[Br:1][C:2]1[CH:7]=[C:6](C=O)[C:5]([Cl:10])=[CH:4][N:3]=1.[CH:11](OC)([O:14][CH3:15])[O:12][CH3:13]>CO.CC1C=CC(S(O)(=O)=O)=CC=1>[Br:1][C:2]1[CH:7]=[C:6]([CH:11]([O:14][CH3:15])[O:12][CH3:13])[C:5]([Cl:10])=[CH:4][N:3]=1To a sol. of 2-bromo-5-chloro-pyridine-4-carbaldehyde (43.9 g, 199 mmol) in MeOH (800 mL) were successively added at rt trimethyl orthoformate (65.3 mL, 597 mmol) and p-TsOH (1.90 g, 10.0 mmol). This reaction mixture was then heated to reflux for 3 h. The mixture was allowed to cool to rt, and was concentrated under reduced pressure. The residue was dissolved in CH2Cl2, and the mixture was washed with aq. 10% K2CO3. The org. layer was dried over MgSO4, filtered, and the solvents were removed under reduced pressure. Drying the residue under high vacuum yielded the crude title compound (51.7 g, 97%) that was used further without purification. LC-MS: tR=0.92 min; ES+: 309.06.
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