Fe3O4?SiO2—CPTMS—Guanidine—SO3H-catalyzed One-Pot Multicomponent Synthesis of Polysubstituted Pyrrole Derivatives under Solvent-Free Conditions

Article abstract of DOI:10.1134/S1070428019080207

A highly efficient procedure for the one-pot synthesis of polysubstituted pyrrole derivatives by the reaction between of aniline derivatives, β-diketones or β-ketoesters, and β-nitrostyrene derivatives in the presence of Fe₃O₄?SiO

Full text of DOI:10.1134/S1070428019080207

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 8, pp. 1204–1211. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Organicheskoi Khimii, 2019, Vol. 55, No. 8, pp. 1309.
Fe3O4@SiO2–CPTMS–Guanidine–SO3H-catalyzed One-Pot
Multicomponent Synthesis of Polysubstituted Pyrrole Derivatives
under Solvent-Free Conditions
H. Rostamia and L. Shiria,*
a Department of Chemistry, Faculty of Basic Sciences, Ilam University, Ilam, Iran
*e-mail: Lshiri47@gmail.com
Received February 12, 2019 Revised April 06, 2019 Accepted May 31, 2019
Abstract—A highly efficient procedure for the one-pot synthesis of polysubstituted pyrrole derivatives by the
reaction between of aniline derivatives, β-diketones or β-ketoesters, and β-nitrostyrene derivatives in the
presence of Fe3O4@SiO2–CPTMS-guanidine–SO3H as a reusable magnetic nanocatalyst is reported. The
magnetic nanocatalyst was prepared and fully characterized by FTIR spectroscopy, scanning electron
microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, and
vibrating sample magnetometry.
Keywords: polysubstituted pyrrole derivatives, magnetic nanocatalyst, aniline derivatives, β-diketones, β-
ketoesters, β-nitrostyrenes
DOI: 10.1134/S1070428019080207
separation, are being more and more extensively used
INTRODUCTION
instead of homogeneous catalysts [15]. The advantages
of magnetic nanoparticles (MNPs) [16], for example
Fe3O4, as heterogeneous catalysts include the possi-
bility of being simply separated by means of external
magnet [17], low toxicity [18], highly active surface
[19], and comfortable recovery and high stability [20].
This explains the increasing use of MNPs as
heterogeneous catalysts in organic reactions.
Pyrrole derivatives [1] is an important group of
heterocyclic compounds [2]. Compounds that contain
the pyrrole ring have diverse biological activities such
as antitumor, antibacterial, anti-inflammatory,
antioxidant, and antifungal [3–9]. Moreover, natural
pigments, such as bile pigments and chlorophyll, and
enzymes similar cytochromes have the pyrrole ring in
their structures [10]. In view of the importance of
biologically active pyrrole derivatives, the develop-
ment of efficient and environmentally friendly proce-
dures for their synthesis is of special urgency.
To improve the mentioned limitations of the
existing protocols, we prepared a new magnetic
nanocatalyst Fe3O4@SiO2–CPTMS–guanidine–SO3H
and tested it in the synthesis of pyrrole derivatives
under solvent-free conditions.
The classical methods for the synthesis of pyrrole
derivatives include the Hantzsch, Knorr, and Paal–
Knorr reactions [11]. However, many reported syn-
theses of pyrrole derivatives feature such drawbacks as
long reaction times, expensive reagents, heavy metal
contaminations, and harsh reaction conditions.
RESULTS AND DISCUSSION
Synthesis and characterization of Fe3O4@SiO2–
CPTMS–guanidine–SO3H MNPs. The method of
synthesis of Fe3O4@SiO2–CPTMS–guanidine–SO3H
MNPs presented in Scheme 1. The catalyst was
synthesized in five steps. Initially, Fe3O4 MNPs were
synthesized from iron(II) and iron(III) salts. In the
second stage, Fe3O4 MNPs were coated with silica
using tetraethoxysilane (TEOS). Then, Fe3O4@SiO2
Multicomponent reactions offer advantages over
classical stepwise procedures, including the lack of
need to isolate intermediates, atom economy, better
yields, and reduction of time, cost, and waste [12, 13].
Heterogeneous catalysts [14], due their easy
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Fe3O4@SIO2–CPTMS–GUANIDINE–SO3H-CATALYZED ONE-POT MULTICOMPONENT
1205
Scheme 1. General scheme of synthesis of Fe3O4@SiO2–CPTMS-guanidine–SO3H MNPs.
OH
OH
HO
OH
OH
HO
HO
SiO2
SiO2
.
FeCl3 6H2O
O
O
NH4OH, N2
TEOS, PEG, EtOH
NH3, H2O, rt, 38 h
CPTMS
Fe3O4
MNPs
Fe3O4
MNPs
Fe3O4
MNPs
OH
OH
OH
Si
Cl
HO
+
80oC, 30 min
H2O/EtOH,
40oC, 8 h
O
.
FeCl2 4H2O
HO
HO
OH
Si
HO
OH
SO3H
SiO2
NaHCO3,
SiO2
NH
N
O
O
O
guanidine chloride
ClSO3H
CH2Cl2, rt, 3 h
Fe3O4
MNPs
Fe3O4
MNPs
N
O
Si
N
H
toluene, reflux, 28 h
NH2
O
NH
O
SO3H
SO3H
MNPs were consecutively modified with (3-chloro-
propyl)trimethoxysilane (CPTMS) and guanidine.
Finally, Fe3O4@SiO2–CPTMS–guanidine MNPs were
treated with chlorosulfonic acid. The resulting
Fe3O4@SiO2–CPTMS–guanidine–SO3H nanoparticles
were characterized by FTIR spectroscopy, scanning
electron microscopy (SEM), energy dispersive X-ray
(EDX) spectroscopy, X-ray diffraction (XRD) analysis,
thermogravimetric analysis (TGA), and vibrating
sample magnetometry (VSM).
The FTIR spectra of Fe3O4 (a), Fe3O4@SiO2 (b),
Fe3O4@SiO2–CPTMS (c), Fe3O4@SiO2–CPTMS–gua-
nidine (d) and Fe3O4@SiO2–CPTMS–guanidine–SO3H
(e) are shown in Fig. 1. The FTIR spectrum of Fe3O4
MNPs displays a stretching vibration band at 3391 cm–1
related to symmetrical and asymmetrical modes of the
O–H bonds and a stretching vibration band at 589 cm–1
of the Fe–O bonds, which confirms the presence of
Fe3O4 (Fig 1a). The observation of a stretching
vibration band at 1084 cm–1 assignable to Si–O bonds
provides evidence for the presence of SiO2 on the
surface of Fe3O4 MNPs (Fig. 1b). The presence of
C–H stretching vibration bands at 2898–3048 cm–1
confirms the presence of grafted of CPTMS on the
Fig. 1. FTIR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2–CPTMS, (d) Fe3O4@SiO2–CPTMS-guanidine,
and (e) Fe3O4@SiO2–CPTMS–guanidine–SO3H.
Fig. 2. SEM image of Fe3O4@SiO2–CPTMS–guanidine–
SO3H.
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ROSTAMI, SHIRI
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Fig. 3. EDX spectrum of Fe3O4@SiO2–CPTMS–guanidine–
Fig. 4. XRD patterns of (a) Fe3O4@SiO2 and (b) Fe3O4@SiO2–
SO3H.
CPTMS-guanidine–SO3H.
nanocatalyst surface (Fig. 1c). The broad stretching
vibration band near 3390 cm–1 related to NH and NH2
groups, as well as the stretching vibration band at
1657 cm–1 related to the C=N bond confirms the
presence of guanidine on the surface of Fe3O4 particles
(Fig. 1d). The presence of SO3H in the nanocatalyst is
confirmed by the stretching vibration band at 2950–
3500 cm–1 (Fig. 1e).
spectrum (Fig. 3) of peaks corresponding to Fe, Si, O,
N, and S confirms that the successful synthesis of
Fe3O4@SiO2–CPTMS–guanidine–SO3H nanoparticles.
The XRD patterns of the Fe3O4@SiO2 and
Fe3O4@SiO2–CPTMS–guanidine–SO3H nanoparticles
are shown in Fig. 4. The two patterns display six peaks
at 2θ 30.40°, 35.60°, 43.30°, 53.40°, 57.20°, and
63.80° with close intensity distributions, which are in a
good agreement with the standard XRD pattern of
Fe3O4.
The particle shape, surface morphology, and size
distribution in the Fe3O4@SiO2–CPTMS–guanidine–
SO3H MNPs we characterized using SEM (Fig. 2). The
SEM images show that the Fe3O4@SiO2–CPTMS–
guanidine–SO3H nanoparticles are nearly spherical in
shape, and their average size falls in the nano range.
The TGA curve of Fe3O4@SiO2–CPTMS–guani-
dine–SO3H (Fig. 5) shows a small weight loss below
200°C, which is associated with the desorption of
physically adsorbed solvents and surface hydroxyl
groups. The Fe3O4@SiO2–CPTMS–guanidine–SO3H
weight loss between 200 and 600°C is related to the
degradation of organic moieties.
The elemental composition of the Fe3O4@SiO2–
CPTMS–guanidine–SO3H nanoparticles was confir-
med by EDX spectroscopy. The presence in the EDX
Fig. 5. TGA curve of Fe3O4@SiO2–CPTMS–guanidine–
Fig. 6. Magnetization curves of (a) Fe3O4, (b) Fe3O4@SiO2,
SO3H.
and (c) Fe3O4@SiO2–CPTMS–guanidine–SO3H.
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Fe3O4@SIO2–CPTMS–GUANIDINE–SO3H-CATALYZED ONE-POT MULTICOMPONENT
Table 1. Optimization of the reaction conditionsa.
1207
O
NO2
EtO
NH2
O
O
Catalyst (g)
+
+
Solvent, Temp (oC), t (h)
N
OEt
Cl
Cl
Entry
1
Entry
Temperature, °C
Catalyst, g
0.03
0.02
0.01
0.008
–
Time, h
Yield, %
95
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
H2O
50
50
50
50
50
50
50
50
50
50
50
rt
3
3
3
3
3
3
3
3
3
3
3
3
3
2
95
3
95
4
87
5
20
6
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
90
7
PEG
20
8
EtOH
20
9
CH3CN
15
10
11
12
13
DMF
50
Toluene
17
Solvent free
Solvent free
20
70
95
a
p-Chloroaniline (0.5 mmol), ethyl acetoacetate (0.5 mmol), β-nitrostyrene (0.5 mmol), solvent (3 mL).
The magnetic properties of the nanocatalyst were
dine–SO3H nanocatalyst, we performed the synthesis
of polysubstituted pyrroles by the reaction of various
aniline derivatives, β-diketones/β-ketoesters, and β-
nitrostyrene derivatives.
studied by VSM. The magnetization curves of Fe3O4,
Fe3O4@SiO2, and Fe3O4@SiO2–CPTMS–guanidine–
SO3H nanoparticles are shown in Fig. 6. The saturation
magnetizations of the studied nanoparticles were
estimated at 47, 45, and 39 emu g–1, respectively. The
decreased saturation magnetization of Fe3O4@SiO2–
CPTMS–guanidine–SO3H confirmed its successful
synthesis.
To optimize the reaction conditions, we selected the
reaction of p-chloroaniline, ethyl acetoacetate, and β-
nitrostyrene as the model reaction. The resulting data
are presented in Table1. Initially, the effect of the
amount of the catalyst was investigated in solvent-free
coditions. As seen from Table 1, the reasonable result
was obtained with 0.01 g of the catalyst at the reaction
time of 3 h. Then, the 3-h reaction was evaluated in
various solvents. Solvent-free was found a suitable
condition for this reaction. Also, the effect of the
temperature was checked, and 50°C was chosed as the
optimum temperature for this reaction.
The concentration of SO3H groups on the catalyst
surface as estimated by back titration with 0.01 M
KOH solution was 1.2 mmol g–1 catalyst.
Evaluation of the catalytic activity of
Fe3O4@SiO2–CPTMS–guanidine–SO3H MNPs in
the synthesis of pyrrole derivatives. To evaluate the
catalytic activity of the Fe3O4@SiO2–CPTMS–guani-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

ROSTAMI, SHIRI
1208
Table 2. Synthesis of functionalized pyrroles 4.
R3
O
NO2
R2
NH2
O
O
Fe3O4@SiO2_CPTMS_guanidine_SO3H
solvent- free, 50oC, 3 h
R2
+
+
N
R1
R3
1
2
3
R1
R1 = H, Cl, Br.
R2 = CH3, OCH3.
R
3 = H, Me, Cl, OMe.
4
Cl
Me
O
O
O
O
EtO
N
N
N
N
4a (87%)
mp 127_129 [11]
4c (90%)
mp 138_140 [22]
4b (87%)
mp 100_102 [21]
4d (95%)
mp 120_122 [23]
Cl
Br
Br
Cl
Cl
Cl
O
O
O
O
EtO
N
N
N
N
4f (95%)
mp 96_98 [24]
4g (95%)
mp 106_108 [24]
4h (83%)
mp 164_166 [25]
4e (93%)
mp 156_158 [24]
Br
Cl
Cl
Having optimized the reaction conditions, we
synthesized a broad range of pyrrole derivatives. The
results are summarized in Table 2.
thesis of pyrrole derivatives, we compared the results
and conditions of the synthesis of pyrrole 4g with this
system with systems used in previous researches
(Table 3).
A possible mechanism of the synthesis of pyrrole
derivatives 4, proposed on the basis of the previously
reported ones [23, 26], is shown in Scheme 2. First, the
the nanocatalyst activates the carbonyl group of the β-
diketone/β-ketoester, and the latter reacts with the
amine to form an enamine. Then, the enamine reacts
with the β-nitrostyrene by way of the Michael addition
to produce intermediate 5. The subsequent intra-
molecular cyclization in the latter leads to pyrrole
precursor 6 which converts into pyrrole 4 via
elimination of HNO and H2O.
The reusability of the Fe3O4@SiO2–CPTMS–guani-
dine–SO3H nanocatalyst was assessed in the synthesis
of pyrrole 4f. The recovered nanocatalyst was recycled
five times without significant loss of activity, yield, %
(run no.): 95 (1), 93 (3), 90 (3), 85 (4), and 80 (5).
CONCLUSIONS
In this research, we have developed an efficient
approach to the one-pot synthesis of pyrroles. The
advantages the developed procedure offers over the
previously reported ones include solvent-free
conditions, use of a nanocatalyst that is easily
To demonstrate the efficiency of the Fe3O4@SiO2–
CPTMS–guanidine–SO3H nanocatalyst in the syn-
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Fe3O4@SIO2–CPTMS–GUANIDINE–SO3H-CATALYZED ONE-POT MULTICOMPONENT
1209
Scheme 2. Proposed mechanism for the synthesis of pyrroles derivatives.
R1
R1
HO3S
NH
O
O
O
O
R2
NH
O
R2
R2
+
N
+
OH
NO2
NH2
R1
R3
R3
5
O
H
R3
R2
N
_HNO
_H2O
HO3S
R1
N
N
R1
OH
HO
O
R3
R2
4
6
extracted from the reaction mixture, short reaction
time, low reaction temperature reaction, and good
yields.
Bruker XFlash 6130 EDS system. The XRD patterns
were obtained on an ItalStructures APD-2000 diffract-
tometer (λ 1.54 Å). Thermogravimetric analysis was
performed on a TA Instruments SDT-Q600 Simul-
taneous TGA/DSC instrument. Superparamagnetic
properties of the catalyst were studied using a vibrating
sample magnetometer (MDKFD, Iran).
EXPERIMENTAL
All reagents and solvents were purchased from
Merck, Sigma-Aldrich, and Fluka and used without
further purification. The IR spectra were measured on
Preparation of Fe3O4 MNPs. A mixture of
FeCl3·6H2O (4.865 g, 0.018 mol) and FeCl2·4H2O
(1.789 g, 0.0089 mol) was dissolved in 100 mL of
deionized water, and then 10 mL of 25% NH4OH was
added to the solution under N2 atmosphere at 80°C.
The reaction mixture was stirred about 30 min with a
1
a Bruker Vertex70 spectrometer in KBr. The H NMR
spectra were obtained on a Bruker DRX-300 Avance
spectrometer in CDCl3 at 300 MHz. Scanning electron
microscopy was performed on a JEOL JEM-2010
instrument. The EDX spectra were measured on a
Table 3. Comparison of the activity various catalysts for the synthesis of pyrrole 4g.
Entry
Catalyst
β-Cyclodextrin
Conditions
H2O, 70–80°C
EtOH, reflux
Time, h
Yield, %
Reference
[27]
1
2
3
4
5
6
8
2
90
78
74
54
88
95
Iodobenzene, Oxone
(Diacetoxyiodo)benzene
FeCl3
[24]
EtOH, reflux
4
[25]
CH3NO2, reflux
CH3NO2, reflux
Solvent-free, 50°C
14
8
[11]
FeCl3
[28]
Fe3O4@SiO2–CPTMS–guanidine–SO3H
3
This work
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 8 2019

ROSTAMI, SHIRI
1210
mechanical stirrer. The black precipitate was separated
by magnetic decantation, washed with 5 portions of
distilled water, and dried at room temperature [29].
was cooled to room temperature, the catalyst was
separated by means of external magnet, and the
product was extracted with dichloromethane and
purified by column chromatography on silica gel
(n-hexane–ethyl acetate, 8 : 1).
Preparation of Fe3O4@SiO2 MNPs. A dispersion
of 2 g of Fe3O4 MNPs in 20 mL of water was sonicated
for 30 min, after which EtOH (50 mL), PEG (5.36 g),
H2O (20 mL), NH4OH (10 mL), and tetraethyl
orthosilicate (TEOS) (2 mL) were successsively added
to the suspension. The mixture was stirred for 38 h at
room temperature and then the product was separated
by magnetic decantation, washed with EtOH, and dried
at room temperature [29].
1-[1-(4-Bromophenyl)-4-(4-chlorophenyl)-2-me-
thyl-1H-pyrrol-3-yl]ethan-1-one (4h). Yield 83%,
yellow solid, mp 164–166°C. IR spectrum, ν, cm–1:
1
1648 (C=O), 1400, 1555 (Ar), H NMR spectrum
(CDCl3), δ, ppm: 2.09 s (3H, CH3), 2.40 s (3H, CH3),
6.64 s (1H, CH), 7.21–7.65 m (8H, CH).
ACKNOWLEDGMENTS
Preparation of Fe3O4@SiO–CPTMS MNPs. A
dispersion of 1 g of Fe3O4@SiO2 MNPs in 25 mL of
water and 25 mL of EtOH was sonicated for 30 min.
Then (3-chloropropyl)triethoxysilane (CPTMS) (2.5 mL)
was added, and the mixture was stirred at 40°C for 8 h.
The precipitate was separated by magnetic decantation,
washed several times with EtOH, and dried at room
temperature [29].
The authors are grateful to the IIam University
Research Council for financial support of this work.
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Fe3O4@SiO2–CPTMS–guanidine MNPs (0.5 g) in
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