BENT ACENES - SYNTHESIS AND MOLECULAR-STRUCTURE OF [6](1,4)NAPHTHALENOPHANE AND [6](1,4)ANTHRACENOPHANE

The first total syntheses and structural studies of [6](1,4)naphthalenophane (4) and [6](1,4)anthracenophane (5), the smallest-bridged isolable cyclophanes with bent acene nuclei, are disclosed. The acenophanes 4 and 5 were successfully synthesized by the oxidative decarboxylation of the benzo- and naphtho-fused propellenecarboxylic acids 10 and 11 to give the bridgehead olefins 12 and 13 followed by subsequent treatment with potassium tert-butoxide. The acids 10 and 11 were obtained conveniently by the Diels-Alder reactions of the diene 7 followed by ring contraction. The electronic spectra and photoclcctron spectra of 4 and 5 were measured and were compared with the corresponding 1,4-diethyl derivatives 14 and 15. The bathochromic shift of the first transition in the UV spectrum, as well as the shift of the first ionization energies of 4 and 5 in comparison to 14 and 15, respectively, can be ascribed mainly to the inductive effect of the hexamethylene chain and not to a bending of the π-system. The 1H NMR chemical shifts of 4 and 5 as well as their dynamic NMR behavior suggest that the bridging methylene groups of 4 and 5 are more relaxed than that of 1. The X-ray crystallographic structure analysis of 5 strongly supports these observations. The bent angle of the bridged aromatic ring of 5 is greater (by 1.5-1.6°) than those of the [6]paracyclophane derivatives 16 and 17, whereas the deformation of the bridging methylene group of 5 is smaller than those of the latter. © 1990, American Chemical Society. All rights reserved.