Lam et al.
907
Table 5. Recycling and reuse of Ru-(R)-P-Phos catalyst for
Typical procedure for asymmetric hydrogenation
asymmetric hydrogenation of methyl actoacetate in ionic liquids.a
A mixture of [bmim][BF4] (0.5 mL) and MeOH (0.5 mL)
was added into a glass-lined stainless-steel autoclave con-
taining methyl acetoacetate (26.7 mg, 0.23 mmol) and
[Ru((R)-P-Phos)Cl2] (18.8 mg, 0.023 mmol) in a drybox un-
der a nitrogen atmosphere. After purging the autoclave with
hydrogen gas several times, the final pressure of the hydro-
gen was adjusted to 1000 psi (1 psi = 6.894 757 kPa), and
the reaction mixture was stirred at room temperature. After
20 h, the hydrogen gas was released, and the product was
extracted with hexane and passed through a small column of
silica gel. The organic volatiles were removed under reduced
pressure to obtain the desired product. The conversion was
Entry
RTIL
Run
eeb (%)
Conv.c (%)
1
2
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][BF4]
[bmim][PF6]
1
2
3
4
5
6
7
8
9
1
>99
98
97
96
95
95
93
94
94
98
>99
87
3
78
4
71
5
62
6
56
7
52
8
33
1
9
39
then assessed based on the H NMR analysis, while the ee
value was determined by GLC using a chiral column.
10
>99
11
12
[bmim][PF6]
[bmim][PF6]
2
3
98
97
99
96
Acknowledgements
13
14
15
16
17
18
[bmim][PF6]
[bmim][PF6]
[bmim][PF6]
[bmim][PF6]
[bmim][PF6]
[bmim][PF6]
4
5
6
7
8
9
97
96
96
96
94
94
96
93
86
78
57
49
We thank the University Grants Committee Area of Excel-
lence Scheme in Hong Kong (Project No. AoE/P-10/01), the
Hong Kong Polytechnic University Area of Strategic Devel-
opment Fund, and the National Natural Science Foundation
of China (No. 20418002) for financial support.
aAll the reactions were carried out with 1 mol% catalyst under 1000 psi
H2 in a 50:50 mixture of RTIL and MeOH at room temperature for 20 h.
bThe ee values (%) were determined by GC on a Supelco γ-Dex 225
column.
References
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1
cThe conversions were determined by H NMR analysis.
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We have developed an efficient Ru-P-Phos catalyst for the
asymmetric hydrogenation of α- and β-keto esters in RTILs
with high conversions and ee values up to >99%. The cata-
lyst was recycled and reused with the reasonable retention of
activity and enantioselectivity.
Experimental
General information
All manipulations with air-sensitive reagents were carried
out under a dry nitrogen atmosphere using standard Schlenk
techniques or in a nitrogen-filled MBRAUN Lab Master 130
glovebox. The hydrogenation reactions were performed in a
stainless-steel autoclave from the Parr company.[bmim][BF4]
and [bmim][PF6] were prepared according to the literature
method (17). Following vacuum drying at 80 °C for 8 h, the
ionic liquid was stored under nitrogen at ambient tempera-
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synthesized based on our previous reports (14). Other chem-
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© 2005 NRC Canada