Rhenium complex-catalyzed allylation of acetals with allyltrimethylsilane

Article abstract of DOI:10.1016/j.tetlet.2008.09.001

It was confirmed that the treatment of acetals with allyltrimethylsilane in the presence of a catalytic amount of the rhenium complex, ReBr(CO)₅, gave the corresponding homoallylic ethers in excellent to good yields.

Full text of DOI:10.1016/j.tetlet.2008.09.001

Tetrahedron Letters 49 (2008) 6533–6535
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Tetrahedron Letters
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Rhenium complex-catalyzed allylation of acetals with allyltrimethylsilane
*
Yutaka Nishiyama , Keiko Shimoura, Noboru Sonoda
Department of Applied Chemistry, Faculty of Engineering, Kansai University, Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
It was confirmed that the treatment of acetals with allyltrimethylsilane in the presence of a catalytic
amount of the rhenium complex, ReBr(CO)5, gave the corresponding homoallylic ethers in excellent to
good yields.
Received 22 August 2008
Revised 28 August 2008
Accepted 1 September 2008
Available online 3 September 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Table 1
The allylation of carbonyl compounds and their derivatives,
such as acetals, with allyltrialkylsilane has been widely utilized
as a method for the preparation of homoallylic alcohols and
ethers.1,2 Usually, these reactions require the presence of a Lewis
or Brönsted acid promoter or catalyst. It is known that TMSOTf,3
(CH3)3SiI,4 trityl perchlorate,5 diphenylboryl triflate,5 montmoril-
lonite,6 TiCp2(CF3SO3)2,7 trimethylsilyl bis(fluorosulfonyl)imide,8
CF3COOH,9 SiO2,9 BiBr3,10 TMSN(SO2F)2,11 Sc(OTf)3,12 Bi(OTf)3,13
FeCl3,14 AlBr3/CuBr,15 Nb/AgClO4,16 and sulfonic acid,17 act as cata-
lysts for the transformations; however, several of these methods
suffer from drawbacks such as the involvement of compounds that
are corrosive, difficult to handle or toxic and strictly anhydrous
conditions.
We have recently shown the hitherto unknown ability of the
rhenium complex, which is an air-stable and water-tolerant com-
pound, to act as an efficient catalyst for the alkylation of arenes
with alkyl halides,18 the Mukaiyama aldol type reaction of carbonyl
compounds with enol silyl ether and allylation of carbonyl com-
pounds with allylstannane.19 It is now found that the rhenium
complex-catalyzed allylation of acetals with allyltrimethylsilane
produced the corresponding homoallylic ethers in moderate to
good yields (Scheme 1).20
Reaction conditions for the allylation of 1 with 2a
cat.ReBr(CO)5
solvent
OC4H9
OC4H9
OC4H9
SiMe3
+
C5H11
C5H11
1
2
3
Entry
Re catalyst
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8c
9
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReBr(CO)5
ReCl(CO)5
Re2(CO)10
Cp*Re(CO)5
MnBr(CO)5
Benzene
Toluene
THF
CH3CN
CH3OH
8
10
27
0
0
68
100 (92)
82
75
CHCl3
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
10
11
12
Trace
Trace
0
a
Reaction conditions; 1 (1.0 mmol), 2 (1.2 mmol), ReBr(CO)5 (0.1 mmol), and
solvent (5 mL) at 60 °C for 5 h.
b
GC yield. The number in the parentheses shows the isolated yield.
ReBr(CO)5 (0.025 mmol) was used for 24 h.
c
To determine the optimized reaction conditions, hexanal
dibutylacetal (1) was allowed to react with allyltrimethylsilane
(2) under various reaction conditions, and these results are shown
in Table 1. The yield of 4-butoxy-1-nonene (3) was affected by the
solvent and rhenium complex used in the reaction. When chlori-
nated hydrocarbon solvents, such as 1,2-dichloroethane and
chloroform, were used as a solvent, the allylation of 1 with 2
efficiently proceeded to give 3 in good yields, whereas the use of
coordinating solvents, such as THF, acetonitrile or methanol, and
the use of aromatic hydrocarbon solvents such as benzene and
toluene caused a distinct decrease in the yield of 3 (entries 1–7).
ReBr(CO)5 and ReCl(CO)5 showed a high catalytic activity for the
reaction (entries 7 and 9). The rhenium carbonyl complexes, such
as Re2(CO)10 and Cp*Re(CO)5, and manganese carbonyl complex
MnBr(CO)5 did not exhibit the same catalytic activity in the reac-
tion (entries 10–12).
In order to determine the application of the allylation of acetals
with allyltrimethylsilane (2), various acetals were reacted with 2 in
the presence of a catalytic amount of ReBr(CO)5 (10 mol %) at
60 °C for 5 h, and the results are shown in Table 2.21 Hexanal di-
methyl and diethyl acetals were converted into the corresponding
OR3
OR3
OR3
cat.ReBr(CO)5
SiMe3
+
R1
R1
R2
R2
Scheme 1.
* Corresponding author. Tel.: +81 6 6368 1121; fax: +81 6 6339 4026.
E-mail address: nishiya@ipcku.kansai-u.ac.jp (Y. Nishiyama).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.09.001

6534
Y. Nishiyama et al. / Tetrahedron Letters 49 (2008) 6533–6535
Table 2
cat.ReBr(CO)5 (0.1 mmol)
OC4H9
Rhenium-catalyzed allylation of various acetals with allyltrimethysilanea
SiMe3
+
C5H11
OC4H9
CH2ClCH2Cl (5 mL)
60 oC, 24 h
cat.ReBr(CO)5
CH2ClCH2Cl
OR3
OR3
OR3
SiMe3
+
(1.0 mmol)
(1.2 mmol)
OC4H9
R2
R2
R1
R1
OC4H9
C5H11
Entry
Acetal
Yieldb (%)
98 (98)
+
C5H11
OCH3
OCH3
OC2H5
OC2H5
1
2
3
26%
6%
(
threo / erythro = 56 / 44)
(E / Z = 72 / 28)
Scheme 2.
95 (82)
98 (84)
lated by allyltrimethylsilane to give the 4-butoxy-4-aryl-1-butene
in excellent to good yields (entries 5–9). For the reaction of cinna-
maldehyde dibutyl acetal, a,b-unsaturated aldehyde dibutyl acetal,
OC4H9
OC4H9
3-butoxy-1-phenyl-1,5-hexadiene was formed in 98% yield;
however, in the case of crotonealdehyde, the yield of the allylated
product was low (23%) due to the formation of various complicated
by-products (entries 11 and 12). Dibutyl ketals derived from 3-
pentanone and cyclopentanone were also allylated with 2 to give
the 4-butoxy-4-ethylhex-1-ene and 1-allyl-1-butoxycyclopenta-
none in 95% and 74% yields (entries 13 and 14). In the case of
the acetophenone dibutyl acetal, the yield of the allylated product
was significantly decreased under the same reaction conditions as
that of the 3-pentanone and cyclopentanone dibutyl ketals;
however, the yield of product was improved by extending the reac-
tion time (entry 15). When hexanal dibutylacetal (1) was allowed
to react with 1-trimethylsilyl-2-butene, 4-butoxy-3-methyl-1-
nonene was formed in 26% yield along with 5-butoxy-2-decene
(6%) (Scheme 2).
Although we cannot show the reaction pathway for the rhe-
nium-catalyzed allylation of acetals with allyltrimethylsilane in
detail, the following reaction pathway was proposed for the reac-
tion. It has already been reported that the coordinative unsaturated
16-electron complex was generated by the dissociation of carbon
monoxide from ReBr(CO)5 under toluene reflux conditions.22 Based
on this information, we suggested that the first step of the present
allylation of acetals is the generation of a 16-electron rhenium spe-
cies by the dissociation of carbon monoxide from the 18-electron
rhenium complex, ReBr(CO)5. The coordinative unsaturated rhe-
nium species generated in situ acts as a Lewis acid for the allylation
of acetal with allyltrimethylsilane.
OC4H9
OC4H9
OC4H9
OC4H9
4
80 (71)
X
5
6
7
X = H
= OCH3
= CH3
= Cl
97 (87)
98 (91)
95 (85)
95 (90)
90 (85)
8
9c
= NO2
OC4H9
OC4H9
10
90 (86)
OC4H9
OC4H9
11
23 (12) (E/Z = 67/33)
OC4H9
OC4H9
12
13
14
98 (90) (E/Z = 79/21)
OC4H9
95 (88)
OC4H9
OC4H9
OC4H9
In summary, it was found that a rhenium complex catalyzed the
allylation of acetals with allyltrimethylsilane to give the corre-
sponding homoallylic ethers in excellent to good yields. The appli-
cation of the catalytic use of a rhenium complex in organic
synthesis is now in progress.
74 (65)
OC4H9
OC4H9
15d
62 (58)
Acknowledgments
a
Reaction conditions: acetal (1.0 mmol), allyltrimethylsilane (1.2 mmol),
This research was supported by a Grant-in-Aid for Science Re-
search (No. 18550100), Research and Development Organization
of Industry-University Cooperation from the Ministry of Education,
Culture, Sports, Science and Technology of Japan and Kansai Uni-
versity Grant-in-Aid for progress of research in graduate course,
2007.
ReBr(CO)5 (0.1 mmol), and CH2ClCH2Cl (5 mL) at 60 °C for 5 h.
b
GC yield. The number in parentheses shows the isolated yield.
At 85 °C.
c
d
ReBr(CO)5 (0.2 mmol) was used for 24 h.
homoallylic ethers in the respective yields of 98% and 95% yields
(entries 1 and 2). For 2-methylbutanal and pivalaldehyde dibutyl
acetal, the allylation of the acetals with 2 efficiently proceeded un-
der the same reaction conditions as that of the hexanal dibutyl ace-
tal to give homoallylic butylethers in 98% and 80% yields,
respectively (entries 3 and 4). Similarly, benzaldehyde and aro-
matic aldehyde dibutyl acetals, in which methoxy, methyl, chloro,
and nitro groups were substituted on the aromatic ring, were ally-
References and notes
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