The invention discloses a synthetic method of 3,5-dichloro-6-ethylpyrazine
formamide, and relates to the technical field of intermediate for synthesizing gilteritinib. The method is technically characterized by comprising the following steps: heating 2,6-dichloropyrazine and
formamide to 70-130 DEG C, and carrying out
free radical oxidation reaction under the action of
persulfate to obtain 3,5-dichloropyrazine
formamide; carrying out heating
reflux on 3,5-dichloropyrazine formamide for 3-6 h under the action of a dehydrating agent, and synthesizing 3,5-dichloropyrazine formonitrile through
dehydration; carrying out a Grignard reactionon the 3,5-dichloropyrazine formonitrile in an
organic solvent A under the action of a
methylation reagent to prepare 3,5-dichloro-2-
acetylpyrazine; under theaction of an acidic catalyst and a
silicon-
hydrogen reducing agent, reducing the 3,5-dichloro-2-acetyl
pyrazine in an
organic solvent B to obtain 3,5-dichloro-2-ethyl
pyrazine; and heating the 3,5-dichloro-2-ethyl
pyrazine and formamide to 50-120 DEG C, and carrying out
free radical oxidation reaction under the action of
persulfate to obtain the 3,5-dichloro-6-ethylpyrazine formamide. According to the invention, the operation method is simple, the
reaction conditions of the synthesis process are mild, the cost is reduced, and meanwhile high
economic benefits can be brought.