Upon cooling by an ice-water bath, 3′-amino-5′-fluoro-2′-hydroxy-biphenyl-3-carboxylic acid 2f (250 mg, 1.01 mmol) was dissolved in 10 mL of hydrochloric acid (1 N) followed by addition of 10 mL of aqueous sodium nitrite (77 mg, 1.12 mmol) and 5-methyl-2-(5,6,7,8-tetrahydro-naphthalen-2-yl)-2,4-dihydro-pyrazol-3-one 4i (230 mg, 1.01 mmol). The mixture was adjusted to pH 8 with saturated aqueous sodium bicarbonate, followed by addition of 10 mL of ethanol. The reaction was warmed up to room temperature overnight and monitored by TLC until the disappearance of the starting materials. The mixture was filtered, dried and recrystallized from methanol to obtain the title compound 5′-fluoro-2′-hydroxy-3′-{N′-[3-methyl-5-oxo-1-(5,6,7,8-tetrahydro-naphthalen-2-yl)-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}-biphenyl-3-carboxylic acid 4 (64 mg, yield 13.1%) as a red solid.
