To a solution of dimethyl(benzyloxycarbonyl)methylphosphonate (2.20 g) in tetrahydrofuran (32.0 mL) was added 55% sodium hydride (406 mg) under ice-cooling, followed by stirring at room temperature for 30 minutes. Subsequently, tert-butyl 3-formylbenzoate (1.60 g) was added thereto, followed by stirring at room temperature for 16 hours. To the reaction mixture were added water and ethyl acetate, and the organic layer was extracted. The organic layer was washed with a saturated aqueous sodium hydrogen carbonate solution and a saturated aqueous sodium chloride solution, then dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (hexane-ethyl acetate) to obtain tert-butyl 3-[(1E)-3-(benzyloxy)-3-oxopropa-1-en-1-yl]benzoate (1.60 g).
