Na2CaP2O7, a new catalyst for Michael addition

Article abstract of DOI:10.1016/S0040-4039(02)01846-4

The synthetic diphosphate Na₂CaP₂O₇ is a new basic catalyst for Michael addition of mercaptans to chalcone derivatives with high yields in a few minutes and mild reaction conditions. Products of undesirable side reactions

Full text of DOI:10.1016/S0040-4039(02)01846-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7729–7730
Na2CaP2O7, a new catalyst for Michael addition
Mohamed Zahouily,* Younes Abrouki and Ahmed Rayadh
UFR de Chimie Applique´e, De´partement de Chimie, Faculte´ des Sciences et Techniques, Universite´ Hassan II,
Mohammadia B. P. 146, 20650 Morocco
Received 9 August 2002; accepted 29 August 2002
Abstract—The synthetic diphosphate Na2CaP2O7 is a new basic catalyst for Michael addition of mercaptans to chalcone
derivatives with high yields in a few minutes and mild reaction conditions. Products of undesirable side reactions resulting from
1,2-addition, polymerisation and bis-addition are not observed. © 2002 Elsevier Science Ltd. All rights reserved.
The Michael addition has attracted enormous attention
as one of the most important carbon–carbon or sulfur–
carbon bond-forming reactions in organic synthesis.1
This reaction may be carried out in homogeneous or
heterogeneous conditions.
CaCO3 and NH4H2PO4 in proportions 1:1:2, respec-
tively (purity of starting materials higher than 99%).
These materials were ground together in an agate mor-
tar and heated in a platinum crucible progressively
from 373 to 973 K. The final product is identified by
X-ray powder diffraction using a Siemens D-500 dif-
,
fractometer (CuKa radiation 1.5406 A; space group:
Various solid catalysts have been found useful in het-
erogeneous media, including aluminium oxide,2 mont-
morillonite/NiBr2,3 Mg–Al hydrotalcite,4 zeolite,5
natural phosphate doped by potassium fluoride6 and
other catalysts with more or less success.7
(
,
,
,
triclinic P1; a=5.361 A, b=7.029 A and c=8.743 A)
and infrared spectroscopy IR.8
The use of Na2CaP2O7 as heterogeneous catalyst in the
Michael addition has allowed the isolation of products
3 rapidly (5–40 min)9 and with good yields (58 to 96%;
Table 1). Products of undesirable side reactions result-
ing from 1,2-addition, polymerisation and bis-addition
are not observed.
We report here the use of a synthetic diphosphate
8
Na2CaP2O7 as a new solid state heterogeneous catalyst
in the Michael addition between chalcone derivatives 1
and mercaptans 2, at room temperature, with a solvent
(Scheme 1).
The Na2CaP2O7 was regenerated by calcination at
500°C during 15 min, and after seven successive recov-
eries, product 3a was obtained with the same yield. We
The synthesis of the diphosphate Na2CaP2O7 (Scheme
2) in powder state has been carried out from Na2CO3,
Scheme 1.
Scheme 2.
Keywords: Michael addition; diphosphate; heterogeneous catalysis; recyclable catalyst.
* Corresponding author. Fax: 212 23 31 53 53; e-mail: zahouily@voila.fr
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01846-4

7730
M. Zahouily et al. / Tetrahedron Letters 43 (2002) 7729–7730
Table 1. Synthesis of products 3 by Michael addition
Lee, P. H.; Ahn, H.; Lee, K.; Sung, S.; Kim, S. Tetra-
hedron Lett. 2001, 42, 37; (c) Christofers, J. Synlett 2001,
723; (d) Cheng, S.; Comer, D. D. Tetrahedron Lett. 2002,
43, 1179.
using Na2CaP2O7
Products
X
R
Yield/% (time/min)a
2. Sharma, U.; Bora, U.; Boruah, R. C.; Sandhu, J. S.
Tetrahedron Lett. 2002, 42, 143.
3. Laszlo, P.; Montaufier, P. M.-T.; Randriamahefa, S. L.
3a
3b
3c
3d
3e
3f
3g
3h
3i
H
H
H
m-NO2
m-NO2
m-NO2
p-Cl
p-Cl
p-Cl
-Ph
94 (20)
96 (05)
58 (40)
96 (10)
91 (02)
82 (40)
95 (30)
93 (05)
63 (40)
-2-NH2Ph
-CH2-CO2Et
-Ph
-2-NH2Ph
-CH2-CO2Et
-Ph
Tetrahedron Lett. 1990, 31, 4867.
4. Choudary, B. M.; Lakshmi Kantam, M.; Venkat Reddy,
Ch.; Koteswara Rao, K.; Figueras, F. J. Mol. Catal.
1999, 146, 279.
-2-NH2Ph
-CH2-CO2Et
5. Sreekurnar, R.; Rugmimi, P.; Padmakumar, R. Tetra-
hedron Lett. 1997, 38, 6557.
6. Sebti, S.; Boukhal, H.; Hanafi, N.; Boulaajaj, S. Tetra-
hedron Lett. 1999, 40, 6207.
a Yields in pure products isolated by recrystallization with AcOEt/
CH2Cl2 and identified by 1H, 13C NMR and IR spectroscopy.
7. (a) Bergbreiter, D. E.; Lalonde, J. J. J. Org. Chem. 1987,
52, 1601; (b) Ranu, B. C.; Saha, M.; Bhar, S. Tetrahedron
Lett. 1993, 34, 1989; (c) Clark, J. H.; Cork, D. G.; Gibs,
H. W. J. Chem. Soc., Perkin Trans. 1 1983, 2253; (d)
Curini, M.; Marcotullio, M. C.; Pisani, E.; Rosati, O.
Synlett 1997, 769; (e) Macquarrie, D. J. Tetrahedron Lett.
1998, 39, 4125; (f) Macquarrie, D. J. Chem. Commun.
1997, 6, 601; (g) Mdoe, J. E. G.; Clark, J. H.; Macquar-
rie, D. J. Synlett 1998, 625.
8. (a) Bennazha, J.; Boukhari, A.; Holt, E. M. Solid State
Sci. 1999, 373; (b) Bennazha, J.; Zahouily, M.; Sebti, S.;
Boukhari, A.; Holt, E. M. Catal. Commun. 2001, 2, 101.
9. The general procedure is as follows: To a flask containing
an equimolar mixture (1 mmol) of thiol 2 and chalcone
derivative 1 in methanol (1.5 ml), Na2CaP2O7 (0.1 g) was
added and the mixture was stirred at room temperature
until completion of the reaction, as monitored by thin
layer chromatography (TLC). The catalyst was filtered,
washed with dichloromethane and the filtrate was con-
centrated under reduced pressure. The crude product was
purified by recrystallization. The product was analysed by
1H, 13C NMR and IR spectrometry.
speculate, in our case, that the reaction occurs on the
surface of the catalyst and not inside tunnels. The
dimensions of the tunnels in our catalyst are smaller8
than of fluoroapatites10 but not as large as those of
zeolites.11
Thus, we estimate that the surface of Na2CaP2O7 pre-
sents certainly multicatalytic active sites. The basic sites
(oxygens of P2O7 group and CaO6 octahedra) abstract
the proton from the thiols. The acidic sites (phosphorus
of P2O7 group, Na+ and Ca2+ cations) probably induced
the polarisation of the CꢀO bond for the Michael
addition. Consequently, the SꢁC bond formation is
facilitated and the final product is obtained by the
transfer of a proton.
In summary, we have reported a selective 1,4-addition
without any side reaction, condensation, dimerisation,
or rearrangements in Michael. Two is made possible
with Na2CaP2O7. This catalyst brings advantages such
as high catalytic activity and selectivity under very mild
liquid phase conditions and easy separation of the
catalyst by simple filtration. Other applications will be
reported elsewhere.
10. (a) Sebti, S.; Nazih, R.; Tahir, R.; Salhi, L.; Saber, A.
Appl. Catal. A 2000, 197, L187; (b) Mathew, M.;
Shroeoer, L. W.; Oickens, B.; Brown, W. E. Acta. Crys-
tallogr. 1974, 10, 232.
11. (a) Reddy, T. I.; Varma, R. S. Tetrahedron Lett. 1997, 38,
1721; (b) Holderich, W. F.; Van Bekkum, H. In Introduc-
tion to Zeolite Science and Practice; Van Bekkum, H.;
Flanigen, E. M.; Jansen, J. C., Eds.; Stud. Surf. Sci.
Catal. 1991, 58, 631.
References
1. (a) Sasai, T.; Arai, T.; Satow, Y.; Houk, K. N.;
Shibasaki, M. J. Am. Chem. Soc. 1995, 117, 6194; (b)