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Synthesis of biologically active chalcon analogues via claisen-schmidt condensation in solvent-free conditions: Supported mixed addenda heteropoly acid as a heterogeneous catalyst

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Biologically active chalcones were synthesized via Claisen-Schmidt condensation of aldehydes with different ketones in solvent-free conditions using H5PMo10V2O40 supported on SiO2 as a reusable heterogeneous catalyst with excellent reusability.
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J. Chil. Chem. Soc., 58, Nº 3 (2013)
1926
SYNTHESIS OF BIOLOGICALLY ACTIVE CHALCON ANALOGUES VIA CLAISEN-SCHMIDT
CONDENSATION IN SOLVENT-FREE CONDITIONS: SUPPORTED MIXED ADDENDA HETEROPOLY ACID AS
A HETEROGENEOUS CATALYST
EZZAT RAFIEE* AND FARZANEH RAHIMI
Faculty of Chemistry, Razi University, Kermanshah, 67149, Iran
(Received: March 14, 2013 - Accepted: May 20, 2013)
ABSTRACT
Biologically active chalcones were synthesized via Claisen-Schmidt condensation of aldehydes with different ketones in solvent-free conditions using
H
5
PMo
10
V
2
O
40
supported on SiO
2
as a reusable heterogeneous catalyst with excellent reusability.
Keywords: Chalcone, Claisen-Schmidt condensation, mixed addenda, heteropoly acid, heterogeneous catalyst.
e-mail: ezzat_raee@yahoo.com
INTRODUCTION
Chalcones belonging to avonoid family have displayed a broad spectrum
of biological activities, among which antimalarial
1
, anticancer
2
, antimitotic
3
,
antibacterial
4
, antiADIS
5
, antihyperglycemic
6
activities have been reported.
These compounds are of high interest due to their use as a key precursor in the
synthesis of many biological important heterocycles such as benzothiazepine
7
,
pyrazolines
8
and avones
9
. Thus, the organic/pharmaceutical chemists
worldwide have paid more attention to the synthesis of chalcones. Chalcones
could be obtained via Claisen-Schmidt condensation carried out in basic or
acidic media under homogenous conditions
10
. There are many drawbacks
under homogenous conditions including catalyst recovery and waste disposal
problems. Heterogeneous processes are industrially favor catalytic processes
in view of the ease of handling, simple work- up and regenerability. There
are different kind of catalysts which have been used for the Claisen-Schmidt
condensation, including Lewis acids
11
, Brönsted acid
12
, solid acid
13
, solid
bases
14
, and other catalysts with more or less success
15,16
. The increasing concern
about the tight legislation on the maintenance of greenness in synthetic strategy
led us to develop a method using green catalyst that is active in solvent-free
conditions as an alternative to volatile organic solvents. Here we have studied
the solvent-free Claisen- Schmidt condensation reaction using heteropoly acids
(HPAs) as solid acid catalysts that are metal- oxygen clusters and they have
attracted much attention as catalyst in organic reactions because of their high
Brönsted acidity and redox properties
17,18
.
EXPERIMENTAL
General
The reagents and solvents used in this work were obtained from Fluka,
Aldrich or Merck and were used without further purication. The commercial
Aerosil silica (S
BET
, 311 m
2
g
−1
; pore volume, 1.7 cm
3
g
-1
) from Degussa
was used. The catalyst sample was characterized with a scanning electron
microscope (SEM) (Philips XL 30 and S-4160) with gold coating.
Typical procedure for Claisen-Schmidt condensation
To a mixture of ketone (1 mmol) and aldehyde (2 mmol for Table 2; 1
mmol for Table 3), Mo
10
V
2
/SiO
2
(produced 40 wt.%: of Mo
10
V
2
to silica
19
, 32.5
wt.% from ICP result, typically, the Mo content from ICP was slightly lower
than expected from the preparation stoichiometry) (0.06 g, 0.085 mol% of
Mo
10
V
2
to ketone as substrate) was added and crushed at 50 °C for appropriate
time. Completion of the reaction was monitored by TLC, using n- hexane/
ethylacetate (10:4) as eluent. After completion of the reaction, 2×10 mL of
ether was added to the mixture and ltered off. Catalyst was washed with
ether and dried for reusing. The solvent of the ltrate was evaporated then
followed by chromatography to obtained pure products. Spectroscopic data of
the products matched well with those in the literature
20-23
and analytical data for
new compounds are presented below:
2,6-Bis-naphthalen-2-ylmethylene-cyclohexanone (2e, C
28
H
22
O) Yellow
solid; Mp: 281-282 °C,
1
H NMR (200 MHz; CDCl
3
, TMS) δ 1.45 (m, 2H), 2.78
(t, 4H, J=5.6), 7.28-7.58 (m, 12H), 7.61 (s, 2H);
13
C NMR (200 MHz, CDCl
3
)
δ 24.4, 28.1, 122.6, 125.5, 126.2, 127.4, 129.2, 133.0, 132.3, 133.8, 143.4,
149.3, 190.2; IR (KBr, cm
-1
) 1660 (C=O), 1622 (C=C) cm
-1
; MS m/z 374.16;
Anal Calcd. for C
28
H
22
O (374.17): C, 89.81; H, 5.92. Found: C, 89.83; H, 5.90.
4-Methyl-2,6-bis-naphthalen-2-ylmethylene-cyclohexanone (2f, C
29
H
24
O)
Yellow solid; Mp: 288-290 °C,
1
H NMR (200 MHz; CDCl
3
, TMS): δ 7.69 (s,
2H), 1.51 (d, 3H, J=6.2), 1.63 (m, 1H), 2.81 (m, 4H), 7.29-7.56 (m, 12H);
13
C
NMR (200 MHz, CDCl
3
) δ 21.5, 28.3, 35.2, 122.0, 125.4, 126.2, 127.4, 128.3,
131.2, 132.7, 135.6, 142.8, 148.1, 190.2; IR (KBr) 1660 (C=O), 1620 (C=C)
cm
-1
; MS m/z 388.16; Anal Calcd. for C
29
H
24
O (388.18): C, 89.66; H, 6.23.
Found: C, 89.63; H, 6.25.
RESULTS AND DISCUSSION
In the beginning of the study, cyclohexanone and benzaldehyde were used
as model reactants in order to nd the optimum reaction conditions by Claisen-
Schmidt condensation using HPAs as catalysts (Scheme 1).
Scheme 1. Model reaction.
Without the addition of the catalyst, no product was formed even after
2 hrs. Various types of mixed addenda catalysts with different ratio of
molybdenum to vanadium were evaluated for the synthesis of chalcones.
H
5
PMo
10
V
2
O
40
(Mo
10
V
2
) showed excellent reactivity among different kinds of
the catalysts (Table 1).
Table 1. Synthesis of chalcones using different HPA catalysts.
Entry Catalyst
a
Time (min) Yield (%)
b
1 - 120 0
2 Mo
10
V
2
15 98
3 Mo
9
V
3
25 93
4 Mo
8
V
4
40 95
5 Mo
10
V
2
/SiO
2
10 98
6 Mo
10
V
2
/SiO
2
50 10
c
a)
Isolated yield.
b) Reaction conditions: cyclohexanone (1 mmol), benzaldehyde (2 mmol),
catalyst (0.06 g), solvent-free, 50 ˚C.
c) Reaction proceed at room temperature.
HPAs with Keggin structures are exible in their acid strength and
have low toxicity and fairly high thermal stability, so they are excellent and
versatile catalysts for a wide variety of organic reactions in both homogeneous
and heterogeneous media
24,25
.
By immobilization of HPAs into convenient
carriers, the reaction easily carry out in a heterogeneous which has some
advantages like increase the accessibility to the acid sites and control solid acid
strength. Moreover, wastes are not produced, helping to incorporate in clean
technologies. Porous silica is one of the solids that has been mainly used for
supporting HPAs in various acid catalyzed reactions so here silica was used as
support for Mo
10
V
2
and as shown in Table 1, the minimum of the reaction time
was need when this catalyst used in the model reaction that is due to increase
in the surface area of the catalyst. When the reaction was carried out in room
J. Chil. Chem. Soc., 58, Nº 3 (2013)
1927
temperature, there is no signicant progress in the reaction so reaction was
carried out in 50 ˚C.
The morphological feature of the Mo
10
V
2
/SiO
2
catalyst was investigated
by SEM techniques. Fig. 1(a) shows the SEM micrograph of the catalyst. The
particles are regular in shape and dispersed uniformly. Wavelength dispersive
X-ray (WDX) image studied that is the map of individual elements of Si, Mo
and V elements in cross-section were shown in Fig. 1(b). It showed an excellent
uniform distribution of Mo
10
V
2
on SiO
2
surface.
Scheme 2. Synthesis of cahcones with cyclic ketones.
To investigate the generality of the method a variety of aldehydes
were used in the optimized reaction conditions with cyclohexanone and
4-methylcyclohexane as cyclic ketones (Scheme 2).
In most cases the reaction
proceeded smoothly to produce the corresponding chalcones. The reactions
were found to be clean and the products were obtained in excellent yields
without the formation of any side products (Table 2).
Table 2. Synthesis of different chalcones from cyclic ketones using
Mo
10
V
2
/SiO
2
as catalyst.
Entry Aldehyde Product
Time
(min)
Yield
(%)
a
mp (°C)
Observed Reported
1
H
O
2a
10 98 116-117 115-117
25
2
H
O
2b
20 96 168-170 170-171
25
3
H
O
Cl
2c
20 97 144-146 147-148
25
4
H
O
HO
2d
30 95 288-290 289-291
25
5
H
O
2e
25 94 281-282 -
6
H
O
2f
40 93 288-290 -
a) Isolated yield.
Encourage by these results, we decided to use aromatic ketones (Scheme
3) and as we expected the products were obtained with high yields and without
any byproducts (Table 3).
In the cases of 3a-3h products,
1
H NMR spectral data clearly indicated
that the compounds were geometrically pure and were congured trans (J
Hα_Hβ
= 15–16 Hz). In other reactions (2a-2f products), we obtained only the E, E
isomer. In the spectra of compounds, the signals for the protons of the CH=
group appear at δ 7.41-7.81. It is known
26-28
that the Z isomers are characterized
by the chemical shifts at δ ~6.8, whereas the signals for the E isomers should
appear at higher eld than 7.2 ppm.
Reaction of 1-methyl-4-pipridone as a heteroaromatic ketone with
4-cholorobenzaldehyde show 87% of 3,5-bis-(4-chloro-benzylidene)-1-
methyl-piperidin-4-one after 1 h
29
.
Fig. 1. SEM images of (a) Mo
10
V
2
/SiO
2
and (b) elemental maps of Si, Mo
and V atoms of Mo
10
V
2
/SiO
2
catalyst.
To optimize the catalyst loading model reaction was performed with
different amounts of the catalyst and the best result was obtained with 0.06 g of
Mo
10
V
2
/SiO
2
as shown in Fig. 2.
Fig. 2. Effect of the amount of the catalyst in the model reaction after 10
min.
J. Chil. Chem. Soc., 58, Nº 3 (2013)
1928
Scheme 3.Claisen- Schmidt condensation reaction with aromatic ketones.
Table 3. Synthesis of different chalcones from aromatic ketones using Mo
10
V
2
/SiO
2
as catalyst.
Entry R
1
R
2
Product Time (min) Yield (%)
a
mp (°C)
Observed Reported
1
3a
20 96 54-56 54-57
21
2 Cl
3b
24 98 111-112 111-113
21
3 CH
3
3c
45 97 97-98 97-98
22
4 OH
3d
20 95 178-180 181-183
23
5 Cl
3e
45 90 98-100 100-101
23
6 OH
3f
25 95 172-174 173-174
23
7 NO
2
_
3g
40 91 158-160 159-160
26
8 OMe NO
2
3h
30 92 193-194 191-192
21
a)
Isolated yield.
The catalyst shows reusability in this reaction and the catalytic activity of
the catalyst has not signicant decrease even after four runs and it shows that
Mo
10
V
2
/SiO
2
is a good catalyst according the economics of reaction and green
chemistry purposes Fig. 3.
Fig. 3. Reusability of the Mo
10
V
2
/SiO
2
in model reaction after 10 min.
The proposed mechanism is shown as Scheme 4. Mo
10
V
2
/SiO
2
activates both of the carbonyl groups. The chalcones are formed with
excellent chemoselectivity. No side products are formed such as product of
decomposition, self-condensation or Michael addition.
Scheme 4. Suggested mechanism of the Claisen-Schmidt condensation.
CONCLUSIONS
An efcient heterogeneous HPA-based catalyst has been prepared by
immobilization of Mo
10
V
2
on commercial Aerosil silica. WDX analysis showed
that the Mo
10
V
2
particles were uniformly distributed on support surface. This
catalyst was successfully used in the synthesis of chalcones via Claisen-
Schmidt condensation of aldehydes with different ketones in solvent-free
conditions. The reactions were found to be clean and the products were obtained
in excellent yields from aromatic and cyclic ketones without the formation of
any side products. Excellent yields, selectivities, and environmentally friendly
procedure, with low cost, easy preparation with high reusability and handling
of catalyst are some of salient advantages of this method.
ACKNOWLEDGEMENTS
We thank the Razi University Research Council for support of this work.
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Ethane bridged mesoporous organosilicas and MCM-41 having sulfonic acid groups in the pore channels were prepared by co-condensation method as well as grafting method, using 3-mercaptopropyltriethoxysilane (3-MPTS) as the sulfur precursor. TEM and N2 sorption isotherm analysis revealed that the mesoporous structural ordering is retained after the functionalization and modifications of organic groups while FT-IR, Raman, XPS and solid-state 13C CP MAS NMR shows the presence of sulfonic acid groups and the stability of the mesoporous framework. The catalytic activity of the developed materials was evaluated in the liquid phase Claisen–Schmidt condensation reaction of acetophenone with benzaldehyde, to probe the effect of mesoporous support surfaces as well as the role of preparation methods. Results showed that sulfonic acid functionalized ethane–silica samples were more active, selective and stable than the conventional sulfonic acid containing mesoporous catalysts.
Article
Novel 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehydes 5 have been synthesized from the 4,5-dihydropyrazolo[3,4-b]pyridine-6-ones 4 via Vilsmeier–Haack reaction. Further treatment of carbaldehydes 5 with acetophenones 6 and hydrazine hydrate afforded chalcone analogues 7 and dipyrazolo[3,4-b:4′,3′-e]pyridines 8, respectively.
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An efficient synthesis of 1,3-diaryl-2,3-dihydro-1,5-benzothiazepines has been developed by the reaction of various 1,3-diaryl-2-propenones with 2-aminothiophenol in water under neutral conditions catalysed by SDS. Excellent chemoselectivity was observed for substrates possessing halogen atoms or nitro/alkoxy/thioalkyl groups which did not undergo competitive aromatic nucleophilic substitution of the halogen atoms or the nitro group, reduction of the nitro or the α,β-unsaturated carbonyl group, or dealkylation of the alkoxy/thioalkoxy groups.
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Anhydrous RuCl3 catalyses the efficient cross aldol condensations of different ketones with various aromatic aldehydes in sealed tube under solvent free conditions without the occurrence of any self condensations. Regioselective self condensation reaction of some ketones and aldehydes are also described. The catalytic effect of Ru(III) is shown by performing similar reactions under thermal conditions without catalyst.
Article
A series of catalysts derived from Keggin-type heteropoly compounds (HPCs) were prepared and used as catalysts for the reaction of indole with benzaldehyde to afford bis(3-indolyl)phenylmethane. The results showed that the difference in catalytic activity of HPCs in this reaction depends on the number of introduced vanadium atoms in H3+nPMo12−nVnO40, kind of support, cesium content in CsxH3−xPW12O40 and nature of the metal cation in [(n-C4H9)4N](7−n)PMo2W9(Mn+·H2O)O39. The product yield was strongly dependent on the acidic characteristics which, in turn, depend on chemical composition of catalysts. In the presence of H3+nPMo12−nVnO40 and CsxH3−xPW12O40, the catalytic activity and acidity decreased with increasing V atom or cesium content. Among supported H3+nPMo12−nVnO40, H5PMo10V2O40/γ-Al2O3 is a weaker catalyst than bulk one. [(n-C4H9)4N](7−n)PMo2W9(Mn+·H2O)O39 catalysts exhibit a high electron-acceptor character and interesting structural and coordination properties. Catalytic activity of these compounds is related to the difference in their ability to coordinate substrates.
Article
trans-Chalcones have been obtained in good yields and selectivities following an environmentally friendly methodology by using montmorillonite KSF as a reusable heterogeneous catalyst.