4-(3-Amino-2-hydroxy-phenyl)-thiophene-2-carboxylic acid hydrobromide 51c (80 mg, 0.25 mmol) was dissolved in 1 mL of 1 N hydrochloric acid upon cooling by an ice-water bath, followed by dropwise addition of 0.3 mL of aqueous sodium nitrite (19 mg, 0.28 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 (52 mg, 0.23 mmol) was added. The mixture was adjusted to pH 8 with saturated aqueous sodium bicarbonate followed by addition of 2 mL of ethanol. 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 20 mL of water. The mixture was adjusted to pH 3˜4 with concentrated hydrochloric acid. The mixture was filtered and 4 mL of ethyl acetate was added to the filter cake. The resulting mixture was stirred for 2 hours and filtered, the filter cake was dried to obtain the title compound 4-(2-hydroxy-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 51 (11 mg, yield 10.2%) as a black solid.
