The Enantioselective Synthesis of 3‐Methoxy‐1, 3, 5 (10)‐estratrien‐11, 17‐dione by a Thermal Intramolecular Cycloaddition Reaction. Preliminary communication

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 from 4 in two steps, followed by one crystallization of the (+)‐ephedrine salt. The key step 10→11 (Scheme 2) involves a thermal intramolecular cycloaddition reaction.