Dimethylformamide → 2,6-Dibromo-4-fluorobenzaldehyde

A solution of 1,3-dibromo-5-fluoro-2-iodobenzene (50 g, 132 mmol) in anhydrous toluene (300 mL) was cooled to −35° C. A solution of isopropylmagnesium chloride (84 mL, 171 mmol, 2.0 M in diethyl ether) over a period of 30 minutes while maintaining the internal temperature below −25° C. See FIG. 1. A clear brown solution was obtained. Stirring was continued for 1.5 h. Then anhydrous DMF (34 mL, 436 mmol) was added over a period of 30 minutes. The temperature of the reaction mixture increased to −19° C. The reaction mixture was warmed to 10° C. (room temperature) over 1 h and stirred at this temperature for 1.5 h. The reaction was quenched with saturated aqueous NH4Cl (100 mL), filtered and evaporated under reduced pressure. The residue was purified by silica-gel column chromatography (eluting with petroleum ether/ethyl acetate:from 50:1 to 20:1) to give 101a (20 g, yield 54%) as a yellow solid.