2-(2-Hydroxy-3-amino-phenyl)-5-methyl-thiazole-4-carboxylic acid hydrobromide 47c (200 mg, 0.60 mmol) was dissolved in 2 mL of hydrochloric acid (1 N) upon cooling by an ice-water bath, followed by dropwise addition of 0.82 mL of aqueous sodium nitrite (46 mg, 0.66 mmol). After the mixture was stirred for 20 minutes, 2-indan-5-yl-5-methyl-2,4-dihydro-pyrazol-3-one 1i (116 mg, 0.544 mmol) was added. The mixture was adjusted to pH 8˜9 by batch addition of saturated aqueous sodium bicarbonate (781 mg, 9.3 mmol). 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 20 mL of water. The mixture was adjusted to pH 3˜4 with concentrated hydrochloric acid. The mixture was filtered and the filter cake was dried and purified by HPLC to obtain the title compound 2-{2-hydroxy-3-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-phenyl}-5-methyl-thiazole-4-carboxylic acid 47 (195 mg, yield 75.9%) as a red solid.
