Asymmetric allylation polymerization of bis(allylsilane) and dialdehyde containing Si-phenyl linkage

Article abstract of DOI:10.1016/S0957-4166(01)00445-1

Repetitive Sakurai-Hosomi allylation between dialdehyde and bis(allylsilane) yielded a polymer having stereogenic carbons in its main chain. In the presence of an enantiopure Lewis acid catalyst such as chiral (acyloxy)borane (CAB), the allylation polymerization proceeded in a stereoselective manner to give optically active polymers. We have prepared new monomers containing Si-phenyl linkages for the asymmetric allylation polymerization. After polymerization, the Si-phenyl linkages in the main chain could be cleaved easily to give the corresponding chiral homoallylic alcohol. The enantiomeric purity of the chiral polymer was then evaluated by chiral HPLC analysis of the alcohol obtained from the degradation.

Full text of DOI:10.1016/S0957-4166(01)00445-1

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 2509–2516
Asymmetric allylation polymerization of bis(allylsilane) and
dialdehyde containing Siꢀphenyl linkage
Toshihiro Kumagai and Shinichi Itsuno*
Department of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan
Received 9 July 2001; accepted 30 July 2001
Abstract—Repetitive Sakurai–Hosomi allylation between dialdehyde and bis(allylsilane) yielded a polymer having stereogenic
carbons in its main chain. In the presence of an enantiopure Lewis acid catalyst such as chiral (acyloxy)borane (CAB), the
allylation polymerization proceeded in a stereoselective manner to give optically active polymers. We have prepared new
monomers containing Siꢀphenyl linkages for the asymmetric allylation polymerization. After polymerization, the Siꢀphenyl
linkages in the main chain could be cleaved easily to give the corresponding chiral homoallylic alcohol. The enantiomeric purity
of the chiral polymer was then evaluated by chiral HPLC analysis of the alcohol obtained from the degradation. © 2001 Elsevier
Science Ltd. All rights reserved.
1. Introduction
degree of asymmetric induction in such systems.10
A
precise model reaction study is an important approach
to gain such information. Another persuasive and reli-
able method to understand the asymmetric induction is
the analysis of the low-molecular-weight chiral com-
pounds derived from degradation of the chiral polymer.
In order for this strategy to succeed, we have designed
a new monomer structure suitable for degradation anal-
ysis. We report herein the preparation of new
monomers possessing Siꢀphenyl linkages and their
asymmetric allylation polymerization. The obtained
optically active polymers were degraded to the low-
molecular-weight chiral compound, which was analyzed
by chiral HPLC to evaluate the degree of asymmetric
induction. The corresponding model reactions have
been also studied.
The synthesis of optically active polymers having main
chain configurational chirality is an important technol-
ogy, which is essential for the molecular design of the
next generation polymeric materials.1–3 A great number
of methods for enantioselective transformations includ-
ing CꢀC bond forming reactions have been extensively
studied.4,5 If an asymmetric CꢀC bond forming reaction
proceeds in quantitative conversion without any side
reactions, it can be used for optically active polymer
synthesis. During our study on asymmetric polymeriza-
tion based on CꢀC bond forming reactions,6,7 we have
found that the enantioselective addition of allylsilane to
an aldehyde (Sakurai–Hosomi allylation8) is a suitable
reaction for the synthesis of optically active polymers.
Repetitive Sakurai–Hosomi allylation between bis(allyl-
silane) and dialdehyde produced a polymer having a
chiral homoallylic alcohol unit structure. When a chi-
rally modified Lewis acid catalyst was used, optically
active polymer having main chain configurational chi-
rality was obtained.9 This is the first example of asym-
metric allylation polymerization. However, a drawback
of this type of asymmetric polymerization is the
difficulty in the evaluation of the degree of asymmetric
induction during the polymerization. Since it is difficult
to determine the enantiomeric purity of chiral polymers
by direct analysis, only a few reports have discussed the
2. Results and discussion
2.1. Monomer synthesis
It is well known that the bond between Si and an aryl
group can be cleaved easily by means of treatment with
fluoride anion.11 We have prepared new monomers (4,
7, 12 and 15) containing Siꢀphenyl bonds, as shown in
Schemes 1–4. After asymmetric polymerization, the
Siꢀphenyl linkages in the main chain of the chiral
polymer may be cleaved readily. Silyl containing dialde-
hyde 4 was prepared by coupling of para-lithiobenz-
* Corresponding author. Fax: +81-(0)532-44-6813; e-mail: itsuno@
tutms.tut.ac.jp
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00445-1

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T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
OMe
OMe
OMe
OMe
BuLi
Me2SiCl2
THF
THF, -78 °C
Br
Li
1
2
Me Me
Si
Me Me
Si
2N HCl
O
O
MeO
OMe
OMe
THF
H
H
OMe
4
3
Scheme 1.
OMe
MeO
Me Me
Si
SiMe2Cl
+
Si
2
ClMe2Si
2N HCl
5
Me Me
OMe
6
O
OMe
H
Me Me
Si
Si
Me Me
H
7
O
Scheme 2.
SiMe3
SiMe3
COOMe
Silica gel
CH3COOH
HO
Me3SiCH2MgCl
Br
Br
8
9
Me2SiCl2
THF
SiMe3
SiMe3
BuLi
THF
Br
Li
11
10
Me Me
Si
Me3Si
SiMe3
12
Scheme 3.
son olefination reaction. The allylsilane moiety of 10
was formed using this method from 8 as a starting
material. Careful lithiation of 10 with n-BuLi at −78°C
followed by coupling with dichlorodimethylsilane led to
12 in good yield (Scheme 3). Another bis(allylsilane) 15
was prepared as shown in Scheme 4. Diester 14 was
prepared from dialdehyde 4 using the Horner–Emmons
reaction,13 followed by hydrogenation. The ester moiety
was then readily converted into the allylsilane using the
above method. These monomers are all stable enough
to be purified by standard silica gel column
chromatography.
aldehyde dimethylacetal 2 with dichlorodimethylsilane,
followed by deprotection of the acetal moiety.
Siꢀphenyl linkage was stable enough under the acidic
conditions used for acetal deprotection to isolate the
desired dialdehyde 4 (Scheme 1). The use of 1,2-bis-
(chlorodimethylsilyl)ethane as the silylating agent gave
another dialdehyde 7 (Scheme 2). Bis(allylsilane)s con-
taining the Siꢀphenyl linkage were then prepared by
coupling of lithiated b-phenylallylsilane 11 and silylat-
ing agent (Schemes 3 and 4). One of the most conve-
nient methods to construct b-substituted allylsilane
structures is Narayanan’s method12 based on the Peter-

T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
2511
Me Me
O
Si
EtO
P CH2CO2Et
EtO
4
EtO2C
CO2Et
NaH, THF
13
Me Me
Si
Me3SiCH2MgCl-CeCl3
Pd/C
Silica gel,
CH3CO2H
EtO2C
CO2Et
AcOEt
14
Me Me
Si
Me3Si
SiMe3
15
Scheme 4.
2.2. Asymmetric allylation polymerization
24 with benzaldehyde using 16 as a catalyst (Scheme 6).
In these reactions quantitative conversion was attained
within a few hours to give the homoallylic alcohol
products 23 and 25. Enantiopurities of the products
were determined by chiral HPLC analysis. Another
model reaction of bis(allylsilane) 26 and benzaldehyde
(Scheme 7) also took place smoothly at −78°C to give
We have examined the asymmetric polymerization of
dialdehyde and bis(allylsilane) monomers mentioned
above. Without catalyst no reaction occurred between
the monomers. Chirally modified Lewis acid catalyst is
required to initiate the asymmetric polymerization.
Although several enantioselective catalysts effective for
the allylation reaction have been reported, one of the
most efficient and reliable catalyst is the chiral
(acyloxy)borane (CAB) developed by Yamamoto.14
This is the only reported catalyst that has been used for
the enantioselective addition of b-substituted allyl-
silanes. We chose this catalyst for the asymmetric allyl-
ation polymerization. In the presence of CAB 16 asym-
metric polymerization of 4 and 12 occurred smoothly to
give the corresponding chiral polymer 17 (Scheme 5).
After the separation of 16 the polymer was isolated as
a white powder whose THF solution showed optical
activity. At 0°C monomers were consumed completely
within 30 min to give an optically active polymer 17
having Mw of 46000 (Table 1, run 1). The structure of
polymer 17 was confirmed by NMR spectroscopy,
which shows the unique main chain structure contain-
ing exo methylene, secondary alcohol, and silicon, as
shown in Scheme 5, and may be difficult to prepare by
other polymerization methods. Lowering the tempera-
ture resulted in the chiral polymer having higher optical
rotation value (entries 1–3). Even at −78°C, the poly-
merization reaction proceeded in homogeneous system
with a complete consumption of the monomers to give
the chiral polymer. This is a new type of synthetic
chiral polymer containing silicon atoms in the main
chain. All other combinations of the monomers were
subjected to the asymmetric polymerization. The corre-
sponding optically active polymers 17, 18, 19 and 20
were obtained in high yields in all cases.
27. Chiral HPLC analysis of 27 resulted in
a
80.7:17.8:1.5 ratio of stereoisomers (R,R)-27:(R,S)-
27:(S,S)-27. This stereoselectivity is similar to the
model reactions in Scheme 6. These model reactions
show that the asymmetric allylation polymerization
should proceed in a stereoselective manner with asym-
metric induction similar to those of model reactions.
2.4. Degradation of chiral polymer
Although the model reaction study gives important
information of stereoselectivity during polymerization,
the enantiomeric purity of the chiral polymers is still
unknown. We have tried to cleave Siꢀphenyl linkages in
the polymer main chain. Although the Siꢀphenyl link-
age of the chiral polymer is quite stable under standard
workup conditions, the polymer could be degraded
readily by treatment with tetrabutylammonium fluoride
(TBAF). A THF solution of 17 was thus treated with
TBAF at 60°C for 24 h (Scheme 8). The chiral polymer
17 was completely degraded under these conditions to
give the corresponding low-molecular-weight chiral
compound 23, which is identical with the product of the
model reaction (Scheme 6). The other chiral polymers
were similarly degraded to 23 and 25. The e.e. of the
degraded product can then be determined by using
chiral HPLC analysis. For example, chiral HPLC anal-
ysis of the degraded product 23 from chiral polymer 17
(obtained from the asymmetric polymerization of 4 and
12 at 0°C) had 57% e.e. (Table 1, entry 1). This
selectivity is the same as that attained in the model
reaction of Scheme 6 at the same temperature. The
same level of enantioselectivity obtained at −20°C is
predictable from the model reaction at this temperature
(entry 2). At −78°C, higher enantioselectivities were
achieved in the asymmetric polymerization. The use of
D-CAB, which was prepared from commercially avail-
2.3. Model reaction
In order to estimate the degree of asymmetric induction
during the polymerization, we investigated the enan-
tioselective addition of b-substituted allylsilanes 21 and

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T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
OiPr O
CO H
O
B
2
O
O
O
OiPr
16
CF3
F3C
2N HCl
Me Me
Si
Me Me
Si
16
+
4
12
EtCN
n
OH
OH
17
OH
Me Me
Si
Me Me
16
2N HCl
Si
+
7
12
Si
EtCN
Me Me
n
OH
18
Me Me
Me Me
Si
Si
16
2N HCl
+
4
15
EtCN
OH
OH
n
19
OH
16
EtCN
2N HCl
Me Me
Si
Me Me
Si
+
7
15
Si
Me
Me
n
OH
20
Scheme 5.
Table 1. Asymmetric allylation polymerization of bis(allylsilane) and dialdehyde using CABa catalyst in propionitrile
b
b
c
Entry
Monomer
Temp. (°C)
Time (h)
Yield (%)
Mw
Mw/Mn
[F]405
E.e.d (%)
1
2
3
4e
5
6
7
4+12
4+12
4+12
4+12
4+15
7+15
7+12
0
−20
−78
−20
−78
−78
−78
0.5
1
10
1
12
12
12
93
89
95
93
98
96
95
46000
32000
57000
30000
11000
22000
32000
5.7
4.6
6.9
4.2
3.7
4.5
4.9
−821.7
−881.4
−990.0
+772.9
−21.1
57
58
72
58
80
72
74
−36.6
−859.8
a CAB derived from
L-tartaric acid was used unless otherwise stated.
b Estimated by size exclusion chromatography (SEC) with polystyrene standards.
c Molar optical rotation was measured as THF solution (c 1.0, THF).
d Determined by HPLC using a chiral column (Chiralpac AD).
e CAB derived from
D-tartaric acid was used.
the polymerization of 4 and 15, the obtained chiral
polymer 19 had e.e. of 80% (entry 5), which, to our
knowledge, is the highest asymmetric induction
achieved in asymmetric polyaddition.
able
D-tartaric acid, afforded the same polymer having
opposite main chain configuration (entry 4). Degrada-
tion of 19 and 20 yielded 25, which was also analyzed
by chiral HPLC to determine the enantiopurity. From

T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
2513
Ph
Ph
OH
0oC: 57% e.e.
-20oC: 58% e.e.
-78oC: 79% e.e.
Ph
16
2N HCl
+
PhCHO
22
SiMe3
EtCN
23
21
Ph
Ph
16
EtCN
2N HCl
Ph
-78 oC: 83% e.e.
+
22
SiMe3
OH
25
24
Scheme 6.
Me3Si
OH
Lewis acid
2N HCl
Ph
+ 2 PhCHO
SiMe3
-78 ˚C
EtCN
Ph
OH
27
26
(R,R):(R,S):(S:S)
Lewis acid
•
BF3 OEt2
24.4 : 51.0 : 24.6
80.7 : 17.8 : 1.5
16
Scheme 7.
1H (300 MHz) and 13C (75 MHz) NMR spectra were
recorded on Varian Mercury 300 spectrometer using
tetramethylsilane as an internal standard. IR spectra
were recorded with a JEOL JIR-7000 FT-IR spectrom-
eter and were reported in reciprocal centimeter (cm−1).
Elemental analyses were performed by the Microanalyt-
ical Center of Kyoto University. HPLC analyses were
performed with a JASCO HPLC system composed of
3-Line Degasser DG-980-50, HPLC pump PV-980,
Column oven CO-965, equipped with a chiral column
(Chiralpac AD, Daicel) using hexane/propan-2-ol as an
eluent. UV detector JASCO UV-975 was used for the
peak detection. Size exclusion chromatography (SEC)
for the characterization of molecular weight and its
distribution was conducted at 40°C with JASCO PU-
980 as a pump, JASCO UVDEC-100-III as a UV
TBAF
17 or 18
19 or 20
23
25
THF, 60 °C, 24 h
TBAF
THF, 60 °C, 24 h
Scheme 8.
3. Conclusions
In conclusion, we have shown that silicon containing
dialdehydes 4 and 7 and bis(allylsilane)s 12 and 15
prepared in this study are useful monomers for asym-
metric
allylation
polymerization
using
chiral
(acyloxy)borane 16 as a catalyst to give chiral polymers
17–20, having unique main chain structure, in high
yield. These chiral polymers could be degraded easily
by treatment with TBAF to give the corresponding
enantioenriched homoallylic alcohols 23 and 25. Chiral
HPLC analysis of the alcohol revealed that the asym-
metric polymerization occurred with a high level of
asymmetric induction. This was also confirmed by the
corresponding model reactions. The above mentioned
methodology can be applied to other asymmetric poly-
merization systems.
,
detector and Shodex column A-802 (pore size: 20 A)
,
and A-803 (pore size: 100 A) as columns. The eluent
was THF and flow rate was 1.0 mL/min. A molecular
weight calibration curve was obtained by using a series
of polystyrene standards (Tosoh Co., Japan). All
reagents and solvents were purified and dried as neces-
sary according to standard procedures.
4.2. Monomer synthesis
4.2.1. Dialdehyde 4. 4-Bromobenzaldehyde dimethyl
acetal 1 (7.40 g, 32 mmol) was dissolved in THF (120
mL) under nitrogen. n-BuLi/hexane solution (1.6 M, 32
mmol, 20 mL) was added slowly at −78°C over 30 min.
4. Experimental
4.1. General
After stirring the mixture for
1 h at −78°C,
dichlorodimethylsilane (1.52 mL, 12.5 mmol) was
added to the above suspension. The reaction mixture
was then stirred for 1 h at −78°C, allowed to warm to
room temperature and was stirred for 12 h. The reac-
tion mixture was quenched with 2N HCl and extracted
Melting points were determined on a Yanaco micro
melting apparatus and were uncorrected. Optical rota-
tions were measured on a JASCO DIP-140 digital
polarimeter using a 10 cm thermostated microcell. Both

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T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
with ether. The organic phase was washed with brine
and dried (MgSO4). Evaporation of the solvent under
reduced pressure gave the crude acetal/aldehyde mix-
ture. To the crude mixture acetic acid (10 mL) and H2O
(3 mL) were added and stirred for 3 h at room temper-
ature. The reaction mixture was poured into a saturated
aqueous solution of NaHCO3 and extracted with ether.
The combined extract was washed with brine, dried
(MgSO4), filtered and concentrated. The crude product
was purified by column chromatography (hex-
ane:AcOEt, 4:1) and/or recrystallization (hexane/
AcOEt) to give dialdehyde 4 as a white solid (2.18 g,
8.1 mmol, 65%); mp 78–80°C, 1H NMR (CDCl3): l
10.02 (s, 2H, CHO), 7.85 (d, J=8.0 Hz, 4H, Ph-H),
7.68 (d, J=8.0 Hz, 4H, Ph-H), 0.64 (s, 6H, SiCH3); 13C
NMR (CDCl3): l 192.8, 146.0, 137.2, 135.0, 129.1,
−2.5; IR (KBr): 3024, 2853, 1699, 1592, 1209, 806 cm−1.
Anal. calcd for C16H16O2Si: C, 71.60; H, 6.01. Found:
C, 70.94; H, 6.04%.
1249, 1100, 852 cm−1. Anal. calcd for C12H17BrSi: C,
53.53; H, 6.36. Found: C, 53.55; H, 6.31%.
4.2.4. Bis(allylsilane) 12. Allylsilane 10 (5.25 g, 19.5
mmol) was dissolved in THF (80 mL) and cooled to
−78°C. A n-BuLi/hexane solution (1.6 M, 20 mmol,
12.5 mL) was added dropwise over 30 min, and stirred
for 1 h at this temperature. The solution became yellow
and then dichlorodimethylsilane (0.85 mL, 7 mmol) was
added slowly. The reaction mixture was stirred for 1 h
at −78°C, allowed to warm to room temperature and
stirred for 12 h. The reaction mixture was poured into
saturated aqueous NaHCO3 and extracted with ether.
The combined extract was washed with brine, dried
(MgSO4), filtered and concentrated. The crude product
was purified by column chromatography (hexane) to
1
give bis(allylsilane) 12 as colorless oil in 87% yield. H
NMR (CDCl3): l 7.45 (d, J=8.2 Hz, 4H, Ph-H), 7.38
(d, J=8.2 Hz, 4H, Ph-H), 5.16 (s, 2H, CꢁCH2), 4.87 (s,
2H, CꢁCH2), 2.01 (s, 4H, CH2Si), 0.54 (s, 6H, Ph-
SiCH3), −0.08 (s, 9H, CH2-Si-CH3); 13C NMR (CDCl3):
l 146.8, 143.7, 137.3, 126.0, 110.6, 26.3, −1.0, −1.9; IR
(film): 3064, 2956, 1614, 1251, 852 cm−1. Anal. calcd for
C26H40Si3: C, 71.48; H, 9.23. Found: C, 71.68; H,
9.27%.
4.2.2. Dialdehyde 7. Prepared as above, Mp 85–87°C;
1H NMR (CDCl3): l 10.02 (s, 2H, CHO), 7.84–7.62 (m,
8H, Ph-H), 0.65 (s, 4H, SiCH3), 0.28 (s, 12H,
SiCH2CH2Si); 13C NMR (CDCl3): l 193.0, 148.3,
136.8, 134.5, 129.0, 7.91, −3.49; IR (KBr): 3029, 2833,
2827, 1701, 1592, 1209, 806 cm−1. Anal. calcd for
C16H16O2Si: C, 67.74; H, 7.39. Found: C, 67.72; H,
7.41%.
4.2.5. Diester 13. A solution of triethyl phosphonoac-
etate (5.4 g, 24 mmol) in THF (10 mL) was added to a
suspension of NaH (0.24 g, 24 mmol) in THF (20 mL)
at 0°C. After stirring for 30 min at 0°C, a THF (10 mL)
solution of dialdehyde 4 (10 mmol) was added and the
reaction mixture was stirred for 2 h at room tempera-
ture. The reaction mixture was quenched with water
and extracted with ether. The combined organic layer
was dried (MgSO4), filtered and concentrated. The
crude product was purified by recrystallization (hexane)
to give diester 13 as a white solid in 90% yield. Mp
87–88°C; 1H NMR (CDCl3): l 7.67 (d, J=15.9 Hz, 2H,
Ph-CHꢁCH) 7.55–7.45 (m, 8H, Ph-H), 6.46 (d, 2H,
J=15.9 Hz, Ph-CHꢁCH), 4.26 (q, J=7.0 Hz, 4H,
COOCH2CH3), 1.34 (t, J=7.0 Hz, 6H, COOCH2CH3),
0.57 (s, 6H, Ph-SiCH3); 13C NMR (CDCl3): l 144.8,
141.0, 135.5, 135.0, 119.0, 60.9, 14.7, −2.3; IR (film):
2983, 1707, 1637, 1312, 1254, 1176, 815 cm−1. Anal.
calcd for C26H40Si3: C, 70.56; H, 6.91. Found: C, 70.45;
H, 7.02%.
4.2.3. 2-(4-Bromophenyl)-3-trimethylsilyl-1-propene 10.
Powdered CeCl3·7H2O (33.5 g, 90 mmol) was dried at
140°C/1 mmHg for 4 h. Under an argon atmosphere,
dry THF (160 mL) was added at room temperature and
the resulting suspension of CeCl3 was stirred for 12 h.
The white slurry obtained was then cooled to −78°C,
and trimethylsilylmethylmagnesium chloride/ether solu-
tion [prepared from chloromethyltrimethylsilane (12.7
g, 100 mmol), magnesium (2.7 g, 110 mmol), and ether
(50 mL)] was added slowly. The cream-colored suspen-
sion was stirred at −78°C for 1 h and 4-bromobenzoic
acid methyl ester 8 (6.45 g, 30 mmol) was added. The
reaction mixture was stirred for 2 h at −78°C, allowed
to warm to room temperature and stirred for additional
12 h. After cooling to 0°C, the reaction was quenched
carefully with dropwise addition of water. The mixture
was extracted with ether, washed with brine and dried
(MgSO4). Evaporation of the solvent under reduced
pressure gave the crude alcohol intermediate 9. Silica
gel (column chromatography grade, 25 g) was added to
a hexane (100 mL) solution of 9 and acetic acid (1.0
mL) was then added to the mixture. Stirring was con-
tinued for 30 min, and silica gel was removed by
filtration. After addition of a saturated aqueous solu-
tion of NaHCO3, the aqueous layer was extracted with
ether. The organic layer was washed with brine and
dried (MgSO4). Chromatographic purification of the
crude mixture (hexane) afforded allylsilane 10 as a
colorless oil (5.25 g, 19.5 mmol, 65%); 1H NMR
(CDCl3): l 7.43 (d, J=8.4 Hz, 2H, Ph-H), 7.28 (d,
J=8.4 Hz, 2H, Ph-H), 5.13 (s, 1H, CꢁCH2), 4.90 (s,
1H, CꢁCH2), 2.00 (s, 2H, CH2Si), −0.08 (s, 9H, Si-
CH3); 13C NMR (CDCl3): l 145.8, 142.0, 131.5, 128.3,
121.4, 111.0, 26.3, −1.1; IR (film): 3084, 2954, 1616,
4.2.6. Diester 14. a,b-Unsaturated diester 13 (8 mmol)
was dissolved in AcOEt (20 mL) and 10% Pd/C powder
(0.25 g) was added. The reaction mixture was stirred for
12 h under a H2 atmosphere. The mixture was filtered
through a Celite pad and the filtrate was concentrated
in vacuo to give diester 14 as a colorless oil in 98%
yield. 1H NMR (CDCl3): l 7.34 (d, J=8.1 Hz, 4H,
Ph-H), 7.08 (d, J=8.1 Hz, 4H, Ph-H), 3.98 (q, J=7.0
Hz, 4H, COOCH2CH3), 2.83 (t, J=8.0 Hz, 2H, Ph-
CH2CH2), 2.50 (t, J=8.0 Hz, 2H, Ph-CH2CH2), 1.11 (t,
J=7.0 Hz, 6H, COOCH2CH3), 0.41 (s, 6H, Ph-SiCH3);
13C NMR (CDCl3): l 173.0, 141.7, 136.0, 136.0, 134.6,
128.0, 60.6, 35.9, 31.1, 14.4, −2.1; IR (film): 2979, 1733,
1372, 1251, 1176, 811 cm−1. Anal. calcd for C26H40Si3:
C, 69.86; H, 7.82. Found: C, 69.90; H, 7.90%.

T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
2515
4.2.7. Bis(allylsilane) 15. Powdered CeCl3·7H2O (29.8 g,
80 mmol) was dried at 140°C/1 mmHg for 4 h. Under
an argon atmosphere, dry THF (160 mL) was added at
room temperature and the resulting suspension of
CeCl3 was stirred for 12 h. The white slurry obtained
was then cooled to −78°C and trimethylsilylmethylmag-
nesium chloride/ether solution, prepared from
chloromethyltrimethylsilane (12.7 g, 100 mmol), magne-
sium (2.7 g, 110 mmol) and ether (50 mL) was added
slowly. The cream-colored suspension was stirred at
−78°C for 1 h and diester 14 (12 mmol) was added. The
reaction mixture was stirred for 2 h at −78°C, allowed
to warm to room temperature and stirred for 12 h.
After cooling to 0°C, the reaction was quenched care-
fully with dropwise addition of water, and then diluted
with ether, washed with brine and dried (MgSO4).
Evaporation of the solvent under reduced pressure gave
the crude diol intermediate. Silica gel (column chro-
matography grade, 25 g) was added to a hexane (100
mL) solution of the intermediate and acetic acid (1.0
mL) was then added. Stirring was continued for 30 min
and silica gel was removed by filtration. After addition
of a saturated aqueous solution of NaHCO3, the
aqueous layer was extracted with ether. The combined
extract was washed with brine, dried over MgSO4,
filtered and concentrated. The crude product was
purified by column chromatography (hexane) to give
are as follows. Daicel Chiralpak AD, hexane:propan-2-
ol=30:1 (v/v), flow rate=0.5 mL/min, tR=34.1 min
(R), 38.2 min (S). The homoallyl alcohol 23 obtained
from the model reaction using 16 was converted to the
known compound (3-hydroxy-1,3-diphenylpropan-1-
one) by Lemieux–von Rudloff oxidation and the abso-
lute configuration was determined to be
R by
comparison of the specific rotation of the correspond-
ing hydroxyketone with the literature value.15
1
4.3.2. Homoallyl alcohol 25. H NMR (CDCl3): l 7.38–
7.27 (m, 10H, Ph-H), 5.00 (s, 1H, ꢁCH2), 4.97 (s, 1H,
ꢁCH2), 4.81 (m, 1H, CHOH), 2.80 (m, 2H, Ph-
CH2CH2), 2.48 (m, 4H, CH2ꢁC-CH2, Ph-CH2CH2),
2.15 (s, 1H, OH); 13H NMR (CDCl3): l 146, 144, 142,
129, 128, 126, 114, 72, 47, 38, 35; IR (film): 3397, 3027,
2932, 1644 cm−1. E.e.=83%. Conditions for HPLC
analysis of the enantiomers of 25 are as follows. Daicel
Chiralpak AD, hexane:propan-2-ol=30:1 (v/v), flow
rate=0.4 mL/min, tR=37.0 min (R), 39.7 min (S). The
absolute configuration of 25 was assigned on the
assumption that the asymmetric induction occurred in
the same sense as the reaction of 21 and 22.
1
4.3.3. Homoallyl alcohol 27. H NMR (CDCl3): l 7.45–
7.27 (m, 14H, Ph-H), 5.47 (br s, 2H, ꢁCH2), 5.19 (br s,
2H, ꢁCH2), 4.75 (m, 2H, CHOH), 3.05 (m, 4H, Ph-
CH2CH2), 2.19 (s, 2H, CHOH); 13H NMR (CDCl3): l
145, 144, 140, 129, 128, 127, 126, 116, 72, 46; IR (film):
3399, 2940, 1623 cm−1. Anal. calcd for C26H26Si2: C,
84.29; H, 7.07. Found: C, 84.21; H, 7.13. (R,R)-
27:(R,S)-27:(S,S)-27=80.7:17.8:1.5. Conditions for
HPLC analysis of the stereoisomers of 27 are as fol-
lows. Daicel Chiralpak AD, hexane:propan-2-ol=3:1
(v/v), flow rate=0.5 mL/min, tR=25.0 min (R,R), 34.0
min (R,S), 39.3 min (S,S). The absolute configuration
of 27 was assigned on the assumption that the asym-
metric induction occurred in the same sense as the
reaction of 21 and 22.
1
bis(allylsilane) 15 in 55% yield as a colorless oil. H
NMR (CDCl3): l 7.72 (d, J=7.9 Hz, 4H, Ph-H), 7.45
(d, J=7.9 Hz, 4H, Ph-H), 4.93 (s, 2H, CꢁCH2), 4.84 (s,
2H, CꢁCH2), 3.01 (m, 2H, Ph-CH2CH2), 2.51 (m, 2H,
Ph-CH2CH2), 1.85 (s, 4H, CH2Si), 0.80 (s, 6H, Ph-
SiCH3), 0.03 (s, 18H, Si-CH3); 13C NMR (CDCl3): l
147.5, 143.6, 135.6, 134.6, 128.2, 107.5, 40.4, 34.9, 27.4,
0.9, −1.86; IR (film): 3011, 2953, 1633, 1250, 849 cm−1.
Anal. calcd for C14H30Si2: C, 73.09; H, 9.81. Found: C,
73.30; H, 10.00%.
4.3. Typical procedure for asymmetric allylation reac-
tion promoted by chiral (acyloxy)borane catalyst
A solution of (2R,3R)-2-O-(2,6-diisopropoxybenzoyl)-
tartaric acid (74 mg, 0.2 mmol) and 3,5-bis(trifluoro-
methyl)phenylboronic acid (51 mg, 0.2 mmol) in dry
propionitrile (1 mL) was stirred for 30 min at room
temperature under argon to form chiral (acyloxy)-
borane. After the above solution was cooled to −78°C,
benzaldehyde (106 mg, 1 mmol) and allylsilane (1
mmol) were added and stirred for 2 h. The reaction
mixture was then quenched with 2N aqueous HCl (1
mL) and extracted with ether, dried (MgSO4) and con-
centrated. The crude product was purified by flash
column chromatography to give homoallyl alcohol. The
enantioselectivity was determined by HPLC analysis
using a chiral stationary-phase column.
4.4. Asymmetric allylation polymerization promoted by
chiral (acyloxy)borane catalyst
4.4.1. Polymerization of 12 and 4. A dry propionitrile (1
mL) solution of chiral (acyloxy)borane 16 prepared
from (2R,3R)-2-O-(2,6-diisopropoxybenzoyl) tartrate
(74
mg,
0.2
mmol)
and
3,5-bis(trifluoro-
methyl)phenylboronic acid (51 mg, 0.2 mmol) was
added to a solution of bis(allylsilane) 12 (219 mg, 0.5
mmol) and dialdehyde 4 (134 mg, 0.5 mmol) in propi-
onitrile (1 mL) at −78°C. The mixture was stirred at
−78°C for 10 h and quenched with 2N HCl (1 mL). The
mixture was poured into MeOH/H2O (2:1), filtered and
dried under vacuum to yield a white solid (266 mg,
95%); Mw=57000, Mw/Mn=6.93, [F]405 −990.0 (c 1.0,
1
4.3.1. Homoallyl alcohol 23. H NMR (CDCl3): l 7.49–
1
7.29 (m, 10H, Ph-H), 5.44 (br s, 1H, ꢁCH2), 5.19 (br s,
1H, ꢁCH2), 4.75 (m, 1H, CHOH), 3.05 (m, 2H, CH2ꢁC-
CH2), 2.19 (s, 1H, OH); 13H NMR (CDCl3): l 145.3,
144.2, 140.6, 128.8, 127.8, 126.6, 126.1, 116.1, 72.3,
46.2; IR (film): 3220, 2940, 1627 cm−1. E.e.=79%.
Conditions for HPLC analysis of the enantiomers of 23
THF), H NMR (CDCl3): l 7.54–7.31 (m, 16H, Ph-H),
5.46 (b, 2H, CꢁCH2), 5.19 (b, 2H, CꢁCH2), 4.70 (m,
2H, CHOH), 2.90 (m, 4H, CH2ꢁC-CH2), 2.10 (b, 2H,
OH), 0.57 (b, 6H, Ph-SiCH3), 0.53 (b, 6H, Ph-SiCH3);
13C NMR (CDCl3): l 145, 141, 138, 135, 116, 72, 46,
−2.0; IR (film): 3395, 3013, 2953, 1597, 1250, 811 cm−1.

2516
T. Kumagai, S. Itsuno / Tetrahedron: Asymmetry 12 (2001) 2509–2516
1
4.4.2. Polymer 19. H NMR (CDCl3): l 7.51–7.18 (m,
16H, Ph-H), 4.99 (b, 2H, CꢁCH2), 4.96 (b, 2H,
CꢁCH2), 4.77 (m, 2H, CHOH), 2.76 (m, 4H, Ph-
CH2CH2), 2.45 (m, 8H, CH2ꢁC-CH2, Ph-CH2CH2),
2.10 (b, 2H, OH), 0.52 (b, 12H, Ph-SiCH3)); IR (film)
3393, 3011, 2925, 1643, 1249, 804 cm−1.
References
1. Coates, G. W. In Comprehensive Asymmetric Catalysis,
Vol. III; Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H.,
Eds.; Springer: Berlin, 1999; pp. 1329–1349.
2. Okamoto, Y.; Nakano, T. Chem. Rev. 1994, 94, 349–372.
3. Wulff, G.; Zweering, U. Chem. Eur. J. 1999, 5, 1898–
1904.
1
4.4.3. Polymer 20. H NMR (CDCl3): l 7.44–7.32 (m,
4. Catalytic Asymmetric Synthesis, 2nd ed.; Ojima, I., Ed.;
Wiley-VCH: New York, 2000.
16H, Ph-H), 5.00 (b, 2H, CꢁCH2), 4.99 (b, 2H,
CꢁCH2), 4.77 (m, 2H, CHOH), 2.76 (m, 4H, Ph-
CH2CH2), 2.45 (m, 8H, CH2ꢁC-CH2, Ph-CH2CH2),
2.10 (b, 2H, OH), 0.64 (b, 4H, SiCH2CH2Si), 0.53 (b,
6H, CH2CH2SiCH3), 0.23 (b, 6H, Ph-SiCH3); IR (film):
3402, 3014, 2951, 1644, 1250, 828 cm−1.
5. Comprehensive Asymmetric Catalysis; Jacobsen, E. N.;
Pfaltz, A.; Yamamoto, H., Eds.; Springer: Berlin, 1999.
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933–934; (b) Kamahori, K.; Tada, S.; Ito, K.; Itsuno, S.
Macromolecules 1999, 32, 541–547.
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4995–4996; (b) Kumagai, T.; Itsuno, S. Macromol. Rapid
Commun. 2001, 22, 741–745.
1
4.4.4. Polymer 18. H NMR (CDCl3): l 7.55–7.17 (m,
16H, Ph-H), 5.46 (b, 2H, CꢁCH2), 5.20 (b, 2H,
CꢁCH2), 4.71 (m, 2H, CHOH), 2.79 (m, 4H, CH2ꢁC-
CH2), 2.18 (b, 2H, OH), 0.64 (b, 4H, SiCH2CH2Si),
0.58 (b, 6H, CH2CH2SiCH3), 0.23 (b, 6H, Ph-SiCH3)
IR (film) 3404, 3015, 2952, 1596, 1248, 812 cm−1.
4.5. Cleavage of allylation polymer
10. Recently, the following papers have dealt with evaluation
of the enantiomeric purity of the chiral synthetic poly-
mers by means of degradation study: (a) Nozaki, K.;
Nakano, K.; Hiyama, T. J. Am. Chem. Soc. 1999, 121,
11008–11009; (b) Cheng, M.; Darling, N. A.; Lobkovsky,
E. B.; Coates, G. W. Chem. Commun. 2000, 2007–2008.
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1989, 54, 4372–4385; (b) Plunkett, M. J.; Elman, J. A. J.
Org. Chem. 1995, 60, 6006–6007; (c) Plunkett, M. J.;
Elman, J. A. J. Org. Chem. 1997, 62, 2885–2893.
12. Narayanan, B. A.; Bunnelle, W. H. Tetrahedron Lett.
1987, 28, 6261–6264.
The allylation polymer (100 mg) was dissolved in
TBAF/THF solution (1.0 M, 3 mL) and heated at 60°C
for 24 h. The reaction mixture was diluted with ether
(50 mL) and washed with 2N aqueous HCl and brine,
dried over MgSO4 and concentrated. The crude product
was purified by flash column chromatography to give
homoallyl alcohol. The enantioselectivity was deter-
mined by HPLC analysis using a chiral stationary-
phase column. Isolated yields of homoallyl alcohol were
80–85% in all cases.
13. (a) Horner, H.; Hoffmann, H.; Klink, W.; Toscano, V.
G. Chem. Ber. 1962, 95, 581; (b) Wardsworth, Jr., W. S.;
Emmons, W. J. Am. Chem. Soc. 1961, 83, 1733–1738.
14. Ishihara, K.; Mouri, M.; Gao, Q.; Maruyama, T.;
Furuta, K.; Yamamoto, H. J. Am. Chem. Soc. 1993, 115,
11490–11495.
Acknowledgements
This work was supported by a Grant-in-Aid for Scien-
tific Research from the Ministry of Education, Science,
Sports and Culture.
15. Mashraqui, S. H.; Kellogg, R. M. J. Org. Chem. 1984,
49, 2513–2516.