Cascade One‐Pot Synthesis of Orange‐Red‐Fluorescent Polycyclic Cinnolino[2,3‐f]phenanthridin‐9‐ium Salts by Palladium(II)‐Catalyzed C−H Bond Activation of 2‐Azobiaryl Compounds and Alkenes

• Published in: Angewandte Chemie International Edition Vol. 59; no. 2; pp. 689 - 694
• Main Authors: Jayakumar, Jayachandran, Vedarethinam, Guganchandar, Hsiao, Huan‐Chang, Sun, Shang‐You, Chuang, Shih‐Ching
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 07.01.2020
• Subjects: alkenes; azobenzenes; Chemistry; Chemistry, Multidisciplinary; C−H activation; fluorescence; palladium catalysis; Physical Sciences; Science & Technology; palladium catalysis; PALLADIUM; azobenzenes; RHODIUM(III)-CATALYZED SYNTHESIS; CINNOLINIUM SALTS; OXIDATIVE ANNULATION; alkenes; AMMONIUM-SALTS; LIGHT-EMITTING-DIODES; CROSS-COUPLING REACTIONS; C-H activation; fluorescence; ALKENYLATION; ISOQUINOLINIUM SALTS; N-HETEROCYCLES; C−H activation
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201910959

Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C−H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C−H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation. Fired up: Orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts were synthesized with high regioselectivity from 2‐azobiaryls and alkenes by palladium(II)‐catalyzed C−H activation under mild reaction conditions (see scheme). The prepared quaternary ammonium salts showed strong fluorescence emission maxima at 575–620 nm with broad bandwidths.