Reaction of 2,1,3-benzoxadiazole 1-oxide with ethyl 2,4-dioxo-4-phenylbutyrate. A route to 2-benzoylquinoxaline, its 1,4-dioxide, and related compounds

Abstract

The Beirut reaction of 2,1,3-benzoxadiazole 1-oxide and ethyl 2,4-dioxo-4-phenylbutryate in ethanol, or acetonitrile, catalysed by triethylamine gave first ethyl 3-benzoylquinoxaline-2-carboxylate 1,4-dioxide and then, in a slower reaction, 2-benzoylquinoxaline 1,4-dioxide. The latter was isolated in two distinct stable crystalline forms. The effects of changing the proportions of the reactants, the tertiary alkylamine used, and the temperature have been studied. Both above-mentioned 1,4-dioxides were reduced to the corresponding quinoxalines. Ethyl 3-benzoylquinoxaline-2-carboxylate 1,4-dioxide decomposed slowly to several products in ethanol in the presence of triethylamine or diethylamine and was converted by ethanolic potassium hydroxide into the potassium salt of quinoxaline-2-carboxylic acid 1,4-dioxide.