Anionic [4+2] cycloaddition strategy in the regiospecific synthesis of carbazoles: formal synthesis of ellipticine and murrayaquinone A

Anionic [4+2] cycloaddition of furoindolones (e.g., 7 and 10) has been developed as an effective means to the synthesis of carbazoles. This reaction has been shown to be feasible with a wide variety of Michael acceptors to give carbazoles and fused carbazoles in good yields. The scope and limitations of the reaction have been briefly studied. The nature of N-protection of the furoindolones (cf. 7) plays a major role in the success of annulation.