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

Abstract

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 ratio was investigated concerning the reactivity of the ring-closure reagent. The structures of reaction products were identified using ¹H, ¹³C and ¹⁵N NMR techniques. A direct synthesis of quinoxaline-2,3(1H,4H)-dione 3-oximes is described.