K. Shimizu et al. / Tetrahedron Letters 43 (2002) 9073–9075
9075
Table 2. Self-aldol condensation of various aldehydes with
NHMe–FSMa
Demicheli, G.; Maggi, R.; Mazzacani, A.; Righi, P.;
Sartori, G.; Bigi, F. Tetrahedron Lett. 2001, 42, 2401.
3. Shimizu, K.; Suzuki, H.; Hayashi, E.; Kodama, T.;
Tsuchiya, Y.; Hagiwara, H.; Kitayama, Y. Chem. Com-
mun. 2002, 1068.
4. (a) Stork, G.; Brizzolara, A.; Landesman, H.;
Szmuskovics, J.; Terrell, R. J. Am. Chem. Soc. 1963, 85,
207; (b) Brown, M. J. Org. Chem. 1968, 33, 162; (c)
Duhamel, P.; Hennequin, L.; Poirier, J. M.; Travel, G.
Tetrahedron 1986, 42, 4777.
5. (a) Haussermann, M. Helv. Chim. Acta 1951, 34, 1482;
(b) Casnati, G.; Pochini, A.; Salerno, G.; Ungaro, R.
Tetrahedron Lett. 1974, 15, 959; (c) Offenhauer, R. D.;
Nelsen, S. F. J. Org. Chem. 1968, 33, 774; (d) Shono, T.;
Kashimura, S.; Ishizaki, K. Electrochim. Acta 1984, 29,
603; (e) Ishikawa, T.; Uedo, E.; Okada, S.; Saito, S.
Synthesis 1999, 450.
Entry
Aldehydes
[N] (mol%)b
t (h)
2 Yield (%)c
1
2
3
4
5
n-Propanal
n-Butanal
n-Octanal
n-Decanal
5
5
10
10
1
2
2
2
8
83
84
93
56
44
Ph(CH2)2CHO 10
a Reactions were conducted with aldehydes (1 mmol) in toluene (5
mL) at reflux temperature under N2.
b Amount of the catalyst tested.
c Yield determined by GC using o-xylene as internal standard.
6. Hagiwara, H.; Ono, H.; Komatsubara, N.; Hoshi, T.;
Suzuki, T.; Ando, M. Tetrahedron Lett. 1999, 40, 6627.
7. Inagaki, S.; Fukushima, Y.; Kuroda, K. J. Chem. Soc.,
Chem. Commun. 1993, 680.
8. Typically, 2.0 g of the FSM-16 sample was evacuated at
150°C and then toluene (20 mL) containing N-methyl-3-
aminopropyl(triethoxy)silane (2 mmol) was introduced.
The mixture was heated at reflux temperature for 3 h and
the solid was filtered off, washed with toluene and ace-
tone and dried at 100°C overnight.
9. Before the reaction, the catalyst was dried in air at 150°C
for 1 h. The reaction was carried out by stirring the
reaction mixture containing aldehyde (1 mmol) in dry
toluene (5 mL) at reflux temperature under nitrogen
atmosphere. Progress of the reaction was monitored by
GC analyses of aliquots using o-xylene as an internal
standard.
ceeded smoothly in the presence of a catalytic amount
of NHMe–FSM to afford enals 2 in high yields. How-
ever, with this catalyst, the self-aldol condensation of
2-butenal or 2-methylpropionaldehyde did not proceed.
In summary, we have demonstrated that the secondary-
amine immobilised FSM-16 mesoporous silica acts as
an effective heterogeneous catalyst in the self-aldol
condensation of unmodified aldehydes. The present sys-
tem is a new heterogeneous catalysis for an environ-
mentally friendly CꢀC bond forming reaction because
the catalyst is easily separated by simple filtration and
is reusable without apparent decrease of the activity.
References
10. The geometry of the products from n-hexanal, n-decanal
and hydrocinnamaldehyde was determined to be E from
NOE enhancements between aldehydic and olefinic pro-
tons.
11. The yield was lower than the conversion of n-hexanal.
This may be due to the oligomerisation or the adsorption
of aldehydes on the catalyst.
12. This observation may be explained as follows. The
organic acids, present as impurities in aldehydes or pro-
duced during the reaction, neutralised the amine cata-
lysts. The organic acids were removed by the treatment
with dilute aqueous K2CO3 solution.
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