5-(3-Amino-2-hydroxy-phenyl)-furan-2-carboxylic acid hydrobromide 9c (150 mg, 0.5 mmol) was dissolved in hydrochloric acid (1.7 mL, 1 mol/L) upon cooling by an ice-water bath, followed by dropwise addition of 0.6 mL of aqueous sodium nitrite (38 mg, 0.55 mmol). After the mixture was reacted for 20 minutes, 2-(2,2-dimethyl-indan-5-yl)-5-methyl-2,4-dihydro-pyrazol-3-one 45d (109 mg, 0.45 mmol), sodium bicarbonate (630 mg, 7.5 mmol) and 1 mL of ethanol were added successively. The reaction mixture was reacted overnight at room temperature. The reaction was monitored by TLC until the disappearance of the starting materials. The mixture was filtered and 15 mL of water was added to the filter cake. The mixture was adjusted to pH 3˜4 with concentrated hydrochloric acid and filtered. The filter cake was washed with ethyl acetate (1 mL×3) and dried to obtain the title compound 5-(3-{N′-[1-(2,2-dimethyl-indan-5-yl)-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}-2-hydroxy-phenyl)-furan-2-carboxylic acid 45 (67 mg, yield 31.6%) as a yellow solid.
