[CH2:1]([C:3]1[CH:4]=[C:5]2[C:10](=[CH:11][C:12]=1[OH:13])[O:9][C:8]([C:14]([O:16]C)=[O:15])=[C:7]([C:18]1[CH:23]=[CH:22][C:21]([O:24][CH3:25])=[CH:20][CH:19]=1)[C:6]2=[O:26])[CH3:2].[OH-].[Na+].Cl>CC(C)=O>[CH2:1]([C:3]1[CH:4]=[C:5]2[C:10](=[CH:11][C:12]=1[OH:13])[O:9][C:8]([C:14]([OH:16])=[O:15])=[C:7]([C:18]1[CH:19]=[CH:20][C:21]([O:24][CH3:25])=[CH:22][CH:23]=1)[C:6]2=[O:26])[CH3:2]Methyl 6-ethyl-7-hydroxy-3-(4-methoxyphenyl)-4-oxo-chromene-2-carboxylate (13.6 g, 41.73 mmol) was dissolved in acetone (200 ml). Then a 2N aqueous solution of Sodium hydroxide (62.59 ml, 125.19 mmol) was added at room temperature. The resulting mixture was stirred at room temperature over night. After the reaction was complete the mixture was acidified under cooling with concentrated hydrochloric acid to pH 2.5. A solid precipitated from the solution. The solid was filtered off, washed with water and diethyl ether and dried at 40° C. under vacuum to yield the title product as an off white solid (11.2 g quantitative). The material was used directly without further purification in the next step. Mass Spectrum: (M+H+) 341.25, (M+H−) 339.19.
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