Abstract
A small amount of 3β, 20β-diacetoxy-9 (8→7)-abeo-5α-pregn-7 (9)-ene-8, 11-dione (4), a compound with a 6-5-7-5 ring system, was formed in the alumina catalyzed cyclization of 3β, 20β-diacetoxy-8, 9-seco-5α-pregnane-8, 9, 11-trione (1). As it was not at first possible to isolate 4 in a pure state, the structure was deduced from a derivative, the saturated ketone (10), the structure of which was confirmed by its synthesis from the known glycol monomesylate (9b) with a 6-6-6-5 ring system by means of the pinacolic type rearrangement. Later, the compounds (4a, b) were obtained by cyclization of 1 with silica gel followed by alumina treatment and all the features of the reaction were clarified. The stereochemistry of the ketone (10) and its derivatives was also discussed.
