General procedure for the synthesis of 3-methyl-2-pyridine aldehyde from (3-methylpyridin-2-yl)methanol: (3-methylpyridin-2-yl)methanol (1.9 mmol) was dissolved in 25 mL of 1,2-dichloroethane, 1.65 g (19 mmol) of activated manganese dioxide was added, and the reaction mixture was stirred for 6 hours at 50°C. The reaction was completed by filtration to remove the precipitate. After completion of the reaction, the precipitate was removed by filtration and the filtrate was evaporated under reduced pressure, the resulting residue was used directly in the next step of the reaction without further purification. 3-Methyl-2-pyridine aldehyde (1c) 185 mg (1.52 mmol, 80% yield) was obtained as a light oil.1H NMR (CDCl3) δ: 2.66 (s, 3H, Me), 7.39 (dd, 1H, 5-H, J = 7.8, 4.6 Hz), 7.62 (d, 1H, 4-H, J = 7.8 Hz), 8.66 ( d, 1H, 6-H, J = 4.6 Hz), 10.20 (s, 1H, CHO). Mass spectrum m/z: 122.06 (Irel 100%) [M+H]+. Calculated value: M 122.06.
