Synthesis and further transformations of 8-chloro-3,4-dihydroisoquinoline

Abstract Two procedures for the synthesis of barely accessible 8-chloro-3,4-dihydroisoquinoline were investigated. The first approach is based on a directed ortho -lithiation of N -pivaloyl meta -chlorophenylethylamine, followed by formylation and subsequent ring closure under acidic conditions. In the second, more advantageous variant, the N -hydroxyethyl ortho -chlorobenzylamine intermediate undergoes a Friedel-Crafts reaction, and the resulting tetrahydro derivative is oxidized with N -bromosuccinimide. The 8-chloro-3,4-dihydroisoquinoline key intermediate is then applied in Suzuki reactions to give various 8-aryl-3,4-dihydroisoquinolines, which are finally treated with alkyl and aryllithiums to give 1-substituted 8-aryl-1,2,3,4-tetrahydroisoquinolines. These novel 1,2,3,4-tetrahydroisoquinoline derivatives can be used as building blocks in the synthesis of potential drug candidates.