(3-oxo-1,3-dihydroisobenzofuran-1-yl)phosphonic acid (5.00 g, 0.021 mol) in tetrahydrofuran (30 mL) was added to a 150 mL round-bottom flask. To this solution, triethylamine(5.6 mL, 0.042 mol) was added. 2-Fluoro-5-formyl benzonitrile( 3.08 g, 0.021 mol) was dissolved in tetrahydrofuran into another round-bottom flask, followed by adding triethylamine (2.9 mL, 0.021 mol) and stirring evenly. Then the reaction fluids in the two flasks were mixed and reacted at room temperature for 12 h. The product was concentrated under reduced pressure and 50 mL of water was added. The suspension was stirred for 30 min until the solids were not precipitated. Finally, filtration was performed, and the filter cake was collected and dried to obtain 2-Fluoro-5-[(3-oxo-1(3H)-isobenzofuranylidene)methyl]-benzonitrile(5.41 g, 97%).