Synthesis of Cationic [4], [5], and [6]Azahelicenes with Extended π-Conjugated Systems

Abstract

The scope of Rh-catalyzed C–C bond cleavage/annulation of biphenylene with various aromatic nitriles was studied. The subsequent Rh- and Ir-catalyzed C–H bond activation/annulation sequence of the formed 9-arylphenanthridines with alkynes gave rise to cationic [4], [5], [6] helical quinolizinium salts. The scope of the reaction with respect to the structural features of the starting 9-arylphenanthridines and alkynes was studied. Their helical arrangement was confirmed through single-crystal X-ray analyses of selected compounds. Most of the prepared quinolizinium salts exhibited fluorescence emission maxima in the region of 525–623 nm with absolute quantum yields up to 25%.

Keywords

• C–C bond activation
• C–H bond activation
• helicenes
• catalysis
• rhodium
• fluorescence