Β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-Dimensional Nanocatalyst in the One-Pot Synthesis of N- Containing Organic Scaffolds

Article abstract of DOI:10.1007/s10562-018-2484-3

The motivation behind the present study was to develop an application of β-cyclodextrin-based nanosponges with the tiny mesh-like structure as porous three-dimensional nanocatalyst in the one-pot three component condensations of various aromatic aldehydes

Full text of DOI:10.1007/s10562-018-2484-3

Catalysis Letters
https://doi.org/10.1007/s10562-018-2484-3
β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-
Dimensional Nanocatalyst in the One-Pot Synthesis of N- Containing
Organic Scaffolds
N. Eskandari Sabzi1 · A. R. Kiasat1,2
Received: 11 March 2018 / Accepted: 7 July 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
The motivation behind the present study was to develop an application of β-cyclodextrin-based nanosponges with the
tiny mesh-like structure as porous three-dimensional nanocatalyst in the one-pot three component condensations of vari-
ous aromatic aldehydes with activated methylene compounds such as dimedone, thiobarbituric acid, 4-hydroxycoumarin,
4-hydroxy-6-methyl-2-pyrone and nucleophiles including indole and amines. This nanosponge catalyst afforded the privileged
N- containing organic scaffolds as key intermediates in pharmaceutical chemistry in very short reaction times.
Graphical Abstract
CHO
Cl
H
N
O
H
N
Cl
O
O
O
Yonemitsu- type condensation reaction
Keywords Nanosponges · β-Cyclodextrin · β-Cyclodextrin based nanosponges · 3-Substituted indole derivatives · N-
containing heterocyclic
1 Introduction
During these last years, cyclodextrins (CDs) have greatly
contributed to the development of innovative homogene-
ous or heterogeneous catalytic processes. More than sim-
ple molecular platforms aiming at designing new ligands
or interfacial additives, CDs have been employed to gen-
erate unconventional reaction media such as nanosponges
capable of stabilizing active catalytic species [1, 2]. The
β-cyclodextrin-based nanosponges (βCD.NS) as new age
* N. Eskandari Sabzi
Nima.eskandari61@gmail.com
1
Department of Chemistry, Faculty of Science, Shahid
Chamran University of Ahvaz, Ahvaz, Iran
2
Petroleum Geology and Geochemistry Research Centre
(PGGRC), Shahid Chamran University of Ahvaz, Ahvaz,
Iran
Vol.:(0123456789)
1 3

N. E. Sabzi, A. R. Kiasat
branched cyclodextrin polymeric systems with tiny mesh
and sponge-like structures can be obtained by crosslinking
different types of cyclodextrin using the crosslinkers like
dialdehydes, epoxides, epichlorohydrin, carbonyl diimi-
dazole, dimethyl carbonate, diphenyl carbonate and etc
[3–5]. Due to their inner hydrophobic cavities and exter-
nal hydrophilic branching, these biocompatible nanoporous
supramolecular materials are able to form stable inclusion
complexes with both hydrophilic and hydrophobic molecules
and thereby exhibiting tremendous potential in the pharma-
ceutical, biomedical, food, photo chirogenesis and catalytic
applications [6–16].
routinely checked with thin-layer chromatography (TLC)
using Merck silica gel 60 F 254 plates. Melting points
recorded in the Electro thermal IA9200 apparatus. Fourier
transmission infrared (FT-IR) spectra of the powders (as
pellets in KBr) were obtained using a Fourier transmission
infrared spectrometer (Perkin Elmer BX-II). X-ray diffrac-
tion (XRD) pattern of the sample was obtained on a Philips
X-ray diffraction model PW 1840. The particle morphol-
ogy was studied with SEM (Philips XL30 scanning elec-
tron microscope. Thermogravimetric analysis (TGA) of the
catalyst was performed on a BAHR SPA 503 system under
an N2 atmosphere at a heating rate of 10 °C min−1, over the
temperature range of 25–750 °C.
Indole frameworks are one of the most widely distributed
classes of heterocyclic compounds, which constitute the key
core of various natural products [17, 18]. They have been
widely considered as target pharmacophores for the develop-
ment of therapeutic agents. Among this exceptionally elite
class of heterocyclic scaffold, 3-substituted indole moieties
have been known as outstanding agents in compounds of
high biological, agrochemical and pharmacological rel-
evance [19, 20].
2.2 Preparation of Nanosponges Based
β‑Cyclodextrin
β-Cyclodextrin based Nanosponge, βCD.NS was prepared
as previously reported in the literature [24]. Briefly, to a
solution of anhydrous β-CD (0.871 gr, 1 mmol) in anhy-
drous DMF (4 ml), anhydrous carbonyl diimidazole (0.498
gr, 4 mmol) was added and the clear solution stirred at
100 °C for 4 h. After completion of the reaction, an excess
of distilled water was added to the mixture, the product sepa-
rated by filtration and purified by SOXHLET extraction with
ethanol. The white powder βCD.NS was dried in an oven at
60 °C overnight.
In view of their significance, various multicomponent
protocols have been recently developed for the construction
of indole incorporating heterocyclic frameworks [21–23].
However, research along this line often encountered some
notorious difficulty such as use of expensive or toxic metal-
based catalysts, using a large quantity of volatile and toxic
organic solvents, harsh reaction conditions, and contamina-
tion of media by undesired products such as bisindole, bis-
coumarin, xanthine and crossed adducts, and therefore the
development of simple, efficient and environmentally benign
synthetic approaches remains a challenging task [23–27].
In the current study, we would like to report efficient cata-
lytic activity of β-cyclodextrin-based nanosponge for one-pot
and regioselective synthesis of 3-substituted indole moieties
using three component condensations of various aromatic
aldehydes and indole with activated methylene compounds
such as dimedone, thiobarbituric acid, 4-hydroxycoumarin,
4-hydroxy-6-methyl-2-pyrone. In the other part of this study,
amines such as N, N-dimethylaniline, 2,4-dimethylaniline or
pyrrolidine were used instead of indole, resulting the privi-
leged N- containing organic scaffolds with medicinal value.
2.3 General Procedure for the Synthesis
of 3‑Substituted Indole
A 50 ml flask was charged with aromatic aldehyde (1 mmol),
indole (0.117 gr, 1 mmol), βCD.NS (0.01 g) and activated
methylene compound such as dimedone (0.14 gr, 1 mmol),
thiobarbituric acid (0.144 gr, 1 mmol) or 4-hydroxycoumarin
(0.162 gr, 1 mmol) in ethanol (3 ml). The reaction mixture
was stirred under reflux conditions and monitored by TLC.
After completion of the reaction, βCD.NS was filtered off
and washed with hot ethanol (2 × 10 ml). Evaporation of
solvent under reduced pressure was produced crude product.
The crude product was further purified by recrystallization
in ethanol to offer pure 3-substituted indole product (4a–h).
2.4 General Procedure for Three‑Component
Reaction of Aromatic Aldehyde, with Two
Different Nucleophiles
2 Experimental
2.1 Materials
To the suspension of aromatic aldehyde (1 mmol) and βCD.
NS (0.01 g) in ethanol (3 ml), activated methylene com-
pounds [dimedone (0.14 gr, 1 mmol), thiobarbituric acid
(0.144 gr, 1 mmol), 4-hydroxy-6-methyl-2-pyrone (0.126 gr,
1 mmol) or 4-hydroxy coumarin (0.162 gr, 1 mmol)] and dif-
ferent amines [N, N dimethylaniline (0.121 gr, 1 mmol), 2,4
Anhydrous β-cyclodextrin was purchased from
Sigma–Aldrich Company and used with no additional
purification. The known products were recognized by com-
parison of their melting points and spectral data with their
announced authentic samples in the articles. Reactions were
1 3

β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-Dimensional Nanocatalyst…
dimethylaniline (0.121 gr, 1 mmol) or pyrrolidine (0.71 gr,
1 mmol)] was added. The reaction mixture was stirred under
reflux conditions and monitored by TLC. After completion
of the reaction, βCD.NS was filtered off and washed with hot
ethanol (2×10 ml). Evaporation of solvent under reduced
pressure was produced crude product. The crude product
was further purified by recrystallization in ethanol to offer a
pure product (5a–f) and (6a–e).
The chemical characteristics of β-cyclodextrin-based
nanosponge are studied by employing FT-IR spectrometer
(Perkin Elmer, USA). The FT-IR spectra of βCD and βCD.
NS at wavelength 400–4000 cm−1 were shown in Fig. 1. In
the βCD.NS spectrum (b), the stretching modes of carbon-
ate groups in the polymer can be observed at 1740 cm−1.
Scanning electron microscopic (SEM) images of
β-cyclodextrin-based nanosponge are shown in Fig. 2
which showed the nanosponge has relatively smooth and
regular surface with mean particle size of about 300 nm
and cavities with a size of 40–200 nm.
3 Results and Discussion
The thermal behavior and stability of the
β-cyclodextrin-based nanosponge was examined by
thermogravimetric analysis (Fig. 3). According to TGA
thermogram, the nanosponge was thermal stable below
300 °C. The chemical stability of nanosponge was also
evaluated at 78 °C (boiling point of ethanol) under both
basic and acidic conditions. Although in acidic conditions
(0.1 N HCl), nanosponage was stable, but under basic
environment (0.1 N NaOH), a limited release of cyclo-
dextrin units was observed after 2 h due to degradation of
the nanosponge structure.
Recent advances in nanotechnology have demonstrated the
applications of β-cyclodextrin-based nanosponges as nano-
metric biomaterials with a close relationship between molec-
ular status and supramolecular properties for housing organic
molecules. They are encapsulating the type of nanoparticles,
which encapsulate the organic molecules within their cores
[28]. Keeping all facts in our mind, firstly, porous insoluble
nanoparticles of β-cyclodextrin-based nanosponges prepared
as shown in Scheme 1 by the reaction of the β-cyclodextrin
monomer with 1, 1′-carbonyl diimidazole [29].
Scheme 1 β-cyclodextrin based
nanosponges preparation
O
N
N
0.7 nm
C
N
+
N
DMF
100 0C/ 4 h
- imidazole
O
: O-C-O linkage
1 3

N. E. Sabzi, A. R. Kiasat
Fig. 1 The FT-IR spectra of βCD and βCD.NS
Fig. 2 SEM images of
β-cyclodextrin-based nano-
sponge
1 3

β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-Dimensional Nanocatalyst…
classification). It presents a sharp adsorption step in the P/
P0, which implies that the β-cyclodextrin-based nanosponge
possesses a large pore size with narrow distributions. This
was further confirmed by pore area and specific pore volume
calculated by the Barrett–Joyner–Halenda (BJH) method
from the adsorption branches (Fig. 4). The characteristic
data on the sample are summarized in Table 1.
After successful characterization of the βCD.NS, its cata-
lytic activity as a host catalyst was checked for the synthesis
of 3-substituted indole moieties via Yonemitsu- type con-
densation reaction. In order to optimize the reaction condi-
tions and attain the best catalytic activity, the reaction of
2-choloro benzaldehyde (0.14 gr, 1 mmol), indole (0.117gr,
1 mmol) and dimedone (0.14 gr, 1 mmol) was used as a
model reaction (Scheme 2). The impression of solvent and
the weight of the catalyst, on the rate of the reaction, were
examined (Table 2). As can be discerned, 0.01 g catalyst, in
ethanol under reflux conditions was beneficial for this reac-
tion (Table 2, entry 6) and the use of the higher loading of
the catalyst (0.02 or 0.03 g) did not have a discernible impact
on the time and yield of the condensation reaction.
Fig. 3 TGA thermogram of β-cyclodextrin based nanosponge
The extent of solvent absorption by nanosponge was car-
ried out by its swelling in ethanol at room temperature. The
average equilibrium EtOH uptake by nanosponge (0.5%) was
calculated by the following equation.
To prove the beneficial effect of the porous property of
the nanocatalyst in the synthesis of the title compounds,
the reaction was also done in the present of unpolymerized
SW = (Wt − W0)∕W0
SW is the swelling degree at a certain time,
Wt is the weight of the nanosponge after immersion in
EtOH at time t,
Table 1 Adsorption/desorption data of βCD.NS
W0 is the weight of the nanosponge at the beginning of
testing.
Pore structure parameters
Surface area (m2g−1
Average pore diameter (nm)
Total pore volume (cm3 g−1
BET
BJH
The mesoporous nature of the synthesized nanosponge
was studied by N2 adsorption–desorption isotherms
(Fig. 4). The Nitrogen adsorption–desorption isotherm
exhibit the typical IV adsorption (according to the IUPAC
)
10.9
4.86
0.013
12.07
1.21
0.016
)
Fig. 4 Adsorption/desorption isotherm and BJH-Plot of βCD.NS
1 3

N. E. Sabzi, A. R. Kiasat
O
O
CHO
H
N
O
O
Cl
+
+
HN
Cl
Scheme 2 Model Yonemitsu- type condensation reaction
Table 2 Optimization the reaction conditions
beta-cyclodextrin in ethanol under reflux conditions. TLC
analysis of the reaction mixture was shown that the reaction
proceed in very poor yield (15%) even after long reaction
time (360 min).
Entry βCD.NS
catalyst
Condition (solvent/
tem)a
Time (min) Yield (%)
(%)
With the optimal reaction conditions in hand, consist-
ing of a 1:1:1 molar ratios of an aromatic aldehyde, indole,
activated methylene compounds (dimedone, thiobarbituric
acid or 4-hydroxy coumarin), in the presence of βCD.NS
(0.01 g) in ethanol under reflux conditions, the generality
and synthetic scope of this coupling protocol were dem-
onstrated through the synthesis of a series of 3-substituted
indole moieties (Scheme 3).
1
2
3
4
5
6
7
8
–
0.01
–
0.005
0.01
0.01
0.02
0.03
SF/100 °C
SF/100 °C
360
360
360
15
360
5
No reaction
Trace
Trace
56
30
97
98
98
EtOH/reflux
EtOH/reflux
H2O/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
5
5
The time is taken for efficiently one-pot multicomponent
synthesis in 3-substituted indole derivatives as well as the
isolated yields are recorded in Table 3.The purity determina-
tion of the products and reaction monitoring were accom-
plished by TLC and the 3-substituted indole products were
SF solvent free
aReaction conditions: 2-choloro benzaldehyde (0.14 gr, 1 mmol),
indole (0.117 gr, 1 mmol) and dimedone (0.14 gr, 1 mmol)
Scheme 3 Synthesis of 3-sub-
stituted indole moieties
O
O
(1a-d)
O
O
Ar
O
S
HN
(1)
HN
NH
Ar
H
N
S
O
HN
NH
O
O
(2a-c)
ArCHO
(2)
HN
O
O
O
OH
O
(3a)
OH
Ar
(3)
HN
1 3

β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-Dimensional Nanocatalyst…
Table 3 Preparation of 3-substituted indole moieties catalyzed by βCD.NS in EtOH
Product
O
O
O
O
O
O
O
O
N
HN
HN
Cl
1b
HN
HN
O2N
1c
1d
1a
Starting aldehyde:2-chloro benzaldehyde
Physical properties: white solid, m.p: 225-227 0
Time: 5 min, Yield: 96%
Starting aldehyde:pyridine-2-carbaldehyde
Physical properties: white solid, m.p:217-220 0C
Time: 10 min, Yield: 90%
Starting aldehyde: benzaldehyde
Physical properties: white solid, m.p: 185-187 0C
Time: 30 min, Yield: 82%
Starting aldehyde:2-nitro benzaldehyde
Physical properties: white solid, m.p:190-192 0C
Time: 15 min, Yield: 89%
C
S
S
S
HN
NH
HN
NH
HN
NH
O
O
O
O
O
O
O
O
OH
HN
N
HN
HN
Cl
2b
N
2a
N
H
2c
Starting aldehyde: benzaldehyde
Physical properties: ted solid, m.p: 187-190 0C
Time: 15 min, Yield: 85%
Starting aldehyde:pyridine-2-carbaldehyde
Physical properties: brown solid, m.p:218220 0
Time: 5 min, Yield:90%
Starting aldehyde:2-chloro benzaldehyde
3a
C
Physical properties: white solid, m.p: 218-220 0C
Time: 30 min, Yield: 95%
Starting aldehyde:pyridine-2-carbaldehyde
Physical properties: white solid, m.p:210-212 0
Time: 15 min, Yield: 95%
C
Reaction condition: aldehyde (1.0 mmol), activated methylene compounds (1.0 mmol), indole (1.0 mmol, 0.117 gr), and βCD.NS (0.01 gr) in
EtOH (3.0 ml) under reflux conditions
Scheme 4 The proposed
mechanism for one-pot three-
component condensation of
various aromatic aldehydes with
activated methylene compounds
and indole
H
H
O
O
O
O
H
O
-H2O
Knoevenagel
Condensation
Ar
Ar
O
O
O
H
N
H
OH
O
O
Ar
O
H
OH
Ar
Mickel Addition
N
O
Ar
OH
N
H
3-substituted indole moieties
1 3

N. E. Sabzi, A. R. Kiasat
Scheme 5 The electrophilic
reaction of aldehydes with two
different nucleophiles in the
absence of the catalyst
O
O
CHO
H
N
O
O
Cl
+
+
+
HN
Cl
product
H
N
Cl
O
O
O
O
O
+
+
O
HN
O
Cl
Cl
by product
in very poor yields even after long reaction time and reaction
media contaminated by side reactions of the aldehyde with
the same nucleophiles (Scheme 5).
The host–guest interaction of βCD.NS with starting sub-
strate, aromatic aldehyde, in EtOH has been investigated
by UV spectroscopy. As shown in Fig. 5, by addition of
βCD.NS to the reaction mixture, the observed spectral band
(λmax) for benzaldehyde at 327 nm was shifted to 267 nm.
Similar changes were also reported by other authors [30, 31].
It should be point out that although the nanosponage is not
soluble in ethanol, but due to its host–guest interaction with
benzaldehyde in ethanol, the clear and gel type suspension
is formed. The UV spectrum of this clear suspension was
without any noise.
Fig. 5 The UV spectra of βCD.NS, aldehyde, and βCD.NS-aldehyde
inclusion complex
To extend the scope of the methodology, the indole was
replaced by primary or secondary amines (Scheme 6).
As shown in Table 4, pyrrolidine and 2,4 dimethylani-
line reacted well with aromatic aldehydes and activated
methylene compounds with the aid of βCD.NS to give the
corresponding N- containing organic scaffold products in
good to excellent yields ranging from 60 to 95%.
characterized by comparison of their physical data, FT-IR,
and 1H and 13CNMR spectra with known samples.
The regioselectivity and high reaction rate observed in
the present method could be attributed to the fact that the
hydrophobic central cavities of β-CD units and carbonate
linkages in the βCD.NS polymer acted as micro-vessels
and accommodated the nonpolar compounds. In addi-
tion, the hydrophilic exterior due to the outer OH of the
β-CD cavity promoted the reaction via hydrogen bonding
(Scheme 4).
In the following, we were examined tertiary aromatic
amine as a nucleophile with various activated methylene
compounds and benzaldehyde, 2-nitro, and 2-chlorobenza-
ldehyde under optimized reaction conditions (Scheme 7).
As shown in Table 5, N, N- dimethylaniline reacted well
with aromatic aldehydes and activated methylene com-
pounds by the attacker from a para position of the aromatic
The catalytic activity and selectivity of βCD.NS in the
electrophilic reaction of aldehydes with two different nucleo-
philes, indole and dimedone, is established by the fact that in
the absence of catalyst, the reaction was observed to proceed
1 3

β-Cyclodextrin Based Nanosponge as a Biodegradable Porous Three-Dimensional Nanocatalyst…
Scheme 6 Three compo-
nents reaction of an aromatic
aldehyde activated methylene
compound and primary or
S
HN
NH
O
O
secondary amine
S
(4a)
N
Ar
HN
NH
(4)
R
O
O
O
N
O
OH
(5)
O
(5a-b)
(6a)
Ar
Primary and
R
O
OH
secondary Amine
O
(6)
ArCHO
O
HO
O
O
HO
O
O
N
R
Ar
(7)
O
O
N
R
Ar
(7a-b)
Table 4 Yonemitsu- type
condensation catalyzed by βCD.
NS in EtOH
Product
S
HN
NH
O
N
O
O
O
O
O
OH
HN
Cl
4a
HN
O2
N
NO2
5b
Starting aldehyde: 2-chloro-benzaldehyde
Physical properties: white solid, m.p: 178-180 o
Time: 20 min, Yield: 95%
1c
C
Starting aldehyde:2-nitro benzaldehyde
Physical properties: white solid, m.p:190-192 0C
Time: 15 min, Yield: 91%
Starting aldehyde: 4-nitro-benzaldehyde
Physical properties: yellow solid, m.p: 212-215oC
Time: 30 min, Yield: 86%
O
HO
O
O
O
O
O
N
H
N
H
O2
N
N
Cl
6d
NO2
7b
7a
Starting aldehyde: 2-chloro-benzaldehyde
Physical properties: white solid, m.p: 78-80oC
Time: 20 min, Yield: 78%
Starting aldehyde: 4-nitro-benzaldehyde
Physical properties: yellow solid, m.p: 200-202oC
Time: 15 min, Yield: 85%
Starting aldehyde: 2-nitro-benzaldehyde
Physical properties: yellow solid, m.p: 192-194oC
Time: 20 min, Yield: 90%
Reaction condition: aldehyde (1.0 mmol), activated methylene compounds (1.0 mmol), amines
(1.0 mmol), and βCD.NS (0.01gr) in EtOH (3.0 ml) under reflux conditions
ring in the presence of βCD.NS and give the correspond-
ing products in high to excellent isolated yields.
We believed that CD units of nanosponges not only
forms the inclusion complex with starting materials and
control the reaction selectivity but is also involved in the
intermolecular hydrogen bonding with the guest to pro-
mote the condensation.
4 Conclusion
In the present study, the application of β-cyclodextrin-
based nanosponges with a tiny mesh-like structure as
porous three-dimensional nanocatalyst in the one-pot three
component condensations of various aromatic aldehydes
with activated methylene compounds and N- containing
1 3

N. E. Sabzi, A. R. Kiasat
Scheme 7 Three component
condensation reaction of an
aromatic aldehyde, activated
methylene compound and N, N-
dimethylaniline
S
HN
NH
O
O
S
Ar
HN
NH
N
(8a-b)
O
O
(8)
O
O
N
Ar
O
O
ArCHO
(9)
N
(9a-b)
O
O
HO
O
HO
O
(10)
(10a)
Ar
N
Table 5 Preparation of N, N- dimethylaniline containing organic scaffolds catalyzed by βCD.NS in EtOH
Product
S
S
HN
NH
HN
NH
O
O
O
O
O
O
N
O2N
8b
N
N
Cl
9a
8a
Starting aldehyde: 2-nitro- benzaldehyde
Physical properties: green solid, m.p: 220-222 oC
Time: 10 min, Yield: 93%
Starting aldehyde: benzaldehyde
Starting aldehyde: 2-chloro- benzaldehyde
Physical properties: white solid, m.p: 260-262 o
Time: 20 min, Yield: 89%
Physical properties: white solid, m.p: 190-192 oC
Time: 35 min, Yield: 92%
C
O
O
HO
O
O
N
O2N
10a
N
O2N
9b
Starting aldehyde: 2-nitro- benzaldehyde
Physical properties: white solid, m.p: 235-237 o
Time: 20min, Yield: 90%
Starting aldehyde: 2-nitro- benzaldehyde
Physical properties: white solid, m.p: 171-173 o
Time: 15min, Yield: 95%
C
C
Reaction condition: aldhyde (1.0 mmol), activated methylene compounds (1.0 mmol), N, N- dimethylaniline (1.0 mmol, 0.121 gr) and βCD.NS
(0.01 gr) in EtOH (3.0 ml) under reflux conditions
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