Synthesis and anomalous structure–reactivity relationship of 8,11-dichloro[5]metacyclophan-3-one

The synthesis, structural characterisation, and reactivity of the title compound are reported. It was prepared in order to investigate the effects of incorporation of an sp2-centre in the bridge of a [5]metacyclophane on its structure and reactivity. An X-ray crystal structure of the cyclophanone demonstrates that the benzene ring is distorted to the same extent as in the hydrocarbon parent compound, while there is less strain in the bridge. Nevertheless, the cyclophanone displays a reduced reactivity in Diels–Alder reactions, which is tentatively ascribed to transition state effects. Calculations indicate that in spite of the close proximity between the ketone functionality and the benzene ring, there are no π–π interactions between them.