- Synthesis of a Sterically Demanding Dispiropiperidine and Its Application in Monoamidodialkyl Zincate Complexes
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The new sterically hindered piperidine analog, dispiro[cyclohexane-2,2′-piperidine-6′,2″-cyclohexane] (CPC(H), 2), and its N-methylated derivative CPC(Me) (3) were synthesized from commercially available starting materials in short steps. The N-lithiated amide LiCPC (4) was also isolated from 2 as a cyclictrimer in single crystals and showed slightly larger steric hindrance than that of lithium 2,2,6,6-tetramethylpiperidide (LiTMP) in the competitive methylation reaction with methyl trifluoromethanesulfonate. In addition, the heterobimetallic heteroleptic zincate complexes [Li(μ-NR2)(μ-Et)Zn(Et)] (NR2 = CPC, 5, and NR2 = TMP, 6) were obtained as THF- and TMEDA-coordinated monomer 5·(THF)2, 6·(THF)2, 5·TMEDA, and 6·TMEDA (THF = tetrahydrofuran, TMEDA = N,N,N′,N′-tetramethylethylenediamine). These molecular structures bearing different amido ligands in single crystals showed little structural differences from crystallographic studies. Diffusion-ordered spectroscopy (DOSY) revealed that the solution structures of the zincate complexes 5·(THF)2 and 6·(THF)2 only differ in the number of coordination THF molecules. In the deprotonation reactions with tert-butyl 3-bromobenzoate, the zincate complexes containing the CPC ligand [Li(μ-CPC)(μ-R)Zn(R)] (R = Et (5), tBu) showed moderately improved regioselectivity for the 6 position in comparison to those containing the TMP ligand [Li(μ-TMP)(μ-R)Zn(R)] (R = Et (6), tBu).
- Morisako, Shogo,Shang, Rong,Yamamoto, Yohsuke
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supporting information
p. 10767 - 10773
(2016/10/26)
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- Large molecular weight nitroxide biradicals providing efficient dynamic nuclear polarization at temperatures up to 200 K
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A series of seven functionalized nitroxide biradicals (the bTbK biradical and six derivatives) are investigated as exogenous polarization sources for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and with ca. 100 K sample temperatures. The impact of electron relaxation times on the DNP enhancement (ε) is examined, and we observe that longer inversion recovery and phase memory relaxation times provide larger ε. All radicals are tested in both bulk 1,1,2,2-tetrachloroethane solutions and in mesoporous materials, and the difference in ε between the two cases is discussed. The impact of the sample temperature and magic angle spinning frequency on ε is investigated for several radicals each characterized by a range of electron relaxation times. In particular, TEKPol, a bulky derivative of bTbK with a molecular weight of 905 g·mol-1, is presented. Its high-saturation factor makes it a very efficient polarizing agent for DNP, yielding unprecedented proton enhancements of over 200 in both bulk and materials samples at 9.4 T and 100 K. TEKPol also yields encouraging enhancements of 33 at 180 K and 12 at 200 K, suggesting that with the continued improvement of radicals large ε may be obtained at higher temperatures.
- Zagdoun, Alexandre,Casano, Gilles,Ouari, Olivier,Schwarzwaelder, Martin,Rossini, Aaron J.,Aussenac, Fabien,Yulikov, Maxim,Jeschke, Gunnar,Coperet, Christophe,Lesage, Anne,Tordo, Paul,Emsley, Lyndon
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supporting information
p. 12790 - 12797
(2013/09/23)
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- A slowly relaxing rigid biradical for efficient dynamic nuclear polarization surface-enhanced NMR spectroscopy: Expeditious characterization of functional group manipulation in hybrid materials
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A new nitroxide-based biradical having a long electron spin-lattice relaxation time (T1e) has been developed as an exogenous polarization source for DNP solid-state NMR experiments. The performance of this new biradical is demonstrated on hybrid silica-based mesostructured materials impregnated with 1,1,2,2-tetrachloroethane radical containing solutions, as well as in frozen bulk solutions, yielding DNP enhancement factors (∈) of over 100 at a magnetic field of 9.4 T and sample temperatures of ~100 K. The effects of radical concentration on the DNP enhancement factors and on the overall sensitivity enhancements (σ?) are reported. The relatively high DNP efficiency of the biradical is attributed to an increased T1e, which enables more effective saturation of the electron resonance. This new biradical is shown to outperform the polarizing agents used so far in DNP surface-enhanced NMR spectroscopy of materials, yielding a 113-fold increase in overall sensitivity for silicon-29 CPMAS spectra as compared to conventional NMR experiments at room temperature. This results in a reduction in experimental times by a factor >12 700, making the acquisition of 13C and 15N one- and two-dimensional NMR spectra at natural isotopic abundance rapid (hours). It has been used here to monitor a series of chemical reactions carried out on the surface functionalities of a hybrid organic-silica material.
- Zagdoun, Alexandre,Casano, Gilles,Ouari, Olivier,Lapadula, Giuseppe,Rossini, Aaron J.,Lelli, Moreno,Baffert, Mathieu,Gajan, David,Veyre, Laurent,Maas, Werner E.,Rosay, Melanie,Weber, Ralph T.,Thieuleux, Chloe,Coperet, Christophe,Lesage, Anne,Tordo, Paul,Emsley, Lyndon
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supporting information; experimental part
p. 2284 - 2291
(2012/03/10)
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- Effective 2,6-substitution of piperidine nitroxyl radical by carbonyl compound
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Nitroxyl radicals (nitroxides) with unpaired electron are widely used as antioxidants, contrast agents, and spin probes. Although piperidine nitroxyl radicals have many applications, these are mainly tetramethylpiperidine compounds, and only a few reports consider the substitution of N-O surround as a reaction site, such as 2,2,6,6-tetrasubstituted piperidine nitroxyl radicals. Our results revealed that the 2,6-position of the 2,2,6,6-tetramethylpiperidin-4-one compound was substituted by cyclohexyl groups to produce 2,2,6,6-tetrasubstituted piperidin-4-one derivatives under mild reaction conditions. An interesting result was obtained by using 15N-labeled NH4Cl instead of 14NH4Cl: it gave 15N-labeled 2,2,6,6-tetrasubstituted piperidin-4-one-1-oxyls with a high 15N content. In conclusion, the new method for the synthesis of nitroxyl radicals readily yields 2,2,6,6-tetrasubstituted piperidin-4-one under mild conditions.
- Sakai, Kiyoshi,Yamada, Ken-ichi,Yamasaki, Toshihide,Kinoshita, Yuichi,Mito, Fumiya,Utsumi, Hideo
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experimental part
p. 2311 - 2315
(2010/06/12)
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- METHOD FOR SYNTHESIS OF NITROXYL RADICAL
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The problem to be solved by the present invention is to provide a highly-versatile method for producing a nitroxyl radical derivative, in which position-2 and position-6 in a TEMPO-based compound can be easily substituted, and further, a method for producing a nitroxyl radical derivative, in which a nitrogen nucleus is labeled with 15N. In the present invention, the above-described problem can be solved by reacting a triacetoneamine derivative with ketone or aldehyde in the presence of ammonium salt or a 15N-labeled compound thereof to obtain a 2,6-substituted-4-piperidone derivative.
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Page/Page column 20-21
(2009/12/23)
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- Oxoammonium Salts. 5. A New Synthesis of Hindered Piperidines Leading to Unsymmetrical TEMPO-Type Nitroxides. Synthesis and Enantioselective Oxidations with Chiral Nitroxides and Chiral Oxoammonium Salts
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A new synthesis of unsymmetrical 2,2,6,6-tetraalkyl-4-piperidones from acetonin (2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine) and several ketones is described.When the ketone was a naturally occurring optically active ketone, the piperidones were optically active.The piperidones were converted to unsymmetrical TEMPO-type nitroxides and chiral nitroxides.The optically active nitroxides were used as catalysts for oxidations or converted to chiral oxoammonium salts.The structures of the chiral compounds were determined by 2D (1)H and (13)C NMR, and the cyclic voltammetric properties of the various nitroxides were measured.Several other pyrrolidine oxoammonium salts were prepared, and both types were used as oxidizing agents.Preliminary results of chiral oxidations are presented.
- Ma, Zhenkun,Huang, Qingtao,Bobbitt, James M.
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p. 4837 - 4843
(2007/10/02)
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