[OH:1][C:2]1[C:6]([CH3:7])=[C:5]([C:8]([OH:10])=[O:9])[O:4][N:3]=1.Cl.[CH3:12][CH2:13]O>>[OH:1][C:2]1[C:6]([CH3:7])=[C:5]([C:8]([O:10][CH2:12][CH3:13])=[O:9])[O:4][N:3]=13-Hydroxy-4-methylisoxazole-5-carboxylic acid (6.0 g, 42 mmol) and a saturated solution of HCl in EtOH (110 mL) was boiled under reflux for 4 h. The solution was concentrated in vacuo and the residue dissolved in EtOAc, dried (MgSO4) and evaporated in vacuo to give crude title compound (7.2 g, 100%). A small sample was recrystallized (EtOAc/heptane) to give colorless crystals: mp 133-134° C. The crude product was used in the next step without further purification.
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