Carbon Dioxide → 7-(2-chloro-4,6-dimethylphenyl)-2-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-3-carboxylic acid

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3-Bromo-7-(2-chloro-4,6-dimethylphenyl)-2-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine (1.46 g) and a few crystals of 1, 10 phenanthroline were dissolved in 25 mL of dry tetrahydrofuran and chilled to −78° C. under an atmosphere of argon. Then a 2.0 M solution of n-butyllithium in cyclohexane was added dropwise until the dark color of the phenanthroline/organolithium complex persisted. Then an additional 2.05 mL of the n-butyllithium solution was added. After 10 minutes, carbon dioxide, generated from dry ice, was bubbled through the reaction mixture for 5 minutes. After the reaction mixture had been stirred at −78° C. for 5 minutes, the cooling bath was removed and the mixture was allowed to warm for 5 minutes before being quenched by the addition of water. The mixture was combined with ethyl acetate and water, acidified with dilute hydrochloric acid, and the phases separated. The ethyl acetate was dried with magnesium sulfate and concentrated. The residue was chromatographed on silica gel eluting with an acetone/hexane gradient to provide 1.11 g of 7-(2-chloro-4,6-dimethylphenyl)-2-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-3-carboxylic acid, mp 247.8–248.3° C.

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