An efficient ionic liquid system was developed for the preparation of various heterocycle-fused pyrimidine-2, 4(1H,3H)-diones in moderate to excellent yields (52-95%). It was found that [HDBN+][TFE-], a simple and easily prepared ionic liquid, could act as both the solvent and reaction promoter, and that the reactions could be efficiently carried out at atmospheric pressures of CO2. (C) 2018 Elsevier Ltd. All rights reserved.