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We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1; phen=1,10-phenanthroline), formed as an intermediate during the Zn(OAc)2/phen-catalyzed synthesis of organic carbamates from CO2, amines, and the reusable reactant Si(OMe)4. Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five-coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five-coordinated silicon species. This sustainable and effective method can be used to synthesize various N-aryl and N-alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure.

A simple and efficient domino reaction has been designed and employed for the one-pot synthesis of N-(hetero)aryl carbamates through the reaction between alcohols and in-situ produced (hetero)aryl isocyanates in the presence of a nickel catalyst. The phenolic C?O bond was activated via the reaction of phenol with cyanuric chloride (2,4,6-trichloro-1,3,5-triazine (TCT)) as an inexpensive and readily available reagent. This strategy provides practical access to N-(hetero)aryl carbamates in good yields with high functional groups compatibility.

A palladium-catalyzed domino method for the direct synthesis of carbamates and ureas has been developed by using readily available and economical starting materials (aryl halide, carbon monoxide, sodium azide, amines and alcohols) in a one-pot approach. The domino process underwent carbonylation, Curtius rearrangement, and nucleophilic addition. This protocol provides a step-economical and highly efficient reaction to access the wide range of valuable carbamates, symmetrical and unsymmetrical ureas with high yields under remarkable mild reaction conditions that are important factors in pharmaceutical science, biochemistry and agricultural industries. Furthermore, the magnetically recoverable nanocatalyst (Fe3O4?SiO2/Pd(II)) can be conveniently and swiftly recycled using external magnet and reused at least for seven times without noticeable loss of its catalytic activity.

A green and eco-friendly solvent/catalyst system based on a deep eutectic solvent (DES) was devised and developed for the simple synthesis of carbamates through three-component coupling of amines, alkyl halides and carbon dioxide (CO2). It was found that choline chloride:zinc(ii) chloride ([ChCl][ZnCl2]2) was very proficient and effective for the activation and utilization of CO2 in carbamate formation reactions from a wide scope of amines. Surprisingly, this strategy provides the desired carbamates under atmospheric CO2 pressure at room temperature. In particular, both aromatic and aliphatic amines were effective and demonstrated excellent yields. Besides, the [ChCl][ZnCl2]2 exhibited very high stability and also could be reused for at least five consecutive cycles without any significant loss of activity. It is worth noting that this is the first solvent/catalyst system which can be recycled successfully from the reaction mixture.

An efficient, convenient and novel method for the selective mono N-arylation of primary O-alkyl thiocarbamates and primary O-alkyl carbamates with aryl halides and arylboronic acids in the presence of a recyclable magnetic Cu(ii) nanocatalyst is described. A variety of mono N-arylated O-alkyl thiocarbamates and O-alkyl carbamates were prepared in good to excellent yields with a broad range of aryl coupling partners. The magnetic nanocatalyst can be easily recovered with an external magnetic field and reused at least five times without noticeable leaching or loss of its catalytic activity. This cost-effective and eco-friendly methodology has some other advantages, such as easy preparation of the catalyst, simple workup procedure, and easy purification, which makes this protocol interesting for the users in various fields of pharmacology and biotechnology systems.

A visible-light-promoted oxo-sulfonylation of ynamides with sulfonic acids is reported, giving rise to a collection of functionalized α-sulfonylated amides in a straightforward manner. The reaction proceeds sequentially through a cascade of electrophilic addition and photoinduced sulfonyl radical-sustained skeleton rearrangement. The high atom economy, mild reaction conditions, and wide substrate scope comprised the merits of this synthetic transformation.

We have developed an efficient one-pot method for the microwave-assisted synthesis of ureas and carbamates via a proposed Lossen rearrangement. Herein we report the first examples of the direct conversion of benzoyl chlorides into N,N′-disubstituted ureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid as reagent. Using our general method, we have produced 11 examples of N,N′-disubstituted phenylureas in yields up to 95% using various substituted anilines, and primary and secondary amines. Additionally, we were able to generate a series of N-aryl carbamates in moderate yields using primary, secondary and tertiary alcohols.

The direct catalytic synthesis of carbamates from CO2, amines and methanol was achieved by controlling both the reaction equilibrium and the reactivity of the three components. The combination of CeO2 and 2-cyanopyridine was an effective catalyst, providing various carbamates including N-arylcarbamates in high selectivities.

PROBLEM TO BE SOLVED: To provide a method for producing carbamate in which a high yield can be obtained and the amount of by-products produced can be reduced. SOLUTION: In the method, carbamate is synthesized using at least one member selected from the group consisting of amine and derivative thereof, alcohol having 3 or more carbon atoms and carbon dioxide as a raw material, cerium oxide as a catalyst, and 2-cyanopyridine as a dehydrating agent. By using an alcohol having 3 or more carbon atoms, a high yield can be obtained and the amount of by-products produced can be reduced. In addition, the pressure of carbon dioxide can be lowered and the production can be of ease. SELECTED DRAWING: Figure 1 COPYRIGHT: (C)2018,JPO&INPIT

A simple, efficient and eco-friendly one-pot synthesis of primary, N-mono- and N-disubstituted carbamates is developed from ureas. The corresponding carbamates were produced at 120 °C, within 18 h, and in the presence of a deep eutectic solvent as a recyclable catalytic system. The catalyst can be reused for several runs without any reduction in its activity. To demonstrate the utility of this approach, a wide variety of alcohols and phenols were studied to find a vast range of carbamate derivatives in moderate to high yields.

Abstract: An efficient, selective and cost-effective procedure has been developed for mono N-arylation of primary alkyl and benzyl carbamates with aryl iodides and bromides by incorporating CuI as an inexpensive and commercially available catalyst. Despite previous reports on C–N coupling reactions, this process does not need expensive ligands and takes advantage of readily available and inexpensive ethylenediamine (EDA) as the ligand. Reaction times were relatively short and related N-arylated carbamates were obtained in excellent yields. Interestingly, replacing CuI with Cu(OAc)2 allowed us to use arylboronic acids as coupling partner for this reaction. All products are well characterized by 1H- and 13C-NMR, MS, melting point, IR and CHNS techniques.

We report the continuous flow synthesis of acyl azides in various continuous flow systems and demonstrate that liquid–liquid separation may be incorporated to prepare anhydrous solutions of the acyl azide, which may be subsequently reacted with appropriate nucleophiles to prepare amines, carbamates and amides within a fully integrated multi-step process in high yields (> 80 %). Interesting effects were also observed when preparing carbamates with long chain alcohols, whereby as the chain length of the alcohol increased the products could be made in high yield even without incorporation of the liquid–liquid separation module.

A direct synthesis of carbamates from amines and carbon dioxide in the presence of Ti(OR)4 (R=nBu (1), Me (2), Et (3), nPr (4)) was investigated. Aniline was reacted with titanium n-butoxide (1) in the presence of carbon dioxide (5 MPa) to give the corresponding n-butyl N-phenylcarbamate (BPC) in nearly quantitative yield (99 %) within 20 min. Furthermore, 1 could be regenerated upon reaction with n-butanol during water removal. The recovered 1 could then be reused in a subsequent reaction.

Inorganic bases such as NaH, KO t -Bu, NaOH, or KOH are efficient catalysts to promote the transcarbamoylation reaction between urethanes and a variety of primary and secondary alcohols under mild conditions. They constitute an alternative to organometallic catalysis and can be applied to aliphatic or aromatic urethanes.

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO2, and silicate esters. Zn(OAc)2 offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc)2 can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in 1H and 15N NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO2. Silicate ester was finally converted to siloxane, which was determined by 29Si NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96 % with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.

A superbase-derived protic ionic liquid (IL, [DBUH][OAc]) catalyst was used to directly synthesize carbamate from an amine, CO2, and a silicate ester. This IL catalyst was easily prepared using its precursors, DBU, and acetic acid. Using 10 mol% of the catalyst under a CO2 pressure of 5 MPa in acetonitrile at 150 °C, carbamate was isolated in up to 96% yield. Specifically, aliphatic and aromatic amines were activated even though aromatic amines exhibited low activities because of their low pKa values. Other functional groups in amines were barely activated, affording exclusive chemoselectivity for amine activation. Isotope labeling experiments indicated that the proton in the counter cation is crucial in the catalytic cycle to produce water. In addition, a chemical shift corresponding to a mixture of aniline and [DBUH][OAc] was observed in the 1H NMR spectrum, related to the formation of hydrogen bonds between aniline and basic acetate anions. The experimental results indicated that the designed IL catalysts require a protonated cation and a basic anion.

Aiming to modify the biological activity of sulfonamides, a number of alkyl (4-arylsulfamoyl)- phenylcarbamates were prepared in 50–70% yield. Biological screening showed that the target compounds possessed a high activity against herpes viruses as well as a traditional antibiotic one.

An efficient, heterogeneous and cost effective method has been developed using an Fe3O4@SiO2/Schiff base/Pd complex as a magnetic and easily recyclable nanocatalyst for rapid and effective N-arylation of carbamates in good to excellent yield. The catalyst can be easily recovered and reused over six runs without significant decrease in the activity. Further highlights of this protocol are operational simplicity, versatility and relatively short reaction times.

A direct transformation of N-aryl formamides to the corresponding carbamates via the formation of isocyanate intermediates is achieved in good yields using hypervalent iodine as an oxidant. This journal is

An efficient method has been developed for the synthesis of carbamates from the corresponding amides via the Hofmann rearrangement using N,N-dibromo-p-toluenesulfonamide (TsNBr2) in the presence of DBU in methanol. The reaction goes into completion in 10-20 min at 65 °C to produce the corresponding carbamate in excellent yield.

Heterogeneous CeO2 catalyst can catalyze the one-pot synthesis of methyl benzylcarbamate from benzylamine, CO2 and methanol. The yield of methyl benzylcarbamate reached 92% at >99% benzylamine conversion and 92% benzylamine-based selectivity even in the absence of the dehydrating agents. The catalyst is reusable after the calcination at 873 K for 3 h. Various carbamates can be synthesized with good yield and high selectivity by the reaction of amines + CO2 + alcohols over CeO2. The main formation route of methyl benzylcarbamate is suggested to be the reaction of dimethyl carbonate or the precursor of dimethyl carbonate formation with benzylamine.

The copper-catalyzed coupling of aromatic boronic acids with potassium cyanate in the presence of an alcohol has been employed for the synthesis of arylcarbamates. This simple and highly efficient approach can be carried out in air at room temperature and, importantly, no base, ligand, or additive is required. Copyright

A facile one-pot, phosgene-free synthesis of N-phenylcarbamates is demonstrated. Catalyzed by selenium, oxidative carbonylation of aniline with alcohols in the presence of carbon monoxide and oxygen affords the corresponding N-phenylcarbamates, mostly in fair to good yields. Selenium can be easily recovered because of its phase-transfer catalysis function. Copyright

Bigger is better: Sterically hindered dialkyl ureas undergo nucleophilic substitution at dramatically faster rates than their less hindered counterparts (see scheme). Steric decompression upon the formation of an intermediate isocyanate can explain this c

Carbonate anions resulting from reaction of primary or secondary alcohols with carbon dioxide, when added to methanesulfonic anhydride in cooled acetonitrile solution, yield methanesulfonyl carbonates, a new class of synthetic intermediate. Base-mediated reaction of the methanesulfonyl carbonates with alcohols, thiols, and amines yields carbonates, thiocarbonates, and carbamates, respectively. Overall yields for the three steps vary from 19% to 42%.

The enantioselectivity of porcine pancreatic lipase-catalyzed resolution of 1-indanol was enhanced up to 3 fold in the presence of carbamates. The optimum incubation time for 4-nitrophenyl-N-hexyl carbamate and the enzyme was 18 h before this biocatalytic resolution. The optimum concentration of the inhibitor 4-nitrophenyl-N-hexyl carbamate in this resolution was 1% mole equivalent of the substrate 1-indanol.

The transformation of meso-butane-2,3-diol into butan-2-ol by a strain of Lactobacillus brevis occurs through a diol-dehydratase-catalyzed conversion of the diol into butan-2-one, which is then reduced to the secondary alcohol by dehydrogenases. Experiments performed with deuterated meso-butane-2,3-diols showed that the dehydration reaction brings about an inversion of configuration at the (R)-configured C-atom of mesobutane-2,3- diol as a consequence of the substitution of the OH group by a H-atom; at the same time, the H-atom already bound to the (R) C-atom is retained in the resulting methylene group. The H-atom replacing the OH group was assessed to come from the medium since the H-atom at the (S)-configured C-atom was completely lost. By contrast, in the case of the conversion of (RS)-propane- 1,2-diol into propan-1-ol under the same fermentation conditions, an extensive H-transfer (ca. 80%) from the primary-alcohol function to the adjacent C-atom was observed. This fact is taken as an indication of different modes in which the two substrates are processed by the enzyme (despite the same stereochemical outcome). A speculative hypothesis is presented to interpret such a dissimilarity.

The reaction of amides with tetrabutylammonium tribromide (TBA Br3) (0.5 equiv) and DBU (one equiv) in dichloromethane at room temperature gave N-substituted acylureas in fairly good yields.In the presence of alcohols, the reaction of amides with TBA Br3 (one equiv) and DBU (two equiv) gave N-substituted carbamates.

Palladium acetate and cupric acetate are effective catalysts for the reaction of nitrosobenzenes with carbon monoxide and alcohol at room temperature and one atmosphere.

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A process for preparing polymethylene polyphenyl polyisocyanates, in which N-phenyl carbamic acid esters are subjected to a condensation reaction with formaldehyde, and the reaction product containing polymethylene polyphenyl polycarbamic acid esters and unreacted N-phenyl carbamic acid esters is thermally decomposed to obtain polymethylene polyphenyl polyisocyanates.