The intramolecular Friedel-Crafts cyclisation of ω-arylalkanoic acids, which is in the benzene series a valuable synthetic route to bicyclic ketones with medium-sized and large rings, has been investigated with ω-(1-naphthyl)alkanoyl chlorides. The lower members, including naphthyl-caproic acid, close the ring at position 2 to form IV. The higher homologous acids show a preference for annellation at