Quinoxalines as Substrates

The oxidation of quinoxalines to pyrazine derivatives has been used for almost a century. Some typical examples from recent literature follow  

Quinoxaline (127) gave 2,3-pyrazinedicarboxylic acid (128) [KMn04 (6 mol), H20, 95°C, 3 h 71% 947 other oxidative procedures were reported840,846 1057 1215 to give up to 79% yield], and hence 2-pyrazinecarboxylic acid (129) by thermal decarboxylation (sublimation at 210°C/4 mmHg 81%).846, cf 1057 

47/)-Quinoxalincdione (133) gave 5,6-dihydro-2,3,5,6(17/,477)-pyra/i-netetrone (134) [Co(OAc)2, AcOH, 03 [, (4 mol), 20°C 45%] 2,3-dichloroquinoxaline (135) gave the same product (134) (similarly 70% clearly involving a hydrolytic step) the mechanisms were discussed.1463 

The sole example of this synthesis appears to be more of interest than utility. Thus 6-(2-amino-2-phcnylacetamido)-3,3-dimcthyl-7-oxo-4-thia-l-azabicyclo[3.2.0]-heptane-2-carboxylic acid (ampicillin 136), in aqueous glucose maintained at pH 9.2 

Primary Syntheses from Other Heterocyclic Systems 

---

Most of the recently reported cyclizations of extranuclear halogenoquinoxalines have involved 2,3- or 6,7-bis(halogenoalkyl)quinoxalines as substrates. These and a few other types of cyclization are illustrated briefly in the following examples. 

---