[C:1]1([C:7]2[NH:8][C:9](=[O:12])[O:10][CH:11]=2)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[CH:13](=[CH:20][C:21](=[O:23])[CH3:22])[C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1.CS(O)(=O)=O.O>C(#N)C>[C:1]1([C:7]2[NH:8][C:9](=[O:12])[O:10][C:11]=2[CH:13]([C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)[CH2:20][C:21](=[O:23])[CH3:22])[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1To a solution of 4-phenyl-2-oxo-4-oxazoline (1.61 g) and benzalacetone (1.46 g) in acetonitrile (20 ml) was added dropwise methanesulfonic acid (0.96 g). After stirring the obtained mixture at room temperature for 30 min, water was added, and the mixture was extracted with ethyl acetate. The extract was washed with water and dried (MgSO4), and the solvent was evaporated. The residue was subjected to silica gel column chromatography and eluted with hexane-ethyl acetate (1:1). The solvent was evaporated. Crystallization from isopropyl ether gave 4-(4-phenyl-2-oxo-4-oxazolin-5-yl)-4-phenyl-2-butanone (2.65 g; yield 86.3%). Recrystallization from ethanol gave colorless crystals.
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