Phosphorus oxychloride → 4-chloro-1-methyl-1H-pyrazolo(3,4-d)pyrimidine

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Reaction Steps

80 g. of 1-methyl-1,5-dihydro-4H-pyrazolo[3,4-d]- pyrimidin-4-one are added to 300 ml. of phosphorus oxychloride and the mixture is refluxed. After distilling off the excess phosphorus oxychloride, the semi-solid residue is extracted with 3 × 100 ml. of boiling benzene. The benzene extracts are combined and concentrated to half-volume, then added to petroleum ether. After standing 12 hours in the refrigerator, the precipitated 1-methyl-4-chloropyrazolo[3,4-d]- pyrimidine is filtered under suction and recrystallized from cyclohexane to obtain 54 g. of white crystals, m.p. 93°-96° (yield 60.5%).

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