[Cl:1][C:2]1[C:11]2[C:6](=[CH:7][C:8]3[O:14][CH2:13][O:12][C:9]=3[CH:10]=2)[N:5]=[CH:4][C:3]=1[C:15]([O:17]CC)=[O:16].[O:20]1CCOCC1>>[ClH:1].[OH:20][C:2]1[C:11]2[C:6](=[CH:7][C:8]3[O:14][CH2:13][O:12][C:9]=3[CH:10]=2)[N:5]=[CH:4][C:3]=1[C:15]([OH:17])=[O:16]Ethyl 4-chloro-6,7-methylenedioxyquinoline-3-carboxylate (18.5 g, 66.2 mmol) was dissolved in dioxane (100 mL) and treated with 50 mL 5 NNaOH and heated at reflux for 2 hour. After this time the solution was concentrated on a rotary evaporator, cooled and extracted with dichloromethane (2×100 mL). The remaining aqueous solution was then acidified with concentrated HCl and the precipitate collected and dried to afford 7 g of crude 4-hydroxy-6,7-methylenedioxyquinoline-3-carboxylic acid hydrochloride.
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