[Cl:1][C:2]1[CH:23]=[CH:22][C:5]2[N:6]([CH:11]3[CH2:16][CH2:15][N:14](C(OCC)=O)[CH2:13][CH2:12]3)[C:7](=[O:10])[N:8]([CH3:9])[C:4]=2[CH:3]=1.[OH-].[K+].CC(O)C>O>[Cl:1][C:2]1[CH:23]=[CH:22][C:5]2[N:6]([CH:11]3[CH2:12][CH2:13][NH:14][CH2:15][CH2:16]3)[C:7](=[O:10])[N:8]([CH3:9])[C:4]=2[CH:3]=1A mixture of 12.8 parts of ethyl 4-(5-chloro-1,3-dihydro-3-methyl-2-oxo-2H-benzimidazol-1-yl)-1-piperidinecarboxylate, 20 parts of potassium hydroxide, 128 parts of 2-propanol and 2.5 parts of water is stirred and refluxed overnight. The reaction mixture is cooled and evaporated. Water is added to the residue and the product is extracted with trichloromethane. The extract is dried, filtered and evaporated. The residue is triturated in 2,2'-oxybispropane. The product is filtered off and dried, yielding 5-chloro-1,3-dihydro-3-methyl-1-(4-piperidinyl)-2H-benzimidazol-2-one; mp. 200.9° C.
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