[CH2:1]([Li])CCC.C(NC(C)C)(C)C.[C:13]([CH:18]1[CH2:22][S:21][C:20]([C:23]2[CH:28]=[CH:27][CH:26]=[CH:25][CH:24]=2)=[N:19]1)([O:15][CH2:16][CH3:17])=[O:14].CI.Cl>CC(OC)(C)C>[C:13]([C:18]1([CH3:1])[CH2:22][S:21][C:20]([C:23]2[CH:28]=[CH:27][CH:26]=[CH:25][CH:24]=2)=[N:19]1)([O:15][CH2:16][CH3:17])=[O:14]152.2 g (0.594 mol, 1.10 eq) of butyllithium solution (25% strength in heptane) were added dropwise under nitrogen in the course of 30 min to a solution of 90.8 ml (65.6 g, 0.648 mol, 1.20 eq) of diisopropylamine in 800 ml of absolute MTBE at −15° C. This solution was stirred at −15° C. for 30 min. 400 ml of the MTBE solution containing the 4-carbethoxy-2-phenyl-thiazoline were added dropwise at −15° C. in the course of 30 min and the mixture was stirred at −15° C. for 1 h, whereby a brown solution resulted. 115.0 g (50.4 ml, 0.81 mol, 1.50 eq) of methyl iodide were added and the reaction mixture was warmed to 23° C. and stirred at this temperature for a further 3 h. 300 ml of 2 M HCl were then slowly added with vigorous stirring, then the mixture was adjusted to pH 2-3 so that the temperature did not exceed 30° C. The two-phase mixture obtained thereby was stirred for a further 30 min. The organic phase was then separated off. This MTBE solution, containing 4-carbethoxy-4-methyl-2-phenylthiazoline, was employed in stage 3.
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