Conformation of Epi-α-cyperone and Related Enones

Article abstract of DOI:10.1021/jo01303a031

The conformations of epi-α-cyperone (10-epieudesma-4,11-dien-3-one, 2) and its dihydro and 14-nor analogues (4 and 15, respectively) have been investigated by a combination of lanthanide induced shift reagent 1H NMR, 13C NMR, and high field 1H NMR techniques.Comparison of these spectral data with those of the normal eudesmane derivatives, α-cyperone (1), dihydro-α-cyperone (3), and 14-noreudesm-4-en-3-one (14) clearly shows that the conformations of all six enones are similar with a half-chair conformation for ring A and a chair conformation for ring B.11-Methyl-10-epieudesm-4-en-3-one (5) was prepared either from 5α-hydroxy-10-epieudesm-11-en-3-one (6) or by the Robinson annulation of 2-methyl-5-tert-butylcyclohexanone with ethyl vinyl ketone. 14-Nor-11-methyl-10-epieidesm-4-en-3-one (15) was prepared by the annulation of 2-methyl-5-tert-butylcyclohexanone with methyl vinyl ketone.The 13C lanthanide induced shift and high-field 1H NMR spectra of enones 5 and 13 indicate that these molecules are not conformationally homogeneous.An X-ray structure determination of the oxime of enone 5 showed that in the solid state ring A exists in a envelope conformation and ring B in a twist conformation with a ψ-equatorial tert-butyl group.Crystals of the oxime of 5 belong to the triclinic system, space group P1, with a = 6.290(3) Angstroem, b = 12.010(5) Angstroem, c = 10.341(5) Angstroem, α = 85.20(2) deg, β = 95.56(2) deg, γ = 101.09(2) deg, and Z=2.Atomic positional and thermal parameters were refined by least-squares calculation to R = 0.068 over 1609 observed reflections measured by a diffractometer.