2468
M. Ga6rilan et al. / Tetrahedron Letters 42 (2001) 2465–2468
be a convenient method to test the redox properties of
these new compounds.
OH and Ph are in a trans relationship, (with respect to
the endoperoxidic cycle) and the Me (in position 11) is
oriented in the anisotropy cone of the phenyl group. For
compound 7b no such effect appeared and a cis relation-
1
References
ship between the OH and Ph groups is proposed. 7a H
NMR (250 MHz, CDCl3): l=7.67 (s, 1H, CꢁCH), 7.34
(m, 5H, Ar), 3.80 (s, OH), 1.64 (s, 3H, CH3 in position
15), 1.41 (s, 3H, CH3 in position 14), 1.37 (s, 3H, CH3 in
position 13), 1.24 (s, 3H, CH3 in position 12), 0.74 (s, 3H,
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210.7 (C9), 198.6 (C7), 141.6 (C5), 141.4, 128.6, 128.1,
125.6 (Ar); 132.4 (C6), 97.5 (C1), 82.3 (C4), 55.0 (C8),
51.9 (C10), 26.7 (C14), 26.2 (C15), 24.3 (C13), 20.6 (C11),
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1H, CꢁCH), 7.40 (m, 5H, Ar), 3.70 (s, OH), 1.87 (s, 3H,
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1
partial assignment of H and 13C spectra, whereas differ-
entiation between methyls in each gem-dimethyl groups
was based on NOESY spectra, as well as determination
of the stereochemistry of each diastereomer 7a, 7b. Fur-
thermore, a shielding effect (Dl=0.39 ppm) on one of the
methyl groups and a deshielding effect on the ethylenic
proton were observed for the major compound 7a and
they have been attributed to the anisotropy of the phenyl
group; these results agree with a configuration in which
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F. J. Am. Chem. Soc. 1997, 119, 9541.
.