Pd-catalyzed three-component [2+2+1] cycloamination toward carbazoles

Conventional approaches using hydroxylamine derivatives as single nitrogen sources for the preparation of N-heterocyclic molecules rely on two chemical processes involving sequential nucleophilic and electrophilic C-N bond formations. Herein, we report a novel Suzuki reaction/C-H activation/amination sequence for building a myriad of carbazoles in a single transformation using bifunctional secondary hydroxylamines. It is noteworthy that the synthetic utility of this methodology is highlighted by the total synthesis of clausine V and glycoborine by incorporating the title [2 + 2 + 1] cycloamination as the key step. Control experiments were performed to gain a better understanding of the reaction mechanism. A novel and efficient diamination route to synthesize carbazole skeletons via a Pd-catalyzed three-component [2 + 2 + 1] cycloamination reaction is developed.