Stereochemical Studies of Unsaturated Acetyl Steroids

The configuration and rotameric conformation of a number of β,γ-unsaturated acetyl steroids were established using ultraviolet absorption and circular dichroism data. It was found that the 4β-acetyl-5-ene system (in 6) and the 6β-acetyl-4-ene system (in 1 and 3) can be regarded as inherently disymmetric chromophores. On the other hand, the analogous β,γ-unsaturated acetyl group in 6α-acetyl-4-ene derivatives (2 and 9), 4β-acetyl-4α-methylandrost-5-en-3-on-17β-ol acetate (5), and also in 2β-acetyl-2α-methylandrost-5-en-17β-ol acetate (8), does not possess this characteristic. This conclusion facilitates the assignment of the configuration and conformation to the acetyl group and rings A and B in these compounds. The stereochemistry of alkylation of Δ4-3-keto steroids was determined using as a basis the configuration at C-4 of 4β-acetyl-4α-methylandrost-5-en-17β-ol (6).