Pentacyclo [5.3. 0.~.~ 10.0@] decane-5, 9-dione (7). Compound 7 was synthesized by the following reaction sequence: 1, 4-dioxaspiro [4.4] nonane, 2, bp 152-155 OC (lit. bp 153 OC)'O was syntheaized in 90% yield via reaction of cyclopentanone with ethylene glycol in the presence of p-toluenesulfonic acid (benzene solvent).'O Bromination of 2 with bromine (2 equiv) in dry dioxane at 10-15 OCll afforded the corresponding dibromide 3 (55%), mp ...