Bisacetals of aromatic ring-annelated benzo[a,d]bis{bicyclo[4.4.1]undeca-3,8-diene-11-one}. [3.3] [3.3l]orthocyclophanes with triple-layered benzo/benzo/benzo- and naphtho/benzo/naphtho-system

Article abstract of DOI:10.1016/S0040-4020(97)00042-2

Tetraesters anti 9a,b and syn-9a,b, which have three aromatic rings, were prepared by the reaction of benzocycloheptenediester 7 with 1,2,4,5-tetrakis(bromomethyl)benzene. Subsequent hydrolysis and pyrolysis gave diketones anti-11a,b and syn-11a,b, which were acetalized to yield bisacetals anti-5a,b and syn-5a,b. X-Ray crystallographic analyses indicate a symmetric (twin-chair)/(twin-chair)- conformation of anti-5a,b, in which two naphtho or benzo rings sandwich one benzene ring. Anti-5a and anti-5b(9b)) are rigid structures. The protons of their central aromatic rings show an up-field shift, due to an anisotropic effect of the facing outer aromatic units. In contrast, syn-5a,b are flexible structures.' The UV-spectra of anti-5a,b show a long wavelength shift, as compared to syn-5a,b, suggesting a through-space interaction among the aromatic rings.