Preparation method of 2, 4-dichloro-7H-pyrrolo [2, 3-D] pyrimidine

The invention is suitable for the technical field of drug synthesis, and provides a preparation method of 2, 4-dichloro-7H-pyrrolo [2, 3-D] pyrimidine, which comprises the following steps: taking 6-aminouracil as an initial raw material, reacting with chloroacetaldehyde under the action of sodium bicarbonate, and controlling the reaction temperature at 45-65 DEG C to obtain an intermediate; and reacting the intermediate with phosphorus oxychloride under the catalytic action of N, N-diisopropylethylamine, controlling the reaction temperature to be 75-90 DEG C, crystallizing, dissolving and extracting, and decolorizing and crystallizing to obtain the compound. According to the invention, the generation of jelly and color impurities can be inhibited, the operation of post-treatment and refining procedures is remarkably simplified, the production efficiency is improved, the production economy is relatively good, the total yield of 30-kilogram-level production and preparation is greater than 50%, the product purit