15-crown-5 (0.5 g, 0.1 equivalents, 2.27 mmol) was dissolved in 30 ml of toluene at room temperature, and added with 20 ml of 50% aqueous sodium hydroxide solution. To the solution, triethyl-3-methyl-4-phosphonocrotonate (7.87 g, 1.05 equivalents, 23.8 mmol) and then 5 ml toluene solution of farnesal (5.0 g, 22.7 ml) were added with stirring at 0° C. The mixture was stirred at room temperature for one hour. The organic and aqueous layers were separated, and the organic layer was washed with saturated ammonium chloride solution and saturated brine, and dried over magnesium sulfate. The solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography to obtain 7.4 g of the title compound (yield 98%, 2E:2Z=>99:1) as a yellow oil.
