The synthesis of novel [5]metacyclophanes 1 has been achieved either by an improved version of the general approach starting from halobicyclo[5.3.0]dec-1(7)-enes 2 or by nucleophilic substitution of 11-chloro[5]metacyclophanes. Conformational analysis of 1 revealed that the exo conformation, in which the pentamethylene bridge is pointing away from the aromatic ring, is strongly preferred both for very small and for very large substituents at the aromatic interbridge position 11, whereas medium-sized substituents induce the occurrence of minor amounts of the endo conformer. In Diels−Alder reactions with dienophiles, compounds 1 behaved like reactive dienes, adding at positions 8 and 11 of the aromatic ring. Substitution by chlorine, though, reduced the reaction rate; the unsymmetrical dienophile acrylonitrile showed little preference for the two possible regioisomeric adducts 8 and 9. Similarly, compounds 1 were unusually reactive towards acid, and interesting and unforeseen rearrangements were observed. Depending on the substituent at position 11, acid treatment of 1 afforded either ortho-annu-