Abstract
The title compounds, [n.2]metacyclophanediquinones 6aβf, were prepared by oxidation of the corresponding diβtertβbutyldihydroxy[n.2]metacyclophanes 5aβf with Tl(OCOCF~3~)~3~ in CF~3~COOH. When [n.2]quinonophanes 6aβe were reduced with Zn powder in acetic acid, the corresponding tetrahydroxy derivatives 8aβe were obtained, which were converted to the tetraacetates 9aβe. The solution conformations of diquinones 6aβf and tetrahydroxy[n.2]MCPs 8aβe are sensitive to the chain length of the bridges. The ring inversion barriers determined by variableβtemperature ^1^HβNMR spectroscopy decrease with increasing length of the bridges. In addition, a solvent effect on the ratio of anti to syn conformers was found to occur in tetrahydroxy[6.2]metacyclophane 8d and dihydroxy[6.2]metacyclophanes 5d, 10d, and 12d. The conformationally rigid tetraacetoxy[n.2]metacyclophanes 9 exhibit fixed βantiβοΈ and βsynβοΈ conformations. The anti and syn ratio is strongly governed by the number of methylene bridges. Thus, a antiβtoβsyn ratio of the tetraacetoxy[5.2]β (9c) and β[6.2]metacyclophane (9d) differing from that of the tetraols 8c and 8d was obtained. This difference is due to the ring inversion of 8c and 8d. The assignment of anti and syn conformations was confirmed by ^1^HβNMR analyses. The dynamics of the ring inversion is also discussed.