Double- to quadruple-layered dihetera[3.3]metacyclophanes containing O, S, and Se atoms in the bridge chains were synthesized by the usual methods. On irradiation, three quadruple-layered cyclophanes 1a-c undergo a photodimerization of two inner benzenes to give good yields of novel cage compounds 2a-c which revert thermally to the starting cyclophanes. The driving forces for such intriguing photoreactions were studied with respect to the strain of the benzene, effect of chalcogen atom species, interfacial constraint, etc., using several reference cyclophanes. It is concluded that the face-to-face stacking of two fairly strained benzene nuclei is responsible for the photodimerization and the two outer benzenes are required for the effective interconversion between quadruple-layered diheteracyclophanes and their isomeric cage compounds. © 1986.
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