[Figure not available: see fulltext.] 5,7,8-Trifluoro-3,4-dihydro-2H-1,4-benzothiazine, corresponding 1-oxide and 1,1-dioxide, as well as some of their 4- and 6-substituted derivatives were prepared in 39–88% yields via the reaction of ammonia or primary aliphatic amines with (2-haloethyl)-2,3,5,6-tetrafluorophenyl sulfides, sulfoxides, or sulfones. Formation of the heterocyclic moiety was shown to proceed as a two-stage process starting from halogen replacement at the side chain followed by intramolecular aminodefluorination. The ratio of the reaction rates of the two processes depends on the nature of the reagent used. Chemical structures of the cyclization products were proved by precise analysis of the NMR spectra and by comparing the experimental NMR parameters with those calculated by an empirical additivity scheme and quantum chemistry methods (DFT).