The Photocycloaddition of Olefins to Unsaturated 3‐Ketosteroids

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Abstract
Photoadditions of ethylene and of cyclopentene to Δ4 ‐ and Δ4,6‐3‐ketosteroids gave mixtures of cis‐4α,5α and trans‐4α. 5β adducts. In the case of cyclopentene and Δ4,6‐androstadiene‐3‐one‐17β‐ol propionate, only the trans adduct was observed. Cis‐4β,5β adducts were obtained by base‐catalyzed isomerization of the trans adducts. The ratio of cis:trans adducts varied considerably with solvent, temperature, and olefin concentration in steroid reactions but not in reactions with cyclohexenone. The different types of adducts exhibited markedly different ORD curves in agreement with the structures assigned. Carbonyl maxima of trans adducts appeared at shorter wavelengths than maxima of cis adducts in both infrared and ultraviolet spectra. The infrared shifts provide a convenient method for differentiating between cis and trans fused isomers.