Very few molecules provoke as much controversy as carbon dioxide (CO₂). Since the beginning of the industrial age, the concentration of CO₂ in the Earth’s atmosphere has increased by about 46% [1]. It is estimated that currently, 93% of anthropogenic CO₂ is generated by fossil fuel combustion [2], with the prediction that the atmospheric concentration of CO₂ will increase between 730 and 1020 ppm by the end of the century [3]. The connection between the increasing concentration of CO₂ and ocean acidity, as well as severe and obvious global climate changes, have initiated the trend towards the substantial reduction in fossil fuels and CO₂ emission [4], moving towards alternative energy sources and a “low-carbon economy”.

The development of new strategies and techniques for carbon capture, utilization, and storage (CCUS) are currently subjects of intense research. However, it is important to note that energy technology deployment is slow [5], and not all CCUS processes are financially viable or amenable for scaling up [6]. In addition, with the advancement of CO₂ storage, scientists have developed novel and innovative approaches to direct the chemical and pharmaceutical industries towards a carbon-sustainable chemical synthesis by using CO₂ gas as an abundant carbon source in terms of the concept of green chemistry. This movement remains challenging because of the exceptional thermodynamic stability of CO₂ and thus, the high energetic cost of its fixation. Indeed, the attempts to reduce CO₂ back to a synthetically useful compound might require comparable or more energy than obtained by its production by the combustion of fossil fuel, as CO₂ represents the final product of the carbon oxidation [7]. Likewise, the kinetic barrier of CO₂ reduction is high. Even though the methanation of CO₂ is an exergonic reaction, as H₂ gas is highly energetically rich, it does not proceed without a metal catalyst, and problems considering H₂ storage should also be addressed. The Sabatier reaction, discovered in 1902, uses an Ni catalyst and H₂ to reduce CO₂ to methane, and this reaction is currently experiencing a revival due to its potential use in long-haul space missions [8].

Cyclic carbonates are of great significance in the chemical industry, with a wide range of important applications. They are used as highly polar solvents [17], electrolytes in lithium batteries [18], precursors for polycarbonates forming the major class of commercial thermoplastics [19], and precursors for other organic compounds [20]. The simplest cyclic carbonate, ethylene carbonate, is synthesized industrially by the reaction of ethylene oxide with CO₂.

Five-Membered Cyclic Carbonates from Allylic Alcohols

Because of its great chemical and proteolytic stability, as well as the ability to easily penetrate into cells, the carbamate motif is a very important peptide bond surrogate in the drug development process [49]. Vacondio et al. reviewed and examined medicinal applications of carbamates, concluding that cyclic carbamates are stable and prone to metabolic hydrolysis [50]. Thus, cyclic carbamates have become a subject of increased research for pharmaceuticals.

For example, a very important antibiotic used to treat infections by various Gram-positive bacteria is Linezolid 107, a drug which contains the 5-membered cyclic carbamate (2-oxazolidinone) motif (Scheme 26a). The first-generation synthesis of linezolid reported by Pfizer employed a glycidyl ester and a strong base (n-BuLi) at a low temperature to obtain the cyclic carbamate moiety (Scheme 26b) [51]. The “greener” second generation synthesis used imine derivative 111 under milder conditions (Scheme 26c). However, the latter method still employs a strong base and generates a lot of waste. Thus, the development of new reactions and reaction conditions with high atom economy, such as the carboxylative cyclizations of unsaturated amines and CO₂, is very desirable and could be directly applied in the green and highly valuable industrial synthesis of linezolid and its derivatives.