General procedure for the synthesis of 2-methylpyridine-3-carbaldehyde from 2-methylpyridine-3-methanol: A mixture of 3-hydroxymethyl-2-methylpyridine (9.0 g, 73.1 mmol) and manganese(IV) dioxide (28.1 g, 322 mmol) in dichloromethane (100 mL) was heated and refluxed for 48 hours. Upon completion of the reaction, the insoluble material was removed by diatomaceous earth filtration and the filter cake was washed with a solvent mixture of methanol/dichloromethane. Subsequently, the solvent in the filtrate was removed by rotary evaporator to give 2-methylpyridine-3-carboxaldehyde (7.5 g, 85% yield) as an oily product. Its nuclear magnetic resonance hydrogen spectrum (NMR) data were as follows: δ 2.78 (s, 3H), 7.43 (dd, 1H), 8.15 (dd, 1H), 8.66 (dd, 1H).
