Mesoporous aluminosilicate-catalyzed allylation of aldehydes with allylsilanes

Article abstract of DOI:10.1016/j.tetlet.2009.04.002

Mesoporous aluminosilicate (Al-MCM-41) was found to catalyze the allylation of both aromatic and aliphatic aldehydes with allylsilanes although amorphous silica-alumina or mesoporous silicates (MCM-41, SBA-15) could not catalyze the reaction under the sam

Full text of DOI:10.1016/j.tetlet.2009.04.002

Tetrahedron Letters 50 (2009) 2967–2969
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Tetrahedron Letters
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Mesoporous aluminosilicate-catalyzed allylation of aldehydes with allylsilanes
*
Suguru Ito, Hitoshi Yamaguchi, Yoshihiro Kubota, Masatoshi Asami
Department of Advanced Materials Chemistry, Graduate School of Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesoporous aluminosilicate (Al-MCM-41) was found to catalyze the allylation of both aromatic and ali-
phatic aldehydes with allylsilanes although amorphous silica–alumina or mesoporous silicates (MCM-41,
SBA-15) could not catalyze the reaction under the same reaction conditions. The solid acid catalyst Al-
MCM-41 could be reused three times without significant loss of activity.
Received 16 February 2009
Revised 27 March 2009
Accepted 2 April 2009
Available online 7 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Al-MCM-41
Solid acid catalyst
Sakurai allylation
Homoallyl silyl ether
Among a wide variety of carbon–carbon bond forming reac-
tions, the addition of allylsilanes to aldehydes is one of the useful
reactions. Typically, these reactions are performed under stoichi-
ometric or near-stoichiometric amounts of strong Lewis acids
(e.g., TiCl4, BF3ÁOEt2, and AlCl3).1,2 Many kinds of catalysts, such
as Sc(OTf)3,3 Yb(OTf)3,4 iodine,5 and FeCl3,6 are also known to pro-
mote this transformation. However, the catalyst separation and
recycling are difficult for these homogeneous systems.
Owing to the economic and environmental considerations,
there has been increasing attention to the heterogeneous organic
reactions catalyzed by solid acid catalysts.7–9 Although some heter-
ogeneous catalysts (metal cations or proton-exchanged montmo-
rillonites10,11 and rare earth metals exchanged zeolite-Y12) have
been investigated for the reaction of aldehydes with allylsilanes,
these catalytic systems sometimes have disadvantages such as
higher reaction temperature or low yields of the allylated products.
On the other hand, mesoporous aluminosilicate, Al-MCM-41, is
well known to show remarkable acidic properties. Since its pore
sizes are larger than those of zeolites, bulky organic substrates
can contact acid sites of mesoporous aluminosilicates. Therefore,
Al-MCM-41 has been shown to catalyze several organic transfor-
mations.13–19 However, most of these reactions are vapor phase
or high-temperature reactions,13–17 and there has been relatively
few reports on the synthetic application of Al-MCM-41 as a solid
acid catalyst for liquid-phase reactions under mild reaction condi-
tions.18,19 Herein, we report the facile catalytic system for the reac-
tion of aldehydes with allylsilanes by using Al-MCM-41.
for 1 h under vacuum. First, the effect of solvent was examined
for the reaction of benzaldehyde (1.0 mmol) and allyltrimethylsi-
lane (1.5 mmol) in the presence of Al-MCM-41 (30 mg). The best
result was obtained when the reaction was carried out in dichloro-
methane at 15 °C for 2.5 h, and the corresponding homoallyl silyl
ether was isolated in 93% yield after filtration of the catalyst, con-
centration of the filtrate, and the purification by silica-gel column
chromatography (Table 1, entry 1). The use of toluene or nitro-
methane as a solvent also afforded the homoallyl silyl ether in al-
most same yields (entries 2 and 3). The reaction did not take place
in ether, THF, cyclohexane, or hexane (entries 4–7). Next, the reac-
tion was performed in the presence of amorphous silica–alumina
(JRC-SAH-1, JRC-SAL-2)22 in dichloromethane at 15 °C. In both
cases, the reaction did not proceed (entries 8 and 9). Furthermore,
benzaldehyde was not reacted in the presence of aluminium-free
MCM-41 or SBA-15 (entries 10 and 11). These results suggest that
both mesoporous structure and the presence of aluminium moiety
are necessary for the catalytic activity of Al-MCM-41. When the
reaction was performed in dichloromethane at 30 °C, the reaction
was completed after 1 h and the corresponding homoallyl silyl
ether was obtained in 92% yield (entry 12).23
Then the Al-MCM-41-catalyzed allylation was applied to vari-
ous aldehydes. The results are summarized in Table 2. Aromatic
aldehydes bearing electron-withdrawing groups were quickly ally-
lated within 30 min in excellent yields (entries 1–6). o-, m-, and
p-Tolualdehyde, bearing electron-donating alkyl substituent, was
less reactive than benzaldehyde and the allylated products were
obtained in moderate to good yields (entries 7–9), whereas p-anis-
aldehyde gave only trace amount of the product (entry 10).
Although the reactivities of naphthaldehydes were also lower than
that of benzaldehyde, the corresponding homoallyl silyl ethers
were obtained in good yields (entries 11–14). Aromatic aldehydes
Al-MCM-41 (Si/Al = 26) was synthesized by a known procedure
with slight modification,20,21 and was used after drying at 120 °C
* Corresponding author. Tel./fax: +81 45 339 3968.
E-mail address: m-asami@ynu.ac.jp (M. Asami).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.04.002

2968
S. Ito et al. / Tetrahedron Letters 50 (2009) 2967–2969
Table 1
Table 3
Allylation of benzaldehyde with allyltrimethylsilane
Reuse of Al-MCM-41a
SiMe
3 (1.5 equiv), cat. (30 mg)
solvent (0.5 M), 15 °C, 2.5 h
Run
4-NO2C6H4CHO (mmol)
Al-MCM-41 (mg)
Yieldb (%)
O
OSiMe3
1
2
3
4
2.0
1.8
1.3
0.8
60
53
38
25
92
94
94
93
Ph
(1.0 mmol)
Entry
H
Ph
Cat.
Solvent
Yielda (%)
a
In the presence of Al-MCM-41 (30 mg/mmol), the reaction of 4-nitrobenzal-
1
2
3
4
5
6
7
8
Al-MCM-41
Al-MCM-41
Al-MCM-41
Al-MCM-41
Al-MCM-41
Al-MCM-41
Al-MCM-41
JRC-SAH-1b
JRC-SAL-2c
MCM-41
CH2Cl2
Toluene
MeNO2
Et2O
93
87
85
dehyde with 1.5 equiv of allyltrimethylsilane was carried out in dichloromethane
(0.5 M) at 30 °C for 0.5 h.
b
Isolated yield after column chromatography.
N.R.
N.R.
N.R.
N.R.
N.R.
N.R.
N.R.
N.R.
92
THF
Cyclohexane
Hexane
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Table 4
Allylation of aldehydes with various allylsilanes catalyzed by Al-MCM-41
9
Si
(1.5 equiv), Al-MCM-41 (30 mg)
CH2Cl2 (0.5 M), 30 °C
R
10
11
12d
O
OSi
SBA-15
Al-MCM-41
R
H
a
b
c
Isolated yield after column chromatography.
Amorphous silica alumina (Si/Al = 2).
Amorphous silica alumina (Si/Al = 5).
Reaction was performed at 30 °C for 1 h.
(1.0 mmol)
Entry
R
Sia
Time (h)
Yieldb (%)
d
1
2
3
4
5
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
Ph
TES
0.5
0.5
0.5
1
93
91
57c
86
87
TBDMS
TBDPS
TBDMS
TBDMS
Table 2
Allylation of various aldehydes with allyltrimethylsilane catalyzed by Al-MCM-41
t-Bu
1
OSiMe3
O
a
b
c
SiMe3
(1.5 equiv), Al-MCM-41 (30 mg)
TES = triethylsilyl, TBDMS = tert-butyldimethylsilyl, TBDPS = tert-butyldiphenylsilyl.
Isolated yield after column chromatography.
Al-MCM-41 (50 mg) was used.
R
R
H
CH2Cl2 (0.5 M), 30 °C, 0.5-2.5 h
(1.0 mmol)
Entry
R
Time (h)
Yielda (%)
catalyst was dried at 70 °C for 15 min and treated in the same man-
ner as the first run. The catalyst could be reused three times with-
out significant loss of catalytic activity (Table 3).
1
2
3
4
4-NO2C6H4
4-BrC6H4
4-ClC6H4
2-NO2C6H4
2-BrC6H4
2-ClC6H4
4-MeC6H4
3-MeC6H4
2-MeC6H4
4-MeOC6H4
2-Naphtyl
2-Naphtyl
1-Naphtyl
1-Naphtyl
PhCH2CH2
PhCH2CH2
c-C6H11
0.5
0.5
0.5
0.5
0.5
0.5
2.5
1
1
1
1
1
1
1
1
1
1
1
1
92
97
93
90
95
93
59
70
83
<3
70
74
61
67
In terms of synthetic application, bulkier silyl ethers are often
useful for the protective groups of alcohols than trimethylsilyl
ether. Then, the reaction of aldehydes with other allylsilanes was
examined. 4-Nitrobenzaldehyde was allylated quickly with allyltr-
iethylsilane or allyltert-butyldimethylsilane under the same reac-
tion conditions given in Table 2. The corresponding homoallyl
silyl ethers were obtained in 93% and 91% yields, respectively
(Table 4, entries 1 and 2). Probably because of the steric hindrance,
the reaction of 4-nitrobenzaldehyde with allyltert-butyldiphenylsi-
lane afforded desired product only in moderate yield even using in-
creased amount of the catalyst (entry 3). Benzaldehyde and
pivalaldehyde were also allylated with allyltert-butyldimethylsi-
lane in 86% and 87% yields, respectively (entries 4 and 5).
In conclusion, allylation of various aldehydes with allylsilanes
was promoted under mild reaction conditions by using Al-MCM-
41 as a solid acid catalyst to afford the corresponding silyl ethers.
The superiority of Al-MCM-41 over amorphous silica–alumina is
probably due to more efficient interaction between organic sub-
strate and solid surface caused by concentration effect inside the
ordered, hydrophobic mesopores with high-surface area. The
recovered Al-MCM-41 could be reused three times without any de-
crease in catalytic activity.
5
6
7b
8
9
10
11
12b
13
14b
15
16b
17
18b
19
26c (20)d
60c (48)d
54c (44)d
86c (73)d
85
c-C6H11
t-Bu
a
b
c
Isolated yield after column chromatography unless otherwise noted.
Al-MCM-41 (50 mg) was used.
Determined by 1H NMR analysis using nitromethane as an internal standard.
Isolated yield of the corresponding homoallylalcohol after hydrolysis.
d
are often diallylated by Lewis acid-catalyzed allylation.6 However,
the diallylated product was not detected in this catalytic system.
The reaction of aliphatic aldehydes was also examined. In the case
of 3-phenylpropanal and cyclohexanecarboxaldehyde, the forma-
tion of the corresponding silyl enol ethers caused the decrease of
the yield of the allylated products (entries 15 and 17). The yields
were improved by increasing the amount of the catalyst (entries
16 and 18). Pivalaldehyde was allylated in 85% yield despite its ste-
ric hindrance (entry 19). The reaction of acetophenone with allyl-
trimethylsilane did not occur and the corresponding self-aldol
adduct was obtained in low yield under the same reaction condi-
tions given in Table 2.
Acknowledgment
Y.K. thanks NEDO for the Project of Development of Microspace
and Nanospace Reaction Environment Technology for Functional
Materials.
References and notes
The recovery and reuse of the catalyst were also examined.
After the reaction of 4-nitrobenzaldehyde with allyltrimethylsi-
lane, Al-MCM-41 was recovered by filtration. Then, the recovered
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