To a 100 ml three-necked flask were added 3,4,7,8-tetrahydro-2,5 (1 H, 6Η) -quinoline dione (0.02 mol) and cyclohexane (25 ml). After stirring to dissolve in the ice bath for 10min, slowly add a dropwise N-bromosuccinimide (0.03mol) in cyclohexane (5ml), and reflux for 3h at the end of the dropwise addition. After completion of the reaction by TLC, cool down to room temperature. Water was added (the amount was 0.7 times the volume of the reactant), and the mixture was allowed to stand with stirring. The aqueous layer was extracted with ethyl acetate (1 × the volume of the aqueous layer 4 times), and the organic layers were combined. Anhydrous sulfuric acid Calcium was dried and filtered, the filtrate was evaporated to remove the solvent, and the residue was dried to give an off-white solid as a 5-Hydroxy-3,4-dihydroquinolin-2(1H)-one (Yield 92.7percent).
