LETTER
Highly Enantioselective Hydrogenation of a-Keto Esters
1171
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Table 2 Asymmetric Hydrogenantion of a-Keto Esters 6
O
OH
OR2
1 mol% 4c, MeOH
OR2
R1
R1
*
H2 (5 atm), r.t., 20 h
O
O
6
7
Entrya Substrate R1
R2
Yield
ee
(%)e
92
94
91
90
95
92
89
90
91
70
75
90
94
93
(%)f
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65, 2043.
1
6a
6b
6c
6d
6e
6f
Ph
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
97.1
94.5
94.1
84.6
93.2
92.4
96.4
95.5
95.0
95.5
96.0
95.3
95.8
94.1
2
p-F-C6H4
m-F-C6H4
o-F-C6H4
p-Cl-C6H4
p-Br-C6H4
p-Me-C6H4
p-MeO-C6H4
m-MeOC6H4
Me
3
4
5b
6b
7
6g
6h
6i
8
9
10
6j
11c
12c
13c
14d
6k
6l
i-Pr
t-Bu
Et
6m
6m
Ph(CH2)2
Ph(CH2)2
Et
Et
a All reactions went to 100% conversion.
b The reaction was performed at 50 °C and 50 atm for 15 h. 91.0% ee
and 90.5% ee were obtained for 6e and 6f, respectively, at r.t. and 5
atm for 20 h.
c EtOH was used as solvent.
d The reaction was carried out by using 0.1 mol% of the catalyst 5 at
50 °C and 50 atm for 48 h.
(7) Noyori, R. Acc. Chem. Res. 1990, 23, 345.
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M.; Heiser, B.; Schonholzer, P.; Hansen, H.-J. Helv. Chim.
Acta 1988, 71, 897.
e Isolated yields. For 6j and 6k lower yields were due to the volatility
of the reductive product.
f Enantiomeric excesses were determined by chiral GC; the configu-
ration of the products is S.
chiral building blocks for organic synthesis. Further stud-
ies of other transition metal complexes of these ligands
and their applications are in progress.
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S. C. J. Am. Chem. Soc. 2000, 122, 11531. (b) Benincori,
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Ratovelomanana-Vidal, V.; Genet, J. P.; Champion, N.;
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101, 5799.
Acknowledgment
This work was supported by National Institute of Health grants.
References and Notes
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