[CH2:1]([O:3][C:4](=[O:12])[C:5]([CH3:11])([CH3:10])[CH2:6][CH2:7][CH2:8]Br)[CH3:2].NC(N)=[S:15].[OH-].[Na+]>C(O)C.O>[CH2:1]([O:3][C:4](=[O:12])[C:5]([CH3:11])([CH3:10])[CH2:6][CH2:7][CH2:8][SH:15])[CH3:2]To a solution of 5-bromo-2,2-dimethylpentanoic acid ethyl ester (2.41 g, 10 mmol) in ethyl alcohol (5 mL) was added thiourea (0.77 g, 10 mmol) and the mixture was refluxed for 3 h under a nitrogen atmosphere. A solution of sodium hydroxide (0.62 g, 15 mmol) in deionized water (2.5 mL) was added and stirring was continued for another 2 h at reflux temperature. The mixture was cooled to rt and the ethanol was distilled off under reduced pressure. Diethyl ether (20 mL) was added and the layers were separated. The organic phase was washed with saturated sodium chloride solution (5 mL), dried over sodium sulfate, filtered, and concentrated in vacuo to give 5-mercapto-2,2-dimethylpentanoic acid ethyl ester (1.41 g, 74%) as a yellow oil. 1H NMR (300 MHz, CDCl3/TMS): d (ppm): 4.12 (q, J=7.0 Hz, 2H), 2.57-2.43 (m, 2H), 1.69-1.45 (t, 4H), 1.25 (t, J=7.0 Hz, 3H), 1.17 (s, 7H). 13C NMR(75 MHz, CDCl3/TMS): d (ppm): 177.55, 41.0, 39.24, 25.07, 24.90, 14.18.
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