Hydrogen Bromide → Ethyl 6-bromo-7-cyclohexylpyrazolo[1,5-a]pyrimidine-3-carboxylate

Participants

Reaction Steps

To a mixture of 1.69 g (6.50 mmol) of 2-bromo-1-cyclohexyl-3-dimethylamino-propenone and 1.01 g (6.50 mmol) of 3-amino-1H-pyrazole-4-carboxylic acid ethyl ester in 6 mL of ethanol was added 1.0 mL of 30% hydrogen bromide in acetic acid solution, and the resulting mixture was heated at reflux for 1 h. Then the reaction mixture was cooled to rt and concentrated to give a residue which was chromatographed on silica gel (gradient elution with dichloromethane to 25% ethyl acetate in dichloromethane) to give 620 mg (27% over 2 steps) of 6-bromo-7-cyclohexyl-pyrazolo[1,5-α]pyrimidine-3-carboxylic acid ethyl ester as indicated by 1H NMR (δ 8.70 (s, 1H), 8.49 (s, 1H), 4.44 (q, J=6.8 Hz, 2H), 2.70–2.57 (b, 1H), 1.98–1.90 (m, 2H), 1.87–1.78 (m, 2H), 1.78–1.69 (m, 2H), 1.59–1.42 (m, 4H), 1.43 (t, J=6.8 Hz, 3H)); LC-MS—calcd for C15H18BrN3O2 [M++H]+: 352.06, found: 352.0.

Provenance & Evidence