Efficient synthesis of 3,3′-bisindoles catalyzed by Fe3O4@MCM-48-OSO3H magnetic core-shell nanoparticles

Article abstract of DOI:10.1016/S1872-2067(14)60281-3

Magnetite nanoparticles coated with sulfuric acid-functionalized mesoporous MCM-48 were synthesized and used as a catalyst in three-component domino reactions of indoles, arylglyoxal monohydrates and N-arylenaminones to furnish the desired 3,3′-bisindoles by formation of two C-C and one C-N bonds in a smooth cascade with good yields under mild reaction conditions. The catalyst was recovered easily and maintained activity in successive runs.

Full text of DOI:10.1016/S1872-2067(14)60281-3

Chinese Journal of Catalysis 36 (2015) 778–784
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Efficient synthesis of 3,3′-bisindoles catalyzed by
Fe3O4@MCM-48-OSO3H magnetic core-shell nanoparticles
Alireza Khorshidi a,*, Shahab Shariati b
a Department of Chemistry, Faculty of Sciences, University of Guilan, Iran
b Department of Chemistry, Rasht Branch, Islamic Azad University, Rasht, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Magnetite nanoparticles coated with sulfuric acid-functionalized mesoporous MCM-48 were syn-
thesized and used as a catalyst in three-component domino reactions of indoles, arylglyoxal mono-
hydrates and N-arylenaminones to furnish the desired 3,3′-bisindoles by formation of two C–C and
one C–N bonds in a smooth cascade with good yields under mild reaction conditions. The catalyst
was recovered easily and maintained activity in successive runs.
Received 17 December 2014
Accepted 4 January 2015
Published 20 May 2015
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Keywords:
Fe3O4
Published by Elsevier B.V. All rights reserved.
Mesoporous
Nanoparticle
Core-shell
3,3′-Bisindole
1. Introduction
ino reactions resulting in polyfunctionalized indoles [15–17].
Our involvement in the study of indoles and solid acid catalysts
The chemistry of indoles has been and continues to be one
of the most active areas of heterocyclic chemistry [1,2]. Various
indole derivatives are pharmacologically and biologically active
compounds [3–7]. For example, topsentin A (Fig. 1) is a
3,3′-bisindole derivative originating from natural sources like
the marine sponge Topsentina genitrix [8] that acts as an anti-
tumor agent [9].
In recent years, many studies have focused on the function-
alization of indoles at the C-3 position because it is the most
nucleophilic site. A large number of 3-substituted indoles, es-
pecially 3,3′-bis(indolyl)methanes, have been reported
[10–14]. However, little attention has been paid to the reac-
tions that involve more than one nucleophilic center, namely
C-3, C-2 and N, of the indole ring system. Some exciting reports
on this subject include Jiang’s work on multicomponent dom-
[18–20], along with a recent report on three-component for-
mation of bis-indole derivatives by Tu’s group [21], prompted
us to investigate the use of functionalized magnetic nanoparti-
cles in their protocol to overcome its associated limitations
such as acidic media and need for specialized instruments, and
the obtained results were satisfying. Functionalized magnetic
nanoparticles were selected because they could be easily sepa-
rated from the reaction mixture by an external magnet. Herein,
we report sulfuric acid-functionalized MCM-48 coated on mag-
Fig. 1. Structure of topsentin A.
* Corresponding author. Tel: +98 911 339 759; Fax: +98 13 33 33 32 62; E-mail: khorshidi@guilan.ac.ir
This work was supported by the Research Council of University of Guilan.
DOI: 10.1016/S1872-2067(14)60281-3 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 5, May 2015

Alireza Khorshidi et al. / Chinese Journal of Catalysis 36 (2015) 778–784
779
Scheme 1. Fe3O4@MCM-48-OSO3H-catalyzed three-component reaction of indoles, phenylglyoxal monohydrates and N-arylenaminones.
netite nanoparticles with a core-shell structure (Fe3O4@MCM-
48-OSO3H, where Fe3O4 nanoparticles serve as a core for a
mesoporous MCM-48 shell functionalized with sulfuric acid) as
an efficient solid acid nanocatalyst for three-component reac-
tion of indoles, phenylglyoxal monohydrates and N-arylenami-
nones under mild reaction conditions (Scheme 1).
NMR spectra were expressed in ppm downfield from tetrame-
thylsilane. Melting points were measured on a Büchi Melting
Point B-540 instrument and were not corrected. Elemental
analyses were performed using a Carlo-Erba EA1110 CNNO-S
analyzer and agreed with the calculated values. TEM images
were obtained on a transmission electron microscope (TEM;
PHILIPS MC 10) with an acceleration voltage of 80 kV. Vibrat-
ing sample magnetometry (VSM) curves were obtained on a
vibrating sample magnetometer (JDM-13) at room tempera-
ture. Analytical gas chromatographic (GC) evaluations of prod-
uct mixtures were carried out on a Varian CP-3800 chromato-
graph using a split/splitless injector, CP Sil 8CB column, and
FID assembly.
2. Experimental
2.1. Materials
Fe3O4 nanoparticles were synthesized according to our pre-
vious report [22]. To synthesize Fe3O4@MCM-48, the
as-prepared Fe3O4 nanoparticles (1.5 g) and ammonia solution
(5 mL, 25%) were mixed with distilled water (50 mL) in a glass
reactor and sonicated for 2 min at 40 °C. Tetraethylorthosili-
cate (10.0 mL), NaOH (0.90 g) and NaF (0.19 g) were added and
then the mixture was stirred for 2 h. Cetyltrimethylammonium
bromide (7.0 g) was added to the mixture, and it was stirred at
40 °C for 2 h. The magnetic composite was then hydrothermally
treated at 120 °C for 48 h in an autoclave. The resulting solid
was filtered, washed with distilled water and dried at 60 °C.
Finally, the template was removed by calcination of the synthe-
sized particles for 3 h at 300 °C. SO3H functionalization of
Fe3O4@MCM-48 was carried out according to the method of
Kiasat et al. [23]. Fe3O4@MCM-48 (2.0 g) was charged into a
suction flask equipped with a constant-pressure dropping fun-
nel, and dispersed in CH2Cl2 (75 mL) by ultrasound for 10 min.
Chlorosulfonic acid (2.92 g, 25 mmol) in CH2Cl2 (20 mL) was
added dropwise over a period of 30 min at room temperature.
The mixture was then stirred for 1.5 h, and evolved HCl was
removed by suction. Fe3O4@MCM-48-OSO3H was then sepa-
rated from the reaction mixture using an external magnet,
washed several times with CH2Cl2, and then dried under vac-
uum at 60 °C. The calculated sulfonic acid loading was 2.3
mmol SO3H per g of catalyst according to a literature method
[23].
2.3. Typical procedure to prepare 3,3′-bisindoles 1a–1i
In a three-necked round-bottom flask equipped with a re-
flux condenser, indole (1.00 mmol), phenylglyoxal monohy-
drate (1.00 mmol), and N-arylenaminone (1.00 mmol) were
dissolved in refluxing ethanol (10 mL). Fe3O4@MCM-48-OSO3H
(0.1 g) was added and the resulting mixture was mechanically
stirred until the starting indole completely disappeared (moni-
tored by TLC). After completion of the reaction, the catalyst was
removed by an external magnet. The resulting hot solution was
quenched with water. The solidified product was filtered,
rinsed with a cold mixture of ethanol and water (70:30) and
then dried under high vacuum overnight to provide pure
product. The recovered catalyst was washed three times with
CH2Cl2 and then dried under vacuum at 60 °C overnight.
2.4. Characterization data for 6,7-dihydro-6,6-dimethyl-3-(2-
methyl-1H-indol-3-yl)-1,2-diphenyl-1H-indol-4(5H)-one (1a)
White solid, Yield 80%; m.p. 255–256 °C; FT-IR (KBr): υmax
=
3275, 1640, 1598, 1498, 1460, 1366, 1123, 1075, 787, 739, 706
cm–1. 1H NMR (400 MHz, DMSO-d6, 25 °C) δ = 10.72 (s, 1H, NH),
7.36–7.43 (m, 3H, ArH), 7.28 (s, 2H, ArH), 7.18 (d, J = 7.6 Hz, 1H,
ArH), 6.87–6.97 (m, 5H, ArH), 6.71–6.77 (m, 3H, ArH), 2.65 (d, J
= 16.8 Hz, 1H, CH2), 2.58 (d, J = 16.9 Hz, 1H, CH2), 2.28 (s, 2H,
CH2), 1.90 (s, 3H, CH3), 1.09 (s, 3H, CH3), 1.08 (s, 3H, CH3). 13C
NMR (100 MHz, DMSO-d6, 25 °C) δ = 193.3, 143.7, 137.9, 135.5,
133.8, 133.0, 131.9, 130.0, 129.3, 129.1, 128.0, 127.6, 126.2,
125.9, 120.3, 119.7, 119.2, 118.8, 113.2, 110.1, 106.1, 53.1, 35.0,
29.1, 28.3, 12.4; Anal. Calc for C31H22N2O (%): C 83.75, H 6.35, N
6.30; Found (%): C 83.81, H 6.39, N 6.29.
2.2. Instrumentation
Powder X-ray diffraction (XRD) measurements were per-
formed on a Philips diffractometer with monochromatized Cu
Kα radiation. Fourier transform infrared (FT-IR) spectra were
recorded on a Shimadzu FTIR-8400S spectrometer. 1H NMR
spectra were obtained on a Bruker DRX-400 Advance spec-
trometer and 13C NMR spectra were recorded on a Bruker
All of the other products are known compounds, and their
spectroscopic and physical data were identical to those de-
1
DRX-100 Advance spectrometer. Chemical shifts of H and 13C

780
Alireza Khorshidi et al. / Chinese Journal of Catalysis 36 (2015) 778–784
scribed in the literature [21].
60
50
40
30
20
10
0
(b)
(a)
3. Results and discussion
Mesoporous MCM-48 was selected as the shell for Fe3O4
magnetite nanoparticles because of its three-dimensional
channel system and numerous external hydroxyl groups. Dep-
osition of the shell onto the surface of Fe3O4 nanoparticles was
performed by a simple, low-cost method. Subsequent treat-
ment of the core-shell nanocomposite with chlorosulfonic acid
in dichloromethane provided the solid acid catalyst
Fe3O4@MCM-48-OSO3H, which was characterized by FT-IR
spectroscopy, TEM, XRD and VSM. In the FT-IR spectrum of
Fe3O4@MCM-48-OSO3H nanoparticles (Fig. 2(2)), basic charac-
teristic vibrations of Fe–O at 588 cm–1 and Si–O–Si asymmetric
stretching, symmetric stretching and bending vibrations at
1072, 795 and 453 cm–1, respectively, were observed. Charac-
teristic bands of the sulfonyl groups were observed at 1229 and
1120 cm–1, along with simultaneous disappearance of the
Si–OH peak of Fe3O4@MCM-48 at 900 cm–1 [23].
5
10 15 20 25 30
Diameter (nm)
Fig. 4. (a) TEM image of Fe3O4@MCM-48-OSO3H nanoparticles and (b)
corresponding particle size distribution.
exhibited peaks at 2θ = 29.72°, 35.57°, 43.17°, 57.15° and
62.77°, consistent with pure magnetite (Fig. 3(b)(1)) and
matched well with the standard XRD pattern of Fe3O4 (JCPDS
No. 19-692) [24]. The siliceous mesoporous structure exhibited
four peaks at 2θ = 1.5°–10° (Fig. 3(a)(2)) from the (211), (220),
(420) and (332) planes, which are characteristic peaks of
MCM-48.
The XRD pattern of Fe3O4@MCM-48-OSO3H (Fig. 3(b)(2))
contained peaks that could be indexed to both mesoporous
structure and Fe3O4 nanoparticles. The Fe3O4 nanoparticles
The nanoscale size of the composite was confirmed by TEM
observation, as shown in Fig. 4(a). An average particle size of
20 nm was determined for Fe3O4@MCM-48-OSO3H according
to a particle size distribution analysis (Fig. 4(b)). TEM image
indicated that the surface of Fe3O4@MCM-48-OSO3H consisted
of an agglomeration of many ultrafine spherical particles with
dark magnetite cores each surrounded by a mesoporous shell.
The magnetic hysteresis curves of the Fe3O4@MCM-48-
OSO3H magnetic nanoparticles were also obtained. Bare Fe3O4
and Fe3O4@MCM-48-OSO3H nanoparticles exhibited typical
superparamagnetic behavior. The large saturation magnetiza-
tion of bare Fe3O4 decreased from 82 to 49 emu/g for the
Fe3O4@MCM-48-OSO3H nanoparticles because of their
non-magnetic mesoporous shell (Fig. 5).
a
(1)
b
(2)
The porosity of the Fe3O4@MCM-48-OSO3H nanoparticles
was evaluated by N2 adsorption-desorption isotherm meas-
urements, which showed a characteristic type-IV curve (Fig. 6).
This curve exhibited a distinct hysteresis loop in the relative
pressure (p/p0) range of 0.6–0.9, indicating the presence of
mesopores with a narrow size distribution. Other physico-
chemical properties of the Fe3O4@MCM-48-OSO3H nanoparti-
2000
1500
1000
500
Wavenumber (cm−1)
Fig. 2. FT-IR spectra of (1) Fe3O4@MCM-48 and (2) Fe3O4@MCM-48-
OSO3H.
(211)
(a)
(b)
(2)
(1)
(2)
(1)
(220)
(420)
(332)
2
4
6
8
10
10
20
30
40
50
2θ/(o )
Fig. 3. XRD patterns of (1) Fe3O4 nanoparticles and (2) Fe3O4@MCM-48-OSO3H nanoparticles. (a) Low-angle; (b) High-angle.
60
70
2θ/(o )

Alireza Khorshidi et al. / Chinese Journal of Catalysis 36 (2015) 778–784
781
100
80
60
(1)
80
(2)
40
20
60
40
20
0
-20
-40
-60
-80
-10000
0
100
200
Temperature (oC)
Fig. 7. TG curve for the Fe3O4@MCM-48-OSO3H nanoparticles.
300
400
500
600
-5000
0
5000
10000
Applied field (nm)
Fig. 5. Hysteresis curves of (1) Fe3O4 and (2) Fe3O4@MCM-48-OSO3H
nanoparticles measured at 27 °C.
water molecules adsorbed on the external surface and those
hosted in the pores, (2) loss of template molecules from 200 to
350 °C and (3) collapse of the –SO3H functional groups or con-
densation of silanol groups from 350 to 600 °C. The TG analysis
reveals that the obtained catalyst has sufficient thermal stabil-
ity to endure recycling processes or harsh reaction conditions
up to 300 °C.
The characterized catalyst was then used in one-pot
three-component condensation reactions of indoles, phenyl-
glyoxal monohydrates and N-arylenaminones. To optimize the
reaction conditions with respect to catalyst type and loading,
and examine the effect of solvent and temperature on the reac-
tion yield, 2-methylindole, phenylglyoxal monohydrate and
5,5-dimethyl-3-(phenylamino)cyclohex-2-enone were used as
model substrates and their reactions were carried out under
different conditions. The results of these reactions are summa-
rized in Table 1.
Table 1 shows that in the absence of catalyst, the desired
product was not formed (entry 1). Although far from giving the
maximum yield, it was proved that the optimum loading of
Fe3O4@MCM-48-OSO3H under ambient conditions was 0.1 g
per mmol of indole (entry 5). The same loading of MCM-48
sulfuric acid (entry 4) was also tested under ambient condi-
tions and gave a comparable yield. However, Fe3O4@MCM-48-
OSO3H has the advantage over MCM-48 sulfuric acid in terms of
easy recycling. It was found that elevated temperature had a
powerful effect on the reaction yield, and an excellent yield of
450
400
350
300
250
200
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Fig. 6. N2 adsorption-desorption isotherms measured at –196 °C for
Fe3O4@MCM-48-OSO3H nanoparticles with core-shell structure.
cles determined from the N2 adsorption-desorption measure-
ments are a Brunauer-Emmett-Teller surface area of 412.5
m2/g (calculated in the p/p0 = 0–0.5), mean Barrett-Joyner-
Halenda pore diameter of 2.6 nm, total pore volume of 0.417
cm3/g and mean pore volume of 0.401 cm3/g.
Thermogravimetric (TG) analysis of the as-synthesized
product (Fig. 7) contained distinct parts: (1) loss of phy-
sisorbed water from 80 to 180 °C, which corresponded to the
Table 1
Effect of various parameters on the three-component reaction of indole, phenylglyoxal monohydrate and 5,5-dimethyl-3-(phenylamino)cyclohex-
2-enone.
Entry a
1
2
3
4
5
6
7
Catalyst
No catalyst
Fe3O4
MCM-48
Solvent
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
MeOH
1,4-Dioxane
1,2-DCE
Toluene
Catalyst loading (g per mmol of indole)
Temperature (°C)
Yield (%)
0
25
25
25
25
0
0
0
0.1
0.1
0.1
0.1
0.1
0.05
0.15
0.1
0.1
0.1
0.1
MCM-48-OSO3H
21
18
80
65
83
77
53
19
14
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
Fe3O4@MCM-48-OSO3H
25
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
8
9
10
11
12
a Each reaction was carried out according to the general experimental procedure.

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Alireza Khorshidi et al. / Chinese Journal of Catalysis 36 (2015) 778–784
80% was obtained under reflux (entry 6). Meanwhile, higher
loads of the catalyst did not have a considerable effect on yield
(entry 8). To evaluate the effect of particle size on catalyst per-
formance, larger Fe3O4@MCM-48-OSO3H nanoparticles with a
diameter of about 50 nm (Fig 8) were synthesized by manipu-
lation of the hydrothermal synthesis conditions (140 °C, 4 d).
However, under the same reaction conditions, the larger parti-
cle size of the new catalyst had only a moderate effect on the
reaction yield (73% vs 80%). This may be because the –SO3H
functionality plays the main role in this catalytic system. It is
noteworthy that the yield of the product depended on solvent,
and the highest yields were obtained using ethanol and meth-
anol. Ethanol was selected as the solvent because it is less toxic
than methanol.
Fig. 8. TEM image of larger Fe3O4@MCM-48-OSO3H nanoparticles.
After determining the optimum reaction conditions
(Scheme 1), a series of 2-substituted indoles, phenylglyoxal
monohydrates and N-arylenaminones were used to investigate
the generality and scope of the reaction. As shown in Table 2,
the results are satisfying, because the same regioselectivity
toward 3,3′-bisindoles was observed in each case.
Table 2 reveals that various indoles, phenylglyoxal mono-
hydrates and N-arylenaminones participated in the reaction,
and this catalytic system tolerated different functional groups.
With regard to substituents, the electron-releasing nature of
the aryl moiety in N-arylenaminones favors the formation of
products. However, 1-methylindole did not yield the desired
product. These observations may be explained by the following
proposed reaction mechanism (Scheme 2).
In general, after activation of the phenylglyoxal monohy-
drate by the solid Brӧnsted acid catalyst, nucleophilic attack
from the C-3 carbon atom of indole gives intermediates I. The
next steps are nucleophilic attacks by the β-C atom of
β-enaminone to give intermediate II and NH group of
β-enaminone resulting in C–C and C–N bond formation via
[3+2] cyclization to provide intermediate III, which then dehy-
Table 2
Fe3O4@MCM-48-OSO3H-catalyzed regioselective three-component synthesis of 3,3′-bisindoles.
Time Yield b
(min) (%)
Time Yield b
(min) (%)
Entry
1
Indole
Ar, Ar′
Product a
Entry
6
Indole
Ar, Ar′
Product a
2-
2-
4-FC6H4,
C6H5
C6H5, C6H5
1a 25
80
1f 25
70
methylindole
phenylindole
2-
4-ClC6H4,
C6H5
2-
4-MeC6H4,
2
3
4
5
1b 25
1c 25
1d 30
1e 25
70
88
75
67
7
8
1g 30
1h 25
1i 25
60
80
82
89
0
methylindole
phenylindole 4-MeC6H4
2-
4-MeC6H4,
C6H5
2-
4-ClC6H4,
methylindole
phenylindole 4-BrC6H4
4-MeOC6H4,
C6H5
2-
4-MeC6H4,
2-methylindole
9
phenylindole 4-BrC6H4
4-FC6H4,
C6H5
1-
2-methylindole
10
C6H5, C6H5
methylindole
No reaction
a All products were characterized by 1H NMR, 13C NMR and FT-IR spectroscopies.
b Isolated yields.

Alireza Khorshidi et al. / Chinese Journal of Catalysis 36 (2015) 778–784
783
loading was determined for the recycled catalyst used in the
third run. The calculated value was 2.3 mmol SO3H/g, similar to
that of the unused catalyst, which confirmed that considerable
leaching did not occur during the course of the reaction. To
further strengthen this assumption, the reaction of
2-methylindole, phenylglyoxal monohydrate and 5,5-dime-
thyl-3-(phenylamino)cyclohex-2-enone was interrupted half-
way during the normal reaction period (after 12.5 min) and the
catalyst was removed by an external magnet. The reaction was
then continued for the rest of the time (up to 25 min). At the
end of this period, the yield was only 39%, and no considerable
change in the concentration of residual 2-methylindole was
observed according to GC analysis of the reaction mixture.
Ar
Ar'
N
R
Ar'
O
NH
OSO3H
OH
HO
O
+H2O
Ar'
O
OSO3H
OH
O
H
R
Ar
HO
N
Ar'
R
NH
III
NH
H
O
Ar'
O
R
NH
OSO3H
O
H
+ H O
2
4. Conclusions
NHAr
Ar'
ArHN
O
R
We developed a convenient method for one-pot three-com-
ponent reaction of indoles, phenylglyoxal monohydrates and
N-arylenaminones under mild conditions. Highlights of the
present work are regioselective one-pot formation of two C–C
and one C–N bonds in a smooth cascade, recyclable catalyst,
which promises minimization of waste, ease of work-up and
good efficiency in terms of solvent, temperature and yield.
Further manipulation of this reaction is currently underway in
our laboratory.
O
I
NH
O
II
+H2O
Scheme 2. Proposed mechanistic pathway for the formation of
3,3′-bisindoles.
drates to form the product.
To evaluate reusability of the catalyst, the reaction of
2-methylindole, phenylglyoxal monohydrate and 5,5-dimethyl-
3-(phenylamino)cyclohex-2-enone was carried out in the
presence of the recycled catalyst in successive runs. For reac-
tion runs 1, 2, 3, 4, 5 and 6, the yields were 80%, 80%, 77%,
70%, 63% and 38%, respectively. Therefore, after five runs, the
efficiency of the catalyst decreased by 17%. This result shows
that Fe3O4@MCM-48-OSO3H can be used as a recyclable cata-
lyst for the formation of 3,3′-bisindoles under moderate condi-
tions. To confirm heterogeneity of the catalyst, the sulfonic acid
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Graphical Abstract
Chin. J. Catal., 2015, 36: 778–784 doi: 10.1016/S1872-2067(14)60281-3
Efficient synthesis of 3,3′-bisindoles catalyzed by Fe3O4@MCM-48-OSO3H magnetic core-shell nanoparticles
Alireza Khorshidi*, Shahab Shariati
University of Guilan, Iran; Islamic Azad University, Iran
Magnetite nanoparticles coated with sulfuric acid-functionalized mesoporous MCM-48 are used as a catalyst in green synthesis of
3,3′-bisindoles via formation of two C–C and one C–N bonds in a smooth cascade with good yields under mild reaction conditions.

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