[Cl:1][C:2]1[C:3]([C:8]2[CH:13]=[CH:12][C:11]([CH3:14])=[CH:10][CH:9]=2)=[N:4][CH:5]=[CH:6][CH:7]=1.[Se](=O)=[O:16]>O1CCOCC1>[Cl:1][C:2]1[C:3]([C:8]2[CH:13]=[CH:12][C:11]([CH:14]=[O:16])=[CH:10][CH:9]=2)=[N:4][CH:5]=[CH:6][CH:7]=1100 g (0.49 mol) of 3-chloro-2-para-tolylpyridine was dissolved in 1 L of 1,4-dioxane in a reactor. 163.4 g (1.47 mol) of selenium dioxide was added, and the mixture was refluxed for 4˜6 hours. The reaction solution was cooled to 25° C., and floating matter was filtered off with celite. A 10% sodium bicarbonate solution was added, and the mixture was extracted with ethyl acetate. The organic layer was dried with magnesium sulfate and concentrated under reduced pressure, yielding 4-(3-chloropyridin-2-yl)benzaldehyde as represented below in a 85% yield.
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