Sodium Hydroxide → 6-(4-Benzyl-phenyl)-7-cyclohexyl-pyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester

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Reaction Steps

According to a modification of a literature procedure (Suzuki, A. et al Tetrahedron Lett. 1986, 27, 6369-6372) a mixture of 57 mg (0.12 mmol) of 7-cyclohexyl-6-(4-iodo-phenyl)-pyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester and 5 mg (0.006 mmol, 5 mol %) of Pd catalyst was placed into a carousel tube. After a vacuum and argon cycle, tetrahydrofuran (THF) (2 mL) was added, followed by 0.29 mL (0.144 mmol, 1.2 equiv) of B-Benzyl-9-BBN 0.5 M solution in THF, and 0.12 mL (0.36 mmol, 3 equiv) of 3 N NaOH solution, and the resulting mixture was heated reflux under argon overnight. Since analysis by LC-MS revealed unreacted starting material still present, 0.12 mL (0.06 mmol) of B-Benzyl-9-BBN, 5 mg (0.006 mmol, 5 mol %) of Pd catalyst, and 0.12 mL (0.36 mmol) of 3 N NaOH solution was added and heating was continued for 24 h. The reaction mixture was then diluted with ethyl acetate, washed with water, dried over sodium sulfate, passed through a small pad of Celite, and evaporated to give a brown residue (crude coupling product), which was chromatographed on silica gel (Biotage; 2% ethyl acetate in dichloromethane) to afford 36 mg (68% yield) of desired 6-(4-benzyl-phenyl)-7-cyclohexyl-pyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester as indicated by 1H NMR (containing traces of impurities); LC-MS—calcd for C28H29N3O2 [M++H]+: 440.23, found: 440.2.

Provenance & Evidence