Synthesis of benzo[a]carbazoles and indolo[2,3-a]carbazoles via photoinduced carbene-mediated C-H insertion reaction

A new synthesis of 5-hydroxy-benzo[a]carbazoles has been achieved by employing the photoinduced intramolecular C-H insertion of 2-aryl-3-(alpha-diazocarbonyl)indoles as the key step. This method is applicable to the synthesis of natural products 6-cyano-5-methoxyindolo[2,3-a]carbazoles 8 and 11 and their derivatives.