Mesoporous aluminosilicate-catalyzed Mukaiyama aldol reaction of aldehydes and acetals

Article abstract of DOI:10.1016/j.tet.2014.09.073

A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both aldehydes and acetals with silyl enol ethers or ketene silyl acetals to give the corresponding aldol adducts in moderate to high yields. The remarkable high catalytic activity of Al-MCM-41 over amorphous silica-alumina and aluminum-free mesoporous silicate was observed in the reaction. The solid acid catalyst could be recovered easily by filtration and the recovered catalyst was reusable in the same reactions without a significant loss of catalytic activity.

Full text of DOI:10.1016/j.tet.2014.09.073

Tetrahedron 70 (2014) 8498e8504
Contents lists available at ScienceDirect
Tetrahedron
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Mesoporous aluminosilicate-catalyzed Mukaiyama aldol reaction
of aldehydes and acetals
Suguru Ito, Kenji Tanuma, Kohei Matsuda, Akira Hayashi, Hirotomo Komai,
*
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:
A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the
reaction of both aldehydes and acetals with silyl enol ethers or ketene silyl acetals to give the corre-
sponding aldol adducts in moderate to high yields. The remarkable high catalytic activity of Al-MCM-41
over amorphous silica-alumina and aluminum-free mesoporous silicate was observed in the reaction.
The solid acid catalyst could be recovered easily by filtration and the recovered catalyst was reusable in
the same reactions without a significant loss of catalytic activity.
Received 2 September 2014
Received in revised form 20 September 2014
Accepted 22 September 2014
Available online 6 October 2014
Keywords:
Al-MCM-41
Ó 2014 Elsevier Ltd. All rights reserved.
Solid acid catalyst
Mukaiyama aldol reaction
Silyl enol ether
Ketene silyl acetal
1. Introduction
catalytic activity of MCM-41 increases by incorporating metals,
such as Ti, Sn, and Al, into its structure.4f However, titanium- or tin-
Lewis acid-promoted aldol reaction of aldehydes, ketones, and
acetals with silyl enolates (Mukaiyama aldol reaction) is a facile and
reliable method for the synthesis of cross-aldol adducts, and
a number of catalysts have been reported as effective catalysts for
the reaction.1 On the other hand, the development of heteroge-
neous organic reaction systems catalyzed by solid acid catalysts is
important from an environmental and economical point of view
since heterogeneous catalysts usually do not require an aqueous
quenching and could be recovered easily from a reaction mixture.2
As for the Mukaiyama aldol reaction, several heterogeneous cata-
lysts, such as montmorillonite,3aec ordered mesoporous silica
MCM-41,3d,3g,3i,3l ScIII-doped zeolites,3k have been reported to
date.3
Among various heterogeneous catalysts, MCM-41 and modified
MCM-41s have been recognized as promising heterogeneous cat-
alysts for a wide variety of reactions owing to its ordered pore
structure, uniform pore diameter (2e10 nm), and high surface area
(>1000 m2/g).4 For example, Iwamoto et al. reported that MCM-41
was found to be an effective catalyst for the Mukaiyama aldol re-
action of acetals with silyl enol ethers.3d It is well known that the
containing MCM-41-catalyzed Mukaiyama aldol reactions of alde-
hydes required relatively long reaction time and high reaction
temperature even using reactive ketene silyl acetals as nucleophi-
les.3g,3i In our preliminary communications, we reported that Al-
MCM-41 catalyzed the Mukaiyama aldol reaction of aldehydes
and acetals with silyl enol ethers under mild reaction conditions to
give the corresponding b-siloxy and b-alkoxy carbonyl compounds
in high yields, respectively.5 Herein, we describe the details of the
reaction of both aldehydes and acetals with silyl enol ethers or
ketene silyl acetals catalyzed by Al-MCM-41.
2. Results and discussion
According to a known procedure with slight modification,6 Al-
MCM-41s (Si/Al¼23 and 26) were synthesized from cetyl-
trimethylammonium bromide, tetramethylammonium hydroxide,
aluminum triisopropoxide, and tetraethyl orthosilicate. The solid
acid catalyst Al-MCM-41 was dried at 120 ꢀC for 1 h under vacuum
prior to use.
Firstly, in the presence of Al-MCM-41 (30 mg, Si/Al¼26), the
reaction of benzaldehyde (1a) (1.0 mmol) with 1-phenyl-1-
trimethylsiloxyethene (2a) was carried out in dichloromethane or
toluene (Table 1, entries 1 and 2). After the reaction mixture was
stirred at 0 ꢀC for 15 min, the catalyst was removed by filtration, and
* Corresponding author. Tel./fax: þ81 45 339 3968; e-mail address: m-asami@
ynu.ac.jp (M. Asami).
http://dx.doi.org/10.1016/j.tet.2014.09.073
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
8499
Table 1
concentration effect inside the ordered, hydrophobic mesopores
with high-surface area. Similar results were observed in the Al-
MCM-41-catalyzed cyanosilylation and allylation of carbonyl
compounds.7
Aldol reaction of benzaldehyde (1a) with 1-phenyl-1-trimethylsiloxyethene (2a)
The Al-MCM-41-catalyzed aldol reaction was then applied to the
reaction of various aldehydes with 2a (Table 3). Aromatic aldehydes
with electron-withdrawing groups (eNO2 and eCl) on the aromatic
Entry
2a (equiv)
Solvent
Yield of 3a (%)a
4 (mmol)a
ring afforded the corresponding b-siloxy ketones 3 in high yields
1
2
3
4
5
6
1.5
1.5
1.5
1.5
1.2
1.1
CH2Cl2
Toluene
CH3CN
THF
CH3CN
CH3CN
99
99
99
28
99
94
0.10
0.10
Trace
N.D.b
N.D.b
N.D.b
(entries 1 and 2). The reaction of 2a with tolualdehydes proceeded
well to give the corresponding aldol adduct in high yields regard-
less of the substituted position (p-, m-, and o-) of the methyl group
(entries 3e5). 4-Anisaldehyde and 2-naphthaldehyde also gave the
corresponding product in high yields, namely, 86% and 92% yields,
respectively (entries 6 and 7). The reaction of 2a with (E)-cinna-
maldehyde, 3-phenylpropanal, or cyclohexanecarboxaldehyde un-
der the same reaction conditions gave the corresponding adduct in
good yields (entries 8e10). When pivalaldehyde was treated with
2a under the same reaction conditions, the reaction was relatively
slow and the yield of the product was 67% even after the reaction
was carried out for 2 h probably due to the steric hindrance of
pivalaldehyde (entry 11).
a
Determined by 1H NMR analysis of the crude product using nitromethane as an
internal standard.
b
Not detected by the 1H NMR analysis of the crude product.
the filtrate was concentrated to give the crude product. The quan-
titative formation of the corresponding
b-siloxy ketone 3a, 1,3-
diphenyl-3-trimethylsiloxypropan-1-one, was observed by the 1H
NMR analysis of the crude product. It should be noted that the
product was obtained as trimethylsilyl ether because an aqueous
workup is unnecessary. In these cases, however, the formation of
undesired self-aldol adduct 4 (0.1 mmol) was detected by the 1H
NMR analysis since the catalytic activity was so high that the re-
action of 2a with acetophenone, generated in the reaction mixture
from silyl enol ether 2a, also proceeded. The formation of 4 was
suppressed by using acetonitrile as the solvent (entry 3), whereas
the yield of 3a was significantly decreased by using THF (entry 4).
The amount of silyl enol ether 2a was then examined using ace-
tonitrile as the solvent (entries 5 and 6). The best result was ob-
tained when 1.2 equiv of 2a was used in the reaction (entry 5). In
Table 3
Aldol reaction of various aldehydes with 1-phenyl-1-trimethylsiloxyethene (2a)
catalyzed by Al-MCM-41
Entry
R
Yield (%)a
1
2
3
4
5
6
7
8
4-NO2C6H4
4-ClC6H4
90
92
87
95
94
86
92
80
74
81
67
this case, b-siloxy ketone 3a was obtained in 99% yield without the
formation of 4.
4-MeC6H4
3-MeC6H4
2-MeC6H4
4-MeOC6H4
2-Naphthyl
(E)-PhCH]CH
PhCH2CH2
c-C6H11
Next, the effects of the mesoporous structure and presence of
aluminum moiety for the reaction of 1a with 2a were examined by
using various silica catalysts in place of Al-MCM-41 (Table 2). In the
presence of amorphous silicaealuminas (JRC-SAH-1, JRC-SAL-2, and
SiO2eAl2O3) or aluminum-free mesoporous silicates (MCM-41 and
SBA-15), 3a was not obtained after the reaction was carried out in
acetonitrile at 0 ꢀC for 15 min (entries 2e6). These results suggest
that the high catalytic activity of Al-MCM-41 is attributed to the
presence of both ordered mesoporous structure and aluminum
moiety in the catalyst. The superiority of Al-MCM-41 over amor-
phous silicaealumina is probably due to more efficient interaction
between organic substrate and solid surface caused by
9
10
11b
t-Bu
a
Isolated yield after column chromatography.
Reaction was carried out for 2 h.
b
A following experiment was carried out to see if the reaction
occurs on the surface of Al-MCM-41. A mixture of Al-MCM-41
(30 mg), 1a (1.0 mmol), and 2a (1.2 mmol) in acetonitrile (2.0 mL)
was stirred at 0 ꢀC. After 15 min, a TLC analysis showed the dis-
appearance of 1a. The catalyst was then removed by filtration. To
the filtrate was successively added 1a (0.5 mmol) in acetonitrile
(0.5 mL) and 2a (0.6 mmol) in acetonitrile (0.5 mL) at 0 ꢀC. Newly
added 1a and 2a remained unreacted after stirring at 0 ꢀC for 1 h.
This result indicates that any homogeneous species, such as a tri-
methylsilyl cation generated in situ or an active aluminum species
leached from the catalyst, are not the actual catalyst of the Al-MCM-
41-catalyzed reaction. The recovery and reuse of the catalyst were
then examined in the reaction of 1a with 2a (Table 4). The catalyst
was recovered from the reaction mixture by filtration and washed
with diethyl ether. The recovered catalyst was then dried at 70 ꢀC
for 15 min, treated at 120 ꢀC for 1 h under vacuum, and used in
a next run. The catalyst was reusable, although the catalytic activity
of the recovered catalyst slightly decreased after repeated use.
As good results were obtained in the reaction of various alde-
hydes 1 with 2a, Al-MCM-41-catalyzed aldol reaction of acetals 5
with 2a was examined under the same reaction conditions used in
Table 2
Aldol reaction of benzaldehyde (1a) with 1-phenyl-1-trimethylsiloxyethene (2a) in
the presence of various silica catalysts
Entry
Catalyst (Si/Al)
Yield (%)
99a
1
2
3
4
5
6
Al-MCM-41 (26)
JRC-SAH-1 (2)b
JRC-SAL-2 (5)b
SiO2eAl2O3 (31)b
MCM-41 (N)d
SBA-15 (N)d
N.D.c
N.D.c
N.D.c
N.D.c
N.D.c
a
Table 1, entry 5.
b
c
Amorphous silicaealumina.
Not detected by the 1H NMR analysis of the crude product.
Aluminum-free mesoporous silicate.
d

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S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
Table 4
Reuse of Al-MCM-41 in the reaction of 1a with 2aa
Run
Al-MCM-41 (mg)
PhCHO (mmol)
Time (min)
Yield (%)b
1
2
3
4
60
47
32
18
2.0
1.6
1.1
0.6
15
15
15
60
99
99
86
85
a
In the presence of Al-MCM-41 (30 mg/mmol), the reaction of 1a with 1.2 equiv
of 2a was carried out in acetonitrile (0.5 M) at 0 ꢀC.
b
Isolated yield after column chromatography.
Scheme 1. Chemoselective aldol reaction of benzaldehyde dimethyl acetal (5a) cata-
lyzed by Al-MCM-41.
the reaction of aldehydes with 2a (Table 5). In the presence of Al-
MCM-41 (30 mg/mmol, Si/Al¼23), the reaction of benzaldehyde
dimethyl acetal (5a) with 2a (1.2 equiv) in acetonitrile at 0 ꢀC for 1 h
gave 3-methoxy-1,3-diphenylpropan-1-one (6a) in 95% yield, and
the catalyst was reusable at least three times (entry 1). The product
was not obtained by the reaction using amorphous SiO2eAl2O3 or
aluminum-free MCM-41 in place of Al-MCM-41 (entries 2 and 3),
though it was reported that MCM-41 could catalyze the same re-
action in toluene.3d The difference in catalytic activity between the
present MCM-41 and previously reported one is probably due to
the difference of silica sources of MCM-41.8 Other aromatic and
aliphatic acetals and cyclohexanone dimethyl acetal also reacted
with 2a under the same reaction conditions to give the corre-
with 2a to give the corresponding b-methoxy ketone 6a in 85%
yield, although 3a was obtained in high yield by the reaction of 1a
with 2a under the same reaction conditions in the absence of 5a.
With regard to the chemoselectivity of the Mukaiyama aldol re-
action, typical strong Lewis acids (e.g., TiCl4, BF3$OEt2, and AlCl3)
are known to show poor chemoselectivity.9a Trimethylsilyl tri-
fluoromethanesulfonate (TMSOTf) and MCM-41 were reported to
catalyze the chemoselective aldol reaction of acetals in the pres-
ence of aldehydes,3d,9 because they usually could not promote the
reaction of aldehydes with silyl enol ethers. Only MgI2 etherate was
reported to show chemoselectivity for acetals over aldehydes in the
reaction although it could activate both acetals and aldehydes.10
The Al-MCM-41-catalyzed aldol reaction of benzaldehyde (1a)
with other silyl enol ethers 2bef was then examined (Table 7). The
reaction of 1a with (Z)-1-phenyl-1-trimethylsiloxypropene (2b) in
sponding b-methoxy ketones 6 in good yields (Table 6).
Table 5
Aldol reaction of benzaldehyde dimethyl acetal (5a) with 1-phenyl-1-
trimethylsiloxyethene (2a)
acetonitrile at 30 ꢀC for 0.5 h afforded the corresponding
b-siloxy
ketone in 88% yield as a diastereomeric mixture (entry 1).11 1-
Trimethylsiloxycyclohexene (2c) also reacted with 1a to give a di-
astereomeric mixture of the corresponding adduct in 86% yield
(entry 2). In the case of the reaction with sterically hindered silyl
Entry
1
Catalyst (Si/Al)
Yield (%)
Table 7
Al-MCM-41 (23)
95 (first run)a
92 (fourth run)a,b
N.D.d
Aldol reaction of benzaldehyde (1a) with silyl enol ethers 2 catalyzed by Al-MCM-41
2
3
SiO2eAl2O3 (31)c
MCM-41 (N)e
N.D.d
a
Isolated yield after column chromatography.
Recovered catalyst was used.
b
c
Amorphous silicaealumina.
d
e
Not detected by the 1H NMR analysis of the crude product.
Aluminum-free mesoporous silicate.
Entry
1
Silyl enol ether
Temp (ꢀC)
30
Time (h)
0.5
Yield (%)a
88b
Table 6
Aldol reaction of various acetals 5 with 1-phenyl-1-trimethylsiloxyethene (2a)
catalyzed by Al-MCM-41
2
0
0.25
86b
Entry
R1
R2
Yield (%)a
3
4
30
24
69
1
2
3
4
5
6
2-ClC6H4
3-ClC6H4
4-MeC6H4
4-MeOC6H4
c-C6H11
H
H
H
H
H
90
78
89
90
89
85
0
0
0.25
0.25
94
87
e(CH2)5e
a
Isolated yield after column chromatography.
5
To estimate the chemoselectivity between aldehyde and acetal
in the Al-MCM-41-catalyzed aldol reaction, the reaction of benz-
aldehyde (1a, 1.0 mmol) and its dimethyl acetal (5a, 1.0 mmol) with
1.0 equiv of 2a was carried out (Scheme 1). Only acetal 5a reacted
a
Isolated yield after column chromatography.
b
Syn/anti¼3:2.

S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
8501
enol ether 2d, the reaction was sluggish even at 30 ꢀC and the
Table 9
Aldol reaction of various aldehydes
trimethylsiloxypropene (7a) catalyzed by Al-MCM-41
1
with 1-methoxy-2-methyl-1-
product was obtained in 69% yield after 24 h (entry 3). Bulkier silyl
ethers are often synthetically more useful than trimethylsilyl ether
as protective groups of hydroxy groups. Thus, the reactions of
triethylsilyl (TES) ether 2e and tert-butyldimethylsilyl (TBDMS)
ether 2f with 1a were also examined. The reactions proceeded at
0 ꢀC for 15 min to give the corresponding silyl ethers in 94% and 87%
yields, respectively (entries 4 and 5).
As the Al-MCM-41-catalyzed aldol reaction of aldehydes and
acetals with silyl enol ethers 2 gave good results, the reaction with
ketene silyl acetals 7 was then examined. Under the optimized
reaction conditions used in the reaction of 1a with 2a (Table 2,
entry 1), 1-methoxy-2-methyl-1-trimethylsiloxypropene (7a)
Entry
R
Yield (%)a
1b
2
3
4
5
6
7
8
9
4-NO2C6H4
4-ClC6H4
99
94
94
94
96
99
55c
81
90
4-MeC6H4
4-MeOC6H4
1-Naphthyl
2-Naphthyl
(E)-PhCH]CH
PhCH2CH2
c-C6H11
reacted with 1a to give the corresponding b-siloxy ester 8a in 89%
yield (Table 8, entry 1). The aldol adduct 8a was not obtained by the
reaction using amorphous SiO2eAl2O3 or aluminum-free MCM-41
(entries 2 and 3), as is the case of the reaction of 1a or 5a with silyl
enol ether 2a (Tables 2 and 5). The effect of solvents in the reaction
of 1a with 7a was then examined (Table 8, entries 4e7). The best
result was obtained when the reaction was carried out in
dichloromethane. In this case, 8a was obtained in 98% yield, and the
catalyst was reusable without a significant loss of catalytic activity
(entry 4).
a
Isolated yield after column chromatography.
Reaction was carried out for 2 h.
Desilylated 1,4-adduct was also obtained in 37% yield after column
b
c
chromatography.
Table 8
Aldol
reaction
of
benzaldehyde
(1a)
with
1-methoxy-2-methyl-1-
trimethylsiloxypropene (7a)
Entry
Catalyst (Si/Al)
Solvent
Yield (%)
Scheme 2. Aldol reaction of (E)-cinnamaldehyde with 1-methoxy-2-methyl-1-
trimethylsiloxypropene (7a) catalyzed by Al-MCM-41.
1
2
3
4
Al-MCM-41 (26)
SiO2eAl2O3 (31)b
MCM-41 (N)d
CH3CN
CH3CN
CH3CN
CH2Cl2
89a
N.D.c
N.D.c
Al-MCM-41 (26)
98 (first run)a
Table 10
97 (fourth run)a,e
Aldol
reaction
of
various
acetals
5
with
1-methoxy-2-methyl-1-
5
6
7
Al-MCM-41 (26)
Al-MCM-41 (26)
Al-MCM-41 (26)
Toluene
CH3NO2
THF
93a
89a
53a
trimethylsiloxypropene (7a) catalyzed by Al-MCM-41
a
Isolated yield after column chromatography.
b
c
Amorphous silicaealumina.
Not detected by the 1H NMR analysis of the crude product.
Aluminum-free mesoporous silicate.
d
e
Recovered catalyst was used.
Entry
R1
R2
Yield (%)a
The Al-MCM-41-catalyzed aldol reaction of ketene silyl acetal 7a
was then applied to the reaction with various aldehydes 1 (Table 9).
Although the reaction of 4-nitrobenzaldehyde with 7a was slower
1
2
3
4
5
6
7
8
Ph
H
H
H
H
H
H
H
H
H
H
99
96
98
99
98
97
99
99
93
93
79
4-ClC6H4
3-ClC6H4
2-ClC6H4
4-MeC6H4
4-MeOC6H4
1-Naphthyl
2-Naphthyl
PhCH2CH2
c-C6H11
than that of 1a, the corresponding b-siloxy ester was obtained in
99% yield after 2 h (entry 1). The reactions of other aromatic al-
dehydes were completed in 15 min to give the corresponding aldol
adducts in high yields (entries 2e6). In the case of (E)-cinna-
maldehyde, the corresponding 1,2-adduct and desilylated 1,4-
adduct were obtained in 55% and 37% yields, respectively (entry 7
and Scheme 2). Aliphatic aldehydes, 3-phenylpropanal and cyclo-
hexanecarboxaldehyde, also reacted with 7a to afford the corre-
9
10
11
e(CH2)5e
a
Isolated yield after column chromatography.
sponding b-siloxy esters in good yields (entries 8 and 9).
The reaction of various acetals with 7a was also investigated
(Table 10). Dimethyl acetals of various aromatic aldehydes with
electron-donating or -withdrawing groups reacted with 7a to give
The catalytic system was then applied to the reaction of 1a with
ketene silyl acetals 7bee (Table 11). 1-Ethoxy-1-trimethylsiloxy
ethene (7b) reacted with 1a to give the corresponding
b-siloxy
the corresponding b-methoxy ester 9 in high yields (entries 1e8).
ester in 96% yield (entry 1). The reaction with ketene silyl acetal 7c
derived from methyl propionate afforded a diastereomeric mixture
of the product in 92% yield (entry 2). Sterically hindered TES and
TBDMS ethers were obtained by the reaction of 1a with 7d or 7e in
95% and 92% yields, respectively (entries 3 and 4).
The reaction with dimethyl acetals of aliphatic aldehydes also
proceeded to afford the aldol adducts in high yields (entries 9 and
10). When cyclohexanone dimethyl acetal was used in the reaction,
the product was obtained in 79% yield (entry 11).

8502
S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
Table 11
200 and Silica gel 60 N (spherical, neutral, 63e210 mm) were used
Aldol reaction of benzaldehyde (1a) with ketene silyl acetals 7 catalyzed by Al-MCM-
for column chromatography. Tetrahydrofuran (THF) (Dehydrated,
stabilizer free) was purchased from Kanto Chemical Co., Inc. Other
solvents were purified and dried according to standard procedures.
All aldehydes were commercially available. All acetals,12 silyl enol
ethers,13 and ketene silyl acetals14 were synthesized according to
the literature procedure and fully characterized by IR and 1H, 13C
NMR spectroscopy. Al-MCM-41 (Si/Al¼26, SBET: 1120 m2/g, BJH:
2.7 nm and Si/Al¼23, SBET: 1031 m2/g, BJH: 2.7 nm), SiO2eAl2O3 (Si/
Al¼31, SBET: 385 m2/g), MCM-41 (SBET: 1080 m2/g, BJH: 2.6 nm), and
SBA-15 (SBET: 925 m2/g, BJH: 7.0 nm) were prepared according to
the previously reported method.7c There was no difference in cat-
alytic activity between Al-MCM-41 (Si/Al¼26) and Al-MCM-41 (Si/
Al¼23).
41
Entry
1
Ketene silyl acetal
Yield (%)a
96
2
92c
4.2. Typical experimental procedure for Al-MCM-41 catalyzed
aldol reaction (Table 4)
3
4
95
92
Under an atmosphere of argon, to a mixture of benzaldehyde
(0.213 g, 2.0 mmol) and Al-MCM-41 (60 mg, dried prior to use at
120 ꢀC for 1 h under vacuum) in acetonitrile (3.0 mL), 1-phenyl-1-
trimethylsiloxyethene (0.462 g, 2.4 mmol) in acetonitrile (3.0 mL)
was added through a syringe at 0 ꢀC. The reaction mixture was
stirred at 0 ꢀC for 15 min. The catalyst was removed by filtration and
washed with Et2O (40 mL). After the filtrate was concentrated
under reduced pressure, crude product was purified by silica-gel
column chromatography (hexane/Et2O¼20:1) to give 1,3-
aIsolated yield after column chromatography.
bE/Z¼8:1.
cSyn/anti¼1:1.
diphenyl-3-trimethylsiloxypropan-1-one15a as
a colorless oil
(0.591 g, 99%). The recovered catalyst was dried at 70 ꢀC for 15 min.
The catalyst (47 mg) was then dried at 120 ꢀC for 1 h under vacuum
and used in a second run.
3. Conclusion
In conclusion, aldol reaction of both aldehydes and acetals with
silyl enol ethers or ketene silyl acetals was promoted under mild
reaction conditions by using Al-MCM-41 as a heterogeneous solid
IR (neat): nmax 2957, 1688, 1598, 1580, 1494, 1449, 1360, 1252,
1204, 1096, 951, 842, 750, 700 cmꢁ1 1H NMR (270 MHz, CDCl3):
;
d
(ppm) 7.94e7.98 (m, 2H), 7.23e7.58 (m, 8H), 5.38 (dd, J¼8.7,
acid catalyst to give the corresponding b-siloxy or b-alkoxy car-
3.8 Hz, 1H), 3.56 (dd, J¼15.7, 8.7 Hz, 1H), 3.02 (dd, J¼15.7, 3.8 Hz,
1H), ꢁ0.04 (s, 9H); 13C NMR (67.8 MHz, CDCl3):
d (ppm) 198.0,144.5,
bonyl compounds in moderate to high yields. Both the mesoporous
structure and the presence of aluminum moiety were indispens-
able for the high catalytic activity of Al-MCM-41. The catalyst was
reusable without a significant loss of catalytic activity.
137.3, 132.7, 128.2, 128.1, 127.1, 125.5, 71.5, 49.6, ꢁ0.03.
All known compounds exhibited satisfactory IR and 1H, 13C NMR
spectra compared with the previously reported ones in the
literature.15e18
4. Experimental section
4.1. General
4.3. Characterization data
4.3.1. 1-Phenyl-3-m-tolyl-3-trimethylsiloxypropan-1-one (Table 3,
The structures of mesoporous materials were characterized by
using X-ray diffraction (XRD). XRD patterns were recorded on a Mac
entry 4). Colorless oil; IR (neat): nmax 2956, 1690, 1598, 1448, 1251,
1079, 953, 842, 751, 690 cmꢁ1; 1H NMR (270 MHz, CDCl3):
d (ppm)
Science M3X Model 1030 diffractometer equipped with a Cu K
a
X-
7.95e8.00 (m, 2H), 7.42e7.59 (m, 4H), 7.10e7.26 (m, 3H), 5.57 (dd,
J¼9.2, 2.8 Hz, 1H), 3.52 (dd, J¼15.5, 9.2 Hz, 1H), 2.87 (dd, J¼15.5,
2.8 Hz, 1H), 2.38 (s, 3H), ꢁ0.06 (s, 9H); 13C NMR (67.8 MHz, CDCl3):
ray source (40 kV, 20 mA). Nitrogen adsorption-desorption mea-
surements were carried out at 77 K using a gas adsorption analyzer
(Belsorp 28SA, Bel Japan). The specific surface areas (SBET) were
estimated using the BrunauereEmmetteTeller (BET) method. The
average pore-size of the mesoporous materials was obtained from
the adsorption branch of the isotherm using the Bar-
retteJoynereHalenda (BJH) method. The contents of Al in alumi-
nosilicates were measured by using inductively coupled plasma
d
(ppm) 198.1, 142.6, 137.4, 133.1, 132.7, 130.1, 128.3, 128.2, 126.8,
126.0, 125.7, 68.3, 48.1, 19.0, ꢁ0.1; Anal. Calcd for C19H24O2Si: C,
73.03; H, 7.74. Found: C, 72.86; H, 7.52.
4.3.2. 3-(3-Chlorophenyl)-3-methoxy-1-phenylpropan-1-one (Table
6, entry 2). Colorless oil; IR (neat): nmax 3113, 3067, 2928, 2817,
1798, 1097, 1162, 1042, 909, 853 cmꢁ1; 1H NMR (300 MHz, CDCl3):
spectrometer (ICP, ICP-8000E, Shimadzu). JRC-SAH-1 (Si/Al¼2, SBET
:
528 m2/g) and JRC-SAL-2 (Si/Al¼5, SBET: 617 m2/g) were obtained
from Catalysis Society of Japan as reference catalysts. All air-
sensitive experiments were carried out under an atmosphere of
argon. IR spectra were recorded on an HORIBA FT-730 spectrome-
ter. 1H and 13C NMR spectra were recorded on JEOL JNM-EX270,
JEOL JNM-AL400 or Brucker DRX-300 spectrometer using CDCl3
as a solvent. Tetramethylsilane (0.00 ppm) served as an internal
standard in 1H NMR and CDCl3 (77.0 ppm) in 13C NMR. TLC analyses
were done on silica-gel 60 F254-precoated aluminum backed sheets
(E. Merck). Toyo filter paper No.1 was used for filtration. Wakogel C-
d (ppm) 7.92e7.96 (m, 2H), 7.52e7.58 (m, 1H), 7.42e7.47 (m, 3H),
7.24e7.31 (m, 3H), 4.87 (dd, J¼8.3, 4.5 Hz, 1H), 3.58 (dd, J¼16.7,
8.4 Hz, 1H), 3.24 (s, 3H), 3.05 (dd, J¼16.8, 4.5 Hz, 1H); 13C NMR
(75.5 MHz, CDCl3):
d (ppm) 197.9, 141.3, 137.3, 137.0, 133.4, 133.3,
128.9, 128.6, 128.3, 128.0, 127.9, 79.4, 56.9, 47.0; Anal. Calcd for
16H15ClO2: C, 69.95; H, 5.50. Found: C, 69.75; H, 5.40.
C
4.3.3. 2,2-Dimethyl-1,3-diphenyl-3-trimethylsiloxypropan-1-one
(Table 7, entry 3). Colorless oil; IR (neat): nmax 2959, 1678, 1453,
1252, 1090, 1065, 957, 876, 842, 753, 707 cmꢁ1; 1H NMR (270 MHz,

S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
8503
CDCl3):
d
(ppm) 7.53e7.59 (m, 2H), 7.24e7.46 (m, 8H), 5.19 (s, 1H),
1095, 767 cmꢁ1; 1H NMR (400 MHz, CDCl3):
d
(ppm) 7.22e7.47 (m,
1.18 (s, 3H), 1.08 (s, 3H), ꢁ0.11 (s, 9H); 13C NMR (67.8 MHz, CDCl3):
4H), 5.18 (s,1H), 3.75 (s, 3H), 3.13 (s, 3H),1.16 (s, 3H),1.09 (s, 3H); 13
C
d
(ppm) 210.8, 140.6, 140.3, 130.0, 128.0, 127.6, 127.3, 127.0, 79.9,
NMR (100 MHz, CDCl3):
128.9, 126.2, 82.6, 57.1, 51.8, 48.6, 22.8, 18.0; Anal. Calcd for
13H17ClO3: C, 60.82; H, 6.67. Found: C, 60.50; H, 6.47.
d (ppm) 176.8, 135.1, 135.0, 129.8, 129.3,
53.5, 24.1, 20.7, ꢁ0.02; Anal. Calcd for C20H26O2Si: C, 73.57; H, 8.03.
Found: C, 73.42; H, 8.13.
C
4.3.4. 1,3-Diphenyl-3-triethylsiloxypropan-1-one (Table 7, entry
4.3.11. Methyl 3-methoxy-2,2-dimethyl-3-(4-methylphenyl) pro-
4). Colorless oil; IR (neat): nmax 2954, 2876, 1688, 1599, 1448, 1096,
pionate (Table 10, entry 5). Colorless oil; IR (neat): nmax 2982, 2948,
1071, 1002, 743, 700 cmꢁ1
;
1H NMR (270 MHz, CDCl3):
d
(ppm)
2822, 1740, 1470, 1363, 1132, 1096, 979, 829, 799 cmꢁ1 1H NMR
;
7.94e7.98 (m, 2H), 7.22e7.57 (m, 8H), 5.38 (dd, J¼8.6, 4.1 Hz, 1H),
3.57 (dd, J¼15.5, 8.6 Hz, 1H), 3.00 (dd, J¼15.5, 4.1 Hz, 1H), 0.78 (t,
J¼7.7 Hz, 9H), 0.45 (q, J¼7.7 Hz, 6H); 13C NMR (67.8 MHz, CDCl3):
(400 MHz, CDCl3):
(s, 3H), 2.35 (s, 3H), 1.11 (s, 3H), 1.00 (s, 3H); 13C NMR (100 MHz,
CDCl3): (ppm) 177.3, 137.3, 134.1, 128.4, 128.2, 87.7, 57.2, 51.8, 47.8,
22.6, 21.1, 18.5; Anal. Calcd for C14H20O3: C, 71.16; H, 8.53. Found: C,
70.99; H, 8.53.
d (ppm) 7.15 (s, 4H), 4.46 (s, 1H), 3.67 (s, 3H), 3.18
d
d
(ppm) 198.2, 144.8, 137.4, 132.7, 128.24, 128.22, 128.1, 127.2, 125.6,
71.8, 49.8, 6.7, 4.7; Anal. Calcd for C21H28O2Si: C, 74.07; H, 8.29.
Found: C, 73.86; H, 8.29.
4.3.12. Methyl 3-methoxy-2,2-dimethyl-3-(1-naphthyl)-propionate
(Table 10, entry 7). Colorless oil; IR (neat): nmax 2982, 2964, 2827,
1736, 1595, 1509, 1470, 1433, 1388, 1367, 1311, 1255, 1196, 1162,
4.3.5. Methyl 3-(4-chlorophenyl)-2,2-dimethyl-3-(trimethylsiloxy)
propionate (Table 9, entry 2). Colorless oil; IR (neat): nmax 2980,
2952, 1742, 1727, 1492, 1471, 1252, 1191, 1132, 1087, 1015, 879, 842,
1131, 1092, 1036, 997, 964, 936, 888, 851, 804, 789, 744 cmꢁ1 1H
;
752 cmꢁ1
;
1H NMR (400 MHz, CDCl3):
d
(ppm) 7.19e7.28 (m, 4H),
NMR (300 MHz, CDCl3): d (ppm) 8.25e8.26 (m, 1H), 7.81e7.89
4.94 (s, 1H), 3.67 (s, 3H), 1.10 (s, 3H), 0.97 (s, 3H), ꢁ0.04 (s, 9H); 13
C
(m, 2H), 7.60e7.62 (m, 1H), 7.45e7.54 (m, 3H), 5.48 (s, 1H), 3.74
NMR (100 MHz, CDCl3):
d
(ppm) 176.9, 139.4, 133.1, 129.0, 127.6,
(s, 3H), 3.19 (s, 3H), 1.22 (s, 3H), 0.99 (s, 3H); 13C NMR
78.4, 51.7, 48.9, 21.3, 19.2, ꢁ0.1; Anal. Calcd for C15H23ClO3Si: C,
(75.5 MHz, CDCl3): d (ppm) 177.4, 133.5, 133.1, 133.0, 128.8,
57.22; H, 7.36. Found: C, 57.14; H, 7.36.
128.3, 126.5, 125.6, 125.2, 124.9, 123.9, 77.2, 57.2, 51.9, 49.0, 23.7,
18.6; Anal. Calcd for C17H20O3: C, 74.97; H, 7.40. Found: C, 74.74;
H, 7.14.
4.3.6. Methyl 2,2-dimethyl-3-(4-methylphenyl)-3-(trimethylsiloxy)
propionate (Table 9, entry 3). White solid; mp: 48.8e49.0 ꢀC; IR
(KBr): nmax 2983, 2957, 1736, 1254, 1196, 1172, 1138, 1086, 1019, 897,
4.3.13. Methyl 3-methoxy-2,2-dimethyl-3-(2-naphthyl)-propionate
(Table 10, entry 8). White solid; mp: 64.4e65.5 ꢀC; IR (KBr): nmax
2979, 2927, 2822, 1733, 1460, 1438, 1381, 1364, 1313, 1258, 1197,
881, 838, 827 cmꢁ1 1H NMR (400 MHz, CDCl3):
; d (ppm) 7.13e7.15
(m, 2H), 7.07e7.09 (m, 2H), 4.93 (s,1H), 3.67 (s, 3H), 2.33 (s, 3H),1.10
(s, 3H), 0.98 (s, 3H), ꢁ0.05 (s, 9H); 13C NMR (100 MHz, CDCl3):
1169, 1136, 1093, 1021, 1000, 980, 947, 902, 859, 833, 791, 748 cmꢁ1
;
d
(ppm) 177.4, 137.7, 136.8, 128.1, 127.6, 79.0, 51.6, 49.0, 21.7, 21.1,
1H NMR (300 MHz, CDCl3):
1H), 7.42e7.52 (m, 3H), 4.66 (s, 1H), 3.74 (s, 3H), 3.24 (s, 3H), 1.17 (s,
3H), 1.07 (s, 3H); 13C NMR (75.5 MHz, CDCl3):
(ppm) 177.2, 135.0,
d (ppm) 7.81e7.86 (m, 3H), 7.23 (br s,
19.0, ꢁ0.04; Anal. Calcd for C16H26O3Si: C, 65.26; H, 8.90. Found: C,
65.06; H, 8.57.
d
133.1, 132.8, 127.9, 127.7, 127.6, 127.3, 126.1, 126.0, 125.9, 88.0, 57.4,
51.9, 48.1, 22.7, 18.7; Anal. Calcd for C17H20O3: C, 74.97; H, 7.40.
Found: C, 74.81; H, 7.18.
4.3.7. Methyl
3-cyclohexyl-2,2-dimethyl-3-(trimethylsiloxy)pro-
pionate (Table 9, entry 9). Colorless oil; IR (neat): nmax 2927, 2853,
1738,1450,1389,1251,1191,1113,1037, 903, 840, 750 cmꢁ1; 1H NMR
(400 MHz, CDCl3):
0.99e1.77 (m, 11H), 1.14 (s, 3H), 1.10 (s, 3H), 0.12 (s, 9H); 13C NMR
(100 MHz, CDCl3): (ppm) 178.1, 81.3, 51.5, 48.3, 40.9, 32.5, 28.9,
26.9, 26.40, 26.36, 23.8, 19.5, 0.80; Anal. Calcd for C15H30O3Si: C,
62.89; H, 10.56. Found: C, 62.78; H, 10.52.
d
(ppm) 3.70 (d, J¼3.8 Hz, 1H), 3.66 (s, 3H),
4.3.14. Methyl 2-(1-methoxycyclohexyl)-2-methylpropionate (Table
10, entry 11). Colorless oil; IR (neat): nmax 2939, 2860, 2835, 1729,
1471, 1447,1434,1389,1367,1288,1265,1234,1189,1144,1126,1081,
d
1048, 1014, 986, 941, 920, 849, 818, 757 cmꢁ1 1H NMR (300 MHz,
;
CDCl3):
1.27e1.70 (m, 7H), 1.20 (s, 6H), 0.99e1.15 (m, 1H); 13C NMR
(75.5 MHz, CDCl3): (ppm) 177.3, 78.6, 77.2, 51.6, 51.2, 50.9, 29.6,
d (ppm) 3.65 (s, 3H), 3.30 (s, 3H), 1.93e1.97 (m, 2H),
4.3.8. Methyl 3-(4-chlorophenyl)-3-methoxy-2,2-dimethylpro
pionate (Table 10, entry 2). Colorless oil; IR (neat): nmax 2983,
2949, 2823, 1739, 1597, 1491, 1470, 1276, 1255, 1132, 1092, 980, 891,
d
25.5, 22.3, 22.1; Anal. Calcd for C12H22O3: C, 67.26; H, 10.35. Found:
C, 67.18; H, 10.38.
836, 799, 731 cmꢁ1; 1H NMR (400 MHz, CDCl3):
d
(ppm) 7.30e7.38
(m, 2H), 7.20e7.23 (m, 2H), 4.46 (s, 1H), 3.71 (s, 3H), 3.18 (s, 3H), 1.10
(s, 3H), 1.00 (s, 3H); 13C NMR (100 MHz, CDCl3):
(ppm) 176.9,
4.3.15. Methyl
2,2-dimethyl-3-phenyl-3-(triethylsiloxy)propionate
d
(Table 11, entry 3). Colorless oil; IR (neat): nmax 2952, 2877, 1742,
135.9, 133.5, 129.6, 128.0, 87.2, 57.4, 51.9, 47.8, 22.4, 18.7; Anal. Calcd
for C13H17ClO3: C, 60.82; H, 6.67. Found: C, 60.45; H, 6.48.
1727, 1386, 1244, 1191, 1131, 1095, 1068, 1006, 841, 768, 741,
705 cmꢁ1 1H NMR (300 MHz, CDCl3):
; d (ppm) 7.23e7.28 (m, 5H),
5.00 (s, 1H), 3.67 (s, 3H), 1.16 (s, 3H), 0.97 (s, 3H), 0.83 (t, J¼6.0 Hz,
4.3.9. Methyl 3-(3-chlorophenyl)-3-methoxy-2,2-dimethylpro
pionate (Table 10, entry 3). White solid; mp: 60.9e61.6 ꢀC; IR
(KBr): nmax 2978, 2935, 2893, 2817, 1721, 1573, 1473, 1445, 1436,
9H), 0.45 (q, J¼6.0 Hz, 6H); 13C NMR (75.5 MHz, CDCl3):
d (ppm)
177.4, 140.9, 127.9, 127.4, 127.3, 79.2, 51.6, 49.1, 21.7, 19.2, 6.69, 4.72;
Anal. Calcd for C18H30O3Si: C, 67.03; H, 9.38. Found: C, 66.84; H,
9.38.
1364, 1272, 1191, 1135, 1102, 1079, 799, 696 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
4.46 (s, 1H), 3.71 (s, 3H), 3.20 (s, 3H), 1.12 (s, 3H), 1.01 (s, 3H); 13C
NMR (100 MHz, CDCl3): (ppm) 176.8, 139.7, 133.9, 129.0, 128.2,
127.9, 126.5, 87.2, 57.5, 51.9, 47.8, 22.3, 18.7; Anal. Calcd for
13H17ClO3: C, 60.82; H, 6.67. Found: C, 60.56; H, 6.49.
d (ppm) 7.26e7.38 (m, 3H), 7.14e7.17 (m, 1H),
d
Acknowledgements
C
The authors are grateful to Mr. Shinji Ishihara and Dr. Hironari
Kurihara (Instrumental Analysis Center, Yokohama National Uni-
versity) for their technical assistance in the elemental analyses. Y.K.
thanks New Energy and Industrial Technology Development Or-
ganization (NEDO) for financial support.
4 . 3 .10 . M e t h y l 3 - ( 2 - c h l o r o p h e n y l ) - 3 - m e t h o x y - 2 , 2 -
dimethylpropionate (Table 10, entry 4). Colorless oil; IR (neat):
nmax 2989, 2951, 2825, 1739, 1716, 1470,1435, 1363, 1272, 1221, 1134,

8504
S. Ito et al. / Tetrahedron 70 (2014) 8498e8504
Chem. Lett. 2009, 38, 1204e1205; (e) Sakai, N.; Moritaka, K.; Konakahara, T. Eur.
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and colloidal silica, respectively.
9. (a) Ooi, T.; Tayama, E.; Takahashi, M.; Maruoka, K. Tetrahedron Lett. 1997, 38,
7403e7406; (b) Murata, S.; Suzuki, M.; Noyori, R. J. Am. Chem. Soc. 1980, 102,
3248e3249.
10. Li, W.-D. Z.; Zhang, X.-X. Org. Lett. 2002, 4, 3485e3488.
11. As for the diastereoselectivity of the product, the ratio of anti-isomer was in-
creased by lowering the temperature (0 ꢀC, syn/anti¼5:4; ꢁ20 ꢀC, syn/anti¼1:2).
However, the reaction was sluggish at ꢁ20 ꢀC, and the yield of the product was
15% after 24 h.
€
Frohlich, R.; Getzschmann, J.; Mueller, U.; Glorius, F.; Kaskel, S. Chem.dEur. J.
2011, 17, 2099e2106; (h) Onishi, Y.; Nishimoto, Y.; Yasuda, M.; Baba, A. Org. Lett.
2011, 13, 2762e2765 See also Ref.15e.
18. For the products of the reactions of acetals with ketene silyl acetals, see: (a)
Soga, T.; Takenoshita, H.; Yamada, M.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1990,
63, 3122e3131; (b) Ooi, T.; Takahashi, M.; Yamada, M.; Tayama, E.; Omoto, K.;
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^
6907e6915; (b) Ladepeche, A.; Tam, E.; Ancel, J.-E.; Ghosez, L. Synthesis 2004,
1375e1380; (c) Wiles, C.; Watts, P.; Haswell, S. J. Tetrahedron 2005, 61,
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Maruoka, K. J. Am. Chem. Soc. 2004, 126, 1150e1160; (c) Barluenga, J.; Perez-
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