[CH2:1]([O:3][C:4](=[O:15])[CH:5]([C:12](=[O:14])[CH3:13])[CH2:6][C:7]([O:9][CH2:10][CH3:11])=[O:8])[CH3:2].[H-].[Na+].[CH2:18](I)[CH2:19][CH3:20].[Na+].[Cl-]>CS(C)=O.O>[CH2:1]([O:3][C:4](=[O:15])[C:5]([C:12](=[O:14])[CH3:13])([CH2:18][CH2:19][CH3:20])[CH2:6][C:7]([O:9][CH2:10][CH3:11])=[O:8])[CH3:2]
To a solution of 2-acetyl-succinic acid diethyl ester (30 g, 139 mmol) in DMSO (250 ml) is added NaH (5.8 g, 60% in mineral oil, 145 mmol) in 10 portions over a period of 1 hour. The resulting solution is stirred at room temperature for another 1.5 hours. PrI (17.1 ml, 174 mmol) is added slowly over the period of 45 minutes and the resulting solution is stirred at room temperature overnight. Water (500 ml) is added, the solution is saturated with NaCl and extracted with EtOAc (3×250 ml). The combined extracts are washed with brine (400 ml), dried over Na2SO4 and evaporated in vacuo. The resulting 2-acetyl-2-propyl-succinic acid diethyl ester is obtained as a yellow oil, which is used for the next step without further purification.
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