[N:1]1[CH:6]=[CH:5][CH:4]=[C:3]([CH2:7][N:8]2[C:13](=[O:14])[C:12](=[C:15]3[S:19][CH:18]=[CH:17][S:16]3)[C:11](=[O:20])[CH:10](C(OC)=O)[CH2:9]2)[CH:2]=1.[OH-].[Na+].O>CO>[N:1]1[CH:6]=[CH:5][CH:4]=[C:3]([CH2:7][N:8]2[CH2:9][CH2:10][C:11](=[O:20])[C:12](=[C:15]3[S:16][CH:17]=[CH:18][S:19]3)[C:13]2=[O:14])[CH:2]=1Methyl 1-(3-pyridylmethyl)-5-(1,3-dithiol-2-ylidene)-4,6-dioxopiperidine-3-carboxylate (244 mg) obtained in Example 27 is dissolved in methanol (15 ml), and thereto is added a 10% sodium hydroxide solution (2 ml). The mixture is refluxed for 2 hours. The mixture is poured into water, and extracted with chloroform. The extract is washed with water, dried and then distilled to remove the solvent. The residue is recrystallized from a mixture of ethyl acetate and and n-hexane to give 1-(3-pyridylmethyl)-3-(1,3-dithiol-2-ylidene)-2,4-dioxopiperidine (114 mg, 66.1%) as yellow plates, m.p. 131.5°-133° C.
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