[CH3:1][CH:2]1[CH2:8][CH2:7][CH2:6][CH:5]([CH3:9])[O:4][C:3]1=[O:10].I.NC(N)=[S:14].[OH-].[Na+]>O>[SH:14][CH:5]([CH3:9])[CH2:6][CH2:7][CH2:8][CH:2]([CH3:1])[C:3]([OH:4])=[O:10]A 10 mL round bottom flask equipped with a stir bar was charged with 3,7-dimethyloxepan-2-one (61, 0.729 g, 5.13 mmol), hydroiodic acid (2.029 ml, 15.38 mmol) and thiourea (2.73 g, 35.91 mmol). The flask was equipped with a water cooled water condenser, placed under a nitrogen atmosphere and heated to reflux. The reaction proceeded at reflux overnight. A sodium hydroxide (3.69 g, 92 mmol) solution in water (5 mL) was then added to the reaction flask. The reaction was refluxed overnight. The reaction mixture was removed from heat, cooled to room temperature and the flask contents were transferred to a separatory funnel. The aqueous layer was extracted with ethyl acetate and the extract was set to the side. The aqueous layer was acidified with HCl to pH 2 and extracted with ethyl acetate (2×100 mL) and methylene chloride (1×100 mL). The organic extracts were combined, washed with 30 mL of brine, dried over anhydrous sodium sulfate and concentrated in vacuo to give 823 mg of crude 6-mercapto-2-methylheptanoic acid (62, 92% yield) as a light brown oil.
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