An active and selective heterogeneous catalytic system for Michael addition

Article abstract of DOI:10.1016/j.cclet.2012.02.006

Potassium fluoride doped natural zeolite was found to be an efficient and selective solid base catalyst for 1,4-Michael addition. The catalyst is easily prepared and the workup procedure simplified by simple filtration. All products were obtained in high

Full text of DOI:10.1016/j.cclet.2012.02.006

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 537–540
www.elsevier.com/locate/cclet
An active and selective heterogeneous catalytic system for
Michael addition
a
Hoda Keipour a, Mohammad A. Khalilzadeh a, , Abolfazl Hosseini ,
*
Afsaneh Pilevar a, Daryoush Zareyee b
a Department of Chemistry, Science and Research Branch, Islamic Azad University, Mazandaran, Iran
b Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr, Iran
Received 5 December 2011
Available online 29 March 2012
Abstract
Potassium fluoride doped natural zeolite was found to be an efficient and selective solid base catalyst for 1,4-Michael addition.
The catalyst is easily prepared and the workup procedure simplified by simple filtration. All products were obtained in high yields as
well as short reaction times.
# 2012 Mohammad A. Khalilzadeh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Michael addition; Potassium fluoride; Natural zeolite; Heterogeneous catalytic system
The current attention toward environmentally friendly, efficient syntheses and economic advantage of zeolites and
zeotype-materials has driven the generation of new strategies for heterogeneous catalysts to facilitate product
recovery, catalyst reuse, reaction workup, and waste disposal [1].
Impregnation of a catalyst to an appropriate solid matrix is a well-known approach to catalyst recovery and reuse
[2]. Creation of C–C bond via Michael reaction is a highly utilized tool in organic transformations, and it is usually
catalyzed by bases under homogeneous conditions [3].
There are many reports available under the category of heterogeneous catalysis for Michael additions mediated
particularly by Ba(OH)2 [4a], KF on g-Al2O3 [4b], hydrotalcites [4c–e], organic resins [4f], MgLa mixed oxides [4g],
magnesium oxide fluorides [4h], KG-60-NEt2 [4i], [bmIm]OH [4j], KF on a-Al2O3 [4k], KF doped phosphates [4l],
surface-anchored amines [4m], high surface area MgO [4n], N-phenyl-tris(dimethylamino)iminophosphorane (P-
BEMP) immobilized on polystyrene resin [4o], and silica gel 60 [4p], vanadium-apatite [4q], organic-inorganic hybrid
catalysts [4r].
However there are some problems using mentioned systems such as the use of expensive or toxic materials and
tedious or time-consuming reagent preparation. Thus, it is clear that there is considerable scope for development of
more applicable heterogeneous catalysts for industrial applications.
* Corresponding author.
E-mail address: khalilzadeh73@yahoo.com (M.A. Khalilzadeh).
1001-8417/$ – see front matter # 2012 Mohammad A. Khalilzadeh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2012.02.006

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H. Keipour et al. / Chinese Chemical Letters 23 (2012) 537–540
NC CN
O
O
NC
NC
Catalyst
Solvent
+
3a
1a
2a
Scheme 1.
Clinoptilolite is an environmentally friendly, nontoxic and inexpensive natural zeolite which is commercially
available. It can act as cation scavenger and this unique property made it possible to increase the basicity of some
anions [5]. We recently demonstrated that a potassium fluoride impregnated on clinoptilolite is exceedingly strong
base to be useful in SNAr and Ullmann reaction [6].
In this study, we describe an efficient solid base for 1,4-addition reactions. In our continued efforts for the
development of the solid base catalysts for organic transformations, herein we report a fast and selective 1,4-addition
reactions in the presence of a solid base catalyst (KF/CP) by direct condensation of various active methylene
compounds and chalcones. The reaction conditions are optimized, to obtain exclusively the appropriate products in
quantitative yields (Scheme 1).
To optimize the reaction conditions, a variety of soluble and solid base catalysts have been explored on chalcone,
chosen as model reactants in the presence of malononitrile (Table 1).
The basicity results correlated with the CP tendency for cation absorption (Table 1, entries 4 and 5). Nearly, complete
conversion toward the corresponding product was obtained with KF/CP catalysts (Table 1, entry 5). In homogeneous
reactions, equimolar amounts of homogeneous analogues of the corresponding solid bases were employed.
Effectively, less than 10% product was obtained with CP even after 100 min (Table 1, entry 1) and no detectable
product formation was observed with KF or NaF (entries 2 and 3). These results provide evidence that the KF/CP is the
best catalyst and that the high activity is attributed to the high dispersion of KF on CP support.
A series of chalcone derivatives were investigated in the Michael reaction with malononitrile using optimal
conditions. Most substrates underwent the reaction smoothly and gave the corresponding products in high yield (Table
2) except in the case of nitromethane (Table 2, entry 13). The electronic property of the substitution at the aromatic ring
R1 as well as R2 had no obvious effect on yield of reaction (Table 2, entries 1–16). Thus, the activity of KF/CP was
higher than KF [7], Al2O3 [8], KF/Al2O3 [9], and Mg–Al hydrotalcite [10] and is comparable with Mg–Al-O-tert-Bu-
hydrotalcite [11], ytterbium triflate hydrate [12] and ionic liquids [13,14].
Among the solvent used, methanol, ethanol and hexane, the first was the best. No by-products resulting from the
undesirable 1,2-adddition and/or bis-addition side reactions were observed.
The negatively charged fluoride moiety abstracts the proton from activated methylene to generate a carboanion
stabilized at the potassium surface. Consequently, the C–C bond formation is accelerated, and the final product is
obtained after protonation of the resulting enolate.
In summary, we have shown that a new heterogeneous solid base KF/CP is a highly efficient catalyst for the
selective 1,4-addition reaction. The main advantages of the described procedure are: facile handling of the solid base;
greater reaction rate and quantitative yields with a variety of substrates tested; elimination of further product
purification, and the use of inexpensive and available solid support which made an economic process.
General procedure
A 50 mL flask was charged with chalcones (1 mmol), malononitrile (1 mmol), KF/CP (30 mg) and methanol. The
mixture was stirred at 45 8C for appropriate time until completion of the reaction, as monitored by TLC. Then the
Table 1
Comparison of KF/CP with several heterogeneous catalysts in the synthesis of products 3a by Michael addition.
Entry
Catalyst
Time (min)
Yield (%)
1
2
3
4
5
CP
100
80
<10
NR
NR
75
NaF
KF
80
NaF/CP
KF/CP
20
12
97

H. Keipour et al. / Chinese Chemical Letters 23 (2012) 537–540
539
Table 2
Michael addition of chalcones with different donors catalyzed by KF/CP.
R3
R1
R
4 O
R3
O
Catalyst
Methanol
+
R2
R1
R2
R4
2a-c
1b-p
3b-p
Entry
R1
R2
R3
R4
Time (min)
Yield (%)
1
2
2-ClC6H4
3-ClC6H4
4-ClC6H4
4-MeC6H4
2-OMeC6H4
4-OMeC6H4
4-NO2C6H4
2-Naphthyl
4-CNC6H4
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
NO2
CN
NO2
25
25
25
30
40
35
18
15
18
40
25
15
300
50
100
95
95
97
97
95
95
96
90
93
94
96
92
70a
96
95
CN
3
CN
4
CN
5
CN
6
CN
7
CN
8
CN
9
CN
10
11
12
13
14
15
a
4-MeOC6H4
4-ClC6H4
C6H5
CN
C6H5
CN
C6H5
CO2Me
H
C6H5
C6H5
4-ClC6H4
4-ClC6H4
C6H5
CO2Me
H
C6H5
1.2 fold excess of KF/CP was used.
reaction mixture was cooled to room temperature and filtered. The catalyst was washed with dichloromethane and the
filtrate was concentrated under reduced pressure. The crude solid was subjected to chromatography or recrystallization
(n-hexane/ethyl acetate), giving the Michael adduct as a solid. The product structure was analyzed by 1H and 13C NMR
and IR spectrometry.
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