Journal of the American Chemical Society
COMMUNICATION
Table 3. Catalytic Asymmetric Aziridination of an r-Unsub-
stituted r-Diazocarbonyl Compound and Ketiminesa
’ ACKNOWLEDGMENT
This work was partially supported by a Grant-in-Aid for
Scientific Research from the MEXT, Japan. T.H. is thankful for
a Grant-in-Aid for Young Scientists (B).
’ REFERENCES
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entry
R3
R4
% yieldc
% eed
1
2
3
4
5
6e
7
8
Ph
Ph
Ph
tBu
Et
6a
6b
6c
6d
6e
6f
89 (8a)
88 (8b)
81 (8c)
86 (8d)
89 (8e)
80 (8f)
92 (8g)
74 (8h)
95
92
90
90
98
91
92
84
Me
tBu
tBu
tBu
tBu
tBu
3-tolyl
4-tolyl
3-MeOC6H4
4-ClC6H4
2-Np
6g
6h
a Reactions were performed with N-Boc R-ketimino ester 6 (0.10 mmol)
and 7 (0.13 mmol) in the presence of 5 mol % (S)-3b (0.005 mmol).
b Determined by 1H NMR analysis of the crude material. c Isolated yield.
d Determined by chiral HPLC analysis. e Performed at ꢀ20 °C.
(8) (a) Hashimoto, T.; Naganawa, Y.; Maruoka, K. J. Am. Chem. Soc.
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Scheme 1. Hydrolytic Kinetic Resolution of the Trisubsti-
tuted Aziridine
(9) (a) Hashimoto, T.; Nakatsu, H.; Watanabe, S.; Maruoka, K. Org.
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(10) Our effort to apply chiral Lewis acid catalysts proved to be in
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because of the preferential coordination of oxophilic Lewis acids to the
Boc moiety (which is distant from the prochiral imine carbon) rather
than the nitrogen atom of the imine.
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bearing three different substituents,18 which had rarely been
accessible directly by any kind of catalytic asymmetric transfor-
mation. The proper choice of substrates, namely, N-R-diazoacyl
oxazolidinones and N-Boc imines, along with N-triflyl phosphor-
amide as the catalyst, was critical to implemention of this strategy.
The synthetic diversity of this aziridination could be broadened
by applying two substrate combinations having a complementary
set of substituents. In addition, hydrolytic kinetic resolution of
the aziridines was revealed, and this will be of interest for future
elaboration.19
’ ASSOCIATED CONTENT
(15) For chiral Brønsted acid-catalyzed desymmetrization of meso-
aziridines, see: (a) Rowland, E. B.; Rowland, G. B.; Rivera-Otero, E.;
Antilla, J. C. J. Am. Chem. Soc. 2007, 129, 12084. (b) Larson, S. E.; Baso,
J. C.; Li, G.; Antilla, J. C. Org. Lett. 2009, 11, 5186. Also see:
(c) Schneider, C. Angew. Chem., Int. Ed. 2009, 48, 2082 and references
therein.
S
Supporting Information. Experimental details and char-
b
acterization data for new compounds. This material is available
’ AUTHOR INFORMATION
(16) See the Supporting Information for details.
Corresponding Author
(17) Hydrolyzed products were not observed in the results show-
cased in Tables 2 and 3.
9732
dx.doi.org/10.1021/ja203901h |J. Am. Chem. Soc. 2011, 133, 9730–9733