3 ISOMERS OF TRICYCLO[10.3.0.0(4,9)]PENTADECANE-2,10-DIONE, (I), (II)AND (III), AND Y-9-METHYLTRICYCLO-[9.3.0.0(3,7)]TETRADECAN-2-ONE, (IV)

The crystal structures of the four title compounds, which were obtaine d during studies of the preparation and reactions of 6-8-5 and 5-8-5 f used-ring compounds, have been determined by X-ray diffraction. (I), ( II) and (III) are cis-cisoid-cis, trans-cisoid-cis and trans-transoid- cis isomers of the 6-8-5 fused-ring compound, respectively. The eight- membered ring takes a boat-chair form in compounds (I) to (IV).