Electrochemical oxidation of dihydroindoloquinazoline and dihydroquinazoline derivatives

The electrochemical properties of tetracyclic dihydroindoloquinazoline and bicyclic dihydroquinazoline derivatives of type 1 and 2 have been studied in dichloromethane, both on Pt and glassy carbon anodes. Cyclic voltammetric results are discussed in terms of substituent and steric effects on the first and second anodic peak potentials. Anodic oxidation of type 1 compounds yields purple solutions (presumablycation radical species), regardless of the nature of the substituent. Exposure of the purple solutions to both light and air results in the formation of decomposition products: benzophenone and cyclic amides of type 4 (the X-ray crystal structure of 4c has been determined). On anodic oxidation, both 2b and 2c undergo mostly ring-closure to form the tetracyclic derivatives 1b and 1c, respectively, whereas 2d, which does not undergo cyclization, yields the bicyclic amide 5d. The mechanism of the formation of products is discussed.