Cl[C:2]1[O:3][C:4]2[C:5](=[C:7]([C:11]([O:13]C)=[O:12])[CH:8]=[CH:9][CH:10]=2)[N:6]=1.Cl.C[C@@H]1CSC[C@@H](C)N1.C(=O)([O-])[O-].[K+].[K+]>CN(C=O)C.O>[O:3]1[C:4]2=[CH:10][CH:9]=[CH:8][C:7]([C:11]([OH:13])=[O:12])=[C:5]2[N:6]=[CH:2]1A mixture of methyl 2-chlorobenzoxazole-4-carboxylate (360 mg, 1.70 mmol), (3S,5S)/(3R,5R)-3,5-dimethylthiomorpholine hydrochloride (270 mg, 1.62 mmol) and potassium carbonate (672 mg, 4.86 mmol), in DMF (5 mL), was stirred at ambient temperature for 6 h. The reaction was then heated at 55° C. for 2 h before it was diluted with H2O (20 mL) and extracted with EtOAc (2×40 mL). The combined organic layers were washed with brine, dried (Na2SO4) and concentrated under reduced pressure. The crude methyl ester was retained for future purification. The remaining aqueous phase was then acidified to pH 5 by addition of 1 N HCl and extracted with CH2Cl2 (2×40 mL). The combined organic extracts were dried (Na2SO4) and concentrated under reduced pressure to afford crude (3S,5S)/(3R,5R)-3,5-dimethylthiomorpholino)benzoxazole-4-carboxylic acid (70 mg, 15%) which was directly elaborated without purification.
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