Gold(I)-catalyzed selective heterocyclization of propargylic thioureas: mechanistic study of competitive gold-activation mode.

A new selective gold(I)-catalyzed intramolecular heterocyclization of propargylic thioureas has been developed, efficiently affording two kinds of cycloadducts in moderate to excellent yields with a broad substrate scope. Further mechanistic investigations indicate that competitive different gold activation modes feature in these cyclization processes. Kinetic experiments reveal that the gold activation mode is influenced by the ligand of the gold catalyst and the reaction conditions.