4, 4-Dimethyl Effect. (3). The Ring A Conformation of 4, 4-Dimethyl-Δ⁷-3-keto Steroids and 4, 4, 8-β-Trimethyl-3-keto Steroids (3-Keto-triterpenoids). The Crystal Structure of Serratenedione

Abstract

Single crystals of serratenedione grown in methanol are orthorhombic, a=14.506, b=10.558, c=16.296 Å, U=2495.8 ų, D_c=1.17 g/cm³, Z=4, with space group P2₁2₁2₁. The structure, solved by use of the MULTAN program, revealed the conformation of the compound to be as follows : ring A, deformed boat ; B, chair ; C, chair-like ; D, half-chair ; and E, distorted chair. Circular dichroism (CD) spectra of 4, 4-dimethyl-3-keto steroids with Δ⁷ or an 8β-methyl group are discussed in connection with the above results.