[OH-].[Na+].[CH3:3][N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[N:7]2[CH:14]=[C:15]([C:17]([O:19]CC)=[O:18])[CH:16]=[C:6]2[C:5]1=[O:22]>O.C(O)C>[CH3:3][N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[N:7]2[CH:14]=[C:15]([C:17]([OH:19])=[O:18])[CH:16]=[C:6]2[C:5]1=[O:22]A solution of 0.9 g of sodium hydroxide in 50 ml of water was added to a suspension of 1.66 g of ethyl 5-methyl-4,5-dihydro-4-oxo-pyrrolo[1,2-a]quinoxaline-2-carboxylate in 30 ml of hot ethanol and the mixture was warmed on a water bath for one hour after which thin layer chromatography showed no ester present. The resulting solution was filtered hot and the filtrate was acidified to a pH of 1-2 with concentrated hydrochloric acid. The mixture was cooled and filtered and the recovered product was rinsed with water and dried over P2O5 under vacuum to obtain 1.40 g (95% yield) of 5-methyl-4,5-dihydro-4-oxo-pyrrolo[1,2-a]quinoxaline-2-carboxylic acid melting at 330°-333° C.
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