Using an Aldehydo Ketone or Related Synthon

5-Dichloro-l,2-benzenediamine (110) and phenylglyoxal (111) gave dichloro-2-phenylquinoxaline (112) (MeOH, 55°C, 30 min 73%).  

2-Benzenediamine gave 2-(2,4-dimethylphenyl)quinoxaline (113) [2,4-Me2C6H3C(=0)CH0, AcOH, 100°C, 30 min 55%] or 2-(4 -acetoxybi-phenyl-4-yl)quinoxalme (114) (P-ACOC6H4C6H4COCHO-P, EtOH, reflux, min 70%).  

4-Fluoro-5-methyl-1,2-benzenediamine (115) gave an apparently inseparable mixture of 6-fluoro-2,7-dimethyl-(116) and 6-fluoro-3,7-dimethylquinoxaline (117) (AcCHO, H2O, reflux, 15 min 75%).  

4-Acetyl-1,2-benzenediamine gave an easily separable mixture of 6-acetyl-2-phenyl- (118, R = Ac) and 6-acetyl-3-phenylquinoxaline (119, R = Ac) (BzCHO, EtOH, reflux, 3 h 61% and 18%, respectively) similarly, 4-trifluoromethyl-1,2-benzenediamine gave 2-phenyl-6-trifluoromethyl- (118, R = CF3) and 2-phenyl-7-trifluoromethylquinoxaline (119, R = CF3) (like- 

2-[(2-Carboxy-l-methylethyl)amino]-5-trifluoromethylaniline (120) gave 2-phenyl-7-trifluoromethylquinoxaline (122), probably by loss of crotonic acid and water from the unisolated intermediate (121) (neat BzCHO, 155°C, 3 h 82% note that no isomer was detected).  

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