[NH2:1][C:2]1[C:7]([NH:8][CH2:9][C:10](OCC)=[O:11])=[CH:6][CH:5]=[C:4]([Cl:15])[N:3]=1.[H-].[Na+].Cl>O1CCOCC1>[Cl:15][C:4]1[CH:5]=[CH:6][C:7]2[NH:8][CH2:9][C:10](=[O:11])[NH:1][C:2]=2[N:3]=1To a solution of ethyl 2-(2-amino-6-chloropyridin-3-ylamino)acetate (E-25) (4.58 g, 20 mmol, 1.0 eq) in dry 1,4-dioxane (50 mL) was added sodium hydride (60% in mineral oil, 240 mg, 6 mmol, 0.3 eq), the resulting mixture was stirred at reflux for 2 h then cooled to RT and neutralized with con. HCl to adjust the pH value to 8˜9, concentrated in vacuo to remove most of solvent and then filtered, the filter cake was washed with water and ethyl acetate/petroleum ether (1:1) and dried to afford the desired product 6-chloro-1,2-dihydropyrido[2,3-b]pyrazin-3(4H)-one (E-26) (2.5 g, 68% yield) as a pale solid. 1H NMR (300 MHz, DMSO-d6) δ: 10.86 (bs, 1H), 6.96 (d, J=8.1 Hz, 1H), 6.79 (d, J=8.1 Hz, 1H), 6.35 (bs, 1H), 3.78 (d, J=1.5 Hz, 2H); ESI-MS m/z: 183.95[M+H]+.
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