Water → 3-Methyl-1-(2-pyridinyl)-1,9-dihydro-4H-pyrazolo[3,4-b]quinolin-4-one

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Reaction Conditions

Reaction Steps

A mixture of methanesulfonic acid (120 mL, 1.85 mmol) and phosphorus pentoxide (24.0 g, 0.17 mol) was heated to 100° C. To the mixture stirred at the same temperature, powdery 2-[[3-methyl-1-(2-pyridinyl)-1H-pyrazole-5-yl]amino]benzoic acid (24.0 g, 82 mmol) was added gradually in small portions. The mixture was heated and stirred at the same temperature for 15 minutes. After the solution was allowed to cool to room temperature, iced water was added to the solution. The solution was made basic by the addition of an aqueous sodium hydroxide solution, and the organic matter was extracted with chloroform. The extract was washed with saturated brine and water, and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue thus obtained was purified by basic silica gel column chromatography (chloroform). The crystals thus obtained we dissolved in a hot mixture of ethyl acetate (300 mL) and methanol (300 mL), and the solution was heated under reflux for 30 minutes in the presence of activated carbon (2.5 g). The hot solution was filtered and the solvents were evaporated under reduced pressure. The residue was recrystallized from ethyl acetate to give the title compound (15.1 g, 67% yield).

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