- Synthesis and spectroscopic characterization of group 4 post-metallocenes bearing (σ-aryl)-2-phenolate-6-pyridyl and -isoquinolinyl auxiliaries
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A new series of group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N] ligands have been prepared, and all derivatives have been characterized by multinuclear NMR spectroscopy. In the 1H NMR spectrum of the Ti derivative where [N] = (ortho-F)-substituted isoquinolinyl, one of the two CH2 resonances is observed as a doublet of doublets (collapsing to a normal d upon 19F-decoupling), whereas the [1H,19F]-HMQC correlation spectrum reveals a strong crosspeak for this dd resonance only, thus indicating the presence of intramolecular C-H·F-C interactions. [1H,19F]-HMBC experiments have been performed which reveal a significant scalar component for this coupling and confirm that the interactions are genuine. The contrasting NMR spectral patterns for the (ortho-F)-pyridyl Hf analogue, which exhibits two sets of non-identical doublet of doublets for the methylene resonances, have been rationalized. The activities of the isoquinolinyl-based Ti-[O,C,N] catalysts for ethylene polymerization are superior to those of pyridyl-based congeners.
- Lo, Jerry C.Y.,So, Loi-Chi,Chan, Michael C.W.
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p. 15905 - 15913
(2015/09/15)
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- Diastereoselective organocatalytic Mannich access to azacyclic system en route to lyconadin A
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Organocatalytic and stereoselective Mannich coupling of hindered and chiral cyclohexylcarboxaldehyde is described for a synthetic approach to the pyrrolidine core of lyconadin A. The strategy led concisely and stereoselectively to complex azaheterocyclic system containing up to five stereocenters.
- Cormier, Morgan,Jean, Alexandre,Blanchet, Jér?me,Rouden, Jacques,Maddaluno, Jacques,De Paolis, Michael
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p. 5074 - 5077
(2015/02/19)
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- Deprotonative metalation of chloro- and bromopyridines using amido-based bimetallic species and regioselectivity-computed CH acidity relationships
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A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithium-metal combinations. Whereas lithium-zinc and lithium-cadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithium-copper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.
- Snegaroff, Katia,Nguyen, Tan Tai,Marquise, Nada,Halauko, Yury S.,Harford, Philip J.,Roisnel, Thierry,Matulis, Vadim E.,Ivashkevich, Oleg A.,Chevallier, Floris,Wheatley, Andrew E. H.,Gros, Philippe C.,Mongin, Florence
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experimental part
p. 13284 - 13297
(2012/02/03)
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- Enantioselective hydrogenation with self-assembling rhodium phosphene catalysts: Influence of ligand structure and solvent
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Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH 2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0-99 % ee Complexation studies and DFT calculations were performed to explain these differences.
- Birkholz, Mandy-Nicole,Dubrovina, Natalia V.,Jiao, Haijun,Michalik, Dirk,Holz, Jens,Paciello, Rocco,Breit, Bernhard,Boerner, Armin
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p. 5896 - 5907
(2008/02/13)
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- Trifluoromethyl-substituted pyridines through displacement of iodine by in situ generated (trifluoromethyl)copper
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A literature method reported for iodobenzene and congeners was successfully extended to the pyridine series. 2-Iodopyridines can be converted into 2-(trifluoromethyl)pyridines almost quantitatively. In contrast, yields are moderate at best if 3- and 4-iodopyridines or 2-bromopyridines are used as the starting materials. WILEY-VCH Verlag GmbH 2002.
- Cottet, Fabrice,Schlosser, Manfred
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p. 327 - 330
(2007/10/03)
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- Unusual C-6 lithiation of 2-chloropyridine-mediated by BuLi-Me2N(CH2)2OLi. New access to 6-functional-2-chloropyridines and chloro-bis-heterocycles
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Formula Presented The reaction of 2-chloropyridine with alkylithium generally results in nucleophilic addition leading to the loss of chlorine atom while exclusive directed ortho metalation is obtained using LDA. Herein it is shown that the BuLi-Me2
- Choppin, Sabine,Gros, Philippe,Fort, Yves
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p. 803 - 805
(2007/10/03)
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- Desymmetrization of dichloroazaheterocycles
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3,6-Dichloropyridizine 1a was converted in good yield into its mono-iodo derivative 1b when treated with a mixture of hydriodic acid and sodium iodide. Pure samples of the mono-iodo derivatives 2b, 3b and 4b could not be obtained from their corresponding dichlorinated precursors with these reagents. Compounds 1b and 4b underwent palladium catalysed Suzuki, Sonogashira and other coupling reactions.
- Goodman, Allan J.,Stanforth, Stephen P.,Tarbit, Brian
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p. 15067 - 15070
(2007/10/03)
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