Convenient One-Pot Synthesis of 9H-Carbazoles by Microwave Irradiation Employing a Green Palladium-Based Nanocatalyst

Abstract An efficient palladium-catalyzed tandem reaction for the one-pot synthesis of 9H-carbazoles under microwave irradiation is developed. This approach involves a sequential Buchwald–Hartwig amination and a direct arylation from affordable and inexpensive anilines and 1,2-dihaloarenes. For the development of this purpose, a novel and magnetically recoverable palladium nanocatalyst supported on a green biochar under ligand-free conditions is used. Compared to other existing palladium-based protocols, the present synthetic methodology shows a drastic reduction in reaction times and excellent compatibility with different functional groups allowing to obtain a small library of 9H-carbazoles in high yields and with good regioselectivity. This procedure represents the first example in the direct synthesis of carbazoles using a heterogeneous palladium nanocatalyst from commercial precursors. To examine the application of this protocol, a direct and scalable synthesis of the bioactive carbazole alkaloid clausenalene from commercially available starting materials is described.