Photochemische Reaktionen 42. Mitteilung [1]. Photoisomerisierung von α, β‐Epoxyketonen II Der sterische Verlauf der Umlagerung von 3‐Oxo‐4, 5‐oxido‐Steroiden

The photorearrangement previously described [3] of saturated and Δ1‐unsaturated 3‐oxo‐4,5‐epoxy‐10β‐steroids to 3,5‐dioxo‐10(5 →4)‐abeo compounds proceeds most likely via a radical 1,2‐alkyl shift (Chart 1). The similar rearrangements of the related 10α‐epoxyketone 10 and the 4‐methyl‐epoxyketones 13, 15, 16, 20 and 21 to the corresponding 3,5‐diketones occurred without epimerization at the migrating carbon atom (C‐10) and the site of substitution (C‐4) (Chart 3). The stereochemical control of the rearrangement is in agreement with the earlier proposed mechanism of a concerted alkyl radical shift in these alicyclic systems.