Cyclic organic carbonates represent a relevant class of chemicals that can be prepared from CO 2 by cycloaddition to epoxides. The application of efficient catalysts is crucial in allowing the cycloaddition reaction to proceed under very mild conditions of temperature, pressure, and CO 2 concentration, thus resulting in a sustainable and carbonbalanced approach to CO 2 conversion. This is particularly the case if impure waste CO 2 could be employed as a feedstock. In this Review, we have critically analyzed the burgeoning literature on the cycloaddition of CO 2 to epoxides with the aim to provide state-of-the-art knowledge on the catalysts that can convert CO 2 to carbonates under ambient conditions. These have been systematically organized in families of compounds and critically scrutinized in terms of catalytic activity, availability and mechanistic features. Finally, we provide an overview on the catalytic systems able to function using diluted and impure CO 2 as a feedstock.

Oleochemicals such as functionalized fatty acid esters and vegetable oils are classes of renewably sourced compounds that are increasingly attracting attention in sustainable chemistry as replacement for fossil-fuel based chemicals. The possibility of coupling CO 2 with epoxidized fatty acids esters (EFAEs) and epoxidized vegetable oils (EVOs) to afford compounds that are attractive as additives or chemical intermediates in the synthesis of non-isocyanate polyhydroxyurethanes (NIPU) can conjugate highly soughtafter CO 2 valorization with the exploitation of bio-based substrates. In this context, there have been very few attempts to employ organocatalytic hydrogen bond donors (HBDs) in the cycloaddition reaction of CO 2 to EFAEs and EVOs and no studies focusing on bio-based and readily available HBDs. In this work we show that ascorbic acid is an efficient HBD for the cycloaddition of CO 2 to EFAEs and EVOs under mild reaction conditions of temperature (80-100°C) and pressure (5-10 bar) that could be applied to several kinds of substrates (monounsaturated EFAEs, polyunsaturated EFAEs and EVOs). In all cases, the formed by-products (ketones, allylic alcohols, cyclic ethers etc.) were identified and the reaction conditions were tuned in order to obtain the target carbonates, generally, in high yields and selectivity.[a] W. Natongchai, S. Pornpraprom,