Synthesis of Benzo[c]cinnolinium Salts from 2-Azobiaryls by Copper(II) or Electrochemical Oxidation.

Synthesis of benzo[c]cinnolinium salts by copper(II)-promoted or electrochemical oxidation of 2-azobiaryls is described. A variety of diversely functionalized benzo[c]cinnolinium salts were easily constructed by this strategy with excellent functional group tolerance and high efficiency. An interesting fluorescence centered at 571 nm is revealed by a benzo[c]cinnolinium salt with electron push-pull substitutions. The mechanism is proposed to go through single-electron transfer driven by oxidant and intramolecular cyclization via nucleophilic addition, followed by an anion exchange.

TfOH-promoted Classical Nazarov-type Cyclization of Benzofulvenes: Synthesis of Polycyclic 5H,10'H-spiro[benzo[k]phenanthridine-5,6'-dibenzopentalenes].

The reaction of o-benzofulvene with TfOH leads to intramolecular cyclization through novel C-C and C-N bond formation, resulting in the formation of 5H,10'H-spiro[benzo[k]phenanthridine-5,6'-dibenzopentalene]. This protocol provides a new molecular framework with reasonable to excellent yields and tolerates various electron-withdrawing/donating substituents. This method yields diastereoselectivity of up to >20:1. Furthermore, it is free of bases, oxidants, and metals and proceeds under mild reaction conditions, which are favorable for synthetic organic chemistry.

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.

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.