- STABILIZATION OF ACTIVE METAL CATALYSTS AT METAL-ORGANIC FRAMEWORK NODES FOR HIGHLY EFFICIENT ORGANIC TRANSFORMATIONS
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Metal-organic framework (MOFs) compositions based on post?synthetic metalation of secondary building unit (SBU) terminal or bridging OH or OH2 groups with metal precursors or other post-synthetic manipulations are described. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations, including the regioselective boryiation and siiylation of benzyiic C—H bonds, the hydrogenation of aikenes, imines, carbonyls, nitroarenes, and heterocycles, hydroboration, hydrophosphination, and cyclization reactions. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
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Paragraph 0349
(2019/01/07)
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- Single-Site Cobalt Catalysts at New Zr8(μ2-O)8(μ2-OH)4 Metal-Organic Framework Nodes for Highly Active Hydrogenation of Alkenes, Imines, Carbonyls, and Heterocycles
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We report here the synthesis of robust and porous metal-organic frameworks (MOFs), M-MTBC (M = Zr or Hf), constructed from the tetrahedral linker methane-tetrakis(p-biphenylcarboxylate) (MTBC) and two types of secondary building units (SBUs): cubic M8(μ2-O)8(μ2-OH)4 and octahedral M6(μ3-O)4(μ3-OH)4. While the M6-SBU is isostructural with the 12-connected octahedral SBUs of UiO-type MOFs, the M8-SBU is composed of eight MIV ions in a cubic fashion linked by eight μ2-oxo and four μ2-OH groups. The metalation of Zr-MTBC SBUs with CoCl2, followed by treatment with NaBEt3H, afforded highly active and reusable solid Zr-MTBC-CoH catalysts for the hydrogenation of alkenes, imines, carbonyls, and heterocycles. Zr-MTBC-CoH was impressively tolerant of a range of functional groups and displayed high activity in the hydrogenation of tri- and tetra-substituted alkenes with TON > 8000 for the hydrogenation of 2,3-dimethyl-2-butene. Our structural and spectroscopic studies show that site isolation of and open environments around the cobalt-hydride catalytic species at Zr8-SBUs are responsible for high catalytic activity in the hydrogenation of a wide range of challenging substrates. MOFs thus provide a novel platform for discovering and studying new single-site base-metal solid catalysts with enormous potential for sustainable chemical synthesis.
- Ji, Pengfei,Manna, Kuntal,Lin, Zekai,Urban, Ania,Greene, Francis X.,Lan, Guangxu,Lin, Wenbin
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supporting information
p. 12234 - 12242
(2016/09/28)
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- Carbon-carbon bond formation and pyrrole synthesis via the [3,3] sigmatropic rearrangement of O-vinyl oxime ethers
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A new method for the synthesis of 2,4- and 2,3,4-substituted pyrroles in two or three steps from commercially available ketones and allyl hydroxylamine is described. An iridium-catalyzed isomerization reaction has been developed to convert O-allyl oximes
- Wang, Heng-Yen,Mueller, Daniel S.,Sachwani, Rachna M.,Londino, Hannah N.,Anderson, Laura L.
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supporting information; experimental part
p. 2290 - 2293
(2010/08/05)
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- Reduction of the indole ring system: Synthesis of 4,5,6,7-tetrahydroindoles
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A general two-step procedure for the reduction of indoles to the corresponding 4,5,6,7-tetrahydroindoles has been developed. A regioselective Birch reduction followed by catalytic hydrogenation is employed to accomplish this transformation. Yields for the sensitive pyrrole products are typically between 40 and 50%. This method provides access to complex chiral pyrroles that cannot be readily prepared by other methods.
- McComas, Casey C.,Van Vranken, David L.
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p. 8039 - 8043
(2007/10/03)
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- New efficient, flexible and regioselective synthesis of 2,4-Di- and 2,3,4-trialkylated and arylated 1H-pyrroles
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Starting from easily available 2-acetoxy aldehyde dimethylhydrazones rac-2, we prepared various alkyl- and aryl-substituted 1H-pyrroles 6 in good overall yield. The titanium-mediated a2-umpolung reaction of rac-2 with different acyclic and cyclic silyl enol ethers 3 leads directly or via 4-oxo hydrazones rac,anti-4 to 1-(dimethylamino)-1H-pyrroles 5. A novel method for the reductive removal of the dimethylamino group affording 1H-pyrroles 6 is presented. VCH Verlagsgesellschaft mbH, 1996.
- Enders, Dieter,Maassen, Ralf,Han, Sin-Ho
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p. 1565 - 1574
(2007/10/03)
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- New Efficient and Flexible Synthesis of Polysubstituted Pyrroles
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The Lewis acid mediated reaction of readily available 2-acetoxypropanal-N,N-dimethylhydrazone 1 with various open chain and cyclic silyl enol ethers 2 leads directly or via 4-oxoaldehyde-N,N-dimethylhydrazones 3 to N-(dimethylamino)-pyrroles 4.The subsequent reductive N-N bond cleavage provides an efficient and flexible method for the preparation of alkyl-aryl-di- and trisubstituted pyrroles 5.
- Enders, Dieter,Han, Sin-Ho,Maassen, Ralf
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p. 8007 - 8010
(2007/10/02)
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- Porphyrins with Exocyclic Rings. Part 3. A Reassessment on the Utility of Cyclopentapyrroles in the Synthesis of Porphyrin Molecular Fossils. Preparation of Three Type II Porphyrins Related to Deoxophylloerythroetioporphyrin (DPEP)
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The utility of cyclopentapyrroles in porphyrin synthesis has been reinvestigated.A 6-oxocyclopentapyrrole 18 was prepared by cyclization of the propanoyl chloride sidechain of an α-unsubstituted pyrrole 17d in the presence of tin(IV) chloride.Subsequent reduction with sodium borohydride afforded the corresponding 6-hydroxy compound 10 and further acid catalyzed condensation with α-unsubstituted pyrroles 11a and 11b gave the novel 6-pyrrolylcyclopentapyrroles 22a and 22b in excellent yields.Attempts to prepare deoxophylloerythroetioporphyrin (DPEP; 2), a widespread sedimentary porphyrin molecular fossil, from these dipyrrolic intermediates using the tripyrrene-a,c-biladiene route were unsuccessful.However, the synthesis of three related meso,β-ethanoporphyrins using the MacDonald condensation was successfully carried out in moderate to good yields.Retention of an sp3 hybridized carbon bridge at the cyclopentene ring fusion site of the intermediary open chain tetrapyrroles appears to be crucial during macrocycle formation, as this diminishes the steric repulsion between the peripheral substituents and the carbocyclic ring.
- Lash, Timothy D.,Catarello, James J.
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p. 4159 - 4172
(2007/10/02)
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