Using a Keto Acid or Related Synthon

As they are essentially unsymmetric, such synthons will give a single quinox-alinone only when the o-phenylenediamine or related substrate is symmetric or one of its amino groups is secondary. The following examples illustrate conditions and the yields to be expected. 

5-Dimethyl-1,2-benzenediamine with phenylglyoxylic acid (PhCOC02H) gave 6,7-dimethyl-3-phenyl-2(17/)-quinoxalinone (212, R = Ph) (EtOH, reflux. 

5-Dimethoxy-l,2-benzenediamine with mesoxalic acid (HO2CCOCO2H) gave 6,7-dimethoxy-3-oxo-3,4-dihydro-2-quinoxalmecarboxylic acid (213) (0.5M HCl, 98°C, 2 h  

2-Cyclohexanediamine with diphenacyl sulhde, appearing to react as ben-zoyl(thiopyruvic) acid, gave a separable mixture of cis- and trani-3-phenyl-4a,5,6,7,8,8a-hexahydro-2(lF/)-quinoxalinethione (214) [HOCH2CH2OH-EtOH, 20°C, 10 days (or reflux, 4 h) 10% and 6%, respectively].  

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