Ethyl orthoformate → 3-(4-Nitrophenyl)-1,2,4-oxadiazole

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Reaction Steps

To a stirred solution of 4-nitrobenzonitrile (1 g, 0.0068 mol) in ethanol (20 mL) and water (8 mL) was added hydroxylamine hydrochloride (1.9 g, 0.0272 mol) followed by sodium carbonate (2.2 g, 0.0204 mol). The resulting mixture was heated to reflux at 85° C. under an atmosphere of nitrogen for 2 hours The reaction was monitored by TLC (50% Ethyl acetate in Hexane). The volatiles were evaporated and the residue was extracted with ethyl acetate. The ethyl acetate was washed with brine solution, dried over Na2SO4 and concentrated under reduced pressure to get afford 1.2 g (98%) of N-hydroxy-4-nitro-benzamidine. 1H NMR (DMSO-d6): δ 10.2 (s, 1H), 8.24 (d, 2H), 7.97 (d, 2H), 6.03 (s, 2H). To a stirred solution of N-hydroxy-4-nitro-benzamidine (1.2 g, 0.0066 mol) in THF (15 mL) was added triethyl orthoformate (2.93 g, 0.0198 mol). The resulting mixture was cooled to between 0 and 5° C. Boron trifluoride dimethyl ether (0.9 g, 0.0079 mol) was then added dropwise and the resulting mixture was stirred at ambient temperature for 3 hours. Volatiles were evaporated under reduced pressure and the resulting residue was washed with ether and dried to afford 0.65 g (55%) of 3-(4-nitro-phenyl)-[1, 2, 4]oxadiazole. To a stirred solution of 3-(4-nitro-phenyl)-[1, 2, 4]oxadiazole (0.2 g, 0.001 mol) in THF (15 mL) was added ammonium chloride (0.214 g, 0.004 mol) in water (5 mL) followed by zinc powder (0.262 g, 0.004 mol) portionwise. The resulting mixture was stirred at ambient temperature for 1 hr and then heated to 65° C. for 5 hours. The mixture was then filtered through celite and the organic layers were concentrated under reduced pressure. The residue was extracted with ethyl acetate. The organic layers were washed with brine solution, dried over Na2SO4 and evaporated under reduced pressure to afford 0.155 g (92%) of 4-[1, 2, 4]oxadiazol-3-yl-phenylamine. 1H NMR (DMSO-d6): δ 9.5 (s, 1H), 7.7 (d, 2H), 6.7 (d, 2H), 5.8 (s, 2H).

Provenance & Evidence