45. The Enantioselective Synthesis of 3-Methoxy-1, 3, 5 (10)-estratrien-11, 17-dione by a Thermal Intramolecular Cycloaddition Reaction. Preliminary communication
    Oppolzer, W.; Bättig, K.; Petrzilka, M.
    Helv. Chim. Acta 1978, 61, 1945-1947

The enantiomerically pure (+)-3-methoxy-1, 3, 5 (10)-estratrien-11, 17-dione 11 (with trans-anti-trans configuration) was synthesized in a highly stereocontrolled fashion from (±)-t-butyl 4-methoxy-1-benzocyclobutene carboxylate (8) and the (+)-carboxylic acid 6, obtained from4 in two steps, followed by one crystallization of the (+)-ephedrine salt. The key step 10→11(Scheme 2) involves a thermal intramolecular cycloaddition reaction.

DOI : 10.1002/hlca.19780610535