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

Org Lett. 2004 Nov 11;6(23):4391-4. doi: 10.1021/ol0480067.

Abstract

2,5-Disubstituted oxazoles are synthesized from the corresponding propargylcarboxamides under mild reaction conditions via homogeneous catalysis by AuCl(3). While monitoring the conversion via (1)H 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 degrees C for several weeks. Deuteration experiments show a stereospecific mode of the two first steps of the reaction.