- Synthesis of N-alkyl-N′-aryl or Alkenylpiperazines: A Copper-Catalyzed C–N Cross-Coupling in the Presence of Aryl and Alkenyl Triflates and DABCO
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Unsymmetrical piperazines are key constituents of many pharmaceuticals. Given that the selective introduction of an aryl and alkyl motif onto the piperazine is not always straightforward, direct arylation and alkenylation of 1,4-diaza-bicyclo[2.2.2]octane would obviate the inefficiencies associated with the preparation of these target molecules. We have utilized alkyl halides, aryl or alkenyl triflates, and 1,4-diaza-bicyclo[2.2.2]octane for the synthesis of N-alkyl-N′-aryl or alkenylpiperazines. The optimum conditions are developed using CuCl, t-BuOLi in NMP. Alkenyl triflates requires N,N′-dimethylethylenediamine and higher temperature to afford the desired cross-coupled product. Substrates bearing electron-deficient and electron-rich groups were successfully coupled under the optimum reaction conditions.
- Ghazanfarpour-Darjani, Majid,Barat-Seftejani, Forugh,Khalaj, Mehdi,Mousavi-Safavi, Seyed Mahmoud
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- Theoretical study of DABCO-based ionic liquid: Synthesis and reaction mechanism
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Quaternary ammonium salt obtained from the Menshutkin reaction between DABCO and benzyl chloride has been used in the synthesis of a novel Bronsted acidic ionic liquid (IL), namely 1-benzyl-4-(sulfobutyl)-diaza-bicyclo-octane hydrogen sulfate. The reaction of DABCO with benzyl chloride is a crucial step in the synthesis of this IL. Density functional theory calculations at B3LYP/6-31G(d,p) level have been employed to investigate the mechanism of Menshutkin reaction by calculating the energy barriers through possible transition states i.e., five-membered ring transition state and SN2 transition state in gas phase and in diethyl ether as a solvent. It was found that while DABCO reacts with benzyl chloride through the well-known S N2 transition state mechanism, the corresponding reaction with chlorodiphenylmethane can proceed through both SN2 and five-membered ring transition state mechanism. However, SN2 transition state mechanism is still the strongly preferred one out of the two possible mechanisms. The electronic structure analysis shows that solvent effects and enhanced resonance stabilization may play a decisive role in guiding the reaction pathway.
- Singh, Amritpal,Singh, Paramjit,Goel, Neetu
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p. 821 - 828
(2014/06/09)
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- Radiosynthesis and evaluation of [18F]Selectfluor bis(triflate)
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(Figure Presented) Selectfluor, one of the most reactive and commonly used electrophilic fluorinating N-F reagents, has been radiolabeled with 18F. The resulting new [18F]-labeled N-F reagent is safe, nontoxic, and easy to handle. The combined use of [18F]Selectfluor bis(triflate) and AgOTf allows for the preparation of electron-rich 18F-aromatic compounds through a simple "shake and mix" protocol at room temperature (see scheme; SA=specific activtiy).
- Teare, Harriet,Robins, Edward G.,Kirjavainen, Anna,Forsback, Sarita,Sandford, Graham,Solin, Olof,Luthra, Sajinder K.,Gouverneur, Veronique
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supporting information; experimental part
p. 6821 - 6824
(2010/12/25)
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- Delineation of the factors governing reactivity and selectivity in epoxide formation from ammonium ylides and aldehydes
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Diastereoselectivity in reactions of aryl-stabilised ammonium ylides are highly sensitive to the nature of the amine and the ylide substituent. DFT calculations are consistent with a mechanism in which reversibility in betaine formation [despite the high energy (and therefore instability) of ammonium ylides] is finely balanced due to the high barrier to ring closure. The Royal Society of Chemistry.
- Robiette, Raphael,Conza, Matteo,Aggarwal, Varinder K.
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p. 621 - 623
(2007/10/03)
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- Dealkylation of Quaternary Ammonium Salts by Thiolate Anions: A Model of the Cobalamin-independent Methionine Synthase Reaction.
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The reactions of thiolate ions derived from thiophenol and homocysteine with substituted quaternary ammonium salts result in alkyl transfer from nitrogen to sulfur.A radical mechanism for this transalkylation, accounts for the reactivity pattern of the substrate salts.In a model study of the cobalamin-independent methionine synthase reaction, 5,5,6,7-tetramethyl-5,6,7,8-tetrahydropteridinium salt (25), which can be considered as a model for the natural coenzyme 5-CH3H4-folate (1), was allowed to react with the thiolate of homocysteine, whereupon the formation of methionine was observed in good yield.These results suggest that in the enzymatic process the N(5)-CH3 bond may be activated for the methyl transfer step, by coordination of the N(5) with an electrophile or a proton at the active site.
- Hilhorst, Ellen,Chen, Tjoe B. R. A.,Iskander, Atef S.,Pandit, Upendra K.
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p. 7837 - 7848
(2007/10/02)
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