Efficient and environmentally-benign three-component synthesis of quinolines and bis-quinolines catalyzed by recyclable potassium dodecatungstocobaltate trihydrate under microwave irradiation

Article abstract of DOI:10.1039/c2ra20639k

Microwave-assisted one-pot three-component reaction between aromatic amines, aromatic aldehydes and phenylacetylene is accomplished efficiently in the presence of catalytic amounts of potassium dodecatungstocobaltate trihydrate (K₅CoW₁₂O₄₀?·3H₂O) to afford the corresponding quinolines and bis-quinolines in excellent yields. Selective conversion of aromatic aldehyde and also arylacetylene to their corresponding quinolines in the presence of aliphatic aldehyde and alkylacetylene, respectively, can be considered as noteworthy advantages of this method and makes it a useful and attractive process for the synthesis of quinoline derivatives. The catalyst could be reused for several cycles without any significant loss of its catalytic activity.

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PAPER
Efficient and environmentally-benign three-component synthesis of quinolines
and bis-quinolines catalyzed by recyclable potassium dodecatungstocobaltate
trihydrate under microwave irradiation{
Salma Anvar,a Iraj Mohammadpoor-Baltork,*a Shahram Tangestaninejad,*a Majid Moghadam,a
Valiollah Mirkhani,a Ahmad Reza Khosropoura and Reza Kiab
Received 8th April 2012, Accepted 18th July 2012
DOI: 10.1039/c2ra20639k
Microwave-assisted one-pot three-component reaction between aromatic amines, aromatic aldehydes
and phenylacetylene is accomplished efficiently in the presence of catalytic amounts of potassium
dodecatungstocobaltate trihydrate (K5CoW12O40?3H2O) to afford the corresponding quinolines and
bis-quinolines in excellent yields. Selective conversion of aromatic aldehyde and also arylacetylene to
their corresponding quinolines in the presence of aliphatic aldehyde and alkylacetylene, respectively,
can be considered as noteworthy advantages of this method and makes it a useful and attractive
process for the synthesis of quinoline derivatives. The catalyst could be reused for several cycles
without any significant loss of its catalytic activity.
environmental and safety problems. Consequently, the design of
Introduction
an efficient and green approach using a reusable catalyst for the
Multi-component reactions (MCR) are some of the most
synthesis of quinoline derivatives is in great demand.
efficient and convenient synthetic tools for the construction of
Polyoxometalates (POMs) as metal–oxygen cluster anions, are
a wide variety of complex molecules. Generally, these reactions
remarkable for their molecular and electronic structural diversity
occur between three or more starting materials in one-pot to give
and their significance in quite diverse disciplines, e.g., catalysis,
the desired products with high atom economy and selectivity.
medicine, and materials science. Catalysis by heteropoly acids
Moreover, the use of multi-component reactions under solvent-
(HPAs) and related POM compounds has several advantages
free conditions provides even more benign processes.1
such as low toxicity, non-corrosive, ease of handling, low cost,
Quinoline derivatives have long been the focus of considerable
stability, reusability, and fewer disposal problems which make
them economically and environmentally attractive.13 In addition,
attention due to their abundance in numerous natural products as
well as their extensive applications in biology and pharmacology.2 A
they are efficient oxidants and exhibit fast reversible multi-
electron redox transformations under mild conditions.14
great number of compounds containing quinoline moieties are
reported to display antimalarial,3 antiasthmatic,4 antidiabetic,5
antibacterial,6 antiviral,7 and antitumor8 activities. These hetero-
cycles are also useful synthetic building blocks in organic chemistry.9
Because of their wide range of applications in pharmaceutical
and synthetic chemistry, various methods for the synthesis of
quinoline derivatives have been reported in the literature.10–12
However, some of these synthetic methods suffer from dis-
advantages such as long reaction times, low yields and tedious
work-up processes. Further, the use of toxic organic solvents,
formation of side products and the use of corrosive, expensive
and non-reusable catalysts limit the usefulness of some of these
methods, especially for large scale operation and lead to serious
Since publication of Chester’s work in 1970, CoIIIW12 and
related POM anions have been used as well-defined outer-sphere
electron-transfer agents. On the other hand, the potential utility
of numerous POM anions as electron-transfer agents in the
selective catalytic oxidations of inorganic and organic substrates
of practical importance has been recognized.15
52
The environmental problems mainly associated with the
handling and disposal of inorganic acids, and their potential
hazards, have attracted chemists attention to the development of
alternative processes using novel catalysts. Among them,
heteropoly compounds are useful and versatile catalysts for a
number of important synthetic transformations.16,17
In continuation of our research directed to develop new and
novel synthetic routes for important heterocyclic compounds and
use of green chemistry techniques in organic synthesis,18 we would
like to report a microwave-assisted one-pot three-component
synthesis of 2,4-disubstituted quinolines and bis-quinolines
through the reaction between aromatic amines, aromatic alde-
hydes and phenylacetylene catalyzed by K5CoW12O40?3H2O
aCatalysis Division, Department of Chemistry, University of Isfahan,
Isfahan 81746-73441, Iran. E-mail: imbaltork@sci.ui.ac.ir;
stanges@sci.ui.ac.ir; Fax: +98(311)6689732; Tel: +98(311) 7932705
bDepartment of Chemistry, Science and Research Branch, Islamic Azad
University, Tehran, Iran
{ Electronic supplementary information (ESI) available. CCDC refer-
ence numbers 841685 and 841686. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c2ra20639k
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In order to evaluate the versatility of this catalytic system, the
reaction of various anilines and aldehydes with phenylacetylene
was investigated in the presence of catalytic amounts of
K5CoW12O40?3H2O under the optimized conditions.20 As shown
in Table 2, anilines and aldehydes containing both electron-
donating and electron-withdrawing groups took part in the
reaction smoothly to give the desired quinolines in excellent
yields.
Scheme 1 One-pot three-component synthesis of quinolines.
under solvent-free conditions (Scheme 1). To the best of our
knowledge, this is the first report on the use of POM as catalyst for
the one-pot three-component synthesis of quinolines and bis-
quinolines under microwave irradiation.
It is worth mentioning that diamines such as 1,4-phenylene-
diamine and dialdehydes such as terephthalaldehyde underwent
the reaction under the same conditions and generated the
corresponding bis-quinolines in high yields (Table 3). The
synthesis of bis-quinolines through a one-pot three-component
reaction has not been previously reported.
At first, 4-nitroaniline was treated with 4-methylbenzaldehyde
and phenylacetylene in the presence of different heteropoly acids
and/or POMs under microwave irradiation19 (Table 1, entries
1–9); K5CoW12O40?3H2O was found to be the most effective
catalyst to carry out this conversion (Table 1, entry 9). To
examine the effect of the catalyst, the reaction was performed in
the absence of K5CoW12O40?3H2O, but no desired product was
obtained under these conditions (Table 1, entry 10). Then
different reaction conditions such as the amount of catalyst,
temperature, reaction time and the microwave power were
checked (Table 1, entries 11–18). The results revealed that the
best yield of the desired quinoline 4b was obtained by carrying
out the reaction with 1 : 1 : 1 : 0.11 molar ratios of 4-nitroani-
line, 4-methylbenzaldehyde, phenylacetylene and K5CoW12O40?
3H2O using a power of 800 W at 90 uC within 10 min under
solvent-free conditions. No further yield increase was evidenced
by increasing these parameters, while by reducing these
parameters the yield of the product was reduced. It was also
found that a significantly lower yield (35%) of 4b was obtained
using conventional heating rather than the MW activated
method even after 4 h. (Table 1, entry 19). Therefore, MW-
assisted synthesis was more advantageous over conventional
heating with regard to the reaction time and product yield.
In contrast, an alkylacetylene such as 1-hexyne did not give the
desired product under the same reaction conditions. In addition,
an aliphatic aldehyde like heptanal did not undergo such a
reaction. These observations prompted us to explore the
chemoselectivity of the presented method in the synthesis of
quinoline derivatives. When an equimolar mixture of phenyla-
cetylene and 1-hexyne was treated with 4-nitroaniline and
4-methylbenzaldehyde in the presence of the catalyst under
microwave irradiation, only phenylacetylene was chemoselec-
tively transformed to its corresponding quinoline with excellent
yield (Scheme 2). Furthermore, 4-methylbenzaldehyde was
converted to its quinoline in the presence of heptanal with
excellent chemoselectively under the same reaction conditions
(Scheme 3). Such selectivities are of practical importance and
can be considered as one of the significant aspects of this
methodology.
Recently, we have reported the synthesis of 2,4-disubstituted
quinolines by the reaction of 2-aminoaryl ketones and arylace-
tylenes catalyzed by K5CoW12O40?3H2O in high yields.18d
A
limitation of our previous work is that a wide variety of
2-aminoaryl ketones are not easily accessible. In contrast, a wide
variety of anilines and aldehydes (both substitutionally and
structurally) are used in the present work, which can afford
different quinoline derivatives. Moreover, ready availability of
the diamines and dialdehydes enables preparation of bis-
quinolines, that were not synthesizable in our pervious work
due to the unavailability of the necessary bis(2-aminoaryl
ketone) precursors. Therefore, this one-pot three-component
reaction is superior to our previously reported method for the
preparation of quinolines and bis-quinolines.
Table 1 Influence of reaction parameters on the yield of 4ba
Entry Catalyst (mol%)
T/uC Time (min) Yield (%)b
1
2
3
4
5
6
7
8
9
AlPW12O40 (11)
AlPMo12O40 (11)
H3PW12O40 (11)
H3PMo12O40 (11)
H4SiW12O40 (11)
90
90
90
90
90
90
90
90
90
90
90
90
90
90
80
100
90
90
90
10
10
10
10
10
10
10
10
10
120
10
10
15
7
35
30
70
55
43
7
12
72
92
0
82
92
92
70
72
92
75
92
35
TBA5[PW11NiO39]?3H2O (11)
TBA5[PW11CuO39]?3H2O (11)
(NH4)8CeW10O36?20H2O (11)
K5WCo12O40?3H2O (11)
No catalyst
K5WCo12O40?3H2O (10)
K5WCo12O40?3H2O (12)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O (11)
K5WCo12O40?3H2O(11)
The structure of the products was characterized by their IR,
1
mass, H NMR and 13C NMR spectra and elemental analysis.
To investigate the electronic effects of different substituents on
the crystal packing, the solid state structures of 4p (Fig. 1, CCDC
841685) and 4q (Fig. 2, CCDC 841686), which both contain an
anthracene ring, were also determined by X-ray crystallography.
The crystal packing of 4p (Fig. 3) is stabilized by the
10
11
12
13
14
15
16
17c
18d
19e
a
10
10
10
10
240
…
intermolecular C–H O hydrogen bonds which connect the
molecules into individual centrosymmetric dimers. The interest-
ing features of the crystal packing of 4q (Fig. 4) are the short
…
…
˚
intermolecular C Cl [C11 Cl1i = 3.376(4) A, (i) symmetry
code: 1 + x, y, z] contacts which are shorter than the sum of the
Reaction conditions: amine (1 mmol), aldehyde (1 mmol),
b
phenylacetylene (1 mmol), MW irradiation (800 W). Isolated yield.
c
˚
van der Waals radii of these atoms [3.45 A; C = 1.70 and Cl =
Reaction was carried out with microwave power of 700 W.
Reaction was carried out with microwave power of 900 W.
Reaction was carried out under conventional heating conditions.
d
21
…
˚
1.75 A] and also the weak intermolecular C–H Cl interactions
which connect the molecules like a tetramer, propagating along
e
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Table 2 K5WCo12O40?3H2O-Catalyzed three-component synthesis of quinolines under microwave irradiation and solvent-free conditionsa
Entry Amine Aldehyde Quinoline Time (min)
Yield (%)b
1
10
90
2
10
92
3
4
5
6
7
5
95
93
92
90
94
10
15
15
10
8
15
87
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Table 2 (Continued)
9
10
90
10
10
94
11
10
92
12
13
14
15
10
10
90
95
92
15
10
96
16
5
95
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Table 2 (Continued)
17
15
95
18
15
98
a
b
Reaction conditions: amine (1 mmol), aldehyde (1 mmol), phenylacetylene (1 mmol), catalyst (11 mol%), MW irradiation (800 W). Isolated
yield.
Table 3 K5WCo12O40?3H2O-Catalyzed synthesis of bis-quinolines under microwave irradiation and solvent-free conditions
Entry
Amine
Aldehyde
Bis-quinoline
Time (min)
Yield (%)a
1b
15
95
2b
15
80
3c
20
15
90
98
4c
5c
15
84
a
b
c
Isolated yield. Diamine (1 mmol), aldehyde (2 mmol), phenylacetylene (2 mmol), catalyst (22 mol%), MW irradiation (800 W). Amine
(2 mmol), dialdehyde (1 mmol), phenylacetylene (2 mmol), catalyst (22 mol%), MW irradiation (800 W).
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Scheme 2 Competitive reaction of arylacetylene in the presence of
alkylacetylene for the synthesis of quinoline derivatives.
Scheme 3 Competitive reaction of arylaldehyde in the presence of
aliphatic aldehyde for the synthesis of quinoline derivatives.
the a-axis of the unit cell. In spite of the presence of different
aromatic rings, there are no p–p interactions in both 4p and 4q
due to the long distances between the centroids of the rings.
To check the reaction pathway of the K5CoW12O40?3H2O
catalyzed three-component synthesis of quinolines, different
experiments were performed. First, a model reaction was carried
out in the presence of acrylamide as a radical scavenger under
MW irradiation; no desired product was obtained under these
conditions. This is a good indication for the presence of radical
species in the reaction. On the other hand, the intermediate
N-arylimine prepared by the reaction of amine with aldehyde,
was treated with phenylacetylene in the presence of K5CoW12O40?
3H2O under MW irradiation. Under these conditions, the
corresponding quinolines were obtained in excellent yield. On
the basis of these experimental results and together with the
previously reported works,15,22 it is reasonable to assume that
K5CoW12O40?3H2O acts as a one-electron transfer catalyst.
Fig. 2 The molecular structure of 4q, showing 30% probability
displacement ellipsoids and the atomic numbering.
Accordingly, a plausible mechanism as shown in Scheme 4 is
proposed. At first the intermediate imine 6 is formed by the
condensation of amine 1 with aldehyde 2. Then transferring an
electron from phenylacetylene 3 to Co(III) results in a radical
cation intermediate 7 and Co(II) species. (On the basis of observed
regiochemistry in the products, it seems that positive charge at
benzylic carbon and single electron at primary carbon of radical
cation is more suitable. It is also important to note that the
observed regiochemistry in products is confirmed unambiguously
by X-ray analysis of products 4p and 4q.) Nucleophilic attack of
imine 6 on radical cation 7 provides 8. One-electron transfer from
Co(II) to 8 and subsequent prototropic shift from nitrogen to
Fig. 3 The crystal packing of 4p, showing individual dimer formation
…
Fig. 1 The molecular structure of 4p, showing 30% probability
through the intermolecular C–H O hydrogen bonds.
displacement ellipsoids and the atomic numbering.
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Fig. 5 Recycling of the catalyst in the synthesis of 4b.
Fig. 4 The crystal packing of 4q, showing tetramer formation through
the intermolecular short C–Cl contacts and the weak intermolecular
…
five times without any significant loss in chemical yield of the
product.
C–H Cl interactions.
On the other hand, the possibility of the presence of metal in
the final product was checked to ensure that the final product is
free of metal. In this manner, the filtrates were used for
determination of the amounts of W or Co which may leached
from catalyst by ICP. No metal was detected in the final product
which confirms the green nature of the present method.
In conclusion, an efficient, selective and green one-pot
synthesis of quinolines and bis-quinolines has been developed
under microwave irradiation and solvent-free conditions. High
yield, neat conditions, short reaction times, environmentally-
friendly experimental procedures, and the avoidance of toxic
organic solvents are the notable advantages of this method.
Besides, the catalyst recovery and reusability is another feature
of this procedure. Thus, this work represents a valuable
complement to the existing procedures for the synthesis of
quinoline derivatives.
carbon gives 9. The intermediate 9 is transformed to dihydroqui-
noline 10 via an electrocyclic reaction followed by prototropic
shift from carbon to nitrogen. Finally, aromatization of 10 under
ambient atmosphere in the presence of catalyst afforded the
corresponding quinoline 4 and releases the Co(III) species for the
next catalytic cycle.
In order to show the actual role of acrylamide, which acts as a
radical scavenger or undergoes a Michael addition with aniline,
the reaction of acrylamide with aniline in the presence of the
catalyst was investigated under MW irradiation and no Michael
adduct was obtained under these conditions. After addition of
aldehyde to the reaction mixture, the imine was formed. While
upon addition of phenylacetylene to this reaction mixture, no
quinoline was produced. It is also noteworthy that, no desired
quinoline was obtained when 2,6-di-tert-butylphenol was applied
as radical scavenger in the model reaction. All these findings
showed that the proposed mechanism is reasonable.
Acknowledgements
The recyclability and reusability of the catalyst are very
important for commercial and industrial applications and are
also highly preferable for a green process. In this respect, the
reusability of the catalyst was investigated in the reaction of
4-nitroaniline, 4-methylbenzaldehyde and phenylacetylene. After
completion of the reaction, the mixture was cooled to room
temperature and diluted with cold EtOH. The catalyst was easily
recovered by simple filtration and then reused for subsequent
reactions. As shown in Fig. 5, the catalyst can be reused at least
The authors are grateful to the Center of Excellence of
Chemistry and also the Research Council of the University of
Isfahan for financial support of this work.
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