[CH2:1]([C:3]1[N:4]=[C:5]([CH3:8])[S:6][CH:7]=1)[CH3:2].C([Li])CCC.[C:14](OCC)(=[O:16])[CH3:15]>C1COCC1>[CH2:1]([C:3]1[N:4]=[C:5]([CH2:8][C:14]([CH3:15])=[O:16])[S:6][CH:7]=1)[CH3:2]1.70 g (13.4 mmol) of the compound from example 16A are dissolved in 15 ml of abs. THF and, at −78° C., 5.88 ml (14.7 mmol) of n-butyllithium (2.5 M solution in hexane) are added dropwise. After stirring at −78° C. for 2 hours, 2.00 g (22.7 mmol) of ethyl acetate are added as a solution in 10 ml of abs. THF. The mixture is stirred at −78° C. for 1 h and then warmed to room temperature. It is then hydrolyzed with sodium bicarbonate solution, and the mixture is extracted three times with diethyl ether. The combined organic phases are dried with magnesium sulfate, and the solvent is removed in a rotary evaporator. 1.89 g (84% of theory) of the title compound are obtained. GC-MS (Method 2): Rt=4.20 min; MS (Elpos): m/z=169 [M]+.
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