Step A: Synthesis of dimethyl 3-bromo-2-oxoglutarate
To a solution of EtOAc (160 mL) in CuBr2 (11.5 g, 51.7 mmol) was added a CHCl3 solution (80 mL) of dimethyl 2-oxoglutarate (3.00 g, 17.2 mmol). The reaction mixture was refluxed overnight and cooled to room temperature. The volatile solvent was evaporated and the residue was purified by SiO2 column chromatography (eluent: hexane/ethyl acetate = 3:2) to afford dimethyl 3-bromo-2-oxoglutarate (4.36 g, quantitatively) as a yellow oil.
1H NMR (CDCl3, Varian 400 MHz): δ 3.06 (1H, ABX, Jab = 17.3 Hz, Jax = 9.3 Hz), 3.34 (1H, ABX, Jab = 17.3 Hz, Jbx = 5.9 Hz), 3.71 (3H, s), 3.95 (3H, s), 5.40 (1H, ABX, Jax = 9.3 Hz). Jax = 9.3 Hz, Jbx = 5.9 Hz).
