[Br:1][C:2]1[CH:3]=[C:4]2[C:18](=[CH:19][CH:20]=1)[O:17][C:7]1=[N:8][C:9]([F:16])=[C:10]([Si:12]([CH3:15])([CH3:14])[CH3:13])[CH:11]=[C:6]1[C:5]2=O.[CH3:22][Mg]Br.Cl.CCOC(C)=O>C1COCC1.O>[Br:1][C:2]1[CH:3]=[C:4]2[C:18](=[CH:19][CH:20]=1)[O:17][C:7]1=[N:8][C:9]([F:16])=[C:10]([Si:12]([CH3:15])([CH3:14])[CH3:13])[CH:11]=[C:6]1[C:5]2=[CH2:22]
7-bromo-2-fluoro-3-(trimethylsilyl)-5H-chromeno[2,3-b]pyridin-5-one (1.05 g, 2.9 mmol) was dissolved in dry THF (30 mL) and treated with methylmagnesium bromide (3.0 M in diethyl ether, 2.0 mL, 6.00 mmol). After 15 minutes 5N HCl (30 mL) was added followed by EtOAc (100 mL) and water (100 mL). The phases were mixed and separated and the organics were dried with magnesium sulfate before evaporating to dryness under reduced pressure. Purification using silica chromatography (hexane to dichloromethane gradient) gave the desired 7-bromo-2-fluoro-5-methylene-3-(trimethylsilyl)-5H-chromeno[2,3-b]pyridine.
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