3
256
M. Zahouily et al. / Tetrahedron Letters 44 (2003) 3255–3257
sites. The distribution of the powder’s particle size was
determined. The result shows that all the sizes were
statistically distributed below 50 mm.
five successive recoveries, product 3b was obtained with
the same yield.
To evaluate the effect of the presence of electron accep-
tor or donor on the aromatic ring of benzaldehyde, the
Knoevenagel condensation was carried out between
phenylsulfonylacetonitrile 2 and substituted benzalde-
The results for a variety of a,b-unsaturated arylsulfones
prepared by Knoevenagel condensation catalyzed by
1
5
Na CaP O are summarized in Table 1. In general the
2
2
7
use of Na CaP O as heterogeneous catalyst in the
hyde derivatives (1a–d) using Na CaP O as catalyst.
2 2 7
2
2
7
Knoevenagel condensation has allowed the isolation of
Results from Table 1 show that the presence of electron
acceptor groups on the aromatic ring increases the
reaction rate. The presence of electron donor groups
decreases the reaction rate, demonstrating the participa-
tion of the aldehyde in the controlling step of the
reaction.
a-phenyl sulfonyl cinnamonitrile with modest yields
(
Table 1).
Under the same conditions, the addition of water
remarkably increases the reaction yields in the Knoeve-
nagel synthesis of a,b-unsaturated arylsulfones (Table
Thus, we estimate that the surface of catalyst
1
). For example, for the alkene 3a, the yield of reaction
Na CaP O presents certainly multicatalytic active sites.
goes from 62 to 68% in methanol and from 58 to 74%
in ethanol. In this, 10% of water is the optimum
condition for the synthesis of alkene 3b (Fig. 1). This
activation is probably due to the interaction between
water and the solid surface. If a large amount of water
is used a thin film of water will be formed between the
organic reagents and catalyst which explain the decreas-
ing of the yields (Fig. 1). The Na CaP O was regener-
2
2
7
The basic sites (oxygens of the P O group and CaO
2
7
6
octahedra) polarize the CꢀH bond of the active methyl-
ene compound. The acidic sites (phosphorus of P O
2
7
+
2+
group, Na and Ca cations) probably coordinate with
the oxygen of the carbonyl carbon on which a partial
positive charge appears. Consequently, the CꢀC bond
formation is facilitated and the final alkene is obtained
by transfer of a proton followed by dehydration.
2
2
7
ated by calcination at 500°C during 15 min, and after
In summary, we have reported an efficient and conve-
nient route to a,b-unsaturated arylsulfones by the Kno-
evenagel reaction. The Na CaP O catalyst shows high
Table 1.
2
2
7
catalytic activity under very mild liquid-phase condi-
tions. The advantages of this method are an easy
separation of the catalyst by filtration, possible recy-
cling of the catalyst, elimination of salts and by-product
pollutants. This solid base catalyst is certainly a practi-
cal alternative to soluble bases.
Arylsulfones
R
Solvent
Yield/% (1 h)a
3
3
3
3
3
3
3
3
3
3
a
a
a
a
b
b
c
c
d
d
H
H
H
H
p-NO2
p-NO2
p-Cl
p-Cl
p-OMe
p-OMe
MeOH
EtOH
MeOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
62
58
68
b
b
b
b
b
74
80
94
69
81
50
68
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2
1
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b
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Figure 1. Influence of water in the synthesis of unsaturated
arylsulfone 3b (with 1 mL of ethanol).