Cl[C:2]([C:5]1[C:6]([Cl:11])=[N:7][CH:8]=[CH:9][CH:10]=1)=[N:3][OH:4].[CH3:12][O:13][C:14](=[O:18])[C:15]#[C:16][CH3:17].C(N(CC)CC)C>C(OCC)C>[CH3:12][O:13][C:14]([C:15]1[C:2]([C:5]2[C:6]([Cl:11])=[N:7][CH:8]=[CH:9][CH:10]=2)=[N:3][O:4][C:16]=1[CH3:17])=[O:18]Combine chloro(2-chloro(3-pyridyl))(hydroxyimino)methane (2.90 g, 0.015 mol) with methyl-2-butynoate (1.19 mL, 0.012 mol) in diethyl ether (75 mL). Cool the mixture in an ice bath under a nitrogen atmosphere. Add a solution of triethylamine (1.77 mL, 0.013 mol) in diethyl ether (10 mL) in a dropwise manner. Stir the mixture overnight while warming to ambient temperature. Quench the mixture with water and extract with diethyl ether. Concentrate the combined extracts and elute over silica gel with 10% methanol/dichloromethane to give the desired isoxazole along with a co-eluting impurity (2.30 g, 60%). MS(ES): (M+1)+ 253.0, 255.0 m/z.
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