Reaction Of Carbamates Research Articles

Nickel-catalyzed cross-coupling reaction of carbamates with silylmagnesium reagents

The CO bonds are kinetically inert in cross-coupling reactions compared to those of carbon–halogen bonds. Thus, developing methodologies for the activation of CO bonds in cross-coupling reactions remains a major challenge. We disclose an unprecedented nickel mediated cross-coupling of carbamates with silylmagnesium reagents that does not require the expensive silylboranes. Silylmagnesium reagents were prepared from either silyllithium or silyl iodides. This methodology is distinguished by the synthesis of trimethylsilyl coupled product and its synthetic applications. Kinetic studies and radical clock experiments revealed the rate-limiting CO bond cleavage, half order with respect to the catalyst and a non-radical transition state.

Nickel-Catalyzed Decarboxylation of Aryl Carbamates for Converting Phenols into Aromatic Amines.

Herein, we describe a new catalytic approach to accessing aromatic amines from an abundant feedstock, namely phenols. The most reliable catalytic method for converting phenols to aromatic amines uses an activating group, such as a trifluoromethane sulfonyl group. However, this activating group is eliminated as a leaving group during the amination process, resulting in significant waste. Our nickel-catalyzed decarboxylation reaction of aryl carbamates forms aromatic amines with carbon dioxide as the only byproduct. As this amination proceeds in the absence of free amines, a range of functionalities, including a formyl group, are compatible. A bisphosphine ligand immobilized on a polystyrene support (PS-DPPBz) is key to the success of this reaction, generating a catalytic species that is significantly more active than simple nonsupported variants.

Convergent synthesis of phosphonopeptides via phospha-Mannich reactions: Rationale on reactivity and mechanistic insights

Phospha-Mannich reactions of benzyl carbamate, aldehydes, and methyl dichlorophosphite followed by aminolysis with amino acid esters or alcoholysis with hydroxyl acid esters produce N-Cbz(benzyloxycarbonyl)-protected phosphonopeptides or phosphonodepsipeptides. However, similar reactions do not work when Cbz-amino amides are used instead of the carbamate. Phospha-Mannich reactions of N-Cbz-amino amides/2-(Cbz-amino)alkanesulfonamides, aldehydes, and dichloroarylphosphines and subsequent aminolysis with amino acid esters or alcoholysis with hydroxyl acid esters yield phosphinopeptides or phosphinodepsipeptides and hybrid sulfonophosphinopeptides or sulfonophosphinodepsipeptides. The different reactivities and mechanistic insights are rationalized that the α-amino alcohols generated from aldehydes and amides/sulfonamides show weaker nucleophilicity than those generated from aldehydes and benzyl carbamate. They can react with stronger electrophilic dichloroarylphosphines rather than weaker electrophilic methyl dichlorophosphite. The nucleophilicity of α-amino alcohols (amine reagents, carbamates, amides, and sulfonamides) and the electrophilicity of phosphorus reagents (dichloroarylphosphines and ethyl dichlorophosphite) control the reactivity of the phospha-Mannich reactions. Phosphorus trichloride is also efficient phosphorus reagent in the phospha-Mannich reactions because it is stronger electrophile as well.

Synthesis of N-glycyl-β-glycopyranosylamines, derivatives of main human secreted oligosaccharide core structures

β-Glycopyranosylamines were synthesized by the reaction of ammonium carbamate with di-, tetra-, and hexasaccharides, corresponding to the human milk and urine oligosaccharide core structures, in aqueous methanolic solution in the presence of NH3. The N-acylation of these β-glycopyranosylamines with N-Boc-glycine N-hydroxysuccinimide ester followed by removal of the Boc group afforded N-glycyl-β-glycopyranosylamines of the corresponding oligosaccharides in yields of up to 60%.

Adsorption behavior of isocyanate/ethylenediamine tetraacetic acid-functionalized graphene oxides for Cu2+ removal.

A special adsorption of Cu2+ removal is demonstrated using specifically functionalized graphene oxide (GO)/isocyanate (MDI) composites, on which ethylenediamine tetraacetic acid (EDTA) is grafted via amidation and carbamate reaction. The structure and morphology of GO and functionalized composites (EDTA/MDI/GO) were characterized by scanning electron microscope (SEM), Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TGA). This study investigated the adsorption and desorption behaviors of heavy metal cations and the effects of solution conditions such as pH on Cu2+ removal. The experimental results illustrated that after introducing EDTA and MDI into the GO, the maximum adsorption capacity reached 254.2 ± 10.4 mg/g within 180 min, obviously higher than the GO prepared without these additions (136.5 ± 7.2 mg/g). The EDTA/MDI/GO adsorption kinetics and equilibrium adsorption isotherm fitted the pseudo-second-order kinetic model (R2 = 0.995) and Langmuir isotherm model (R2 = 0.986) well, respectively. Furthermore, EDTA/MDI/GO also displayed good reusability for the efficient removal of Cu2+ after being washed with HCl, suggesting potential application in Cu2+ cleanup.

Ag(I)/(C2H5)4NCl Cooperation Catalysis for Fixing CO2 or Its Derivatives into β‐Oxopropylcarbamates

AbstractIt remains a great challenge to convert CO2 into high value‐added products under ambient pressure. Herein, an efficient dual‐component catalytic system, i. e., Ag(I)/(C2H5)4NCl was developed for the synthesis of various β‐oxopropylcarbamates via one‐pot three‐component coupling of CO2, secondary amines and propargylic alcohols under atmospheric pressure. Besides, the strategy avoided the use of any additional ligand and basic species, and excellent selectivity was achieved with a yield of up to 98%. Additionally, 13Ccarbonyl‐labeled and control experiments were carefully performed to demonstrate the mechanism. Notably, this new method was also applied efficiently in quantitative chemical fixation of CO2, i. e., the two‐component reaction of propargylic alcohols and ammonium carbamates.

Synthesis of bicyclic tetrahydropyridine enamides and enecarbamates by hetero-Cope rearrangement of nitroso cycloadducts

The hetero-Cope rearrangement reactions of inverse carbamate and amide nitroso Diels–Alder cycloadducts with 1,2-dihydropyridines to give novel tetrahydropyridine enamides and enecarbamates have been studied in detail identifying optimal reaction conditions. The possibility to obtain tetrahydropyridine enamides and carbamates containing a free OH at the C-4 position is restricted to only particular substitution patterns when dealing with carbamate nitroso cycloadducts. On the other hand, starting from easily available amide nitroso cycloadducts and catalytic amounts of cuprous salts, it is now possible to obtain several substituted 4a,7,8a-tetrahydropyrido[4,3-e]-[1,4,2]dioxazines in moderate to good yields.

Formation of Olefins by Eliminative Dimerization and Eliminative Cross-Coupling of Carbenoids: A Stereochemical Exercise.

Two carbenoids combine to generate an olefin by a mechanism involving formation of an ate complex, 1,2-metalate rearrangement, and β-elimination. As each stage of this eliminative coupling is stereospecific, the overall stereochemical outcome can be understood and, in principle fully controlled, providing that the absolute stereochemical configurations of the reacting carbenoid species are defined. In contrast to traditional alkene syntheses, the eliminative cross-coupling of carbenoids offers a connective approach to olefins capable of precisely targeting a given isomer regardless of the nature of the features distinguishing the isomers. The formation of olefins by the eliminative dimerization and eliminative cross-coupling of carbenoids is reviewed with a range of illustrative examples, including the reactions of α-lithiated haloalkanes, epoxides, and carbamates. An emphasis is placed on stereochemical analysis and methods to generate sp3 -hybridized carbenoids in stereodefined form are surveyed.

Theoretical Studies on the Aminolysis Mechanism of Methomyl: Effect of the Catalysis to the Reaction of Carbamate with Ammonia

AbstractThe aminolysis mechanisms of methomyl are systematically investigated through the M06‐2X/6‐311++G(d,p) and MP2/6‐311+G(d,p) methods. The uncatalyzed, base‐catalyzed and water‐catalyzed aminolysis processes are also taken into consideration together with the concerted, BAC2 (a stepwise channel through a neutral tetrahedral intermediate) and E1cB (a stepwise mechanism via an isocyanate intermediate) pathways. The solvent effects are discussed in detail by using the CPCM (conductor‐like polarized continuum model) with the M06‐2X/6‐311++G(d,p) method. The computational values provide convincing evidence that three alternative pathways possess similar energy barriers for the uncatalyzed aminolysis. It can be concluded that the base‐catalyzed and water‐catalyzed aminolysis processes are more favorable compared with the uncatalyzed reaction. Concerning the base‐catalyzed process, the E1cB pathway is preferable to other channels. However, the water‐catalyzed aminolysis is dominated by the BAC2 mechanism. In a word, the aminolysis reactions in solution could readily occur and the solvent effects do not remarkably alter the mechanism.

An experimental and modeling study of CO2 solubility in a 2-amino-2-methyl-1-propanol (AMP) + N-methyl-2-pyrrolidone (NMP) solution

In this study, an experimental setup based on the static-synthetic method was used to measure the new experimental data of CO2 solubility in an aqueous solution of 2-amino-2-methyl-1-propanol (AMP) + N-methyl-2-pyrrolidone (NMP) solution. For the static-synthetic method, the mass balance of compositions and the pressure–volume–temperature conditions were used for measuring the amount of absorbed CO2 by the AMP+NMP solution. The measurements were performed over a temperature range of 313.15–353.15 K, CO2 partial pressure up to 316.7 kPa, and in different concentrations of the AMP+NMP solution. Two models, modified Kent–Eisenberg, and Deshmukh–Mather, based on the empirical correlations and activity-fugacity approach, respectively, were used for the prediction of experimental data. The parameters of the equilibrium constants of the protonation and carbamate reactions for the modified Kent–Eisenberg model and the interaction parameters for Deshmukh–Mather model were obtained. For validation of our setup, a new set of experimental data for the solubility of CO2 in an aqueous solution of AMP, methyldiethanolamine (MDEA) and diethanolamine (DEA) were measured and compared with existing experimental data in the literature, and good results were obtained. The results of the modeling study showed that the Deshmukh–Mather model gave a better prediction of experimental CO2 loadings data than the modified Kent–Eisenberg. Also, the results showed that the solubility of CO2 in an aqueous solution of AMP+NMP increases as the CO2 partial pressure increases while the temperature decreases.

Custom Glycosylation of Cells and Proteins Using Cyclic Carbamate-Derivatized Oligosaccharides

The structural complexity of glycosylation restrains the functional characterization of glycans. We present a versatile carbohydrate ligation technique based on the reaction of cyclic carbamates with primary amines. Cyclic-carbamate-derivatized carbohydrates can be added to primary amine-containing molecules in aqueous solution to yield glycoconjugates. This method enabled the presentation of carbohydrate epitopes on live animal cells, as shown by the acquisition of E-selectin binding sites on mouse MC-38 cells decorated with 3-fucosyllactose or 3-fucosyl-3-sialyllactose. Ligation of 3- and 6-sialyllactose to Escherichia coli demonstrated theimportance of sialic acid linkages in regulating complement factor H binding. Proteins were modified with oligosaccharides to study their role in stimulating cytokine secretion by dendritic cells, thus pointing to interactions between glycoproteins and phosphoinositide 3-kinase signaling in controlling interleukin-12, tumor necrosis factor alpha and interleukin-1β release. Overall, cyclic-carbamate-mediated ligation is useful to study the biology ofcarbohydrate epitopes on proteins and on cell membranes.

Asymmetric catalyzed intramolecular aza-Michael reaction mediated by quinine-derived primary amines

An intramolecular organocatalytic enantioselective aza-Michael reaction of carbamates, sulfonamides and acetamides to α,β-unsaturated ketones was developed. This process is promoted by 9-amino-9-deoxy-epi-quinine and diphenyl hydrogen phosphate to afford a straightforward and expeditious synthesis of several synthetically useful five- and six-membered heterocycles with excellent enantioselectivity (92%–97.5% ee) and very good yields (up to 99%).

Ruthenium-catalyzed olefinic C-H alkenylation of enol-carbamates: highly stereo-selective synthesis of (Z,Z) and (Z,E)-butadienes.

Cross-coupling reactions of enol carbamates with alkynes or alkenes are reported, using an inexpensive ruthenium catalyst. With the assistance of the directing group OCONMe2, the protocols provide mild, stereo-selective and efficient routes for the preparation of valuable (Z,Z) and (Z,E)-butadiene skeletons.

The Two Alternative Rate-Determining Steps in Benzylic Lithiation Reactions of Esters and Carbamates

Lithiation reactions of tertiary benzylic esters and carbamates have been studied. Kinetic methodology revealed that a two-step reaction pathway should be considered for these reactions, where either the lithium precomplexation and/or the proton transfer steps can be rate determining. Kinetic isotopic effects were evaluated by comparison of the lithiations of the corresponding protio/deutero substrates, and the results obtained support the notion that lithium precomplexation is taking place on the reaction pathway and that it is the rate-determining step in this transformation.

Gas-Phase Mechanisms of the Reactions of Reduced Organic Nitrogen Compounds with OH Radicals.

Research on the fate of reduced organic nitrogen compounds in the atmosphere has gained momentum since the identification of their crucial role in particle nucleation and the scale up of carbon capture and storage technology which employs amine-based solvents. Reduced organic nitrogen compounds have strikingly different lifetimes against OH radicals, from hours for amines to days for amides to years for isocyanates, highlighting unique functional group reactivity. In this work, we use ab initio methods to investigate the gas-phase mechanisms governing the reactions of amines, amides, isocyanates and carbamates with OH radicals. We determine that N-H abstraction is only a viable mechanistic pathway for amines and we identify a reactive pathway in amides, the formyl C-H abstraction, not currently considered in structure-activity relationship (SAR) models. We then use our acquired mechanistic knowledge and tabulated literature experimental rate coefficients to calculate SAR factors for reduced organic nitrogen compounds. These proposed SAR factors are an improvement over existing SAR models because they predict the experimental rate coefficients of amines, amides, isocyanates, isothiocyanates, carbamates and thiocarbamates with OH radicals within a factor of 2, but more importantly because they are based on a sound fundamental mechanistic understanding of their reactivity.

The Synthesis of 5-Amino-dihydrobenzo[b]oxepines and 5-Amino-dihydrobenzo[b]azepines via Ichikawa Rearrangement and Ring-Closing Metathesis.

The combination of Ichikawa's rearrangement and a ring-closing metathesis reaction of allyl carbamates is presented as a method for the preparation of 5-amino-substituted 2,5-dihydro-benzo[b]oxepines, 2,5-dihydro-benzo[b]azepines, and 2,5-dihydro-benzo[b]thiepins. It was demonstrated that the use of nonracemic allyl carbamates enables the synthesis of enantioenriched benzo-fused seven-membered heterocycles. Finally, it was shown that further functionalization of the obtained structures allows access to pharmacologically active 5-amino-substituted 2,3,4,5-tetrahydro-1-benzo[b]oxepine scaffolds.

ChemInform Abstract: N‐Boc‐Aminals as Easily Accessible Precursors for Less Accessible N‐Boc‐Imines: Facile Synthesis of Optically Active Propargylamine Derivatives Using Mannich‐Type Reactions.

We developed a facile and practical synthesis of N-Boc-aminals, which can be used as precursors for less accessible N-Boc-imines. Aminals were obtained via simple dehydration condensation reactions of t-butyl carbamate (BocNH2) and various aldehydes in acetic anhydride, followed by filtration and washing with hexane. The obtained N-Boc-alkynylaminals could be successfully applied in enantioselective Mannich-type reactions, catalyzed by chiral phosphoric acids, to afford optically active propargylamine derivatives.

Thermodynamic and mass transfer modeling of carbon dioxide absorption into aqueous 2-piperidineethanol

Amine scrubbing is a necessary technology to offset CO2 emissions from fossil-fuel power plants. Of the many solvents studied, hindered amines are of particular interest for their marriage of the capacity of tertiary amines with rates a hundredfold greater than tertiary amines. The relatively rapid rates of hindered amines have not been adequately explained, despite their extensive use in commercial solvents. This work seeks to explain the rapid rate of mass transfer of 2-piperidineethanol (2PE) and uses this rationale to draw general conclusions on hindered amines.Quantitative 13C NMR data were collected to determine the equilibrium of carbamate in 30wt% 2PE. Using these data along with VLE and pKa data, a rigorous thermodynamic model of 8 molal 2PE was built with electrolyte-NRTL and activity-based kinetics. Wetted-wall column flux data were fit to create the activity-based mass transfer model. Using this comprehensive model, the mass transfer rate was examined through sensitivity studies and Brønsted correlations.This work shows that 2PE forms a more stable carbamate than 2-amino-2-methyl-1-propanol. The carbamate reaction is the most significant component of mass transfer at 40°C. The Brønsted correlation for carbamate reactions of unhindered amines predicts the rate of carbamate reaction of 2PE, but the Brønsted correlation for bicarbonate underpredicts the regressed rate. The CO2 solubility is fit with five parameters with an ARD of 0.84%. The kinetics are fit with a carbamate- and a bicarbonate-forming reaction with an ARD of 7.03%.The chief conclusions are (1) that the rapid mass transfer of hindered amines is due to the formation of carbamate and the high pKa of the amine, (2) the carbamate formation rate appears unimpeded by steric hindrance and is predicted by a Brønsted correlation, suggesting that hindered amines react in the same manner as unhindered amines.

Nickel-Catalyzed Cross-Coupling Reactions of Unreactive Phenolic Electrophiles via C-O Bond Activation.

Nickel-catalyzed cross-coupling reactions of aryl esters, carbamates, carbonates, ethers and arenols are reviewed. Carbon-oxygen bonds in these phenol derivatives cannot be activated by palladium, a typical cross-coupling catalyst, but a low valent nickel species in conjunction with a strong σ-donor ligand is uniquely effective for achieving this. The review is organized primarily by substrate class and secondarily by coupling partners, encompassing organometallics, heteroatom nucleophiles, C-H bonds and many others. Although the reactions in this category are covered thoroughly, each reaction is described only briefly, so that it is possible to quickly overview the spectrum of nickel-catalyzed cross-coupling reactions of inert phenol derivatives. The robustness of inert phenol derivatives under typically used catalytic conditions as well as their utility as a directing group allow unique synthetic applications of these new C-O cross-coupling reactions, which is also included in cases where appropriate. Mechanistic aspects of C-O bond activation by nickel are also summarized, highlighting their diversity compared with the C-X bond activation involved in conventional cross-coupling processes.

Solvent effects in the thermal decomposition reaction of ammonium carbamate: A computational molecular dynamics study of the relative solubilities of CO2 and NH3 in water, ethylene glycol, and their mixtures

The endothermic decomposition of ammonium carbamate has been proposed as a novel heat sink mechanism for aircraft thermal management (Johnson et al., 2012). The products of the reversible decomposition are carbon dioxide and ammonia which need to be efficiently removed from the carrier fluid in order to better control the reaction and thus the heat transfer. Molecular dynamics simulations can provide insight into the transport properties of carbon dioxide and ammonia in the carrier fluid. In this work, extensive classical non-reactive molecular dynamics simulations were carried out to explore the solvent effects in the thermal decomposition reaction of ammonium carbamate by studying the temperature and concentration dependence of relative solubility and diffusivity of carbon dioxide and ammonia in water, ethylene glycol, and their mixtures at standard temperature and pressure and at the elevated temperature of the thermal decomposition reaction of ammonium carbamate. This comparative study shows that ammonia is more soluble than carbon dioxide in either water or ethylene glycol and that both carbon dioxide and ammonia are more soluble in ethylene glycol than in water. Our simulations of water–ethylene glycol mixtures show that increasing the molar fraction of ethylene glycol leads to increased solubility of carbon dioxide and ammonia in the mixture. Even though this is a non-reactive study, it is able to capture the general solubility trends. Accounting for the reactions of carbon dioxide and ammonia in the solution would further amplify the observed trends by amplifying the retaining of CO2 and NH3 in the solution. We present a low-cost computational procedure for relative solubility evaluation that can be used in a broader engineering design context.