- Towards redox-switchable organocatalysts based on bidentate halogen bond donors
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Redox-active bidentate halogen bond donors based on halopyridinium groups as halogen-bond donating units were synthesized and their structures were elucidated by X-ray diffraction analyses and DFT calculations.Viareversible twofold reduction, these dicationic species can be transformed to neutral compounds which should be much weaker Lewis acids. The corresponding electrochemical data were obtained, and CV as well as UV-vis and NMR techniques were also used to determine binding constants of these halogen bond donors to halides. While all titrations agree on the relative order of binding strengths (with chloride being bound strongest), there are marked deviations in the overall affinity constants which are discussed. In contrast to earlier azo-bridge analogues, the ethylene-linked variants presented herein do not oxidize halides, and thus the novel halogen bond donors could also be used as Lewis acidic organocatalysts in a halide abstraction benchmark reaction, yielding a performance similar to bis(haloimidazolium)-derived catalysts.
- Engelage,Hijazi,Gartmann,Chamoreau,Sch?llhorn,Huber,Fave
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p. 4344 - 4352
(2021/03/03)
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- Nickel-Catalyzed Cross-Coupling of Anisoles with Alkyl Grignard Reagents via C-O Bond Cleavage
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Nickel-catalyzed cross-coupling of methoxyarenes with alkyl Grignard reagents, which involves the cleavage of the C(aryl)-OMe bond, has been developed. The use of 1,3-dicyclohexylimidazol-2-ylidene as a ligand allows the introduction of a variety of alkyl groups, including Me, Me3SiCH2, ArCH2, adamantyl, and cyclopropyl. The method can also be used for the alkylative elaboration of complex molecules bearing a C(aryl)-OMe bond.
- Tobisu, Mamoru,Takahira, Tsuyoshi,Chatani, Naoto
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supporting information
p. 4352 - 4355
(2015/09/15)
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- Comparison of carbon-silicon hyperconjugation at the 2- and 4-positions of the N-methylpyridinium cation
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(Chemical Equation Presented) N-Methyl-2-trialkylsilylmethylpyridinium cations 6a-c and 4-trialkylsilylmethylpyridinium cations 5a-c were prepared and investigated using 29Si and 13C NMR and single-crystal X-ray crystallography. Syst
- Hassall, Kathryn,Lobachevsky, Sofia,White, Jonathan M.
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p. 1993 - 1997
(2007/10/03)
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- Carbon-silicon hyperconjugation X-ray structural study of N-methyl-4-trimethylsilylmethylpyridinium triflate
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Hyperconjugation between the CH2-Si bond and the charged pyridinium π system in the N-methyl 4-trimethylsilylmethyl pyridinium ion (8), manifests in the crystal structure as lengthening of the CH2-Si bond, shortening of the CH2
- Happer, Alan,N.G, Janice,Pool, Brett,White, Jonathan
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- Oxidation of substituted pyridines PyrCHRSiMe3 (R=H, Me, Ph) and substituted quinolines QnCH2SiMe3 with hypervalent iodine reagents
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Oxidation of a variety of substituted pyridines, PyrCHRSiMe3 (R = H, Me, Ph) and quinolines, QnCH2SiMe3 with hypervalent iodine reagents PIDA, (PhI(OCOCH3)2) and PIFA, (PhI(OCOCF3)2) has been studied. Oxy-desilylation with PIDA/TBAF gives low to moderate yields of PyrCHROR1 and QnCH2OR1 (R1 = H, Ac), while good yields of PyrCHROH and QnCH2OH are obtained when PIFA is used.
- Andrews, Ian P.,Lewis, Norman J.,McKillop, Alexander,Wells, Andrew S.
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p. 1151 - 1158
(2007/10/03)
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- Enamines from formamides. Synthesis of 1,2,3,4-tetrahydro-1-substituted β-carbolines
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Pyridines and benzopyridines substituted with trimethylsilylmethyl groups, α or γ to the nitrogen atom, have been found to react with formamides by way of a Peterson reaction to form enamines. Trimethylsilylmethylbenzene behaved similarly. The enamines pr
- Vohra,Maclean
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p. 1660 - 1667
(2007/10/02)
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- Lithiation of 2-Me3SiCHRC5H4N (R = H or SiMe3): Influence of Solvent on the Nature of the Product (from X-Ray Structure Determinations) and Asymmetric Induction. A Note on the Lithiation of Some Analogous 3- and 4-Methylpyridines
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Metallation of 2-Me3SiCHRC5H4N (R = H or SiMe3) using LiBun in hexane, and in the presence of diethyl ether, and the ditertiary amines tmen (N,N,N',N'-tetramethylethylenediamine) or sp yields crystalline lithium complexes.These have been characterized using X-ray diffraction data for > (1), >2> (2), > (3), >2> (4), >2> (5), and > (6).In (1), (3), (4), and (6) the hydrocarbyl group acts as an η3-aza-allyl through the ring nitrogen , ipso-carbon , and adjacent ring carbon ; in (4) the nitrogen centre also bridges to another metal centre .Complex (2) has two co-ordinated lithium centres, each lithium bound by the ipso-carbon and a nitrogen centre from a centrosymmetric ligand and is thus an alkylmetal species; it can be recrystallized from tetrahydrofuran even though the lithiums are co-ordinatively unsaturated.In complex (5), the anionic ligand acts as an amide bridging two metal centres through the ring N .Treating (6) with MeI in hexane at -78 deg C yields 2-pyridine of 20percent estimated optical purity.The isomeric complex > under the same conditions gave no asymmetric induction; other metallations of 4-Me3SiCH2C5H4N, and some of 3-Me3SiCH2C5H4N are also reported.
- Papasergio, Rocco I.,Skelton, Brian W.,Twiss, Paul,White, Allan H.,Raston, Colin L.
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p. 1161 - 1172
(2007/10/02)
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- Preparation of N-Silyl-enamines from α-Silyl Carbanions and Aromatic Nitriles
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The preparations of seven N-silyl-enamines (1a) - (1g) and their chemical behaviour are reported.Lithiated 4-(trimethylsilylmethyl)pyridine (2b) easily reacted with benzonitrile (4a) in tetrahydrofuran to give only (E)-1-phenyl-2-(4-pyridyl)-1-(trimethylsilylamino)ethene (1b) in 90percent yield.On the other hand, lithiated t-butyl trimethylsilylacetate (2c) did not react with (4a) at all, but reacted readily with 2- or 4-cyanopyridines, (4b) or (4c), and scarcely at all reacted with 3-cyanopyridine (4d) to give the corresponding t-butyl (Z)-3-trimethylsilylamino-3-pyridylpropenoates (1c), (1d), and (1e) in 68, 75, and 4percent yields, respectively.The reaction of 3-methyl-5-(trimethylsilylmethyl)isoxazole (2d) with the nitriles (4a) or (4b) gave the corresponding N-silyl-enamine (1g) or the desilylated enamines (5b,c), which were unstable and were readily hydrolyzed to the corresponding ketones (6a) or (6b).
- Konakahara, Takeo,Kurosaki, Yoshihiro
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p. 1068 - 1086
(2007/10/02)
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