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 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.
Hashmi
A Stephen K
AS
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany. hashmi@hashmi.de
Weyrauch
Jan P
JP
Frey
Wolfgang
W
Bats
Jan W
JW