Reactions of nitroxides with sulfur‐containing compounds,part IV: Synthesis of novel nitroxide (thio)ureas1

The reactions of 4‐isothiocyanato‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl 2 and 4‐isocyanato‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl 3 with selected amines and lower alcohols give the corresponding novel thioureas 4 , ureas 5 , thiocarbamates 6 , and carbamates 7 , all bearing the nitroxyl moiety. The characteristic features of EI mass spectra of (thio)ureas 4 and 5 are described. Some of the synthesized thioureas 4 , ureas 5 , thiocarbamates 6 , and carbamates 7 are moderately or weakly active against pathogenic fungi. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:393–401, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20228     

Fragmentation of Optically Active (1-Phenylethyl)- and (1-Naphthylethyl)ureas in Refluxing Alcohols: Easy Preparation of Optically Active Amines of High Optical Purity

(1-Phenylethyl)- and (1-naphthylethyl)ureas, obtained in the reaction of racemic amines with optically pure isocyanates, are separated and then decomposed in refluxing alcohols, to afford optically pure secondary amines and optically pure alkyl carbamates in quantitative yields. The scope of this fragmentation for the resolution of racemic mixtures of amines is illustrated by several examples of biologically important compounds. Carbamates obtained by this fragmentation can readily be recycled.     

An efficient one-pot synthesis of N,N′-disubstituted phenylureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid

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.     

Copper-catalyzed aerobic oxidative amidation of terminal alkynes: efficient synthesis of ynamides

A copper-catalyzed method for the preparation of ynamides has been identified that proceeds via aerobic oxidative coupling of terminal alkynes with various nitrogen nucleophiles, including cyclic carbamates, amides and ureas, and N-alkyl-arylsulfonamides and indoles.     

Synthesis of cyclic sulfamoyl carbamates and ureas via ring-closing metathesis

Synthetic routes to a diverse set of cyclic sulfamoyl carbamates and ureas are reported. These routes utilize 3-component coupling, Mitsunobu alkylation, and ring-closing metathesis using the second-generation Grubbs catalyst to achieve the synthesis of the target S-heterocyclic compounds. Cyclic S-heterocycles ranging from 9- to 11-membered rings have been obtained.     

The direct conversion of carbamates to ureas using aluminum amides

The conversion of carbamates into ureas using aluminum amide complexes is reported. This reaction is a convenient method to prepare bi-, tri- and tetra-substituted ureas from carbamate-protected primary or secondary amines by reaction with primary or secondary amines in the presence of stoichometric quantities of trimethylaluminum. A reactivity trend of the various carbamates was observed and methyl and benzyl carbamates were reacted selectively in the presence of t-butyl carbamates.     

Practical synthesis of unsymmetrical ureas from isopropenyl carbamates

A very convenient method for the synthesis of unsymmetrical ureas is described, based on isopropenyl carbamates. The synthetic efficiency of traditional methods for urea formation, such as use of phosgene or alkyl and aryl carbamates, is limited by the formation of symmetrical urea side products or reaction reversibility. Isopropenyl carbamates react with amines cleanly and irreversibly and give unsymmetrical ureas in high yield and purity. This method is ideal for the rapid synthesis of compound libraries.     

Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts

Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox‐neutral azocycloamination. In general, N‐aryl O‐prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron‐deficient diazonium salts, electronic matching with an electron‐rich N‐aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen‐atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton‐coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.     

Pd（OAc）2／[mmim]I催化体系催化胺氧化羰化合成氨基甲酸酯、脲和2-噁唑啉酮

采用Pd(OAc)2/[mmim]I催化体系,在不同反应条件下可以将烷基胺、芳香胺及氨基醇(酚)一步转化为氨基甲酸酯、脲和2-噁唑啉酮.N-苯基氨基甲酸甲酯、二苯基脲及苯并-2-噁唑酮的催化转化频率分别为12417,17638和4114h-1.     

Stereospecific synthesis of urea-tethered neoglycoconjugates starting from glucopyranosyl carbamates

Silyl-assisted elimination reaction of glucopyranosyl carbamates has been established for the synthesis of α- and β-d-glucopyranosyl isocyanates and ureas. This method proved to be useful for the synthesis of urea-tethered neoglycoconjugates.     

Intramolecular vinylation of secondary and tertiary organolithiums

Deprotonation of benzylic ureas, carbamates, and thiocarbamates bearing N'-alkenyl substituents generates carbanions which undergo intramolecular migration of the alkenyl group to the carbanionic center. Solvolysis of the urea products generates α-alkenylated amines. With an enantiomerically pure starting urea, migration proceeds stereospecifically, generating in enantiomerically enriched form products containing allylic quaternary stereogenic centers bearing N. Computational and in situ IR studies suggest that the reaction, formally a nucleophilic substitution at an sp(2) carbon atom, proceeds by a concerted addition-elimination pathway.     

(11)C] Carbon monoxide in selenium-mediated synthesis of (11)C-carbamoyl compounds

Using either amines, amino alcohols, or alcohols in selenium-mediated synthesis with [(11)C]carbon monoxide, 3 ureas, 6 carbamates, and 1 carbonate were labeled. Tetrabutylammonium fluoride ((TBA)F) was discovered to form a soluble and reactive complex with selenium and drastically increase the radiochemical yields. Of the selected carbamoyl compounds, one was a receptor ligand, one was an enzyme inhibitor, and one was a muscular relaxant pharmaceutical. The (11)C-target compounds were obtained in radiochemical yields ranging from low to almost quantitative and with specific radioactivity up to 1300 GBq/micromol. The radiochemical purity of the final products exceeded 98%. In one case, the corresponding (13)C-substituted compound was produced to verify the position of the (11)C-label. In a typical experiment starting with 16.4 GBq [(11)C]carbon monoxide, 7.0 GBq of LC-purified 5-phenyl-1,3-oxazolidin-[2-(11)C]-2-one was obtained within 20 min from start of the carbonylation reaction (84% decay-corrected radiochemical yield). The presented approach is an interesting alternative to the use of [(11)C]phosgene in labeling chemistry.     

Smart cleavage reactions: the synthesis of an array of ureas from polymer-bound carbamates

The solid-phase synthesis of a library of di-, tri-, and tetrasubstituted ureas is described. In this approach, an array of polymer-bound carbamates was synthesized. These polymer-bound primary and secondary amine carbamates were then treated under "smart" diversity-building cleavage conditions using a series of aluminum amide complexes to form the corresponding urea cleavage products. The crude cleavage products from this study were isolated in excellent yield and purity. To show the applicability of this strategy, a series of biaryl ureas were synthesized using sequential solid-phase Suzuki coupling and urea formation reactions.     

Mécanisme de l'hydrolyse acide des carbamates

N, N-dialkyl carbamates decompose in strongly acidic media to carbon dioxide, olefin, alkyl halide and alcohol, the rate of reaction of the secondary esters closely following the acidity function. This fact, together with the variation in rate of hydrolysis of carbamates of cyclic alcohols with the ring size, shows that, unlike the solvolyses of the corresponding chloroformates which lead to carboxonium ions (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R - O -}\mathop {\rm C}\limits^{{\rm (+)}} = {\rm O} $\end{document}), these reactions involve the intermediate formation of carbonium ions.     

CO2 Conversion with Alcohols and Amines into Carbonates,Ureas, and Carbamates over CeO2 Catalyst in the Presence and Absence of 2‐Cyanopyridine

Recent progress on the CeO₂ catalyzed synthesis of organic carbonates, ureas, and carbamates from CO₂+alcohols, CO₂+amines, and CO₂+alcohols+amines, respectively, is reviewed. The reactions of CO₂ with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H₂O is essential in order to get the target product in high yield. One of the effective method of the H₂O removal from the related reaction systems is the combination with the hydration of 2‐cyanopyridine to 2‐picolinamide, which is also catalyzed by CeO₂.     

A Pd(OAc)2/[mmim]I Catalyst System for Oxidative Carbonylation of Amines to Carbamates, Ureas, and 2-Oxazolidinones

A Pd(OAc)₂/[mmim]I ([mmim]I=1-methyl-3-methylimidazolium iodide) catalyst system was applied to the oxidative carbonylation of aliphatic amines, aromatic amines, and amino alcohols to carbamates, ureas, and 2-oxazolidinones under different conditions. The catalytic turnover frequencies (TOF, moles of amines converted per mole of catalyst per hour) were 12417, 17368, and 4114 h⁻¹ for the production of methyl N-phenyl carbamate, N,N′-diphenyl urea, and 2-benzoxazolinone, respectively.     

Synthesis of carbamates and ureas using Zr(IV)-catalyzed exchange processes

[reaction: see text] Zirconium(IV)-catalyzed exchange processes have been developed to prepare both carbamates and ureas from dialkyl carbonates and carbamates employing 2-hydroxypyridine (HYP) and 4-methyl-2-hydroxyquinoline (MeHYQ) as catalytic additives, respectively. A microwave acceleration effect was observed in Zr(IV)-catalyzed carbamate-urea exchange.     

α-Haloalkyl Haloformates and Related Compounds 3.1 A Facile Synthesis of Symmetrical and Unsymmetrical Ureas via Chloromethyl Carbamates

Chloromethyl carbamates were prepared by the reaction of chloromethyl chloroformates with amines and found to produce mono-, symmetrically or unsymmetrically di-and trisubstituted ureas including their N-hydroxy and N-alkoxy derivatives in moderate to good yield.     

The mass spectra of some selenoureas and selenothiocarbamic esters

The mass spectra of five selenoureas and two selenothiocarbamic esters are reported and discussed. Fragmentation modes are compared with those reported for the ureas, thioureas, carbamates and thiocarbamates.