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.