The synthesis of 1,1-dichloro and 1,1-difluoronaphtho[b]cyclopropenes 1 and 2 starting from 4,5-dimethylenecyclohexene and tetrachloro- or 1,2-dichloro-3,3- difluorocyclopropene, respectively, is described. Both 1 and 2 ionize in cold fluorosulfonic acid to yield stable aromatic cations 3 and 4. Upon quenching with water, 1-chloronaphtho[b]cyclopropenium ion 3 affords β-naphthoic acid.