CRYSTAL-STRUCTURES OF 4,11-PREGNADIENE-3,20-DIONE AND 21-METHYL-20-OXA-4-PREGNENE-3,20-DIONE

The structures of the title compounds were solved by direct methods an d refined by anisotropic full-matrix least-squares methods. 4,11-Pregn adiene-3,20-dione, C21H28O2 (1) crystallizes in the monoclinic space g roup P2(1) (Z = 2). The unit cell parameters a, b, c (Angstrom), and b eta (degrees) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). The A- a nd C-rings exhibit intermediate sofa-half-chair conformations. The B-r ing has a chair conformation and the D-ring assumes an intermediate en velope-half-chair conformation. The progesterone side chain has a typi cal conformation; the C16-C17-C20-O20 torsion angle is - 15.1(4)degree s. 21-Methyl-20-oxa-4-pregnene-3,20-dione, C21H30O3 (2) crystallizes i n the orthorhombic space group P2(1)2(1)2(1) (Z = 4) The unit cell par ameters a, b, c (Angstrom) were: 12.926(2), 19.447(4), 7.313(1), The p rogesterone side chain has an unusual conformation; the C16-C17-C20-O2 0 torsion angle is 174.6(4)degrees. The A-ring has a 1 alpha,2 beta-ha lf-chair conformation, rings B and C exhibit chair conformations and r ing D is in a 13 beta,14 alpha-half-chair conformation.