Chemistry Letters 2001
255
introduction of methoxy group was effective to enhance the
enantioselectivity up to 97% ee (Entry 3). When (S,S)-DIPT
was used as a chiral auxiliary instead of (R,R)-DIPT, (S)-enan-
tiomer of the product was obtained enantioselectively (Entry 4).
The asymmetric addition to p-methoxy substituted imines 1d–f
was also carried out to furnish the corresponding β-amino acid
esters 3d–f with excellent enantioselectivity up to 98% ee
(Entries 5–7).6
way for the enantioselective synthesis of both enantiomers of β-
amino acids.
The present work was partially supported by Mitsubishi
Chemical Corporation Fund and Grant-in-Aid for Scientific
Research from the Ministry of Education, Science, Sports, and
Culture.
References and Notes
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2
a) H. Ishitani, M. Ueno, and S. Kobayashi, J. Am. Chem.
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The absolute configuration of the compound 3c (97% ee)
was confirmed to be R by comparing the specific rotation of the
3
4
5
Direct asymmetric Mannich reaction was recently reported;
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Asymmetry, 11, 733 (2000).
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25
corresponding N-deprotected β-amino acid ester 4 ([α]D
+21.4° (c 0.18, CHCl3)) with that of the known (R)-4 (lit.,2l
23
96% ee; [α]D +22.4° (c 1.05, CHCl3)). The stereochemistry
of 3a was also determined to be R by transformation into (R)-4
[1) MeI, Na2CO3, 72%. 2) CAN, 39%].2a The absolute config-
urations of 3b,d–f were tentatively assigned to be R.
6
All new β-amino acid ester derivatives 3 were character-
ized by H NMR spectra, IR spectra, and elemental analy-
1
ses or MS spectra.
7
8
R. J. Herold, S. L. Aggarwal, and V. Neff, Can. J. Chem.,
41, 1368 (1963).
The enhancement of the enantioselectivity by addition of
water in the conjugate addition of diethylzinc to enones
with copper catalyst involving chiral ligand was reported;
G. Delapierre, T. Constantieux, J. M. Brunel, and G.
Buono, Eur. J. Org. Chem., 2000, 2507.
As described above, a new type of asymmetric Mannich-
type reaction has been developed. Because of easy availability
of (R,R)- and (S,S)-DIPT, the present method provides a useful