An efficient synthesis of highly substituted functionalized pyrroles via a four-component coupling reaction catalyzed by Fe(III)-Schiff base/SBA-15

Article abstract of DOI:10.1080/24701556.2020.1744650

An environmentally friendly, straightforward, and cheap synthesis of highly substituted functionalized pyrrole derivatives via one pot four-component reactions of 1,3-dicarbonyl compounds, amines, aromatic aldehydes, and nitroalkanes have been developed. This methodology provides desired pyrroles in good-to-excellent yields in the presence of Fe (III)-Schiff base/SBA-15 as a heterogeneous catalyst.

Full text of DOI:10.1080/24701556.2020.1744650

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: https://www.tandfonline.com/loi/lsrt21
An efficient synthesis of highly substituted
functionalized pyrroles via a four-component
coupling reaction catalyzed by Fe(III)-Schiff base/
SBA-15
Ghasem Rezanejade Bardajee, Aseyeh Ghaedi, Hamideh Hazrati & Farnaz
Jafarpour
To cite this article: Ghasem Rezanejade Bardajee, Aseyeh Ghaedi, Hamideh Hazrati & Farnaz
Jafarpour (2020): An efficient synthesis of highly substituted functionalized pyrroles via a four-
component coupling reaction catalyzed by Fe(III)-Schiff base/SBA-15, Inorganic and Nano-Metal
Chemistry, DOI: 10.1080/24701556.2020.1744650
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2020.1744650
An efficient synthesis of highly substituted functionalized pyrroles via
a four-component coupling reaction catalyzed by Fe(III)-Schiff base/SBA-15
Ghasem Rezanejade Bardajeea, Aseyeh Ghaedia, Hamideh Hazratib, and Farnaz Jafarpourb
b
aDepartment of Chemistry, Payame Noor University (PNU), Tehran, Iran; School of Chemistry, College of Science, University of Tehran,
Tehran, Iran
ABSTRACT
ARTICLE HISTORY
Received 17 October 2019
Accepted 24 February 2020
An environmentally friendly, straightforward, and cheap synthesis of highly substituted functional-
ized pyrrole derivatives via one pot four-component reactions of 1,3-dicarbonyl compounds,
amines, aromatic aldehydes, and nitroalkanes have been developed. This methodology provides
desired pyrroles in good-to-excellent yields in the presence of Fe (III)-Schiff base/SBA-15 as
a heterogeneous catalyst.
KEYWORDS
SBA-15; Fe (III)-Schiff base;
pyrrole derivatives;
heterogeneous catalysis
Introduction
high surface area, tunable pore size distribution, high
hydrothermal and mechanical stability.[12,13] Beside, Fe (III)
complexes of Schiff base ligands was found to be very effect-
ive catalysts and have wide applications in organic synthesis.
In fact, both Fe (III)-Schiff base and SBA-15 are important
in catalytical activity.
Generally, Schiff base ligands are compounds with
functional groups that contain carbon-nitrogen double bonds,
coordinate metals through imine nitrogen and are prepared
by the condensation of primary amines and aldehydes or
ketones (Scheme 1).[13–20] The covalent anchoring of Fe (III)-
Schiff base onto the SBA-15 is an effective way for extending
benefits of the silica solid support to the Schiff base ligand.
The benefits may include ease of work-up procedures, the
potential for reuse of the supported catalysts, high activity
and selectivity and metals leaching reduction.[19,21]
Multicomponent reactions are very popular due to their
improved efficiency, a single-step procedure, avoiding com-
plicated purification processes and saving both solvents and
reagents.[14,15,20,21] There are several synthetic procedures
for preparation of Pyrroles derivatives under different
conditions for instance, One-pot four-component synthesis
of highly substituted pyrroles in gluconic acid aqueous
solution,[22] synthesis of new 3-cyanoacetamide pyrrole and
3-acetonitrile pyrrole derivatives,[23] Iron-Catalyzed Radical
Cycloaddition of 2H-Azirines and Enamides for the
Synthesis of Pyrroles,[24] Synthesis of Polyfunctionalized
Pyrroles via a Tandem Reaction of Michael Addition
and Intramolecular Cyanide-Mediated Nitrile-to-Nitrile
Condensation.[25] However these compounds have been
produced using different methodologies but low yields,
hazardous chemicals and harsh reaction conditions are some
The pyrrole heterocycle core is an important structural motif
in wide varieties of biologically and medicinally vital com-
pounds.[1] They has key roles such as anti-inflammatory
drug (Ketorolac 1)[2] (Figure 1), antitumor agents,[3]
immunosuppressants[4] but also it has proven to be useful
building block in organic synthesis.[5] The classical methods
of preparing pyrrole compounds include Hantzsch and
Paal–Knorr reactions.[6,7] Furthermore a variety of transition
metal catalyzed reactions[8,9] and multicomponent coupling
strategies[10,11] have been developed during the last decade.
Despite the numerous approaches for the synthesis of
pyrroles, a novel, simple process, straightforward and cheap
synthetic method is still an attractive goal.
Mesoporous silicate-aluminosilicates are Santa Barbara
Amorphous (SBA) materials characterized by uniform
pore size (4.6–30 nm), well-defined pore structure and size-
distribution, high surface area, high thermal stability and
the capability to support a large panel of active species
including Lewis acid metal ions. One of the most promising
components of this family is SBA-15.[12]
SBA-15 materials have been well recognized as a promis-
ing support template for the synthesis of catalytic materials
due to its uniform, hexagonally-arrayed channels with
a narrow pore size distribution. These features, together
with high surface area and hydrothermal stability, make it
as an ideal support for the incorporation of various active
molecules on its surface. Transition metals such as Fe, Pd,
Cu, etc with acid Lewis character are suitable for supporting
on SBA-15 for obtaining an active heterogeneous catalyst.
In recent past decades, SBA-15 has witnessed remarkable
advances in the field of heterogeneous catalysis due to its of their drawbacks. For example acid aqueous solution,
CONTACT Ghasem Rezanejade Bardajee
ghrezanejad@yahoo.com
Department of Chemistry, Payame Noor University (PNU), P.O. BOX 19395-3697,
Tehran, Iran.
ß 2020 Taylor & Francis Group, LLC

2
G. REZANEJADE BARDAJEE ET AL.
environmentally friendly condition in this process. The use
of mesostructure to link the iron (III) catalytic center to the
solid support can provide good convenience without steric
effects.[26] The role Fe (III)-Schiff base/SBA-15 is as Lewis
acid and catalyst in pyrrole synthesis.
According to the proposed mechanism, the carbonyl
groups were activated by Fe (III)-Schiff base/SBA-15 and
then these were attacked by amine and nitro groups
to give the intermediates 1 and 2. Next, the interaction
between intermediate 1 and 2 and cyclization reaction and
elimination of H2O led to the formation of final product.
Figure 1. Ketorolac, a drug product containing pyrrole core.
Results and discussion
Here, at first we report characterization of Fe (III)-Schiff
base anchored on SBA-15, then its application as an efficient
heterogeneous catalyst in four-component synthesis of
highly substituted pyrroles.
Techniques for physicochemical characterization of
nanomaterials such as FT-IR, N2 adsorption/desorption
(BET), X-ray diffraction (XRD), transmission electron
microscopy (TEM) and thermogravimetric analysis (TGA)
were used to characterized the successful grafting of the
Fe(III)-Schiff base onto SBA-15.
The FT-IR spectra of SBA-15 and Fe (III)-Schiff base/
SBA-15 is shown in (Figure 2). According to the FTIR
spectra of SBA-15, the bands are attributed to at 3413 cmꢀ1
OH, 1631 cmꢀ1 C¼N, 1091 cmꢀ1 Si-O-Si, 806 cmꢀ1 Si-OH
and 462 cmꢀ1 Si-O separately. The FTIR spectra of Fe
(III)–Schiff base/SBA-15 shows characteristic vibration peaks
at 3417, 2900, 1606, 1103 cmꢀ1 which are assigned to the
vibrations of OH, -CH2, C¼N, Si-O-Si, respectively.
Nitrogen adsorption/desorption isotherms and also size
distributions of SBA-15 and Fe (III)-Schiff base/SBA-15 are
shown in (Figure 3A). These isotherms are of type IV with
H1-type hysteresis loops, according to the IUPAC classifica-
tion,[22,27] typically for mesoporous materials. Furthermore,
as can be seen in Table 1, the surface area and pore volume
of Fe (III)-Schiff base/SBA-15 decreases in comparison
with SBA-15, due to the anchoring of Fe (III)-Schiff base
on SBA-15 surface.
In XRD pattern of both SBA-15 and Fe (III)-Schiff base/
SBA-15 (Figure 3B), the peaks at about (100), (110), and
(200) arise from ordered hexagonal unit cell of mesoporous
materials. The lower angle in XRD pattern of Fe(III)-Schiff
base/SBA-15 (Figure 3B), is due to the development of
unit cell arises from the connection of the complex within
SBA-15 and the lower intensities is due to a decrease in the
mesoscopic order.[23,24,28,29]
Scheme 1. Preparation of Fe (III)-Schiff base/SBA-15
hazardous solvent, unrecyclable catalysts, low product yields
for aromatic amines, use of expensive reagents and inaccessible
starting materials, were used in these reactions.
Despite the mentioned disadvantages some reported
procedures have opened new prospects for the synthesis
pyrroles, in this paper, accessible initial materials, possible
catalyst recycling, high activity and selectivity, high yield
products and easy catalyst separation are considerable
Therefore, we decided to develop a catalytic synthesis
of pyrroles by means of a novel four-component domino
reactions of 1,3-dicarbonyl compounds, aldehydes, amines,
and nitroalkanes. The proposed mechanism for the synthesis
of substituted pyrroles in the presence of Fe (III)-Schiff
base/SBA-15 can be presented as follow (Scheme 2).
The TEM image of the supported complex confirms the
retaining of hexagonal structure of uniform linear channels
of Fe (III)-Schiff base/SBA-15 (Figure 3C).
Thermo gravimetric (TG) analysis of the samples is
presented in Figure 3D. TG analysis determines the amount
of decomposition of species. The TG curve of both SBA-15
and Fe (III)-Schiff base/SBA-15 show a weight loses at
In this study, the use of a nontoxic and heterogeneous
catalyst along with a simple and clean catalyst separation
from reaction mixture, the reusable catalyst and no need for around 100 ꢁC which is attributed to the loss of physically
high boiling point chemical solvent, can confirm the adsorbed water. Besides, the thermogram of Fe (III)-Schiff-

INORGANIC AND NANO-METAL CHEMISTRY
3
Scheme 2. Proposed mechanism for the synthesis of substituted pyrroles in the presence of Fe (III)-Schiff base/SBA-15
Figure 2. FT-IR spectra of (a) SBA-15 and (b) Fe (III)-Schiff base/SBA-15 Catalytic synthesis of heterocycles.

4
G. REZANEJADE BARDAJEE ET AL.
Figure 3. (A) Nitrogen adsorption/desorption isotherms and corresponding pore size distribution profile (inset) of (a) SBA-15 and (b) Fe (III)-Schiff base/SBA-15. (B)
XRD patterns of SBA-15 and Fe (III)-Schiff base/SBA-15. (C) TEM images of Fe (III)-Schiff base/SBA-15. (D) Thermogravimetric analysis results of SBA-15 and
Fe (III)-Schiff base/SBA-15.
Table 1. Textural properties of the SBA-15 and Fe (III)-Schiff base/SBA-15.
With the optimal reaction conditions established in hand,
the generality of the procedure was evaluated by reactions of
various aromatic amines and aldehydes with nitroalkanes,
and 1,3-dicarbonyl compounds (Table 3, entries 1–16). As
can be seen, most of the examined substrates provided good
to excellent yields. The first step of our investigation on
the generality of the reaction, we next examined the scope
of this reaction with various aromatic amines. The desired
substituted pyrroles were afforded in almost good yields
regardless of the aromatic substituent but the weakly
electron-deficient halogen-containing aromatic amines and
the aliphatic amine, afforded the target product in lower
yield (Table 3, entries 13,14, and 11). We also tried to do
the reaction with very strong electron-withdrawing group
such as -NO2, but the result was not satisfactory and the
reaction was not followed anymore. Having successfully
achieved the catalytic multicomponent synthesis of substi-
tuted pyrroles, the scope of the reaction was expanded by
performing the reaction with various aromatic aldehydes. It
seems that the reactivity is influenced by neither electron
withdrawing nor electron donating functionalities. At last,
when this methodology was applied to unsymmetrical 1,3-
diketones, pyrroles 5k and 5p were chemo selectively
formed, this could be attributed to the participation of the
more activated acetyl group.
Materials
C(M)a
Sb
Vc
BJH
BET
SBA-15
Fe(III)-Schiff base/SBA-15
–
0.14
539
472
1.01
0.85
aInitial concentration of iron species (mmol gꢀ1).
bspecific surface area (m2 gꢀ1).
cpore volume (cm3 gꢀ1).
base anchored SBA-15 represents another weight loss between
200 and 700 ꢁC (Figure 3D) through the decomposition
of the covalently bonded Schiff ligand.
After the survey of the structure and morphology of the
prepared Fe (III)-Schiff base functionalized SBA-15, we
intended to test its efficiency as heterogeneous catalysts for
the preparation of pyrrole derivatives. At first, aromatic
amine 2, aldehyde 3, acetylacetone 4, and nitro methane 5
were selected as the model substrates to investigate the best
reaction conditions (Table 2). Some parameters such as tem-
perature, the type and amount of catalyst were examined to
determine the efficiency of the model reaction. At first, we
tried to accomplish this reaction at reflux temperature in the
absence of catalyst, but it gave less than 5% yield after
12hours. Then, we tried using anhydrous FeCl3 and
Fe (III)-Schiff base/SBA-15 as catalysts and we found that
Fe (III)-Schiff base/SBA-15 was the most effective catalyst
for this transformation. The best yield was obtained in
the presence of 0.001 g (0.00014 mmol based on Fe ions)
of Fe (III)-Schiff base/SBA-15, under reflux conditions
(Table 2, entry 6).
In continue, to test the lifetime and the reusability of the
catalyst, a series of experiments were examined for the
model reaction compound 5h. For this, after completion of

INORGANIC AND NANO-METAL CHEMISTRY
5
Table 2. Screening of the reaction conditions for four-component coupling reactions of aromatic amine 1, aldehyde 2, acetylacetone
3, and nitro methane 4.a
Entry
Catalyst
Catalyst amount (g)
Temperature (ꢁC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
–
–
reflux
reflux
rt
12
12
12
12
6
12
12
12
24
<5
36
50
FeCl3
0.008
0.001
0.001
0.001
0.001
0.01
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
Fe(III)-Schiff base/SBA-15
60
60
70
reflux
reflux
reflux
reflux
reflux
88 (87)c,d
88
0.0005
0.001
34
79
aAll reactions were runing under the following conditions: Aromatic amine 1 (1.5 mmol), aldehyde 2 (1 mol) and acetylacetone 3
(1 mmol) in nitromethane 4 (1 mL) and catalyst (0.001 g) were heated for appropriate time.
b% (based on GC yields).
cOptimum conditions.
dIsolated yield in parentheses.
Table 3. Synthesis of desired heterocyclic derivatives catalyzed by Fe (III)-Schiff base/SBA-15a.
NH2
CHO
O
O
O
Ph
Catalyst
+
+
Me NO2
+
N
2
3
4
1
5
Ph
Entry
1
Amine 1
Aldehyde 2
Nitroalkane 3
1,3-dicarbonyl 4
Product
O
Yield (%)
88
m.p.
CH3NO2
118–120
Me
PhCl-p
Me
N
PhOMe-p
5a
2
CH3CH2NO2
O
78
126–128
Ph
N
PhOMe-p
5b
O
3
4
CH3NO2
43
63
135–137
92–93
PhOMe-p
Me
Me
N
PhOMe-p
5c
CH3NO2
O
PhMe-p
Me
Me
N
PhMe-p
5d
O
5
CH3NO2
65
109–110
PhCl-p
Me
Me
N
PhMe-p
5e
(continued)

6
G. REZANEJADE BARDAJEE ET AL.
Table 3. Continued.
Entry
6
Amine 1
Aldehyde 2
Nitroalkane 3
1,3-dicarbonyl 4
Product
Yield (%)
58
m.p.
O
CH3NO2
62–64
EtO
Ph
Me
N
PhMe-p
5f
O
7
CH3NO2
78
104–106
Me
Ph
Me
N
Ph
5g
O
8
CH3CH2NO2
73
114–116
Me
Ph
Me
Me
N
Ph
5h
O
9
CH3CH2NO2
70
82–83
EtO
Ph
Me
Me
N
Ph
5i
O
10
11
CH3NO2
76
43
86–88
53–55
PhBr-p
Me
Me
N
Ph
5j
O
CH3NO2
C6H4
H
Me
Me
N
CH2C6H4
5k
O
12
13
CH3NO2
76
60
145–147
142–144
C6H4
Me
H
N
Me
Naphthyl
O
CH3CH2NO2
Ph
Me
Me
N
PhCl-p
5m
(continued)

INORGANIC AND NANO-METAL CHEMISTRY
7
Table 3. Continued.
Entry
14
Amine 1
Aldehyde 2
Nitroalkane 3
1,3-dicarbonyl 4
Product
O
Yield (%)
51
m.p.
CH3NO2
115–118
PhOMe-p
Me
Me
N
PhCl-p
5n
O
Br
15
16
CH3NO2
50
52
105–107
115–117
PhBr-m
Me
Me
OHC
N
CH2ph
5o
O
CH3NO2
PhBr-p
Me
Me
N
CH2ph
5p
aAll reactions were carried out using aldehyde (0.1 mmol), amine (0.15 mmol), and 1,3-dicarbonyl compounds (0.1 mmol) with nitromethane (0.1 mL), catalyst
(0.001 gr) under reflux,12–16 h. The structures of all products 5a-5p were established by melting point, IR, 1H NMR, and 13C NMR spectra.[30–38]
non-covalently grafted complex and physisorbed metal species
were removed. At last, the product was dried in an oven at 80 ꢁC
for 8 h (Scheme 1).
Table 4. Reuse of the catalyst for the synthesis of 1-[4-(4-Chloro-phenyl)-1-(4-
methoxy-phenyl)-2-methyl-1H-pyrrol-3-yl]-ethanone 6.
Run
1
2
3
4
5
6
2. General procedure for the synthesis of pyrazine based heterocycles:
A round-bottomed flask equipped with a magnet and condenser was
charged with desired aldehyde (0.1 mmol), amine (0.15 mmol), and
1,3-dicarbonyl compounds (0.1mmol) with nitromethane (0.1mL),
catalyst (Fe(III)-Schiff base/SBA-15, 0.001gr). The resulting mixture
was heated at reflux temperature for the appropriate times, and the
course of the reaction was monitored using TLC on silica gel (n-
hexane/ethylacetate: 4/1). Finally, the reaction mixture was cooled
and the crude mixture was purified by column chromatography
after removal of excess amount of nitroalkan.
Yielda (%)
aIsolated yield.
88
88
88
87
87
87
the first reaction with 88% yield, the catalyst was separated
and reused after washing with hot ethanol and drying at
80 ꢁC for 60 min. The recovered catalyst was used again
under the same reaction conditions and it showed excellent
reusability over six runs (Table 4).
Data for selected products:
1-[4-(4-Chlorophenyl)-1-(4-methoxyphenyl)-2-methyl-1H-pyrrol-3-
Conclusion
yl]-ethanone, compound 6:
White powder; m.p. 118–120 ꢁC; IR (KBr, v, cmꢀ1): 3010, 2880, 1620,
1560, 1251.1H NMR (300 MHz, CDCl3): d 2.03(s, 3H), 2.10 (s, 3H), 3.70
(s, 3H), 6.71 (s, 1H), 6.99 (d, J ¼ 8.9 Hz, 2H), 7.21 (d, J ¼ 8.6 Hz, 2H),
7.24-7.33 (m, 4H). 13C NMR (CDCl3, 75MHz): d 12.7, 31.2, 55.4, 114.6,
121.1, 122.5, 124.3, 127.4, 128.6, 130.2, 131.1, 132.7, 134.5, 135.5, 159.6,
197.2.
In conclusion, we have reported a one-pot, four-component
protocol for the synthesis of highly substituted pyrroles in
the presence of Fe (III)-Schiff base/SBA-12 as a catalyst.
Using readily available and inexpensive starting materials,
operational simplicity, good to excellent products yields and
reusability of catalyst are prominent among the advantages
of this new method.
1-[1,4-Bis(4-methoxyphenyl)-2-methyl-1H-pyrrol-3-yl]-ethanone,
compound 8:
White powder; m.p. 135–137 ꢁC; IR (KBr, v, cmꢀ1): 3010, 2884, 1625,
1502, 1263. 1H NMR (300 MHz, CDCl3): 2.05 (s, 3H), 2.32 (s, 3H),
3.85(s, 3H), 3.80 (s, 3H), 6.61 (s, 1H), 6.90-6.97 (m, 4H), 7.12–7.21 (m,
4H). 13C NMR (CDCl3, 75 MHz): 12.0, 30.5, 55.0, 55.3, 113.7, 114.1,
120.5, 122.1, 125.4, 127.1, 128.3, 130.2, 131.6, 135.4, 158.4, 159.1, 197.7.
Notes
1. Anchoring of Fe (III)-Schiff base complex on SBA-15: Synthesis of
SBA-15 was carried out as previously reported by Huisgen et al.[34]
Fe (III)-Schiff base complex was prepared by applying the
procedure reported by Li et al.[35] Activated SBA-15 (1.5 g) was
suspended in 20 mL methanol solution containing (0.38 g) Schiff
base complex, and the mixture was stirred for 24 h. The solvent
was removed using a rotary evaporator, and the resulting solid was
dried at 80 ꢁC overnight. The product was washed with MeOH and
Acknowledgments
University of Tehran, School of Chemistry is thanked for financial sup-
deionized until the washings were colourless to ensure that the port of this work.

8
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