Pyridazino quinoxalin-4-ones

Ethyl 3-dichloromethyl-2-quinoxalinecarboxylate 1,4-dioxide (281) with hydrazine gave pyridazino[4,5-h]quinoxalin-l(2//)-one (283, presumably via the intermediate hydrazone (282) (substrate, EtOH, H2NNH2 H2OJ, dropwise, 0°C 20°C, 24 h 60% note loss of A -oxide entities during the reactions) ... 

In a different type of cyclization, the pyrazolo[3, 4 5,6]pyridazino[3,4-A]quinoxalin-3-one 83 results from the oxidation of the n-hydroxyhydrazide 82 (Scheme 26) <2005JHC551>. 

Chloro derivative 291 was obtained from dioxo derivative 70 by treatment of phosphoryl chloride in dimethylformamide at 100°C for 2 hours (80CPB3537). The treatment of chloro derivative 291 with methylhydra-zine in a mixture of ethanol and chloroform under reflux gave 2H-pyrido[ 1,2-a]pyrimidin-2-one 295 and rearranged pyridazino[3,4-6]-quinoxaline 296 in 4.8% and 78% yields, respectively (Scheme 21) (80CPB3537). 3,4-Dihydroquinoxalinone 70 could not be rearranged into pyridazino[3,4-6]quinoxaline 296 by treatment with methylhydrazine. When hydrazine hydrate was employed instead of methylhydrazine, tricyclic ethyl ester 297 (R1 = Et) was obtained. The latter reaction gave methyl ester 297 (R1 = Me) when carried out in a mixture of methanol and chloroform (80CPB3537). 

Treatment of quinoxaline /V-oxides with 4,4,4-trifluoroacetoacetate gave l-methyl-3-trifluoromethylpyridazino[3,4-fc]quinoxalin-4(17/)-oncs <02H(56)291>, and treatment with diethyl ethoxymethylenemalonate gave l-methyl-pyridazino[3,4-i)]quinoxalin-4(17/)-ones <02H(58)359>. 

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