To a mixture of 3-benzyloxy-1-phenyl-1H-pyrazole-4-carbaldehyde (1.00 g), tetraethyl methylenediphosphonate (1.15 g) and N,N-dimethylformamide (30 mL) was added sodium hydride (60% in oil, 0.17 g) at 0° C. The mixture was stirred at room temperature for 15 hrs. Water was poured into the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate and concentrated. The residue was subjected to silica gel column chromatography, and eluted with ethyl acetate-hexane (3:1, v/v) to give diethyl (E)-2-(3-benzyloxy-1-phenyl-1H-pyrazol-4-yl)ethenylphosphonate as colorless crystals (1.08 g, yield 73%). Recrystallization from ethyl acetate-hexane gave colorless prism crystals. melting point: 89-90° C.
