CC(C)([O-])C.[K+].[C:7]([OH:10])(=[S:9])[CH3:8].[C:11]([O:15][C:16]([NH:18][C@@H:19]1[CH2:24][CH2:23][C@H:22](OS(C)(=O)=O)[CH2:21][CH2:20]1)=[O:17])([CH3:14])([CH3:13])[CH3:12].C(OCC)(=O)C>CN(C=O)C.O>[C:11]([O:15][C:16]([NH:18][C@H:19]1[CH2:24][CH2:23][C@H:22]([S:9][C:7](=[O:10])[CH3:8])[CH2:21][CH2:20]1)=[O:17])([CH3:14])([CH3:12])[CH3:13]
To a stirred suspension of potassium tert-butoxide (0.78 g, 7.00 mmol) and DMF (10 mL), thioacetic acid (0.50 mL, 7.0 mmol) was added at 0° C. The mixture was stirred for ˜5 mins and then a solution of cis methanesulfonic acid 4 tert-butoxycarbonylamino-cyclohexyl ester (1.36 g, 4.70 mmol) in DMF (4.1 mL) was added. The mixture was heated to 80° C. for 3.75 hours and was then poured into a mixture of ethyl acetate (50 mL) and water (50 mL). The phases were separated and the aqueous phase was extracted with ethyl acetate (×2). The combined organic extracts were washed with 10% aqueous citric acid solution, saturated sodium hydrogen carbonate solution, and brine, dried with sodium sulfate and concentrated under vacuum. Purification by column chromatography on silica gel (ethyl acetate/cyclohexane, 1:6) gave 325 mg (26%) of trans thioacetic acid S-(4-tert-butoxycarbonylamino-cyclohexyl) ester as an orange solid. 1H NMR (400 MHz, CDCl3) δ: 4.38 (br s, 1H), 3.42 (br s, 1H), 3.33 (m, 1H), 2.29 (s, 3H), 2.02 (m, 5H), 1.44 (s, 9H), 1.26-1.25 (m, 3H).
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