Baeyer-Villiger oxidation of Δ⁴-3-Oxo-steroids and 4,5-Epoxy-3-oxo-steroids. A route to some novel A-nor-steroids

Abstract

Evidence is presented that the Baeyer-Villiger oxidation of Δ4-3-oxo-steroids yields enol-e-lactones which are further oxidized to β-epoxy-e-lactones. The latter are acid labile and rearrange to 5α-acyl-∂-lactones. The sequence appears to be stereospecific, and no 5β-acyl-∂-lactones could be isolated. Baeyer-Villiger oxidation of 4,5-epoxyoholestan-3-ones results in oxygen insertion between C3 and C4. The epoxy-e-lactones were not isolated, since they rearranged under the acidic conditions to give 5-acyl-4-oxacholestan-3-ones. The 5α-acyl epimers differ from the 5β-compounds, by undergoing an internal Claisen-type condensation to give A-norcholestans with a 2,5-lactone bridge. The photochemical, thermal, and boron trifluoride-catalysed conversion of the enol lactone (IIIa) into a-nor-5β-cholestan-3-one is reported.