[6]metacyclophane and Related Compounds

The title phane (IV) with the shortest aliphatic bridge among [n]metacyclophanes has been obtained from the enone I. The PMR spectra indicate the pseudorotation of the hexamethylene chain occurring with abnormally high energy barrier of 11.1 kcal/mol at −31.5°C for IV and 12.4 kcal/mol at −4.5°C for its 12-bromo derivative (III).