Quinolone analogues 1. A convenient synthesis of 1-alkyl-4-oxo-1,4-dihydropyridazino[3,4-b]quinoxaline-3-carboxylic acids

The reaction of the alkylhydrazinoquinoxaline N-oxides 2a-d with dimethyl a cetylenedicarboxylate gave the dimethyl l-alkyl-l,5-dihydropyridazino[3,4-b ]quinoxaline-3 3a-d, whose reaction with nitrous acid effected the C-4-oxid ation to afford the dimethyl 1-alkyl-4-hydroxy-1,4-dihydropyridazino[3,4-b] quinoxaline-3,4-dicarboxylates 4a-d, respectively. The reaction of compound s 4a-d with 1,8-diazabicyclo[5.4.0]-7-undecene in ethanol provided the ethy l 1-alkyl-4-oxo-1,4-dihydropyridazino[3,4-b]quinoxaline-3-carboxylates 5a-d , while the reaction of compounds 4a-d with potassium hydroxide furnished t he 1-alkyl-4-oxo-1,4-dihydropyridazino[3,4-b]quinoxaline-3-carboxylic acids 6a-d, respectively. Compounds 6c,d were also obtained by the reaction of c ompounds 5c,d with potassium hydroxide, respectively.