5-(3-Amino-2-hydroxy-phenyl)-1,2,4-trimethyl-1H-pyrrole-3-carboxylic acid ethyl ester hydrobromide 6h (180 mg, 0.66 mmol) was dissolved in 2.2 mL of hydrochloric acid (1 N) upon cooling by an ice-water bath, followed by dropwise addition of 0.8 mL of aqueous sodium nitrite (50 mg, 0.72 mmol). After the mixture was stirred for 20 minutes, 2-indan-5-yl-5-methyl-2,4-dihydro-pyrazol-3-one 1i (126 mg, 0.59 mmol) was added. The mixture was adjusted to pH 8˜9 with saturated aqueous sodium bicarbonate. Then the generated bubbles were quenched with 2 mL of ethanol. The reaction mixture was warmed up to room temperature and reacted overnight. The reaction was monitored by TLC until the disappearance of the starting materials. The mixture was filtered and the filter cake was dissolved in a mixture of 20 mL of chloromethane and 20 mL of water. After mixing well, the mixture was adjusted to pH 3˜4 with concentrated hydrochloric acid. The separated organic layer was washed with saturated brine, dried over anhydrous sodium sulfate, filtered to remove the drying agent and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography to obtain the title compound 5-{2-hydroxy-3-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-phenyl}-1,2,4-trimethyl-1H-pyrrole-3-carboxylic acid ethyl ester 48 (80 mg, yield 25.8%) as a red solid.
