Y. Kurasawa et al., Quinolone analogues 2. A facile synthesis of novel 3-substituted 1-alkyl-4-oxo-1,4-dihydropyridazino[3,4-b]quinoxalines, J HETERO CH, 37(5), 2000, pp. 1257-1263
The reaction of the 2-(1-alkylhydrazino)-6-chloroquinoxaline 4-oxides 1a,b
with diethyl acetone-dicarboxylate or 1,3-cyclohexanedione gave ethyl 1-alk
yl-7-chloro-3-ethoxycarbonylmethylene-1,5- dihydropyridazino[3,4-b]quinoxal
ine-3-carboxylates 5a,b or 6-alkyl-10-chloro-1-oxo-1,2,3,4,6,12-hexahydroqu
inoxalino[2,3-c]cinnolines 7a,b, respectively. Oxidation of compounds 5a,b
with nitrous acid afforded the ethyl 1-alkyl-7-chloro-3-ethoxycarbonylmethy
lene-4-hydroxy-1,4-dihydropyridazino[3,4-b]quinoxaline-4-carboxylates 9a,b,
whose reaction with base provided the ethyl 2-(1-alkyl-7-chloro-4-oxo-1,4-
dihydropyridazino[3,4-b]quinoxalin-3-yl)acetates 6a,b, respectively. On the
other hand, oxidation of compounds 7a,b with N-bromosuccinimide/water furn
ished the 4-(1-alkyl-7-chloro-4-oxo-1,4-dihydropyridazino[3,4-b]quinoxalin-
3-yl)butyric acids 8a,b, respectively. The reaction of compound 8a with hyd
roxylamine gave 4-(7-chloro-4-hydroxyimino-1-methyl-1,4-dihydropyridazino[3
,4]quinoxalin-3-yl)-butyric acid 12.