To a solution of methyl 2-chloro-4-bromobenzoate (31.4 mmol) in dioxane (154 mL) was added pinacol ester of bis(boronic acid) (8.6 g, 31.4 mmol), PdCl2(PPh3)2 (0.42 mmol), and KOAc (94.2 mmol), and the mixture was stirred for 2-6 hr at 100 C under nitrogen. The mixture was diluted with EtOAc and water. The organic layer was separated, washed with brine, dried over MgSO4 and evaporated. The residue was purified by silica gel column chromatography (hexane/EtOAc 5/1) to give 3-chloro-4-methoxycarbonylphenylboronic acid pinacol ester. To a suspension of the above product (29.4 mmol) in acetone (175 mL) and water (175 mL) was added NH4OAc (66.2 mmol) and NaIO4 (14.2 g, 66.4 mmol) and the mixture was stirred for 15 hours at room temperature. The solvent was evaporated and the residue was diluted with EtOAc. The organic layer was separated, washed with water and brine, dried over MgSO4 and evaporated under reduced pressure to give the title compound as a white solid.
