Elemental fluorine: Part 22. Fluorination of 3β-acetoxy-5α-androstan-17-one using fluorine and Selectfluor®

Reactions of 3β-acetoxy-5α-androstan-17-one with elemental fluorine and Selectfluor® are reported and give contrasting results. Fluorine gives a mixture of mono-fluorinated steroids in which fluorine atoms are attached to tertiary carbon sites whereas Selectfluor® gives fluoro-steroid systems arising from electrophilic aliphatic substitution of the most sterically accessible secondary saturated positions. The identities of the fluoro-steroid products were determined by NMR analysis and X-ray crystallography.