[F:1][C:2]([C:5]1[CH:9]=[C:8]([NH2:10])[O:7][N:6]=1)([CH3:4])[CH3:3].C(=O)([O-])[O-].[K+].[K+].Cl[C:18]([O:20][C:21]1[CH:26]=[CH:25][C:24]([Cl:27])=[CH:23][CH:22]=1)=[O:19]>C1COCC1>[F:1][C:2]([C:5]1[CH:9]=[C:8]([NH:10][C:18](=[O:19])[O:20][C:21]2[CH:26]=[CH:25][C:24]([Cl:27])=[CH:23][CH:22]=2)[O:7][N:6]=1)([CH3:4])[CH3:3]3-(2-fluoropropan-2-yl)isoxazol-5-amine (11.26 g, 78.19 mmol) described in Example 42A in THF (300 mL) was treated with potassium carbonate (21.58 g, 156 mmol) and p-chlorophenyl chloroformate (14.94 g, 78.19 mmol). After stirring at rt for 1 h, additional p-chlorophenyl chloroformate (7.5 g, 39.26 mmol) was introduced, and the reaction mixture was stirred at rt overnight. The mixture was filtered through a celite pad, washed with ethyl acetate and concentrated to dryness. The residue was taken into ethyl acetate, washed with brine, and the organics dried (MgSO4) and concentrated. The residue was purified by silica gel chromatography (eluting with 10 to 50% ethyl acetate in hexanes) to give 4-chlorophenyl 3-(2-fluoropropan-2-yl)isoxazol-5-ylcarbamate (16.51 g, 71%) as a cream solid. 1H NMR (300 MHz, CDCl3) δ 7.87 (brs, 1H), 7.36-7.41 (m, 2H), 7.13-7.17 (m, 2H), 6.27 (s, 1H), 1.74 (d, J=21 Hz, 6H); LC-MS (ESI) m/z 299 (M+H)+.
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