Silver-Catalyzed Conversion of CO2 and 2-Ethynylanilines into 4-Hydroxyquinolin-2(1H)-ones in Protic Ionic Liquid at Atmospheric Pressure

Abstract

Hydroxyquinolin-2(1H)-ones are core structural subunits frequently found in many pharmacological compounds and the synthesis of this kind of compounds is highly desirable. An efficient protic ionic liquid and AgNO3 catalytic system was developed for the preparation of various 4-hydroquinolin-2(1H)-ones from CO2 and 2-ethynylanilines in moderate to excellent yields (65-94%). It was found that [HTMG][Im], a simple and easily prepared protic ionic liquid comprising a 1,1,3,3-tetramethylguanidinium cation and a imidazolide anion, could act as both the solvent and reaction promoter, and that the reaction could be efficient carried out with a mount of 2 mol% AgNO3 under atmospheric pressure of CO2 at 60 ℃. This method provides a new approach for the synthesis of 4hydroxyquinolin-2(1H)-ones.Due to the environmental advantage of CO2 as a C1 building block, as well as the importance of CO2 emission reduction in mitigate climate change, chemical conversion of CO2 has paid much attention in recent decades. In this field, ionic liquids (IL), because of their unique properties, have showed outstanding performance in CO2 capture and utilization processes. Many value-added chemicals have been synthesized from CO2, using ILs as solvents and/or catalysts, such as quinazoline-2,4-(1H,3H)-diones, 1-6 cyclic carbonates, 7 2-benzimidazolones, 8 carbamates, 9 oxazolidinones, 10 ureas, 11 and so on. Although much progress has been made, expanding the scope of the chemical conversion of CO2 in ILs, especially under mild conditions is still a challenge. 4-Hydroxyquinolin-2(1H)-one derivatives are important intermediates due to their pharmacological activities, 12 including antitubercular potency, 13 anti-HIV activity, 14 antibacterial activity, 15 and anticancer 1486