Regioselectivity in preparation of unsymmetrically substituted 3-aminoquinoxalin-2(1H)-ones

Regioisomer formation has to be considered in the preparation of quinoxalin es having different substituents at the 2- and 3-position. Oxalomonoimidic acid dimethyl ester or oxalomonoimidic acid diethyl ester, chloro(methyl-im ino)acetic acid ethyl ester, chloro[(Z)-hydroxyimino]acetic acid ethyl este r and (Z)-2-[(E)-hydroxyimino]aceto-hydroximoyl chloride were applied to th e synthesis of 3-aminoquinoxalin-2(1H)sone derivatives, and the isomer rati o was investigated concerning the reactivity of the ring-closure reagent. T he structures of reaction products were identified using H-1, C-13 and N-15 NMR techniques. A direct synthesis of quinoxaline-2,3(1H,4H)-dione 3-oxime s is described.