4,5-Dihydro-1,2,4-oxadiazole as a Single Nitrogen Transfer Reagent: Synthesis of Functionalized Isoxazoles Assisted by Sc(OTf) 3 or Au(I)/Sc(OTf) 3 Synergistic Catalysis.

A five-membered N-O heterocycle, 4,5-dihydro-1,2,4-oxadiazole, was found to act as a single nitrogen atom transfer reagent via elimination of a ketone/aldehyde and a nitrile. This reagent was successfully applied for the synthesis of isoxazoles from ynones promoted by Sc(OTf) 3 or through Au(I)/Sc(OTf) 3 synergistic catalysis. The efficiency of this protocol was also demonstrated by its application in modifications of structurally complex natural products and pharmaceuticals.