Sodium methoxide (2.28 g,0.042 mol) was dissolved in methanol (40 mL) into a 150 mLround-bottom flask. To this solution, dimethyl hydrogen phosphite(4.8 mL, 0.049 mol) and 2-carboxybenzaldehyde (compound5, 5.00 g, 0.033 mol) were added by dripping at 0 °Cfor 30 min. Then the mixture was stirred at room temperaturefor 8 h.
After the reaction was completed, methanesulfonicacid (3.1 mL, 0.047 mol) was added dropwise and stirred for30 min. The solvent was removed under reduced pressure,following by adding 40 mol water.
The aqueous phase wasextracted with dichloromethane for three times, the combinedorganic phase was washed with water until neutral and driedwith anhydrous sodium sulfate. Dichloromethane was evaporatedunder reduced pressure to afford 3-oxo-1,3-dihydroisobenzofuran-1-ylphosphonic acid(4.93 g, 99%)as white solid.
1H-NMR (500 MHz, DMSO-d6) δ: 3.62 (3H,d, J = 8 Hz), 3.86 (3H, d, J = 12 Hz), 6.36 (1H, d, J = 8 Hz),7.74-7.70 (2H, m), 7.91-7.88 (1H, m), 7.98-7.96 (1H, m).
