Bishomochinon

Abstract

Abstract Two isomeric 2,4,6,8‐tetrabromo‐cyclooctane‐1,5‐diones ( 8a and 8b ) are formed in the tetrabromination of cyclooctane‐1,5‐dione ( 7 ). Treatment of a mixture of 8a and 8b 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 sys ‐isomer ( 5 ). The anti ‐configuration was assigned to 4 on the basis of its reduction to two diols, one of which showed NMR. coupling 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 exo ‐ and endo ‐methylene protons when comparing the NMR.‐spectra of anti ‐ and syn ‐bishomoquinone.