[C:1]([C:4]1[O:8][N:7]=[C:6]([C:9]([O:11][CH2:12][CH3:13])=[O:10])[CH:5]=1)(=[O:3])[CH3:2].[CH2:14](O)[CH2:15][OH:16]>C1C=CC=CC=1.CC1C=CC(S(O)(=O)=O)=CC=1>[CH3:2][C:1]1([C:4]2[O:8][N:7]=[C:6]([C:9]([O:11][CH2:12][CH3:13])=[O:10])[CH:5]=2)[O:16][CH2:15][CH2:14][O:3]1A reaction mixture consisting of ethyl 5-acetylisoxazole-3-carboxylate (2.53 g, 13.8 mmol), ethylene glycol (1.29 g, 20.7 mmol) and p-TsOH (0.13 g, 0.69 mmol) in benzene (50 mL) was refluxed with the Dean-Stark adapter for 24 hours (scheme 59). Most of the solvent was removed under reduced pressure and the residue was partitioned between saturated NaHCO3 and EtOAc. Organic layer was collected, washed with brine, water, and dried over MgSO4. Evaporation of the dried extract under reduced pressure afforded the title compound as an oil (3.14 g, 100% yield), which was used for next step without further purification. 1H NMR (DMSO-d6) δ (ppm): 6.89 (s, 1H), 4.35 (q, J=7.2 Hz, 2H), 4.07-4.01 (m, 2H), 4.01-3.94 (m, 2H), 1.70 (s, 3H), 1.32 (t, J=7.0 Hz, 3H). MS (m/z): 227.21 (calc) 228.1 (MH+) (found).
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