- Highly Selective Hydrogenative Conversion of Nitriles into Tertiary, Secondary, and Primary Amines under Flow Reaction Conditions
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Flow reaction methods have been developed to selectively synthesize tertiary, secondary, and primary amines depending on heterogeneous platinum-group metal species under catalytic hydrogenation conditions using nitriles as starting materials. A 10 % Pd/C-packed catalyst cartridge affords symmetrically substituted tertiary amines in good to excellent yields. A 10 % Rh/C-packed catalyst cartridge enables the divergent synthesis of secondary and primary amines, with either cyclohexane or acetic acid as a solvent, respectively. Reaction parameters, such as the metal catalyst, solvent, and reaction temperature, and continuous-flow conditions, such as flow direction and second support of the catalyst in a catalyst cartridge, are quite important for controlling the reaction between the hydrogenation of nitriles and nucleophilic attack of in situ-generated amines to imine intermediates. A wide variety of aliphatic and aromatic nitriles could be highly selectively transformed into the corresponding tertiary, secondary, and primary amines by simply changing the metal species of the catalyst or flow parameters. Furthermore, the selective continuous-flow methodologies are applied over at least 72 h to afford three different types of amines in 80–99 % yield without decrease in catalytic activities.
- Yamada, Tsuyoshi,Park, Kwihwan,Furugen, Chikara,Jiang, Jing,Shimizu, Eisho,Ito, Naoya,Sajiki, Hironao
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- A Protocol for Direct Stereospecific Amination of Primary, Secondary, and Tertiary Alkylboronic Esters
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The direct, stereospecific amination of alkylboronic and borinic esters can be conducted by treatment of the organoboron compound with methoxyamine and potassium tert -butoxide. In addition to being stereospecific, this process also enables the direct amination of tertiary boronic esters in an efficient fashion.
- Edelstein, Emma K.,Grote, Andrea C.,Palkowitz, Maximilian D.,Morken, James P.
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p. 1749 - 1752
(2018/06/26)
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- Cobalt-Porphyrin-Catalysed Intramolecular Ring-Closing C?H Amination of Aliphatic Azides: A Nitrene-Radical Approach to Saturated Heterocycles
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Cobalt-porphyrin-catalysed intramolecular ring-closing C?H bond amination enables direct synthesis of various N-heterocycles from aliphatic azides. Pyrrolidines, oxazolidines, imidazolidines, isoindolines and tetrahydroisoquinoline can be obtained in good to excellent yields in a single reaction step with an air- and moisture-stable catalyst. Kinetic studies of the reaction in combination with DFT calculations reveal a metallo-radical-type mechanism involving rate-limiting azide activation to form the key cobalt(III)-nitrene radical intermediate. A subsequent low barrier intramolecular hydrogen-atom transfer from a benzylic C?H bond to the nitrene-radical intermediate followed by a radical rebound step leads to formation of the desired N-heterocyclic ring products. Kinetic isotope competition experiments are in agreement with a radical-type C?H bond-activation step (intramolecular KIE=7), which occurs after the rate-limiting azide activation step. The use of di-tert-butyldicarbonate (Boc2O) significantly enhances the reaction rate by preventing competitive binding of the formed amine product. Under these conditions, the reaction shows clean first-order kinetics in both the [catalyst] and the [azide substrate], and is zero-order in [Boc2O]. Modest enantioselectivities (29–46 % ee in the temperature range of 100–80 °C) could be achieved in the ring closure of (4-azidobutyl)benzene using a new chiral cobalt-porphyrin catalyst equipped with four (1S)-(?)-camphanic-ester groups.
- Kuijpers, Petrus F.,Tiekink, Martijn J.,Breukelaar, Willem B.,Broere, Dani?l L. J.,van Leest, Nicolaas P.,van der Vlugt, Jarl Ivar,Reek, Joost N. H.,de Bruin, Bas
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supporting information
p. 7945 - 7952
(2017/06/19)
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- Deoxygenation of Unhindered Alcohols via Reductive Dealkylation of Derived Phosphate Esters
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Primary alcohols can be deoxygenated cleanly and in yields of 60-95% by reduction of derived diphenyl phosphate esters with lithium triethylborohydride in tetrahydrofuran at room temperature. Selective deoxygenation of a primary alcohol in the presence of a secondary alcohol was demonstrated. The two-step process can be performed in one pot, making it simple and convenient.
- Chowdhury, Sarwat,Standaert, Robert F.
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p. 9957 - 9963
(2016/11/02)
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- N-substituted 5-aryl-1,3-oxazolidin-2-ones from arylethylene oxides
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Substituted 5-aryl-1,3-oxazolidin-2-ones can be efficiently prepared from arylethylene oxides and tert-butyl alkylcarbamates in the presence of catalytic amount of potassium tert-butoxide as a base. Their further hydrolysis under basic conditions provides aryl substituted aminoethanols in high yields.
- Wrobel,Bobin,Karczewski
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p. 907 - 912
(2007/10/03)
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- A generic approach for the catalytic reduction of nitriles
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The scope of nickel boride mediated reduction of nitriles has been extended further to allow the preparation of Boc protected amines via a mild catalytic process. It is noteworthy that the toxicity of this procedure is greatly reduced due to its catalytic
- Caddick, Stephen,Judd, Duncan B.,Lewis, Alexandra K. De K.,Reich, Melanie T.,Williams, Meredith R. V.
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p. 5417 - 5423
(2007/10/03)
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- Selective nitrolytic deprotection of N-BOC-amines and N-BOC-amino acids derivatives
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The extension of the deprotection procedure using HNO3 in CH2Cl2 to a number of appropriately selected N-BOC-masked amines and derivatives of natural amino acids was investigated. The method was found to work effectively with almost all tested substrates, with the exception of activated aromatic amines and heterocycles which underwent unavoidable faster oxidation. Alanine, phenylalanine, serine and lysine derivatives were efficiently deprotected, as well as dipeptide Ala-Phe, preserving the configuration of the substrates and without affecting copresent Z and ester functions, with a remarkable selectivity towards acid sensitive t-butyl esters. The obtained amino acids esters, isolated and characterized in the form of nitrates salts, proved to be suitable intermediates to be used in peptide synthesis.
- Strazzolini, Paolo,Melloni, Tiziana,Giumanini, Angelo G
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p. 9033 - 9043
(2007/10/03)
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- Convenient protection of amines as carbamates using polymer-bound HOBT as catalyst
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A method for the facile protection of primary and secondary amines as carbamate (Cbz, Fmoc and t-Boc) derivatives using polymer bound 1-hydroxybenzotriazole (HOBT) is reported.
- Dendrinos, Kleanthis G.,Kalivretenos, Aristotle G.
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p. 1463 - 1464
(2007/10/03)
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- Alkoxycarbonyl groups transfer to amines by the N,N'-dibenzyl- and N,N'-di-tert-butyl-carbamates of cyclic thioureas
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The use of the dicarbamates of cyclic thioureas as alkoxycarbonyl-transfer reagents for the protection of amino groups is described.
- Matsumura, Noboru,Noguchi, Akiko,Kitayoshi, Aya,Inoue, Hiroo
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p. 2953 - 2954
(2007/10/03)
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