Reaction and spectra of [n.2.1](1,2,3)cyclophanes

Abstract

Novel triply bridged [n.2.1](1,2,3)cyclophanes, which contain a dibenzo[a,d]cycloheptene unit as a basic structure, were prepared. The mobility of the molecule and the orientation of two aromatic rings were deduced from the NMR and UV spectra. Each aromatic ring can flip with conformational inversion on the NMR time-scale at 27 °C when the length of the third methylene chain (m or n) is longer than five for the dithiacyclophanes 9 and ten for the cyclophanes 3. Red shifts of λ_max for the aromatic rings and upfield shifts of aromatic protons are observed when the methylene chain becomes shorter. An X-ray study showed the benzene rings of the cyclophane 11c be slightly bent. Pyrolysis of the sulfones 10a and b gave the anthracene 7a rather than the cyclophanes 3a and b. Transalkylation of the cyclophanes 3a and b with AlCl₃–MeNO₂–benzene did not afford the de-tert-butylated cyclophanes 11a and b but instead gave the phenylated products 13a and b.