- Lanthanum(III) Trifluoromethanesulfonate Catalyzed Direct Synthesis of Ureas from N-Benzyloxycarbonyl-, N -Allyloxycarbonyl-, and N -2,2,2-Trichloroethoxycarbonyl-Protected Amines
-
A novel lanthanum triflate mediated conversion of N -benzyloxycarbonyl-, N -allyloxycarbonyl-, and N -trichloroethoxycarbonyl-protected amines into nonsymmetric ureas was discovered. In this study, lanthanum triflate was found to be an effective catalyst for preparing various nonsymmetric ureas from protected amines. A variety of protected aromatic and aliphatic carbamates reacted readily with various amines in the presence of lanthanum triflate to generate the desired ureas in high yields. This result demonstrated that this novel lanthanum triflate catalyzed preparation of ureas from Cbz, Alloc, and Troc carbamates can be employed for the formation of various urea structures.
- Bui, Tien Tan,Kim, Hee-Kwon
-
supporting information
p. 997 - 1002
(2020/06/17)
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- Palladium-Catalyzed Synthesis of Symmetrical and Unsymmetrical Ureas Using Chromium Hexacarbonyl as a Convenient and Safe Alternative Carbonyl Source
-
Pd-catalyzed synthesis of urea derivatives from aryl iodides and different aliphatic and aromatic amines using sodium azide and chromium hexacarbonyl is described. In this process, carbonylation of aryl iodides, Curtius rearrangement of aroyl azides, and nucleophilic addition of amines sequentially occur to afford the products in good to excellent yields. This protocol is operationally simple and displays a broad substrates scope.
- Mozaffari, Mozhdeh,Nowrouzi, Najmeh
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supporting information
p. 7541 - 7544
(2019/12/12)
-
- A Fe3O4?SiO2/Schiff Base/Pd Complex as an Efficient Heterogeneous and Recyclable Nanocatalyst for One-Pot Domino Synthesis of Carbamates and Unsymmetrical Ureas
-
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.
- Inaloo, Iman Dindarloo,Majnooni, Sahar
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p. 6359 - 6368
(2019/11/05)
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- CaI2-Catalyzed direct transformation of: N -Alloc-, N -Troc-, and N -Cbz-protected amines to asymmetrical ureas
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A novel and facile CaI2-catalyzed direct synthesis of asymmetrical ureas from N-Alloc-, N-Troc-, and N-Cbz-protected amines is developed. In this study, the efficient reaction of Alloc-, Troc-, and Cbz-carbamates with amines in the presence of catalytic CaI2 successfully generated various asymmetrical ureas. This catalytic synthetic procedure provided the desired ureas via reactions of these protected aromatic and aliphatic amines with various amines in high yields without side products. This suggests that novel direct synthesis of ureas from Alloc-, Troc-, and Cbz-carbamates can be a promising approach for the synthesis of useful ureas.
- Tran, Van Hieu,Kim, Hee-Kwon
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p. 14093 - 14101
(2019/09/18)
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- An efficient one-pot synthesis of N,N′-disubstituted phenylureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid
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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.
- Bao, Jennifer,Kuik, Dale,Tranmer, Geoffrey K.
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supporting information
p. 5546 - 5553
(2018/06/12)
-
- Metal-Free Synthesis of Unsymmetrical Ureas and Carbamates from CO2 and Amines via Isocyanate Intermediates
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A mild and metal-free synthesis of aryl isocyanates from arylamines under an atmosphere of CO2 was developed. The carbamic acid intermediate, derived from the arylamine starting material and CO2 in the presence of DBU, is dehydrated by activated sulfonium reagents to generate the corresponding isocyanate. The latter can be detected by in situ IR and trapped by various amines and alcohols to make unsymmetrical ureas and carbamates, respectively. Dicarbamates can also be prepared in good yields via the mild dehydration of the corresponding dicarbamic acids.
- Ren, Yiming,Rousseaux, Sophie A. L.
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p. 913 - 920
(2018/01/28)
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- Chloromethylated polystyrene immobilized ruthenium complex of 2-(2-pyridyl)benzimidazole catalyst for the synthesis of bioactive disubstituted ureas by carbonylation reaction
-
Polymer supported transition metal complex catalysts have numerous applications as heterogeneous catalysts due to their ease of synthesis and commercial availability. Ru-Py-Merf was synthesized by anchoring 2-(2-pyridyl)benzimidazole to the polymer matrix, followed by loading of ruthenium salt. This Ru-Py-Merf material was thoroughly characterized by FTIR spectroscopy, UV-vis absorption spectroscopy, FE-SEM analysis, EDAX analysis, CHN analysis, AAS spectroscopy and TGA. Ru-Py-Merf showed excellent catalytic activity in the synthesis of symmetric and asymmetric disubstituted ureas by reductive carbonylation of nitrobenzenes and anilines. The as-synthesized Ru-Py-Merf catalyst is entirely heterogeneous in nature, thermally stable and can be easily reused up to six times.
- Dey, Tusar Kanto,Ghosh, Kajari,Basu, Priyanka,Molla, Rostam Ali,Islam, Sk. Manirul
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p. 9168 - 9176
(2018/06/08)
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- Facile direct synthesis of unsymmetrical ureas from N-Alloc-, N-Cbz-, and N-Boc-protected amines using DABAL-Me3
-
A practical synthetic method for the direct synthesis of unsymmetrically substituted ureas from N-Alloc-, N-Cbz-, and N-Boc-protected amines is described. In this study, efficient direct conversion of the Alloc-, Cbz-, and Boc-carbamate compounds to ureas was achieved in the presence of DABAL-Me3, an air stable and easily handled reagent. Using this reaction method, both protected aromatic and aliphatic amines were successfully transformed into various trisubstituted and tetrasubstituted ureas with high yields without side product. Our findings offer promising guidelines for direct preparation of useful ureas from N-Alloc-, N-Cbz-, and N-Boc-carbamates.
- Kang, Soosung,Kim, Hee-Kwon
-
p. 4036 - 4046
(2018/06/13)
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- Pd/C Catalyzed Carbonylation of Azides in the Presence of Amines
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A facile and efficient Pd/C-catalyzed carbonylation of both aliphatic and aromatic azides in the presence of amines is reported. Serving as the widely existed fragments in an array of biological pharmaceuticals, functionalized unsymmetrical ureas were str
- Zhao, Jin,Li, Zongyang,Yan, Shuaihu,Xu, Shiyang,Wang, Ming-An,Fu, Bin,Zhang, Zhenhua
-
supporting information
p. 1736 - 1739
(2016/05/19)
-
- A high-yielding, expeditious, and multicomponent synthesis of urea and carbamate derivatives by using triphenylphosphine/trichloroisocyanuric acid system
-
An efficient method for the synthesis of urea and carbamate derivatives from amines and alcohols is described by using triphenylphosphine (PPh3)/trichloroisocyanuric acid system. The protocol allows for the preparation of symmetrical, unsymmetrical di, tri-, and tetra-substituted ureas and carbamates and is tolerant of a wide range of functional groups. To optimize the reaction conditions, experimental variables including temperature, the concentration of amine and alcohol, solvent, and reaction time were studied. Satisfactory yields were obtained at the optimized conditions. The present methodology is experimentally simple, mild, and represents a valuable alternative to the existing methods.
- Ghodsinia, Sara S.E.,Akhlaghinia, Batool
-
p. 104 - 110
(2016/01/25)
-
- Preparation method for alkyl/benzyl/aryl urea compounds through heterogeneous-phase catalysis
-
The invention discloses a preparation method for formula (I) compounds, and the compounds are obtained by reacting a formula (II) compound with a formula (III) compound in a solvent in carbon monoxide atmosphere under catalysis of a heterogeneous-phase pa
- -
-
Paragraph 0063-0071; 0072; 0073; 0074; 0076; 0078; 0082
(2016/10/09)
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- Lossen rearrangements under heck reaction conditions
-
The classical Lossen rearrangement converts activated hydroxamic acids to isocyanates that form numerous products upon their reaction with nucleophiles. We report a simple and highly efficient method of using Heck reaction conditions to initiate Lossen rearrangements of hydroxamic acids. In addition, Lossen rearrangements occur in the presence of palladium(II) acetate or triethylamine, components of the Heck reaction, alone. A potential mechanism is provided to explain this reactivity and these results show that Heck reactions and Lossen rearrangements occur under the same conditions and may provide new methods for facile initiation of Lossen rearrangements.
- AbdelHafez, El-Shimaa M.N.,Aly, Omar M.,Abuo-Rahma, Gamal El-Din A.A.,King, S. Bruce
-
supporting information
p. 3456 - 3464
(2015/02/05)
-
- Practical synthesis of N -substituted cyanamides via tiemann rearrangement of amidoximes
-
A facile and general synthesis of various N-substituted cyanamides was accomplished by the Tiemann rearrangement of amidoximes with benzenesulfonyl chlorides (TsCl or o-NsCl) and DIPEA.
- Lin, Chia-Chi,Hsieh, Tsung-Han,Liao, Pen-Yuan,Liao, Zhen-Yuan,Chang, Chih-Wei,Shih, Yu-Chiao,Yeh, Wen-Hsiung,Chien, Tun-Cheng
-
supporting information
p. 892 - 895
(2014/03/21)
-
- Polystyrene anchored ruthenium(II) complex catalyzed carbonylation of nitrobenzene and amines for the synthesis of disubstituted ureas
-
The catalytically active complex [Ru(PS-imd)(CO)2Cl2] (PS-imd = polystyrene anchored imidazole) was synthesized and characterized using various spectroscopic techniques. The complex is well characterized and highly stable. The catalytic activity of the resulting species was investigated towards the synthesis of diphenyl urea and other disubstituted ureas. The experiments were carried out under high CO pressure, high temperature condition in mild coordinating media. The catalyst was found to produce excellent yields with high product selectivity. Variable yields are obtained depending on the substituent on nitrobenzene and aniline. The effects of co-solvent and co-catalyst were also studied. The catalyst was very stable and could be reused for more than five times without any noticeable loss of its catalytic activity.
- Islam, Sk Manirul,Ghosh, Kajari,Roy, Anupam Singha,Molla, Rostam Ali,Salam, Noor,Chatterjee, Tanmay,Iqubal, Md. Asif
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p. 152 - 160
(2015/01/09)
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- Polystyrene anchored ruthenium(II) complex catalyzed carbonylation of nitrobenzene and amines for the synthesis of disubstituted ureas
-
The catalytically active complex [Ru(PS-imd)(CO)2Cl2] (PS-imd = polystyrene anchored imidazole) was synthesized and characterized using various spectroscopic techniques. The complex is well characterized and highly stable. The catalytic activity of the resulting species was investigated towards the synthesis of diphenyl urea and other disubstituted ureas. The experiments were carried out under high CO pressure, high temperature condition in mild coordinating media. The catalyst was found to produce excellent yields with high product selectivity. Variable yields are obtained depending on the substituent on nitrobenzene and aniline. The effects of co-solvent and co-catalyst were also studied. The catalyst was very stable and could be reused for more than five times without any noticeable loss of its catalytic activity.
- Islam, Sk Manirul,Ghosh, Kajari,Roy, Anupam Singha,Molla, Rostam Ali,Salam, Noor,Chatterjee, Tanmay,Iqubal, Md. Asif
-
p. 152 - 160
(2015/01/30)
-
- Spectroscopic kinetic study of the interaction of urethanes with amines
-
The exchange reactions of phenyl-N-phenylurethane with amines varying in structure and nature have been investigated in o-dichlorobenzene. In the absence of a catalyst and proton-donating compound, the unimolecular decomposition of phenyl-N-phenylurethane into isocyanate and alcohol takes place at a noticeable rate starting at 250°C. The exchange reactions at 60-80°C proceed as a direct exchange between the urethane and the proton donor and are second-order up to high conversions, practically until the disappearance of the entire urethane. The activation energies and apparent rate constants of the exchange reactions of phenyl-N-phenylurethane with various amines have been determined. The results have been explained in terms of the dependence of kinetic parameters of the reaction on the amine nature, structure, and nucleophilicity, on the steric accessibility of the amino group, and on the molecular organization of the solution. Pleiades Publishing, Ltd., 2013.
- Dzalmukhanova,Lodygina,Komratova,Badamshina
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p. 656 - 661
(2014/01/23)
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- The use of aqueous potassium dichloroiodate for the synthesis of ureas
-
We report a straightforward and efficient reaction protocol for the syntheses of substituted ureas via treatment of thioureas with aqueous potassium dichloroiodate (KICl2). By tuning the reaction condition, thioureas bearing activated N-aryl substituents may undergo either selective oxidation or sequential oxidation and iodination, forming iodoaryl ureas in the latter case.
- Viana, Gil Mendes,De Sequeira Aguiar, Lúcia Cruz,De Araújo Ferr?o, Jonas,Simas, Alessandro Bolis Costa,Vasconcelos, Marcela Guariento
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p. 936 - 940
(2013/03/13)
-
- Flash vacuum pyrolysis of 1,2,5-oxadiazole 2-oxides and 1,2,3-triazole 1-oxides
-
The flash vacuum pyrolysis (FVP, 450-600 °C/10-3 mmHg) of 3,4-diaryl- and 3,4-dialkyl-1,2,5-oxadiazole 2-oxides (furoxans) has been investigated. In all cases the 1,2,5-oxadiazole ring cleaved cleanly at O(1)-N(2) and C(3)-C(4) to afford two nitrile oxide fragments, which were trapped in high yield (75-97%) as their isoxazoline cycloadducts by reaction with alk-1-enes. At higher temperatures (700-800 °C) isocyanates were formed as by-products. The dimerisation of acetonitrile oxide to dimethylfuroxan was followed by 1H NMR spectroscopy, and the rate constant for the 2 nd order reaction determined. The furoxans were converted into isocyanates in good yield (61-95%) by FVP, followed by sulfur dioxide-mediated isomerisation of the resulting nitrile oxides. 2,4,5-Trisubstituted-1,2,3- triazole 1-oxides showed greater thermal stability, but at 700-800 °C decomposition of the 4,5-dimethyl compound 25b lead to 1,2-di(5-methyl-2-phenyl- 1,2,3-triazol-2-yl)ethane as the major product; attempts to trap acetonitrile oxide were unsuccessful. ARKAT USA, Inc.
- Mitchell, William R.,Paton, R. Michael
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experimental part
p. 34 - 54
(2011/02/21)
-
- Trapping! of isocyanates with benzotriazole in situ - Preparation of carbamoyl benzotriazoles as an isocyanate alternative via curtius rearrangement
-
N-Aryl and N-alkenyl carbamoyl benzotriazoles were prepared in good to excellent yields from acyl azides and benzotriazole via Curtius rearrangement, while N-alkylcarbamoyl benzotriazoles were formed from N-alkanoyl benzotriazoles and sodium azide in one
- Zhong, Zhiyun,Wang, Xiaoxia,Kong, Lichun,Zhu, Xiangming
-
experimental part
p. 2461 - 2464
(2010/01/07)
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- A general method for the synthesis of unsymmetrically substituted ureas via palladium-catalyzed amidation
-
A general and practical method for the preparation of unsymmetrically substituted ureas has been developed utilizing palladium-catalyzed amidation. Both aryl bromides and chlorides, as well as heteroaryl chlorides, have been coupled to aryl, benzyl, and a
- Kotecki, Brian J.,Fernando, Dilinie P.,Haight, Anthony R.,Lukin, Kirill A.
-
supporting information; experimental part
p. 947 - 950
(2009/08/07)
-
- Phenyl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylate as carbonyl source: Facile and selective synthesis of carbamates and ureas under mild conditions
-
The selective syntheses of carbamates, symmetric -ureas, and unsymmetrical ureas have been accomplished by the -reaction of amines with phenyl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylate as a carbonyl source under mild conditions. It is noteworthy that this process is mild, economic, and convenient.
- Lee, Hyung-Geun,Kim, Min-Jung,Park, Song-Eun,Kim, Jeum-Jong,Kim, Bo Ram,Lee, Sang-Gyeong,Yoon, Yong-Jin
-
experimental part
p. 2809 - 2814
(2010/03/03)
-
- Organometallic chemistry and catalysis on gold metal surfaces
-
As in transition metal complexes, C{triple bond, long}N-R ligands adsorbed on powdered gold undergo attack by amines to give putative diaminocarbene groups on the gold surface. This reaction forms the basis for the discovery of a gold metal-catalyzed reaction of C{triple bond, long}N-R, primary amines (R′NH2) and O2 to give carbodiimides (R′-N{double bond, long}C{double bond, long}N-R). An analogous reaction of C{triple bond, long}O, RNH2, and O2 gives isocyanates (R-N{double bond, long}C{double bond, long}O), which react with additional amine to give urea (RNH)2C{double bond, long}O products. The gold-catalyzed reaction of C{triple bond, long}N-R with secondary amines (HNR′2) and O2 gives mixed ureas RNH(C{double bond, long}O)NR′2. In another type of gold-catalyzed reaction, secondary amines HN(CH2R)2 react with O2 to undergo dehydrogenation to the imine product, RCH{double bond, long}N(CH2R). Of special interest is the high catalytic activity of gold powder, which is otherwise well-known for its poor catalytic properties.
- Angelici, Robert J.
-
p. 847 - 856
(2008/03/30)
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- Non-nanogold catalysis of carbon monoxide oxidative amination
-
Bulk metallic gold particles (~1000 nm) catalyze the reaction of CO, O2, and primary amines (R-NH2) to give ureas (RNH)2C=O. Isocyanates (R-N=C=O) are identified as intermediates in the reactions and are shown to react with primary and secondary amines to give ureas under the conditions of the gold-catalyzed reactions. Although many recent studies indicate that nanosized particles of gold are required for the catalytic oxidation of CO, the results presented in this paper show that bulk gold is capable of catalyzing the oxidative amination of CO under mild conditions (45 °C, 1 atm CO and O2). Copyright
- Zhu, Bolin,Angelici, Robert J.
-
p. 14460 - 14461
(2008/02/02)
-
- Silica gel confined ionic liquid + metal complexes for oxygen-free carbonylation of amines and nitrobenzene to ureas
-
A new kind of silica gel confined ionic liquid containing a metal complex as heterogenized catalysts was prepared for the carbonylation of amines and nitrobenzene without molecular oxygen to afford the corresponding ureas with greatly enhanced catalytic activity (TOF exceeded 11000 mol·mol -1· h-1), with a much lower amount of ionic liquids being needed, with easy catalyst separation and possible reusability, and avoidance of the using of explosive CO + O2 gas mixtures. Such an enhancement in catalytic activity may be derived from the effect of a high concentration of ionic liquid containing a metal complex due to the confinement into the nanopores or cavities of the silica gel matrix.
- Shi, Feng,Zhang, Qinghua,Gu, Yanlong,Deng, Youquan
-
p. 225 - 230
(2007/10/03)
-
- Efficient Synthesis of Polysubstituted Acylguanidines and Guanylureas
-
(Benzotriazol-1-yl)carboximidamides were applied for the preparation of polysubstituted acylguanidines and guanylureas. The reaction sequence utilized mild conditions and gave high yields for final compounds and intermediates. The protocol developed allows for variation of the substituents at all positions of the products.
- Katritzky, Alan R.,Rogovoy, Boris V.,Cai, Xiaohong,Kirichenko, Nataliya,Kovalenko, Katherine V.
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p. 309 - 313
(2007/10/03)
-
- 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.
- Lee, Sang-Hyuep,Matsushita, Hana,Clapham, Bruce,Janda, Kim D.
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p. 3439 - 3443
(2007/10/03)
-
- NEW FLUOROUS TAGGING AND SCAVENGING REACTANTS AND METHODS OF SYNTHESIS AND USE THEREOF
-
The present invention includes methods and compositions for increasing the fluorous nature of an organic compound by reacting it with at least one fluorous compound to produce a fluorous tagged organic compound. The increased fluorous nature of the fluorous tagged organic compound can then be utilized to separate the fluorous organic compound from untagged reagents, reactants, catalysts and/or products derived therefrom. The resultant fluorous tagged organic compound can be subjected to subsequent chemical transformations, wherein the fluorous nature of the tagged compound is utilized to increase the ease of separation of the fluorous tagged organic compound from untagged reagents, reactants, catalysts and/or products derived therefrom, after each chemical transformation. The chemical transformations result in a second fluorous tagged organic compound wherein the fluorous nature of the second fluorous tagged organic compound can then be reduced by removing the fluorous group therefrom, thereby producing a second organic compound that may be employed as a pharmaceutical compound or intermediate, or a combinatorial library component.
- -
-
Page 58, 59, 61, 62
(2008/06/13)
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- A novel ZrO2-SO42- supported palladium catalyst for syntheses of disubstituted ureas from amines by oxidative carbonylation
-
The syntheses of disubstituted ureas by carbonylation of a series of amines in the presence of a sulfate modified zirconia supported palladium catalyst was investigated at an initial total pressure of 4.0 MPa and 135°C. High conversions and yields were achieved for the synthesis of symmetric dialkylureas. This supported catalyst could also be easily separated and recovered after reaction.
- Shi, Feng,Deng, Youquan,SiMa, Tianlong,Yang, Hongzhou
-
p. 2161 - 2163
(2007/10/03)
-
- Synthesis of aromatic urea herbicides by the selenium-assisted carbonylation using carbon monoxide with sulfur
-
Commercially useful aromatic urea herbicides were synthesized in good yields from lithium amides of aromatic amines with thiocarbamates, which were prepared by the selenium-assisted carbonylation of secondary amines with carbon monoxide and sulfur under mild conditions.
- Mizuno, Takumi,Kino, Takanobu,Takatoshi, Ito,Miyata, Toshiyuki
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p. 1675 - 1688
(2007/10/03)
-
- An efficient two-step synthesis of mono-, di- and triureas from resin- bound amides
-
An efficient method for the solid-phase synthesis of mono-, di- and triureas from resin-bound mono-amines, diamines and triamines is described. The exhaustive reduction of solid support-bound amides generated the requisite amines, which, following treatme
- Nefzi, Adel,Ong, Nhi A.,Houghten, Richard A.
-
p. 5441 - 5446
(2007/10/03)
-
- 2-chloro-1,3-dimethylimidazolinium chloride. 3. Utility for chlorination, oxidation, reduction, and rearrangement reactions
-
2-Chloro-1,3-dimethylimidazolinium chloride (1), which can act as a powerful dehydrating equivalent to DCC (2), is also applicable to chlorination, oxidation, reduction, and rearrangement under nearly neutral conditions. The utility of 1 for these reactions is described.
- Isobe, Toshio,Ishikawa, Tsutomu
-
p. 5832 - 5835
(2007/10/03)
-
- Conversion of carbonimidodithioates into unsymmetrical Di- and Tri- substituted ureas including urea dipeptides
-
Selective hydrolysis of carbonimidodithioates (3) leads to the thiocarbamates (4), which can be easily transformed to the unsymmetrical ureas (5) by treatmeat with the appropriate amines. This constitutes a synthesis of ureas without the use of phosgene o
- Anbazhagan, Mariappan,Deshmukh, Abdul Rakeeb A. S.,Rajappa, Srinivasachari
-
p. 3609 - 3612
(2007/10/03)
-
- Mechanism of a chain-extending reaction in the synthesis of segmented poly(urethane-urea) using blocked ethylenediamine
-
An attempt was made to clarify the mechanism of a chain-extending reaction of NCO-terminated prepolymers in the synthesis of segmented poly(urethane-urea) using blocked ethylenediamine (EDA) with acetone (ACE). For this purpose, an ACE/EDA mixture was allowed to react with phenyl isocyanate (PhNCO) as a model of the prepolymer. The reaction of PhNCO with the ACE/EDA mixture, which was proved to contain ketimine and imidazolidine compounds by NMR measurements, gave 1,1′-ethylenebis[3-phenylurea] (M-Ur-1) as the main product; at the same time 1,3-diphenylurea (1, 3-DPU) was assumed to be formed as a side-reaction product between PhNCO and H2O, inevitably existing in the mixture as the result of condensation. From a considerable increase in the yield of M-Ur-1 upon the addition of an excess amount of H2O to the reaction system, H2O was elucidated to participate in the acceleration of the main reaction, giving M-Ur-1 as well as in the side reaction, yielding 1,3-DPU. The excess H2O added to the system might preferentially facilitate the former reaction, rather than the latter.
- Nakano, Yasuhiro,Yamazaki, Emiko,Hanahata, Hiroyuki,Okajima, Kunihiko,Kitahama, Yoshiharu
-
p. 1185 - 1192
(2007/10/03)
-
- Ureas from Lossen Rearrangements of Hydroxamic Acids Induced by p-Toluenesulfonyl Chloride or 2-Chloro-1-methylpyridinium Iodide in the Presence of Amines: A Correction
-
Hydroxamic acids reacted with amines in the presence of either p-toluenesulfonyl chloride or 2-chloro-1-methylpyridinium iodide to produce compounds whose structures are different from those which had been reported.These reactive halides converted hydroxamic acids first to Lossen-type of intermediates, which rearranged spontaneously in basic media to isocyanates which reacted further.In the absence of primary or secondary amines in the medium, the intermediate isocyanates acylated the starting hydroxamic acids to form O-carbamyl hydroxamic acids.However, when the reaction mixtures contained either primary or secondary amines, addition to the intermediate isocyanates provided ureas.Furthermore, it was found that amines caused the O-carbamyl hydroxamic acids to undergo facile Lossen degradations to furnish ureas.
- Pihuleac, Justin,Bauer, Ludwig
-
-
- Kinetics and Mechanism of Aminolysis of Carbamates
-
The kinetics of the n-butylaminolysis of three series of mono- and disubstituted phenyl N-phenylcarbamates 1-3 have been studied spectrophotometrically under pseudo-first-order conditions in dioxane.The relation kobsd = k2 + k32 was found applicable for all esters.The rate constants k2 and k3 were correlated by the Hammett equation, and the corresponding activation parameters were determined.The reaction was found to be much more sensitive to a substituent on the leaving group (OAr) than to a substitutent on the amine portion (NHAr) of the esters.Results from crossover experiments revealed the absence of isocyanate intermediate.The mechanism of the aminolysis of carbamates is discussed in terms of these facts.
- Shawali, Ahmad S.,Harhash, Abdelhamid,Sidky, Mohmoud M.,Hassaneen, Hamdi M.,Elkaabi, Sherifa S.
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p. 3498 - 3501
(2007/10/02)
-
- PLATINUM COMPLEX CATALYZED SYNTHESIS OF UREA DERIVATIVES FROM NITROARENES AND AMINES UNDER CARBON MONOXIDE
-
N,N'-Diarylureas were obtained in good yields from nitroarenes and aminoarenes at 140 deg C under carbon monoxide (initial 60 kg cm-2) in the presence of a catalytic amount of dichlorobis(triphenylphosphine)platinum(II), the yields of N,N'-diphenylurea, N,N'-bis(4-methylphenyl)urea, and N,N'-bis(4-chlorophenyl)urea were 65, 67 and 61percent, respectively.Benzimidazole derivatives were obtained by the intramolecular cyclization reaction.An attempted synthesis of unsymmetric ureas resulted in the formation of a mixture of symmetric and unsymmetric products.
- Tsuji, Yasushi,Takeuchi, Ryo,Watanabe, Yoshihisa
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p. 249 - 256
(2007/10/02)
-