Nano silica-bonded aminoethylpiperazine: A highly efficient and reusable heterogeneous catalyst for the synthesis of 4H-chromene and 12H-chromeno[2,3-d]pyrimidine derivatives

Article abstract of DOI:10.1007/s13738-015-0607-y

Abstract The reaction of nano silica with 3-chloropropyltrimethoxysilane followed by treatment with aminoethylpiperazine afforded nano silica-bonded aminoethylpiperazine (SB-APP). The structure of the synthesized SB-APP was characterized by FT-IR, TGA, BE

Full text of DOI:10.1007/s13738-015-0607-y

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0607-y
ORIGINAL PAPER
Nano silica‑bonded aminoethylpiperazine: a highly efficient
and reusable heterogeneous catalyst for the synthesis
of 4H‑chromene and 12H‑chromeno[2,3‑d]pyrimidine derivatives
Mahmood Tajbakhsh · Mohaddeseh Kariminasab · Heshmatollah Alinezhad ·
Rahman Hosseinzadeh · Parizad Rezaee · Mahgol Tajbakhsh ·
Helia Janatian Gazvini · Mohammadreza Azizi Amiri
Received: 6 September 2014 / Accepted: 6 February 2015
©
Iranian Chemical Society 2015
Abstract The reaction of nano silica with 3-chloro-
propyltrimethoxysilane followed by treatment with ami-
noethylpiperazine afforded nano silica-bonded aminoeth-
ylpiperazine (SB-APP). The structure of the synthesized
SB-APP was characterized by FT-IR, TGA, BET, SEM
and elemental analysis and identified as an efficient basic
catalyst for the preparation of 2-amino-4H-chromenes
and 12H-chromeno[2,3-d]pyrimidine derivatives. One-
pot three-component reaction of phenols, aromatic alde-
hydes and malononitrile in the presence of the catalytic
amounts of SB-APP afforded high yield of the correspond-
ing 2-amino-4H-chromenes under mild reaction condi-
tions. 12H-Chromeno[2,3-d]pyrimidines were successfully
synthesized with reasonable yield by reacting the 2-amino-
Graphical abstract
Nano silica-bonded aminoethylpiperazine: a highly efficient and reusable heterogeneous
catalyst for the synthesis of 4H-chromene and 12H-chromeno[2,3-d]pyrimidine derivatives
Mahmood Tajbakhsh,a, Mohaddeseh Kariminasab, Heshmatollah Alinezhad,a Rahman
Hosseinzadeh,a Parizad Rezaee,b Mahgol Tajbakhsh,a Helia Janatian Gazvinic and
Mohammadreza Azizi Amiria
a
a
faculty of Chemistry, University of Mazandaran, P. O. Box 47416 -95447, Babolsar, Iran.
b
Department of Chemical Engineering, Abadan Branch, Islamic Azad University, Abadan, Iran
c
School of Chemistry, College of Science, University of Tehran, P. O. Box 14155-6455, Tehhran, Iran
(
*Corresponding Author Tel & Fax: +981135302351; E-mail: tajbaksh@umz.ac.ir)
NC
CN
CHO
NH
OH
O
N
Si
N
H
O
OMe
4
H-chromenes with acetic anhydride in the same pot with-
NH2
NH
O
N
out purification of the corresponding chromene intermedi-
Si
N
O
OMe
CN
1
ates. All products were characterized by FT-IR, H NMR,
NH2
O
N
1
3
O
C NMR and MS data. The catalyst was simply recovered
Si
OMe
N
H
O
from the reaction mixture and reused several times without
significant loss of catalytic activity.
More Basic Sites
26 Example (80-95%)
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-015-0607-y) contains supplementary
material, which is available to authorized users.
Keywords Nano silica · Aminoethylpiperazine ·
Basic catalyst · Chromene
M. Tajbakhsh (*) · M. Kariminasab · H. Alinezhad ·
R. Hosseinzadeh · M. Tajbakhsh · M. A. Amiri
Faculty of Chemistry, University of Mazandaran,
P. O. Box 47416-95447, Babolsar, Iran
Introduction
e-mail: tajbaksh@umz.ac.ir
Heterogeneous catalysts play an important role in the cur-
rent industrial scenario because of their significant advan-
tages in terms of easier product recovery, minimizing
disposal problems, regeneration of active sites and environ-
mental perspectives [1]. However, due to the ever growing
demand of the day-to-day products, hazardous homogene-
ous reagents (H SO , HF, NaOH, KOH, CH COOH and
P. Rezaee
Department of Chemical Engineering, Abadan Branch,
Islamic Azad University, Abadan, Iran
H. J. Gazvini
School of Chemistry, College of Science, University of Tehran,
P. O. Box 14155-6455, Tehran, Iran
2
4
3
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J IRAN CHEM SOC
Scheme 1 Preparation of
SB-APP
Cl
Cl
HO
OH
MeO
MeO
Cl
Toluene
OH
OH
Si
Cl
SiO2
Cl
SiO2
+
HO
OMe
Cl
Cl
HO
SiCPMS
H
H N
2
NH2
N
N
Et N
3
N
N
NH
N
HN
H
N
NH
N
SiO2
N
N
H N
2
N
NH
N
N
NH2
HN
SB-PAPP
transition metal containing catalysts) are still in use as cata-
lysts for many organic transformations. The heterogeneous
catalysts are known to suppress side reactions and proceed
selectively with higher rates and product yield [2]. This
means cost and energy savings for the downstream separa-
tion and purification of the product. It also avoids the com-
plex neutralization and separation steps needed to recover
the homogeneous catalyst from the reaction mixture. The
recovered solid catalysts can be readily regenerated for
further use. The covalently bonded groups are resistant to
removal from the surface of the supporting materials by
solvent molecules [3].
It is well known that one-pot multi-component conden-
sations represent a possible instrument to perform a near
ideal synthesis because of their ability for the possibility of
building up complex molecules with maximum simplicity
and brevity [4]. Reactions under solvent-free conditions [5]
are also attractive for researchers, both from academia and
industry, due to the fact that without solvent, reactions usu-
ally need shorter reaction time, simpler reactors and simple
and efficient workup procedures.
in the synthesis of the well-known 2-amino-4H-chromene
family. 2-Amino-4H-chromenes are interesting derivatives
of chromenes which are used as cosmetics and pigments
[6], anticoagulant, spasmolytic, antianaphylactic, diuretic
[7], antibacterial [8] and anticancer agents [9]. On the other
hand, pyrimidine scaffold is the base of many bioactive
molecules such as antitubercular [10], antibacterial [11] and
antitumor compounds [12]. Moreover, nitrogen-containing
heterocycles are also of broad pharmaceutical interest and
significance, which justifies our continuing efforts in explor-
ing synthetic strategies which lead to structures formed
from a combination of both types of heterocycles [13].
A literature survey revealed several modified procedures
using different catalysts for the synthesis of 2-amino-4H-
chromenes including cetyltrimethylammonium chloride
(CTAC) [14], cetyltrimethylammonium bromide (CTAB)
coupled with ultrasound [15], c-alumina [16], K CO [8],
2
3
nano size MgO [17], heteropolyacid [18], hexadecyltri-
methylammonium bromide (HTMAB) [19], triethylben-
zylammonium chloride (TEBA) [20], TiCl4 [21], N,N-
dimethylaminoethylbenzyldimethylammonium
chloride
Beside these remarkable properties which led to a num-
ber of industrial usages of heterogeneous catalysts based
on silica, utilizing these structures in organic synthesis has
been well studied. A large surface area, high thermal and
chemical stability and numerous active sites especially in
functionalized nano size silica make it excellent candidate
to catalyze organic reactions. To explore its sufficiency, we
intended to survey functionalized nano silica as a catalyst
[22], sodium carbonate [23], NaOAc/KF [24], Amberlyst
A21 [25], NaI [26], acetic acid functionalized ionic liquid
[27] and DABCO/agar–agar [28]. Recently, electrochemi-
cally induced multi-component condensation for the syn-
thesis of chromenes by electrolysis in an undivided cell in
the presence of NaBr as an electrolyte was reported [29,
30]. However, most of these methods suffer from some
drawbacks such as low yields, long reaction times, harsh
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J IRAN CHEM SOC
4
H-chromene derivatives under solvent-free conditions.
Also, chromeno pyrimidines were further synthesized by
reacting the 2-amino-4H-chromenes with acetic anhydride
in the same pot without purification of the corresponding
chromene intermediates.
Experimental section
General procedure
Nano silica with average grain size (10 nm) and specific
2
surface area (>600 m /g) was purchased from US Research
Nanomaterial and other materials were purchased from
1
Fluka, Merck and Aldrich chemical companies. H and
1
3
C NMR spectra were recorded on a Bruker DRX-400
1
13
AVANCE (400 and 100 MHz for H and C respectively)
in DMSO-d as solvent. Chemical shifts were on the δ
6
Fig. 1 FTIR spectra of a nano SiO , b SiCPMS, c SB-APP and d
pure APP
scale, relative to internal Me Si. Melting points were deter-
2
4
mined on a Thermo Scientific IA9200 and uncorrected.
Mass spectra were obtained on an Agilent Technolo-
gies instrument and FT-IR spectra were determined on a
Bruker instrument. Thermogravimetric analysis (TGA) was
recorded on a Stanton Redcraft STA-780 (London, UK).
All the products were characterized by comparison of their
1
13
FT-IR, H NMR, and C NMR spectra, and their melting
points with the reported data.
Preparation of nano silica-bonded n-propyl chloride
(SiCPMS)
The modified catalyst was prepared as previously described
38]. Initially, the surface of nano silica was activated by
refluxing of nano silica (5.0 g) in HCl (6 M, 50 mL) for
4 h. Then, activated nano silica was filtered and repeat-
[
2
edly washed with double distilled water until the pH of the
solution was adjusted to 6. Finally, the treated nano silica
was dried in an oven at 110 °C for 12 h. Afterward, 2 g of
activated nano silica was suspended in 20 mL of dry tolu-
ene containing 2 mL of 3-chloropropyltrimethoxysilane
(CPMS) as silylating reagent and refluxed for 12 h to pro-
duce the chloro functionalized nano silica (SiCPMS). At
the end of this period, the SiCPMS was filtered off, washed
with toluene (70 mL), ethanol (40 mL) and diethyl ether
(40 mL), respectively, to eliminate the unreacted reagent
and then dried at 70 °C for 6 h.
Fig. 2 The thermogeravimetric analysis of SB-APP
reaction conditions, tedious workup procedures and appli-
cation of expensive catalysts. Moreover, in many of the
reported methods, catalysts are not recyclable.
Therefore, use of supported and reusable catalysts in
organic transformations has economic and environmental
benefits. Some attempts have been made to immobilize sil-
ica framework catalysts for the synthesis of 4H-chromenes
[31–37], which leads us to present a green procedure for
the synthesis of 4H-chromene derivatives by immobilized
heterogeneous catalysts.
Preparation of nano silica-bonded aminoethylpiperazine
(SB-APP)
Due to the advantages of one-pot multi-component
reactions and heterogeneous catalysts, herein we report
the preparation of nano silica-bonded n-propyl-aminoeth-
ylpiperazine as a novel heterogeneous and recyclable
catalyst and its successful application in the synthesis of
SiCPMS (1.5 g), aminoethylpiperazine (1.5 mL), triethyl-
amine (1 mL) and dry toluene (20 mL) were added into a
50 mL round bottom flask, under continuous stirring and
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J IRAN CHEM SOC
Fig. 3 The SEM images of
SB-APP
Table 1 Effect of solvent and evaluation of catalytic activity of SB-
APP on the rate of the reaction and yield of the product
Entry Solvent
Catalyst (g) T (°C) Time (min) Yield (%)a
1
2
3
4
5
6
7
8
9
1
1
Toluene
Xylene
Water
0.10
0.10
0.10
0.10
0.10
110
140
100
87
24 h
24 h
24 h
24 h
24 h
24 h
30
40
10
–
Ethanol
DMF
–
120
80
–
Acetonitrile 0.10
Solvent free 0.10
Solvent free 0.05
Solvent free 0.08
Solvent free 0.15
–
80
95
85
95
95
–
80
45
80
30
0
1
80
40
Solvent free
–
80
60
Reaction conditions: β-naphthol (0.5 mmol), 4-chlorobenzaldehyde
0.5 mmol), malononitrile (0.5 mmol) and solvent volume (3 mL) at
(
reflux temperature
a
Isolated yields
Fig. 4 The N adsorption–desorption isotherm of SB-APP
2
SB-APP (0.08 g) was added and the mixture was heated at
80 °C under solvent-free conditions. After completion of
the reaction (monitored by TLC), ethanol was added and
the reaction mixture was filtered. The remaining solid was
washed with warm ethanol to separate the catalyst. The
solvent was evaporated and the crude product purified by
recrystallization from ethanol–water. The recycled catalyst
was washed with acetone, dried and reused.
argon atmosphere at 70 °C for 48 h. Afterward, the reac-
tion mixture was cooled to room temperature, transferred
to a vacuum glass filter and washed with toluene and eth-
anol. Then, the solid product was transferred to a Soxhlet
extractor with ethanol as extraction solvent to eliminate the
excess amount of reagents and the resulting SB-APP was
separated and dried in vacuum at 80 °C for 12 h.
General procedure for the preparation
General procedure for the preparation
of 2-amino-4H-chromene derivatives
of 12H-chromeno[2,3-d]pyrimidines
To a mixture of phenol derivatives (0.5 mmol), aromatic
aldehydes (0.5 mmol) and malononitrile (0.5 mmol),
To a mixture of β-naphthol (0.5 mmol), aromatic alde-
hydes (0.5 mmol) and malononitrile (0.5 mmol), SB-APP
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J IRAN CHEM SOC
Table 2 Preparation of various 2-amino-4H-chromenes in the presence of SB-APP
Reaction conditions: phenols (0.5 mmol), aromatic aldehydes (0.5 mmol), malononitrile (0.5 mmol) and SB-APP (0.08 gr) under solvent-free
conditions at 80 °C
a
Isolated yields
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J IRAN CHEM SOC
Table 3 One-pot synthesis
of 12H-chromeno[2,3-d]
pyrimidines
a
Isolated yields
(0.08 g) was added and the mixture was heated at 80 °C
under solvent-free conditions. After completion of the
reaction (monitored by TLC), acetic anhydride (1 ml) was
added and the reaction mixture heated at 80 °C for 24 h.
After cooling, the reaction mixture was diluted with dichlo-
romethane and then filtered to separate the catalyst. The
filtrate was washed with brine and dried over magnesium
sulfate. The solvent was evaporated and the solid product
crystallized from ethyl acetate.
Spectral data for selected products:
2
‑Amino‑4‑(4‑chlorophenyl)‑4H‑benzo[f]chromene‑
1
3
‑carbonitrile (Table 2, entry 2) H NMR (400 MHz,
Fig. 5 Catalyst recyclability
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J IRAN CHEM SOC
Table 4 Comparison of SB-APP with some other reported catalysts
Entry
Solvent and catalyst
T (°C)
Time (h)
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Solvent free, tetrabutylammonium chloride (TBAC) (10 mol %)
DCM, thiourea-tertiary amines (20 mol %)
Solvent free, Na CO (10 mol %)
100
r.t.
0.6
48
80
72
100
86
90
90
91
90
72
94
[40]
[41]
125
80
0.6
2
[23]
2
3
a
3-Butyl-1-methylimidazolium hexafluorophosphate [bmim ][PF ] (1.5 ml)
[42]
6
a
H O, 1-butyl-3-methylimidazolium hydroxide [bmim ][OH] (50 mol %)
100
105
110
150
r.t.
1
[43]
2
M.W., aq.K CO (10 ml)
3.2 min
0.5
0.25
6
[8]
2
3
b
Acetic acid functionalized ionic liquid {[cmmim]Br }(10 mol %), H O/EtOH
[27]
2
c
2+
Solvent free, [Cu(bpdo) .2H O] /SBA -15
[31]
2
2
EtOH, Amberlyst A21 (30 mg)
Solvent free, SB-APP (0.08 gr)
[25]
1
0
80
0.6
This work
Reaction conditions: β-naphthol, benzaldehyde and malononitrile
a
[bmim]: 1-butyl-3-methyl imidazolium
b
c
[
cmmim]Br: 1-carboxymethyl-3-methylimidazolium bromide
(bpdo) = 2,20-bipyridine,1,10-dioxide
DMSO-d ): δ = 5.36 (s, 1H, CH), 7.05 (s, 2H, NH ), 7.19–
The immobilization of aminoethylpiperazine onto the
nano silica have led to formation of a high loading of multi-
ple types of amine sites on the silica surface. For each mol-
ecule of aminoethylpiperazine, three amine groups would
be immobilized and the loading amounts increased. There-
fore, a lower weight percent would be required for catalytic
reaction.
6
2
7
2
.22 (d, 2H, J = 8.4 Hz), 7.31–7.35 (m, 3H), 7.4–7.47 (m,
13
H), 7.8–7.82 (d, 1H, J = 7.2 Hz), 7.91–7.96 (m, 2H).
C
NMR (100 MHz, DMSO-d ): δ = 37.74, 57.79, 115.62,
6
1
1
1
1
17.27, 120.82, 124.02, 125.48, 127.65, 128.99, 129.17,
29.32, 130.17, 130.49, 131.28, 131.61, 145.17, 147.24,
60.16. IR (KBr) υ: 3,424, 3,324, 2,196, 1,654, 1,592,
−
1
,234 cm .
The FT-IR spectra of the nano silica (a), SiCPMS (b),
SB-APP (c) and aminoethylpiperazine (APP) (d) are pre-
1
2‑(4‑Chlorophenyl)‑9‑methyl‑10,12‑dihydro‑
1
1H‑benzo [5, 6] chromeno[2,3‑d] pyrimidine‑11‑one
sented in Fig. 1. The pure nano SiO shows characteristic
2
1
−1
(Table 3, entry 1) H NMR (400 MHz, DMSO-d6):
absorbance peaks at 1,098 cm for stretching vibration of
−1
δ = 2.28 (s, 3H, CH ), 5.75 (s, 1H, CH), 7.25-7.27 (d, 2H,
Si–O–Si and at 3,447 cm for stretching vibration of the
OH group (Fig. 1a). In the spectrum of nano silica-bonded
3
J = 8.4 Hz), 7.32–7.34 (d, 2H, J = 8.8 Hz), 7.42–7.46 (td,
−
1
1
H, J = 8 Hz, J = 2.4 Hz), 7.47–7.51 (m, 2H), 7.93–7.98
n-propyl chloride, peaks at 1,460 and 1,210 cm were
observed which indicate the presence of CH bending and
Si–C stretching vibrations, respectively. The FT-IR spec-
trum shows an overlap of the CH bending and Si–C stretch-
ing bands with the Si–O–Si stretching bands in the func-
tionalized nano silica (Fig. 1b). Figure 1c shows the FT-IR
spectrum of SB-APP with characteristic peaks of Si–O–Si
1
3
(m, 3H), 12.56 (s, 1H, NH). C NMR (100 MHz, DMSO-
d ): δ = 21.44, 35.28, 100.63, 116.36, 117.89, 123.81,
6
1
1
25.52, 127.8, 128.67, 129.08, 130.17, 130.42, 130.81,
31.49, 131.52, 143.67, 148.21, 159.14, 161.02, 162.72.
IR (KBr) υ: 3,425, 3,005, 2,867, 2,781, 1,646, 1,599,
1
1
− +
,231 cm . m/z 347 (M , 15 %), 263.1 (M-C H Cl,
6 4
1
−1
00 %), 75 (6 %).
Complete experimental and spectral data are available
and OH groups at 1,098 and 3,447 cm , respectively. As
seen in Fig. 1c, the absorption peak of NH of aminoethyl-
−
1
−1
online in the Supplementary Material.
piperazine at 3,273 cm and C–N at 1,330 cm (Fig. 1d)
overlapped with peaks of OH and Si–O–Si. However, CH
−1
stretching at 2,938 and 2,808 cm and CH bending at
−1
Results and discussion
1,456 cm were observed. These results prove that the
APP was successfully grafted onto the nano silica-bonded
n-propyl chloride to give SB-APP.
The synthesis of SB-APP is shown in Scheme 1. The sur-
face of nano silica was activated by HCl (6 M) at reflux
temperature. Afterward, activated nano silica was sus-
pended in dry toluene containing CPMS as silylating rea-
gent and the mixture was refluxed to produce SiCPMS.
Then, aminoethylpiperazine was reacted with SiCPMS to
yield SB-APP.
The thermal stability of SB-APP was investigated by TG
analysis, and the result is shown in Fig. 2. The weight loss
around 100 °C is related to the water molecules and other
volatile organic compounds which have been adsorbed on
the surface of the catalyst. Following the thermogram, the
weight decrease observed in the diagram starting at around
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J IRAN CHEM SOC
O
NC
CN
Ar
H
H
Ar
NH
N
N
N
CN
CN
N
H
NH
N
NH2
NH3
N
N
N
O
H
H
CN
CN
N
C
H
N
Ar
Ar
H
CN
N
N
H
NH2
N
N
O
H
N
O
NH2
H
Ar
N
N
N
CN
NH
N
NH
2
NH
N
NH2
N
N
OH
NH
N
CN
N
H
NH2
Ar
NH2
N
N
O
CN
O
H
N
HN
O
O
CN
O
Ar
NH2
O
O
Ar
NH
Ar
N
Ar
N
O
O
O
O
-
CH CO H
Dimorth
Rearrangement
3
2
Scheme 2 Plausible mechanism for synthesis of chromene derivatives
2
50 °C can be related to the loss of the covalently bounded
respectively. From the CHN analysis, the loading amount
of APP was calculated to be 0.78 mmol/g, which is in good
agreement with TG analysis.
The scanning electron microscopy (SEM) images are
shown in Fig. 3. The SEM images show that the sample
is granular and porous. The size of granular particles are
between 25 and 33 nm.
organic group. Weight loss of 15 % occurred in the range
of 250–800 °C, corresponding to the decomposition of the
organic groups, which yielded the final siloxane groups.
From this weight loss, the loading amount of APP was cal-
culated to be 0.88 mmol/g.
The elemental analysis data along with the summary of
the measured and calculated values for C, H and N, gave
the following results: C, H and N, 9.82, 2.56 and 3.28 %,
Figure 4 shows the nitrogen adsorption isotherm
obtained for SB-APP, the hysteresis loop observed in the
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J IRAN CHEM SOC
range of 0.57 < P/P < 1.0, is associated with capillary
malononitrile, followed by the cyclo-condensation reaction
with β-naphthol to form the desired 2-amino-4H-chromene.
Although the detailed mechanism of the synthesis of
chromeno pyrimidine was not very clear, a possible mecha-
nism has been proposed in Scheme 2.
0
condensation according to IUPAC classification. The iso-
therm exhibited by SB-APP is of type IV and exhibited
an H3 hysteresis loop [39]. The specific surface area and
the total pore volume were calculated by the BET method,
2
3
1
06.07 m /g and 0.89 cm /g, respectively. The pore size
was found to be 18.94 nm with the BJH method.
The catalytic activity of the synthesized SB-APP was
investigated in the three-component condensation reaction
of 4-chlorobenzaldehyde, malononitrile and β-naphthol
as a model reaction for the preparation of 2-amino-4H-
chromene. To evaluate the effect of solvent, various solvents
such as toluene, acetonitrile, xylene, DMF, ethanol and
water were used for the synthesis of 2-amino-4H-chromene
in the presence of SB-APP (Table 1). Use of toluene and
xylene as the reaction solvent afforded a low yield of the
product after 24 h. In the presence of water, ethanol, DMF
and acetonitrile, no product was obtained. The reaction
under solvent-free conditions not only went to completion
efficiently, but also furnished the product in excellent yield.
When the reaction was carried out in the absence of
any catalyst, no product was detected. In the presence of
SB-APP the reaction was possible and, to determine the
appropriate amount of the catalyst, we investigated the
model reaction at different amounts of SB-APP, 0.05, 0.08,
Conclusions
We have developed a novel and highly efficient protocol for
the multi-component synthesis of 2-amino-4H-chromenes
by the reaction of malononitrile with various aryl aldehydes
and phenols in the presence of SB-APP. The synthesis of
various 12H-chromeno[2,3-d]pyrimidines in the same pot
without isolating the chromene intermediate was also per-
formed. The method offers several significant advantages
such as high conversion, easy handling, clean reaction pro-
file and short reaction times which makes it a useful and an
attractive protocol compared to the existing ones.
Acknowledgments We are thankful to the Research Council of
University of Mazandaran for the partial support of this work.
References
0
0
.1 and 0.15 g (Table 1, entries 7–10). This indicates that
.08 g of SB-APP is sufficient to carry out the reaction
1
2
. A. Wight, M. Davis, Chem. Rev. 102, 3589 (2002)
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by the three-component condensation of various aromatic
aldehydes, malononitrile and phenols in the presence of
SB-APP under solvent-free conditions. In all the cases,
excellent yield of the products was observed (Table 2).
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