1-(4-Methoxyphenyl)-7-oxo-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxylic acid ethyl ester

545445-40-7

27143-07-3

503614-56-0

Under the protection of nitrogen atmosphere, 5,6-dihydro-3-(4-morpholinyl)-2(1H)-pyridinone (18.2 g) and [(4-methoxyphenyl)hydrazinylidene]ethyl chloroacetate (30.8 g) were dissolved in ethyl acetate (360 mL). Diisopropylethylamine (19.4 g) was added to the reaction system under stirring conditions and the reaction mixture was subsequently heated to 85-95 °C with continuous stirring for 20 hours. Upon completion of the reaction, the mixture was cooled to 15-25 °C, filtered, and trifluoroacetic acid (35 mL) was added slowly and dropwise to the filtrate, followed by continued stirring at the same temperature for 2 hours. The reaction was quenched with 10% aqueous sodium bicarbonate (by mass of sodium bicarbonate) and subsequently extracted once with ethyl acetate. The organic phase was washed sequentially with 10% aqueous sodium bicarbonate and 15% brine (by mass of sodium chloride) and dried over anhydrous sodium sulfate. After filtration, it was concentrated under vacuum at 45-55°C and -0.085 MPa to -0.1 MPa to give a yellow solid. The yellow solid was dissolved in 150 mL of ethyl acetate, heated to 75-85°C and stirred for 1 hr until completely dissolved, then cooled to 0-5°C and stirred for 2 hr, filtered and washed with pre-cooled ethyl acetate. Finally, it was dried under vacuum at 45-55 °C and -0.01 MPa to -0.1 MPa for 8-12 h. 25.6 g of light yellow solid was obtained in 81.2% yield and 98.30% HPLC purity.