[OH:1][CH:2]1[C:11]2[N:10]=[CH:9][C:8]([CH3:12])=[CH:7][C:6]=2[CH2:5][CH2:4][CH2:3]1>C(Cl)Cl.[O-2].[O-2].[Mn+4]>[CH3:12][C:8]1[CH:9]=[N:10][C:11]2[C:2](=[O:1])[CH2:3][CH2:4][CH2:5][C:6]=2[CH:7]=18-Hydroxy-3-methyl-5,6,7,8-tetrahydroquinoline (42.5g) in methylene chloride (21/21) was stirred at room temperature with manganese dioxide (425g) for 16 hours. The manganese dioxide was removed by filtration and washed with methylene chloride. The filtrate was evaporated to dryness under reduced pressure and the residue was distilled to give 5,6-dihydro-3-methyl-7H-quinolin-8-one (30g) b.p. 142°-4° C at 0.5mm.
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