[CH3:1][O:2][C:3](=[O:22])[CH:4]([C:9]1[C:18]2[C:13](=[CH:14][CH:15]=[C:16]([O:19][CH3:20])[N:17]=2)[N:12]=[CH:11][C:10]=1[Cl:21])C(OC)=O.[Cl-].[Li+].O.C(OCC)(=O)C>CS(C)=O>[CH3:1][O:2][C:3](=[O:22])[CH2:4][C:9]1[C:18]2[C:13](=[CH:14][CH:15]=[C:16]([O:19][CH3:20])[N:17]=2)[N:12]=[CH:11][C:10]=1[Cl:21]To a solution of dimethyl[3-chloro-6-(methyloxy)-1,5-naphthyridin-4-yl]propanedioate (56.23 g, 173 mmol) in DMSO (1210 ml) was added lithium chloride (14.9 g, 350 mmol) and water (3.24 ml, 180 mmol). The mixture was heated to 100° C. for 16 h then cooled and treated with ethyl acetate and water. The organic phase was washed twice with water, the aqueous extracted with ethyl acetate and this water-washed. The combined organic phases were dried and the solvent was removed. The residue was subjected to column chromatography on silica gel using a hexane and ethyl acetate gradient to provide the desired compound containing a little of the starting material (43.3 g, 94%).
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