Intramolecular electrophilic aromatic substitution (SAr) reaction at the 5-position of isoxazoles was achieved. The electron-donating heteroatoms (N and O) at the 4-position of isoxazoles, which can be readily prepared based on our originally developed synthetic procedure, and a cationic gold(I) catalyst are essential for the intramolecular SAr reaction to synthesize isoxazole-containing fused heterocycles. Structurally diverse isoxazolopyridines 6 and isoxazolopyrans 9, including base-labile 3-unsubstituted derivatives, were synthesized in good to high yields. The addition of N-phenylbenzaldimine as a hydrogen acceptor improved yields in the synthesis of isoxazolopyridines. Furthermore, synthesis of the tetracyclic fused ring system 12 was achieved by tandem cyclization from the corresponding diyne 11.

A unique synthetic approach to 3-hydroxy-4-substituted picolinonitriles is achieved via gold(I)-catalyzed cyclization of 4-propargylaminoisoxazoles and subsequent N–O bond cleavage of isoxazolopyridines under mild reaction conditions in a stepwise and one-pot fashion.

Propargyl aza-Claisen rearrangement of 4-propargylaminoisoxazoles 1 proceeded in the presence of cationic gold(i) catalysts to give 4-amino-5-allenylisoxazoles 2 in good to high yields.