4,6-dichloro-1-methyl-1H-pyrazolo[3,4-d]pyrimidine

4,6-dichloro-1-methyl-1H-pyrazolo[3,4-d]pyrimidine is prepared by the reaction of Methylhydrazine and 2,4,6-trichloropyrimidine-5-carbaldehyde. The specific synthesis steps are as follows:
To a solution of 2,4,6-trichloropyrimidine-5-carbaldehyde (8 g, 37.84 mmol, 1.00 equiv) in ethanol (120 mL) was added a 40percent water solution of methylhydrazine (4 mL, 37.98 mmol, 1.00 equiv) and triethylamine (16 mL) at -78° C. The resulting mixture was stirred for 30 min at -78° C. and then 2 h at 0° C. After completion the reaction was concentrated under vacuum without heating. Then ethyl acetate was added and the solution was washed with saturated ammonium chloride solution. The organic layer was dried over anhydrous sodium sulfate and concentrated under vacuum without heating. The residue was purified by silica gel column chromatography eluting with ethyl acetate/petroleum ether (1:1) to afford 6 g (78percent) of 4,6-dichloro-1-methyl-1H-pyrazolo[3,4-d]pyrimidine as a white solid. LC-MS (ES, m/z): 203 [M+H]+.