[C:1]([C:5]1[O:9][CH:8]=[N:7][C:6]=1[CH:10]=[C:11](O)[C:12]([NH:14][C@H:15]([C:23](=[O:25])[NH2:24])[CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:13])([CH3:4])([CH3:3])[CH3:2].C1(C)C=CC(S(O)(=O)=O)=CC=1>>[C:1]([C:5]1[O:9][CH:8]=[N:7][C:6]=1/[CH:10]=[C:11]1/[C:12](=[O:13])[NH:14][C@@H:15]([CH2:16][C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)[C:23](=[O:25])[NH:24]/1)([CH3:4])([CH3:3])[CH3:2]The effect of the amount of acid catalyst and reaction time was evaluated. (S,Z)-3-[(5-tert-Butyloxazol-4-yl)methylene]-6-benzylpiperazine-2,5-dione was prepared by reacting 3-(5-tert-Butyloxazol-4-yl)-N-((S)-1-carbamoyl-2-phenylethyl)-2-hydroxyacrylamide with various amounts of p-toluenesulfonic acid for various times. Enantiomeric excess of the product was determine by chiral HPLC using a CHIRALCEL OD column eluted with n-Hexane:Ethanol (5:1). The reaction conditions, product yields, and enantiomeric excess is present is Table 4.
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