Triethylamine → 3-(4-Nitro-phenyl)-isoxazole-5-carboxylic acid ethyl ester

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To a solution of N-hydroxy-4-nitro-benzimidoyl chloride (2.0 g; 10 mmol) and ethyl propiolate (2.02 ml; 20 mmol) in toluene (25 ml) was added Et3N (1.46 ml; 10.5 mmol) drop wise for 10 minutes. The resulting reaction mixture was heated at 80° C. for 2.5 hours, and then diluted with EtOAc (50 ml) and transferred in a separating funnel. The EtOAc layer was washed with 0.1N HCl (10 ml) followed by water (3×10 ml) and brine (10 ml). The EtOAc layer was dried over anhydrous Na2SO4, solvent was evaporated and the residue was crystallized from CHCl3 and light petroleum to afford the title compound of step 1 (1.35 g; 51.7%). Mass (ES+), 263 (M++1); 1H NMR (CDCl3) δ: 1.45 (t, 3H), 4.48 (q, 2H), 7.26 (s, 1H), 8.02 (d, 2H), 8.35 (d, 2H).

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