- Dehydrogenative Synthesis of Carbamates from Formamides and Alcohols Using a Pincer-Supported Iron Catalyst
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We report that the pincer-ligated iron complex (iPrPNP)Fe(H)(CO) [1, iPrPNP- = N(CH2CH2PiPr2)2-] is an active catalyst for the dehydrogenative synthesis of N-alkyl- and N-aryl-substituted carbamates from formamides and alcohols. The reaction is compatible with industrially relevant N-alkyl formamides, as well as N-aryl formamides, and 1°, 2°, and benzylic alcohols. Mechanistic studies indicate that the first step in the reaction is the dehydrogenation of the formamide to a transient isocyanate by 1. The isocyanate then reacts with the alcohol to generate the carbamate. However, in a competing reaction, the isocyanate undergoes a reversible cycloaddition with 1 to generate an off-cycle species, which is the resting state in catalysis. Stoichiometric experiments indicate that high temperatures are required in catalysis to facilitate the release of the isocyanate from the cycloaddition product. We also identified several other off-cycle processes that occur in catalysis, such as the 1,2-addition of the formamide or alcohol substrate across the Fe-N bond of 1. It has already been demonstrated that the transient isocyanate generated from dehydrogenation of the formamide can be trapped with amines to form ureas and, in principle, the isocyanate could also be trapped with thiols to form thiocarbamates. Competition experiments indicate that trapping of the transient isocyanate with amines to produce ureas is faster than trapping with an alcohol to produce carbamates and thus ureas can be formed selectively in the presence of alcohols. In contrast, thiols bind irreversibly to the iron catalyst through 1,2 addition across the Fe-N bond of 1, and it is not possible to produce thiocarbamates. Overall, our mechanistic studies provide general guidelines for facilitating dehydrogenative coupling reactions using 1 and related catalysts.
- Bernskoetter, Wesley H.,Hazari, Nilay,Mercado, Brandon Q.,Townsend, Tanya M.
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p. 10614 - 10624
(2021/09/02)
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- Design, synthesis and SAR of antitubercular benzylpiperazine ureas
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Abstract: N-furfuryl piperazine ureas disclosed by scientists at GSK Tres Cantos were chosen as antimycobacterial hits from a phenotypic whole-cell screen. Bioisosteric replacement of the furan ring in the GSK Tres Cantos molecules with a phenyl ring led to molecule (I) with an MIC of 1?μM against Mtb H37Rv, low cellular toxicity (HepG2 IC50 ~ 80?μM), good DMPK properties and specificity for Mtb. With the aim of delineating the SAR associated with (I), fifty-five analogs were synthesized and screened against Mtb. The SAR suggests that the piperazine ring, benzyl urea and piperonyl moieties are essential signatures of this series. Active compounds in this series are metabolically stable, have low cellular toxicity and are valuable leads for optimization. Molecular docking suggests these molecules occupy the Q0 site of QcrB like Q203. Graphic Abstract: Bioisosteric replacement of N-furfuryl piperazine-1-carboxamides yielded molecule (I) a novel lead with satisfactory PD, metabolism, and toxicity profiles.[Figure not available: see fulltext.]
- Satish, Sohal,Chitral, Rohan,Kori, Amitkumar,Sharma, Basantkumar,Puttur, Jayashree,Khan, Afreen A.,Desle, Deepali,Raikuvar, Kavita,Korkegian, Aaron,Martis, Elvis A. F.,Iyer, Krishna R.,Coutinho, Evans C.,Parish, Tanya,Nandan, Santosh
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- Metal-free Photocatalytic Intermolecular anti-Markovnikov Hydroamination of Unactivated Alkenes
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The development of photocatalytic intermolecular hydroamination reaction between N-aminated dihydropyridines and unactivated alkenes is reported. Metal-free co-catalysts, rhodamine 6G and thiophenol, in presence of visible light are used to initiate the process. The transformation shows a broad substrate scope, both alkenes and amidyl radical can act as coupling partners. The radical strategy provides excellent anti-Markovnikov selectivity and regioselectivity in diene substrates.
- Li, Juncheng,Wang, Ting,Zhao, Gaoyuan
-
supporting information
p. 2650 - 2654
(2021/06/25)
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- Coupling biocatalysis with high-energy flow reactions for the synthesis of carbamates and β-amino acid derivatives
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A continuous flow process is presented that couples a Curtius rearrangement step with a biocatalytic impurity tagging strategy to produce a series of valuable Cbz-carbamate products. Immobilized CALB was exploited as a robust hydrolase to transform residual benzyl alcohol into easily separable benzyl butyrate. The resulting telescoped flow process was effectively applied across a series of acid substrates rendering the desired carbamate structures in high yield and purity. The derivatization of these products via complementary flow-based Michael addition reactions furthermore demonstrated the creation of β-amino acid species. This strategy thus highlights the applicability of this work towards the creation of important chemical building blocks for the pharmaceutical and speciality chemical industries.
- Leslie, Alexander,Moody, Thomas S.,Smyth, Megan,Wharry, Scott,Baumann, Marcus
-
supporting information
p. 379 - 384
(2021/03/15)
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- Photo-on-Demand Synthesis of Chloroformates with a Chloroform Solution Containing an Alcohol and Its One-Pot Conversion to Carbonates and Carbamates
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Chloroformates are key reagents for synthesizing carbonates and carbamates. The present study reports a novel photo-on-demand in situ synthesis of chloroformates with a CHCl3 solution containing a primary alkyl alcohol. It further allowed the one-pot synthesis of carbonates and carbamates through subsequent addition of alcohols or amines, respectively.
- Liang, Fengying,Suzuki, Yuto,Tsuda, Akihiko,Yanai, Masaki
-
supporting information
(2020/04/21)
-
- Carbonylative C-C bond activation of aminocyclopropanes using a temporary directing group strategy
-
Temporary directing groups (TDGs) underpin a range of C-C bond activation methodologies; however, the use of TDGs for the regiocontrolled activation of cyclopropane C-C bonds is underdeveloped. In this report, we show how an unusual ring contraction process can be harnessed for TDG-based carbonylative C-C bond activations of cyclopropanes. The method involves the transient installation of an isocyanate-derived TDG, rather than relying on carbonyl condensation events as used in previous TDG-enabled C-C bond activations.
- Wang, Gang-Wei,Sokolova, Olga O.,Young, Tom. A.,Christodoulou, Ektor M. S.,Butts, Craig P.,Bower, John F.
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supporting information
p. 19006 - 19011
(2020/11/13)
-
- Synthesis of Sterically Congested Carbamates of Carbohydrates through Organic Base Catalysis
-
4,6-O-Benzylidene acetal protected α-methoxy D-glucose and D-glucosamine are useful building blocks for the syntheses of carbohydrate derivatives and functional molecular assemblies. In this research, we have developed a general method for the preparation of C-3 carbamate derivatives of densely functionalized glucose and glucosamine with isocyanates using organic bases as catalysts. Without a suitable catalyst, the C-3 hydroxy group of the glucosamine derivative could not be converted into the corresponding carbamates when treated with isocyanates. Several organic bases were screened as the catalysts for the reactions, and we discovered that 5.0 molpercent of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was an effective catalyst for the carbamoylation reaction. A library of both alkyl and aryl carbamate derivatives of the two sterically congested carbohydrates have been effectively synthesized using the current method.
- Chen, Anji,Wang, Dan,Samankumara, Lalith P.,Wang, Guijun
-
supporting information
p. 2897 - 2908
(2019/07/22)
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- One stone two birds: Cobalt-catalyzed in situ generation of isocyanates and benzyl alcohols for the synthesis of N-aryl carbamates
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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.
- Li, Sida,Khan, Ruhima,Zhang, Xia,Yang, Yong,Wang, Zheting,Zhan, Yong,Dai, Yuze,Liu, Yue-E,Fan, Baomin
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p. 5891 - 5896
(2019/06/24)
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- Anti-Markovnikov Radical Hydro- and Deuteroamidation of Unactivated Alkenes
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Radical anti-Markovnikov hydro- and deuteroamidation of unactivated alkenes was achieved by merging photoredox and thiol catalysis. Reactions proceed by addition of the electrophilic CbzHN-radical (Cbz=carbobenzyloxy), readily generated by single-electron-transfer (SET) oxidation of an α-Cbz-amino-oxy acid to an alkene. The adduct radical is reduced by thiophenol added as an organic polarity reversal cocatalyst, which mediates the H transfer from H2O to the alkyl radical intermediate. Accordingly, deuteroamidation of alkenes was realized with excellent D incorporation by using D2O as the stoichiometric formal radical-reducing reagent. The reaction features low redox catalyst loading, excellent anti-Markovnikov selectivity, and the use of a large alkene excess is not required. Diverse Cbz-protected primary amines, including β-deuterated amines, can be obtained by applying this method.
- Jiang, Heng,Studer, Armido
-
supporting information
p. 7105 - 7109
(2019/05/15)
-
- A Simple, efficient, Catalyst-Free and Solvent-Less Microwave-Assisted process for N-Cbz Protection of Several amines
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A simple, green and chemo-selective method for the N-benzyloxycarbonylation of amines, β-amino alcohols, α-amino esters and sulfonamides has been developed under microwave irradiation. Good to excellent yields of the N-benzyloxy-carbamates compounds were obtained in short times without any side products.
- Aouf, Zineb,Mansouri, Rachida,Lakrout, Salah,Berredjem, Malika,Aouf, Nour-Eddine
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p. 151 - 156
(2017/08/02)
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- Oximes as reusable templates for the synthesis of ureas and carbamates by an: In situ generation of carbamoyl oximes
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Oximes have been identified as reusable templates for the synthesis of ureas and carbamates by an in situ generation of carbamoyl oximes under metal-free conditions. The recovered oxime has been utilised for three trials in the synthesis of urea derivatives without any loss in the yield and efficiency. In addition, this template approach could override the usage of hazardous and less stable isocyanates as substrates.
- Senadi, Gopal Chandru,Mutra, Mohana Reddy,Lu, Ting-Yi,Wang, Jeh-Jeng
-
supporting information
p. 4272 - 4277
(2017/09/28)
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- One-pot synthesis of carbamates and thiocarbamates from Boc-protected amines
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A highly efficient one-pot procedure for the synthesis of carbamates and thiocarbamates has been described. In the presence of 2-chloropyridine and trifluoromethanesulfonyl anhydride, the isocyanate intermediates were generated in situ for further reactions with alcohols and thiols to afford the desired carbamates and thiocarbamates in high yields.
- Kim, Hee-Kwon,Lee, Anna
-
supporting information
p. 4890 - 4892
(2016/10/21)
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- BMIm HCO3: an ionic liquid with carboxylating properties. Synthesis of carbamate esters from amines
-
1-Butyl-3-methylimidazolium hydrogen carbonate (BMIm HCO3) was used as an ionic liquid with carboxylating properties able to convert, in the presence of an alkyl halide, amines into the corresponding carbamate esters. Moderate to good yields of
- Di Nicola,Arcadi,Rossi
-
supporting information
p. 9895 - 9898
(2016/12/07)
-
- A base-mediated self-propagative Lossen rearrangement of hydroxamic acids for the efficient and facile synthesis of aromatic and aliphatic primary amines
-
A variety of aromatic and aliphatic hydroxamic acids were converted to the corresponding primary amines via base-mediated rearrangement. This rearrangement could proceed with less than 1 equiv. of K2CO3 in polar solvents under thermal conditions with no external reagents. This rearrangement has several features including no external activating agents needed for promoting the rearrangement, less than one equivalent of a base is sufficient for the reaction, and a clean reaction in which only carbon dioxide is produced as a by-product. A self-propagating mechanism via an isocyanate intermediate is proposed and elementary reaction steps, namely, chain propagation reactions are supported by experiments.
- Ohtsuka, Naoya,Okuno, Moriaki,Hoshino, Yujiro,Honda, Kiyoshi
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p. 9046 - 9054
(2016/10/05)
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- N-methylimidazole-catalyzed synthesis of carbamates from hydroxamic acids via the lossen rearrangement
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An efficient, one-pot, N-methylimidazole (NMI) accelerated synthesis of aromatic and aliphatic carbamates via the Lossen rearrangement is reported. NMI is a catalyst for the conversion of isocyanate intermediates to the carbamates. Moreover, the utility of arylsulfonyl chloride in combination with NMI minimizes the formation of often-observed hydroxamate-isocyanate dimers during the sequence. Under the present conditions, lowering of temperatures is also possible, enabling a mild protocol.
- Yoganathan, Sabesan,Miller, Scott J.
-
supporting information
p. 602 - 605
(2013/04/11)
-
- Stereoselective direct reductive amination of ketones with electron-deficient amines using Re2O7/NaPF6 catalyst
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The first example of direct reductive amination (DRA) of ketones with electron-deficient amines (EDA) such as Cbz-, Boc-, EtOCO-, Fmoc-, Bz-, ArSO2-, etc. protected amines have been achieved using catalytic Re2O7/NaPF6. Excellent chemoselectivities as well as diastereoselectivity (for 2-alkyl cyclohexanones) were obtained. The Royal Society of Chemistry 2013.
- Das, Braja Gopal,Ghorai, Prasanta
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supporting information
p. 4379 - 4382
(2013/08/23)
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- A facile protocol for N-Cbz protection of amines in PEG-600
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An efficient and eco-friendly protocol for the chemoselective N-benzyloxycarbonylation of amines was described. The reaction of amines with benzyl chloroformate (Cbz-Cl) in the presence of PEG-600 at room temperature afforded the corresponding N-Cbz derivatives in excellent yields. The method is applicable to the N-Cbz protection of aliphatic (acyclic and cyclic) and aromatic amines.
- Zhang, Chun Lin,Zhang, Dong Feng,Zhao, Hong Yi,Lin, Zi Yun,Huang, Hai Hong
-
experimental part
p. 789 - 792
(2012/08/08)
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- Amberlyst-15 catalyzed Cbz protection of amines under solvent-free conditions
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Amberlyst-15 can effectively catalyze Cbz protection of aliphatic and aromatic amines within 10-15 min under solvent-free conditions. The catalyst can be used repeatedly without loss of activity, and the reaction requires no workup and gives excellent yields. Taylor & Francis Group, LLC.
- Bora, Pranja P.,Vanlaldinpuia, Khiangte,Rokhum, Lalthazuala,Bez, Ghanashyam
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experimental part
p. 2674 - 2683
(2011/08/22)
-
- Chemo- and diastereoselective cyclopropanation of allylic amines and carbamates
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A highly chemo- and diastereoselective protocol for the cyclopropanation of tertiary allylic amines with Shi's carbenoid [CF3CO 2ZnCH2I] is described. The high levels of diastereoselectivity observed in these reactions may be attributed to chelation of the nitrogen atom to the zinc reagent, which then transfers a methylene unit to the syn-face of the olefin. Furthermore, a stereodivergent protocol for the cyclopropanation of a range of allylic carbamates has been developed, which provides access to both diastereoisomers of the corresponding cyclopropanes with very high levels of diastereoselectivity: cyclopropanation with the Wittig-Furukawa reagent [Zn(CH2I)2] proceeds under chelation control to give the corresponding syn-product, whilst reaction with Shi's carbenoid proceeds under steric control to give the corresponding anti-cyclopropane, in >95:5 dr in both cases.
- Csatayová, Kristína,Davies, Stephen G.,Lee, James A.,Ling, Kenneth B.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.
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supporting information; experimental part
p. 8420 - 8440
(2010/12/20)
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- An excellent method for Cbz-protection of amines
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Cbz-protection of aliphatic and aromatic amines can be accomplished with benzylchloroformate using a catalytic amount of dodecatungstophosphoric acid hydrate (0.05 equiv). The reaction is simple, fast, does not require aqueous work-up and gives excellent yields.
- Vanlaldinpuia, Khiangte,Sema, H. Atoholi,Rokhum, Lalthazuala,Bez, Ghanashyam
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experimental part
p. 228 - 229
(2010/08/20)
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- A catalyst-free N-benzyloxycarbonylation of amines in aqueous micellar media at room temperature
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N-Benzyloxycarbonylation of amines was carried out in aqueous micellar media. Aliphatic (open and cyclic), aromatic and heteroaromatic amines react with Cbz-Cl to give excellent yields of products. The reactions were carried out in water and at room temperature.
- Shrikhande, Janhavi J.,Gawande, Manoj B.,Jayaram, Radha V.
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p. 4799 - 4803
(2008/12/22)
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- DI-SUBSTITUTED AMIDES FOR ENHANCING GLUTAMATERGIC SYNAPTIC RESPONSES
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This invention relates to compounds, pharmaceutical compositions and methods for use in the prevention and treatment of cerebral insufficiency, including enhancement of receptor functioning in synapses in brain networks responsible for basic and higher order behaviors. These brain networks, which are involved in regulation of breathing, and cognitive abilities related to memory impairment, such as is observed in a variety of dementias, in imbalances in neuronal activity between different brain regions, as is suggested in disorders such as Parkinson's disease, schizophrenia, respiratory depression, sleep apneas, attention deficit hyperactivity disorder and affective or mood disorders, and in disorders wherein a deficiency in neurotrophic factors is implicated, as well as in disorders of respiration such as overdose of an alcohol, an opiate, an opioid, a barbiturate, an anesthetic, or a nerve toxin, or where the respiratory depression results form a medical condition such as central sleep apnea, stroke- induced central sleep apnea, obstructive sleep apnea, congenital hypoventilation syndrome, obesity hypoventilation syndrome, sudden infant death syndrome, Rett syndrome, spinal cord injury, traumatic brain injury, Cheney-Stokes respiration, Ondines curse, Prader-Willi's syndrome and drowning. In a particular aspect, the invention relates to compounds useful for treatment of such conditions, and methods of using these compounds for such treatment.
- -
-
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- Versatile synthesis of free and N-benzyloxycarbonyl-protected 2,2-disubstituted taurines
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An effective and versatile method was developed to synthesize N-benzyloxycarbonyl-protected and free 2,2-disubstituted taurines. Several novel 2,2-disubstituted taurines, including aliphatic/aromatic and cyclic/acyclic derivatives, were obtained, which demonstrates the generality of this method. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Wang, Boyuan,Zhang, Wei,Zhang, Leilei,Du, Da-Ming,Liu, Gang,Xu, Jiaxi
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p. 350 - 355
(2008/09/18)
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- N-tosyloxycarbamates as reagents in rhodium-catalyzed C-H amination reactions
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Metal nitrenes for use in C-H insertion reactions were obtained from N-tosyloxycarbamates in the presence of an inorganic base and a rhodium(II) dimer complex catalyst. The C-H amination reaction proceeds smoothly, and the potassium tosylate that forms as a byproduct is easily removed by filtration or an aqueous workup. This new methodology allows the amination of ethereal, benzylic, tertiary, secondary, and even primary C-H bonds. The intramolecular reaction provides an interesting route to various substituted oxazolidinones, whereas the intermolecular reaction gives trichloroethoxycarbonyl-protected amines that can be isolated with moderate to excellent yields and that cleave easily to produce the corresponding free amine. The development, scope, and limitations of the reactions are discussed herein. Isotopic effects and the electronic nature of the transition state are used to discuss the mechanism of the reaction.
- Huard, Kim,Lebel, Helene
-
scheme or table
p. 6222 - 6230
(2009/05/27)
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- An efficient and chemoselective Cbz-protection of amines using silica-sulfuric acid at room temperature
-
A simple, facile, and chemoselective N-benzyloxycarbonylation of amines using silica-sulfuric acid that proceeds under solvent-free conditions at room temperature has been achieved. These reactions are applicable to a wide variety of primary (aliphatic and cyclic) secondary amines, amino alcohols, and heterocyclic amines.
- Gawande, Manoj B.,Polshettiwar, Vivek,Varma, Rajender S.,Jayaram, Radha V.
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p. 8170 - 8173
(2008/03/13)
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- One-step RhCl3-catalyzed deprotection of acyclic N-allyl amides
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(Chemical Equation Presented) A convenient one-step RhCl 3-catalyzed deprotection of acyclic N-allyl amides is described. Preliminary mechanistic studies reveal that the key to the success of the one-step deprotection process is the dual function of RhCl3 in alcohol solvents. Reaction of RhCl3 with n-PrOH not only provides an active rhodium hydride species to catalyze isomerization of N-allyl amides to corresponding enamides but also generates a crucial catalytic amount of HCl to convert the enamides to deallylated amides through N,O-acetal exchange.
- Zacuto, Michael J.,Xu, Feng
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p. 6298 - 6300
(2008/02/10)
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- Iron-catalyzed four-component reaction for the synthesis of protected primary amines
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The first catalytic four-component reaction (4CR) of carbonyl compounds with alkyl chloroformate, HMDS and Et3SiH has been developed to produce protected primary amines by a novel tandem nitrogen protection/direct reductive amination of carbonyl compounds. In the presence of 5 mol-% of an iron(II) salt, a wide variety of aldehydes and ketones were transformed into their corresponding protected primary amines in good to excellent yields under "pure" multicomponent reaction (MCR) conditions. This chemistry was further extended to masked carbonyl compounds such as acetals, ketals, and vinyl ethers. When compared with previous methods to prepare protected primary amines from a large excess of ammonia or ammonium salts, this 4CR not only saved at least one step of synthetic manipulation, but also utilized nearly stoichiometric nitrogen and hydrogen sources and avoided the formation of (protected) secondary amines. Additional advantages of this protocol include broader substrate scope, the use of an inexpensive and environmentally friendly catalyst, and mild reaction conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Yang, Bai-Ling,Tian, Shi-Kai
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p. 4646 - 4650
(2008/03/12)
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- De novo synthesis of troc-protected amines: Intermolecular rhodium-catalyzed C-H amination with N-tosyloxycarbamates
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The rhodium-catalyzed intermolecular C-H insertion of the nitrene derived from 2,2,2-trichloroethyl-N-tosyloxycarbamate proceeded in good to excellent yields to produce a variety of Troc-protected amines. With cyclic aliphatic alkanes, it is possible to use only 2 equiv of substrate, whereas the reaction with aromatic alkanes is run neat. Not only does the nitrene insertion proceed in benzylic, secondary, and tertiary C-H bonds but also primary C-H insertion products were obtained in good yields. Finally, the use of chiral rhodium catalysts to provide an enantioselective version of this process is discussed.
- Lebel, Helene,Kim, Huard
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p. 639 - 642
(2008/02/03)
-
- A mild and convenient synthesis of N-carbobenzyloxy ketimines
-
N-Carbobenzyloxy (Cbz) ketimines were prepared conveniently from N-Cbz amines by oxidation with N-tert-butylbenzenesulfinimidoyl chloride. The Royal Society of Chemistry 2006.
- Matsuo, Jun-Ichi,Tanaki, Yumi,Kido, Aimi,Ishibashi, Hiroyuki
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p. 2896 - 2898
(2008/09/18)
-
- Photochemical protection of amines with Cbz and Fmoc groups
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The photochemical conversion of amines into carbamates was achieved using N-Cbz-, N-Fmoc-, and N-Boc-5,7-dinitroindolines. This reaction allows the protection of amines in neutral medium. Primary and unhindered secondary amines were protected to yield their benzyloxycarbonyl- and 9-fluorenylmethoxycarbonyl derivatives efficiently, whereas bulky amines or anilines gave low yields or no product. On the other hand, the formation of N-Boc compounds, although possible, proceeded only with low yields.
- Helgen, Celine,Bochet, Christian G.
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p. 2483 - 2486
(2007/10/03)
-
- Benzyl 4,6-dimethoxy-1,3,5-triazinyl carbonate as N-protecting reagent
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A new active carbonate ester, benzyl 4,6-dimethoxy-1,3,5-triazinyl carbonate (Z-DMT), was prepared, and found to be a useful reagent for the introduction of benzyloxycarbonyl group into amines. Since Z-DMT is neither unstable nor irritating, it is practically useful.
- Hioki, Kazuhito,Fujiwara, Miho,Tani, Shohei,Kunishima, Munetaka
-
-
- The reaction of amines with benzyl halides under CO2 atmosphere
-
To find a useful, practical, and ecologically safer way to synthesize protected amines, the reactions of amines with benzyl halides under CO2 atmosphere were systematically examined. For primary amines, the CO2-inserted products were obtained in higher yields in the presence of DBU as a base, under a high pressure of CO2, and in a low-polarity solvent (toluene/hexane 1:1). Secondary amines gave only low yields of CO2-inserted products.
- Shi,Shen
-
p. 3357 - 3365
(2007/10/03)
-
- Carbon Dioxide as a Phosgene Replacement: Synthesis and Mechanistic Studies of Urethanes from Amines, CO2, and Alkyl Chlorides
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Several carbamate esters were synthesized from amines, carbon dioxide, and alkyl chlorides.The effect of added base on the yield and selectivity of carbamate ester formation was found to be highly important with the use of sterically hindered guanidine bases giving the best results.Relative rate studies were carried out giving the following order of reactivity between carbamate anions in acetonitrile with benzyl chloride giving carbamate esters: Et2NCO2(-) = Bu2NCO2(-) > t-BuNHCO2(-) = CyNHCO2(-) = s-BuNHCO2(-) > PhNHCO2(-) > CyCH2NHCO2(-) = n-octylNHCO2(-) = n-BuNHCO2(-).Rate studies were carried out with the diethyl, s-butyl, phenyl, and n-butyl carbamates and activation parameters were determined to be Et2NCO2(-), ΔH(excit.) = 11.8 kcal/mol, ΔS(excit.) = -33 eu; s-BuNHCO2(-), ΔH(excit.) = 12.8 kcal/mol, ΔS(excit.) = -33 eu; PhNHCO2(-), ΔH(excit.) = 14.3 kcal/mol, ΔS(excit.) = -28 eu; n-BuNHCO2(-), ΔH(excit.) = 23.4 kcal/mol, ΔS(excit.) = -3 eu.The unusual results obtained from the use of n-BuNHCO2(-) prompted further studies which showed that the rate of the reaction was inversely dependent on carbon dioxide pressure (20 psig CO2, k = 4.84E-4 M-1 s-1; 120 psig CO2, k = 1.83E-4 M-1 s-1).Nitrogen NMR spectroscopy indicated, via a labeling study with 15N amines and 13C enriched carbon dioxide, the formation of doubly inserted product from the addition of two carbon dioxides to ethylamine in acetonitrile.
- McGhee, William,Riley, Dennis,Christ, Kevin,Pan, Yi,Parnas, Barry
-
p. 2820 - 2830
(2007/10/02)
-
- Highly Selective Generation of Urethanes from Amines, Carbon Dioxide and Alkyl Chlorides
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Generation of carbamate anions from either a primary or secondary amine, carbon dioxide and a stoichiometric amount of a pentaalkylguanidine followed by the addition of alkyl chlorides gives high yields of urethanes.
- McGhee, William D.,Pan, Yi,Riley, Dennis P.
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p. 699 - 700
(2007/10/02)
-
- Role of the macrocyclic polyether in the synthesis of N-alkylcarbamate ester from primary amines, CO2 and alkyl halides in the presence of crown-ethers
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Primary amines, RNH2 1, and CO2 easily afford monoalkylammonium N-alkylcarbamates, [RNH3][O2CNHR] 2, that have been reacted with alkyl halides, R'X, in the presence of crown-ethers to give organic carbamates in good yield. We report here the synthesis and spectroscopic characterization of some alkylammonium carbamates 2, where R - benzyl 2a, allyl 2b, ter-butyl 2c, cyclohexyl 2d, and discuss their stability in solution and the conditions in which they can react with alkyl halides to give organic carbamates, RNHC(O)OR'. The role played by the macrocyclic ligand in modifying the reactivity of monoalkylammonium carbamates 2 towards R'X has been rationalized and the influence of parameters such as solvent, temperature and CO2 pressure on the yield and selectivity of the process leading to organic carbamates has been also settled.
- Aresta,Quaranta
-
p. 1515 - 1530
(2007/10/02)
-
- Boron trifluoride promoted cleavage of benzyl carbamates
-
A new efficient method for the cleavage of benzyl carbamates (CBZ protective groups) is described that involves a hard acid (BF3·OEt2) - soft nucleophile (EtSH) system. Unlike other available methods, this combination avoids the reduction of olefins, acetylenes, imines, halides and nitro groups, or the possibility of carboxylic ester hydrolysis.
- Subhas Bose,Thurston, David E.
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p. 6903 - 6906
(2007/10/02)
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- A CONVENIENT MODIFICATION OF THE CURTIUS REACTION
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A simple one-pot reaction which converts acids into urethanes is described.Acyl chlorides are converted into isocyanates under anhydrous conditions by sodium azide in the presence of a quaternary ammonium salt, followed by alcohol addition to complete the transformation.
- Scalzo, Roberto Lo,Mascitelli, Livia,Scarpati, Maria Luisa
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p. 819 - 820
(2007/10/02)
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- The Reaction of Isocyanides with Halogens or N-Halosuccinimides and Alcohols
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The reaction of aliphatic isocyanides with bromine or chlorine in primary alcohols, followed by hydrolysis, afforded the corresponding carbamates in moderate yields, together with various amounts of amines.Bromine was superior to chlorine as a halogen source for the formation of carbamates, unexpectedly, the addition of HgCl2 resulted in a decrease in the carbamate yield.When N-halosuccinimides were used in the place of halogens, an additional formation of the succinimide-incorporated product was observed to some extent.
- Yamada, Hideyo,Wada, Yasuo,Tanimoto, Shigeo,Okano, Masaya
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p. 2480 - 2483
(2007/10/02)
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