- Covalent Post-assembly Modification Triggers Multiple Structural Transformations of a Tetrazine-Edged Fe4L6 Tetrahedron
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Covalent post-assembly modification (PAM) reactions are useful synthetic tools for functionalizing and stabilizing self-assembled metal-organic complexes. Recently, PAM reactions have also been explored as stimuli for triggering supramolecular structural transformations. Herein we demonstrate the use of inverse electron-demand Diels-Alder (IEDDA) PAM reactions to induce supramolecular structural transformations starting from a tetrazine-edged FeII4L6 tetrahedral precursor. Following PAM, this tetrahedron rearranged to form three different architectures depending on the addition of other stimuli: an electron-rich aniline or a templating anion. By tracing the stimulus-response relationships within the system, we deciphered a network of transformations that mapped different combinations of stimuli onto specific transformation products. Given the many functions being developed for self-assembled three-dimensional architectures, this newly established ability to control the interconversion between structures using combinations of different stimulus types may serve as the basis for switching the functions expressed within a system.
- Roberts, Derrick A.,Pilgrim, Ben S.,Sirvinskaite, Giedre,Ronson, Tanya K.,Nitschke, Jonathan R.
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- Reaction rates and mechanisms for radical, photoinitated addition of thiols to alkynes, and implications for thiol-yne photopolymerizations and click reactions
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Because of its utility in network polymerization, dendrimer synthesis, and monomer development, the photoinitiated addition of thiols to alkynes has rapidly become an important tool for polymer scientists. Yet, because this chemistry has only recently been applied to cross-linked polymer development, understanding of the nature of how the yne structure affects the reactions and information on the relative reactivities of alkynes bearing various substituents is unavailable as is the relative addition rate of the thiol to the yne as compared to the vinyl sulfide. Herein, the photoinitiated addition of octanethiol to various alkynes is explored. The most rapid addition of thiols to alkynes is that to cyclooctyne, although the resulting vinyl sulfide does not permit subsequent thiol addition. Furthermore, in the absence of radical initiators and light, thiols add spontaneously to cyclooctynes, suggesting limitations to the orthogonality of the strain-promoted copper-less azide, alkyne cycloadditions. In order of decreasing reaction rates, the consecutive addition of two thiols occurs with the aliphatic 1-octyne > propargyl acetate > methyl propargyl ether > 2-octyne. Ethyl propiolate and methyl propargylamine exhibit very small reaction rates with thiols, and no consecutive addition is observed.
- Fairbanks, Benjamin D.,Sims, Evan A.,Anseth, Kristi S.,Bowman, Christopher N.
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- Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid-Liquid Phase-Transfer Catalysis by N, N, N′, N″, N″-Pentamethyldiethylenetriamine
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Sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) and DMEA-hydrocarbon mixtures with added N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA) reacts with alkyl halides, epoxides, hydrazones, arenes, alkenes, and allyl ethers. Comparisons of PMDTA with N,N,N′,N′-tetramethylethylenediamine (TMEDA) accompanied by detailed rate and computational studies reveal the importance of the trifunctionality and κ2-κ3 hemilability. Rate studies show exclusively monomer-based reactions of 2-bromooctane, cyclooctene oxide, and dimethylresorcinol. Catalysis with 10 mol % PMDTA shows up to >30-fold accelerations (kcat > 300) with no evidence of inhibition over 10 turnovers. Solid-liquid phase-transfer catalysis (SLPTC) is explored as a means to optimize the catalysis as well as explore the merits of heterogeneous reaction conditions.
- Ma, Yun,Woltornist, Ryan A.,Algera, Russell F.,Collum, David B.
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supporting information
p. 13370 - 13381
(2021/09/03)
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- Efficient Synthesis of Amines by Iron-Catalyzed C=N Transfer Hydrogenation and C=O Reductive Amination
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Here we report the catalytic transfer hydrogenation (CTH) of non-activated imines promoted by a Fe-catalyst in the absence of Lewis acid co-catalysts. Use of the (cyclopentadienone)iron complex 1, which is much more active than the classical ‘Kn?lker complex’ 2, allowed to reduce a number of N-aryl and N-alkyl imines in very good yields using iPrOH as hydrogen source. The reaction proceeds with relatively low catalyst loading (0.5–2 mol%) and, remarkably, its scope includes also ketimines, whose reduction with a Fe-complex as the only catalyst has little precedents. Based on this methodology, we developed a one-pot CTH protocol for the reductive amination of aldehydes/ketones, which provides access to secondary amines in high yield without the need to isolate imine intermediates. (Figure presented.).
- Facchini, Sofia Vailati,Cettolin, Mattia,Bai, Xishan,Casamassima, Giuseppe,Pignataro, Luca,Gennari, Cesare,Piarulli, Umberto
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supporting information
p. 1054 - 1059
(2018/01/27)
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- Sodium Diisopropylamide in N,N-Dimethylethylamine: Reactivity, Selectivity, and Synthetic Utility
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The reactivities and chemoselectivities of sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) are compared with those of lithium diisopropylamide (LDA) in tetrahydrofuran (THF). Metalations of arenes, epoxides, ketones, hydrazones, dienes, and alkyl and vinyl halides are represented. The positive attributes of NaDA-DMEA include high solubility, stability, resistance to solvent decomposition, and ease of preparation. The high reactivities and chemoselectivities often complement those of LDA-THF.
- Ma, Yun,Algera, Russell F.,Collum, David B.
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p. 11312 - 11315
(2016/11/29)
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- Electronic effects versus distortion energies during strain-promoted alkyne-azide cycloadditions: A theoretical tool to predict reaction kinetics
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Second-order reaction kinetics of known strain-promoted azide-alkyne cycloaddition (SPAAC) reactions were compared with theoretical data from a range of ab initio methods. This produced both detailed insights into the factors determining the reaction rates and two straightforward theoretical tools that can be used to predict a priori the reaction kinetics of novel cyclooctynes for strain-promoted cycloaddition reactions. Multiple structural and electronic effects contribute to the reactivity of various cyclooctynes. It is therefore hard to relate a physical or electronic property directly and independently to the reactivity of the cyclooctyne. However, we show that Hartree-Fock LUMO energies, which were acquired while calculating activation energies at the MP2 level of theory, correlate with second-order kinetic rate data and are therefore usable for reactivity predictions of cyclooctynes towards azides. Using this correlation, we developed a simple theoretical tool that can be used to predict the reaction kinetics of (novel) cyclooctynes for SPAAC reactions. Activation energies, distortion energies, and TS conformational data were compared in a set of strained cyclooctynes in strain-promoted azide-alkyne cycloaddition (SPAAC) reactions. Only electronic effects could be accurately related to experimental rate data. Copyright
- Garcia-Hartjes, Jaime,Dommerholt, Jan,Wennekes, Tom,Van Delft, Floris L.,Zuilhof, Han
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supporting information
p. 3712 - 3720
(2013/07/26)
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- Clicking 1,2,4,5-tetrazine and cyclooctynes with tunable reaction rates
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Substituted tetrazines have been found to undergo facile inverse electron demand Diels-Alder reactions with "tunable" reaction rates.
- Chen, Weixuan,Wang, Danzhu,Dai, Chaofeng,Hamelberg, Donald,Wang, Binghe
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supporting information; scheme or table
p. 1736 - 1738
(2012/03/09)
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- Heterocycles from phosphonium-iodonium ylides. Photochemical synthesis of λ5-phosphinolines
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(Chemical Equation Presented) A photochemical reaction of mixed phosphonium-iodonium ylides with acetylenes yielding λ5- phosphinolines, a rare class of phosphorus heterocycles hardly accessible by other methods, was found. The yields of λ5-phosphinolines vary from 35% to 80%. The structures of two phosphinolines were established by single-crystal X-ray diffraction. The X-ray diffraction and NMR spectra data indicate the superposition of ylidic and aromatic structures for phosphinolines.
- Matveeva, Elena D.,Podrugina, Tatyana A.,Pavlova, Anna S.,Mironov, Andrey V.,Borisenko, Anatoliy A.,Gleiter, Rolf,Zefirov, Nikolay S.
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supporting information; experimental part
p. 9428 - 9432
(2010/03/24)
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- Lithium diisopropylamide solvated by hexamethylphosphoramide: Substrate-dependent mechanisms for dehydrobrominations
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Lithium diisopropylamide-mediated dehydrobrominations of exo-2-bromonorbornane, 1-bromocyclooctene, and cis-4-bromo-tert-butylcyclohexane were studied in THF solutions and THF solutions with added hexamethylphosphoramide (HMPA). Rate studies reveal a diverse array of mechanisms based on mono-, di-, and trisolvated monomers as well as triple ions. The results are contrasted with analogous eliminations in THF in the absence of HMPA.
- Ma, Yun,Ramirez, Antonio,Singh, Kanwal Jit,Keresztes, Ivan,Collum, David B.
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p. 15399 - 15404
(2007/10/03)
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- Hemilabile Ligands in Organolithium Chemistry: Substituent Effects on Lithium Ion Chelation
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The lithium diisopropylamide-mediated 1,2-elimination of 1-bromocyclooctene to provide cyclooctyne is investigated using approximately 50 potentially hemilabile polyethers and amino ethers. Rate laws for selected ligands reveal chelated monomer-based pathways. The dependence of the rates on ligand structure shows that anticipated rate accelerations based on the gem-dimethyl effect are nonexistent and that substituents generally retard the reaction. With the aid of semiempirical and DFT computational studies, the factors influencing chelation are discussed. It seems that severe buttressing within chelates of the substitutionally rich ligands precludes a net stabilization of the chelates relative to nonchelated (η 1-solvated) forms. One ligand-MeOCH2CH2NMe 2-appears to promote elimination uniquely by a higher-coordinate monomer-based pathway.
- Ramirez, Antonio,Lobkovsky, Emil,Collum, David B.
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p. 15376 - 15387
(2007/10/03)
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- Unusual sulfur chemistry in the thermal reaction of sultene and thiophene endoperoxide sulfur donors with cyclic alkynes: Reversible formation of a persistent thiirenium ion and trapping of a thiirene by [4 + 2] cycloaddition
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The highly reactive cyclooctyne 2b serves as sulfur acceptor for both sulfur donors, namely the sultene 1A and thiophene endoperoxide 1B to afford sulfur-transfer products. With the acid-activated sultene 1A, the persistent thiirenium ion 3Ab is formed, which has allowed the direct observation of the initial sulfur-transfer adduct. On treatment with base, the thiirenium ion 3Ab reverts quantitatively to the cyclooctyne and sultene, whereas in neutral media it rearranges to the diene 6Ab. The rearrangement to the diene 6Ab, as well as the formation of spirocyclic adduct 6Ac in the reaction with dithiocyclononyne 2c, is proposed to proceed through a carbene mechanism. In the reaction of the cyclooctyne 2b with thiophene endoperoxide 1B, a thiirene is formed through sulfur transfer by an intermediary oxathiirane derived from the thiophene endoperoxide; as final product, the episulfide (R*,R*,R*)-3Bb is produced diastereoselectively by immediate [4 + 2] cycloaddition of the thiirene with the heterodiene 4B.
- Adam, Waldemar,Bosio, Sara G.,Froehling, Bettina,Leusser, Dirk,Stalke, Dietmar
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p. 8316 - 8320
(2007/10/03)
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- A spontaneous fragmentation: From the Criegee zwitterion to coarctate Mobius aromaticity
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The extremely fast fragmentation of the spiroozonides prepared from formaldehyde O-oxide and three-membered ring ketones proceeds via the coarctate transition state 1. The ozonides decompose at temperatures as low as -90°C to form carbon dioxide, alkene/alkyne, and formaldehyde (the topology of the structure of 1 is depicted on the right). The mechanism is in accordance with the rules for the stereochemical course of coarctate reactions.
- Berger, Christian,Bresler, Christian,Dilger, Ulrich,Geuenich, Daniel,Herges, Rainer,Roettele, Herbert,Schroeder, Gerhard
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p. 1850 - 1853
(2007/10/03)
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- Cycloalkylidenselenoketenes, Products of the Gas-phase Pyrolysis of 1,2,3-Selenadiazoles - An Investigation Using Variable Temperature Photoelectron Spectroscopy and Matrix-IR-Spectroscopy
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The gas-phase pyrolysis of cyclohexeno-1,2,3-selenadiazole and cycloocteno-1,2,3-selenadiazole has been investigated by variable temperature photoelectron spectroscopy and matrix IR spectroscopy.The ring contracted, highly reactive products cyclopentylidenselenoketene (cyclopentylidenmethanselone) and cycloheptylidenselenoketene (cycloheptylidenmethanselone) - which had not been found in liquid phase thermolysis experiments - have been detected.Additionally HeI photoelectron and IR spectra of analogous ketenes and thioketenes are presented for comparative reasons. - Key words: PE Spectra, IR Spectra, Reactive Intermediates, Selenoketenes
- Schulz, Reinhard,Schweig, Armin
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p. 1536 - 1540
(2007/10/02)
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- Application of Phase Transfer Catalysis, 14.- Preparation of Alkynes from Halides with Solid Potassium tert-Butoxide and Crown Ether
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Preparatively very simple and mild HX eliminations with solid potassium tert-butoxide in petroleum ether in the presence of catalytic amounts of crown-6 are described. 1,2-Dihalides (from alkenes) and 1,1-dihalides (from aldehydes) yield 1-alkynes; internal geminal dihalides (from symmetric ketones) give internal alkynes in excellent yields. 2,2-Dihalides (from methyl ketones) yield homogeneous 1-alkynes only if the 3-position is blocked. (E)-Haloalkenes lead also to alkynes in a syn-elimination process.
- Dehmlow, Eckehard V.,Lissel, Manfred
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