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 groupP2₁ (Z=2). The unit cell parametersa, b, c (Å), and (°) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). TheA- andC-rings exhibit intermediate sofa-halfchair conformations. TheB-ring has a chair conformation and theD-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 groupP2₁2₁2₁ (Z=4). The unit cell parametersa, 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)°. TheA-ring has a 1, 2-half-chair conformation, ringsB andC exhibit chair conformations and ringD is in a 13,14-half-chair conformation.