Efficient Cs2CO3-promoted solution and solid phase synthesis of carbonates and carbamates in the presence of TBAI

Introducing the Reversible Reaction of CO2 with Diamines into Nonisocyanate Polyurethane Synthesis

Nonisocyanate polyurethanes (NIPUs) are considered greener alternatives to traditional polyurethanes, and the preparation of NIPUs considerably depends on the design and synthesis of suitable monomers. Herein, we propose a toolbox for in situ capturing and conversion of CO2 into α,ω-diene-functionalized carbamate monomers by taking advantage of the facile reversible reaction of CO2 with diamines in the presence of organic superbases. The activation of CO2 into carbamate intermedia was demonstrated by NMR and in situ FTIR, and the optimal conditions to prepare α,ω-diene-functionalized carbamate monomers were established. Thiol-ene and acyclic diene metathesis (ADMET) polymerization of these monomers under mild conditions yielded a series of poly(thioether urethane)s and unsaturated aromatic-aliphatic polyurethanes with high yield and glass transition temperatures ranging from -26.8 to -1.1 °C. These obtained NIPUs could be further modified via postpolymerization oxidation or hydrogenation to yield poly(sulfone urethane) and saturated polyurethane with tunable properties.

Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO2 Valorization

Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon's energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H2O as the stoichiometric byproduct.

En Route to CO2-Based (a)Cyclic Carbonates and Polycarbonates from Alcohols Substrates by Direct and Indirect Approaches

This review is dedicated to the state-of-the art routes used for the synthesis of CO2-based (a)cyclic carbonates and polycarbonates from alcohol substrates, with an emphasis on their respective main advantages and limitations. The first section reviews the synthesis of organic carbonates such as dialkyl carbonates or cyclic carbonates from the carbonation of alcohols. Many different synthetic strategies have been reported (dehydrative condensation, the alkylation route, the “leaving group” strategy, the carbodiimide route, the protected alcohols route, etc.) with various substrates (mono-alcohols, diols, allyl alcohols, halohydrins, propargylic alcohols, etc.). The second section reviews the formation of polycarbonates via the direct copolymerization of CO2 with diols, as well as the ring-opening polymerization route. Finally, polycondensation processes involving CO2-based dimethyl and diphenyl carbonates with aliphatic and aromatic diols are described.

One stone two birds: cobalt-catalyzed in situ generation of isocyanates and benzyl alcohols for the synthesis of N-aryl carbamates

An efficient method for the synthesis of N-aryl carbamates from N-Boc-protected amines has been developed. The cobalt-catalyzed in situ generation of isocyanates from N-Boc-protected amines and benzyl alcohols from benzyl formates has been achieved for the first time, which in turn furnished the corresponding benzyl carbamates in moderate to high yields. The reaction was catalyzed by CoI₂ with tris-(4-dimethylaminophenyl)-phosphine as the ligand and zinc powder as the reductant. The developed reaction conditions were found to be compatible for aromatic amines with both electron-donating and -withdrawing substituents.

Direct Incorporation of [11C]CO2 into Asymmetric [11C]Carbonates

A novel carbon-11 radiolabelling methodology for the synthesis of the dialkylcarbonate functional group has been developed. The method uses cyclotron-produced short-lived [¹¹C]CO₂ (half-life 20.4 min) directly from the cyclotron target in a one-pot synthesis. Alcohol in the presence of base trapped [¹¹C]CO₂ efficiently forming an [¹¹C]alkylcarbonate intermediate that subsequently reacted with an alkylchloride producing the di-substituted [¹¹C]carbonate (34% radiochemical yield, determined by radio-HPLC) in 5 minutes from the end of [¹¹C]CO₂ cyclotron delivery.

Direct Photochemical C-H Carboxylation of Aromatic Diamines with CO2 under Electron-Donor- and Base-free Conditions

We report the photochemical carboxylation of o-phenylenedimamine in the absence of a base and an electron donor under an atmosphere of CO₂, which afforded 2,3-diaminobenzoic acid (DBA) in 28% synthetic yield and 0.22% quantum yield (Φ(%)). The synthetic yield of DBA in this reaction increased to 58% (Φ(%) = 0.47) in the presence of Fe(II). The photochemical reaction described in this work provides an effective strategy to use light as the driving force for the direct carboxylation of organic molecules by CO₂.

Synthesis of Polycarbonates and Poly(ether carbonate)s Directly from Carbon Dioxide and Diols Promoted by a Cs2CO3/CH2Cl2 System

Recently, polycarbonates have attracted considerable research interest because of their potential biodegradability and sustainability. Here, we present a direct route for the synthesis of polycarbonates and poly(ether carbonate)s from carbon dioxide (CO₂) and diols, promoted by Cs₂CO₃ and CH₂Cl₂ under 1 atm of CO₂. Quantitative conversion of diols and polymers with up to 11 kg/mol molecular weight could be obtained. While benzylic diols lead to predominantly carbonate linkage, aliphatic diols result in the incorporation of the methylene unit of CH₂Cl₂ that produces poly(ether carbonate)s. Both primary and secondary diols have been successfully incorporated into the polymer chain.

Iron-Catalyzed Reaction of Urea with Alcohols and Amines: A Safe Alternative for the Synthesis of Primary Carbamates

A general study of the iron-catalyzed reaction of urea with nucleophiles is here presented. The carbamoylation of alcohols allows for the synthesis of N-unsubstituted (primary) carbamates, including present drugs (Felbamate and Meprobamate), without the necessity to apply phosgene and related derivatives. Using amines as nucleophiles gave rise to the respective mono- and disubstituted ureas via selective transamidation reaction. These atom-economical transformations provide a direct and selective access to valuable compounds from cheap and readily available urea using a simple Lewis-acidic iron(II) catalyst.

Cs2CO3-promoted polycondensation of CO2 with diols and dihalides for the synthesis of miscellaneous polycarbonates

A one-pot protocol for the direct synthesis of polycarbonates through polycondensation of diols, dihalides and CO₂ in the presence of Cs₂CO₃ is described.

Organic carbamates in drug design and medicinal chemistry

The carbamate group is a key structural motif in many approved drugs and prodrugs. There is an increasing use of carbamates in medicinal chemistry and many derivatives are specifically designed to make drug-target interactions through their carbamate moiety. In this Perspective, we present properties and stabilities of carbamates, reagents and chemical methodologies for the synthesis of carbamates, and recent applications of carbamates in drug design and medicinal chemistry.

A facile one-step synthesis of star-shaped alkynyl carbonates from CO2

The synthesis of new star-shaped compounds containing three or six pendant carbonates with terminal alkynes at 1 atm CO₂ and room temperature.

Catalytic dehydrogenative N-((triisopropylsilyl)oxy)carbonyl (Tsoc) protection of amines using iPr3SiH and CO2

Heterogeneous Pd/C efficiently catalyzes the dehydrogenative N-((triisopropylsilyl)oxy)carbonyl (Tsoc) protection of amines using iPr₃SiH and CO₂ without the liberation of any salts.

[11C]GR103545: novel one-pot radiosynthesis with high specific activity

INTRODUCTION

GR103545 is a potent and selective kappa-opioid receptor agonist. Previous studies in non-human primates demonstrated favorable properties of [(11)C]GR103545 as a positron emission tomography tracer for in vivo imaging of cerebral kappa-opioid receptor. Nonetheless, advancement of [(11)C]GR103545 to imaging studies in humans was hampered by difficulties of its multiple-step radiosynthesis, which produces a final product with low specific activity (SA), which in turn could induce undesirable physiological side effects resulting from the mass associated with an injected amount of radioactivity. We report herein an alternative radiosynthesis of [(11)C]GR103545 with higher SA and radiochemical yields.

METHODS

The TRACERLab FXC automated synthesis module was used to carry out the two-step, one-pot procedure. In the first step, the desmethoxycarbonyl precursor was converted to the carbamic acid intermediate desmethyl-GR103545 via transcarboxylation with the zwitterionic carbamic complex, 1,8-diazabicyclo[5.4.0]undec-7-ene-carbon dioxide, in the presence and/or absence of cesium carbonate and tetrabutylammonium triflate. In the second step, the intermediate was radiolabeled at the carboxyl oxygen with [(11)C]methyl trifluoromethanesulfonate to give [(11)C]GR103545.

RESULTS

This novel synthesis produced [(11)C]GR103545 with ≥90% chemical and radiochemical purities and an SA of 290.45±99.9 MBq/nmol at the end of synthesis (n=26). Injectable radioactivity was 1961±814 GBq/μmol with 43 min of average synthesis time from the end of beam.

CONCLUSION

We have developed a practical one-pot method for the routine production of [(11)C]GR103545 with reliably high SA and radiochemical yield, thus allowing the advancement of this radiotracer to imaging applications in humans.

Electrochemically Promoted C−N Bond Formation from Amines and CO2 in Ionic Liquid BMIm−BF4: Synthesis of Carbamates

A new electrochemical procedure for the synthesis of organic carbamates from amines and carbon dioxide has been developed using selective cathodic reduction of carbon dioxide in CO2-saturated room-temperature ionic liquid BMIm-BF4 solutions containing amines 1a-j, followed by addition of EtI as an alkylating agent. The synthesis was carried out under mild (PCO2 = 1.0 atm, t = 55 degrees C) and safe conditions, and the use of volatile and toxic solvents and catalysts (according to the growing demand for ecofriendly synthetic methodologies), as well as of any supporting electrolyte (for a very easy workup of the reaction mixture), was avoided. Carbamates 2a-j were isolated in good to high yields.

Amidations Using N,N ‘-Carbonyldiimidazole: Remarkable Rate Enhancement by Carbon Dioxide

Carbon dioxide catalyzes the reaction of imidazolides with amines to form amides. A substantial rate enhancement is observed in the presence of CO(2) compared to the CO(2)-free case. The scope and limitations of this reaction are discussed.

Cyanomethyl anion/carbon dioxide system: an electrogenerated carboxylating reagent. Synthesis of carbamates under mild and safe conditions

A new carboxylating reagent ((-)CH(2)CN/CO(2)) was obtained by bubbling CO(2) in a CH(3)CN-TEAP (tetraethylammonium perchlorate) solution previously electrolyzed under galvanostatic control. Organic carbamates were isolated from these solutions after addition of amines and an alkylating agent. In this paper, we describe the optimized conditions for the electrochemical synthesis of carbamates from amines and CO(2), in mild and safe conditions, without any addition of bases, probases, or catalysts. Carbamates were isolated from primary and secondary aliphatic amines in high to excellent yields and from aromatic amines in moderate yields (dependent on the nucleophilicity of the nitrogen atom).