The homo-l, 4 adduct obtained from difluorocarbene and bicyclo [2.2.1]hepta-2, 5-diene (1) was treated successively with HCl, FSO3H and SbF5 in SO2ClF at low temperature. The protic acids underwent electrophilic addition to the cyclopropane part of 1, giving the corresponding derivatives. However, in FSO3H at - 50°, protonation of the gem-difluoro grouping also occurred to give the 2-fluoro-6-fluorosulfonylbicyclo [3.2.1]oct-2-en-3-yl cation. The reaction of 1 with SbF5 at -78° led initially to the formation of the 2-fluorobicyclo [3.2.1 ]octa-2, 6-dien-4-yl cation, which rearranged to 4-fluorotricyclo [5.1.0.05,8]oct-3-en-2-yl cation at -40°. These rearrangements are discussed in the light of those expected for C8H8F square pyramidal cations.