.alpha.-Heptacyclene 6b,6c,12b,12c-Tetrahydrocyclobuta[1,2-a:3,4-a']diacenaphthylene 7259-03-2 Cyclobuta[1,2-a:3,4-a']diacenaphthylene, 6b,6c,12b,12c-tetrahydro- NSC149615