Acetic Acid → [7-(2,4-Dichlorophenyl)-2-ethylpyrazolo[1,5-a]pyridin-3-yl]amine

Participants

Reaction Conditions

Reaction Steps

7-(2,4-Dichlorophenyl)-2-ethyl-3-nitropyrazolo[1,5-a]pyridine (110 mg) was suspended in ethanol (6 mL), and then water (3 mL), acetic acid (1 mL) and zinc powder (220 mg) were added and the mixture was heated and stirred at 60° C. for 1 hour. The reaction mixture was filtered, water was added to the filtrate, extraction was performed with ethyl acetate and the extract washed with saturated aqueous sodium hydrogencarbonate and brine. After drying over anhydrous magnesium sulfate and filtration, the solvent was concentrated under reduced pressure to obtain [7-(2,4-dichlorophenyl)-2-ethylpyrazolo[1,5-a]pyridin-3-yl]amine (90 mg) as crude crystals. These were dissolved in tetrahydrofuran (1 mL), and after adding propionaldehyde (0.059 mL) and 3 M aqueous sulfuric acid (0.294 mL), sodium borohydride (22.2 mg) was added in five portions while vigorously stirring on ice, and stirring was continued for 30 minutes. Water was added to the reaction mixture, extraction was performed with diethyl ether and the extract washed with saturated sodium hydrogencarbonate and brine. After drying over anhydrous magnesium sulfate and filtration, the solvent was concentrated under reduced pressure, the residue was purified by silica gel column chromatography, and the title compound (59 mg) was obtained from the n-hexane:ethyl acetate (100:1) fraction as a yellow oil.

Provenance & Evidence