The green basic IL [DBUH][BO₂] was easily synthesized for the first time and used to catalyze the cycloaddition of CO₂ and epoxides under solvent- and halogen-free conditions at atmospheric pressure and room temperature with high target product yields. Moreover, this IL could be easily recovered and reused at least five times without activity loss. The basic anion and the cation with N–H had excellent synergistic catalytic effects on promoting these reactions. Particularly, this basic IL, the anion of which had a strong nucleophilic ability, was also very effective for the reactions of CO₂ and 2-aminobenzonitriles into quinazoline-2,4(1H,3H)-diones, giving the desired products in high yields at atmospheric pressure and room temperature.