Patent ID: 7205335

Claim:
A process for preparing each individual diastereoisomer of formula (I): wherein the substituents on carbon atoms 3a and 12b have the cis configuration, the substituent on carbon atom 2 may have the R or the S configuration, comprising the step of cyclizing a compound of formula (II) wherein R represents C 1-3 alkylcarbonyl; R 1 is hydrogen and OR 2 is a leaving group, or OR 1 is a leaving group and R 2 is hydrogen; and the substituents —OR and —CH 2 —CHOR 1 —CH 2 OR 2 have the cis configuration, in a reaction inert solvent in the presence of a base, whereby alternatively cyclizing a compound of formula wherein R represents C 1-3 alkylcarbonyl; R 1 is hydrogen and OR 2 is a leaving group, or OR 1 is a leaving group and R 2 is hydrogen; and the substituents —OR and —CH 2 —CHOR 1 —CH 2 OR 2 have the cis configuration, in a reaction inert solvent in the presence of a base, whereby (ent-II-a) yields (I-d), (ent-II-b) yields (I-c), (ent-II-c) yields (I-b), and (ent-II-d) yields (I-a).