Oxidative Benzannulation of Indoles with 3-Alkynyl-4-pyrones for the Synthesis of Furo[2,3-b]carbazoles.

We report a mild and operationally simple strategy for the synthesis of furo[2,3-b]carbazoles via the oxidative benzannulation of 2,3-unsubstituted indoles with 3-alkynyl-4-pyrones. This domino transformation proceeds at room temperature in the presence of methanesulfonic acid as the sole promoter. The method allows for the construction of a broad scope of polysubstituted furo[2,3-b]carbazoles in up to 92% yield. The photophysical properties of the polycyclic products were determined to assess their potential as fluorophores.