Water → 4-Chloro-3-methylisoxazole-5-carboxylic acid

A solution of ethyl 3-chloro-2,4-dioxovalerate (3.0 g, 15.6 mmol) and hydroxylamine hydrochloride (1.08 g, 15.6 mmol) in a mixuture of 1.5 mL of H2O and 1 mL of CH3OH was heated to reflux. After four hours TLC analysis indicated that all of the starting material had been consumed. Sodium hydroxide (0.31 g, 7.8 mmol) was added to the hot solution. After four hours the mixture was allowed to cool to room temperature and concentrated in vacuo. The residue was taken up in a 1:1 mixture to ethyl acetate/H2O. The aqueous layer was made basic with 2N NaOH and separated. The aqueous layer was then acidified with 2M HCl and extracted with ethyl acetate (125 mL). The ethyl acetate extract was washed with H2O (2×100 mL), dried over anhydrous MgSO4, filtered and concentrated in vacuo to give 600 mg (24% yield) of the desired product a gummy tan solid: 1H NMR (CDCl3) 67 8.8 (bs, 1H), 2.3 (s, 3H).