Five-membered 2,3-dioxo heterocycles:: L.: Synthesis and thermolysis of 3-aroyl- and 3-hetaroyl-5-phenyl-1,2,4,5-tetrahydropyrrolo[1,2-a]quinoxalin-1,2,4-triones

(Z)-3-Phenacylidene- and (Z)-3-hetaroylmethylidene-1-phenyl-1,2,3,4-tetrahydroquinoxalin-2-ones react with oxalyl chloride to give 3-acyl-5 -phenyl - 1,2,4,5-tetrahydropyrrolo[1,2-a]quinoxaline- 1,2,4-triones. V Thermolysis of the latter generates acyl(3-oxo-4-phenyl-3,4-dihydroquinoxalin-2-yl)ketenes which are stabilized via [4 + 2]-cyclodimerization followed by [ 1,3]-acylotropic shift to afford 4-acyl-3-acyloxy-2-(3-oxo4-phenyl-3,4-dihydroquinoxalin-2-yl)-6-phenyl-5,6-dihydro-1H-pyrido[1,2-a]quinoxaline-1,5-diones.