One‐pot synthesis of dihydro-1H-indeno[1,2-b] pyridines and tetrahydrobenzo[b] pyran derivatives using a new and efficient nanocomposite catalyst based on N‐butylsulfonate‐functionalized MMWCNTs-D-NH2

Article abstract of DOI:10.1016/j.poly.2019.114179

In this study, magnetic multi-walled carbon nanotubes were functionalized with polyamidoamine (PAMAM) dendrimers and modified with butylsulfonate to afford MMWCNTs-D-(CH₂)₄-SO₃H. The synthesized nanocomposite (MMWCNTs-D-(C

Full text of DOI:10.1016/j.poly.2019.114179

Journal Pre-proofs
One-Pot Synthesis of Dihydro-1H-Indeno[1,2-b] Pyridines and Tetrahydroben-
zo[b] Pyran Derivatives using a New and Efficient Nanocomposite Catalyst
Based on N-Butylsulfonate-Functionalized MMWCNTs-D-NH2
Fatemeh Adibian, Ali Reza Pourali, Behrooz Maleki, Mehdi Baghayeri,
Amirhassan Amiri
PII:
S0277-5387(19)30616-3
DOI:
https://doi.org/10.1016/j.poly.2019.114179
POLY 114179
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
7 June 2019
5 October 2019
13 October 2019
Please cite this article as: F. Adibian, A.R. Pourali, B. Maleki, M. Baghayeri, A. Amiri, One-Pot Synthesis of
Dihydro-1H-Indeno[1,2-b] Pyridines and Tetrahydrobenzo[b] Pyran Derivatives using a New and Efficient
Nanocomposite Catalyst Based on N-Butylsulfonate-Functionalized MMWCNTs-D-NH2, Polyhedron (2019), doi:
https://doi.org/10.1016/j.poly.2019.114179
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One‐Pot Synthesis of Dihydro-1H-Indeno[1,2-b] Pyridines and
Tetrahydrobenzo[b] Pyran Derivatives using a New and Efficient
Nanocomposite Catalyst Based on N‐Butylsulfonate‐Functionalized
MMWCNTs-D-NH2
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Fatemeh Adibian,1 Ali Reza Pourali,*1 Behrooz Maleki,*2 Mehdi Baghayeri,2 Amirhassan
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Amiri2
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1School of Chemistry, Damghan University, 36715-364, Damghan, Iran
pourali@du.ac.ir
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2Department of Chemistry, Hakim Sabzevari University, Sabzevar, 96179-76487, Iran
b.maleki@hsu.ac.ir
ABSTRACT
In this study, magnetic multi-walled carbon nanotubes were functionalized with
polyamidoamine (PAMAM) dendrimers and modified with butylsulfonate to afford
MMWCNTs-D-(CH2)4-SO3H. The synthesized nanocomposite (MMWCNTs-D-(CH2)4-
SO3H) was characterized by various techniques such as Fourier transform infrared
spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron
microscopy (SEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). This
nanocomposite catalyst effectively catalyzed four and three component reactions for the
synthesis of dihydro-1H-Indeno[1,2-b] pyridines and tetrahydrobenzo[b] pyrans (85-98%
yield in 15-20 min and 80-98% yield in 12-30 min, respectively). In addition, the
magnetically recoverable catalyst could be easily recycled at least five times without
significant loss of catalytic activity. In the first step of synthesis of nanocomposite the Fe3O4
nanoparticles were deposited on oxidized MWCNTs, then a modified PAMAM dendrimer
was used to bond to the carbonyl groups. Finally MMWCNTs-D-NH2 functionalized with
1,4‐butanesultone.
KEYWORDS
Dendrimer, Dihydro-1H-Indeno[1,2-b] pyridines, Magnetic Catalyst, MMWCNTs-D-(CH2)4-
SO3H nanocomposite, tetrahydrobenzo[b] pyrans.
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1. INTRODUCTION
Acid catalysts play an important role in organic reactions. Sulfuric, hydrochloric, nitric and
phosphoric acids are the most commonly used acidic catalysts. However, these catalysts are
of homogeneous catalysts that have disadvantages such as corrosive properties and difficult
separation, also they are not reusable. This is while heterogeneous catalysts have several
advantages such as easy separation, recyclability, minimization of waste product and
toleration of a wide range of temperatures and pressures [1-3]. Therefore, the design and
application of novel heterogeneous catalysts has been well investigated in the last few
decades [4–5].
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A very used method to preparation of heterogeneous catalysts is the stabilize of organic
molecules containing active catalytic sites on the surface of insoluble solids such as inorganic
materials, hybrid materials or synthetic organic polymers [6]. Over the past decade carbon
nanotubes (CNTs) have been used in heterogeneous catalyst systems due to their uniform
nano-structure, high mechanical strength, electrical properties, thermal stability and most
importantly because of their high surface area which enhance significantly the contact
between reactants and catalyst [7–11].
Nevertheless the use of CNTs as supports is restricted in industry due to difficulty in
separation and manipulation which increases the environmental pollution, as well as cost
requirements. In addition, in many applications, external control on materials is also an
important point. That's why magnetic nanoparticles have been loaded on CNTs which leads
to the formation of magnetic CNTs [12]. Among them, magnetic nanoparticles containing
Fe3O4 has attracted intense attention because of their high recycling capability, low
cytotoxicity, high commercially availability, easy handling, unique magnetic response and
chemically modifiable surface [13, 14].
The poor solubility of CNTs in aqueous [15] and organic solutions makes them hard to
disperse. Dendrimers are a new category of artificial macromolecules, which have highly
branched, highly ordered and three-dimensional, architectures with very high degrees of
surface functionality and versatility. Their particular 3-D structure and unique single
dispersity make specific quality, so that they are usable in a wide range of applications such
as chemistry, nanomaterials, molecular diagnostics, and contaminated water purifiers. In
recent years studies on dendrimers have been considered in biochemical, catalytic, and
nanomaterial branches [16, 17].
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Sultone is cyclic ester of sulfonic acid -mostly with 5 or 6 members in the ring - that have -
SO2-O- group in the ring. A wide variety of nucleophiles can attack to the sulfone group of
the aryl sultone till sultone acts as a sulfoalkylating agent. Sultons are also effective acidic
catalysts in many organic reactions [18, 19].
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Multi-component reactions (MCRs) involve three or more component reacting in a single
flask to make a new product. One example of an MCRs is synthesis of tetrahydrobenzo[b]-
pyrans. These compounds are significant groups of heterocyclic compounds which have
noted pharmacological and biological properties such as antibacterial [20], antihypertensive,
hepatoprotective, cardiotonic [21], and antitumor [22]. These compounds generally
synthesized via a three-component one-pot reaction in the presence various catalyst such as
amines [23], ionic liquids [24], hexadecyltrimethyl ammonium bromide (Fe3O4@D-NH-
(CH2)4-SO3H) [25], [PVPH]HSO4 [26], [Ch][OH] [27], Ru immobilized in zeolite beta [28],
ZnO-beta zeolite [29], hydroxy sodalite zeolite [30] and Zeolite Y [31].
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MCRs used for the synthesis of dihydro-1H-indeno[1,2-b] pyridines have also gained
remarkable notice in organic synthesis because dihydropyridines have a diversity of
biological activities and generate some drugs to treatment of hypertension such as
amlodipine, nicardipine and nifedipine. Generally, these compounds have been prepared
through the four-component cyclo-condensation of a 1,3-indanedione with an aldehyde, alkyl
acetoacetate and ammonium acetate catalyzed by L-proline [32], Yb(OTf)3 or Sc(OTf)3 [33]
and 2,2,2-trifluoroethanol [34], But these methods have limitations such as low product
yields, several side products, long reaction times and tedious work-up.
Many applications of multifunctional nanomaterials in many fields such as biomedicine [35],
separation [36] and catalysis [37] have paid much attention to them. To production of
multifunctional nanomaterials, the integration of two or more functional components into a
single entity is used. A multitude of reactions have been catalyzed by CNTs or their
composites. For example hydrogenation of nitrobenzene and some substituted nitroarenes
was carried out in the presence of H2O2 functionalized CNTs as catalyst [38]. Also the CNT-
supported iridium–N-heterocyclic carbene materials were utilized in the heterogeneous
cyclohexanone hydrogen-transfer reduction reaction as catalyst [39].
In continuation of our studies of organic reactions in the presence of catalysts [40-43] and the
design of nanomagnetic heterogeneous catalysts for organic transformations [44-46]. In this
work, we successfully synthesized and characterized a novel nano‐magnetic carbon
nanotubes based PAMAM composite as a recoverable heterogeneous catalyst and its
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application for one-pot synthesis of tetrahydrobenzo[b] pyrans and dihydro-1H-indeno[1,2-b]
pyridines (Scheme 1).
O
R
R
CN
CN
CHO
O
H2C
O
O
CN
NH2
O
5
2
OEt
) -
MMWCNTs-D-(CH SO H
+
4
2
3
O
O
R1
R2
O
O
N
R
H
OEt
1
6
R1
7
O
4
NH4OAc
solvent-free, 120 oC
R2
3
EtOH/reflux
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5
6
7
SCHEME 1 Schematic shape for the synthesis of tetrahydrobenzo[b] pyrans (4) and
dihydro-1H-Indeno[1,2-b] pyridines (7) in the presence of MMWCNTs-D-(CH2)4-SO3H
nanocomposite as catalyst
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2. EXPERIMENTAL
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2.1. Materials and Method
Oxidized multi-walled carbon nanotubes (MWCNTs-COOH) with specific surface area of 25
m2.g−1 and average tube inner diameter of 10 to 50 nm were purchased from Sigma-Aldrich.
Other chemicals of high purity were purchased from Merck as analytical reagent (AR) grade
and were used straight without extra purification. For the recording of TEM and SEM images
a Philips CM200 instrument and a S-4300, Hitachi, Japan scanning electron microscope were
respectively used and energy dispersive X-ray analysis (EDAX) attached to the SEM.
Thermal analysis was carried out by thermo gravimetric analysis (TGA) (Q50, TA
Instruments, USA). The Powder X-ray diffraction (XRD) measurements were carried out
using DMAX-2500, Rigaku X-ray diffractometer. IR spectra were recorded with potassium
bromide pellets from 4000 to 400 cm-1 at room temperature using a VERTEX 80V
spectrometer. A Bruker AVANCE 300 MHZ spectrometer was used for recording H &13C
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NMR spectra at 400 MHz and 100 MHz in DMSO-d6 using tetramethylsilane as internal
standard. A vibrating sample magnetometer (VSM) (JDM-13D magnetometer) was used to
characterize the magnetic properties of nanocomposite.
2.2. Preparation of catalyst
2.2.1. Synthesis of MWCNTs-COOH/Fe3O4 (MMWCNTs)
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Magnetic MWCNTs-COOH (MWCNTs-COOH/Fe3O4 or MMWCNTs) was synthesized via
modifying the method proposed by Chan et al [47]. 1.5 g FeCl3.6H2O and 0.8 g FeCl2.4H2O
were added to the mixture of 0.05 g MWCNTs-COOH in 200 mL distilled water which was
stirred at 50 ºC. After one hour, about 20 mL NH3 was drop wise added to the mixture to
obtain an alkaline environment that was monitored by litmus paper. The mixture was allowed
to cool. After precipitation of nanocomposites, an external magnet was used to separate
product. At the end, nanocomposite was washed several times with ethanol and acetone to get
pure product.
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2.2.2. Functionalization of MWCNTs-COOH/Fe3O4 with a modified PAMAM
dendrimer (MMWCNTs-D-NH2)
MMWCNTs-D-NH2 were synthesized according to the reported procedure [4]. 0.5 g of
MMWCNTs was sonicated in 300 ml of deionized water for 30 min. In order to activate the
carbonyl group of MMWCNTs, 0.052 g of 1-ethyl-3- (3-dimethy lamino propyl)
carbodiimide hydrochloride (EDC.HCl) and 0.015 g of N-hydroxysuccinimide (NHS) were
added to the solution and stirred for 10 min. After this time, the dendrimer (5 ml) was added
dropwise and the reaction continued for 24 h at room temperature. The resulting sediment
was separated by an external magnetic field and dried in the oven vacuum at 70 °C after
being washed several times with deionized water and ethanol. Scheme 3 schematically shows
the dendrimer connection to MMWCNTs.
2.2.3. Synthesis of N‐butylsulfonate‐functionalized MMWCNTs-D-NH2
1 g of MMWCNTs-D-NH2 in 25 ml of toluene was dispersed by sonication. After 30 minutes,
0.7 g of 1,4‐butanesultone was added to the reaction mixture and the reaction continued for
48 h at 100 °C under stirring. The product were collected via an external magnetic field and
washed several times with toluene and acetone to eliminate the unreacted compounds and
finally was dried in oven vacuum at 70 °C for 24 h [4].
2.3. General procedure for one-pot synthesis of tetrahydrobenzo[b] pyrans
A mixture of MMWCNTs-D-(CH2)4-SO3H nanocomposite (0.04 g), the aldehyde (1 mmol),
1,3-dicarbonyl compounds (1 mmol) and malononitrile (2 mmol) in EtOH (azeotropic
composition of 96% ethanol containing 4% water, 3 ml) was stirred under reflux condition
for the appropriate time (Table 2). After recognition of the end of the reaction by TLC
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(hexane-ethyl acetate, 3:1), the catalyst was separated using an external magnet. The resulting
mixture was poured into crushed ice and the final product was obtained through filtration and
pure product was obtained by recrystallization from ethanol (96%). The products were
characterized by 1H and 13C NMR and IR spectroscopic data.
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2.4. General procedure for one-pot synthesis of Dihydro-1H-Indeno[1,2-b] pyridines
A mixture of MMWCNTs-D-(CH2)4-SO3H nanocomposite (0.06 g), the aldehyde (1 mmol),
1,3-indandione (1 mmol), ethyl acetoacetate (1 mmol) and ammonium acetate (3 mmol) was
stirred at 120°C for the appropriate time (Table 2). The reaction progress was monitored by
TLC (n-hexane:ethyl acetate, 2:1). After completion of the reaction we added 2 ml hot
ethanol to the reaction mixture and it was stirred for 2 minutes, then the catalyst was
separated using an external magnet. The resulting mixture was poured into crushed ice and
the final product was obtained through filtration and pure product was obtained by
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recrystallization from ethanol (96%). The final products were identified by IR, H and C
NMR spectral data.
3. RESULTS AND DISCUSSION
3.1. Characterizations of catalyst
Magnetic MWCNTs, that was synthesized via blending of MWCNTO with FeCl3.6H2O and
FeCl2.4H2O in the presence of distilled water and NH3, functionalized with a modified
PAMAM dendrimer in the presence of EDC and NHS (scheme 2). The MMWCNTs-D-
(CH2)4-SO3H nanocomposite was synthesized by the heating of MWCNTs-D-NH2 and
1,4‐butanesultone at 100 °C under stirring (Scheme 3). The resulting product was
characterized by various techniques including FT-IR, TEM, SEM, XRD and TGA.
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HN
NH
HOOC
HOOC
C
HOOC
HOOC
O
COOH
CO
COOH
O
O
C
H
C
N
H
N
COOH
COOH
FeCl2.4H2O/ FeCl3.6H2O
NH3/ H2O
COOH
COOH
PAMAM
EDC/ HNS
CO
OC
HOOC
HOOC
NH
HN
H2N
NH2
NH
HN
O
O
O
N
NH2
HN
NH2
O
N
NH
O
N
O
N
NH
O
H
N
N
N
N
N
H
NH2
H
N
H
O
H2N
Fe3O4 nanoparticle
O
O
NH
O
HN
N
O
N
O
HN
NH2
C2H4NH
NH2
NH
O
O
NH
HN
H2N
G2 Dendrimer (PAMAM)
H2N
NH2
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3
SCHEME 2 Preparation of MWCNTs-COOH/Fe3O4 and functionalization of it with a
modified PAMAM dendrimer
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NH
NH
C
O
C
O
O
toluene
O
O
O
C
O
C
H
NH2
N
N
S
H
100O C/ 48h
O
C
CO
NH
NH
N
H
OH
S
O
NH
O
C
O
O
C
H
N
O
C
NH
NH(CH2)4SO3H
1
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SCHEME 3 Reaction of the terminal NH2 of the MMWCNTs-D-NH2 with 1,4-butanesultone
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FT‐IR spectra was used to assessment of the successful attachment of functional groups onto
the surface of the MWCNTs-COOH at each step of the catalyst synthesis (Fig. 1, 2). As
shown in Fig. 1a, a broad peak between 3000 and 3600 cm−1 corresponding to the vibration
of O-H groups and the sharp peak in the region 1635 cm−1 is attributed to the stretching
vibrations of C=O of -COOH groups. Moreover, the peak at 1095 cm−1 correspond to the C-
OH of COOH, confirming the presence of carboxyl group within the structure of the
MWCNTs-COOH. The FT‐IR spectrum of MMWCNTs which is illustrated in Figure 1b
shows a specific peak at 582 cm−1 relating to the stretching vibration of the Fe-O bond. In the
FT-IR spectrum of MWCNTs-D-NH2 (Figure 1c), C-H stretching of the alkyl group in the
modified PAMAM component are detected by the peak at 2925 and 2847 cm−1. The
characteristic peaks of MWCNTs-D-NH2 at 1637, 1565 and 1425 cm−1 are attributed to NH
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deformation vibration of primary amine, the coupling of N-H bending and C-N stretching of
amide, respectively. The symmetric and asymmetric stretching vibrations of S=O assigned by
two significant peaks at 1052 and 1223 cm−1, respectively, confirm the reaction of
MWCNTs-D-NH2 with 1,4-butanesultone (Fig. 2a). The FT-IR spectrum of MMWCNTs-D-
(CH2)4-SO3H nanocomposite after five runs of recyclability (Fig. 2b) revealed that recycling
process has not changed the locations of IR absorptions of the nanoparticles.
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FIGURE 1 FT-IR spectra of MWCNTs-COOH (a), MMWCNTs (b), MWCNTs-D-NH2 (c)
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FIGURE 2 FT-IR spectra of MMWCNTs-D-(CH2)4-SO3H (a) and MMWCNTs-D-(CH2)4-
SO3H nanocomposite after five runs of recyclability (b)
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TEM analysis was used to evaluation the nanoparticles size distribution more accurately and
the results have been shown in Fig. 2a,b with their size distribution histograms. All of the
samples have the size range of 5-21 nm with average diameter of about 10 nm. High
magnification TEM image of sample (Figure 2b) reveals the loading of nanoparticles on the
CNTs surface and demonstrates that magnetic nanoparticles have been well distributed and
anchored on CNTs surface. Dendrimer shells can also be observed clearly with thickness of
2-5 nm. Figure 2c shows SEM images of prepared samples. Clearly, the CNTs surface has
been covered uniformly by magnetic nanoparticles and there is almost no agglomeration.
Diameter difference between pure and covered CNTs is about 18 nm, indicating that
nanoparticles have formed a shell with thickness of about 9 nm around the CNTs. The shell
thickness is close to nanoparticles average size (about 10 nm), in agreement with TEM
results.
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FIGURE 3 Micrograph of MMWCNTs-D-(CH2)4-SO3H nanocomposite: TEM, 50 nm (a),
high magnification TEM, 20 nm (b) and SEM, 100 nm (c)
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The XRD patterns of MMWCNTs -D-(CH2)4-SO3H nanocomposite was shown in Fig. 4. The
sharp peaks at 2θ = 62.90°, 57.37°, 53.25°, 43.07, 35.59° and 30.09° are corresponding peaks
of (440), (511), (400), (422), (311) and (200) crystal planes, respectively, which are related to
the crystalline nature of Fe3O4 nanoparticles [48]. According to obtained XRD pattern and
using Debye-Scherrer equation, the crystallite size of Fe3O4 nanoparticles was estimated to be
about 12 nm, which is in agreement with the size obtained via TEM and SEM analyses.
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FIGURE 4 XRD patterns of MMWCNTs-D-(CH2)4-SO3H nanocomposite
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TGA curves of Fe3O4, MWCNTs-COOH/Fe3O4, MMWCNTs-D-NH2 and MMWCNTs-D-
(CH2)4-SO3H nanocomposites at the temperature range of 50 to 800 ºC shown in Fig. 4. As
shown in Figure 4, Fe3O4 nanoparticles showed good thermal stability and had not any
apparent weight loss (curve a). In the case of MWCNTs-COOH/Fe3O4 (curve b), 10% weight
loss between 100 °C and 300 °C is due to loss of COOH groups on MWCNTs. TGA curve of
MMWCNTs-D-NH2, as shown in Figure 4c, exhibited an initial ascending behaviour as the
consequence of the buoyancy effect of the instrument. Similar ascending trends in TGA
curves have also been reported in several studies and explained in that this initial weight gain
for the sample and platinum pan stems from the differences in heat capacity and thermal
conductivity of the purging gas [4]. 10% weight loss between 350 and 500°C is due to the
decomposition of the modified PAMAM dendrimer on MMWCNTs-D-NH2. TGA curve of
MMWCNTs-D-(CH2)4-SO3H shows three distinct steps of weight loss (curve d). The first
step (weight loss = ca. 8 wt %) between 100 °C and 300 °C is referred to the elimination of
COOH groups. The second step contains 10% weight loss between 350 and 500°C which was
assigned to the modified PAMAM dendrimer. The third step indicated a weight loss (ca. 15
wt %) between 550 and 700°C originated from the decomposition of n‐butyl –SO3H group.
Fig. 4d indicates that MMWCNTs-D-(CH2)4-SO3H is stable to 100 °C (only 5% weight loss
in this temperature range).
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FIGURE 5 TGA curves of Fe3O4 (a), MMWCNTs (b), MWCNTs-D-NH2 (c) and
MMWCNTs-D-(CH2)4-SO3H (d)
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3.2. Catalytic activity studies
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To study of the catalytic activity of MMWCNTs-D-(CH2)4-SO3H nanocomposite, various
benzaldehyde (1 mmol) was reacted with malononitrile (2 mmol) and 1,3-dicarbonyl
compounds (1 mmol) in the presence of nanocomposite (0.04 g) as catalyst in reflux
conditions to produce tetrahydrobenzo[b] pyran derivatives (Scheme 1).
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To define the optimal condition of reaction, the reaction of synthesis of 2-amino-7,7-
dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (as model) was
carried out in polar (CH3CN, MeOH, H2O) and nonpolar (CH2Cl2, CCl4) solvents in the
presence of various amount of catalyst (0.03, 0.04 and 0.05 g) and at different temperatures
(25, 50, 60, 70ºC and reflux) (Table 1). Comparison of different solvents revealed that the
least time and the best efficiencies were obtained in the presence of ethanol (Table 1, entry
1). Then different amounts of catalysts were investigated in ethanol solvent (Table 1, entry 8
and 9). By increasing the reaction temperature an increasing trend was observed in the
efficiencies. Finally the best result was obtained with 0.04 g of catalyst at reflux in the
presence of ethanol solvent (Table 1, entry 1). To investigate the effectiveness of the
presented catalytic system the model reaction was performed in the absence of catalyst and in
the presence of several nanocatalysts such as Fe3O4, MWCNTs-COOH, MMWCNTs-COOH
and MMWCNTs-D-NH2 (Table 1, entry 14- 19). The obtained values of time and yield
(presented in Table 1) showed that the nanomagnetic MMWCNTs-D-(CH2)4-SO3H has the
best catalytic efficiency by comparison with the other nanocatalysts.
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TABLE 1. Optimization of Reaction Conditions for synthesis of tetrahydrobenzo[b] pyransa
O
CHO
O
Conditions
CN
CN
CN
+
O
+
O
NH2
1
2
3
4
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Entry Amount of Catalyst (g, mol%)
Conditions
Time Yieldb
15

(min) (%)
1
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) EtOH/reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) CH3CN/ reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) CH3OH/ reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) H2O/ reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) CH2Cl2/ reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) CCl4/ reflux
15
15
15
15
30
30
93
75
88
55
45
40
80
86
92
42
65
70
84
trace
40
trace
51
54
70
2
3
4
5
6
7
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) Solvent-free/80ºC 20
8
MMWCNTs-D-(CH2)4-SO3H (0.03, 0.25 mol %) EtOH/reflux
MMWCNTs-D-(CH2)4-SO3H (0.05, 0.40 mol %) EtOH/reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) EtOH/25 ºC
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) EtOH/50 ºC
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) EtOH/60 ºC
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) EtOH/70 ºC
20
15
60
30
30
30
60
60
15
30
25
15
9
10
11
12
13
14
15
16
17
18
Blank
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
Fe3O4 (0.04)
Fe3O4 (0.04)
MWCNTs-COOH (0.04)
MMWCNTs-COOH (0.04)
MMWCNTs-D-NH2 (0.04)
19
a
1
2
3
1 mmol benzaldehyde (106 mg), 2 mmol malononitrile (132 mg) and 1 mmol 5,5-dimethylcyclohexane-1,3-
dione (140.2 mg).
b Isolated yield
4
5
6
7
8
9
To specify the extent of the reaction we react various aromatic aldehydes with 1,3-dicarbonyl
compounds and malononitriles to produce various tetrahydrobenzo[b] pyrans under refluxing
EtOH (Table 2, entry 1-18). According to the results it was found that electron-withdrawing
groups (such as nitrile, nitro and halides) on aldehyde especially on the meta and para
position provide better results (Table 2, entry 2- 8).
16

1
2
3
TABLE 2 Preparation of tetrahydrobenzo[b] pyrans and Dihydro-1H-Indeno[1,2-b] pyridines
Entry
Product
Time
(min)
Yield
(%)
Mp (ºC)
Reported
Found
O
1
15
12
93
94
228-231 225–227 [24]
CN
Me
Me
O
NH2
Cl
2
3
4
5
207-209 211–213 [26]
O
CN
Me
Me
O
NO2
NH2
12
12
12
98
98
92
177-180 177–178 [24]
224-227 224–226 [26]
189-192 190-191 [42]
O
O
O
CN
Me
Me
O
NH2
CN
CN
Me
Me
O
F
NH2
CN
Me
Me
O
NH2
17

Br
6
12
93
196-199 197-199 [42]
O
O
CN
Me
Me
O
NH2
Cl
7
8
12
10
92
98
213-215 214-216 [26]
CN
Me
Me
O
NH2
Cl
191-192 190-192 [42]
O
O
O
Cl
CN
Me
Me
O
O
NH2
Cl
9
15
15
15
90
92
94
232-234 224-225 [25]
210-214 212-214 [26]
212-213 214-216 [25]
CN
Me
Me
NH2
NO2
10
11
CN
Me
Me
O
NH2
Me
O
CN
Me
Me
O
NH2
18

O
O
Me
CN
12
13
14
20
25
18
83
86
90
210-213 210-212 [42]
210-213 204-205 [23]
197-198 188-189 [24]
Me
Me
O
O
NH2
OMe
CN
Me
Me
NH2
OMe
O
CN
Me
Me
O
NH2
OH
O
15
16
30
13
80
96
236-237 236-238 [23]
CN
Me
Me
O
NH2
NO2
229-232 230-232 [26]
O
CN
O
NH2
OH
17
15
88
257-259 256-257 [25]
O
CN
O
NH2
19

Cl
O
18
13
90
223-227 220-222 [26]
O
CN
NH2
O
O
19
20
20
15
92
94
219-221
220 [32]
OEt
N
H
Cl
225-228 227-229 [34]
175-177 176-178 [34]
220-223 220-222 [46]
O
O
O
O
O
O
OEt
OEt
OEt
N
H
Br
21
15
94
N
H
F
22
15
93
N
H
20

Cl
O
O
O
23
15
90
223-226 225-227 [46]
OEt
OEt
N
H
Cl
O
24
25
15
15
85
95
196-199 195-197 [46]
N
H
OMe
210-213 213-214 [34]
O
O
O
OEt
N
H
OMe
O
26
15
85
198-202 199-201 [32]
OEt
N
H
Me
27
20
89
160-162 161-163 [32]
O
O
OEt
N
H
21

NO2
28
15
98
215-220 216-218 [34]
O
O
O
OEt
N
H
NO2
O
29
15
91
239-244 240-242 [32]
OEt
N
H
1
2
To determine the utility scope of our catalyst in organic reactions we also designed the
synthesis reaction of dihydro-1H-Indeno [1,2-b] pyridines using various aldehydes, 1,3-
indandione, ethyl acetoacetate and ammonium acetate in the presence of MMWCNTs-D-
(CH2)4-SO3H nanocomposite as catalyst at 120 ºC (Scheme 1). We tried again to use different
kinds of aldehydes containing electron-withdrawing and electron donating groups (Table 2,
entry 19-29). Again it was found that aldehydes containing electron withdrawing groups led
to a higher percentage of the product. Also the results showed that the reaction efficiency
with the aldehyde containing a group in the ortho position was slightly less than aldehyde
containing the same group in the para position; this can be attributed to steric hindrance.
Here too the conditions were optimized at first. The optimization results for the reaction of
synthesis of ethyl 5-oxo-4-phenyl-4,5-dihydro-1H-indeno[1,2-b]pyridine-3-carboxylate (as
model reaction) are shown in Table 3. Among different catalyst values and different
temperature and solvent conditions the best results were achieved in the presence of 0.06 g of
catalyst at 120 °C under solvent-free conditions (Table 3, entry 1).
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

1
2
TABLE 3 Optimization of Reaction Conditions for synthesis of dihydro-1H-indeno[1,2-b]
pyridinesa
CHO
O
O
O
O
O
Conditions
NH4OAC
+
+
OEt
+
OEt
N
H
O
1
2
3
4
5
3
4
Entry Amount of Catalyst (g, mol%)
Conditions
Time Yieldb
(min) (%)
1
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Solvent-free/120 ºC
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) EtOH/reflux
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Toluene/reflux
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) water/reflux
20
60
60
60
60
60
20
20
20
20
60
60
35
25
25
92
48
30
35
25
39
72
92
86
91
trace
30
52
63
68
2
3
4
5
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Dichloromethane/reflux
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Acetonitrile/reflux
MMWCNTs-D-(CH2)4-SO3H (0.04, 0.34 mol %) Solvent-free/120 ºC
MMWCNTs-D-(CH2)4-SO3H (0.08, 0.7 mol %) Solvent-free/120 ºC
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Solvent-free/110 ºC
MMWCNTs-D-(CH2)4-SO3H (0.06, 0.5 mol %) Solvent-free/130 ºC
6
7
8
9
10
11
12
13
14
15
Blank
Solvent-free/120 ºC
Solvent-free/120 ºC
Solvent-free/120 ºC
Solvent-free/120 ºC
Solvent-free/120 ºC
Fe3O4 (0.06)
MWCNTs-COOH (0.06)
MMWCNTs-COOH (0.06)
MMWCNTs-D-NH2 (0.06)
5
6
7
a 1 mmol benzaldehyde (106 mg), 1 mmol 1,3-indandione (146.14 mg), 1 mmol ethyl acetoacetate (130.14 mg)
and 3 mmol ammonium acetate (231.3 mg)
b Isolated yield
8
23

1
2
Hot filtration test was carried out to make sure no leaching of catalyst during the course of
reactions. For this purpose synthesis of 2-amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile (as model reaction) was carried out under the
optimized condition for 7 min. At this stage, the catalyst was separated from the reaction
mixture by use of an external magnetic field (1.4 T field strength). Then, the reaction
proceeded for another 8 min under same condition. No increase in the amount of the product
was observed, which suggests that the leaching of glutathione is low and the prepared catalyst
is stable. This result was confirmed by recyclability investigations of the catalyst.
3
4
5
6
7
8
9
We compared the gained results for the catalytic activity of MMWCNTs-D-(CH2)4-SO3H
with the reported results for other catalysts especially heterogeneous acid catalysts (e.g.,
zeolites) in the synthesis of dihydro-1H-Indeno[1,2-b] pyridines and tetrahydrobenzo[b]
pyrans to show the efficiency of our synthesized catalyst (Table 4). For a more obvious
quantitative comparison, the turnover frequency (TOF) of all catalysts were measured. TOF
is one of the criteria for selecting a catalyst that the higher the TOF value, the better the
catalyst. The TOF was obtained from the following equation:
10
11
12
13
14
15
16
17
18
19
20
Comparison of the TOFs in Table 4 showed that our synthetic catalyst is one of the best
catalysts for selective reactions.
21
22
23
TABLE 4 Comparison of MMWCNTs-D-(CH2)4-SO3H with some reported catalysts in the
synthesis of tetrahydrobenzo[b]pyrans and dihydro-1H-indeno[1,2-b]pyridines
Compound
Conditions
Time Yield TOF
Ref.
[42]
[26]
[24]
(min)
15
(%)
86
(h-1)
a
NH4H2PO4/Al2O3 (0.03
g)/EtOH/reflux
-
[PVPH]HSO4 (3.5 mol%)
/H2O:EtOH (7:3), 80°C
[DABCO‐PDO][CH3COO](1
10
15
96
95
165
38
24

0 mol%)/H2O, 80°C
NH2CH2CH2OH (10 mol%)/
H2O, rt
15
120
5
97
96
95
39
4.8
[23]
[27]
[4]
[Ch][OH] (10
mol%)/H2O/reflux
MGO‐D‐NH‐(CH2)4‐SO3H
(0.12 mol%)/H2O–EtOH
(4:1), rt
9495
Ru immobilized in zeolite
beta (25 mol%)/EtOH/reflux
ZnO-beta zeolite (0.1
g)/EtOH/reflux
35
35
180
30
15
60
45
10
15
85
95
96
64
93
95
92
93
95
6
[28]
[29]
[30]
[31]
a
-
a
Hydroxy sodalite zeolite (0.5
g)/solvent-free/rt
-
a
Zeolite Y (0.14
-
g)/EtOH/reflux
MMWCNTs-D-(CH2)4-SO3H
(0.34 mol%)/EtOH/reflux
L-proline (10
1094
9.5
this
work
[32]
mol%)/water/reflux
Yb(OTf)3 (5 mol%) /EtOH/us,
rt
25
[34]
[46]
HNPBS (2.5 mol%)/solvent-
free/rt
223
760
MMWCNTs-D-(CH2)4-SO3H
(0.5 mol%)/solvent-free/120
ºC
this
work
1
2
3
4
5
aThe amount mol% of catalyst was not available in the paper.
Our proposed mechanism for one-pot synthesis of tetrahydrobenzo[b] pyrans and dihydro-
1H-indeno[1,2-b] pyridines in the presence of MMWCNTs-D-(CH2)4-SO3H nanocomposite
as catalyst were given in Scheme 4. In both reactions it can be suggested that in the first step
25

1
2
3
the Knoevenagel condensation reaction was performed between benzaldehyde and
malononitrile (or diketone in second reaction) activated with catalyst.
O
N
C
H
H
MMWCNTs-D-(CH2)4-SO3H
5
2
C
CN
H
H+
O
O
O
O
Ar
H
Ar
H
1
H
H
C
NC
NH
O
O
O
Ar
CN
CN
Ar
H
O
O
O
O
O
NH2
Me
O
OH
Me
H+
H+
Keto–enol
NH4OAC
-H2O
R
R
R
R
EtO
Me
EtO
EtO
O
OH
3
6
Ar
O
O
Ar
O
H
CO2Et
CN
NH
R
N
H
R
Ar
O
O
Ar
O
CO2Et
CN
R
NH2
N
H
R
4
7
4
5
SCHEME 4 Proposed mechanisms for one-pot synthesis of tetrahydrobenzo[b] pyrans and
6
dihydro-1H-Indeno[1,2-b] pyridines
7
8
In accordance with the reaction mechanism (Scheme 4), activation of the carbonyl group by
acidic protons produced from MMWCNTs-D-(CH2)4-SO3H is the major driver of the reaction
progress. Based on the comparison of the carbonyl group activated by MMWCNTs-D-
(CH2)4-SO3H and MMWCNTs-D-NH2 (Fig. 6) it is found that the reaction is more likely to
progress through the formation of intermediate A (entry 1 vs. entry 19 in Table 1 and entry 1
vs. entry 15 in Table 3), which may be explained by more steric hindrance of basic groups in
MMWCNTs-D-NH2 than acid groups in MMWCNTs-D-(CH2)4-SO3H, because amino group
9
10
11
12
13
14
15
is part of a bulk dendrimer, while sulphonic group is sufficiently distant from the bulk
26

1
2
3
4
dendrimer due to the presence of -(CH2)4. Resende Filho et al. [49] also achieved similar
results for Fe3O4@SiO2-nN catalyst when the distance (n) between the terminal amino group
and the nanoparticle surface was increased.
MMWCNTs-D-(CH2)4-SO3H
H
H+
O
O
Ar
Ar
H
H
1
[A]
O
OH
H
Ar
H
Water Elimination
H
H
MMWCNTs-D-NH2
MMWCNTs-D
N
MMWCNTs-D
N
Ar
H
Ar
1
[B]
5
6
FIGURE 6. Activation of carbonyl group by a) acidic and b) basic catalysts
7
8
Also, in other experimental method, to determine the catalytic performance differences of
NH2 terminated CNTs and SO3H terminated CNTs, we performed the tetrahydrobenzo [b]
pyran reactions in Table 2 in the presence of MMWCNTs-D-NH2 as catalyst. The
experiments were repeated three times and the average of yields were reported (Table 5). As
can be seen in the Table 5, the yields in the presence of NH2 terminated CNTs were between
22–32% lower than those in the presence of SO3H terminated CNTs. This significant
difference is a confirmation of the correct choice of MMWCNTs-D-(CH2)4-SO3H as the
catalyst.
9
10
11
12
13
14
15
16
17
18
TABLE 5 Comparison one-pot synthesis of tetrahydrobenzo[b] pyrans with MMWCNTs-D-
(CH2)4-SO3H and MMWCNTs-D-NH2
Entry
Product
Time
(min)
Yield(%)
MMWCNTs-D-
(CH2)4-SO3H
MMWCNTs-D-
a
NH2
O
1
15
93
70
CN
Me
Me
O
NH2
27

Cl
2
3
4
5
6
12
12
12
12
12
94
98
98
92
93
70
72
73
68
67
O
O
O
O
O
CN
Me
Me
O
NH2
NO2
CN
Me
Me
O
NH2
CN
CN
Me
Me
O
F
NH2
CN
Me
Me
O
NH2
Br
CN
Me
Me
O
NH2
28

O
Cl
7
8
12
10
92
98
68
72
CN
Me
Me
O
NH2
Cl
O
O
O
Cl
CN
Me
Me
O
O
NH2
Cl
9
15
15
15
90
92
94
65
66
70
CN
Me
Me
NH2
NO2
10
11
CN
Me
Me
O
NH2
Me
O
O
CN
Me
Me
O
O
NH2
Me
CN
12
20
83
52
Me
Me
NH2
29