[N:1]1([C:6]2[CH:11]=[CH:10][C:9]([C:12]#[C:13][CH2:14][OH:15])=[CH:8][CH:7]=2)[CH:5]=[CH:4][CH:3]=[N:2]1>CC(C)=O.O=[Mn]=O>[N:1]1([C:6]2[CH:11]=[CH:10][C:9]([C:12]#[C:13][CH:14]=[O:15])=[CH:8][CH:7]=2)[CH:5]=[CH:4][CH:3]=[N:2]1A mixture of the compound from step A (0.71 g, 3.58 mmol) and MnO2 (3.10 g, 35.66 mmol) in acetone (40 mL) was heated to reflux for 3 h. The cooled reaction mixture was filtered through Celite and the filtrate was concentrated. Purification by chromatography (SiO2, 6:1 hexane/ethyl acetate) yielded 0.19 g (27%) of the title compound as an off-white solid. MS 197 (M+H)+.
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