Study on asymmetric syntheses of steroids: XIII. Synthesis of two new (±)-3-oxa-A-nor steroids 1a and 1b

This paper deals with the synthesis of two new (±)-3-oxa-A-nor steroids 1a and 1 b. The conjugated addition of 5′-methylfurandithane anion 8b to the CD-ring synthon 9 in HMPA-THF afforded 9, 10-seco-3-oxa-A-nor steroid 22. The intramolecular cyclization of 22 in acidic medium gave 23, which underwent hydrolytic desulfurization at elevated temperature in acidic medium to give 1b. The desulfurization of 23 over Raney nickel gave 1a.