[Cl:1][C:2]1[C:11]2[C:6](=[N:7][C:8]([CH3:15])=[C:9]([O:12][CH2:13][CH3:14])[CH:10]=2)[N:5]=[CH:4][C:3]=1[C:16]([O:18][CH2:19][CH3:20])=[O:17].[CH3:21][O:22][C:23]1[CH:29]=[CH:28][C:26]([NH2:27])=[CH:25][CH:24]=1>C(O)C>[ClH:1].[CH2:13]([O:12][C:9]1[CH:10]=[C:11]2[C:6](=[N:7][C:8]=1[CH3:15])[N:5]=[CH:4][C:3]([C:16]([O:18][CH2:19][CH3:20])=[O:17])=[C:2]2[NH:27][C:26]1[CH:28]=[CH:29][C:23]([O:22][CH3:21])=[CH:24][CH:25]=1)[CH3:14]A mixture of ethyl 4-chloro-6-ethoxy-7-methyl-1,8-naphthyridine-3-carboxylate (3.5 g) and 4-methoxyaniline (1.5 g) in ethanol (50 ml) was boiled under reflux for 1.5 hours. The mixture was concentrated to half the volume, cooled and ether added. The solid was collected by filtration to give ethyl 6-ethoxy-4-(4-methoxyanilino)-7-methyl-1,8-naphthyridine-3-carboxylate hydrochloride, m.p. 260°-262° C.
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