[CH3:1][C:2]1([CH3:10])[CH2:7][C:6](=[O:8])[CH2:5][C:4](=[O:9])[CH2:3]1.[OH-].[K+].C([O:15][C:16](=[O:21])[C:17](=O)[CH2:18]Br)C.[OH-].[Na+].Cl>CO>[CH3:1][C:2]1([CH3:10])[CH2:3][C:4](=[O:9])[C:5]2[C:17]([C:16]([OH:21])=[O:15])=[CH:18][O:8][C:6]=2[CH2:7]1
5,5-Dimethyl-1,3-cyclohexandione is dissolved in 15 ml of methanol and cooled to 0° C. A solution of KOH (2 g, 35.7 mmol) in 15 ml of methanol is added drop wise. A solution of 3-bromo-2-oxo-propionic acid ethyl ester (4.7 ml, 37.5 mmol) in 15 ml of methanol is added drop wise. The mixture is allowed to warm up to room temperature and is stirred for 16 h. Then 15 ml of a 45% aqueous sodium hydroxide solution is added. After additional 4 h at room temperature, 25 ml of concentrated HCl is added. Methanol is evaporated slowly under reduced pressure whereas the product precipitates as light crystals. The product is filtrated off and washed with water.
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