Photochemische Reaktionen 30. Mitteilung. Die UV.‐Bestrahlung von 3β‐Hydroxy‐11‐oxo‐lanostan

Upon irradiation of an ethanolic solution of 3β‐hydroxy‐11‐oxo‐lanostane(1) with ultraviolet light and subsequent acetylation of the crude reaction mixture, a single tertiary alcohol, the 11,18‐cyclobutanol derivative 4 , could be isolated in about 40% yield (corrected for recovered starting material). According to previous findings[4] and in contrast to this result, the steroidal 4,4‐dimethyl‐ketone 15 is exclusively converted into the 11,19‐cyclobutanol 16 . It is assumed that the additional methyl group in the 14α position of 1 causes this shift of the selective attack in the photo‐chemical cyclization process from CH 3 ‐19 to CH 3 ‐18.