Rearrangement of 18-iodo- and 20-iodopregnanes mediated by iodosyl derivatives

Conversion of 20-acetoxy-18-iodopregn-4-en-3-one 1 to the 18-iodosyl deriva tive by MCPBA resulted in a Wagner-Meerwein-type rearrangement with regiose lective migration of the C13-C17 bond to give, in high yield, an abeo-pregn ane in which C-18 was incorporated into ring D. The rearranged steroid was epoxidized in situ yielding a mixture of beta and alpha 13,14-epoxides (3 a nd 4) which were characterized spectroscopically and by X-ray crystallograp hy. When (20R)-20-iodopregn-4-en-3-one 9a was used as substrate, regioselec tive migration of the C16-C17 bond gave the D-homoandrostane with incorpora tion of C-20 into ring D in up to 95% yield. The 20S epimer 9b however, gav e a mixture of substitution and rearrangement products. The crystal structu res of the deacetylated beta -epoxide 3 (5), the methanolysis product of al pha -epoxide 4 (7) and 20-iodopregnanes 9a and 9b are reported.