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Polyphosphoric acid (0.29 g) was solubilized in chlorobenzene (10.0 mL) and heated at reflux for 3 hours under nitrogen. A solution of compound 3 (0.225 g, 0.464 mmol) in chlorobenzene (3.0 mL) was added dropwise to the reaction mixture. The mixture was stirring was continued at reflux overnight. After the mixture was cooled down to room temperature, dichloromethane (100 mL) was added, and the mixture was washed with NaHCO3 (saturated, 2×50 mL) and brine (50 mL). The solution was dried over Na2SO4 and concentrated under vacuum. The residual was refluxed in isopropanol (30 mL) for 2 hours. After cooling down to room temperature, compound 4 was obtained by filtration as a pale yellow solid (120 mg, 86%). 1H NMR (500 MHz, CDCl3): δ 7.59 (d, J=5.5 Hz, 2H), 7.45 (d, J=5.5 Hz, 2H), 7.44 (s, 2H), 4.19 (s, 6H).

1. temperatureheated
2. temperatureat reflux for 3 hours under nitrogen
3. temperatureat reflux overnight
4. washthe mixture was washed with NaHCO3 (saturated, 2×50 mL) and brine (50 mL)
5. dry with materialThe solution was dried over Na2SO4
6. concentrationconcentrated under vacuum
7. temperatureThe residual was refluxed in isopropanol (30 mL) for 2 hours
8. temperatureAfter cooling down to room temperature