Methanesulfonic Acid → 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, 0.84 mol) and phosphorus pentoxide (24.0 g, 0.17 mol) was heated at 100° C. The mixture was stirred thoroughly at the same temperature, with the gradual addition of powdery 2-[[3-methyl-1-(2-pyridinyl)-1H-pyrazol-5-yl]amino]benzoic acid (24.0 g, 82 mmol). The reaction mixture was heated and stirred at the same temperature further for 15 minutes. The mixture was allowed to cool to room temperature, and water was added thereto. The solution was made basic by the addition of an aqueous sodium hydroxide solution, and organic matter was extracted with chloroform. The extract was washed with saturated brine and water, 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 mixture of ethyl acetate (300 mL) and methanol (300 mL) under heating, and heated under reflux for 30 minutes after the addition 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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