7-Chloro-5-methyl-1H-pyrazolo[4,3-b]pyridine

268547-52-0

94220-38-9

Step 1: 5-methyl-1H-pyrazolo[4,3-b]pyridin-7-ol (4.58 g, 30.7 mmol) was dissolved in phosphorochloridic acid (30 mL) and the reaction was heated at 110 °C for 30 min. Upon completion of the reaction, the mixture was cooled to room temperature and subsequently slowly poured into ice water. The pH of the mixture was adjusted with 6N NaOH solution to 5. The precipitated solid product was collected by filtration. The mother liquor layer was extracted with ethyl acetate (3 x 250 mL). The above solids were dissolved in the combined organic phases, washed with brine solution (1 x 250 mL), dried over anhydrous sodium sulfate, filtered and concentrated. Purification of the concentrate by short silica gel column chromatography afforded 7-chloro-5-methyl-1H-pyrazolo[4,3-b]pyridine (Compound Ie) as a light yellow solid (4.50 g, 26.8 mmol, 87% yield).GC/MS analysis: m/z = 167 (100%); LC/MS analysis: [M + H]+ = 168.