4-nitro-1H-pyrazole-3-carboxylic acid (2-amino-4,5-dimethoxy-phenyl)-amide → 5,6-Dimethoxy-2-(4-nitro-1,2-dihydro-3H-pyrazol-3-ylidene)-2H-benzimidazole

Participants

Reaction Conditions

Reaction Steps

To a solution of EDC (4.81 g 25 mmol), HOBt (3.40 g, 25 mmol) and triethylamine (4.67 g, 46 mmol) in DMF (100 ml) was added 4-nitro-1H-pyrazole-3-carboxylic acid (3.63 g, 23.09 mmol) and 4,5-dimethoxy-benzene-1,2-diamine dihydrochloride (5.06 g, 20.99 mmol) and the mixture was stirred at room temperature overnight. The solvent was removed in vacuo and the resulting solid partitioned between EtOAc (50 ml) and saturated aqueous NaHCO3 (50 ml). A precipitate was formed and removed by filtration. The filtrate was washed with water followed by diethyl ether and then azeotroped with MeOH and toluene to yield 4-nitro-1H-pyrazole-3-carboxylic acid (2-amino-4,5-dimethoxy-phenyl)-amide (2.35 g, 36%). 4-Nitro-1H-pyrazole-3-carboxylic acid (2-amino-4,5-dimethoxy-phenyl)-amide (2.35 g, 7.65 mmol) was dissolved in acetic acid (150 ml) and refluxed at 140° C. for 5 hours. The solution was left to cool and the solvent removed in vacuo. The resulting solid was partitioned between EtOAc (25 ml) and brine (25 ml). The organic layer was separated, dried (MgSO4), filtered and the solvent removed in vacuo to yield 5,6-dimethoxy-2-(4-nitro-1H-pyrazol-3-yl)-1H-benzimidazol (2.08 g, 94%).

Provenance & Evidence