Carbazole Annulation via Cascade Nucleophilic Addition–Cyclization Involving 2‑(Silyloxy)pentadienyl Cation

We report a new strategy toward the
synthesis of highly functionalized
carbazoles via 2-(silyloxy)­pentadienyl cation intermediates, which
were generated upon ionization of vinyl-substituted α-hydroxy
silyl enol ethers under Brønsted acid catalysis. These electrophilic
species were found to readily undergo cascade reactions with substituted
indoles to generate carbazole molecular scaffolds in good yields via
a sequence of regioselective nucleophilic addition, followed by intramolecular
dehydrative cyclization.