The silver ion-catalysed ring-opening of 2- t-butyl-1-chloro-1-fluoro-2-methyl-cyclopropane (see Scheme 2) gave the expected mixture of primary and tertiary fluoroalkenols, whereas a tricyclic analog (bornane- spiro-chlorofluorocyclopropane) (see Scheme 3) exclusively underwent a Wagner/ Meerwein rearrangement upon ionization to lose finally a proton affording a 2-fluoro-1,4-diene.