Copper-Catalyzed N-Arylation of Tautomerizable Heterocycles with Boronic Acids and Its Application to Synthesis of Oxygenated Carbazoles

A general and mild strategy has been developed for the selective N-arylation of tautomerizable heterocycles with a series of arylboronic acids, using CuOTf as the catalyst and 1,10-Phen as the ligand, under base free conditions at ambient atmosphere. The reaction mechanism explored by using density functional methods revealed that both kinetic and thermodynamic controls favour N-arylation. This "open-flask" chemistry successfully applied for N-arylation of benzo[d] oxazol-2(3H)-one and the designed N-arylated product was subsequently manipulated in synthesizing various naturally occurring oxygenated carbazole alkaloids (e.g. clausenine, clauraila A, clausenal).