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

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.