[CH2:1]1[O:9][C:8]2[CH:7]=[CH:6][C:5]([OH:10])=[CH:4][C:3]=2[O:2]1.[ClH:11].O=[C:13]1[CH2:18][CH2:17][NH:16][CH2:15][CH:14]1[C:19](OC)=[O:20].[OH-].[NH4+]>S(=O)(=O)(O)O>[ClH:11].[CH2:18]1[CH2:17][NH:16][CH2:15][C:14]2[C:19](=[O:20])[O:10][C:5]3[CH:4]=[C:3]4[C:8]([O:9][CH2:1][O:2]4)=[CH:7][C:6]=3[C:13]1=2A mixture of 3,4-methylenedioxyphenol (125 g, 0.91 moles) and methyl 4-oxo-3-piperidinecarboxylate hydrochloride (125 g, 0.65 moles) is cooled in ice and treated over one hour with 600 ml of 72% sulfuric acid. The mixture is then stirred at room temperature for 64 hours. Ice/water (1.0 kg) is added, followed by conc. ammonium hydroxide, until the pH of the mixture is 9.0. The crude product is filtered, stirred briefly in 2.5% aqueous sodium hydroxide (1.0 l), and refiltered. Several recrystallizations from dilute aqueous hydrochloric acid yielded the product (86.2 g) as the hydrochloride, mp 258°-259° C.
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