8
952
Y. Abrouki et al. / Tetrahedron Letters 43 (2002) 8951–8953
1
8
We showed in our previous works that supporting KF
on NP causes the formation of a more open structure
which incorporates KF in such a way that crystalline
KF is not formed in significant quantities. However, it
appears that the basic structure of the NP is not
destroyed, indicating a less profound interaction of KF
with NP than is the case with alumina. The surface area
The best solvents to carry out this addition by NP/KF
are methanol, ethanol, butanol and isopropanol. A
similar effect of solvent has been observed in the hydra-
21
tion of nitriles
hydroxyphosphonates.
and in the preparation of a-
22
In conclusion the selective Michael addition of mercap-
tans to simple and substituted chalcones was achieved
in good yields and few minutes, under mild reaction
conditions, in the presence of 0.1 g of natural phos-
phate alone or doped by KF. The high reactivity and
specificity of our catalysts coupled with their ease of use
and reduced environmental problems makes them
attractive alternatives to homogenous base reagents.
2
−1
of calcined KF/NP is 8.9 m g .
Thiophenol and chalcone (X=H, Scheme 1) were cho-
sen as model substrates to determine suitable reaction
conditions.
In the presence of NP various solvents were tested.
Thus, after 15 min of reaction the yields obtained of
product 3a are 95 and 91 in the presence of methanol
and ethanol, respectively. In the cases of butanol, iso-
propanol, dimethylformamide, tetrahydrofurane, diox-
ane or hexane no product 3a was observed under the
reaction conditions, only the starting material was
isolated.
References
1. (a) Cheng, S.; Comer, D. D. Tetrahedron Lett. 2002, 43,
1179; (b) Kobayashi, S.; Ogawa, C.; Kawamura, M.;
Sugiura, M. Synlett 2001, 983; (c) Koulocheri, S. D.;
Magiatis, P.; Skaltounis, A.-L.; Haroutounian, S. A.
Tetrahedron 2000, 56, 6135; (d) Emori, E.; Arai, T.; Sasai,
H.; Shibasaki, M. J. Am. Chem. Soc. 1998, 120, 4043; (e)
Athawale, V.; Manjrekar, N. Tetrahedron Lett. 2001, 42,
The NP shows an interesting catalytic activity in
Michael addition and yields superior to 86% are
obtained in all cases (Table 1). The products of unde-
sirable side reactions resulting from 1,2-addition, poly-
merisation and bis-addition are not observed. The
surface of NP to acidic character probably induced
the polarization of the CꢀO bond for the Michael
addition.
19
4541.
2
3
4
5
6
7
8
. Sharma, U.; Bora, U.; Boruah, R. C.; Sandhu, J. S.
Tetrahedron Lett. 2002, 42, 143.
. Bergbreiter, D. E.; Lalonde, J. J. J. Org. Chem. 1987, 52,
2
0
1
601.
. Ranu, B. C.; Saha, M.; Bhar, S. Tetrahedron Lett. 1993,
4, 1989.
The use of NP is particularly interesting since its regen-
erated by calcinations at 700°C during 15 min, and
after five successive recoveries, product 3a was obtained
with same yield.
3
. Clark, J. H.; Cork, D. G.; Gibs, H. W. J. Chem. Soc.,
Perkin Trans. 1 1983, 2253.
. Laszlo, P.; Montaufier, P. M.-T.; Randriamahefa, S. L.
Tetrahedron Lett. 1990, 31, 4867.
. Curini, M.; Marcotullio, M. C.; Pisani, E.; Rosati, O.
Synlett 1997, 769.
. (a) Macquarrie, D. J. Tetrahedron Lett. 1998, 39, 4125;
19
Under the same conditions, the use of NP doped by
KF, remarkably, increases the catalytic activity in the
Michael addition. The yields are very high (92–97%) in
few minutes (Table 1). For example, for the product 3b,
the yield is 96% (2 min). The best weight ratio of
NP/KF is 8/1. In the presence of 0.01 g of KF alone
the present quantity in the KF/NP: 1/8 catalyst) the
product of 1,4-addition was obtained with low yield
40%).
(
b) Macquarrie, D. J. Chem. Commun. 1997, 6, 601; (c)
Mdoe, J. E. G.; Clark, J. H.; Macquarrie, D. J. Synlett
998, 625.
1
(
9. Choudary, B. M.; Lakshmi Kantam, M.; Venkat Reddy,
Ch.; Koteswara Rao, K.; Figueras, F. J. Mol. Catal.
(
1999, 146, 279.
1
0. Sreekurnar, R.; Rugmimi, P.; Padmakumar, R. Tetra-
Table 1. Synthesis of products 3 by Michael addition
using NP and KF/NP
hedron Lett. 1997, 38, 6557.
1
1. (a) Sebti, S.; Saber, A.; Rhihil, A. Tetrahedron Lett. 1994,
35, 9399; (b) Sebti, S.; Saber, A.; Rhihil, A.; Nazih, R.;
Tahir, R. Appl. Catal. A: General 2001, 206, 217.
2. (a) Sebti, S.; Boukhal, H.; Hanafi, N.; Boulaajaj, S.
Tetrahedron Lett. 1999, 40, 6207; (b) Sebti, S.; Solhy, A.;
Tahir, R.; Boulaajaj, S.; Mayoral, J. A.; Fraile, J. M.;
Kossir, A.; Oumimoun, H. Tetrahedron Lett. 2001, 42,
7953.
Yield/% (time/min)a
Products
X
R
1
NP
KF/NP
3
3
3
3
3
3
3
3
3
a
b
c
d
e
f
g
h
i
H
H
H
-Ph
-2-NH Ph
-CH -CO Et
-Ph
-2-NH Ph
-CH -CO Et
-Ph
-2-NH Ph
95 (15)
97 (10)
56 (45)
92 (10)
94 (10)
96 (20)
96 (15)
96 (10)
86 (20)
96 (05)
96 (02)
95 (05)
93 (02)
92 (02)
95 (05)
93 (05)
97 (02)
97 (05)
2
2
2
m-NO2
13. (a) Sebti, S.; Nazih, R.; Tahir, R.; Salhi, L.; Saber, A.
Appl. Catal. A: General 2000, 187, 197; (b) Bennazha, J.;
Zahouily, M.; Sebti, S.; Boukhari, A.; Holt, E. M. Catal.
Commun. 2001, 2, 101; (c) Sebti, S.; Tahir, R.; Nazih, R.;
Boulaajaj, S. Appl. Catal. A: General 2001, 218, 25.
m-NO2
m-NO2
p-Cl
p-Cl
p-Cl
2
2
2
2
-CH -CO Et
2
2
1
4. Natural phosphate (NP) comes Khouribga region
(Morocco). It is readily available (raw or treated) from
CERPHOS 37, Bd My Ismail, Casablanca, Morocco.
a
Yields in pure products isolated by recrystallization with AcOEt/
1
13
CH Cl2 and identified by H, C NMR and IR spectroscopy.
2