Synthesis of 4-Isoxazolines through Gold(I)-Catalyzed Cyclization of Propargylic N-Hydroxylamines.

New catalytic methods for the synthesis of 4-isoxazolines have been developed via catalytic intramolecular cyclizations of propargylic N-hydroxylamines. The reactions proceed rapidly in less than 1 h at room temperature in the presence of 5 mol % (PPh3)AuCl/5 mol % AgOTf or 5 mol % (PPh3)AuNTf2. This process features an efficient route to 4-isoxazolines with high yields, short reaction times, and mild reaction conditions.