General procedure for the synthesis of 4-bromo-2-iodobenzaldehyde (17b) from 4-bromo-1-(bromomethyl)-2-iodobenzene: A solution of N-methylmorpholine-N-oxide (2.81 g, 23.2 mmol) and 4A molecular sieves (19 g) in acetonitrile (60 mL) was added to a dry 250 mL Schlenk flask under nitrogen protection and cooled to 0 °C. This was followed by rapid addition of benzyl bromide 15b (2.9 g, 7.7 mmol). The reaction mixture was kept at 0 °C for 2 h and then slowly warmed up to room temperature. Upon completion of the reaction, it was filtered through a short column of silica gel (SiO2:hexane) to afford the off-white solid product 17b (2.15 g, 6.92 mmol, 90% yield). The product was characterized as follows: 1H-NMR (400 MHz, CDCl3) δ: 9.99 (s, 1H), 8.13 (d, 1H, J = 0.8 Hz), 7.73 (dd, 1H, J = 8.3, 0.8 Hz), 7.61 (dd, 1H, J = 8.3, 0.8 Hz); 13C-NMR (100 MHz, CDCl3) δ: 194.7, 142.8, 134.1, 132.3, 131.1, 130.2, 100.9; HRMS (EI) m/z calculated value of C7H4BrIO [M]+: 309.8490, measured value: 309.8489.
