X. Chaminade et al. / Tetrahedron Letters 49 (2008) 2384–2387
2387
6. Arisawa, M.; Yamaguchi, M. Org. Lett. 2000, 3, 311–312.
obtained in 74–82% yields as approximately 1:1 mixtures
(entries 7 and 8).
7. Narasaka, K.; Kitamura, M. Eur. J. Org. Chem. 2005, 4505–4519;
Kitamura, M.; Mori, Y.; Narasaka, K. Tetrahedron Lett. 2005, 46,
2373–2376.
8. Arnesto, D.; Austin, M. A.; Griffiths, O. J.; Horspool, W. M.;
Carpintero, M. Chem. Commun. 1996, 2715–2716.
To explain the cyclisation regioselectivity, an electro-
philic attack of the oxime proton on the double bond, after
its activation by complexation to the highly electrophilic
Al3+, can be proposed. The acidity of the oxime proton
should be strongly enhanced by Al(OTf)3, as in the case
of the cyclisation of unsaturated alcohols.4
9. Ruck-Braun, K.; Freysoldt, T. H. E.; Wierschem, F. Chem. Soc. Rev.
¨
2005, 34, 507–516.
10. Gothelf, K. V.; Jørgensen, K. A. Chem. Rev. 1998, 98, 863–
909.
In conclusion, this work presents the use of alumin-
ium(III) triflate as an efficient catalyst in the cycloisomeri-
sation of non-activated olefinic oximes. The reaction is
completely regiospecific and allows the formation of differ-
ently substituted cyclic 1,2-oxaza derivatives such as oxa-
zepines, oxazines and oxazolines in good yields with
oximes bearing di- and trisubstituted double bonds. The
cyclisation follows a Markovnikov-type addition of the
oxime–O–H group on the double bond.
11. Kobayashi, S.; Akiyama, R. Tetrahedron Lett. 1998, 39, 9211–
9214.
12. Tamura, O.; Mitsuya, T.; Huang, X.; Tsutsumi, Y.; Hattori, S.;
Ishibashi, H. J. Org. Chem. 2005, 70, 10720–10725.
13. Bishop, R.; Hawkins, S. C.; Quobuyen, T. A. O.; Brooks, P. R.
Tetrahedron Lett. 1988, 29, 6805–6808.
14. Grimaldi, J.; Cormons, A. Tetrahedron Lett. 1985, 26, 825–828.
15. Procedure for cycloisomerisation of oximes, 1: Al(OTf)3 (0.2 mmol)
was added under nitrogen to freshly distilled solvent (5 mL) and the
solution heated to reflux. The oxime (1 mmol, neat) was introduced
and the solution stirred for the reported time. After complete
consumption (or negligible evolution, GC analysis), the reaction
mixture was quenched with aqueous 0.1 M HCl solution and
extracted with Et2O. The organic layers were dried over MgSO4,
concentrated under vacuum and purified by column chromatography
on silica-gel, using hexane/Et2O mixtures (95:5 to 80:20) as eluents.
Compounds 2 were obtained as colourless liquids and were chara-
cterised by 1H and 13C NMR and by mass spectrometry. Spectral data
for 2a, 7,7-dimethyl-3-(2-phenylethyl)-4,5,6,7-tetrahydro-1,2-oxa-
zepine, as a representative example: 1H NMR (500 MHz): d 7.27–
Acknowledgement
We thank the French Ministry of Education for a
doctoral scholarship to X.C.
References and notes
3
3
3
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7.07 (m, 5H), 2.96 (dd, J = 7.2, J = 7.7 Hz, 2H), 2.74 (dd, J = 7.2,
3J = 7.7 Hz, 2H), 2.41 (t, 3J = 6.4 Hz, 2H), 1.87–1.78 (m, 2H), 1.66–
1.55 (m, 2H), 1.49 (s, 6H). 13C NMR (125 MHz): d 158.73, 141.06,
128.90, 128.74, 126.52, 66.12, 37.47, 35.06, 31.30, 30.45, 27.49, 16.02.
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