Synthesis of 2-(16,17-Epoxy-3β,20-dihydroxypregn-5-en-20-yl)-1,3-dithiane from Diosgenin

–2-(16,17-Epoxy-3β,20-dihydroxypregn-5-en-20-yl)-1,3-dithiane, a new promising synthon for the OSW-1 aglycone and its analogs, was synthesized from diosgenin. In an alternative approach, a low-temperature version of the decyclization of the diosgenin F-ring by the action of the Et 3 SiOTf –(CF 3 CO) 2 O–CH 2 Cl 2 system was implemented to obtain pseudodiosgenin bis-trifluoroacetate, which was then transformed in the key block.