Opening of the Macrocyclic Ring in 5,10:8,9‐Disecosteroids ( = Steroklastanes)

Abstract

Catalytic hydrogenation of the Δ3‐unsaturated (9R,10 R)‐ and (9S,10 S)‐epoxyenol lactones 3a, b., and 4a, b., respectively, affords, in addition to the expected saturated epoxylactones 5a, b and 7a, b, also open‐chain products, i.e. the diastereoisomeric (9R,10R)‐ and (9S,10S)‐9,10‐expoxy‐8‐oxo‐4,5‐secosteroklastan‐5‐oic acids 6a, b. and 8a, b. Alkaline hydrolysis of the lactone ring of compounds 5 and 7 and subsequent acetylation of the corresponding hydroxy derivatives give as the major products the open‐chain, diasteroisomeric (9R,10R)‐ and (9S,10S)‐4‐acetoxy‐9,10‐epoxy‐methyl esters 9a, b and 11a, b, respectively, and, but only in the androstane series, the tetrahydropyran derivatives 10a and 12a, as the minor components.