- 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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- Formation of Ketenimines via the Palladium-Catalyzed Decarboxylative π-Allylic Rearrangement of N-Alloc Ynamides
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A new approach for the formation of ketenimines via a decarboxylative allylic rearrangement pathway that does not require strong stabilizing or protecting groups has been developed. The products can be readily hydrolyzed into their corresponding secondary amides or reacted with sulfur ylides to perform an additional [2,3]-Wittig process. Mechanistic studies suggest an outer-sphere process in which reductive alkylation is rate-limiting.
- Alexander, Juliana R.,Cook, Matthew J.
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supporting information
p. 5822 - 5825
(2017/11/10)
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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.
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supporting information
p. 602 - 605
(2013/04/11)
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- Library of 1,4-disubstituted 1,2,3-triazole analogs of oxazolidinone RNA-binding agents
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The design and synthesis of small molecules that target RNA is immensely important in antibacterial therapy. We had previously reported on the RNA binding of a series of 4,5-disubstituted 2-oxazolidinones that bind to a highly conserved bulge region of bacterial RNA. This biological target T box antitermination system, which is found mainly in Gram-positive bacteria, regulates the expression of several amino acid related genes. In an effort to amplify our library, we have prepared a library of 1,4-disubstituted 1,2,3-triazole analogs that entails an isosteric replacement of the oxazolidinone nucleus. The synthesis of the new analogs was enhanced via copper(I) catalysis of an azide and alkyne cycloaddition reaction. A total of 108 1,4-disubstituted 1,2,3-triazole compounds have been prepared. All compounds were evaluated as RNA binding agents.
- Acquaah-Harrison, George,Zhou, Shu,Hines, Jennifer V.,Bergmeier, Stephen C.
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scheme or table
p. 491 - 496
(2010/09/15)
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- Unmodified nano-powder magnetite catalyzes a four-component aza-Sakurai reaction
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A new catalyst for an old material: magnetite is an excellent Lewis acid catalyst for the four-component aza-Sakurai reaction. The process could be repeated up to 15-times without losing effectiveness, with the catalyst recycling being as easy as the use of a simple magnet. The catalyst is selective and could discriminate between aldehyde and ketone functionalities, catalyzing first the reaction with the higher electrophilic aldehyde.
- Martinez, Ricardo,Ramon, Diego J.,Yus, Miguel
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supporting information; experimental part
p. 1235 - 1240
(2009/05/30)
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- Synthesis of carbamates and ureas using Zr(IV)-catalyzed exchange processes
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Equation presented Zirconium(IV)-catalyzed exchange processes have been developed to prepare both carbamates and ureas from dialkyl arbonates 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.
- Han, Chong,Porco Jr., John A.
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p. 1517 - 1520
(2008/02/02)
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- Study of the stability of carbocations by chlorosulfonyl isocyanate reaction with ethers
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The stability order of various alkyl, allyl, and benzyl carbocations was investigated using the novel technique for comparing the stability of carbocations in solution developed by using a simple CSI reaction with various ethers. The p-methoxycinnamyl carbocation was the most stable in our reaction system and the next stable carbocation was the p-methoxybenzyl carbocation. The stability of the other carbocations decreased with methacryl, t-butyl, cinnamyl, acryl, benzyl, 2° and allyl carbocations in that order.
- Kim, Ji Duck,Han, Gyoonhee,Jeong, Lak Shin,Park, Hyun-Ju,Zee, Ok Pyo,Jung, Young Hoon
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p. 4395 - 4402
(2007/10/03)
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- Liquid chromatography stationary phases with reduced silanol interactions
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Novel carbamate compounds, novel silylcarbamate compounds and novel reversed phase materials comprising a silica substrate modified with a modified novel silylcarbamate compound are disclosed which may, for example, be used as stationary phases for liquid chromatography applications. Attached to the carbamate group are several reversed or normal phase producing groups such as cyanoalkyl, tertiary butyl, dibutyl, octyl, dodecyl, tetradecyl, octadecyl or benzyl. The new stationary phases may be endcapped with a short chain alkyl silane. One particular advantage of these stationary phases is decreased interaction with basic samples due to shielding of the unreacted silanol groups on the silica surface. The new phases are particularly useful in the chromatographic analysis of basic samples or more generally for samples having an undesirable interaction with the unmodified silanols.
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- 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
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p. 1515 - 1530
(2007/10/02)
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