1-Chloroalkyl-, 1-(2, 2-dichloroalkyl)-, and 1-(trichloromethyl)-3, 4-dihydroisoquinolines are synthesized by chlorination of 1-alkyl-3, 4-dihydroisoquinolines with N-chlorosuccinimide. These novel chlorinated 3, 4-dihydroisoquinolines are suitable precursors for functionalized isoquinolines by aromatization involving sequential 1, 4-dehydrochlorination, tautomerization, and nucleophilic substitution.