Conformation of epi-α-Cyperone and Related Enones
The conformations of epi-a-cyperone (10-epieudesma-4,ll-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 NMR, 13C NMR, and high-field NMR techniques. Comparison of these spectral data with those of the normal eudesmane derivatives, -cyperone (1), dihydro-a-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. ll-Methyl-10-epieudesm-4-en-3-one (5) was prepared either from 5a-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-llmethyl- 10-epieudesm-4-en-3-one (15) was prepared by the annulation of 2-methyl-5-fert-butylcyclohexanone with methyl vinyl ketone. The 13C lanthanide induced shift and high-field 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 11-equatorial tert-butyl group. Crystals of the oxime of 5 belong to the triclinic system, space group PI, with a = 6290 (3) A, b = 12.010 (5) A, c = 10.341 (5) A, α = 85.20 (2)°, β = 95.56 (2)°, γ = 101.09 (2)°, and Z = 2. Atomic positional and thermal parameters were refined by least-squares calculations to R = 0.068 over 1609 observed reflections measured by a diffractometer. © 1980, American Chemical Society. All rights reserved.
Huffman, JW; Swain, WE; Jacobus, J; McPhail, AT
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