Efficient Catalytic Synthesis of Condensed Isoxazole Derivatives via Intramolecular Oxidative Cycloaddition of Aldoximes

The intramolecular oxidative cycloaddition reaction of alkyne- or alkene-tethered aldoximes was catalyzed efficiently by hypervalent iodine(III) species to afford the corresponding polycyclic isoxazole derivatives in up to a 94% yield. The structure of the prepared products was confirmed by various methods, including X-ray crystallography. Mechanistic study demonstrated the crucial role of hydroxy(aryl)iodonium tosylate as a precatalyst, which is generated from 2-iodobenzoic acid and m-chloroperoxybenzoic acid in the presence of a catalytic amount of p-toluenesulfonic acid.