Synthetic Development and Mechanistic Study on Pd(II)-Catalyzed Cyclization of Enediynes to Benzo[a]carbazoles

Treatment of N,N-dimethyl 2[2-(2-ethynylphenyl)ethynyl]anilines (1) with 10 mol he of palladium chloride and 2 equiv of cupric chloride in refluxing THF gave benzo[a]carbazoles (6) in good yields. A mechanistic study showed that this reaction must proceed through formation of haloindole (7) followed by a palladium(II)-catalyzed atom transfer cyclization reaction to give the benzo[a]carbazoles.