Palladium-Catalyzed Triple Successive C–H Functionalization: Direct Synthesis of Functionalized Carbazoles from Indoles

A novel Pd­(II)-catalyzed approach
for the direct synthesis of differentially
substituted carbazoles from free (NH) indoles via regioselective triple
successive oxidative Heck (Fujiwara–Moritani reaction) has
been achieved. It is demonstrated that both electron-deficient and
electron-rich alkenes could be used successively for the incorporation
of two different functional groups into the product. The proposed
mechanistic pathway was well supported by isolating the first and
second successive oxidative Heck intermediates as well as by trapping
with styrene-d3.