General procedure for the synthesis of 3-bromo-4-methylbenzaldehyde from 3-bromo-4-methylbenzyl alcohol: To a solution of 3-bromo-4-methylbenzyl alcohol (4.5 g, 22.4 mmol) in chloroform (100 mL) was added manganese dioxide (15 g, 172 mmol). The reaction mixture was refluxed under stirring in an oil bath at 70°C for 18 hours. Upon completion of the reaction, the mixture was filtered through diatomaceous earth and the solvent was removed under vacuum to give the crude product. The crude product was purified by column chromatography (150 mL SiO2, eluent was a mixture of ethyl acetate and hexane, 1:9, v/v) to afford 3-bromo-4-methylbenzaldehyde (3.2974 g, 74% yield) as a white crystalline solid. The product characterization data were as follows: 1H NMR (400 MHz, CDCl3) δ 9.91 (s, 1H), 8.02 (d, J = 1.6 Hz, 1H), 7.70 (dd, J = 7.6, 1.6 Hz, 1H), 7.39 (d, J = 8.0 Hz, 1H), 2.47 (s, 3H); 13C NMR (100.6 MHz CDCl3) δ 190.4, 145.1, 135.8, 133.4, 131.3, 128.3, 125.6, 23.4; GC-MS (M)+ C8H7OBr calculated value 197.9680, measured value 197.9665.
