Preparation of cis-fused 3,3a,8,12b-tetrahydro-2h-dibenzo[3,4:6,7]cyclohepta[1,2-b]furan derivatives

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 C1-3 alkylcarbonyl;
• R1 is hydrogen and OR2 is a leaving group, or
• OR1 is a leaving group and
• R2 is hydrogen;
• and
• the substituents —OR and —CH2—CHOR1—CH2OR2 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 C1-3alkylcarbonyl;
• R1 is hydrogen and OR2 is a leaving group, or
• OR1 is a leaving group and R2 is hydrogen;
• and the substituents —OR and —CH2—CHOR1—CH2OR2 have the cis configuration,
• in a reaction inert solvent in the presence of a base, whereby
• (ent-II-a) yields (1-d),
• (ent-II-b) yields (1-c),
• (ent-II-c) yields (1-b), and
• (ent-II-d) yields (1-a).