UNEXPECTED FORMATION OF A 5-TRIFLUOROMETHYLOXAZOLE FROM A 1,2-DIBENZAMIDOALKENE

An unusual cyclisation of Z-1,2,4-tris(benzamido)butene with trifluoro acetic anhydride gives Z-4- ido)prop-1-enyl]-2-phenyl-5-trifluoromethy loxazole (3). The structure and stereochemistry were confirmed by H-1, C-13 and F-19 NMR, together with H-1-H-1 COSY, H-1-H-1 NOESY and H-1- ->F-19 and F-19 --> H-1 heteronuclear NOE experiments. Trifluoroacetyl ation at the less sterically hindered N-acyl-enamine position, with su bsequent cyclisation and 1,4-elimination is proposed.