The Crystal Structure of d,l-1,1,4aα-Trimethyl-2α-hydroxy-8α-acetoxy-1,2,3,4,4α,5,6,7,8,9-decahydrophenanthrene

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The conformation of d,l-1,1,4aα-trimethyl-2α-hydroxy-8α-acetoxy-1,2,3,4,4α,5,6,7,8,9-decahydrophenanthrene has been studied by means of X-ray methods. The crystals are triclinic, with two molecules in a unit cell with the dimensions of a=11.463, b=11.509, c=7.430 Å, α=84°42′, β=102°47′, and γ=115°40′. The space group is P\bar1. The intensity data were collected on an automatic four-circle diffractometer with CuKα radiation. The structure was solved by the symbolic-addition method, and was refined by the block-diagonal-matrix leastsquares method with anisotropic temperature factors for all the non-hydrogen atoms. From a difference Fourier map, all the 28 hydrogen atoms were also found. Further least-squares refinement including these hydrogen atoms reduced the R factor to 5.4%. In the present molecule, the cyclohexene ring has the normal half-chair conformation, and does not show the unusual behavior found in the p-bromobenzoate of 1,1,4aα-trimethyl-2α-hydroxy-8β-methoxy-1,2,3,4,4α,5,6,7,8,9-decahydrophenanthrene. The 8α-acetoxyl group, like the 8β-methoxyl group in the p-bromobenzoate, takes the axial orientation notwithstanding the inversion of the configuration. Such a conformation seems to be the preferred one for a cyclohexene ring which has a methoxyl or an acetoxyl group at the allylic position.
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