22. 11. 7 2 ) Summary. Two isotneric 2,4,6,8-tetrabrorno-cycIooctanc-lI 5-diones (8a and 8b) arc formed in the tetrabromination of cyclooctane-l,5-dione (7). Treatment of a mixture of 8a and 8 b with triethylamine gives rise to anti-1,3-dibromo-bishomoquinone (9), which is reduced with zinc to anti-bishomoquinone (4) in a 65% overall yield. Either 8a or 8b. when heated with copper powder in a high vacuum, affords 1-bromo-(11) and 1,3-dibromo-anti-bishomoquinone (9), anti-bishomoquinone (4) itself as well as its syn-isomer ( 5 ) . T h c anti-configuration was assigned t o 4 on the basis of its reduction t o two dials, one of which showed NMR. cuupling of its two isochronic carbinol protons with one cis-vicinal proton and one trans-vicinal proton. Spectral data of the compounds are discussed. Of particular interest is the inversion of the chemical shifts of exoand endo-mcthylene protons when comparing the XMR.-spectra of untiand s?i7z-bishonioquinone.Einleitung. -Polycyclische Systeme mit gespannten Ringen sind wegen der starren Anordnung ihrer Atome oft besonders geeignet zum Studium der Strukturabhangigkeit von physikalischen Eigenschaften. In der Reihe der Tricyclo[5. 1.0.03,5]octan-2,6-dione (1) -im folgenden ((Bishomochinone)) genanntwaren bisher die Methylderivate 2 und 3 bekannt [Z] [3] [4], welche durch Addition von Diazo-methan und -8than an Durochinon und anschliessende Pyrolyse, Photolyse oder saurekatalysierte Zersetzung der Bis-pyrazoline entstanden waren. In der vorliegenden Arbeit 1 2 3 4 5