One‐Step Synthesis of 3,4‐Disubstituted 2‐Oxazolidinones by Base‐Catalyzed CO 2 Fixation and Aza‐Michael Addition

CO2 Capture and Low-Temperature Release by Poly(aminoethyl methacrylate) and Derivatives

Poly(aminoethyl methacrylate) (PAEMA), poly(ethylene oxide)-block-(aminoethyl methacrylate) (PEO-PAEMA), and their guanidinylated derivates, poly(guanidine ethyl methacrylate) (PGEMA) and poly(ethylene oxide)-block-(guanidine ethyl methacrylate) (PEO-PGEMA), were prepared to study their capabilities for CO₂ adsorption and release. The polymers of different forms or degree of guanidinylation were thoroughly characterized, and their interaction with CO₂ was studied by NMR and calorimetry. The extent and kinetics of adsorption and desorption of N₂ and CO₂ were investigated by thermogravimetry under controlled gas atmospheres. The materials did not adsorb N₂, whereas CO₂ could be reversibly adsorbed at room temperature and released by an elevated temperature. The most promising polymer was PGEMA with a guanidinylation degree of 7% showing a CO₂ adsorption capacity of 2.4 mmol/g at room temperature and a desorption temperature of 72 °C. The study also revealed relations between the polymer chemical composition and CO₂ adsorption and release characteristics that are useful in future formulations for CO₂ adsorbent polymer materials.

Diethylammonium iodide as catalyst for the metal-free synthesis of 5-aryl-2-oxazolidinones from aziridines and carbon dioxide

The catalytic potential of ammonium halide salts was explored in the coupling reaction of a model aziridine with carbon dioxide, highlighting the superior activity of [NH2Et2]I. Then, working at room temperature, atmospheric CO2 pressure and in the absence of solvent, the [NH2Et2]I-catalyzed synthesis of a series of 5-aryl-2-oxazolidinones was accomplished in good to high yields and excellent selectivity, from 2-aryl-aziridines with N-methyl or N-ethyl groups. NMR studies and DFT calculations outlined the pivotal role of both the diethylammonium cation and the iodide anion. The proposed method represents a convenient choice for obtaining a limited number of valuable molecules for which more complex and more expensive catalytic systems have been reported even in recent years.

Construction of fully substituted carbon centers containing a heteroatom and a CF3 group via in situ generated p-quinone methides

1,6-Conjugate additions of in situ generated δ-CF3-δ-substituted p-quinone methides have been achieved with a variety of heteronucleophiles under mild conditions, which led to facile and practical construction of fully substituted carbon centers including a heteroatom and a CF3 group. In particular, it was revealed that some amines themselves worked for efficient cleavage of the TBS protective group, and addition of a catalytic amount of an appropriate Brønsted acid was found to sometimes improve the progress of the desired process.

Mechanistic insights into carbamate formation from CO2 and amines: the role of guanidine–CO2 adducts

This work explores the reactivity of a reversible superbase–CO2 zwitterion, which can be used as a stoichiometric source of CO2.

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2-Oxazolidinones: Catalyst-Free Synthesis Under Ambient Conditions

The development of sustainable synthetic routes to access valuable oxazolidinones via CO₂ fixation is an active research area, and the aziridine/carbon dioxide coupling has aroused a considerable interest. This reaction features a high activation barrier and thus requires a catalytic system, and may present some other critical issues. Here, the straightforward gram-scale synthesis of a series of 5-aryl-2-oxazolidinones was developed at ambient temperature and atmospheric CO₂ pressure, in the absence of any catalyst/co-catalyst. The key to this innovative procedure consists in the direct transfer of the pre-formed amine/CO₂ adduct (carbamate) to common aziridine precursors (dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation of aziridine) and then CO₂ . The reaction mechanism was investigated by NMR spectroscopy and DFT calculations applied to model cases.

Organocatalytic Trapping of Elusive Carbon Dioxide Based Heterocycles by a Kinetically Controlled Cascade Process

A conceptually novel approach is described for the synthesis of six-membered cyclic carbonates derived from carbon dioxide. The approach utilizes homoallylic precursors that are converted into five-membered cyclic carbonates having a β-positioned alcohol group in one of the ring substituents. The activation of the pendent alcohol group through an N-heterocyclic base allows equilibration towards a thermodynamically disfavored six-membered carbonate analogue that can be trapped by an acylating agent. Various control experiments and computational analysis of this manifold are in line with a process that is primarily dictated by a kinetically controlled acylation step. This cascade process delivers an ample diversity of six-membered cyclic carbonates in excellent yields and chemoselectivities under mild reaction conditions.

Intertwined chemistry of hydroxyl hydrogen-bond donors, epoxides and isocyanates in the organocatalytic synthesis of oxazolidinones versus isocyanurates: rational catalytic investigation and mechanistic understanding

The efficiency and chemoselectivity of the cycloaddition of isocyanates to epoxides to afford oxazolidinones were investigated using hydroxyl hydrogen-bond donors as organocatalysts.