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 1H 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 −25 °C for several weeks. Deuteration experiments show a stereospecific mode of the two first steps of the reaction.