3) δ: 1.16
(s, 6H), 2.27 (s, 2H), 3.22 (d, 1H, J = 19.10 Hz), 3.41 (d,
1H, J = 19.15 Hz), 6.54 (s, 1H), 7.37–7.42 (m, 3H), 7.71–
7.90 (m, 6H), 8.16–8.33 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ: 28.7, 29.0, 35.0, 38.4, 51.3, 65.4, 118.8, 124.6,
126.6, 126.7, 127.2, 128.0, 128.0, 128.3, 128.6, 129.0,
129.4, 133.5, 133.7, 133.9, 134.1, 134.9, 151.3, 154.7,
156.4, 192.4; IR (KBr, cm−1): 2954, 1665, 1617, 1578,
1470, 1265; Anal. Calcd for C27H22N2O3: C, 76.76; H,
5.25; N, 6.63 %, Found: C, 76.61; H, 5.17; N, 6.51 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(4‑isopropylphenyl)‑2H‑inda
zolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5q)
Yellow powder, M.P. = 229–230 °C, 1H NMR (500 MHz,
CDCl3) δ: 1.22–1.25 (m, 12H), 2.37 (s, 2H), 2.9 (m, 1H),
3.26 (d, 1H, AB system, J = 19.05 Hz), 3.42 (d, 1H, AB
system, J = 19.05 Hz), 6.47 (s, 1H), 7.19–7.36 (m, 4H),
7.86–7.88 (m, 2H), 8.3–8.4 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ: 24.2, 28.5, 29.0, 34.1, 35.3, 35.9, 51.9, 64.8,
111.3, 112.0, 114.6, 118.3, 119.2, 121.4, 123.0, 123.9,
127.2, 127.5, 128.3, 128.4, 132.2, 132.3, 135.5, 136.8,
156.4, 158.8, 191.3.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(thiophen‑2‑yl)‑
2H‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5v)
1
Yellow powder, M.P. = 219–220 °C, H NMR (500 MHz,
CDCl3) δ: 1.22 (s, 6H), 2.34 (2H, AB system), 3.25
(1H, AB system, J = 18.5 Hz), 3.46 (1H, AB system,
J = 18.00 Hz,), 6.24 (s, 1H), 6.79 (d, 1H, J = 9.00 Hz),
6.98 (t, 1H, J = 9.00 Hz), 7.09 (d, 1H, J = 9.00 Hz), 7.68
(d, 2H, J = 8.25 Hz), 8.04 (d, 2H, J = 8.20 Hz); 13C NMR
(125 MHz, CDCl3) δ: 24.4, 28.1, 29.3, 34.4, 35.0, 35.6,
51.9, 64.7, 116.0, 123.5, 125.6, 126.6, 127.0, 127.4, 128.5,
128.9, 132.1, 132.5, 135.7, 139.0, 155.4, 158.6, 191.3; IR
3,4‑Dihydro‑3,3‑dimethyl‑13‑(2,3,4‑trimethoxy‑phenyl)‑2H
‑indazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5r)
Yellow, M.P. = 185–187 °C, 1H NMR (500 MHz, CDCl3)
δ: 1.20 (s, 3H), 1.23 (s, 3H), 2.34 (d, 2H, J = 2.60 Hz),
3.26 (d, 1H, AB system, J = 18.60 Hz), 3.42 (d, 1H, AB
system, J = 18.60 Hz), 3.83 (s, 3H), 3.84 (s, 3H), 3.86 (s,
1 3

J IRAN CHEM SOC
(KBr, cm−1): 2958, 1661, 1575, 1470, 1258; Anal. Calcd
for C21H18N2O3S: C, 66.65; H, 4.79; N, 7.40 %, Found: C,
66.54; H, 4.86; N, 7.31 %.
(dd, 2H), 2.47–2.50 (m, 1H), 3.15–3.39 (2H, AB sys-
tem, J = 19.25 Hz), 5.73–5.74 (m, 1H), 7.88–7.93 (m,
2H), 8.37–8.41 (m, 2H); 13C NMR (125 MHz, CDCl3) δ:
14.3, 22.9, 23.7, 28.8, 29.2, 29.3, 29.7, 32.0, 34.9, 38.5,
51.4, 63.3, 117.7, 127.9, 128.3, 129.4, 133.8, 134.8,
152.0, 155.0, 156.5, 193.4; IR (KBr, cm−1) 2960, 2927,
1656, 1625, 1574, 1473, 1419, 1362, 1255; Anal. Calcd
for C23H28N2O3: C, 72.60; H, 7.42; N, 7.36 %, Found: C,
72.49; H, 7.52; N, 7.27 %.
3,4‑Dihydro‑3,3‑dimethyl‑13‑(5‑bromothiophen‑2‑yl)‑2H‑i
ndazolo[2,1‑b]phthalazine‑1,6,11(13H)‑trione (5w)
Yellow, M.P. = 205–207 °C, 1H NMR (500 MHz, CDCl3)
δ: 2.29–2.34 (m, 2H), 2.52–2.61 (m, 2H), 3.28–3.35
(m, 1H), 3.56–3.62 (m, 1H), 6.73 (s, 1H), 6.94 (d, 1H,
J = 3.60 Hz), 7.06 (d, 1H, J = 4.50 Hz), 7.86–7.92 (m, 2H),
8.34–8.37 (m, 2H); 13C NMR (125 MHz, CDCl3) δ: 22.3,
24.5, 36.9, 59.5, 113.2, 117.7, 127.8, 128.2, 128.5, 128.8,
128.9, 129.9, 133.8, 134.7, 140.1, 153.4, 154.4, 156.0,
192.4; IR (KBr, cm−1): 3451, 1664, 1363, 1263, 1141,
1109, 1004, 806, 702; Anal. calcd for C19H13BrN2O3S: C,
53.16; H, 3.05; N, 6.53. Found: C, 52.27; H, 2.95; N, 6.69.
Acknowledgments Authors are grateful to the council of Iran
National Science Foundation and University of Shiraz for their unend-
ing effort to provide financial support to undertake this work.
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Yellow powder, M.P. = 250–251 °C, 1H NMR (500 MHz,
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2.07–2.17 (m, 1H), 2.39 (m, 2H), 2.39 (s, 2H) 2.51–2.59
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1
Yellow powder, M.P. = 84–86 °C, H NMR (500 MHz,
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(m, 12H, 3CH2, 2CH3), 2.12–2.13 (m, 1H), 2.44–2.46
1 3

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