[N+:1]([C:4]1[CH:9]=[CH:8][C:7]([S:10]([O:13][CH2:14][C:15]([CH3:32])([C:17]2[O:21][N:20]=[C:19]([NH:22]C(OC3C=CC=CC=3)=O)[CH:18]=2)[CH3:16])(=[O:12])=[O:11])=[CH:6][CH:5]=1)([O-:3])=[O:2].[O-2].[Mg+2].O1CCOCC1>O>[N+:1]([C:4]1[CH:9]=[CH:8][C:7]([S:10]([O:13][CH2:14][C:15]([C:17]2[O:21][N:20]=[C:19]([NH2:22])[CH:18]=2)([CH3:16])[CH3:32])(=[O:11])=[O:12])=[CH:6][CH:5]=1)([O-:3])=[O:2]A stirred mixture of 2-methyl-2-(3-(phenoxycarbonylamino)isoxazol-5-yl)propyl 4-nitrobenzenesulfonate (130 mg, 0.22 mmol), magnesium oxide (45 mg, 0.87 mmol), 1,4-dioxane (8 mL) and water (2 mL) was stirred at 60° C. for 5 h. The reaction mixture was cooled to rt and filtrated. The filtrate was concentrated under reduced pressure to give the crude product. Purification via recrystallization from a 1:1 mixture of diethyl ether and hexane, afforded 2-(3-aminoisoxazol-5-yl)-2-methylpropyl 4-nitrobenzenesulfonate (66 mg, 69%) as a pale yellow solid. 1H NMR (400 MHz, CDCl3) δ 8.38-8.40 (m, 2H), 7.99-8.00 (m, 2H), 5.55 (s, 1H), 4.13 (s, 2H), 1.32 (s, 6H).
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