5-(3-Amino-2-hydroxy-5-methyl-phenyl)-thiophene-2-carboxylic acid hydrobromide 24d (366 mg, 1.11 mmol) was dissolved in 3.7 mL of 1 N hydrochloric acid upon cooling by an ice-water bath, followed by dropwise addition of 1.5 mL of aqueous sodium nitrite (85 mg, 1.22 mmol). After the mixture was reacted for 20 minutes, 5-methyl-2-(5,6,7,8-tetrahydro-naphthalen-2-yl)-2,4-dihydro-pyrazol-3-one 3i (228 mg, 1 mmol), sodium bicarbonate (1.4 g, 16.67 mmol) and 2 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 the filter cake was added to 30 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 silica gel column chromatography to obtain the title compound 5-(2-hydroxy-5-methyl-3-{N′-[3-methyl-5-oxo-1-(5,6,7,8-tetrahydro-naphthalen-2-yl)-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}-phenyl)-thiophene-2-carboxylic acid 33 (88 mg, yield 18.09%) as a red solid.
