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Acid-induced decomposition of rigid polycyclic py-unsaturated diazomethyl ketones (2a and b) and (4a and b) is shown to give, in excellent yields, the respective angularly fused unsaturated cyclobutanones (5a and b) and (6a and b) and/or the rearranged bridged hydroxycyclopentanones (7a) and (9a) depending upon the reagents, reaction conditions, and the nature of the substrates. Under certain conditions (5a) and (7a) undergo rearrangement to 3a-methyl-l,2,3,3a,6,7-hexahydropentaleno[l,6a-aJnaphthalen-4-one (1 2a). The unsaturated cyclobutanones undergo stereoselective catalytic hydrogenation to the respective trans-angularly substituted hydrophenanthrene and hydrofluorene cyclobutanones (13a and b) and (14a and b) which on facile gayer-Villiger oxidation produce the y-lactones (18a and b) and (1 9a and b). The unsaturated cyclobutanones (5a and b) also afford the respective y-lactones (20a and b) on oxidation with alkaline hydrogen peroxide. * For application of this reaction for the preparation of a D-norsteroidal skeleton see ref. 9.
Reductive cleavage of the bridged hydroxycyclopentanones (I) followed by Jones oxidation proceeds with retention of configuration to give the ketones (II); (IIb) is also obtained with better yield along with its epimer (III) by catalytic hydrogenolysis of (Ib).
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