Triethylamine → Ethyl 5-(1-methylcyclopropyl)isoxazole-3-carboxylate

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To a mixture of 1-ethynyl-1-methylcyclopropane (Preparation 4B, 5.0 g, 62.4 mmol) and (Z)-ethyl 2-chloro-2-(hydroxyimino)acetate (4.73 g, 31.2 mmol) in diethyl ether (80 mL) was added a solution of triethylamine (8.67 mL, 62.4 mmol) in diethyl ether (20 mL) dropwise over 75 min. After complete addition, the reaction mixture was stirred at room temperature for 2 h. The reaction mixture was filtered, and the filtrate was concentrated under reduced pressure. The crude product was purified by flash silica gel chromatography using a 10% mixture of ethyl acetate in hexane to give ethyl-5-(1-methylcyclopropyl)isoxazole-3-carboxylate (3.54 g, 65% yield) as a yellow liquid. The product had an HPLC ret. time=2.23 min.-(condition B); LC/MS M+1=196.07. 1H NMR (400 MHz, CDCl3) δ ppm 0.79 (m, 2H), 1.13 (m, 2H), 1.26 (t, J=7.15 Hz, 3H), 1.35 (s, 3H), 4.31 (q, J=7.12 Hz, 2H), and 6.23 (s, 1H).

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