Advances in catalytic conversion of CO<sub>2</sub> for synthesis of quinazoline-2,4(1<italic>H</italic>,3<italic>H</italic>)-diones and their derivatives

To mitigate climate change, the reduction of anthropogenic carbon dioxide (CO2) emissions is of paramount importance. Also CO2 is an abundant, cheap, and non-toxic C1 resource. Chemical fixation of CO2 into high valuable chemicals or fuels has been attracting much attention from the viewpoints of CO2 emission reduction and energy structure reformation. Carbon atom in CO2 is present in its most oxidized state, which gives CO2 inherent thermodynamic stability and kinetic inertness, the highly efficient and selective utilization of CO2 as a reagent in modern organic synthesis without sensitive and expensive organometallic reagents are highly challenging. Quinazoline-2,4(1 H ,3 H )-diones and their derivatives have multiple biological and pharmacological activities, and are also important pharmaceutical intermediates. They can be used for the synthesis of important drugs such as bunazosin, doxazosin, prazosin, and zenarestat. Compared with traditional synthetic methods using toxic or specialized reagents, the coupling reaction of CO2 and 2-aminobenzonitriles for the synthesis of quinazoline-2,4(1 H ,3 H )-diones is an alternative strategy. The synthetic route conforms to the concepts of “green chemistry” and “atomic economy”, and it also realizes the CO2 resource utilization. In this mini review, the latest research progress and catalytic behaviors of various homogeneous and heterogeneous catalysts for the carboxyclization reaction of CO2 and 2-aminobenzonitriles are systematically summarized, such as organic bases, ionic liquids, metal oxide, and inorganic/organic supported catalyst. Nevertheless, most of them often suffer from the requirement for high temperature and pressure, from poor reusability, and from the requirement for volatile organic solvents (e.g., DMF, DMSO, THF). Herein, the effects of catalyst structures, reaction parameters, and catalyst recyclability of the reported catalyst systems are contrastively described, and the key scientific problems about the current catalysts are pointed out. In comparison with the reported catalysts, it concludes that the ionic liquids as green solvent and catalyst show obvious advantages in catalytic activity, separation and scope of substrate due to their attractive properties, which make them interesting candidates for the cleaner synthesis of quinazoline-2,4(1 H ,3 H )-diones. By rational designing of the anions and cations structure, the ionic liquids can realize simultaneous activation of CO2 and the substrates, and exhibit comparable catalytic performance and simple separation under milder and greener conditions without any additional organic solvents. Especially for the superbase-based protic ionic liquids, the literatures have reported that they can realize chemical conversion of CO2 and 2-aminobenzonitriles into various quinazoline-2,4(1 H ,3 H )-diones under mild reaction conditions, even at atmospheric pressure and room temperature. The ionic liquids provide new insights into fundamental chemical transformations and gives great opportunity to redesign the processes to improve their efficiency and sustainability. In this review, the feasible reaction mechanisms without a catalyst and with various catalysts and solvents are also provided and analyzed. In addition, the results of density functional theory (DFT) calculations to the reactants activation and catalytic conversion are given and compared, which will indicate the development direction for designing new catalytic materials.