Cl[C:2]1[C:11]2[C:6](=[N:7][CH:8]=[CH:9][CH:10]=2)[N:5]=[C:4]([CH3:12])[C:3]=1[C:13]([O:15][CH2:16][CH3:17])=[O:14].[NH:18]1[CH2:23][CH2:22][CH2:21][CH2:20][CH2:19]1>>[CH3:12][C:4]1[C:3]([C:13]([O:15][CH2:16][CH3:17])=[O:14])=[C:2]([N:18]2[CH2:23][CH2:22][CH2:21][CH2:20][CH2:19]2)[C:11]2[C:6](=[N:7][CH:8]=[CH:9][CH:10]=2)[N:5]=1In a screw cap pressure tube ethyl 4-chloro-2-methyl-1,8-naphthyridine-3-carboxylate (250 mg, 1.0 mmol) was suspended in piperidine (2.0 ml, 20 mmol). The tube was sealed and the mixture heated to 80° C. for 1.0 h. The mixture was then adsorbed on silica and chromatographed (CH2Cl2/MeOH 98:2→97:3) giving 189.4 mg (63%) of the title compound.
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