Fluorination of polyfluoro-derivatives of benzene and diphenyl with vanadiumpentafluoride at −25 to −10 °C afforded fluorinated cyclohexadienes and cyclohexenes. Octafluoro- naphthalene was converted under these conditions to perfluoro- 1,4-dihydronaphthalene, perfluorotetralin, perfluoro-l,4,5,8- tetrahydronaphthalene and perfluoro-l,2,3,4,5,8-hexahydro- naphthalene.