T. Ooi et al. / Tetrahedron Letters 45 (2004) 1675–1678
1677
40% MeNH2
in MeOH
O
O
O
H
H
1) 1 N HCl/THF, r.t., 2 h
BocN
BocN
N
Ph2C
OEt
NHMe
OEt
2) (Boc)2O, sat. NaHCO3
/THF, r.t., 30 min
r.t., 8 h
H
H
H
α-Np
α-Np
α-Np
7
6
3b [R = CH2(α-Np)]
quant.
98% (97% ee)
(97% ee)
O
H
H
DIBAH
BocN
toluene
—78 °C, 2 h
H
α-Np
8
95% (97% ee)
O
O
O
H
H
BocN
H
(Boc)2O, NaHCO3
DIBAH
H2N
Me
BocN
OEt
Ph
OEt
Ph
THF
r.t., 12 h
toluene
—78 °C, 2 h
Me
97%
Me
Ph
9
5b (R = CH2Ph)
81% (98% ee)
(98% ee)
Scheme 3.
2689; (e) OÕDonnell, M. J. Aldrichim. Acta 2001, 34, 3; (f)
Maruoka, K.; Ooi, T. Chem. Rev. 2003, 103, 3013.
2. Effect of ester group on the enantioselectivity has been
documented. See: (a) OÕDonnell, M. J.; Bennett, W. D.;
Wu, S. J. Am. Chem. Soc. 1989, 111, 2353; (b) Chinchilla,
(Boc)2O afforded 6 quantitatively, which was readily
transformed into the corresponding secondary amide 7
by simple treatment with excess methyl amine in meth-
anol and a-amino aldehyde 8 with DIBAH in toluene,6
respectively, without loss of enantiomeric excesses.
Similarly, optically active a,a-dialkyl-a-amino ester 5b
(R ¼ CH2Ph) can be converted to the corresponding
stereochemically stable a-amino aldehyde 9 in excellent
chemical yield.6;7
ꢀ
R.; Mazon, P.; Najera, C. Tetrahedron: Asymmetry 2000,
11, 3277, See also Ref. 3b.
ꢀ
3. (a) Ooi, T.; Takeuchi, M.; Kameda, M.; Maruoka, K.
J. Am. Chem. Soc. 2000, 122, 5228; (b) Ooi, T.; Kameda,
M.; Maruoka, K. J. Am. Chem. Soc. 2003, 125, 5139; (c)
Ooi, T.; Uematsu, Y.; Maruoka, K. J. Org. Chem. 2003,
68, 4576; See also: (d) Ooi, T.; Kameda, M.; Maruoka, K.
J. Am. Chem. Soc. 1999, 121, 6519; (e) Ooi, T.; Kameda,
M.; Tannai, H.; Maruoka, K. Tetrahedron Lett. 2000, 41,
8339; (f) Ooi, T.; Doda, K.; Maruoka, K. Org. Lett. 2001,
3, 1273; (g) Ooi, T.; Takeuchi, M.; Maruoka, K. Synthesis
2001, 1716; (h) Ooi, T.; Uematsu, Y.; Maruoka, K. Adv.
Synth. Catal. 2002, 344, 288; (i) Ooi, T.; Uematsu, Y.;
Kameda, M.; Maruoka, K. Angew. Chem., Int. Ed. 2002,
41, 1551; (j) Ooi, T.; Takahashi, M.; Doda, K.; Maruoka,
K. J. Am. Chem. Soc. 2002, 124, 7640; (k) Ooi, T.;
Taniguchi, M.; Kameda, M.; Maruoka, K. Angew. Chem.,
Int. Ed. 2002, 41, 4542; (l) Ooi, T.; Tayama, E.; Maruoka,
K. Angew. Chem., Int. Ed. 2003, 42, 579; (m) Ooi, T.;
Miki, T.; Taniguchi, M.; Shiraishi, M.; Takeuchi, M.;
Maruoka, K. Angew. Chem., Int. Ed. 2003, 42, 3796.
4. 2a and 2b have often been employed in the transition
metal-catalyzed asymmetric allylic alkylations. For recent
selected examples, see: (a) You, S.-L.; Hou, X.-L.; Dai,
L.-X.; Cao, B.-X.; Sun, J. Chem. Commun. 2000, 1933; (b)
Trost, B. M.; Dogra, K. J. Am. Chem. Soc. 2002, 124,
7256; (c) Kanayama, T.; Yoshida, K.; Miyabe, H.;
Kimachi, T.; Takemoto, Y. J. Org. Chem. 2003, 68, 6197.
5. The 3,4,5-trifluorophenyl group as 3,30-substituents (Ar) is
crucial to attain excellent level of enantioselectivity as
demonstrated by the following results of the allylation
of 2a; Ar ¼ b-Np: 91%, 85% ee (0 °C, 1 h); Ar ¼ 3,5-Ph2-
C6H3: 87%, 92% ee (0 °C, 1 h). This tendency is similar to
that observed with tert-butyl glycinate benzophenone Schiff
base [2 (Ak ¼ t-Bu)]3b.
In summary, we have shown that the efficient chiral
phase-transfer catalysis of (S,S)-1 enables highly enan-
tioselective alkylation of methyl and ethyl esters of
N-protected a-amino acids under mild conditions,
greatly expanding the scope of this well-elaborated
asymmetric methodology. Facile conversion of the
resulting a-alkylated a-amino esters to the correspond-
ing optically active a-amino amides and aldehydes rep-
resents the usefulness of this method.
Acknowledgements
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
References and notes
1. For recent reviews, see: (a) Shioiri, T. In Handbook of
Phase-Transfer Catalysis; Sasson, Y., Neumann, R., Eds.;
Blackie Academic & Professional: London, 1997, Chapter
14; (b) OÕDonnell, M. J. In Catalytic Asymmetric Synthe-
sis; Ojima, I., Ed.; 2nd ed.; Wiley-VCH: New York, 2000,
Chapter 10; (c) Shioiri, T.; Arai, S. In Stimulating
Concepts in Chemistry; Vogtle, F., Stoddart, J. F.,
Shibasaki, M., Eds.; Wiley-VCH: Weinheim, 2000; p 123;
6. For the vast synthetic utility of optically active a-amino
aldehydes, see: (a) Tramontini, M. Synthesis 1982, 605; (b)
Jurczak, J.; Golebiowski, A. Chem. Rev. 1989, 149; (c)
Blaser, H.-U. Chem. Rev. 1992, 92, 935; (d) Ager, D. J.;
Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96, 835;
ꢀ
(d) Abellan, T.; Chinchilla, R.; Galindo, N.; Guillena,
G.; Najera, C.; Sansano, J. M. Eur. J. Org. Chem. 2000,
ꢀ