Über Steroide und Sexualhormone. 223. Mitteilung. UV.‐Bestrahlung von 11‐Oxo‐Steroiden I Die Darstellung von 11β, 19‐Cyclo‐, 9β, 19‐Cyclo‐ und 19‐Hydroxy‐5α‐pregnan‐Verbindungen

A new two‐step process for the functionalisation of the non‐activated methyl group 19 of 5α‐steroids is described. In the first step UV.‐irradiation of the 11‐oxo‐5α‐pregnane derivate I in ethanol gives rise to a preferential attack of the photochemically excited carbonyl on methyl group 19, leading to the formation of the tertiary cyclobutanol compound II in high yield. The latter, upon treatment with lead tetraacetate in benzene solution, undergoes selective fragmentation of the photochemically formed C‐11β‐C‐19 bond furnishing the 19‐hydroxy‐11‐oxo‐5α‐ pregnane compound V.