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

The synthesis, structural characterisation, and reactivity of the title com pound are reported. It was prepared in order to investigate the effects of incorporation of an sp(2)-centre in the bridge of a [5]metacyclophane on it s structure and reactivity. An X-ray crystal structure of the cyclophanone demonstrates that the benzene ring is distorted to the same extent as in th e hydrocarbon parent compound, while there is less strain in the bridge. Ne vertheless, the cyclophanone displays a reduced reactivity in Diels-Alder r eactions, which is tentatively ascribed to transition state effects. Calcul ations indicate that in spite of the close proximity between the ketone fun ctionality and the benzene ring, there are no pi-pi interactions between th em. (C) 2001 Elsevier Science Ltd. All rights reserved.