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Under argon protection, 2-amino-5-fluorobenzonitrile (1 mmol) was dissolved in DMSO-d6 (1 mL), catalyst (0.01 mmol) was added and placed in a stainless steel autoclave. After sealing the autoclave, the mixture was heated to 110 °C and carbon dioxide was poured in until the pressure reached 2 MPa. The cyclization reaction was completed by magnetically stirring the mixture at 110 °C for 3 h. After the reaction was completed, the autoclave was heated to 110 °C and carbon dioxide was poured in. At the end of the reaction, the autoclave was cooled in an ice bath followed by slow pressure release. The chemical yield of 6-fluoroquinazoline-2,4(1H,3H)-dione was determined by 1H NMR analysis using 3,5-dimethoxybenzyl alcohol as an internal standard. For the scale-up experiment (6 mmol 2-amino-5-fluorobenzonitrile, 6 mL DMSO), the carboxycyclization reaction was carried out under the same conditions. After completion of the reaction, the same was cooled and depressurized and the reaction mixture was poured into water (60 mL). The precipitate was collected by filtration, washed sequentially with water and ether, and finally dried under vacuum at 35 °C for 15 h to give pure 6-fluoroquinazoline-2,4(1H,3H)-dione.