[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([C@H:8]([CH3:13])[C:9]([O:11][CH3:12])=[O:10])=[CH:4][CH:3]=1.[S-:14][C:15]#[N:16].[Na+]>C1(C)C=CC=CC=1.OS(O)(=O)=O>[C:15]([NH:1][C:2]1[CH:3]=[CH:4][C:5]([C@H:8]([CH3:13])[C:9]([O:11][CH3:12])=[O:10])=[CH:6][CH:7]=1)(=[S:14])[NH2:16]In a 500 ml round-bottomed flask equipped with condenser and magnetic stirrer, at room temperature methyl (2S)-2-(4-aminophenyl)propanoate (17.5 g, 98 mmol) was dissolved in toluene (300 ml) and conc. H2SO4 (2.6 mmol, 50 mmol) was slowly added to the solution Sodium thiocyanate (10.29 g, 128 mmol) was added and the reaction mixture refluxed 24 h. After cooling at room temperature, the solution was washed with a saturated solution of NH4Cl (2×100 ml), dried over anhydrous Na2SO4 and evaporated under vacuum to give a crude which, after purification by flash chromatography (n-hexane/EtOAc 1/1), afforded pure (S)-methyl 2-[4-(carbamothioylamino)phenyl]propanoate (10.7 g, 48.4 mmol) as white solid (49%). 1H-NMR (CDCl3): δ 8.25 (bs, 1H, CSNH), 7.40 (d, 2H, J=7 Hz), 7.20 (d, 2H, J=7 Hz), 6.20 (bs, 2H, CSNH2), 3.75 (m, 1H), 3.65 (s, 3H), 1.50 (d, 3H, J=7 Hz).
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