Synthesis of polysubstituted pyridines via reactions of chalcones and malononitrile in alcohols using Amberlite IRA-400 (OH-)

Article abstract of DOI:10.1016/j.tetlet.2013.07.080

Polysubstituted pyridine derivatives were synthesized through economical one-pot multicomponent reactions of different α,β-unsaturated ketones, malononitrile, and ethanol or methanol in the presence of Amberlite IRA-400 (OH^-) at room temperatur

Full text of DOI:10.1016/j.tetlet.2013.07.080

Accepted Manuscript
Synthesis of polysubstituted pyridines via reactions of chalcones and malono‐
-
nitrile in alcohols using Amberlite IRA-400 (OH )
Kiumars Bahrami, Mohammad M. Khodaei, Fardin Naali, Behrooz H. Yousefi
PII:
S0040-4039(13)01229-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.07.080
TETL 43278
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
19 May 2013
29 June 2013
12 July 2013
Please cite this article as: Bahrami, K., Khodaei, M.M., Naali, F., Yousefi, B.H., Synthesis of polysubstituted
-
pyridines via reactions of chalcones and malononitrile in alcohols using Amberlite IRA-400 (OH ), Tetrahedron
Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.2013.07.080
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Tetrahedron Letters
1
Synthesis of polysubstituted pyridines via reactions of chalcones
and malononitrile in alcohols using Amberlite IRA-400 (OH-)
Kiumars Bahrami*a, Mohammad M. Khodaei*a, Fardin Naalia, Behrooz H. Yousefib
aDepartment of Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, 67149-67346, Iran
bPharmaceutical Radiochemistry, Faculties of Chemistry and Medicine, Technische Universität München, Walther-Meißner-Str. 3, 85748
Garching, Germany
Fax +98(831)4274559; E-mail: Kbahrami2@hotmail.com
Abstract— Polysubstituted pyridine derivatives were synthesized through economical one-pot multicomponent reactions of different α,β-
unsaturated ketones, malononitrile and ethanol or methanol in the presence of Amberlite IRA-400 (OH-) at room temperature. The catalyst
is recyclable several times without substantial loss of activity. Other valuable features include the wide range of functional group tolerance,
easy and clean synthesis with a simple work-up procedure, and excellent yields under mild conditions.
An increasing number of studies have reported on the
environmentally friendly production of fine chemicals
using recyclable solid base catalysts via multi-component
reactions (MCRs). MCRs are considered to be superior
synthetic strategies,1 and are highly efficient and atom
economic. Compared to conventional organic reactions,
MCRs represents environmentally friendly processes by
reducing the number of steps, energy consumption, and
waste production.2
The pyridine framework is found in natural products,
pharmaceuticals, and functional materials3-5 (Figure 1). It is
also of widespread interest in coordination and
supramolecular chemistry, as well as in materials science.6
As a result, endeavors to develop new routes to pyridines
have occupied the synthetic community for several
decades, and constitute an active area of research.7 Among
them, the direct condensation of carbonyl compounds with
a source of ammonia is well documented,8 but suffers from
limitations in the substrates,9 or involves an oxidative
agent.10 Thus, the development of efficient synthetic
pathways toward these compounds remains both an
industrial and an academic challenge.11
Chemical synthesis is greatly facilitated by catalysis and
further by catalyst recovery and recycling. Catalyst reuse
increases the overall productivity and cost effectiveness of
chemical transformations while minimizing their
environmental impact, ultimately contributing considerably
to the sustainability of chemical processes. In this regard,
ion-exchange resins have certain inherent advantages over
conventional acid and base catalysts. Their insolubility
renders them environmentally compatible since the cycle of
loading/regeneration/reloading allows them to be used for
many years. At the end of the reaction, the resin can be
separated quantitatively by filtration and recycled.
Niphatesine C (antimicrobial)4
O
Br
N
N
C
C
S
Br
O
H2N
N
Ion-exchange resins are used in a variety of specialized
applications such as chemical processing, pharmaceuticals,
mining, food, and beverage processing.12 Organic reactions
in the presence of ion-exchange resins is a growing field of
research as the demand for clean and eco-friendly chemical
processes is increasing. Their applicability as catalysts has
been recognized in numerous publications.12b,c, 13-19
O
O
A potent inhibitor of HIV-1 integrase8d
Figure 1. Examples of pyridine frameworks as drug candidates.

2
Tetrahedron Letters
Solid base catalysts have many advantages over liquid
bases. They are noncorrosive and environmentally benign,
present fewer disposal problems, and easier separation and
recovery of the products, catalysts and the solvent. The
replacement of liquid bases with heterogeneous catalysts is
becoming more and more important in the chemical
industry.20 Furthermore, high activities and selectivities are
often obtained only by solid base catalysts in various kinds
of reaction.
In an initial investigation, we examined the reaction of (E)-
3-phenyl-1-phenylprop-2-en-1-one (1 mmol), malononitrile
(1 mmol) and ethanol as a model reaction in the presence of
Amberlite IRA-400 (OH-) (0.2 g, containing 0.2 mmol of
OH-), as a solid heterogeneous catalyst at 25 ºC for 3 hours.
As shown in Table 1, the use of Amberlite IRA-400 (OH-)
allowed the direct conversion of (E)-3-phenyl-1-
phenylprop-2-en-1-one into the corresponding 2-ethoxy-
4,6-diphenylnicotinonitrile in 98% yield.
Recently, Dong’s group reported the reaction of chalcone
with malononitrile in the presence of a guanidinium ionic
liquid at room temperature.21 This reaction afforded 2,6-
dicyano-3,5-diphenylaniline in 89% yield. When we ran
this reaction in ethanol in the presence of Amberlite IRA-
400 (OH-), to our surprise, no polysubstituted benzene was
observed, and instead, 2-ethoxy-4,6-diphenylnicotinonitrile
was produced in 98% yield ( Scheme 1).
Table 1. Optimization of the reaction conditionsa
OEt
+
-
O
ps
NMe3 (OH )
NC
CN
CN
N
+
Ph
Ph
EtOH
Ph
Ph
Entry
Amberlite IRA-400(OH-) (g)
Yield%b
1
2
3
4
5
0
0
0.1
0.15
0.2
0.5
60
80
98
98
a
Reaction conditions: (E)-3-phenyl-1-phenylprop-2-en-1-one (1 mmol),
malononitrile (1 mmol), Amberlite IRA-400 (OH-), 3.5 h, 25 ºC, EtOH (5
mL).
b Isolated yields.
It is noteworthy that in a control experiment (Table 1, entry
1), no significant promotion was observed in the absence of
Amberlite IRA-400 (OH-). The use of greater than 0.2
grams of Amberlite IRA-400 (OH-) did not enhance the
yield (Table 1, entry 5).
Scheme 1. The reaction of chalcone with malononitrile.
As part of our ongoing efforts to develop environmentally
benign processes,22 and in continuation of our program
directed toward the development of efficient reagents for
use under mild conditions,23 we focused our attention on
Subsequently, we turned our attention to catalyst recycling
and reuse. After completion of the reaction, the catalyst
was recovered by filtration, washed with methanol and then
reused in the next reaction. Thus, after recovery the catalyst
was subjected to a second reaction from which it gave the
desired product in 96% yield; the average chemical yield
for six consecutive runs was 96%, which clearly
demonstrates the practical recyclability of this catalyst
(Figure 2).
the three-component condensation of
a
chalcone,
malononitrile, and ethanol or methanol as both the solvent
and nucleophile in the presence of Amberlite IRA-400
(OH-)
for
the
synthesis
of
4,6-diaryl-2-
methoxynicotinonitriles. These compounds are precursors
in the synthesis of antimicrobial drugs,24a and conjugated
polymers used as potential fluorescent24b and photonic24c
materials. The route used for the synthesis of the pyridine
derivatives is shown in Scheme 2.
OR
O
NC
CN
CN
Amberlite IRA-400 (OH-)
N
Ar1
Ar2
+
Ar1
Ar2
ROH, r.t.
R = Et, Me
+
ps
NMe3
Amberlite IRA-400 =
Fugure 2. Recyclability of Amberlite IRA-400 (OH-) for the preparation
of 2-ethoxy-4,6-diphenylnicotinonitrile.
Scheme 2. Synthesis of pyridine derivatives.

Tetrahedron Letters
3
Table 2. Synthesis of 2-alkoxy-3-cyano-4,6-diarylpyridines in the presence of the Amberlite IRA-400 (OH-)a
Entry
1
Ar1
Ar2
R
Time (h)
3.5
Product
Yield (%)b
98
Mp (oC)Ref
96-9825
C6H5
C6H5
Et
6a
2
4-MeC6H4
4-H2NC6H4
Et
3.2
92
164-166
6b
6c
3
4
5
6
7
8
9
4-MeC6H4
2-MeOC6H4
4-ClC6H4
4-H2NC6H4
Me
Et
3.2
3.5
3
94
91
93
94
92
93
95
250-252
156-158
207-20925
196-198
180-182
195-197
213-215
C6H5
6d
C6H5
Et
6e
6f
4-ClC6H4
C6H5
Me
Et
3
2,4-Cl2C6H3
2,4-Cl2C6H3
4-O2NC6H4
4-H2NC6H4
4-H2NC6H4
4-H2NC6H4
3
6g
6h
6i
Me
Et
3
3

4
Tetrahedron Letters
Table 2. Continued
Entry
Ar1
Ar2
R
Time (h)
3
Product
Yield (%)b
94
Mp (oC)Ref
256-258
10
4-O2NC6H4
4-H2NC6H4
Me
6j
11
12
13
4-NCC6H4
4-NCC6H4
1-naphthyl
4-H2NC6H4
4-H2NC6H4
4-PhC6H4
Et
Me
Et
3
3
93
94
94
195-197
249-251
85-87
6k
6l
4.5
6m
14
1-naphthyl
4-PhC6H4
Me
4
93
92-94
6n
15
16
17
1-naphthyl
4-pyridyl
4-pyridyl
4-H2NC6H4
4-H2NC6H4
4-H2NC6H4
Et
Et
3.5
3.2
3.2
95
95
92
212-214
245-247
254-256
6o
6p
Me
6q
a The structures of the products were characterized by FT-IR, 1H NMR, 13C NMR, and MS spectrometric methods.
b Yields refer to those of pure isolated products.

Tetrahedron Letters
5
Next, we investigated the scope and limitations of the
multicomponent reaction with different chalcones,
malononitrile, and ethanol or methanol under the optimized
reaction conditions. As listed in Table 2, all the reactions
proceeded smoothly and both electron-rich and electron-
deficient chalcones provided the desired products in
excellent yields.
The heterocyclic chalcone, (E)-1-(4-aminophenyl)-3-
(pyridin-4-yl)prop-2-en-1-one reacted without the
formation of any side products (Table 2, entries 16 and 17).
Moreover, the reactions of (E)-1-(biphenyl-4-yl)-3-
(naphthalen-1-yl)prop-2-en-1-one also gave excellent
yields of products (Table 3, entries 13 and 14).
The preparative scale-up was carried out by reaction of (E)-
These substrates were converted into the corresponding
substituted pyridines without undergoing further structural
changes in their functional groups as was indicated by
NMR analyses of the products. For example, amine, ether,
nitro, cyano and halide functional groups tolerated the
reaction conditions.
3-(4-chlorophenyl)-1-phenylprop-2-en-1-one
with
malononitrile in ethanol on a 30 mmol scale. As expected,
the reaction proceeded well, being similar to the case on
smaller scale (Table 2, entry 5), and the corresponding
product was produced in 95% isolated yield.
The utility and regioselectivity of this catalyst, was studied
in the synthesis of 2-alkoxy-4,6-diarylnicotinonitrile in the
presence of an ester, alkene, aldehyde, and carboxylic acid
(Scheme 3). These studies show that this catalyst can be
applied for the chemoselective synthesis of 2-alkoxy-4,6-
diarylnicotinonitriles in the presence of the above
mentioned functional groups.
The results also showed that the reaction times for the
substrates containing electron donating groups were
slightly longer. For example, 4-(2-methoxyphenyl)-2-
ethoxy-6-phenylnicotinonitrile was obtained in 91% yield
after 3.5 hours (Table 2, entry 4) and 4-(4-chlorophenyl)-2-
ethoxy-6-phenylnicotinonitrile was produced in 93% yield
after 3 hours (Table 2, entry 5). Steric effects did not
influence the yield significantly. For example, in the
reactions of (E)-3-(4-chlorophenyl)-1-phenylprop-2-en-1-
This method has limitations. When the reaction of
malononitrile with (E)-3-phenyl-1-phenylprop-2-en-1-one
was carried out in n-propanol or n-butanol, this procedure
failed to produce clean products. These alcohols produced
mixtures of products which were difficult to separate. After
laborious separation, we obtained unacceptable yields of
the pyridines from these reactions.
one
and
(E)-1-(4-aminophenyl)-3-(2,4-
dichlorophenyl)prop-2-en-1-one (Table 2, entries 6 and 7)
the corresponding products were obtained in 94% and 92%
yields, respectively.
OEt
NC
O
N
NC
Ar1
CN
O
O
Cat-OH
-H2O
Ar1
Ar2
Ar2
+
NC
CN
96%
Cat-OH
NC
NC
1
2
+
O
O
C
EtOH, 25 °C
RO
RO
C
OMe
OMe
NC
Ar1
NC
Ar1
NH2
NH
C
C
100%
ROH
Cat-OH
Ar2
O
O
OEt
N
Ar2
NC
3
4
O
OR
OR
H
NC
Ar1
NC
Ar1
Cl
Cl
91%
O2 (air)
-H2O
N
N
NC
NC
Cat-OH
Cat-OH
+
-H2O
+
Ar2
Ar2
CHO
EtOH, 25 °C
CHO
5
6
100%
NMe3+(OH-)
ps
Cat-OH =
OEt
N
NC
O
Scheme 4. Possible mechanism for the multi-component synthesis of 2-
alkoxy-4,6-diarylnicotinonitrile.
MeO
OMe
90%
COOH
Cat-OH
NC
NC
+
EtOH, 25 °C
COOH
100%
The proposed mechanism for the reaction is outlined in
Scheme 4. Michael addition of chalcone 1 to malononitrile
produces compound 2. Nucleophilic addition of the alcohol
to the C≡N bond of the adduct gives intermediate 3.
Dehydrative cyclization of 4 affords dihydropyridine 5.
+
-
Cat-OH = ps
NMe3 (OH )
Scheme 3. Reagents and conditions: molar ratio of substrates to Cat-OH
(1:1:1: 0.2), EtOH, 25 ºC.

6
Tetrahedron Letters
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Finally, aromatization of 5 via an aerobic oxidation process
leads to the formation of substituted pyridine 6.26
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In conclusion, herewith we have reported a simple,
versatile, efficient and economic one-pot multi-component
reaction for the synthesis of 2-alkoxy-3-cyano-4,6-
diarylpyridines from the reaction of α,β-unsaturated
ketones, malononitrile and ethanol or methanol in the
presence of Amberlite IRA-400 (OH-) as a recyclable
heterogeneous catalyst. Particularly valuable features of
this synthesis include excellent yields, the recyclability and
ready availability of the catalyst, the easy and clean work-
up with high chemoselectivity. This synthesis also
overcomes the formation of unwanted by-products and
should open new possibilities for medicinal chemistry and
material sciences.
6. Balasubramanian, M. Keay, J. G. Comprehensive
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General procedure for the synthesis of 2-alkoxy-4,6-
diarylnicotinonitriles
A mixture of aromatic chalcone (1 mmol), malononitrile (1
mmol), and Amberlite IRA-400 (OH-) (0.2 g, containing
0.2 mmol of OH-) in ethanol or methanol (5 mL) was
stirred at room temperature for the time indicated in Table
2. The reaction was monitored by thin-layer
chromatography (TLC) using EtOAc/n-hexane (2:8) as
eluent. After completion of the reaction, EtOH (15 mL)
was added to the mixture, which was then heated for 5 min
at 80 ºC. The catalyst was removed by filtration. The
filtrate was poured into ice water, filtered and recrystallized
from EtOH (96%) to afford the pure product. Spectral data
for the compound 6b follows.
11. (a) Mongin, F.; Quéguiner, G. Tetrahedron 2001, 57, 4059;
(b) Henry, G. D. Tetrahedron, 2004, 60, 6043; (c) Katritzky,
A. R. Chem. Rev. 2004, 104, 2125.
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Aboul-Enei, H. Y. FABAD J. Pharm. Sci. 2007, 32, 91; (b)
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26, 4874.
6-(4-Aminophenyl)-2-ethoxy-4-p-tolylnicotinonitrile
(6b): Yellow solid: mp = 164-166 °C; [Found: C, 76.35; H,
5.88; N, 12.84. C21H19N3O requires C, 76.57; H, 5.81; N,
12.76]; Rf = 0.65 (8:2 n-hexane/EtOAc); IR (KBr, cm-1)
1
3354, 3238, 2220, 1583, 1541, 1512; H NMR (200 MHz,
CDCl3): δH = 1.41 (t, J = 7.1 Hz, 3H, CH3CH2O), 2.33 (s,
3H, Me), 3.89 (brs, 2H, NH2), 4.55 (q, J = 7.0 Hz, 2H,
CH3CH2O), 6.66 (d, J = 8.7 Hz, 2H, Ph), 7.16-7.46 (m, 3H,
Ph, pyridyl), 7.41 (d, J = 8.7 Hz, 2H, Ph), 7.84 (d, J = 8.7
Hz, 2H, Ph); 13C NMR (50 MHz, CDCl3): δC = 14.5, 21.4,
63.0, 91.2, 111.6, 113.8, 114.9, 116.3, 127.5, 128.8, 130.50,
133.9, 139.9, 148.6, 156.2, 157.8, 164.7; ESI-MS [M + 1],
found 330.2. C21H19N3O requires 329.15.
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Chem. 2010, 12, 893.
Acknowledgements
We are thankful to the Razi University Research Council
for partial support of this work.
22. (a) Bahrami, K.; Khodaei, M. M.; Nejati, A. Green Chem.
2010, 12, 1237; (b) Khodaei, M. M.; Bahrami, K.; Farrokhi,
A. Synth. Commun. 2010, 40, 1492.
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2008, 73, 6835; (b) Bahrami, K.; Khodaei, M. M.; Farrokhi,
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Graphical Abstract
.
Leave this area blank for abstract info.
Synthesis of polysubstituted pyridines via
reactions of chalcones and malononitrile in
alcohols using Amberlite IRA-400 (OH-)
Kiumars Bahrami, Mohammad M. Khodaei, Fardin Naali,
Behrooz H. Yousefi