A mesoporous SBA-15 silica catalyst functionalized with phenylsulfonic acid groups (SBA-15-Ph-SO3H) as a novel hydrophobic nanoreactor solid acid catalyst for a one-pot three-component synthesis of 2H-indazolo[2,1-b]phthalazine-triones and tria

Article abstract of DOI:10.1039/c5ra04949k

Phenyl sulfonic acid functionalized mesoporous SBA-15 silica (SBA-15-Ph-SO₃H) was prepared through the silanization of activated mesoporous SBA-15 with diphenyldichlorosilane (DPCS) followed by silylation and sulfonation, and characterized by X

Full text of DOI:10.1039/c5ra04949k

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A mesoporous SBA-15 silica catalyst functionalized
with phenylsulfonic acid groups (SBA-15-Ph-SO3H)
as a novel hydrophobic nanoreactor solid acid
catalyst for a one-pot three-component synthesis
of 2H-indazolo[2,1-b]phthalazine-triones and
triazolo[1,2-a]indazole-triones
Cite this: RSC Adv., 2015, 5, 68523
Hojat Veisi, a Alireza Sedrpoushan,b Ali Reza Faraji,c Masoud Heydari,b Saba Hemmatia
*
and Behnaz Fatahia
Phenyl sulfonic acid functionalized mesoporous SBA-15 silica (SBA-15-Ph-SO3H) was prepared through the
silanization of activated mesoporous SBA-15 with diphenyldichlorosilane (DPCS) followed by silylation and
sulfonation, and characterized by XRD, FT-IR, nitrogen adsorption analyses, BET theory and TEM. The
sulfonic acid groups anchored to the silica surface of the pore walls were resistant to leaching in organic
and aqueous solutions under mild conditions. This catalyst was found to be a recyclable heterogeneous
catalyst for the rapid and efficient synthesis of various 2H-indazolo[2,1-b]phthalazine-triones and triazolo
[1,2-a]indazole-triones. Also, this silylated mesoporous material containing phenylsulfonic acid groups
has a greater stability of the sulfonic acid surface toward water than that of silica sulfuric acid (SSA) and
sulfonated SBA-15.
Received 20th March 2015
Accepted 30th July 2015
DOI: 10.1039/c5ra04949k
www.rsc.org/advances
attachment of sulfonic acid groups to the surface of silica
derivatives, several types of solid sulfonic acids, based on
1. Introduction
ordered mesoporous silicas, have been created in recent
years.21–31 Silylation and direct synthesis procedures have been
used for the preparation of these sulfonic acid functionalized
silica-based materials.
In recent years, organically functionalized ordered mesoporous
silicas1–4 with a tunable pore structure, high surface area and
tailored composition have received great attention with broad
applications ranging from adsorbents,5–8 gas separation,9 and
catalysis,10–15 to biological uses.16 Some characteristics of these
materials are: a mechanically stable structure, high surface
area, and large, ordered pores with a narrow size distribution on
an inorganic backbone. This organic mesoporous functionali-
zation has been widely achieved by the graing of functional
groups. Ordered mesoporous silicas (OMSs), particularly SBA-
15, compared to other silica materials have a relatively good
hydrothermal stability, and possess a hexagonal array of
uniform pores with a high specic surface area and large pore
volume.
The active sulfonic acid groups are obtained post-
synthetically by the oxidation of propanethiol groups previ-
ously anchored to the surface17,24–30 or by sulfonation reac-
tions.21,22,31 Multi-component reactions (MCRs) have proven to
be valuable assets in organic and medicinal chemistry.32–34 Such
protocols can be used for drug design, and drug discovery
because of their simplicity, efficiency, and high selectivity.35
This environmentally friendly process can reduce the number of
synthetic steps and the synthesis of bioactive and complex
molecules should be facile, fast, and efficient with minimal
workup using this methodology.36,37 The combination of
solvent-free conditions with a multi-component reaction has
been shown to be a powerful strategy to yield complex molec-
ular structures using few synthetic steps.38,39
The direct synthesis involving the co-condensation of
siloxane and organosiloxane species in the presence of different
templating surfactants has been shown to be a promising
alternative to graing procedures.17–20 By the covalent
Aza-containing heterocyclic compounds are widespread in
nature, and their applications as pharmaceuticals, agrochemi-
cals, and functional materials are becoming more and more
important.40 Among a large variety of N-containing heterocyclic
compounds, those containing a hydrazine moiety at the ‘fusion
site’ have received considerable attention because of their
aDepartment of Chemistry, Payame Noor University (PNU), 19395-4697 Tehran, Iran.
E-mail: hojatveisi@yahoo.com
bInstitute of Industrial Chemistry, Iranian Research Organization for Science and
Technology, Tehran, Iran
cYoung Researchers and Elite Club, Pharmaceutical Sciences Branch, Islamic Azad
University, Tehran, Iran
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pharmacological properties and clinical applications.41 More-
over, fused phthalazines and urazole derivatives were found to
possess multiple biological activities, such as antimicrobial,42
anticonvulsant,43 antifungal,44 anticancer,45 hypolipidemic,46
and anti-inammatory activities.47 Nevertheless the develop-
ment of new synthetic methods for the efficient preparation of
heterocycles containing phthalazine and urazole ring fragments
is an interesting challenge. Recently, several elegant multi-
component strategies for the synthesis of 2H-indazolo[2,1-b]
phthalazine-triones and triazolo[1,2-a]indazole-triones by
multi component reactions utilizing catalysts have been
reported.48–61
2.3. General procedure for the synthesis of 2H-indazolo[2,1-
b]phthalazine-triones and triazolo[1,2-a]indazole-triones in
the presence of SBA-15-Ph-SO3H under solvent-free conditions
Phthalhydrazide or 4-phenylurazole (1 mmol), dimedone (1
mmol), aldehyde (1.1 mmol) and SBA-15-Ph-SO3H (20 mg z 5
mol%) were heated at 80 ꢀC. The reaction was followed by thin
layer chromatography (TLC) using hexane/ethyl acetate (3 : 1) as
an eluent (Rf ¼ 0.70). Aer completion of the reaction, the
mixture was washed with ethyl acetate and ltered to recover
the catalyst. The ltrate was evaporated, and the crude product
was recrystallized from EtOH–H2O (4 : 1) to afford the pure
products. The desired pure products were characterized by the
comparison of their physical data with those of known
compounds. In order to recover the catalyst, the solid was
washed with ethanol, ethyl acetate and dried. The recovered
catalyst was reused another time.
2. Experimental section
2.1. Preparation of SBA-15
All chemicals were purchased from Merck except Pluronic123
and metformin hydrochloride which were obtained from
Aldrich. The synthesis of SBA-15 was performed according to a
reported procedure.64 As a short explanation of the SBA-15
synthesis, 4.0 g of Pluronic P123 was dissolved in 50 mL of
water and was stirred for 5 h at room temperature. The
mixture was added to 120 mL of 2 M hydrochloric acid solu-
tion and was le for 2 h. Then, 8.5 g of TEOS was added to the
solution and was stirred for 24 h at 35 ꢀC. The mixture was
then aged at 80 ꢀC for 24 h without stirring. Aer completion
of the reaction, the solid products were ltered, washed with
deionized water, and air-dried overnight. The P123 was
removed thoroughly with a hot ethanol–water mixture (3 : 2)
using a Soxhlet apparatus for 24 h. It was dried in air at 100 ꢀC
for 3 days.
3. Results and discussion
3.1. Catalyst characterization
There has been considerable interest in the development of
heterogeneous solid acid catalysts to avoid the use of traditional
homogeneous acid catalyst systems (H2SO4, HF, AlCl3, BF3,.)
which present serious drawbacks including hazardous
handling, corrosiveness, production of toxic waste, and diffi-
culties in separation. In this context, we wish to report the
preparation of SBA-15-Ph-SO3H as a modied sulfonic acid and
a novel hydrophobic nanoreactor solid acid catalyst. In the
present work SBA-15 was modied to contain covalently bonded
phenylsulfonic acid groups on the inside surface of the chan-
¨
nels and to provide the silica supported material with Bronsted
acid properties. SBA-15 was synthesized according to a previ-
ously described method using Pluronic P123, as the templating
agent.31 The P123 was then removed thoroughly with a hot
ethanol–water mixture (3 : 2) using a Soxhlet apparatus for 24 h.
Then the activated mesoporous SBA-15 was reacted with
2.2. Preparation of SBA-15-Ph-SO3H
To a reaction mixture of SBA-15 (1 g) in dry toluene (30 mL), diphenyldichlorosilane (DPCS) to introduce phenyl groups to
dichlorodiphenylsilane (5 mL) was added and reuxed under a the inside of the channels. In continuation, before the sulfo-
N2 atmosphere for 12 h. Aer completion of the reaction, the nation with chlorosulfonic acid, the solid was reacted with tri-
white solid material was ltered off and washed with toluene, methylsilylchloride (TMSC) as a powerful silylating agent, for
dichloromethane, and methanol, and was then dried in an oven trimethylsilylation of the surface hydroxyl groups of the phenyl-
ꢀ
at 80 C overnight to give SBA-15-Ph.
modied SBA-15, to form trimethylsilyl phenyl modied SBA-15
Phenyl-modied SBA-15 was dispersed in dry hexane (50 mL) (3). Subsequent treatment with chlorosulfonic acid afforded the
under nitrogen and then trimethylsilylchloride (TMSC, 3 mL) nal catalyst, SBA-15-Ph-SO3H as a new solid acid catalyst with
was added to the dispersion and reuxed for 8 h. Then it was greater stability in the presence of moisture (Scheme 1).
cooled down to room temperature, ltered and washed with
The mesoporous SBA-15 silica catalyst functionalized with
hexane to get trimethylsilylated phenyl-modied SBA-15. The phenylsulfonic acid groups (SBA-15-Ph-SO3H) was conveniently
dry white solid was soaked in a solution of ClSO3H (0.6 mL) in synthesized from commercially available and cheap materials
dry CHCl3 (20 mL) and was reuxed for 2 h. Then it was ltrated graed onto SBA-15. The formation of SBA-15-Ph-SO3H was
and washed with dry CHCl3. The solid achieved during this veried using CHN, FT-IR, UV-vis, BET theory, SEM, TEM and
process was dried under vacuum at 60 ꢀC for 10 h to obtain SBA- XRD studies. The pathway of SBA-15-Ph-SO3H fabrication is
15 functionalized with phenyl sulfonic acid groups (SBA-15-Ph- shown in Scheme 1 and was conrmed by FT-IR (Fig. 1). As is
SO3H). The sulfonic acid content (the number of H+) of seen from curve A, the formation of the SBA-15 structure is
the catalyst based on elemental analysis (CHNS) (C 12.3%, H evidenced by the IR bands located at 3420 cmꢁ1 (nas O–H of
2.88%, S 8.12%), and titration with NaOH is estimated to be silanols), 1088 cmꢁ1 (nas Si–O), 807 cmꢁ1 (ns Si–O), 467 cmꢁ1 (s
2.45 mmol gꢁ1
.
Si–O–Si) (n represents stretching, s bending, s symmetric, and as
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Scheme 1 Preparation of SBA-15-Ph-SO3H.
Fig. 1 FT-IR spectra of (A) SBA-15; (B) SBA-15-Ph; (C) SBA-15-Ph-
SO3H.
asymmetric vibrations, Fig. 1). The signals appearing at 3100
cmꢁ1 and 1508 cmꢁ1 (n phenyl), 878 cmꢁ1 and 856 cmꢁ1 (s
phenyl) in curve B indicate the existence of phenyl rings and the
successful attachment of dichlorodiphenylsilane to SBA-15.
SBA-15-Ph-SO3H exhibits additional absorbance peaks corre-
sponding to sulfonic acid groups in curve C. The characteristic
peaks of the sulfonic acid groups occur at 1169 cmꢁ1 (n SO2) and
574 cmꢁ1 (n S–O).
Fig. 2 XRD small angle patterns of the parent SBA-15 and SBA-15-Ph-
SO3H catalysts.
capacity of catalyst was determined to be 2.45 mmol gꢁ1. This
amount is different from the results acquired via CHN analysis
(2.54 mmol gꢁ1) which can be related to the limitation of the
titration regarding the heterogeneous acid.
The sulfonic acid content (the number of H+) of the catalyst
based on CHN analysis and titration with sodium hydroxide was
estimated. In order to estimate the number of sulfonic acid
groups, 60 mg of SBA-15-Ph-SO3H was added to a 25 mL
aqueous solution of 1 M sodium chloride and was stirred for 72
h. Previous studies have indicated that heterogeneous acid
titrations involve mass transfer limitations.32 It seems that the
presence of sodium chloride is needed for a proper potentio-
metric titration. The addition of sodium chloride is required to
enhance the ion-exchange, facilitating the proton loss of the
acid and the proton uptake of the base. While the salt aids in
improving the titration, the extensive addition leads to activities
that deviate signicantly from the actual proton concentration.
In this process ion exchange occurred between the sulfonic acid
protons and the sodium ions. Then titration of this solution
with NaOH (0.05 M) was carried out and the acid exchange
The small-angle XRD patterns of SBA-15 and SBA-15-Ph-
SO3H are shown in Fig. 2. Three well-resolved diffraction peaks
in the 2q range of 0.8–2ꢀ are observed for SBA-15-Ph-SO3H as an
organic–inorganic hybrid material similar to the SBA-15 parent.
However, the ordered structure of SBA-15-Ph-SO3H has
remained intact, as supported by the XRD results. This pattern
features distinct Bragg peaks in the 2q range of 0.8–2ꢀ, which
can be indexed as (1 0 0), (1 1 0) and (2 0 0) reections of the two-
dimensional hexagonal structure of the SBA-15 material. The
presence of these peaks indicates that the crystallographic
ordering of the mesopores in SBA-15-Ph-SO3H is retained aer
graing. Also a noticeable change for SBA-15-Ph-SO3H in the
intensity of these reections (1 0 0), (1 1 0) and (2 0 0) was
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the modied support were signicantly reduced compared to
the parent SBA-15 (this decrease indicates a decrease in the
interaction between the adsorbate, N2 molecules, and the nano-
sized SBA-15 surface aer the modication with organic
groups). Therefore this observation conrms that the organic
groups prefer to be graed in the ordered nanopores.
Furthermore, the structural elucidation of the SBA-15 and
SBA-15-Ph-SO3H catalytic supports was performed in some
detail using TEM and SEM techniques. The SEM images of the
catalysts (Fig. 4a1 and a2) show that the attachment of the
organic components to the SBA-15 material has no distinct
inuence on the morphology of composition. The TEM images
of the catalysts (Fig. 4b1 and b2) show the ordered mesostruc-
ture in large domains and no distinct defects are observed.
Fig. 3 Nitrogen adsorption–desorption profiles and pore size distri-
bution of the SBA-15 and SBA-15-Ph-SO3H catalysts.
3.2. Catalytic studies
In a continuation of our interest in using the solid acid
catalysts in organic transformations,63 herein we report the
catalytic activity of phenylsulfonic acid modied mesoporous
SBA-15 (SBA-15-Ph-SO3H) as a novel nanoreactor solid acid
catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine-
triones and triazolo[1,2-a]indazole-triones via
a one-pot
three-component reaction of dimedone and aldehydes with
phthalazine or N-phenylurazoles under solvent-free condi-
ꢀ
tions at 80 C (Scheme 2).
In order to achieve the optimum conditions, we initially
investigated the reaction of phthalhydrazide (1.0 mmol), 3-
nitrobenzaldehyde (1.1 mmol), and 5,5-dimethylcyclohexane-
1,3-dione (1.0 mmol) in the presence of the prepared catalyst
under different conditions. The best result was obtained under
solvent-free conditions in the presence of a catalytic amount
of SBA-15-Ph-SO3H (5 mol%). The reaction afforded 96% of
3,4-dihydro-3,3-dimethyl-13-(3-nitrophenyl)-2H-indazolo[2,1-b]-
phthalazine-1,6,11(13H)-trione by a simple work-up aer 5 min.
In order to deduce the capability of the catalyst, the above
reaction was repeated without the catalyst under solvent free
conditions. The reaction did not proceed even aer a prolonged
reaction time and no desired product was formed which
supports the catalytic activity of SBA-15-Ph-SO3H.
Fig. 4 (a) SEM and (b) TEM images of (1) SBA-15 and (2) SBA-15-Ph-
SO3H.
The generality of this reaction was examined by using
different aromatic and aliphatic aldehydes. The reactions pro-
ceeded smoothly and equally well for electron-withdrawing as
well as electron-donating substituents on the aldehydes to
afford the corresponding phthalazine-triones in good to excel-
lent yields (Table 1, entries 1–9) and in very short reaction times.
This method offers signicant improvements with regard to the
scope of the transformation, the simplicity, and the green
aspect by avoiding expensive or corrosive catalysts.
Finally, to assess the present protocol with respect to other
reported methods for the preparation of 3,4-dihydro-3,3-
dimethyl-13-(3-nitrophenyl)-2H-indazolo[2,1-b]phthalazine-
1,6,11(13H)-trione, the presented procedure using SBA-15-Ph-
SO3H as the catalyst was compared with other systems. From
Table 2, it can be seen that the present system gave higher
conversions and yields compared to the other reported systems.
observed, they are lower than that of SBA-15, implying that the
change in the electron density contrast aer the graing,
changes the distribution of the scattering angles within the unit
cell which affects the diffraction intensities.
The nitrogen adsorption–desorption isotherms of SBA-15
and SBA-15-Ph-SO3H are shown in Fig. 3. The isotherms were
both type IV with a H1 hysteresis loop and a steep increase in
the adsorption at relative pressures of 0.6–0.8, for the SBA-15
sample this can be attributed to capillary nitrogen condensa-
tion according to IUPAC classication.62 The BET surface area
(SBET), total pore volume (VBJH), and mean pore diameter (MPD)
of SBA-15 were 830 m2 gꢁ1, 0.85 cm3 gꢁ1, and 6.56 nm,
respectively. Remarkably, aer functionalization of SBA-15, the
SBA-15-Ph-SO3H catalyst possessed a SBET of 783 m2 gꢁ1, VBJH of
0.82 cm3 gꢁ1, and a MPD of 5.94 nm. The SBET, VBJH and MPD of
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Scheme 2 Synthesis of 2H-indazolo[2,1-b]phthalazine-triones and triazolo[1,2-a]indazole-triones.
In the next step, the scope and efficiency of the prepared phthalhydrazide to intermediate A occurred in the catalytic
catalyst were explored under the optimized reaction conditions, media, followed by cyclization to afford the corresponding
for the condensation of N-phenyl urazoles with various alde- product B in the catalytic cycle (Scheme 3).
hydes and dimedone to furnish the corresponding products
(Scheme 1). The results are displayed in Table 3. As can be seen
the triazolo[1,2-a]indazole-trione derivatives were obtained in
high yields and short reaction times.
The formation of the 2H-indazolo[1,2-b]phthalazine-trione
derivatives in the presence of SBA-15-Ph-SO3H, which should
be synthetically useful and practical, is presented in Scheme 3.
A plausible pathway involves an initial SBA-15-Ph-SO3H cata-
3.3. Reusability of the catalyst
The reusability of the catalyst in the reaction of 3-nitro-
benzaldehyde, dimedone, and phthalhydrazide under solvent-
free conditions at 80 ꢀC for 5 minutes was studied. In this
procedure, aer the completion of each reaction, hot ethyl
acetate was added to the reaction mixture and was shaken for a
few minutes to dissolve the product. The catalyst (insoluble in
lyzed Knoevenagel condensation of dimedone with an aldehyde
to form intermediate A. A subsequent Michael addition of
the solvent) was ltered and washed with hot ethanol and ethyl
acetate, and dried. The recovered catalyst was reused ve times
Table 1 Synthesis of indazolo[2,1-b]phthalazine-triones in the presence of SBA-15-Ph-SO3H
Mp (ꢀC)
Entry
Aldehyde
Time (min)
Yielda (%)
TOFb (hꢁ1
)
Found
Reportedlit.
1
2
3
4
5
6
7
8
9
C6H5
4-Cl–C6H4
4-Br–C6H4
4-MeO–C6H4
3-NO2–C6H4
2,4-Di-Cl–C6H3
3,4,5-Tri-MeO–C6H2
Propanal
10
7
5
5
5
15
10
50
45
90
85
95
96
96
85
95
75
80
1.08
1.45
2.29
2.31
2.31
0.68
1.15
0.18
0.21
203–205
263–265
264–266
217–219
268–269
234–236
187–189
145–147
135–137
204–206 (ref. 48)
262–254 (ref. 54)
265–267 (ref. 55)
218–220 (ref. 55)
267–268 (ref. 55)
234–236 (ref. 54)
188–190 (ref. 58)
145–147 (ref. 54)
136–138 (ref. 54)
Butanal
a
Isolated yields. b TOF, turnover frequencies.
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Table 2 Comparison of the activity of different processes for the synthesis of 3,4-dihydro-3,3-dimethyl-13-(3-nitrophenyl)-2H-indazolo[2,1-b]
phthalazine-1,6,11(13H)-trione
Aldehyde
Catalyst
Reaction conditions
Yield (%)
Ref.
3-NO2C6H4CHO
SBA-15-Ph-SO3H
N-Bromosulfonamide
PEG-OSO3H
[bmim]BF4
Ce(SO4)2$4H2O
Solvent-free, 80 ꢀC, 5 min
Solvent-free, 100 ꢀC, 10 min
Solvent-free, 80 ꢀC, 10 min
Solvent-free, 80 ꢀC, 30 min
Solvent-free, 125 ꢀC, 5 min
96
91
92
90
84
This study
54
59
49
51
Table 3 Synthesis of triazolo[1,2-a]indazole-triones in the presence of SBA-15-Ph-SO3H
Mp (ꢀC)
Found
Entry
Aldehyde
Time (min)
Yielda (%)
TOFb (hꢁ1
)
Reportedlit.
1
2
3
4
5
6
C6H5
30
40
30
35
20
45
92
95
95
90
96
80
0.37
0.29
0.38
0.31
2.90
0.21
189–191
170–172
185–187
163–165
130–132
177–178
190–192 (ref. 57)
166–168 (ref. 61)
185–187 (ref. 57)
160–162 (ref. 61)
131–133 (ref. 57)
177–178 (ref. 57)
4-Cl–C6H4
4-Br–C6H4
4-Me–C6H4
3-NO2–C6H4
2-Cl–C6H4
a
Isolated yields. b TOF, turnover frequencies.
and a smooth loss of catalytic activity was observed from the 5th was observed upon heating for 3 h. Therefore, we may conclude
time of reuse (Fig. 5). that any sulfonic acid groups that leach into the reaction
The loss of catalytic activity for SBA-15-Ph-SO3H may be due mixture are not active homogeneous catalysts and that the
to the catalyst channels being lled by reactant molecules or observed catalysis is truly heterogeneous in nature.
products, and subsequently decreasing the catalytic activity.
3.4. Stability and leaching of the catalyst
4. Conclusion
In another study, the stability and leaching of SBA-15-Ph-SO3H
In conclusion, we have prepared phenyl sulfonic acid func-
tionalized mesoporous SBA-15 silica (SBA-15-Ph-SO3H) as a
novel hydrophobic nanoreactor solid acid catalyst, which was
characterized by XRD, FT-IR, nitrogen adsorption analyses,
BET theory and TEM. The sulfonic acid groups anchored to
the silica surface of the pore walls are resistant to leaching in
organic and aqueous solutions under mild conditions. This
catalyst was found to be a recyclable heterogeneous catalyst
for the rapid and efficient synthesis of various 2H-indazolo
[2,1-b]phthalazine-triones and triazolo[1,2-a]indazole-triones.
Also, this silylated mesoporous material containing phenyl-
sulfonic acid groups has a greater stability of the bonded
sulfonic acid surface toward water than that of silica sulfonic
acid (SSA) and sulfonated SBA-15. Moreover, the catalyst has
suitable hydrophobicity to drive out the water which is formed
during the reaction from the mesochannels.
were compared with silica sulfuric acid (SSA) and sulfonated
SBA-15. We added 0.5 g of each catalyst to a separate column
and then washed them with 20 mL of water 2 times to investi-
gate the stability and leaching of the bonded sulfonic acid
surfaces toward water. Aer washing, pH value analysis of the
water showed that only the pH of our catalyst was unchanged.6,14
This observation indicated the greater stability of SBA-15-Ph-
SO3H as a solid acid heterogeneous nano catalyst toward water
and hydrolysis conditions. This stability may be because of the
steric and hydrophobic effects of the phenyl groups in SBA-15-
Ph-SO3H toward water attack.19–33
Our preliminary investigations demonstrate that the cata-
lyst SBA-15-Ph-SO3H is very stable to air and moisture. The
leaching and heterogeneous pathways inside the nanospace
of the prepared catalyst were tested for the reaction of
phthalhydrazide (1.0 mmol), benzaldehyde (1.1 mmol), and
5,5-dimethylcyclohexane-1,3-dione (1.0 mmol) to afford
the 3,4-dihydro-3,3-dimethyl-13-(phenyl)-2H-indazolo[2,1-b]-
phthalazine-1,6,11(13H)-trione under solvent-free conditions in
the presence of a nanoreactor. The reaction was quenched (by
dilution with EtOAc) aer 3 min and ltered off (ꢂ40%
Acknowledgements
conversion). Next, the EtOAc was evaporated, and the residue We are thankful to the Iran National Science Foundation (INSF)
was then subjected to further heating under solvent-free and Payame Noor University (PNU) for partial support of this
conditions at 80 C. We found that no further catalytic activity work.
ꢀ
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Scheme 3 Proposed mechanism for the SBA-15-Ph-SO3H-catalyzed synthesis of indazolo[2,1-b]phthalazine-triones.
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