- Molybdenum-Catalyzed Deoxygenation of Heteroaromatic N-Oxides and Hydroxides using Pinacol as Reducing Agent
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A molybdenum-catalyzed deoxygenation of pyridine N-oxides and N-hydroxybenzotriazoles, as well as other azole N-oxides, has been developed using pinacol as an environmentally friendly oxo-acceptor. The only by-products are acetone and water making the process a convenient alternative to established protocols in terms of waste generation. The reaction is highly chemoselective and a variety of functional groups are tolerated. The processes are usually very clean allowing the isolation of the pure deoxygenated products after a simple extraction in most cases. (Figure presented.).
- Rubio-Presa, Rubén,Fernández-Rodríguez, Manuel A.,Pedrosa, María R.,Arnáiz, Francisco J.,Sanz, Roberto
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supporting information
p. 1752 - 1757
(2017/05/22)
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- Concerted amidation of activated esters: Reaction path and origins of selectivity in the kinetic resolution of cyclic amines via N-heterocyclic carbenes and hydroxamic acid cocatalyzed acyl transfer
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The N-heterocyclic carbene and hydroxamic acid cocatalyzed kinetic resolution of cyclic amines generates enantioenriched amines and amides with selectivity factors up to 127. In this report, a quantum mechanical study of the reaction mechanism indicates that the selectivity-determining aminolysis step occurs via a novel concerted pathway in which the hydroxamic acid plays a key role in directing proton transfer from the incoming amine. This modality was found to be general in amide bond formation from a number of activated esters including those generated from HOBt and HOAt, reagents that are broadly used in peptide coupling. For the kinetic resolution, the proposed model accurately predicts the faster reacting enantiomer. A breakdown of the steric and electronic control elements shows that a gearing effect in the transition state is responsible for the observed selectivity.
- Allen, Scott E.,Hsieh, Sheng-Ying,Gutierrez, Osvaldo,Bode, Jeffrey W.,Kozlowski, Marisa C.
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supporting information
p. 11783 - 11791
(2014/11/08)
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- Spectrophotometric determination of pKa's of 1-Hydroxybenzotriazole and oxime derivatives in 95% acetonitrile-water
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1-hydroxybenzotriazole derivatives are used with carbodiimide as additives to generate active esters during peptide bond formation. They are also used as additives during the peptide bond formation. Dissociation constants of the 1-hdroxybenzotriazole (HOBt) and its derivatives, 1- hydroxy-6- chlorobenzotriazole, 1-hydroxy-6-trifluoromethylbenzotriazole, 1-hydroxy-6-nitrobenzotriazole were determined spectrophotometrically in 95% acetonitrile-water. In addition, 7-aza-1- hydroxybenzotriazole (7-HOAt) and 4-aza-1-hydroxybenzotriazole (4-HOAt) were also studied. Recently, oxyma was reported as a good replacement for the benzotriazole derivatives. As alcoholic components of active esters, the oximes seem to be good leaving groups. Therefore it was expected, that the strongly acidic and nucleophilic oximes, which possess electron-withdrawing groups in the molecule, are suitable as additives during the peptide bond formation. The dissociation constant of some oximes,such as diethyl 2-(hydroxyimino)malonate, ethyl 2-cyano-2-(hydroxyimino) acetate (oxyma), hydroxycarbonimidoyl dicyanide and N-hydroxypicolinimidoyl cyanide in 95% acetonitrile-water are reported.
- Fathalla, Magda Fouad,Khattab, Sherine Nabil
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experimental part
p. 324 - 332
(2012/05/04)
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- Synthesis and aminolysis of N,N-diethyl carbamic ester of HOBt derivatives
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The reaction of N,N-diethyl carbamates of 1H-[1,2,3]triazolo[4,5-b]pyridin- 1-ol (4-HOAt) 7, 3H-[1,2,3]triazolo[4,5- b]pyridin-3-ol (7-HOAt) 8, 1H-benzo[d][1,2,3]triazol-1-ol (HOBt) 9, 6-chloro-1H-benzo[d][1,2,3]triazol-1-ol (Cl- HOBt) 10, 6-(trifluoromethyl)-1H-benzo[d][1,2,3]triazol-1-ol (CF3 3-HOBt) 11, and 6-nitro-1H-benzo[d][1,2,3]triazol- 1-ol (NO2 2-HOBt) 12 with morpholine and piperidine in CH3CN underwent acyl nucleophilic substitution to give the corresponding carboxamide derivatives. The reactants and products were identified by elemental analysis, IR and NMR. We measured the kinetics of these reactions spectrophotometrically in CH3 3CN at a range of temperatures. The rates of morpholinolysis and piperidinolysis were found to fit the Hammett equation and correlated with s-Hammett values. The values were 1.44 - 1.21 for morpholinolysis and 1.95 - 1.72 for piperidinolysis depending on the temperature. The Bronsted-type plot was linear with a βlg = -0.49 ± 0.02 and -0.67 ± 0.03. The kinetic data and structure-reactivity relationships indicate that the reaction of 9-12 with amines proceeds by a concerted mechanism. The deviation from linearity of the correlation ?H# vs. ?S# and plot of logkpip vs. logkmorph and Bronsted-type correlation indicate that the reactions of amines with carbamates 7 and 8 is attributed to the electronic nature of their leaving groups.
- Khattab, Sherine Nabil,Hassan, Seham Yassin,Hamed, Ezzat Awad,Albericio, Fernando,Ayman, El-Faham
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experimental part
p. 75 - 81
(2010/07/15)
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