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 and refined by anisotropic full-matrix least-squares methods. 4,11-Pregnadiene-3,20-dione, C₂₁H₂₈O₂ (1) crystallizes in the monoclinic space group P2₁ (Z = 2). The unit cell parameters a, b, c (Å), and β (°) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). The A-and C-rings exhibit intermediate sofa-half-chair conformations. The B-ring has a chair conformation and the D-ring assumes an intermediate envelope-half-chair conformation. The progesterone side chain has a typical conformation; the C16-C17-C20-O20 torsion angle is -15.1(4)°. 21-Methyl-20-oxa-4-pregnene-3,20-dione, C₂₁H₃₀O₃ (2) crystallizes in the orthorhombic space group P2₁2₁2₁ (Z = 4). The unit cell parameters a, b, c (Å) were: 12.926(2), 19.447(4), 7.313(1). The progesterone side chain has an unusual conformation; the C16-C17-C20-O20 torsion angle is 174.6(4)°. The A-ring has a 1α,2β-half-chair conformation, rings B and C exhibit chair conformations and ring D is in a 13β,14α-half-chair conformation.