1-Hydroxybenzotriazole → 5-(5-Nitro-1H-pyrazol-3-yl)-3-[4-(trifluoromethoxy)phenyl]-1,2,4-oxadiazole

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Reaction Steps

To a mechanically stirred solution of 5-nitro-1H-pyrazole-3-carboxylic acid (1.0 g, 6.24 mmol) in dry DMF (50 mL) was added EDCl (1.20 g, 6.24 mmol), HOBT (0.84 g, 6.24 mmol) and N′-hydroxy-4-(trifluoromethoxy)benzenecarboximidamide (1.37 g, 6.24 mmol). The mixture was stirred at rt for 2 h, and then warmed to 140° C. and stirred for additional 2 h. After being cooled to rt, the mixture was diluted with water (100 mL) and extracted with ethyl acetate. The organic extract was successively washed with water and brine. After drying over anhydrous magnesium sulfate and filtration, the solvent was removed in vacuo, and the residue was redissolved in warm acetonitrile (3 mL) to which tert-butyl methyl ether (2 mL) was added. The title compound precipitated and was obtained as a white solid after filtration, washing with tert-butyl methyl ether and drying in vacuo (1.2 g, 56%): 1H NMR (500 MHz, DMSO-d6) δ 8.20 (d, 2H), 7.58 (d, 2H), 7.34 (s, 1H); ES-MS m/z 340 (M-H)−; HPLC RT (Method J) 4.87 min.

Provenance & Evidence