Using an Aldehydo Acid or Related Synthon

Such synthons with o-phenylenediamines afford 2(lF/)-quinoxalmones a single product or two isomers will be formed according to the symmetry of the substrate. Related synthons at a lower oxidation state produce dUiydroquinoxahnones. The following examples illustrate typical results. 

4-Chloro-l,2-benzenediamine (137) and glyoxylic acid gave a mixture of 6-chloro- (138) and 7-chloro-2(l//)-quinoxalinone (139) from which only 6-isomer could be isolated in a pure state (OHCCO2H, H20-Me0H, 20°C, 24h 37%).  

2-Benzenediamino (140) and chloroacetic acid (1 equiv) gave 3,4-dihydro-2(lH)-quinoxalinone (141) (ClCH2C02Na, H2O, reflux, 5 h %) an excess of synthon gave 4-carboxymethyl- (142, Q = H) and/or 1,4-bis- 

These synthons behave much as do the foregoing aldehydo acids but they are usually more convenient and reactive, as indicated by the following examples. 

5-Dimethyl-1,2-benzenediamine (143) gave 6,7-dimethyl-2(lF/)-quinoxali-none (144) [0HCC02Me, EtOH, reflux, 2 h 72% or OHCCO2BU, similarly 69%].  

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