A new synthetic approach to fused nine-ring systems of the indolo[3,2-b] carbazole family through double Pd-catalyzed intramolecular C-H arylation

A series of new polycyclic compounds bearing the 5,11-dihydroindolo[3,2-b] carbazole ring system, as the common motif of their nine-ring scaffolds, has been successfully prepared with the usage of an efficient two-step strategy, based on the double Friedel-Crafts acylation of 5,11-dihexyl-6,12-di(hetero) aryl-substituted 5,11-dihydroindolo[3,2-b] carbazoles with 2-iodobenzoyl chloride in the presence of SnCl4, followed by regioselective palladium-catalyzed cyclization of the obtained 2,8-bis(2-iodobenzoyl) derivatives into the desired fused 9H-fluoren-9-ones. Some modifications of these nine-ring structures have been performed to afford compounds of the same family bearing the 9H-fluorene fragments. Basic photophysical and electrochemical properties as well as thermal stability of the new fused indolo[3,2-b] carbazole derivatives have been determined.