CRYSTAL STRUCTURE OF 2-P-BROMOBENZOYL-1,5,5-TRIMETHYLBICYCLO[2,2,2]-OCTA-6,8-DIONE

An unexpected product of formula C18H20O3, obtained by treatment of β-dimethylaminopropiophenone at its boiling point with isophorone. has been shown to be 2-benzoyl-1,5,5-trimethylbicyclo[2,2,2] octa-6.8-dione by a single-crystal X-ray analysis of the p-bromo-derivative. The crystals, of formula C18H19O3Br, are monoclinic, space group P21/c with Z = 4 in a unit cell of dimensions a = 17.71, b = 9-25, c = 10.63 Å, and β = 106.5°. The structure was solved by the heavy-atom method and refined by least-squares calculations to R 0.099 for 1828 reflexions. The elucidation of the structure has yielded further information about the mechanisms of thermal Michael condensations.