Silver catalyzed domino aza-annulation/Diels-Alder cyclization of 2-ene-yne anilines: a facile one-pot access to carbazole, dihydrocarbazole and tetrahydrocarbazole frameworks.

An unprecedented and efficient AgSbF6-catalyzed domino aza-annulation/Diels-Alder/aromatization cascade for the construction of carbazoles, dihydrocarbazoles and tetrahydrocarbazoles was achieved using 2-(but-3-en-1-yn-1-yl) anilines in the presence of suitable dienophiles. The reaction proceeds via the in situ generation of 2-vinyl indoles and their subsequent trapping by various dienophiles with concomitant aromatization. A series of symmetrical, unsymmetrical and base sensitive dienophiles provide the corresponding carbazoles under mild conditions in excellent yields with high regioselectivity.