On reactions of steroidal 23-oxo and 23,24-epoxysapogenins with Lewis acids

The reaction of 23-oxotigogenin acetate with TMSOTf in THF afforded the corresponding bisnorcholanic lactone in 60% yield. The analogous reactions carried out in dichloromethane or benzene gave the rearranged products—the isomeric spirostanic ketone (10–15%) and bisfuran (40–42%). Similar products were also obtained upon treatment of 23,24-epoxysapogenins with BF3. The epoxides treated with TiCl4 afforded mostly chlorohydrins and no rearranged products were detected.