2,2-Difluorocyclopropane-1-carbaldehyde → tert-Butyl 2-[4-(5-chloro-2-cyanophenyl)-5-methoxy-2-oxopyridin-1(2H)-yl]-3-(2,2-difluorocyclopropyl)prop-2-enoate

At −78° C., 1.87 ml (1.87 mmol) of bis(trimethylsilyl)lithium amide (1M in THF) were added dropwise to a solution of 500 mg (1.33 mmol) of tert-butyl [4-(5-chloro-2-cyanophenyl)-5-methoxy-2-oxopyridin-1(2H)-yl]acetate in 10 ml of THF, and the mixture was stirred for another 10 min 488 mg (4.60 mmol) of 2,2-difluorocyclopropanecarbaldehyde were then added, and after a further 10 min the mixture was warmed to −20° C. After 3 h at −20° C., the reaction was terminated by addition of 30 ml of saturated aqueous ammonium chloride solution and the reaction mixture was extracted three times with 20 ml of ethyl acetate. The combined organic phases were washed with saturated aqueous sodium chloride solution, dried over magnesium sulphate and filtered, and the solvent was removed under reduced pressure. The residue was taken up in a little dichloromethane and purified by flash chromatography (24 g silica cartridge, 35 ml/min, cyclohexane/ethyl acetate gradient). Yield: 240 mg (purity 78%, 30% of theory)