Guanine-La complex supported onto SBA-15: A novel efficient heterogeneous mesoporous nanocatalyst for one-pot, multi-component Tandem Knoevenagel condensation–Michael addition–cyclization Reactions

Article abstract of DOI:10.1002/aoc.5504

In this work, we present a simple, environmentally-friendly and economical route for the preparation of a novel lanthanum (III) organometallic complex immobilized onto a highly stable mesoporous silica SBA-15 (La-guanine@SBA-15) using an inexpensive and s

Full text of DOI:10.1002/aoc.5504

Received: 7 December 2019
DOI: 10.1002/aoc.5504
Revised: 18 December 2019
Accepted: 20 December 2019
F U L L P A P E R
Guanine-La complex supported onto SBA-15: A novel
efficient heterogeneous mesoporous nanocatalyst for one-
pot, multi-component Tandem Knoevenagel condensation–
Michael addition–cyclization Reactions
Mohsen Nikoorazm
| Maryam Khanmoradi | Masoud Mohammadi
Department of Chemistry, Faculty of
Science, Ilam University, P. O. Box
69315516, Ilam, Iran
In this work, we present a simple, environmentally-friendly and economical
route for the preparation of a novel lanthanum (III) organometallic complex
immobilized onto
a
highly stable mesoporous silica SBA-15 (La-
Correspondence
guanine@SBA-15) using an inexpensive and simple method and available
materials. This mesoporous heterogenized complex was comprehensively char-
acterized using FT-IR, XRD, EDS, ICP, MAP, SEM, TGA and BET techniques.
The catalytic activity of this mesoporous material was studied in one-pot
multi-component tandem Knoevenagel condensation–Michael addition–
cyclization reactions in order to prepare a series of benzo [a] pyrano [2, 3-c]
phenazine and 4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols)
derivatives under green conditions. This catalyst exhibited highly recoverable
and recyclable features in consecutive reaction runs. Besides, the products
were obtained in high yields and short reaction times. In this sense, simple
preparation of the catalyst from the commercially available materials, simple
operation, high catalytic activity, short reaction times, high yields and the use
of green reaction conditions in the mentioned organic synthesis are the most
significant advantages of this protocol. In addition, this nanocatalyst was easily
recovered, using simple filtration, and reused several times without significant
loss of its catalytic efficiency. Moreover, the leaching, heterogeneity and stabil-
ity of La-guanine@SBA-15 were studied by hot filtration test and ICP tech-
nique. Finally, stability of the catalyst after recycling was confirmed by SEM
and FT-IR techniques.
Mohsen Nikoorazm; Department of
Chemistry, Faculty of Science, Ilam
University, P.O. Box 69315516 Ilam, Iran.
Email: e_nikoorazm@yahoo.com
K E Y W O R D S
4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols), Benzo [a] pyrano [2, 3-c]
phenazines, La-guanine@SBA-15, mesoporous nanocatalyst, Tandem Knoevenagel
condensation–Michael addition–cyclization
1 | INTRODUCTION
renaissance as a powerful method for the preparation of
products in a single-step and synthetic operation with
Over the past decade, the field of synthetic chemistry has
witnessed the multicomponent reactions (MCRs)
high efficiency.[1,2] MCRs comprise an important class of
chemical transformations which has been applied to
Appl Organometal Chem. 2020;e5504.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5504

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NIKOORAZM ET AL.
almost all fields of organic and medicinal chemistry.[3,4]
Tandem or domino (cascade) reactions consist of two or
more successive independent reactions performed in a
one-pot system without separating and purifying the
intermediates.[5–7] These convergent procedures incorpo-
rate three or more reactants into the final product in just
one pot. Thus, they can combine high levels of complex
and diverse generations with low synthetic cost and high
atom-economy and also reduce the waste generation and
synthetic efficiency.[8–10] Consequently, tandem reactions
not only reduce the number of reaction steps, energy con-
sumption and waste but also minimize the use of solvents
and reagents.[11] These advantages make tandem reac-
tions sustainably green processes that illustrate the con-
cepts of efficiency and atom economy.[11–13] Tandem
reactions offer many opportunities to improve chemical
transformations such as Lewis acid–base catalysis, hydro-
genation reactions and alkene metathesis.[14,15] MCRs are
currently well-established methods for the synthesis of
heterocycles,[16–19] natural products[13,20,21] and poly-
mers[22,23] while Double and Triple Cascade Reactions
are still a growing field of research. Knoevenagel
condensation–Michael addition (Double Cascade Reac-
tions) and Knoevenagel condensation–Michael addition–
cyclization (Triple Cascade Reactions) Sequences have
been widely studied and frequently applied to the synthe-
sis of natural products and biologically active com-
pounds.[15,24] These methods are highly valuable for the
formation of chiral carbo- and heterocyclic compounds
with multiple stereocenters which are relevant to the
pharmaceutical and medicinal chemistry and useful in
the synthesis of various natural products.[14,15,25–30]
materials i.e. increasing the temperature and time which
leads to increase the pore size and decreases the specific
surface area.[46] Moreover, the solvent which can be used
for washing prior to the calcinations in the synthesis of
SBA-15 can be a crucial step because different washing
procedures per washing cycle of SBA-15 surface (solvent
volume and types of solvents) led to different porosity
values/characteristics.[43]
Therefore, we can change characteristics of SBA-15 to
desirable features. Based on the pore types, various meso-
porous structures have been classified into three catego-
ries: 1) nearly spherical cage 2) bi-continuous channel
and 3) cylindrical channel.[47] During the last decade,
numerous efforts have been devoted to the catalytic
reforming technology and obtaining molecular sieves
showing larger pore size. Besides, it is worth mentioning
that a permanent effort has also been made in order to
develop textured inorganic or hybrid phases. More
recently, SBA-15 was used as a promising inorganic sup-
port due to its structural properties and various techno-
logical applications such as molecular sieves, sensors,
catalysts,
nanoelectronics,
drug
delivery
and
separation.[48–54] Recent studies have demonstrated that
several factors can control the condensation rates of SBA-
15 which contains amounts of inorganic salts, shape of
surfactant micelles, stirring rate and condensation rate of
silica.[55] On the other hand, metal–organic complexes,
involving rare earth elements such as lanthanide ions,
are often used in catalysis field because they have the
oxophilic nature and can easily build a framework
structure.[14,56–60]
Herein, we describe the synthesis of an efficient and
reusable catalyst by the immobilization of a lanthanum
(III) complex with guanine as a coordinate ligand on
Benzo [a] pyrano [2, 3-c] phenazine and 4,40-
(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols)
compounds have a great potential in order to be applied
in biological and pharmaceutical systems such as antifun-
chloro-functionalized
SBA-15
mesoporous
silica
nanoparticles and its catalytic activities for one-pot syn-
thesis of domino of benzo [a] pyrano [2, 3-c] phenazine
gal,
antibacterial,
anticancer,
antiplasmodial,
antimalarial,
and
antiparasitic,
anticancer
and
4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-
antichagasagen systems.[27,28,31–39] However, synthesis of
these useful compounds needs a better method which
should be in agreement with green chemistry rules.
pyrazol-5-ols) derivatives. The results of this study differ
from the previously-reported researches due to the natu-
ral origin of ligand, stable complex of ligand with La and
support, high yields of products and excellent selectivity
and recoverability and reusability of the catalyst. In addi-
tion, ethanol was utilized as a green solvent under aero-
bic reaction conditions.
Mesoporous materials are interesting materials hav-
ing highly ordered pores and a large surface area.
Besides, they are widely applied in catalysis as catalyst
supports, separations, adsorption, gas sensors and drug
delivery systems.[40–43] After the discovery of mesoporous
silica structures in the early 1990s, various types of these
materials, such as MCM (Mobil Crystalline Material),
MSU (Michigan State University) and SBA (Santa
Barbara Amorphous), have been developed.[42,44,45]
Noticeably, different types of surfactants, pH, tempera-
ture, time, etc. can significantly change the material
properties and produce different types of mesoporous
2 | EXPERIMENTAL
2.1 | Synthesis of La-guanine@SBA-15
In a typical synthesis, 4 g of the nonionic surfactant
(Pluronic P123: EO20PO70EO20) was dissolved under

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
3 of 18
stirring in a solution containing water and 2 M HCl
(90 ml) at 35 ꢀC until the solution became homogeneous.
Then, 9.04 ml of the silica precursor (TEOS:
tetraethylorthosilicate) was slowly added to the reaction
mixture and, then, the stirring continued for another
20 hr. Subsequently, the white solid product was filtered
and washed with deionized water several times which
can be regarded as a critical step before the final calcina-
tion aimed at removing the surfactant (P123) 35. After
and washed with hot acetone and, then, the catalyst was
separated from other materials (the reaction mixture was
soluble in hot acetone and the catalyst was insoluble).
Afterwards, the solvent removal was carried out and, for
further purification, the crude product was recrystallized
in ethanol.
2.3 | General pathway for the synthesis
of 4,40-(arylmethylene)-bis-(3-methyl-
1-phenyl-1H-pyrazol-5-ols)
ꢀ
washing, the product was dried at 80 C and the surfac-
tant was removed by calcination at 823 K for 5 hr at a
rate of 2 ꢀC/min.
In order to functionalize mesoporous SBA-15, 1 g of
the purely obtained SBA-15 was transferred into a clean
flask, containing 20 ml n-hexane and 1.5 ml
3-chloropropyltriethoxysilane (nPrCl), and refluxed for
24 hr. After completion of the reaction, the resulting mix-
ture was separated by simple filtration, washed with n-
hexane and dried at 40 ꢀC for 4 hr.
A mixture of aldehyde (1 mmol), 3-Methyl-1-phenyl-
5-pyrazolone (2 mmol) and La-guanine-SBA-15
(0.5 mol%) was dissolved in 3 ml EtOH. Then, the
ꢀ
flask was sealed and stirred at 80 C under reflux con-
ditions. The progress of the reaction was monitored by
TLC (n-hexane/ethyl acetate: 4/1). After completion of
the reaction, the mixture was cooled down to room
temperature, filtered and washed with hot EtOH to
separate the catalyst from other materials (the reaction
mixture was soluble in hot EtOH and the solid catalyst
was insoluble). Finally, the solvent removal was car-
ried out and, for further purification and to yield the
pure products, the crude product was recrystallized by
ethanol.
Continuously, 0.5 g of the Cl-functionalized SBA-15
was mixed with 0.181 g guanine (2-amino-1H-purin-
ꢀ
6(9H)-one) (1.2 mmol) in toluene and refluxed at 120 C
under nitrogen atmosphere for 24 hr. Then, the obtained
guanine@SBA-15 product was separated by simple filtra-
tion, washed with ethanol in order to removꢀe the
unreacted nucleobase and dried in an oven at 60 C for
4 hr.
Finally, in order to prepare the La-guanine@SBA-15
heterogenized complex, 0.5
g
of the synthesized
3 | RESULTS AND DISCUSSION
3.1 | Catalyst preparation
guanine@SBA-15, in the previous step, reacted with La
(NO3)3.6H2O (1.5 mmol, 0.649 g) in ethanol under reflux
conditions for 20 hr. Ultimately, the obtained product
was separated by simple filtration, washed with ethanol
and water to remove the excess La, and dried in an oven
at 80 ꢀC for 4 hr.
The presented work tries to describe a novel La-guanine
Complex supported onto mesoporous SBA-15 as an effi-
cient and green nanocatalyst for multicomponent organic
2.2 | General pathway for the synthesis
of benzo [a] pyrano [2, 3-c] phenazine
derivatives
A mixture of 2-hydroxynaphthalene-1,4-dione (1 mmol)
and benzene-1,2-diamine (1 mmol) was dissolved in
10 ml EtOH. Then, La-guanine-SBA-15 (0.5 mol%) was
added to the mixture, and the flask was sealed and stirred
at 80 ꢀC under reflux conditions. The progress of the
reaction was monitored by TLC. Upon the completion of
the first step of the reaction, aromatic aldehyde
(1.0 mmol) and malononitrile (1.5 mmol) were added
into the reaction mixture and stirred for an appropriate
time at reflux conditions. After completion of the reaction
(monitored by TLC (n-hexane/ethyl acetate: 7/3), the
mixture was cooled down to room temperature, filtered
SCHEME 1 Synthesis of La@guanine@SBA-15 nanostructure
[Colour figure can be viewed at wileyonlinelibrary.com]

4 of 18
NIKOORAZM ET AL.
transformations. Initially, the SBA-15 nanoparticles
which were modified by immobilization of CPTMS on its
surface (CPTMS@SBA-15) have been prepared according
to our previously reported procedure.[14] In order to pre-
pare guanine@SBA-15 NPs, 2-Amino-1,7-dihydro-6H-
thermogravimetric analysis (TGA) and Brunauer–
Emmett–Teller (BET) techniques.
The FT-IR spectra of the parent SBA-15 (a) nPrCl-
SBA-15 (b), guanine-SBA-15 (c) and La@guanine@SBA-
15 (d) are shown in Figure 1. Considering SBA-15, the
present bands at about 1082 cm−1, 807 cm−1 and
462 cm−1 attributed to the vibration modes of asymmetric
stretching, symmetric stretching and bending Si-O–
Si.[14,61,62] The presence of hydroxyl groups is well seen at
3443 cm−1 (Figure 1 (a)).[14,63] In Figure 1 (b), the charac-
teristic band at around 2935 cm−1 is duo to CH2 vibra-
tions corresponding to the C–H stretching and
confirming the successful chloro-functionalization of
SBA-15.[14,64] In Figure 1 (c) the band at 1678 cm−1 and
1588 cm−1 can be attributed to C=N and aromatic C-C
groups on the guanine ring.[58] In Figure 1 (d), the band
purin-6-one
(guanine)
has
been
grafted
on
CPTMS@SBA-15 NPs via the substitution reaction of
NH2 with terminal Cl groups. Finally, the catalyst was
synthesized by the reaction of guanine@SBA-15 with lan-
thanum (III) nitrate (Scheme 1).
3.2 | Catalyst characterizations
The prepared La-guanine@SBA-15 heterogeneous cata-
lyst was also characterized by Fourier transform infrared
spectroscopy (FT-IR), X-Ray Diffractometer (XRD),
energy-dispersive X-ray spectroscopy (EDS), inductively
coupled plasma atomic emission spectroscopy (ICP), X-
ray mapping, scanning electron microscopy (SEM),
corresponding to N–H stretching vibrations (2983 cm−1
)
)
displays a small shift to the higher frequency (3012 cm−1
that can be due to the N group coordination of the gua-
nine ring to the La metal.[14,58]
FIGURE 1 FT-IR spectra of
(a) SBA-15, (b) nPrCl-SBA-15,
(c) guanine-SBA-15 and
(d) La@guanine@SBA-15 [Colour figure
can be viewed at wileyonlinelibrary.
com]

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
5 of 18
Figure 2. shows the low-angle XRD pattern of
Moreover, energy dispersive X-ray spectroscopy
La@guanine@SBA-15. The lattice parameter on SBA-15
which can be indexed as the (100), (110), (200) reflections
corresponds to p6mm space group of the two-
dimensional hexagonal lattice.[47,65,66] Decreasing in the
diffraction intensity of these three peaks for the catalyst
indicated successful formation of La complex in the SBA-
15 hexagonal channels. Thus far, only one well-resolved
(EDS) analysis of La@guanine@SBA-15 is carried out to
indicate the adsorption of La3+ on SBA-15 surface. These
results are presented in Figure 3. In EDS image, the
peaks associated with Si, O, C, N and La can be observed.
It is found that the adsorption of lanthanum complex on
SBA-15 surface was successfully performed. In addition,
the exact amount of La, which was immobilized on
guanine@SBA-15, was obtained by ICP-OSE as
1.33 × 10−3 mol g−1. Finally, in order to find the exact of
carbon and nitrogen in the described catalyst, elemental
analysis has been performed. Accordingly, the amounts
of carbon and nitrogen immobilized on SBA-15 NPs were
found to be 24.1 and 11.3, % respectively.
The X-ray mapping of La@guanine@SBA-15 was
studied in order to explore the dispersion of all
elements of the catalyst. As shown in Figure 4, the ele-
mental map images illustrated good dispersion of La on
La@guanine@SBA-15 surface and also showed that most
of the particles are quasi-spherical.
peak at 2θ ≈ 1.20ꢀ (d100) can be recognized and the (d 110
)
and (d 200) reflections disappeared. Also, it was found
that the position of the d100 peak in the catalyst shifted to
lower values, which are due to the shrinking pore size,
and reduced the order of homogeneity of the pores in
comparison to SBA-15. This may correspond to the re-
condensation reactions of the silica with lanthanum
nanoparticles in the pore channel.[46,62,65–67]
Scanning electron microscopy (SEM) images of
La@guanine@SBA-15 are shown in Figure 5 in which
small particles' size and uniform morphology can be
observed illustrating the vermicular-shaped particles in
nanometer size.
The thermogravimetric analysis (TGA) was used to
explore the presence of organic functional groups
chemisorbed onto the SBA-15 heterogeneous surfaces. As
shown in Figure 6, the thermogravimetric analysis (TGA)
curves of La@guanine@SBA-15 are located in the follow-
ing temperature ranges: from 100–300 ꢀC due to the
removal of physically adsorbed water and organic
solvents,[14,58] from 300–350 ꢀC and 350–650 as related to
P123 decomposition and decomposition of other
maintained functional organic groups chemisorbed onto
the surface of SBA-15 nanoparticles.[14]
FIGURE 2 The low-angle XRD pattern of La@guanine@SBA-
15 [Colour figure can be viewed at wileyonlinelibrary.com]
FIGURE 3 The EDS spectrum of
La@guanine@SBA-15 [Colour figure can be
viewed at wileyonlinelibrary.com]

6 of 18
NIKOORAZM ET AL.
FIGURE 4 The Map analysis of La@guanine@SBA-15 [Colour figure can be viewed at wileyonlinelibrary.com]
FIGURE 5 SEM images of La@guanine@SBA-15 nanostructure [Colour figure can be viewed at wileyonlinelibrary.com]
Textural parameters of La@guanine@SBA-15 were
determined by nitrogen adsorption/desorption iso-
therms that illustrate type IV isotherm with an H1-type
hysteresis loop at a relative pressure between 0.4–1.0,
corresponding to mesoporous materials (Figure 7). The
amounts of surface area, pore volume and pore size
distribution of La@guanine@SBA-15 were determined
by applying the Brunauer–Emmett–Teller (BET)
method and Barrett–Joyner–Halenda (BJH) models
and, then, collected in Table 1. The values of these
parameters are much lower as compared to that of the
SBA-15 mesoporous.[14,61,65,68] This can be duo to the
fact that these value parameters which are closely
related to the complex loading confirmed the successful
incorporation of metal nanoparticles on SBA-15 hetero-
geneous surfaces.

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
7 of 18
conditions in the presence of catalytic amount of La-gua-
nine-SBA-15 mesoporous nanoparticles.
In catalytic studies, initially, the catalytic activity of
La@guanine@SBA-15 is examined for the synthesis of
benzo [a] pyrano [2, 3-c] phenazine derivatives by the
reaction of benzene-1,2-diamine, 2-hydroxynaphthalene-
1,4-dione, aldehydes and malononitrile. According to
scheme 2, this was a one-pot and tow-step procedure.
In this sense, the Schiff base condensation reaction
between 2-hydroxynaphthalene-1,4-dione (1 mmol) and
benzene-1,2-diamine (1 mmol) in the first step and
4-chlorobenzaldehyde (1 mmol) and malononitrile
(1.5 mmol) in the second step were selected as the model
reaction. The influence of effective parameters was also
examined.
FIGURE 6 TGA curves of La@guanine@SBA-15 [Colour
figure can be viewed at wileyonlinelibrary.com]
Examining the effect of various amounts of the cata-
lyst was the first step of our optimization. The results in
Table 2 showed that in the absence of a catalyst, no
product was obtained after 48 hr (Table 2, entry 1) and
the yield of the product was improved with increasing
the amount of the catalyst (Table 2, entries 5–11).
Therefore, the best result was obtained in the presence
of 0.5 mol% of the catalyst on the basis of La. Next, we
have successfully exploited the effect of several solvents;
including, ethanol, water, ethanol:water, THF, PEG-400,
DMF, DMSO, acetone, n-hexane Acetonitrile and
solvent-free conditions (Table 2, entries 13–22) and also
various temperatures in the range of 25 ꢀC to reflux
FIGURE 7 Adsorption/Desorption isotherm of
La@guanine@SBA-15 [Colour figure can be viewed at
wileyonlinelibrary.com]
4 | EVALUATION OF THE
CATALYTIC ACTIVITY OF
LA@GUANINE@SBA-15
In continuation of our previous researches,[14,15] we wish
to report a facile, efficient, and environmentally-friendly
process for the preparation of benzo [a] pyrano [2, 3-c]
phenazine and 4,40-(arylmethylene)-bis-(3-methyl-1-phe-
nyl-1H-pyrazol-5-ols) derivatives under green reaction
SCHEME 2 Optimization of reaction conditions for the
Preparation of 3-Amino-1-(4-chloro-phenyl)-1H-benzo[a]pyrano
[2,3-c]phenazine-2-carbonitrile in the presence of
La@guanine@SBA-15 catalyst
TABLE 1 Surface properties of La@guanine@SBA-15
Sample
S
BET (m2/g)
430.22
Pore diam. By BJH method (nm)
Pore vol. (cm3/g)
La@guanine@SBA-15
3.526
0.3793

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NIKOORAZM ET AL.
TABLE 2 Optimization of reaction conditions for the Preparation of 3-Amino-1-(4-chloro-phenyl)-1H-benzo[a]pyrano [2,3-c]
phenazine-2-carbonitrile in the presence of La@guanine@SBA-15 catalyst
Entry Catalyst
Amount of Catalyst (mol %) Solvent
Temperature (ꢀC) Time (min) Yielda (%)
1
-
-
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
THF
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
100
2 day
60
60
60
60
60
60
60
60
60
60
60
60
60
Trace
35
2
Guanine
0.5
3
SBA-15
30 mg
30 mg
0.5
Trace
Trace
47
4
guanine@SBA-15
La (NO3)3.6H2O
5
6
La@guanine@SBA-15 0.05
La@guanine@SBA-15 0.1
La@guanine@SBA-15 0.2
La@guanine@SBA-15 0.3
La@guanine@SBA-15 0.4
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
Trace
57
7
8
70
9
83
10
11
12
13
14
91
98
70
Water
100
71
Ethanol:
Reflux
76
Water (1:1)
15
La@guanine@SBA-15 0.5
Ethanol:
Reflux
60
83
Water (2:1)
16
17
18
19
20
21
22
23
24
25
26
27
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
La@guanine@SBA-15 0.5
PEG-400
DMF
100
100
100
Reflux
Reflux
100
120
25
60
60
60
60
60
60
60
60
60
60
60
60
81
64
DMSO
71
Acetone
n-hexane
Solvent-free
Solvent-free
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
37
Trace
65
71
N.R
40
37
57
73
84
50
60
70
aIsolated yield.
(Table 2, entries 11, 23–27). The obtained result showed
that the reaction rate was strongly influenced by the
type of solvent nature and temperatures. The reaction
did not proceed in ethanol at 25 C (Table 2, entry 11)
and the best result was achieved in ethanol at reflux
condition (Table 2, entry 5). For other solvents no
further improvement in the product yield was observed
even at higher temperatures (100 C).
In order to recognize the applicability of our proce-
dure, the reaction scope was explored using various alde-
hydes with several functionalities such as F, Cl, CH3,
NO2 and OCH3 under the optimized reaction conditions
ꢀ
ꢀ
SCHEME 3 One-pot, domino,
multicomponent synthesis of benzo[c]
pyrano[3,2-a]phenazine derivatives in the
presence of La@guanine@SBA-15

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
9 of 18
TABLE 3 One pot, domino, multi component synthesis of benzo[c]pyrano[3,2-a]phenazine derivatives using La@guanine@SBA-15
(50 mg) in ethanol at reflux condition
M.P ꢀC
Entry
Aldehyde
Product
Time (h)
Yielda (%)
TON
TOF(h−1
)
Measured
Literature
1
4
93
186
46.5
288–290
288–291[25]
2
3
4
5
3
98
99
90
95
196
198
180
190
65.33
286–288
308–310
295–298
274–275
286–288[69]
307–310[69]
295[69]
3
66
5
36
4.5
42.22
273[69]
(Continues)

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NIKOORAZM ET AL.
TABLE 3 (Continued)
M.P ꢀC
Entry
Aldehyde
Product
Time (h)
Yielda (%)
TON
TOF(h−1
)
Measured
Literature
6
4
96
192
48
251–252
>250[70]
7
2
87
174
87
280–282
281–283[25]
8
4
98
196
49
282–284
282–285[71]
9
4.5
92
184
40.88
274–276
275[69]
10
5.5
94
188
34.18
250–252
>250[72]
aIsolated yield.
bReaction conditions: -hydroxynaphthalene-1,4-dione (1 mmol) and benzene-1,2-diamine (1 mmol), aromatic aldehyde (1.0 mmol), malononitrile (1.5 mmol)
and La@guanine@SBA-15 (0.5 mol %), in ethanol at reflux conditions.
(Scheme 3). As shown in Table 3, all the reactions were
successfully performed and good to excellent yields have
been achieved.
The suggested reaction mechanism for the described
combination has been depicted in Scheme 4 based on the
previously-reported reaction pathway.[15] Initially, the

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
11 of 18
SCHEME 4 Proposed mechanism
for the synthesis of 3-amino-1H-
benzo[c]pyrano[3, 2-a]phenazines
[Colour figure can be viewed at
wileyonlinelibrary.com]
intermediate
condensation
A
was formed from the Schiff-base
of benzene-1,2-diamine and
In order to optimize the reaction conditions, the reac-
tion of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (1 mmol)
and para-chloro benzaldehyde (2 mmol) was selected as
the model reaction and the sample reaction was consid-
ered in different conditions such as the amounts of the
catalyst, temperatures and solvents (Scheme 5). The
obtained results are in Table 4. At first, the effect of vari-
ous amounts of the catalyst were examined. We find out
that the reaction does not proceed in the absence of
La@guanine@SBA-15 even after 48 hr (Table 4, entry 1)
and, in the presence of 0.1 mol% of the catalyst, only 53%
yield of the product was achieved (Table 4, entry 2). Also,
the increase in the amount of the catalyst up to 0.5 mol%
increased the product yields up to 95% (Table 4, entry 5).
Afterwards, we have successfully explored the effect of
the solvents and temperature on the progress of the reac-
tion. The results showed that a good yield was obtained
in ethanol at reflux condition (Table 4, entry 5). A lower
yield was observed when the temperatures were
decreased (Table 4, entries 10–13). Therefore, 0.5 mol% of
the catalyst, ethanol as solvent and reflux condition were
selected as the best reaction conditions for the synthesis
2-hydroxynaphthalene 1,4-dione in the presence of La-
guanine@SBA-15 NPS. Sequentially, a possible interme-
diate C was formed via Michael addition of B with
Benzo[a]phenazin-5-ol (intermediate B is formed via the
Knoevenagel
condensation
of
aldehyde
with
malononitrile in the presence of La-guanine@SBA-15
NPS). In the next step, intermolecular cyclization of
intermediate C produced intermediate D. Finally, a tau-
tomeric proton shift produced the final 3-amino-1H- ben-
zo[c]pyrano[3, 2-a]phenazines product (Scheme 4).
Moreover, the role of the catalyst for the synthesis of
4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-
5-ols) derivatives was examined. The synthesis of these
products using the reaction between aldehydes and
3-methyl-1-phenyl-1H-pyrazol-5(4H)-one in the presence
of La@guanine@SBA-15 is shown in Scheme 5.
of
pyrazol-5-ols)
La@guanine@SBA-15.
4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-
derivatives in the present of
For future investigations on the generality and scope
of this protocol, various electron-donating and electron-
withdrawing aldehydes were explored under optimized
SCHEME 5 Optimization of the reaction condition for the
preparation of 4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-
pyrazol-5-ols)

12 of 18
NIKOORAZM ET AL.
TABLE 4 Optimization of the reaction condition for the preparation of 4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols)
Entry
Amount of Catalyst (mol%)
Solvent
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Acetonitrile
DMSO
Temperature (ꢀC)
Time (min)
Yielda (%)
1
-
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
100
2 day
30
30
30
30
30
30
30
30
30
30
30
30
Trace
53
63
84
95
87
83
64
81
b
2
0.1
0.2
0.4
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
3
4
5
6
7
8
PEG-400
DMF
100
9
100
10
11
12
13
Ethanol
Ethanol
Ethanol
Ethanol
25
60
63
84
87
70
75
aIsolated yield.
bNo reaction.
reaction conditions (Scheme 6). As shown in Table 5, the
obtained results show that all the products were obtained
in high to excellent yields.
benzaldehyde (1.0 mmol) and malononitrile (1.5 mmol)
for the synthesis of benzo[c]pyrano[3,2-a]phenazine
derivatives (column b) under the optimized reaction con-
ditions. After completion of the reaction, the solid cata-
lyst was separated by simple filtration, washed by ethanol
and acetone and, then, subjected to the next run. The cat-
alyst has been reused up to over five runs without any
significant loss of its catalytic activity (Figure 8).
Besides, in order to examine the stability of the cata-
lyst after recycling, the recycled catalyst has been charac-
terized by FT-IR and SEM techniques. These
characterizations confirmed that the recovered catalyst is
in good agreement with the fresh catalyst. These charac-
terizations are strong evidences for the high stability of
La-guanine-Sba-15 after recycling.
The suggested reaction mechanism for the described
combination via tandem Knoevenagel–Michael reaction
in the presence of La-guanine@SBA-15 nanocatalyst has
been depicted in Scheme 7 based on the previously-
reported reaction pathway.[77] Initially, the intermediate
III was formed from the Knoevenagel condensation of
aldehyde and Pyrazolone in the presence of La-
guanine@SBA-15 nanocatalyst. Sequentially, a possible
intermediate IV was formed via Michael addition of the
second mol of Pyrazolone with the intermediate III in
order to give bis (pyrazolyl)methanes.
FT-IR spectrums of the recycled catalyst are shown in
Figure 9. The results show that a good agreement can be
observed for FT-IR of the fresh La@guanine@SBA-15
(Figure 9a) and the recycled catalyst (Figure 9b). In this
5 | CATALYST REUSABILITY
To check the reusability of La@guanine@SBA-15, we
examined the reaction between 3-methyl-1-phenyl-1H-
pyrazol-5(4H)-one (1 mmol) and para-chloro benzalde-
hyde (2 mmol) for the synthesis of 4,40-(arylmethylene)-
bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives (col-
umn a), and also, 2-hydroxynaphthalene-1,4-dione
(1 mmol), benzene-1,2-diamine (1 mmol), para-chloro
sense, Figure
9
illustrates good stability of
La@guanine@SBA-15 after recycling.
The SEM image of the recycled catalyst is shown in
Figure 10 in which the particles of the recovered catalyst
were observed between 15–20 nm with homogeneous size
and morphology. SEM image of the recycled catalyst is in
SCHEME 6 Synthesis of 4,40-(arylmethylene)-bis-
(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives in the
presence of La@guanine@SBA-15

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
13 of 18
TABLE 5 Synthesis of 4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives catalyzed by La@guanine@SBA-15a
M.P ꢀC
Time
(min)
Yield
(%)b
TOF
Entry Aldehyde
Product
TON (min−1
)
Measured Literature
169–171
170–172[73]
1
40
98
196
4.9
2
30
95
190
6.33
212–214
213–215[74]
3
30
95
190
6.33
198–200
198–200[75]
4
45
94
188
4.17
200–203
202–204[73]
5
55
87
174
3.16
172–174
173–175[74]
153–155[74]
(Continues)
6
50
88
176
3.52
153–155

14 of 18
NIKOORAZM ET AL.
TABLE 5 (Continued)
M.P ꢀC
Measured Literature
194–197
194–196[74]
Time
(min)
Yield
(%)b
TOF
Entry Aldehyde
Product
TON (min−1
)
7
90
93
186
2.06
8
25
91
182
7.28
226–228
225–227[75]
9
35
89
178
5.08
150–152
151–153[76]
10
120
84
168
1.4
214–216
214–216[75]
aReaction conditions: 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (1 mmol), aldehyde (2 mmol), La@guanine@SBA-15 (0.5 mol %), in ethanol at reflux
condition,
bIsolated yield.
good agreement with SEM image of the fresh catalyst
(Figure 5). Therefore, size and shape of the catalyst have
not been changed after recycling.
pyrano[2,3-c]phenazine-2-carbonitrile
and
4,40-
((4-chlorophenyl)methylene)bis(3-methyl-1-phenyl-1H-
pyrazol-5-ol) in the presence of La@guanine@SBA-15
was performed under the optimal reaction conditions.
After half-time of the reactions, they were terminated,
and the corresponding products were obtained in 57 and
45% of yields, respectively. Afterwards, both of the reac-
tions were repeated, then, at the half-time of the reaction,
the catalyst was separated by simple filtration from the
reaction mixture and, finally, the filtrate was allowed to
react further. We found out that only a trace conversion
6 | HOT FILTRATION TEST
Moreover, hot filtration test was performed in order to
prove that the La was not leaching out from the solid cat-
alyst during the organic reactions. Accordingly, the syn-
thesis
of
3-amino-1-(4-chlorophenyl)-1H-benzo[a]

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
15 of 18
SCHEME 7 Proposed mechanism for the synthesis of
4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-
5-ols) [Colour figure can be viewed at wileyonlinelibrary.
com]
(< 3and 4% respectively) of the tandem Knoevenagel
condensation–Michael addition–cyclization reactions was
observed upon heating the catalyst-free solution for other
half time of the reaction. In addition, the exact amount of
La, in the recovered catalyst, was obtained by ICP-OSE as
content in the reaction media in the synthesis of
3-amino-1-(4-chlorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile
and
4,40-((4-chlorophenyl)
1.30 × 10−3 mol g−1
.
7 | LEACHING TEST
In order to consider the leaching of La into the reaction
media, ICP-AES analysis was performed. Besides, the La
FIGURE 8 Reuse of the La@guanine@SBA-15 for the for the
synthesis of 4,40-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-
pyrazol-5-ols) derivatives (column a) and benzo[c]pyrano[3,2-a]
phenazine derivatives (column b) [Colour figure can be viewed at
wileyonlinelibrary.com]
FIGURE 9 FT-IR spectra of (a) La@guanine@SBA-15 and
(b) recovered La@guanine@SBA-15 catalyst [Colour figure can be
viewed at wileyonlinelibrary.com]

16 of 18
NIKOORAZM ET AL.
methylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) was
found to be 0.79 and 0.67%, respectively. The results show
that the leaching of La into the reaction media is
negligible.
8 | COMPARISON
In order to demonstrate the superiority of our catalyst to
other reported catalysts for the synthesis of bis
(pyrazolyl)methanes (Table 5) and polyhydroquinolines
(Table 6), using p-Clbenzaldehyde, as the representative
example, they were compared to the best of the well-
known data from the literature as outlined in the Table 6
and 7, respectively. As it can be seen in this Table 6 & 7,
this new method was better than the other catalysts in
terms of reaction temperature, time and yield factors.
9 | CONCLUSION
Herein, we have utilized La@guanine@SBA-15 as a
green and heterogeneous catalyst for the one pot, domino
multi-component synthesis of benzo [a] pyrano [2, 3-c]
FIGURE 10 SEM image of recovered La@guanine@SBA-15
nanocatalyst
TABLE 6 Comparison results of efficiency of La@guanine@SBA-15 in the synthesis of 4,40-((4-chlorophenyl)methylene)
bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) with other catalysts reported in the literature
Entry
Catalyst
Conditions
Time (min)
Yield (%)a
TON
6.1
TOF (min−1
0.20
)
Ref.
[78]
1
2
3
4
5
6
7
8
aspirin
EtOH/H2O, 60 ꢀC
30
5
92
97
80
96
94
85
90
95
[79]
[80]
[81]
[82]
[83]
[77]
AP-SiO2
CH3CN, r.t
3.2
0.64
DCDBTSD
Solvent-free, 80 ꢀC
Solvent-free, 80 ꢀC
Solvent-free, 50 ꢀC
EtOH, Reflux
40
8
8.0
0.20
CuFe2O4
24.0
94
3.00
[Pyridine–SO3H]Cl
SASPSPE
8
11.75
0.18
132
20
30
25
Ni-guanidine@MCM-41 NPs
La@guanine@SBA-15
Acetonitrile, 80 ꢀC
11.2
190
0.56
EtOH, Reflux
6.33
This work
aIsolated yield.
TABLE 7 Comparison results of efficiency of La@guanine@SBA-15 in the synthesis of 3-amino-1-(4-chlorophenyl)-1H-benzo[a]
pyrano[2,3-c]phenazine-2-carbonitrile with other catalysts reported in the literature
Entry
Catalyst
Conditions
Time (min)
Yield (%)a
Ref.
[72]
1
2
3
4
5
6
DABCO
EtOH, Reflux
Solvent –Free, 75 ꢀC
Solvent –Free, 75 oC
PEG, 90 ꢀC
300
7
91
94
94
90
90
98
[84]
[69]
[15]
[28]
Nano CuO
1-butyl-3-methylimidazolium hydroxide
FeAl2O4 (Hercynite)
Ni-Gly-isatin@boehmite
La@guanine@SBA-15
6
180
120
180
PEG, 80 ꢀC
EtOH, Reflux
This work
aIsolated yield.

LA CATALYZED KNOEVENAGEL CONDENSATION-MICHAEL ADDITION-CYCLIZATIONS
17 of 18
phenazine and the synthesis of 4,40-(arylmethylene)-bis-
(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives. The
solid catalyst was characterized by TGA, XRD, FT-IR,
EDS, SEM, MAP and BET techniques. This procedure
has the advantages of minimizing the chemical wastes,
being safe and environmentally-friendly, having mild
reaction conditions, ease of separation and non-toxic and
reusable catalyst and also giving the products in high
yields within short reaction times.
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ACKNOWLEDGMENTS
This work was supported by the Iran National Science
Foundation and research facilities of Ilam University,
Ilam, Iran.
[27] H. Naeimi, M. F. Zarabi, RSC Adv. 2019, 9, 7400.
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ORCID
Mohsen Nikoorazm https://orcid.org/0000-0002-4013-
0868
Masoud Mohammadi https://orcid.org/0000-0002-
1043-3470
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How to cite this article: Nikoorazm M,
Khanmoradi M, Mohammadi M. Guanine-La
complex supported onto SBA-15: A novel efficient
heterogeneous mesoporous nanocatalyst for one-
pot, multi-component Tandem Knoevenagel
condensation–Michael addition–cyclization
Reactions. Appl Organometal Chem. 2020;e5504.
https://doi.org/10.1002/aoc.5504