A general and efficient synthesis
of 4,9-dihydro-1<i>H</i>-carbazoles from 3-allenylmethylindoles
is reported. The process,
catalyzed by a cationic gold(I) complex, involves a formal C2–H
bond activation of the indole unit by reaction with the allene. The
nature of the substituents at the allylic and terminal positions of
the allene moiety has a crucial effect on the regioselectivity of
the cyclization, which is also influenced by the catalyst and the
solvent employed. Moreover, some evidence of the contribution of different
reaction routes is provided, which led us to propose a plausible multipathway
mechanism consistent with all of the results described
