Skeletal rearrangement of O-propargylic formaldoximes by a gold-catalyzed cyclization/intermolecular methylene transfer sequence

Abstract Skeletal rearrangement of O-propargylic formaldoximes, in the presence of gold catalysts, afforded 4-methylene-2-isoxazolines in good to excellent yields by an intermolecular methylene transfer. In addition, the cascade reaction with maleimide in the presence of a gold catalyst afforded isoxazole derivatives by cyclization/methylene transfer and a subsequent ene reaction, whereas that using a copper catalyst gave oxazepines through a 2,3-rearrangement. Au is not like Cu: Skeletal rearrangement of O-propargylic formaldoximes, in the presence of gold catalysts effectively afforded 4-methylene-2-isoxazolines by intermolecular methylene transfer. The cascade reaction in the presence of gold proceeds by cyclization/methylene transfer and a subsequent ene reaction, whereas with a copper catalyst it proceeds by a 2,3-rearrangement.