C. Bo¨rner et al. / Tetrahedron Letters 42 (2001) 327–329
329
O
O
O
O
NaOH
or
or
Et
Et2O
H
Et
CHO
OH
n
Et
Et
n
6
4a n = 0
4b n = 1
4c n = 2
7
5a n = 0
5b n = 1
Scheme 3. Base-promoted cyclisations.
suggest that linear enones bind this particular catalyst
in an anti-s-cis arrangement prior to 1,4-delivery of the
ethyl nucleophile. Finally, we note that the product
aldehydes derived from 1i–h are useful precursors in
simple base-promoted cyclisations (Scheme 3).§ In all
cases the thermodynamic product is favoured, e.g. 6 is
formed from 4c instead of the expected 7-ring product.
By running the reaction of at 0°C some aldol product 7
may be isolated as a single syn diastereomer from 4b;
but the majority of the species readily looses water
fashioning 5b.
Engl. 1997, 36, 187–204. (c) Feringa, B. L. Acc. Chem.
Res. 2000, 33, 346–353.
2. Alexakis, A.; Benha¨ım, C.; Fournioux, X.; van der
Heuvel, A.; Leveˆque, J.-M.; March, S.; Rosset, S. Synlett
1999, 1811–1813.
3. Bennett, S. M. W.; Brown, S. M.; Muxworthy, J. P.;
Woodward, S. Tetrahedron Lett. 1999, 40, 1767–1770.
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Dennis, M. R.; Muxworthy, J. P.; Oakley, M. A.; Wood-
ward, S. Tetrahedron 2000, 56, 2847–2856.
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401.
6. Krauss, S. R.; Smith, S. G. J. Am. Chem. Soc. 1981, 103,
141–148.
Acknowledgements
7. Ullenius, C.; Christenson, B. Pure Appl. Chem. 1988, 60,
57–64.
We thank the EPSRC for support of this project
through grants GR/M75341, GR/M84909, GR/N37339
and for access to their Mass Spectrometry Service
(University of Swansea). S.W. is grateful to the EU for
support through the COST (working groups D12/0009/
98 and D12/0022/99).
8. Vellekoop, A. S.; Smith, R. A. J. J. Am. Chem. Soc. 1994,
116, 2902–2913.
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mon: Oxford, 1991; Vol. 1, Chapter 1.10, pp. 283–353.
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§ Diethyl ether solutions of 4 (2.0 mL of a 0.08 M solution, 0.16
mmol) were stirred with NaOH (2.0 mL of 1% w/w aq. solution) at
ambient temperature. Normal extractive workup followed by flash
chromatography afforded 5–6 in (80–87% yield). Reaction of 4b at
0°C afforded 7 together with 5b.