CO₂-Promoted Hydration of Propargylic Alcohols: Green Synthesis of α-Hydroxy Ketones by an Efficient and Recyclable AgOAc/Ionic Liquid System

α-Hydroxy ketones are a series of biologically active fragments in nature as well as important synthons for organic chemistry. Herein, an AgOAc/1-ethyl-3-methylimidazolium acetate ionic liquid system was developed for the CO2-promoted hydration of propargylic alcohols and H2O to produce α-hydroxy ketones. Diverse desired products could be obtained in satisfactory yields under 1 bar of CO2 pressure with the catalysis of only a trace amount of silver (0.005-0.25 mol %), which is the lowest level ever reported for the metal-catalyzed systems. In particular, this system had robust recyclability, and it could be reused effectively at least 5 times. Furthermore, an unprecedented turnover number (TON) of 9200 was achieved, which is considered to be the highest TON ever reached for this hydration.