4.1 g of Na2CO3 (39 mmol), 2.0 g of 4-formylphenylboronic acid (13 mmol), and 0.45 g of Pd(PPh3)4 were added to 2.5 g of compound (8) (14.9 mmol) prepared in Example 5 dissolved in 50 mL of 1,2-dimethoxyethane and 50 mL of distilled water, and refluxed under heating and stirring for 18 hours. The mixture was cooled to room temperature, and concentrated about 50% under reduced pressure. The aqueous layer was extracted with ethyl acetate, the organic layer was dried over magnesium sulfate, and then concentrated under reduced pressure. The residue was separated by column chromatography (eluting solvent: ethyl acetate/hexane=1/4) to obtain 3.0 g 4-(3-chloro-5-vinylpyridin-2-yl)benzaldehyde (yield 82%).
