3′-Amino-2′-hydroxy-5′-methyl-biphenyl-3-carboxylic acid hydrochloride 11f (346 mg, 1.07 mmol) was dissolved in hydrochloric acid (5 mL, 2 mol/L) upon cooling by an ice-water, followed by addition of 2 mL of aqueous sodium nitrite (81 mg, 1.17 mmol). After the mixture was reacted for 30 minutes, 2-indan-5-yl-5-methyl-2,4-dihydro-pyrazol-3-one 1i (229 mg, 1.07 mmol) was added. The mixture was adjusted to pH 8 with saturated aqueous sodium bicarbonate, followed by addition of 5 mL of ethanol. The 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 the filter cake was washed with ethanol. The filtrate was poured into a mixture of ice and water. The resulting mixture was adjusted to pH 4 with concentrated hydrochloric acid to form precipitates. The mixture was filtered and the filter cake was washed three times with ethyl acetate, and then dried to obtain the title compound 2′-hydroxy-3′-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-5′-methyl-biphenyl-3-carboxylic acid 29 (75 mg, yield 15%) as a red solid.
