a
Table 2 Cycloaddition of O-silyloximes 1 with BF
3
·OEt
2
consumed by the formation of complex C from the initial
cycloadduct B.14 The possibility of further coordination of
1
5
3 2
BF ·OEt with nitrone-oxygen of A cannot be ruled out.
We have developed the first intramolecular cycloaddition of
N-metallo-nitrones. Extension of this reaction to its inter-
molecular counterpart and application of the concept to a novel
asymmetric cycloaddition using a chiral Lewis acid are
currently under investigation.
This work was supported by NOVARTIS Foundation (Japan)
for the Promotion of Science.
Notes and references
Entry
Oxime
Time
Product
Yield (%)
3a,8
‡
For facile equilibration between 1 and 2, use of ZnCl
2
and reactions in
6c,7
polar solvents
have been examined.
1
2
3
4
5
a
1b
1c
1d
1 h
1 h
1 h
5 d
3b
3c
3d
87
80
92
73
38
§
Indeed, treatment of 3a with Cu(OTf)
2
in acetonitrile afforded a complex
mixture.
b
c
1e
3e
3e
1 R. Grigg, F. Heaney, J. Markandu, S. Surendrakumar, M. Thornton-Pett
and W. J. Warnock, Tetrahedron, 1991, 47, 4007.
2 N. P. Peet, E. W. Huber and R. A. Farr, Tetrahedron, 1991, 47, 7537.
3 (a) A. Hassner, R. Maurya and E. Mesko, Tetrahedron Lett., 1988, 41,
b
d
c
1e
5 d
Unless otherwise noted, all reactions were carried out with 2.1 equiv. of
b
c
d
BF
BF
3
·OEt
·OEt
2
in CH
was used.
2
Cl
2
at rt. E/Z = 1+1. Trans/cis = 1+1. One equiv. of
5
(
1
313; (b) A. Hassner and R. Maurya, Tetrahedron Lett., 1989, 30, 2289;
c) A. Hassner, R. Maurya, A. Padwa and W. H. Bullock, J. Org. Chem.,
991, 56, 2775; (d) A. Hassner, S. Singh, R. Sharma and R. Maurya,
3
2
Tetrahedron, 1993, 49, 2317; (e) A. Hassner, R. Maurya, O. Friedman,
H. E. Gottlieb, A. Padwa and D. Austin, J. Org. Chem., 1993, 58,
4
539.
4
5
6
A. Arnone, M. Cavicchioli, A. Donadelli and G. Resnati, Tetrahedron:
Asymmetry, 1994, 5, 1019.
J. E. Bishop, K. A. Flaxman, B. S. Orlek, P. G. Sammes and D. J. Weller,
J. Chem. Soc., Perkin Trans. 1, 1995, 2551.
(a) M. Gotoh, T. Mizui, B. Sun, K. Hirayama and M. Noguchi, J. Chem.
Soc., Perkin Trans. 1, 1995, 1857; (b) M. Gotoh, B. Sun, K. Hirayama
and M. Noguchi, Tetrahedron, 1996, 52, 887; (c) M. Noguchi, H.
Okada, S. Nishimura, Y. Yamagata, S. Takamura, M. Tanaka, A.
Kakehi and H. Yamamoto, J. Chem. Soc., Perkin Trans. 1, 1999, 185;
(d) M. Noguchi, H. Okada, M. Tanaka, S. Matsumoto, A. Kakehi and H.
Scheme 1
Yamamoto, Bull. Chem. Soc. Jpn., 2001, 74, 917.
U. Chiacchio, A. Corsaro, V. Pistara, A. Rescifina, G. Romeo and R.
Romeo, Tetrahedron, 1996, 52, 7875.
7
8
9
olefin moiety reflected into the product (Table 1, entry 4; Table
, entry 1), the present reaction seems not to be a stepwise
process via cation D but to be a concerted reaction via N-
3 2
borano-nitrone A. The second equivalent of BF ·OEt might be
A. Abiko, J.-F. Liu, G. Wang and S. Masamune, Tetrahedron Lett.,
2
1
997, 38, 3261.
S. Moutel and M. Shipman, Synlett, 1998, 1333; P. J. Dransfield, S.
Moutel, M. Shipman and V. Sik, J. Chem. Soc., Perkin Trans. 1, 1999,
3
349.
1
1
1
0 M. Frederickson, R. Grigg, M. Thornton-Pett and J. Redpath, Tetra-
hedron Lett., 1997, 38, 7777.
1 For related N-silylazomethine ylides, see: K.-I. Washizuka, S. Mina-
kata, I. Ryu and M. Komatsu, Tetrahedron, 1999, 55, 12969.
3 2
2 For related deprotection of O-trimethylsilylethyl group with BF ·OEt ,
see: K. Jansson, T. Frejd, J. Kihlberg and G. Magnusson, Tetrahedron
Lett., 1986, 27, 753.
3 For Lewis acid-mediated Michael addition of oximes to a,b-unsaturated
ketones, see: I. S. Saba, M. Frederickson, R. Girigg, P. J. Dunn and P.
C. Levett, Tetrahedron Lett., 1997, 38, 6099; K. Nakama, S. Seki and S.
Kanemasa, Tetrahedron Lett., 2001, 42, 6719.
1
1
4 D. G. Hall, C. Laplante, S. Manku and J. Nagendran, J. Org. Chem.,
1
999, 64, 698.
5 N. Katagiri, M. Okada, Y. Morishita and C. Kaneko, Chem. Commun.,
996, 2137; N. Katagiri, M. Okada, Y. Morishita and C. Kaneko,
Tetrahedron, 1997, 53, 5725.
1
1
Scheme 2
CHEM. COMMUN., 2002, 1128–1129
1129