Gold catalysis:: Mild conditions for the synthesis of oxazoles from N-propargylcarboxamides and mechanistic aspects

2,5-Disubstituted oxazoles are synthesized from the corresponding propargylcarboxamides under mild reaction conditions via homogeneous catalysis by AuCl3. While monitoring the conversion via H-1 NMR spectroscopy, an intermediate 5-methylene-4,5-dihydrooxazole can be observed and accumulated up to 95%, being the first direct and catalytic preparative access to such alkylidene oxazolines. The intermediate was fully characterized and can be trapped at -25degreesC for several weeks. Deuteration experiments show a stereospecific mode of the two first steps of the reaction.