[Study on asymmetric synthesis of steroids. XVI. Synthesis of dl-3-oxa-A-nor steroid]

A synthesis of racemic 3-oxa-A-nor steroid, 8, is reported. The conjugated addition of anion 5 of 5'-methylfuryl dithiane with 4, an intermediate formed from the racemic dionesulfone 3 afforded 6, which was converted to 7 by cyclization under acidic condition. Desulfurization of 7 with tri-n-bu-tyltin hydride gave the title compound 8, which is an intermediate of the target molecule 1b.