Crystal and molecular structures of 8,9-dibromo-1,4,4,8-tetramethyltricyclo[5,4,0,0]undecane and 8,9-dibromo-2,2,4,8-tetramethyltricyclo[5,3,1,0]undecane, derivatives of rearrangement products of caryophyllene dihydrochloride and isocaryophyllene respectively

Abstract

The structures of the title compounds (I) and (IV) have been determined by single-crystal X-ray analyses. Crystals of both are orthorhombic, space group P2₁2₁2 for (I), P2₁2₁2₁ for (IV), with Z= 4 in unit cells of dimensions: (I), a= 15·47(2), b= 14·02(1), c= 7·01(1)Å; (IV), a= 6·63(1), b= 8·96(1), c= 26·35(2)Å. Both structures were solved from photographic data by the heavy-atom method, and refined by least-squares calculations to R= 0·106 for 1336 independent reflexions (I), and R 0·096 for 860 independent reflexions (IV). In each case the absolute stereochemistry was determined by consideration of anomalous dispersion effects. The analyses of the two dibromo-derivatives have allowed us to deduce the structures and stereochemistries of their parent hydrocarbons [(II) and (V)], and hence to postulate possible mechanisms by which these latter may be formed from caryophyllene dihydrochloride (III) and (–)-isocaryophyllene (VI) respectively.