Asymmetric hydroesterification of styrene using catalysts with planar-chiral ferrocene oxazoline ligands

Article abstract of DOI:10.1016/S0957-4166(03)00455-5

Chiral P,N-ferrocene ligands, 1-diphenylphosphino-1′-[(S)-4-isopropyl-2.5-oxazolinyl]-2′-(S _p)-(trimethylsilyl)-ferrocene and its diastereomer, and 1-diphenylphosphino-1′-[(S)-4-isopropyl-2.5-oxazolinyl]-2′(S _p)-(diphenylphosphino)-ferrocene and its diastereomer were used in the palladium-catalyzed asymmetric hydroesterification of styrene. The role of these ligands, which contain central, axial, and planar chirality, on the stereochemical outcome was investigated. A significant effect of using CuCl₂ as a co-catalyst on the reaction was observed. Excellent regioselectivity (b/n >99:1) with low ee (28%) was obtained in the presence of CuCl₂; moderate enantioselectivity (64% ee) but low regioselectivity (b/n, 40/60) was obtained in the absence of CuCl₂.

Full text of DOI:10.1016/S0957-4166(03)00455-5

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 2291–2295
Asymmetric hydroesterification of styrene using catalysts with
planar-chiral ferrocene oxazoline ligands
Lailai Wang,a,b Wai Him Kwok, Albert S. C. Chan,a,* Tao Tu,c Xuelong Houc,* and Lixin Daic
aOpen Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis,
and Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong, China
bState Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, China
cLaboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, China
Received 15 May 2003; accepted 4 June 2003
Abstract—Chiral P,N-ferrocene ligands, 1-diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxazolinyl]-2%-(Sp)-(trimethylsilyl)-ferrocene
and its diastereomer, and 1-diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxazolinyl]-2%(Sp)-(diphenylphosphino)-ferrocene and its
diastereomer were used in the palladium-catalyzed asymmetric hydroesterification of styrene. The role of these ligands, which
contain central, axial, and planar chirality, on the stereochemical outcome was investigated. A significant effect of using CuCl2
as a co-catalyst on the reaction was observed. Excellent regioselectivity (b/n >99:1) with low ee (28%) was obtained in the presence
of CuCl2; moderate enantioselectivity (64% ee) but low regioselectivity (b/n, 40/60) was obtained in the absence of CuCl2.
© 2003 Elsevier Ltd. All rights reserved.
1. Introduction
taining central, axial, and planar chirality has not
been reported for this reaction. As illustrated in
Scheme 1, ligand 1 itself has no planar chirality on
the ferrocene backbone. However, its coordination to
The hydroesterification of vinyl aromatics produces
valuable intermediates for perfumes and pharmaceuti-
cals. For example, the production of 2-arylpropionic
acids, which constitute an important class of non-
steroidal anti-inflammatory drugs (e.g. ibuprofen and
naproxen),1 is a scientifically interesting and poten-
tially useful pursuit. Over the past three decades,
excellent progress on asymmetric hydrogenation has
been made. In contrast the progress on the asymmet-
ric hydroesterification of vinyl aromatics is still lim-
ited. Hayashi’s pioneering work using Pd(dba)2-
neomenthyldiphenylphosphine-trifluoroacetic acid in
the asymmetric hydroesterification of a-methyl-
styrene showed moderate ee (42% ee; b/n=94:6;
dba=dibenzylideneacetone).2 Recently, Inoue et
al. used a chiral ferrocene ligand containing amino-
a
metal center gives rise to two diastereomeric
complexes 2 and 3, due to the opposite twists of the
Cp rings in the ligand.4 It is worth noting that by
introducing planar chirality to ligand 1 and through its
coordination to a metal center, three kinds of chiral
elements (namely central, axial, and planar chirality)
exist in one catalyst.
In this study, we investigated the role of central, axial,
and planar chirality on the palladium-catalyzed asym-
metric hydroesterification of styrene by using the new
planar-chiral ferrocenyl oxazoline ligands (S,Sp)-
1, (SRp)-1, (S,Sp)-2, and (S,Rp)-2 (Fig. 1). In the
meantime, the effects of different palladium sources
and the use of CuCl2 as a co-catalyst on the reaction
were also studied. Excellent regioselectivity (b/n,
>99:1) was obtained in the presence of CuCl2 as a
co-catalyst albeit with only 28% ee. In contrast, mod-
erate enantioselectivity (64% ee) but low regioselectiv-
ity (b/n, 40/60) was obtained in the absence of CuCl2.
phosphine,
(S)-1-[(R)-1%,2-bis(diphenylphosphino)-
ferrocenyl]ethyldimethylamine, (S,Rp)-BPPFA (Fig. 1)
in the reaction and achieved high ee (86%) but rather
low yield and regioselectivity.3 Chiral ligands con-
* Corresponding author. E-mail: bcachan@polyu.edu.hk
0957-4166/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0957-4166(03)00455-5

2292
L. Wang et al. / Tetrahedron: Asymmetry 14 (2003) 2291–2295
Figure 1.
zoline were working in concert to preferentially generat-
ing the (R)-product (Table 1, entries 11 and 15).
2. Results and discussion
The hydroesterification of styrene is shown in Scheme
2. Enantiomeric branched ester (b) is the desired
product while the linear ester (n) is considered to be a
byproduct. The effects of different reaction conditions
on the hydroesterification of styrene using CO and
methanol are summarized in Table 1.
Wan et al. reported that polymer-supported PVP–
PdCl2–4CuCl2–PPh3 bimetallic system [PVP=poly(N-
vinyl-2-pyrrolidone)] was effective for the hydro-
esterification of styrene with CO and methanol, and the
addition of CuCl2 was essential for obtaining higher
regioselectivity in the corresponding reaction.12 Lee et
al. studied the effects of promoters and reaction condi-
tions on the regioselectivity of palladium complex-cata-
lyzed hydroesterification of 4-methylstyrene and found
that PdCl2–CuCl2–PPh3 dissolved in a nonpolar solvent
provided nearly regiospecific conversion to the
branched ester in high rates at 100°C and under 41 bar
of CO pressure.13 In this study we found that in the
Chiral P,N-ligands have been proved to be effective in
several metal-catalyzed asymmetric reactions.5–8 Von
Matt and Pfaltz,9a Sprinz and Helmchen,9b and Daw-
son et al.9c established that the oxazoline center chiral-
ity of bidentate P,N-ligands furnishes exceptional
stereocontrol in palladium-catalyzed allylic alkylations
(up to 99% ee). Ahn10a,b and Helmchen11 reported that
the central chirality of the oxazoline subunit, not the
planar-chirality, is the primary determinant factor of
the stereochemical outcome of alkylation catalyzed by
Pd complexes.
In the present study we also found that the central
chirality of the oxazoline subunit, not the planar-chiral-
ity, was the primary determinant factor for the enan-
tioselectivity (Table 1, entries 1–5).
Ligand (S,Sp)-1 gave moderate enantioselectivity (45%
ee) with a regioselectivity (b/n) of 79/21 (Table 1, entry
3), while ligand (S,Rp)-1 gave the best regioselectivity
(b/n, >99/1) (Table 1, entries 4 and 5). A comparison of
the results of using ligand (S,Sp)-2 and (S,Rp)-2 clearly
showed that the enantioselectivity of the catalyst was
predominantly influenced by the planar-chirality of the
ferrocene unit, and the central chirality of oxazoline
was a minor factor. The higher ee from the reaction
using ligand (S,Rp)-2, relative to that from the reaction
using ligand (S,Sp)-2, indicated that for ligand (S,Rp)-2
the planar-chirality and the central-chirality of the oxa-
Scheme 1.

L. Wang et al. / Tetrahedron: Asymmetry 14 (2003) 2291–2295
2293
Scheme 2.
Table 1. Asymmetric hydroesterification of styrene using PdCl2–CuCl2–ligands–p-toluenesulfonic acid systema
Entry
Ligands
Cu/Pd (M/M)
Conv.b (%)
Yieldb (%)
b/nb
Ee (abs. conf.)b
1
2
3
4
5
6
7
8
(S,Sp)-1
(S,Sp)-1
(S,Sp)-1
(S,Rp)-1
0/1
3/1
5/1
3/1
5/1
0/1
1/1
3/1
5/1
0/1
3/1
5/1
0/1
3/1
5/1
68
72
37
16
12
>99
>99
94
84
>99
92
62
63
33
8.2
5.7
>99
>99
93
81
>99
91
61
74
38/62
89/11
79/21
>99/1
>99/1
29/71
43/57
58/42
70/30
16/84
39/61
40/60
23/77
65/35
69/31
22 (R)
42 (R)
45 (R)
12 (R)
28 (R)
63 (S)
40 (S)
16 (S)
9.0 (S)
10 (S)
38 (S)
36 (S)
37 (R)
43 (R)
48 (R)
(S,Rp)-1
(S,Rp)-BPPFA
(S,Rp)-BPPFA
(S,Rp)-BPPFA
(S,Rp)-BPPFA
(S,Sp)-2
(S,Sp)-2
(S,Sp)-2
(S,Rp)-2
(S,Rp)-2
9
10
11
12
13
14
15
63
74
14
5.8
14
5.8
(S,Rp)-2
a Reaction conditions: 25 mL, 0.225 mmol styrene; 2 mg PdCl2 (0.01125 mmol); 21.5 mg toluenesulfonic acid (0.1125 mmol); 6.25 mg ligands
(0.01125 mmol); 1.0 mL methanol; 1.0 mL 1.4-dioxane; 1800 psi CO; reaction temperature=80°C; reaction time=20 h.
b The data on conversion and yields of the asymmetric hydroesterification products were determined by GC–MS on a Bexs column (30 m×0.25
mm I.D.) using acetophenone as an internal standard. The enantiomeric excess of the chiral product was determined by GC with a Chrompack
Chirasil-Dex CB column (50 m×0.25 mm I.D.). The absolute configuration of methyl 2-phenylpropionate was determined by the comparison of
the retention time with that of a pure authentic sample.
absence of copper salt, both the branched/linear ratio
and the ee of branched product were substantially
lower when ligands (S,Sp)-1, (S,Rp)-2, and (S,Sp)-2
were used (Table 1, entries 1, 10, and 13). It is worth
noting that by increasing the molar ratio of copper(II)
to palladium(II) from 0/1 to 5/1 brought about a
marked decrease in the conversion and a significant
increase in regioselectivity and enantioselectivity (Table
1, entries 1–3; 4–5; 10–12; 13–15). This effect was in
sharp contrast with the (S,Rp)-BPPFA ligand system,
in which the addition of copper salt lowered the
product ee (Table 1, entries 6–9). It appeared that the
Pd/Cu mixed metal catalyst system exhibited a synergis-
tic effect, although the role of CuCl2 is still not fully
understood.
The effect of using different palladium precursors is
shown in Table 2. When PdCl2(NCPh)2 was used as the
catalyst precursor in the absence of copper salt, ligand
(S,Rp)-2 gave similar conversion and yield but poorer
Table 2. Asymmetric hydroesterification of styrene using different palladium catalyst precursors–CuCl2–ligands–p-toluenesul-
fonic acid systema
Entry
Pd source
Ligand
Cu/Pd (M/M)
Conv.b (%)
Yieldb (%)
B/nb
Eeb (conf.)
1
2
3
4
5
6
7
8
PdCl2
(S,Rp)-2
(S,Rp)-2
(S,Sp)-2
(S,Sp)-2
(S,Sp)-2
(S,Rp)-2
(S,Rp)-2
(S,Rp)-2
0/1
0/1
0/1
3/1
5/1
0/1
3/1
5/1
14
14
70
10
13
17
11
6.3
14
8.1
70
10
13
17
11
6.3
40/60
46/54
39/61
65/35
64/36
36/64
54/46
59/41
64 (R)
35 (R)
34 (R)
20 (S)
22 (S)
14 (S)
33 (R)
44 (R)
PdCl2(NCPh)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
a Reaction conditions: 12.5 mL, 0.1125 mmol styrene; 0.00225 mmol Pd source; 4.28 mg toluenesulfonic acid (0.0225 mmol); 1.50 mg ligands
(0.00225 mmol); 0.25 mL methanol; 0.25 mL 1,4-dioxane; 2500 psi CO; reaction temperature=50°C; reaction time=20 h.
b The data on conversion and yield, the enantiomeric excess, and the assignment of absolute configuration of the chiral product was determined
using the same conditions as noted in Table 1.

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L. Wang et al. / Tetrahedron: Asymmetry 14 (2003) 2291–2295
enantioselectivity in comparison to the reaction using
PdCl2 as catalyst precursor (Table 2, entries 1–2). In
the case of Pd(acac)2 as catalyst precursor in the
absence of copper salt, ligand (S,Sp)-2 provided a
moderate asymmetric induction of 34% ee (R) at high
conversion and yield with low regioselectivity (b/n=
39/61, Table 2, entry 3).
ters. Elemental analyses were performed on a Foss-
Heraeus Vario EL instrument.
1 - Diphenylphosphino - 1% - [(S) - 4 - isopropyl - 2.5 - oxa-
zolinyl]-2%(Sp)-(trimethylsilyl)-ferrocene (S,Sp)-1 and 1-
diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxazolinyl]-2%
(Rp)-(trimethylsilyl)-ferrocene (S,Rp)-1 were synthe-
sized according to a previously published methods.4b
It is interesting to note that by increasing the molar
ratio of copper(II) and palladium(II) to 3/1, higher
regioselectivity (b/n) of 65/35 with opposite enantiose-
lectivity was observed (Table 2, entry 4). A slight
improvement of enantioselectivity and regioselectivity
were achieved by increasing the Cu/Pd molar ratio to
5/1 (Table 2, entry 5), but with substantial decrease
in conversion and yield. In the case of Pd(OAc)2/
(S,Rp)-2 as catalyst precursor in the absence of cop-
per salt, the asymmetric induction decreased markedly
to 14% ee (S) and low regioselectivity (b/n) of 39/61
was obtained (Table 2, entry 6). By increasing the
Cu/Pd molar ratio to 3/1, an opposite enantioselectiv-
ity of 33% ee (R) and an enhanced regioselectivity
(b/n) of 54/46 were observed (Table 2, entry 7). Slight
improvements in enantioselectivity and regioselectivity
were achieved by increasing the Cu/Pd molar ratio to
5/1, but with a decrease in the catalytic activity of the
system (Table 2, entry 8).
4.2. 1-Diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxa-
zolinyl]-2%-(Sp)-(diphenylphosphino)ferrocene, (S,Sp)-2
1-Diphenylphosphino-1%-[(S)-isopropyl-2.5-oxa-
zolinyl]ferrocene (0.240 g, 0.5 mmol, synthesized
according to a previously published methods4b) was
dissolved in anhydrous Et2O (6 mL) under a nitrogen
at room temperature, TMEDA (0.1 mL, 0.7 mmol)
was added to the solution using a syringe. n-BuLi
(0.4 mL, 0.64 mmol, 1.6 M in hexane) was then
slowly added to the mixture at −78°C. After stirring
for 2 h, Ph2PCl (0.14 mL, 0.8 mmol) was added and
the mixture was stirred at 0°C for 20 min. The reac-
tion was monitored by TLC and the mixture was
quenched using saturated NaHCO3 and extracted by
Et2O. The extract was washed by brine and dried
using anhydrous Na2SO4. The solvents were removed
and the residue was purified by column chromatogra-
phy (10:1 petroleum ether/AcOEt). Yellow solid of
(S,Sp)-2 (0.230 g, 68% yield) was obtained. [h]2D0=−
65.5 (c 0.15, CHCl3). 1H NMR: l=0.64 (d, J=6.8
Hz, 3H), 0.80 (d, J=6.8 Hz, 3H), 1.63 (m, 1H), 3.44
(m, 1H), 3.70 (t, J=8.2 Hz, 1H), 3.80–3.91 (m, 1H),
3.96 (s, 1H), 4.18–4.30 (m, 3H), 4.48–4.51 (m, 2H),
4.92 (t, J=1.2 Hz, 1H), 7.17–7.48 (m, 20H) ppm. 31P
NMR: l=−16.49 (s, 1P), −17.28 (s, 1P) ppm. MS
m/z (relative intensity) 666 (M+, 100), 480 (70.4), 393
(38.6), 183 (39.6), 171 (44.8). IR (KBr) 2955, 1658,
1478, 1433, 1026, 980, 741, 695, 498 cm−1. Anal.
calcd for C40H37NOP2Fe: C, 72.19; H, 5.60; N, 2.11.
Found: C, 72.10; H, 5.60; N, 1.94.
3. Conclusion
It has been demonstrated in this study that palla-
dium-catalyzed asymmetric hydroesterification of sty-
rene using new planar-chiral ferrocenyl oxazoline
ligands (S,Sp)-1, (S,Rp)-1, (S,Sp)-2, and (S,Rp)-2
exhibit high regioselectivity and moderate asymmetric
induction. In addition, the use of CuCl2 as a co-cata-
lyst enhances the regioselectivity (b/n) of this reaction.
4. Experimental
4.3. 1-Diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxa-
zolinyl]-2%(Rp)-(diphenylphosphino)-ferrocene, (S,Rp)-2
4.1. Reagents and materials
PdCl2(NCPh)2, Pd(OAc)2, PdCl2, and Pd(acac)2 were
purchased from Aldrich and were used without fur-
ther purification. Styrene and methanol were distilled
and degassed with dry N2 before use. The enan-
tiomerically pure ligand (S,Rp)-BPPFA was pur-
chased from Aldrich. The other commercially
available reagents were used as received without fur-
ther purification. 1H NMR and 31P NMR were
recorded on a Varian AS 500 at room temperature.
1H NMR spectra are reported in ppm with TMS as
an internal standard (l=0 ppm). 31P NMR spectra
are reported in ppm with 85% H3PO4 as an external
(S,Sp)-1 (0.276 g, 0.5 mmol) was dissolved in anhy-
drous THF (4 mL) under nitrogen at room tempera-
ture, n-BuLi (0.4 mL, 0.64 mmol, 1.6 M in hexane)
was then slowly added to the mixture at −78°C. After
stirring for 2 h, Ph2PCl (0.13 mL, 0.7 mmol) was
added and the mixture was stirred at 0°C for 20 min.
The reaction was monitored by TLC and the mixture
was quenched with water and extracted by Et2O. The
extract was washed by brine and dried using anhy-
drous Na2SO4. The solvents were removed and the
residue was purified by column chromatography (30:1
petroleum ether/AcOEt). 1-Diphenylphosphino-1%-[(S)-
4-isopropyl-2.5-oxazolinyl]-2%(Rp)-(diphenylphosphino)-
5%-(trimethylsilyl)ferrocene (0.538 g, 73% yield) was
obtained as an orange solid. [h]2D0=192.7 (c 0.51,
CHCl3). 1H NMR: l=0.30 (s, 9H), 0.56 (d, J=6.7
Hz, 3H), 0.63 (d, J=6.7 Hz, 3H), 1.42 (m, 1H), 3.25
(d, J=2.4 Hz, 1H), 3.72–4.05 (m, 4H), 4.21 (d,
reference. Optical rotations were recorded on
a
Perkin–Elmer 241 MC polarimeter with a thermally
jacketed 10 cm cell at 25°C. IR spectra were recorded
in KBr and measured in inverse centimeters, using a
Shimadzu IR-440 infrared spectrophotometer. Mass
spectra were taken using HP 5989A mass spectrome-

L. Wang et al. / Tetrahedron: Asymmetry 14 (2003) 2291–2295
2295
J=6.7 Hz, 1H), 4.36 (s, 1H), 4.42 (s, 1H), 4.74 (s, 1H),
7.02–7.24 (m, 20H). MS m/z (relative intensity) 737
(M+, 100.0), 694 (16.7), 660 (23.1), 652 (28.9). IR (KBr)
2954, 1650, 1478, 1433, 1244, 1160, 994, 836, 740, 695
cm−1. Anal. calcd for C43H45NOSiP2Fe: C, 70.01; H,
6.15; N, 1.89. Found: C, 70.06; H, 6.30; N, 1.84.
mined by the comparison of the retention time with
those of pure authentic samples.
Acknowledgements
We thank the University Grants Committee Area of
Excellence Scheme in Hong Kong (AoE P/10-01), and
The Hong Kong Polytechnic University ASD Fund for
financial support of this study.
1-Diphenylphosphino-1%-[(S)-4-isopropyl-2.5-oxazo-
linyl] - 2%(Rp) - (diphenylphosphino) - 5% - (trimethylsilyl)-
ferrocene (0.074 g, 0.1 mmol) was dissolved in anhy-
drous THF (1 mL) under nitrogen, TBAF (1 mL, 1
mmol, 1.0 M in THF) was then added and the mixture
was stirred under reflux for 5 h. The reaction was
monitored by TLC and the mixture was quenched with
water and extracted by Et2O. The extract was washed
by brine and dried using anhydrous Na2SO4. The sol-
vents were removed and the residue was purified by
column chromatography (10:1 petroleum ether/AcOEt).
Yellowish orange solid of (S,Rp)-2 (0.066 g, 98% yield)
References
1. (a) Ishihara, K.; Nakashima, D.; Hiraiwa, Y.;
Yamamoto, H. J. Am. Chem. Soc. 2003, 125, 24–25; (b)
Acemoglu, L.; Williams, J. M. J. J. Mol. Catal. A: Chem.
2003, 196, 3–11.
2. Hayashi, T.; Tanaka, M.; Ogata, I. Tetrahedron Lett.
1
was obtained. [h]2D0=161.0 (c 0.16, CHCl3). H NMR:
1978, 41, 3925–3926.
l=0.61 (d, J=6.2 Hz, 6H), 1.55 (m, 1H); 3.47 (m, 1H),
3.85–4.05 (m, 4H), 4.16 (t, J=2.5 Hz, 1H), 4.26 (m,
1H), 4.50 (t, J=1.8 Hz, 2H), 4.87 (m, 1H), 7.1–7.50 (m,
20H) ppm. 31P NMR: l=−17.38 (s, 1P), −17.70 (s, 1P)
ppm. MS m/z (relative intensity) 665 (M+, 100.0), 622
(16.33), 588 (13.7), 518 (13.7), 480 (32.4), 305 (15.2). IR
(KBr) 2955, 1657, 1478, 1433, 1027, 981, 742, 695, 487
cm−1. Anal. calcd for C40H37NOP2Fe: C, 72.19; H, 5.60;
N, 2.11. Found: C, 72.14; H, 5.80; N, 2.22.
3. Oi, S.; Nomura, M.; Aiko, T.; Inoue, Y. J. Mol. Catal. A:
Chem. 1997, 115, 289–295.
4. (a) Zhang, W.; Yoneda, Y.; Kida, T.; Nakatsuji, Y.;
Ikeda, I. Tetrahedron: Asymmetry 1998, 9, 3371; (b)
Deng, W. P.; You, S. L.; Hou, X. L.; Dai, L. X.; Yu, Y.
H.; Xia, W.; Sun, J. J. Am. Chem. Soc. 2001, 123,
6508–6519.
5. Kim, S. G.; Cho, C. W.; Ahn, K. H. Tetrahedron 1999,
55, 10079–10086.
6. Shintani, R.; Fu, G. C. Org. Lett. 2002, 4, 3699–3702.
7. Hayashi, T.; Hayashi, C.; Uozumi, Y. Tetrahedron:
Asymmetry 1995, 6, 2503–2506.
4.4. General procedure for the asymmetric hydroester-
ification of styrene
8. Malone, Y. M.; Guiry, P. J. J. Organomet. Chem. 2000,
630, 110–115.
A 50 mL stainless steel autoclave was charged with
z-toluenesulfonic acid, a chosen source of palladium
salt, ligand, styrene, and methanol under an atmo-
sphere of N2. The autoclave was pressurized with CO
and heated to the desired reaction temperature. The
reaction mixture was stirred well with a magnetic stir-
rer. After a prescribed reaction time, the autoclave was
cooled to room temperature and the residue gas was
released. The data on conversion and yield were deter-
mined by GC-MS using acetophenone as an internal
standard on an HPG 1800c GCD system on a Bexs
column (30 m×0.25 m I.D.). The enantiomeric excess of
the product was determined by GC using an HP5890
gas chromatograph equipped with a Chrompack Chi-
rasil-Dex CB column (50 m×0.25 mm). The absolute
configuration of methyl 2-phenylpropionate was deter-
9. (a) Von Matt, P.; Pfaltz, A. Angew. Chem., Int. Ed. Engl.
1993, 32, 566–568; (b) Sprinz, J.; Helmchen, G. Tetra-
hedron Lett. 1993, 34, 1769–1772; (c) Dawson, G. J.;
Frost, C. G.; Williams, J. M. J.; Coote, S. J. Tetrahedron
Lett. 1993, 34, 3149–3150.
10. (a) Ahn, K. H.; Cho, C.-W.; Park, J.; Lee, S. Tetra-
hedron: Asymmetry 1997, 8, 1179–1185; (b) Ahn, K. H.;
Cho, C.-W.; Park, J.; Lee, S. Bull. Korean Chem. Soc.
1997, 18, 789–791.
11. Kudis, S.; Helmchen, G. Angew. Chem., Int. Ed. 1998, 37,
3047–3050.
12. Wan, B. S.; Liao, S. J.; Xu, Y.; Y, D. R. J. Mol. Catal.
A: Chem. 1998, 136, 263–268.
13. Yun, H. S.; Lee, K. H.; Lee, J. S. J. Mol. Catal. A: Chem.
1997, 95, 11.