[C:1]([S:4][CH2:5][CH2:6][C:7]([OH:9])=[O:8])(=[O:3])[CH3:2].[CH:10]1[C:15]([N+:16]([O-:18])=[O:17])=[CH:14][CH:13]=[C:12](O)[CH:11]=1.C1(N=C=NC2CCCCC2)CCCCC1>C(OCC)(=O)C>[N+:16]([C:15]1[CH:10]=[CH:11][C:12]([O:8][C:7](=[O:9])[CH2:6][CH2:5][S:4][C:1](=[O:3])[CH3:2])=[CH:13][CH:14]=1)([O-:18])=[O:17]To a stirred ice cold solution of ethyl acetate (75 ml.) containing 3-(acetylthio)propanoic acid (7.4 g. 50 mmol.) and p-nitrophenol (8.4 g., 60 mmol.) dicyclohexylcarbodiimide (10.3 g., 50 mmol.) is added in portions. After thirty minutes, the ice bath is removed and the solution stirred at room temperature overnight. The precipitated dicyclohexylurea is filtered off, ethyl acetate evaporated, and the residue dissolved in ethanol. The 3-(acetylthio)propanoic acid p-nitrophenyl ester crystallizes out, yield 8.6 g. (63.7%), m.p. 71°-73°.
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