Sodium Carbonate → 4-Chloro-6-methyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid ethyl ester

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A mixture of 10.0 g (37.4 mM) of 4-chloro-1-ethyl-6-methyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid ethyl ester, prepared according to Examples 1b. and 1c. from 5-amino-1-ethylpyrazole in place of 5-amino-1-pentylpyrazole, and 7.65 g (43.0 mM) of N-bromosuccinimide in 75 ml of carbon tetrachloride was illuminated with a sunlamp and stirred under N2 at gentle reflux for 2 hours. The cooled reaction mixture was filtered and the filtrate concentrated to leave an orange residue which was dissolved in 50 ml of THF. 35 ml of saturated aqueous sodium carbonate were added, and the mixture was stirred vigorously at room temperature for 18 hours and then diluted with water and extracted with ethyl acetate. The combined extracts were dried with MgSO4, filtered and concentrated to leave a white solid which was chromatographed over silica gel using the solvent system of ethyl acetate:hexane (1:3) as the eluant. The fractions containing the desired product were combined and concentrated to leave a white solid. Recrystallization of the solid from toluene/hexane gave 4.88 g of the desired ester as white needles, mp=156°-157.5° C.; tlc, Rf =0.2, silica gel, ethyl acetate:hexane (1:3).

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