Preparation method of pyrazine derivative

The invention discloses a preparation method of a pyrazine derivative, namely 3-amino-6-(3, 5-dimethylphenyl) pyrazine-2-carboxamide. 3-aminopyrazine-2-carboxylic acid is taken as a starting raw material, a target product is obtained by esterification, amidation, bromination and coupling reaction, and the compound is an important pharmaceutical intermediate.