[CH2:1]([O:3][C:4](=[O:12])[C:5]([S:8][C:9](=O)[CH3:10])([CH3:7])[CH3:6])[CH3:2].C[O-].[Na+].BrCC[CH2:19][C:20]([F:23])([F:22])[F:21]>C(O)C>[CH2:1]([O:3][C:4](=[O:12])[C:5]([CH3:7])([S:8][CH2:9][CH2:10][CH2:19][C:20]([F:23])([F:22])[F:21])[CH3:6])[CH3:2]To a solution of 149 g (785.4 mmol) of 2-acetylsulfanyl-2-methyl-propionic acid ethyl ester (prepared as described in Method C, step 1) in ethanol (1.2 L, degassed under nitrogen for 1 h) are added 169.7 g (105 mmol) of sodium methoxide, followed by a solution of 150 g (785.4 mmol) of 4-bromo-1,1,1-trifluoro-butane. The reaction is heated to 85° C. for 3 d. The solvent is removed under reduced pressure. The residue is dissolved in DCM (1 L) and washed with saturated aqueous NaHCO3 solution (2×1 L). The organic layer is dried over Na2SO4, filtered and the filtrate is concentrated under reduced pressure to afford 171 g of 2-methyl-2-(4,4,4-trifluoro-butylsulfanyl)-propionic acid ethyl ester as a brown oil. Yield: 84%; ES-MS: m/z 259 [M+H]; 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.29 (3 H, t, J=7.17 Hz), 1.51 (6 H, s), 1.76-1.86 (2 H, m), 2.12-2.27 (2 H, m), 2.69 (2 H, t, J=7.17 Hz), 4.18 (2 H, q, J=7.17 Hz)
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