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J. M. Castro et al.
LETTER
Tetrahedron: Asymmetry 2009, 20, 1637. (b) Snowden,
In conclusion, it has been found that the cyclic enol ether
(+)-sclareol oxide (6) can be efficiently converted into the
g-lactone (+)-sclareolide (1) under the usual experimental
conditions of the Baeyer–Villiger oxidation. When a lim-
ited amount of peroxy acid was added to 6 it was possible
to isolate hemiketal 8, which is one likely intermediate in
the proposed reaction pathway. It has also been found that
when the reaction media was deliberately left acidic, the
g-lactone 1 was formed as a single product, while the use
of buffers increases the amount of the related g-hydroxy-
acid 7a. To our knowledge, the direct conversion of a six-
membered cyclic enol ether into a g-lactone has never
been described before. This procedure offers a facile path-
way to prepare products related to 1, and further efforts
have to be made in order to know the general scope of this
reaction.
R. L. Chemistry & Biodiversity 2008, 5, 958.
(16) Recent examples: (a) Wei, J.; Wu, Y.; Shi, X.; Zhang, Y.
CN 1,683,352, 2005; Chem. Abstr. 2006, 145, 145522.
(b) Igarashi, K.; Takizawa, S.; Higaki, N.; Hagiwara, H.
JP 2007222110, 2007; Chem. Abstr. 2007, 147, 299478.
(17) Recent example: Álvarez-Manzaneda, E.; Chahboun, R.;
Cabrera, E.; Álvarez, E.; Haïdour, A.; Ramos, J. M.;
Álvarez-Manzaneda, R.; Hmamouchi, M.; Es-Samti, H.
Chem. Commun. 2009, 592.
(18) (a) Barrero, A. F.; Altarejos, J.; Álvarez-Manzaneda, E. J.;
Ramos, J. M.; Salido, S. J. Org. Chem. 1996, 61, 2215.
(b) Barrero, A. F.; Altarejos, J.; Álvarez-Manzaneda, E. J.;
Ramos, J. M.; Salido, S. Tetrahedron 1993, 49, 6251.
(c) Barrero, A. F.; Altarejos, J.; Álvarez-Manzaneda, E. J.;
Ramos, J. M.; Salido, S. Tetrahedron 1993, 49, 9525.
(d) Barrero, A. F.; Altarejos, J.; Álvarez-Manzaneda, E. J.;
Ramos, J. M. ES 2,044,780, 1994; Chem. Abstr. 1994, 120,
299025. (e) Barrero, A. F.; Altarejos, J.; Salido, S. ES
2,069,469, 1995; Chem. Abstr. 1995, 123, 257086.
(f) Barrero, A. F.; Sánchez, J. F.; Álvarez-Manzaneda, E. J.;
Altarejos, J.; Muñoz, M.; Haïdour, A. Tetrahedron 1994, 50,
6653; see also ref. 23b.
Supporting Information for this article is available online at
(19) Castro, J. M.; Salido, S.; Altarejos, J.; Nogueras, M.;
Sánchez, A. Tetrahedron 2002, 58, 5941.
(20) (a) Cocker, J. D.; Halsall, T. G.; Bowers, A. J. Chem. Soc.
1956, 4259. (b) Cocker, J. D.; Halsall, T. G. J. Chem. Soc.
1956, 4262.
(21) Acid traces present in commercial CDCl3 were capable of
transforming 5 into 6 during the NMR experiments.
Previous neutralisation of the deuterated solvent was
necessary.
Acknowledgment
We wish to thank the Junta de Andalucía for general financial sup-
port, and the Spanish Ministerio de Educación, Cultura y Deporte
for a fellowship to J. M. Castro. We also want to thank the Centro
de Instrumentación Científico-Técnica of the University of Jaén for
technical support in spectroscopy and spectrometry.
(22) Gerke, T.; Bruns, K. DE 3,942,358, 1991; Chem. Abstr.
References and Notes
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(23) Other oxidants normally yield mixtures of products 7 and 1
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Synlett 2010, No. 18, 2747–2750 © Thieme Stuttgart · New York