Nano Fe3O4 as a magnetically recyclable, powerful, and stable catalyst for the multi-component synthesis of highly functionalized dihydro-2-oxopyrroles

Article abstract of DOI:10.1007/s11164-015-2185-0

A mild and efficient method for the one-pot synthesis of functionalized dihydro-2-oxopyrroles is described via four-component domino reaction of amines, dialkyl acetylenedicarboxylates, and formaldehyde in the presence of super magnetic nano iron oxide (nano Fe₃O₄) in EtOH at room temperature. The major advantages of the present method are mild and green reaction conditions, high yields, short reaction times, clean reaction, magnetically recyclable catalyst, atom economy (63-76 %), operational simplicity, and no need for column chromatography. It is found that the catalyst is recyclable and can be used up to six times without significant loss of its activity.

Full text of DOI:10.1007/s11164-015-2185-0

Res Chem Intermed
DOI 10.1007/s11164-015-2185-0
Nano Fe3O4 as a magnetically recyclable, powerful,
and stable catalyst for the multi-component synthesis
of highly functionalized dihydro-2-oxopyrroles
Mohammad Nickraftar1 Nahid Najafi Hajivar2
•
•
Jasem Aboonajmi3 Elham Fereidooni1
•
Received: 7 May 2015 / Accepted: 17 July 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A mild and efficient method for the one-pot synthesis of functionalized
dihydro-2-oxopyrroles is described via four-component domino reaction of amines,
dialkyl acetylenedicarboxylates, and formaldehyde in the presence of super magnetic
nano iron oxide (nano Fe3O4) in EtOH at room temperature. The major advantages of the
present method are mild and green reaction conditions, high yields, short reaction times,
clean reaction, magnetically recyclable catalyst, atom economy (63–76 %), operational
simplicity, and no need for column chromatography. It is found that the catalyst is
recyclable and can be used up to six times without significant loss of its activity.
&
&
1
Mohammad Nickraftar
nikraftar67@gmail.com
Nahid Najafi Hajivar
nnh.chem@gmail.com
Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan,
PO Box 98135-674, Zahedan, Islamic Republic of Iran
2
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan,
Islamic Republic of Iran
3
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454,
Islamic Republic of Iran
123

M. Nickraftar et al.
Graphical Abstract
Keywords Nano Fe3O4 Á Heterocycle Á Dihydro-2-oxopyrrole Á Dialkyl
acetylenedicarboxylate Á Green Á Magnetically recyclable Á Multi-component
Introduction
Nitrogen heterocycles have been the subject of intense research because of their
outstanding biological properties and wide range of applications to pharmaceutical
compounds, agrochemicals, and synthetic intermediates. For example, pyrrole and
its derivatives such as dihydro-2-oxypyrroles (dihydropyrrol-2-ones) and pyrrolodi-
nes are the important structural motifs that are found in natural and synthetic
compounds [1]. Especially, functionalized dihydro-2-oxopyrroles are an important
class of nitrogen-containing five-membered heterocycles. They are the building
blocks of many natural products such as bilirubins [2, 3] and indolocarbazole
alkaloids [4]. They have also been used as inhibitors of HIV integrase [5], cardiac
cyclic AMP phosphodiesterase [6], vascular endothelial growth factor receptors [7],
pesticides [8], herbicides [9]h and also as antitumor agents [10]. They are also
considered as a precursor to pyrrolizidine alkaloids [11]. Structures of some
biologically important dihydro-2-oxopyrrole are shown in Fig. 1. As a result,
considerable efforts have been made for the synthesis of this important class of
compounds [12–17].
Green chemistry and the development of new processes that reduce pollution in
chemical synthesis have received considerable attention due to increasing environ-
mental concerns. Among other factors, two major adverse effects on the
environment are consumption of energy for heating and cooling of reactions and
using volatile organic solvents. The performance of reactions at ambient temper-
ature in green solvents such as water and ethanol may be a viable option [18, 19].
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Nano Fe3O4 as magnetically recyclable, powerful, and…
Fig. 1 Bioactive compounds containing dihydro-2-oxopyrrole unit
On the other hand, one active area to access green chemistry is multi-component
reactions (MCRs).
Recently, multi-component reactions (MCRs) have received great attention from
research groups in medicinal chemistry, drug discovery, and materials science due to
their significant advantages over conventional linear-type syntheses, including simple
procedures, eco-friendliness, atom economy, and the ability to generate architec-
turally complex molecules in one synthetic step [20]. Nevertheless, few methods have
been reported for the preparation of dihydro-2-oxopyrroles by one-pot MCR using
catalysts, such as acetic acid [21], molecular iodine [22], Al(H2PO4)3 [23],
Cu(OAc)2ÁH2O [24], 1-methyl-2-oxopyrrolidinium hydrogen sulfate ([Hpyro]
[HSO4]) [25], TiO2 nanopowder [26], tetrabutylammonium hydrogen sulfate ([n-
Bu4N][HSO4]) [27], (S)-camphorsulfonic acid [28], sucrose [29], InCl3 [30], maltose
[31], xylose [32], and Cl3CCO2H [33]. However, many of these catalysts are
expensive, highly corrosive, and involve tedious separation procedures and also
require prolonged reaction times. Therefore, the development of a simple, convenient,
and an efficient protocol using inexpensive and readily available reagents would
extend the scope of the synthesis of highly functionalized dihydro-2-oxopyrroles.
Recently, transition-metal-catalyzed organic reactions are often considered to follow
the principles of ‘‘green chemistry’’ due to the use of minimum energy, cleaner
reagents or auxiliaries and minimization of waste. Nanocatalysts are considered to be
a bridge between heterogeneous and homogeneous catalysis [34, 35]. One of the
attractive properties of the nanomaterials is that the active component has a high
specific surface area, leading to an increase of the contact with the reactants [36].
Also, a higher surface area gives nanomaterials a more active surface; they are hard to
be separated. Therefore, it is important to design a recoverable and well-dispersed
catalyst. Magnetite nanoparticles (MNPs) as catalysts are very promising due to their
large specific surface area and their magnetic properties [37, 38]. They can be
collected very easily using a magnet for reusing it to prevent any loss of the catalyst.
Recently, chemists have focused on the catalytic aspects of nano-Fe3O4 to improve
the protocols of catalytic activity [39–42].
As a part of our current studies on the development of efficient multi-component
reactions for the preparation of interesting bioactive molecules [43–46], in this
article we report that nano Fe3O4 (10 mol %) is a highly efficient and economically
123

M. Nickraftar et al.
viable catalyst for the one-pot synthesis of highly functionalized dihydro-2-
oxopyrroles from amines, dialkyl acetylenedicarboxylates, and formaldehyde in
EtOH at room temperature (Scheme 1). Interestingly, this method has none of the
above-mentioned drawbacks for the dihydro-2-oxopyrroles. The catalyst can be
easily collected by a magnet and recovered without significant loss in the catalytic
activity.
Results and discussion
It is well known that nano Fe3O4 as a Lewis acid catalyst have gained interesting
attraction in recent years due to operational simplicity, efficient, low cost, magnetically
recyclable catalyst, being more stable, and economic considerations [47, 48].
Initially, a test reaction using aniline, dimethyl acetylenedicarboxylate (DMAD),
and formaldehyde was performed in the absence of a catalyst in EtOH at room
temperature. The corresponding product, 5a, was obtained in trace amounts after
24 h (Table 1, entry 15). To optimize the reaction conditions, the above reaction
Scheme 1 Synthesis of highly functionalized dihydro-2-oxopyrroles 5
Table 1 Optimization of the
Entry
Catalyst (mol%)
Solvent
Time (h)
Yield (%)a
reaction conditions for the
synthesis 5a
1
5
EtOH
MeOH
MeCN
CHCl3
CH2Cl2
EtOAC
THF
4
70
62
56
45
48
41
35
50
53
40
82
89
89
86
Trace
2
5
6
3
5
7
4
5
8
5
5
8
6
5
8
7
5
10
7
8
5
Acetone
H2O
9
5
12
12
3
10
11
12
13
14
15
5
–
7.5
10
12.5
15
–
EtOH
EtOH
EtOH
EtOH
EtOH
2.5
2.5
2.5
24
a
Yield of isolated product
123

Nano Fe3O4 as magnetically recyclable, powerful, and…
was examined under different conditions and the results are presented in Table 1.
The best result was obtained in the presence of 10 mol % Fe3O4 in EtOH (Table 1,
entry 12). As shown in Table 1, a higher percentage loading of the catalyst neither
increased the yield of product nor decreased the reaction time. Additionally, the
effect of different solvents including MeOH, MeCN, CHCl3, CH2Cl2, EtOAc, THF,
acetone, and H2O was also investigated on the yield and time of reaction, which was
found to be ineffective. When the reaction was carried out under solvent-free
conditions, the product was obtained in a moderate yield (40 %), which may be due
to the lack of effective interaction of reactants with the catalyst in the absence of a
solvent (Table 1, entry 10). Next, the scope of this reaction has been extended by
means of reaction between various aromatic amines, dialkyl acetylenedicarboxy-
lates, and formaldehyde under optimized conditions. The results are summarized in
Table 2.
In general, all the reactions are clean, and the dihydro-2-oxopyrrole
derivatives were obtained in quantitative yields (Table 2, entries 1–11).
Encouraged by these results, substituted dihydro-2-oxopyrroles with different
Table 2 Synthesis of highly substituted dihydro-2-oxopyrroles 5
Entry R1
R2
Ar
Compound Time Yield Mp (°C) Lit. mp (°C)
(h)
(%)a
(Refs.)b
1
Ph
Me Ph
Et Ph
Me 4-Me–C6H4
Et 4-Me–C6H4
Me 4-Cl–C6H4
5a
5b
5c
5d
5e
5f
2.5
3
89
84
86
85
85
83
80
89
80
85
85
85
82
81
83
85
79
77
79
75
77
80
153–155 155–156 [22]
137–139 138–140 [21]
177–178 177–178 [22]
129–131 131–132 [21]
170–172 173–174 [22]
169–171 168–170 [27]
173–174 172–173 [21]
174–176 176–177 [22]
152–153 152–154 [23]
178–180 179–180 [22]
170–171 169–171 [21]
139–141 140–141 [21]
127–129 130–132 [21]
125–127 129–130 [22]
145–147 147–148 [22]
122–123 120–121 [22]
2
Ph
3
4-Me–C6H4
4-Me–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-F-C6H4
2.5
2.5
2.5
3
4
5
6
Et
Et
4-Cl–C6H4
4-F–C6H4
7
5g
3.5
2.5
3
8
4-OMe–C6H4 Me 4-OMe–C6H4 5h
9
4-OMe–C6H4 Et
4-OMe–C6H4 5i
10
11
12
13
14
15
16
17
18
19
20
21
22
a
4-Br–C6H4
4-Br–C6H4
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
n-C4H9
n-C4H9
C6H11
Me 4-Br–C6H4
Et 4-Br–C6H4
Me Ph
Et Ph
5j
2.5
3
5k
5l
2.5
4.5
3
5m
Me 4-OMe–C6H4 5n
Me 4-Cl–C6H4
Me 4-Br–C6H4
Me Ph
5o
5p
5q
5r
5s
3
3
4
58–60
108–110 108–109 [22]
92–93 94–95 [21]
60 [22]
Me 4-Br–C6H5
Me Ph
4
3.5
4
C6H11
Me 4-OMe–C6H4 5t
127–129 128–129 [22]
123–125 124–125 [22]
121–122 123–124 [22]
C6H11
Me 4-Cl–C6H4
Me 4-Br–C6H5
5u
5v
4
C6H11
3.5
Isolated yields
b
The references of known products in the literature
123

M. Nickraftar et al.
Table 3 Comparison of nano Fe3O4 with previously reported catalyst for the synthesis of dihydro-2-
oxopyrrole 4b
Entry
Catalyst
Conditions
Time (h)
Yield (%)
(Refs.)
1
2
3
4
5
6
7
8
[Hpyro][HSO4]
AcOH
MeOH, r.t.
EtOH, 70 °C
MeOH, r.t.
MeOH, r.t.
MeOH, r.t.
MeOH, 60 °C
MeOH, r.t.
EtOH, r.t.
6
4
5
1
4
4
3
3
80
85
80
81
86
84
85
84
[25]
[21]
Al(H2PO4)3
I2
[23]
[22]
[n-Bu4N][HSO4]
Sucrose
[27]
[29]
InCl3
[30]
Nano Fe3O4
This work
Table 4 Recycling of the
catalyst for the four-component
coupling reaction of diethyl
acetylenedicarboxylate,
Run
Time (h)
Yield (%) (isolated)
1
2
3
4
5
6
2.5
2.5
2.5
2.5
2.5
2.5
85
85
84
83
83
81
4-methyl aniline, and
formaldehyde (product 5d)
substitutions were synthesized via one-pot four-component domino reaction of
aliphatic amines 1, dialkyl acetylenedicarboxylates 2, aromatic amine 3, and
formaldehyde 4 (Table 2, entries 12–22). Aliphatic amines include benzyl amine,
n-butyl amine and cyclo hexyl amine were used and the corresponding products
were achieved in good to high yields. As all products were precipitated in EtOH,
separated from reaction mixture by simple filtration and washed with EtOH to
give pure products.
To show the merit of the present work in comparison with reported results in the
literature, we compared results of nano Fe3O4 with the other catalysts for the
synthesis of compounds 4b. As shown in Table 3, nano Fe3O4 can act as more
effective catalyst with respect to reaction times and yields of products.
In addition, a catalytic recycle experiment (Table 4) was done with the standard
reaction. After the completion of the reaction, as indicated by TLC, the solid
material was separated, dried, and then dissolved in acetone (10 ml). The
nanoparticles were separated with an external magnet (Fig. 2) and then washed
four times with acetone, dried, and reused for the standard reaction for up to six
cycles without significant loss of its activity.
On the basis of above experimental results together with the related reports [24,
25], a plausible mechanism for this four-component domino reaction is proposed as
shown in Scheme 2. The first two steps involve the reaction of amine 1 with dialkyl
acetylenedicarboxylate 2 to form dialkyl 2-(aryl or alkylamino) fumarate 7, and the
123

Nano Fe3O4 as magnetically recyclable, powerful, and…
Fig. 2 Schematic representation of nano Fe3O4 and its magnetic recyclable capability
condensation of aromatic amine 3 with formaldehyde 4 to generate imine 8. Next,
intermediate 7 undergoes a Mannich-type reaction with imine 8 to furnish reactive
intermediate 9, followed by intramolecular cyclization to afford intermediate 10. In
the final step, cyclic intermediate 10 tautomerizes to obtain the functionalized
dihydro-2-oxopyrroles 5.
Experimental
General
Melting points were taken on an Electrothermal 9100 apparatus. IR spectra were
1
obtained on a JASCO FT/IR-460 plus spectrometer. The H and 13C NMR spectra
were recorded on a Bruker DPX-250 Avance instrument with CDCl3 as solvent and
using TMS as internal reference at 250 and 62.9 MHz, respectively. Chemicals were
purchased from Merck (Darmstadt, Germany), Acros (Geel, Belgium), and Fluka
(Buchs, Switzerland), and used without further purification.
General procedure for the synthesis of dihydro-2-oxopyrroles 5
A mixture of amine 1 (1 mmol) and dialkyl acetylenedicarboxylate 2 (1 mmol) in
ethanol (3 ml) was stirred for 20 min. Next, aromatic amine 3 (1 mmol),
formaldehyde 4 (37 % solution, 1.5 mmol), and nano Fe3O4 (10 mol %) were
added successively. The reaction mixture was allowed to stir at room temperature
for the appropriate time (see Table 2). The progress of the reaction was monitored
by TLC. After completion, the solid material was separated, dried, and then
dissolved in acetone (10 ml). The nanoparticles were separated with an external
magnet and then washed five times with acetone. The solvent was evaporated under
vacuum. The obtained solid was washed with EtOH (3 9 2 ml) to give the pure
product 5. It was found that the catalyst is recyclable and can be used up to six
cycles without significant loss of its activity.
123

M. Nickraftar et al.
Scheme 2 Proposed mechanism for the synthesis dihydro-2-oxopyrroles 5
Spectral data of selected products are represented below
Compound 5a 1H NMR (250 MHz, CDCl3) d: 3.73 (3H, s,OCH3), 4.54 (2H,
s,CH2), 7.12–7.42 (8H, m, ArH), 7.78 (2H, d, J = 8.75 Hz,ArH), 8.02 (1H, br s,
NH).
Compound 5c 1H NMR (250 MHz, CDCl3) d: 2.34 (6H, s, 2Me), 3.74 (3H, s,
OCH3), 4.48 (2H, s,CH2), 7.04 (2H, d, J = 8.25), 7.12 (2H, d, J = 8.5 Hz), 7.18
(2H, d, J = 8.5 Hz), 7.66 (2H, d, J = 8.3), 8.02 (1H, br s, NH).
Compound 5d 1H NMR (250 MHz, CDCl3) d: 1.22 (3H, t, J = 7.1 Hz,
OCH2CH3), 2.34 (6H, s, 2CH3), 4.21 (2H, q, J = 7.2 Hz, OCH2CH3), 4.50 (2H,
s, CH2), 7.03 (2H, d, J = 8.5 Hz, ArH), 7.11 (2H, d, J = 8.2 Hz, ArH), 7.18 (2H, d,
J = 8.25 Hz, ArH), 7.66 (2H, d, J = 8.5 Hz, ArH), 7.98 (1H, br s, NH).
123

Nano Fe3O4 as magnetically recyclable, powerful, and…
Compound 5g 1H NMR (250 MHz, CDCl3) d: 1.54 (3H, t, J = 7.1 Hz,
OCH2CH3), 4.51 (2H, m, OCH2CH3), 4.77 (2H, s, CH2), 7.25-7.42 (6H, m, ArH),
8.0 (2H, m, ArH), 8.32 (1H, br s, NH).
Conclusions
In summary, the magnetically recoverable iron oxide nanoparticles are found to be
more efficient for the synthesis of highly functionalized dihydro-2-oxopyrroles via
one-pot, four-component reaction of amines, dialkyl acetylenedicarboxylates and
formaldehyde in EtOH at room temperature. The salient features are mild and green
reaction conditions, high yields, short reaction times, simple experimental
procedure, atom economy (63–76 %), low cost, no need for column chromatog-
raphy, and the use of easily recyclable catalyst without loss of considerable catalytic
activity.
Acknowledgments Financial support from the Research Council of the University of Sistan and
Baluchestan, the University of Kashan and the University of Shiraz is gratefully acknowledged.
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