Two methods for generation of aroyl(quinoxalin-2-yl)ketene

Abstract

By heating a solution of 3-(4-chlorobenzoyl)-4-(4chlorophenyl)pyrrolo[1,2-a]quinoxaline-1,2-dione (I) [1] in boiling anhydrous 1,2,4-trimethylbenzene (pseudocumene, 169–170°C) or a solution of 5-(4-chlorophenyl)-4-[3-(4-chlorophenyl)quinoxalin-2yl]furan-2,3-dione (II) in boiling anhydrous p-xylene (138–139°C) we obtained 4-(4-chlorobenzoyl)-5-(4chlorophenyl)-2-[3-(4-chlorophenyl)quinoxalin-2-yl]1-oxo-1H-pyrido[1,2-a]quinoxalin-3-yl 4-chlorobenzoate (III) in almost quantitative yield. Compound III is formed as a result of thermal decarbonylation of pyrroloquinoxalinedione I or furandione II, with generation of aroyl(quinoxalinyl)ketene IV which undergoes dimerization via [4 + 2]-cycloaddition involving imidoylketene fragment of one molecule IV and ketene C=C bond of the other and subsequent [1,3]-acylotropic migration of the aroyl group. The different decarbonylation temperatures of compounds I and II indicate different thermal stabilities of the dioxopyrrole and dioxofuran rings. The spectral parameters of compound III were very similar to those of model 4-benzoyl-5-phenyl-2-(3phenylquinoxalin-2-yl)-1-oxo-1H-pyrido[1,2-a]quinoxalin-3-yl benzoate whose structure was determined