Solvent-free synthesis of quinazoline-2,4(1H,3H)-diones using carbon dioxide and a catalytic amount of DBU

An ideal reaction system, which is aimed at sustainable chemistry, was developed. Under solvent-free conditions, quinazoline-2,4(1H,3 H)-diones were obtained in good to excellent yields from 2-aminobenzonitriles with only carbon dioxide (1 bar) and a catalytic amount of base (DBU or DBN). For example, 6,7-dimethoxyquinazoline-2,4(1H,3H)-dione, which is a key intermediate of several drugs (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in 97% yield [DBU (0.2 equiv), CO2 (1 bar), 120 degrees C].