8.2 g (40 mmol) of 2-methyl-4-(4-fluorobenzylidene)-oxazol-5-one of Example (II-1) in 100 ml of toluene are heated overnight under reflux with 6.3 g (50 mmol) of 3,4,4-trifluorobut-3-enol, with the addition of 200 mg of 4-dimethylaminopyridine. After cooling, the solution is washed with water and concentrated under reduced pressure and the brown solid is chromatographed over silica gel using the system chloroform/ethyl acetate (4:1). 6.5 g (Yield 49% of theory) of 3,4,4-trifluorobut-3-enyl 3-(4-fluorophenyl)-2-acetylamino-prop-2-enoate of mp.: 116° are obtained.
