Using a Keto Ester or Related Synthon

Like keto acids, the corresponding esters can give a single product or a mixmre of isomers according to the symmetry of the reactants. Keto esters and the like have 

2-Benzenediamine (218) and ethyl pyruvate (219) gave 3-methyl-2(l//)-quinoxalinone (220) (EtOH, reflux, 3 h 95%).  

The same substrate (218) and ethyl ethoxalylacetate (Et02CC0CH2C02Et) gave 3-ethoxycarbonylmethyl-2(l//)-quinoxalinone (221, R = H) (EtOH, reflux, 3 h 80% ° likewise but 15 min 64%) the homologous substrate, 3,6-dimetyl-l,2-benzenediamine, and the same synthon gave 3-ethoxycarbonyl-methyl-5,8-dimethyl-2(l//)-quinoxalinone (221, R = Me) (AcOH, reflux, briefly 61%).  

2-Benzenediamine (218) and the hydrochloride of ethyl 2-[A-cyclohexyl-(ethoxyformimidoyl)]glyoxalate [Et02CCOC(OEt)=N(CeHn)] (prepared in situ) gave A-cyclohexyl-3-oxo-3,4-dihydro-2-quinoxalinecarboxamide (222) (PhH-EtOH-CH2Cl, 40°C, 2 h 81% clearly needing an hydrolytic step). o-Anilinoaniline gave ethyl 3-oxo-4-phenyl-3,4-dihydro-2-quinoxalinecarboxy- 

2-Benzenediamine gave 3-perfluoro(2-isopropoxyethyl)-2(l//)-quinoxahnone (224) [Et02CC(=0)CF2CF20CF(CF3)2, EtOH, reflux, 48 h 77%].  

4-Dimethylamino-l,2-benzenediamine (225) gave a separable mixture of 7-dimethylamino- (226) and 6-dimethylamino-3-methyl-2(l //)-quinoxali-none (227) (AcC02Et, EtOH, reflux, N2, 4 h 70% and 25%, respectively).72 

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