O.[SH2:2].[Na].Br[CH:5]([C:12](=[O:14])[CH3:13])[CH2:6][C:7]([O:9][CH2:10][CH3:11])=[O:8].CCOCC>O>[SH:2][CH:5]([C:12](=[O:14])[CH3:13])[CH2:6][C:7]([O:9][CH2:10][CH3:11])=[O:8]A round bottom flask was charged with sodium hydrogensulfide hydrate (1.23 g, 16.9 mmol) in water (14.2 mL). The solution was cooled to about 0° C. followed by the addition of ethyl 3-bromo-4-oxopentanoate (3.79 g, 16.9 mmol) dropwise over about 30 min. The mixture was stirred at about 0° C. for about 3 h. To the reaction mixture was added Et2O (40 mL) and the reaction was warmed to ambient temperature. The crude product was partitioned between Et2O (15 mL) and water (15 mL). The layers were separated and the aqueous layer was back extracted with Et2O (10 mL). The combined organic layers were dried over MgSO4, filtered and concentrated under reduced pressure to afford ethyl 3-mercapto-4-oxopentanoate (1.74 g, 9.87 mmol, 58%, which was used without further purification). LC-MS (Table 1, Method g) Rt=2.24 min, m/z 177 (M+H)+.
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