O[CH:2]([CH:5]1[CH2:9][S:8][CH:7]([C:10]2[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=2)[N:6]1[C:16]([O:18][CH3:19])=[O:17])[CH:3]=[CH2:4].C[C:21](C)(C)[C:22]([O-:25])([O-])[O-:23].[C:28](O)(=O)CC>C1C=CC=CC=1>[C:16]([N:6]1[CH:5]([CH:2]=[CH:3][CH2:4][CH2:21][C:22]([O:25][CH3:28])=[O:23])[CH2:9][S:8][CH:7]1[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1)([O:18][CH3:19])=[O:17]A solution of 44.0 g. (0.1575 mol) of crude 4-(1-hydroxyprop-2-en-1yl)-3-carbomethoxy-2-phenylthiazolidine, 191.5 g. (1.570 mol) of trimethylorthoacetate and 100 ml. of a 20% solution of propionic acid in benzene in 2 L. of benzene was heated for 24 hours, at 92°-93° C. The vapors were condensed and collected in a Dean-stark moisture receiver. After cooling, the resulting yellow solution was washed with 100 ml. of a 2N solution of sodium carbonate, then 3 × 100 ml. of water. Drying with magnesium sulfate and evaporation in vacuo gave 50.0 g. (95% yield) of crude methyl 5-(3-carbomethoxy-2-phenylthiazolidin-4-yl)-4-pentenoate. Gas chromatographic analysis showed a purity of 65-70%. If pure starting material is used instead in the process, no detectable impurities were detected in the final product.
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