Au(I)/Sc(III)-co-catalyzed tandem spiroannulation/cycloisomerization of 3-(2-ethynylaryl)- N -tosylaziridines with indoles to access 5 H -benzo[ b ]carbazoles.

An unusual spiroannulation/cycloisomerization cascade of 3-(2-ethynylaryl)- N -tosylaziridines with indoles enabled by cooperative gold/scandium catalysis is presented, which facilitates the synthesis of 5 H -benzo[ b ]carbazoles in moderate to excellent yields. This protocol features a broad substrate scope and good functional-group compatibility. Additionally, the resulting 5 H -benzo[ b ]carbazoles exhibit good fluorescence properties, demonstrating the synthetic practicality of this method. Moreover, control experiments were performed to illustrate the reaction mechanism.