C[Mg]Br.[Br:4][C:5]1[CH:6]=[C:7]2[C:12](=[CH:13][C:14]=1[O:15][CH3:16])[O:11][C:10]([CH3:18])([CH3:17])[CH2:9][C:8]2=O.[C:20]1(C)C=CC(S(O)(=O)=O)=CC=1>C1COCC1.ClCCl>[Br:4][C:5]1[CH:6]=[C:7]2[C:12](=[CH:13][C:14]=1[O:15][CH3:16])[O:11][C:10]([CH3:18])([CH3:17])[CH:9]=[C:8]2[CH3:20]A solution of methylmagnesium bromide (3.0 M in THF, 1.67 mL, 5.0 mmol) was added slowly into a solution of 6-bromo-7-methoxy-2,2-dimethyl-chroman-4-one (Compound 4, 710 mg, 2.5 mmol) in 10 mL of THF at −30° C. The mixture was stirred and warmed to 10° C. for 2 h. The reaction mixture was quenched with 10% HCl and extracted with ethyl acetate. The combined organic layers were washed with a saturated solution of NH4Cl, dried (MgSO4) and concentrated at reduced pressure to give a crude oil, which was then dissolved in 10 mL of dichloromethane and cooled to 0° C. with an ice bath. To this solution was added p-toluenesulfonic acid (100 mg). After stirring for 3 h at 0° C., the reaction mixture was quenched with water, extracted with dichloromethane, washed with brine, dried (MgSO4) and concentrated at reduced pressure to give a colorless oil. Purification by flash chromatography (silica gel, 95.5 hexane/ethyl acetate) gave the title compound as a colorless oil.
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