A versatile and convenient method for the synthesis of substituted benzo[a]carbazoles and pyrido[2,3-a]carbazoles

Treatment of 2-(o-tolyl)- or 2-(3-methyl-2-pyridyl)-substituted indole-3-carbaldehydes with potassium tert-butoxide in DMF at 70–80 °C with simultaneous irradiation from a 400 W high-pressure mercury lamp afforded benzo[a]carbazoles and pyrido[2,3-a]carbazoles respectively in good yields.