Regioisomer formation has to be considered in the preparation of quinoxalines having different substituents at the 2-and 3-position. Oxalomonoimidic acid dimethyl ester or oxalomonoimidic acid diethyl ester, chloro (methylimino) acetic acid ethyl ester, chloro [(Z)- hydroxyimino] acetic acid ethyl ester and (Z)-2-[(E)-hydroxyimino] acetohydroximoyl chloride were applied to the synthesis of 3-aminoquinoxalin-2 (1H)-one derivatives, and the isomer ...