5-endo-Trigonal cyclization of o-substituted gem-difluorostyrenes: syntheses of 2-fluorinated indoles, benzo[b]furans and benzo[b]thiophenes

β,β-Difluorostyrenes bearing tosylamido, hydroxy ormethylsulfinyl groups at the o-position undergo intramol-ecular substitution of the nitrogen, oxygen or sulfur withloss of fluorine via a 5-endo-trigonal process leading to2-fluorinated heterocyclic systems in high yields.