[C:1]1([N:7]=[C:8]=[O:9])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[OH:10][CH:11]([C:16]([CH3:18])=[CH2:17])[C:12]([O:14]C)=[O:13].[N-]=C=O>C1C=CC=CC=1>[C:8](=[O:9])([O-:10])[NH2:7].[C:1]1([NH:7][C:8]([O:10][CH:11]([C:16]([CH3:18])=[CH2:17])[C:12]([O-:14])=[O:13])=[O:9])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1A benzene solution (50 ml) of phenyl isocyanate (1.19 g, 10 mmol) and methyl 2-hydroxy-3-methyl-3-butenoate (2.0 g, 10 mmol) was stirred at room temperature for 2 hours. It was confirmed by NMR and IR analysis of the reaction mixture that the isocyanate was completely consumed and a carbamate, 2-(N-phenylcarbamoyloxy)-3-methyl-3-butenoate, was produced. After the addition of triethylamine to the reaction mixture, the solution was further heated at reflux for 3 hours. The solvent was then removed under reduced pressure and methanol (10 ml) was added to the resulting residue to precipitate white crystals of the desired product. These crystals (1.51 g) were separated by filtration and identified as 3-phenyl-5-isopropylidne-1,3-oxazolidine-2,4-dione by NMR and IR analysis.
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