Br[C:2]1[C:10]2[O:9][CH:8]=[CH:7][C:6]=2[CH:5]=[C:4]([F:11])[CH:3]=1.[Mg].[C:13](OCC)(=[O:19])[C:14]([O:16][CH2:17][CH3:18])=[O:15]>O1CCCC1>[CH2:17]([O:16][C:14](=[O:15])[C:13]([C:2]1[C:10]2[O:9][CH:8]=[CH:7][C:6]=2[CH:5]=[C:4]([F:11])[CH:3]=1)=[O:19])[CH3:18]Dissolve 7-bromo-5-fluorobenzofuran (2 g, 9.3 mmol) in 5 ml tetrahydrofuran under nitrogen. Add magnesium turnings (0.25 g, 1.1 equivalents) and heat to reflux to facilitate Grignard formation. In a separate flask place diethyl oxalate (1.3 mL, 2 equivalents) in 3 mL tetrahydrofuran, and cool to 0° C. under nitrogen. When Grignard formulation is complete, add via canula to the diethyl oxalate solution. Stir the reaction for 2-4 hours while slowly warming to 20° C. Extract with diethyl ether. Wash organic layer with brine. Dry over magnesium sulfate, filter and concentrate to a light yellow oil. Purifacation by column chromatography (4:1 hexanes:ethyl acetate) affords 1.74 g (79%) of an oil which solidifies upon standing. MS (ES, m/z): 237.0 (M+1).
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