[CH:1]([C:3]1[CH:4]=[CH:5][C:6]2[C:15]3[CH:14]=[C:13]4[CH2:16][CH2:17][CH2:18][C:19](=[O:20])[C:12]4=[CH:11][C:10]=3[O:9][CH2:8][C:7]=2[CH:21]=1)=[CH2:2].C1C(=O)N([Br:29])C(=O)C1.[OH2:30]>C1COCC1.CS(C)=O.CCOC(C)=O.O=[Mn]=O>[Br:29][CH2:2][C:1]([C:3]1[CH:4]=[CH:5][C:6]2[C:15]3[CH:14]=[C:13]4[CH2:16][CH2:17][CH2:18][C:19](=[O:20])[C:12]4=[CH:11][C:10]=3[O:9][CH2:8][C:7]=2[CH:21]=1)=[O:30]3-Vinyl-10,11-dihydro-5H-dibenzo[c,g]chromen-8(9H)-one (9.98 g, 36.1 mmol) was dissolved in a stirred solution of THF (70 mL), DMSO (70 mL) and H2O (35 mL). NBS (6.75 g, 37.9 mmol) was added in a single portion and the reaction mixture was stirred at RT for 33 min. Upon completion, the reaction medium was diluted with EtOAc and washed twice with H2O and once with brine. The organic phase was dried over MgSO4, filtered and concentrated under reduced pressure. The resulting crude bromohydrin was suspended in DCM (200 mL) and treated with activated MnO2 (62.7 g, 722 mmol). After stirring for 15 h at RT, the reaction mixture was filtered over celite and the filter cake was rinsed several times with DCM. The combined filtrate (˜400 mL) was treated with MeOH (˜100 mL) and the mixture was gradually concentrated under reduced pressure, causing solid material to precipitate from solution. When the liquid volume reached ˜200 mL, the solid was filtered off and rinsed with MeOH. The concentration/precipitation/filtration/rinsing sequence was performed 2× more, resulting in the collection of 3 crops of powdered 3-(2-bromoacetyl)-10,11-dihydro-5H-dibenzo[c,g]chromen-8(9H)-one (7.49 g, 56% over 2 steps).
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