- Synthesis of 2,5-difunctionalised-3,3-dimethylpiperidines via ω-halogenated imines
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2,5-Difunctionalised-3,3-dimethylpiperidines were prepared by addition of nucleophiles to piperideinium salts, formed by electrophile-induced cyclisation of γ,δ-unsaturated imines with N-bromosuccinimide in alcoholic medium.
- Stevens, Christian V,Peristeropoulou, Maria,De Kimpe, Norbert
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Read Online
- Synthesis and DNA cleavage activity of bis-3-chloropiperidines as alkylating agents
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Nitrogen mustards are an important class of bifunctional alkylating agents routinely used in chemotherapy. They react with DNA as electrophiles through the formation of highly reactive aziridinium ion intermediates. The antibiotic 593A, with potential antitumor activity, can be considered a naturally occurring piperidine mustard containing a unique 3-chloropiperidine ring. However, the total synthesis of this antibiotic proved to be rather challenging. With the aim of designing simplified analogues of this natural product, we developed an efficient bidirectional synthetic route to bis-3-chloropiperidines joined by flexible, conformationally restricted, or rigid diamine linkers. The key step involves an iodide-catalyzed double cyclization of unsaturated bis-N-chloroamines to simultaneously generate both piperidine rings. Herein we describe the synthesis and subsequent evaluation of a series of novel nitrogen-bridged bis-3-chloropiperidines, enabling the study of the impact of the linker structure on DNA alkylation properties. Our studies reveal that the synthesized compounds possess DNA alkylating abilities and induce strand cleavage, with a strong preference for guanine residues.
- Zuravka, Ivonne,Roesmann, Rolf,Sosic, Alice,Wende, Wolfgang,Pingoud, Alfred,Gatto, Barbara,G?ttlich, Richard
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Read Online
- Consecutive borylcupration/C-C coupling of ?-alkenyl aldehydes towards diastereoselective 2-(borylmethyl)cycloalkanols
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Copper(i) catalyzes the borylative cyclization of ?-alkenyl aldehydes through chemo- and regioselective addition of Cu-B to C?C and concomitant intramolecular 1,2-addition of Cu-C on C?O. The products are formed in an exclusive diastereoselective manner and computational analysis identifies the key points for the observed chemo- and diastereoselectivity.
- Carbó, Jorge J.,Fernández, Elena,Maza, Ricardo J.,Royes, Jordi
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supporting information
p. 5973 - 5976
(2020/06/05)
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- Aromatic Linkers Unleash the Antiproliferative Potential of 3-Chloropiperidines Against Pancreatic Cancer Cells
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In this study, we describe the synthesis and biological evaluation of a set of bis-3-chloropiperidines (B?CePs) containing rigid aromatic linker structures. A modification of the synthetic strategy also enabled the synthesis of a pilot tris-3-chloropiperidine (Tri-CeP) bearing three reactive meta-chloropiperidine moieties on the aromatic scaffold. A structure–reactivity relationship analysis of B?CePs suggests that the arrangement of the reactive units affects the DNA alkylating activity, while also revealing correlations between the electron density of the aromatic system and the reactivity with biologically relevant nucleophiles, both on isolated DNA and in cancer cells. Interestingly, all aromatic 3-chloropiperidines exhibited a marked cytotoxicity and tropism for 2D and 3D cultures of pancreatic cancer cells. Therefore, the new aromatic 3-chloropiperidines appear to be promising contenders for further development of mustard-based anticancer agents aimed at pancreatic cancers.
- Helbing, Tim,Carraro, Caterina,Francke, Alexander,Sosic, Alice,De Franco, Michele,Gandin, Valentina,G?ttlich, Richard,Gatto, Barbara
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supporting information
p. 2040 - 2051
(2020/09/21)
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- A One-Pot Intramolecular Tandem Michael-Aldol Annulation Reaction for the Synthesis of Chiral Pentacyclic Terpenes
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A chiral tricyclic terpene possessing a 6,6,6-tricyclic framework and a 3,3-dimethyl-7-oxooctylidenyl side chain undergoes a double ring-closing reaction to give two chiral pentacyclic terpenes in a ratio of 4:3 via an intramolecular Michael addition followed by aldol condensation under basic conditions. Three new stereogenic centers are introduced in the initial Michael annulation reaction. Stereoselective installation of an ethoxycarbonyl group at C17 of the two pentacyclic terpenes separately gives the corresponding highly functionalized pentacyclic terpenoids with seven stereogenic centers. The structures and stereochemistry of key intermediates and products are established through X-ray crystallographic analysis. A mechanism is proposed for explaining the stereochemistry in the Michael annulation reaction.
- Lu, Jianyu,Koldas, Serkan,Fan, Huafang,Desper, John,Day, Victor W.,Hua, Duy H.
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p. 3964 - 3972
(2019/10/28)
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- Metal-Free Oxidative Decarbonylative [3+2] Annulation of Terminal Alkynes with Tertiary Alkyl Aldehydes toward Cyclopentenes
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A new metal-free oxidative decarbonylative [3+2] annulation of terminal alkynes with tertiary alkyl aldehydes is presented, which features broad substrate scope and excellent selectivity. The selectivity of this reaction toward cyclopentenes and indenes relies on the nature of the aldehyde substrates. While treatment of tertiary γ,δ-unsaturated aldehydes with common terminal alkynes assembles cyclopentenes, 2-methyl-2-arylpropanals succeed in accessing indenes.
- Zou, Hua-Xu,Li, Yang,Yang, Xu-Heng,Xiang, Jiannan,Li, Jin-Heng
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p. 8581 - 8588
(2018/06/13)
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- Synthesis of a biofuel target through conventional organic chemistry
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In this work, the biofuel target compound 2-ethyl-5,5-dimethylcyclopenta-1,3-diene (1) and its exo isomers (9a and 9b), were successfully synthesized via two different pathways from the common intermediate 4,4-dimethylcyclopent-2-ene-1-one (2). The first pathway produced the endocyclic product as a pure isomer via a triflate intermediate obtained from ketone 2 in 60% yield, followed by copper-catalyzed coupling with ethyl magnesium bromide in 63% yield. The second pathway employed a Grignard reaction with ketone 2, which generated an alcohol that was immediately subjected to mild acid-catalyzed elimination to yield primarily a mixture of exo isomers 9a and 9b in 46% yield. The preparation method developed by this work allowed for the production of a sufficient quantity of these targets to evaluate their fuel properties, which will be reported in a separate study.
- Page, Jordan P.,Robinson, Joshua W.,Albrecht, Karl O.,Cosimbescu, Lelia
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supporting information
p. 1421 - 1423
(2018/03/07)
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- Synthesis and Neurotrophic Activity Studies of Illicium Sesquiterpene Natural Product Analogues
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Neurotrophic natural products hold potential as privileged structures for the development of therapeutic agents against neurodegeneration. However, only a few studies have been conducted to investigate a common pharmacophoric motif and structure–activity relationships (SARs). Here, an investigation of structurally more simple analogues of neurotrophic sesquiterpenes of the illicium family is presented. A concise synthetic route enables preparation of the carbon framework of (±)-Merrilactone A and (±)-Anislactone A/B on a gram scale. This has allowed access to a series of structural analogues by modification of the core structure, including variation of oxidation levels and alteration of functional groups. In total, 15 derivatives of the natural products have been synthesized and tested for their neurite outgrowth activities. Our studies indicate that the promising biological activity can be retained by structurally simpler natural product analogues, which are accessible by a straightforward synthetic route.
- Richers, Johannes,P?thig, Alexander,Herdtweck, Eberhardt,Sippel, Claudia,Hausch, Felix,Tiefenbacher, Konrad
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supporting information
p. 3178 - 3183
(2017/03/13)
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- Nickel-Catalyzed α-Allylation of Aldehydes and Tandem Aldol Condensation/Allylation Reaction with Allylic Alcohols
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An additive-free nickel-catalyzed α-allylation of aldehydes with allyl alcohol is reported. The reaction is promoted by 1 mol % of in situ formed nickel complex in methanol, and water is the sole by-product of the reaction. The experimental conditions allow the conversion of various α-branched aldehydes and α,β-unsaturated aldehydes as nucleophiles. The same catalyst and reaction conditions enabled a tandem aldol condensation of aldehyde/α-allylation reaction.
- Bernhard, Yann,Thomson, Brodie,Ferey, Vincent,Sauthier, Mathieu
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supporting information
p. 7460 - 7464
(2017/06/13)
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- Bis-3-chloropiperidines containing bridging lysine linkers: Influence of side chain structure on DNA alkylating activity
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A series of bis-3-chloropiperidines containing lysine linkers was synthesised as DNA alkylating model compounds by using a bidirectional synthetic strategy. These novel piperidine mustard based agents have been evaluated for their alkylating properties towards nucleic acids and were shown to alkylate and cleave DNA with strong preference for guanine residues. Our studies reveal that the introduction of aromatic groups in the side chain of the lysine linker has an impact on DNA alkylating activity. Analysis by ESI mass spectrometry enabled the verification of the reactive aziridinium ion formation. Overall, the results confirm our recently proposed reaction mechanism of bis-3-chloropiperidines.
- Zuravka, Ivonne,Roesmann, Rolf,Sosic, Alice,G?ttlich, Richard,Gatto, Barbara
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p. 1241 - 1250
(2015/03/04)
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- Synthesis and evaluation of a bis-3-chloropiperidine derivative incorporating an anthraquinone pharmacophore
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With the aim to attain an alkylating agent with enhanced DNA-affinity, we have successfully synthesised lysine-linked bis-3-chloropiperidine 1 bearing an anthraquinone moiety known to bind double-stranded DNA. Consistent with our expectations, compound 1 appears to intercalate into the DNA double helix, which can be observed by conformational changes of plasmid DNA suggesting alkylation and intercalation-induced DNA unwinding. The results of this work can provide a meaningful starting point for investigating the molecular mechanism of action of this novel DNA alkylating conjugate 1 with improved affinity for DNA.
- Zuravka, Ivonne,Sosic, Alice,Gatto, Barbara,G?ttlich, Richard
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supporting information
p. 4606 - 4609
(2015/10/12)
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- Iminoxyl radical-promoted dichotomous cyclizations: Efficient oxyoximation and aminooximation of alkenes
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A novel iminoxyl radical-involved metal-free approach to vicinal oxyoximation and aminooximation of unactivated alkenes is developed. This method utilizes the dichotomous reactivity of the iminoxyl radical to furnish a general difunctionalization on alkenes using simple tert-butyl nitrite (TBN) as the iminoxyl radical initiator as well the carbon radical trap. By using this protocol, oxime featured 4,5-dihydroisoxazoles and cyclic nitrones were facilely prepared from β,γ- and γ,δ-unsaturated ketoximes, respectively.
- Peng, Xie-Xue,Deng, Yun-Jing,Yang, Xiu-Long,Zhang, Lin,Yu, Wei,Han, Bing
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supporting information
p. 4650 - 4653
(2015/01/08)
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- Diversity-oriented synthesis of hydrazine-derived compounds from amino isocyanates generated in situ
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Behind the mask: Nitrogen-substituted isocyanates are rare and their synthetic potential is virtually untapped. Simple masked precursors can form amphoteric amino isocyanate intermediates in situ, and allows the synthesis of complex hydrazine derivatives upon addition with amines. This reactivity was used in a cascade substitution/hydroamination sequence, and in the assembly of azadipeptide analogues. Copyright
- Clavette, Christian,Vincent Rocan, Jean-Francois,Beauchemin, Andre M.
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supporting information
p. 12705 - 12708
(2013/12/04)
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- Enantioselective thiourea-catalyzed intramolecular cope-type hydroamination
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Catalysis of Cope-type rearrangements of bis-homoallylic hydroxylamines is demonstrated using chiral thiourea derivatives. This formal intramolecular hydroamination reaction provides access to highly enantioenriched α-substituted pyrrolidine products and represents a complementary approach to metal-catalyzed methods.
- Brown, Adam R.,Uyeda, Christopher,Brotherton, Carolyn A.,Jacobsen, Eric N.
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supporting information
p. 6747 - 6749
(2013/06/05)
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- Efficient entry to the [2.2.2]-diazabicyclic ring system via diastereoselective domino reaction sequence
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A domino reaction sequence involving aldol condensation, alkene isomerization, and intramolecular hetero-Diels-Alder cycloaddition for the synthesis of [2.2.2]-diazabicyclic structures is reported. Excellent diastereofacial control during the cycloaddition is enforced with a removable chiral phenyl aminal diketopiperazine substituent. The reaction sequence rapidly generates molecular complexity and is competent with both enolizable and nonenolizable aldehyde substrates (nine examples total). Progress toward the synthesis of malbrancheamide B, a protypical member of the [2.2.2]-diazabicyclic natural product family, is also disclosed.
- Margrey, Kaila A.,Chinn, Alex J.,Laws, Stephen W.,Pike, Robert D.,Scheerer, Jonathan R.
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supporting information; experimental part
p. 2458 - 2461
(2012/07/27)
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- Total synthesis of the terpenoid buddledone A: 11-membered ring-closing metathesis
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The first total synthesis of buddledone A was accomplished in seven steps from methyl ethyl ketone (MEK). The key step in the sequence featured an 11-membered ring formation by ring-closing metathesis.
- Cai, Zhengxin,Yongpruksa, Nattawut,Harmata, Michael
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supporting information; experimental part
p. 1661 - 1663
(2012/07/01)
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- Discovery of novel thieno[2,3-d]pyrimidin-4-yl hydrazone-based cyclin-dependent kinase 4 inhibitors: synthesis, biological evaluation and structure-activity relationships
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The design, synthesis, and evaluation of novel thieno[2,3-d]pyrimidin-4-yl hydrazone analogues as cyclin-dependent kinase 4 (CDK4) inhibitors are described. In continuing our program aim to search for potent CDK4 inhibitors, the introduction of a thiazole group at the hydrazone part has led to marked enhancement of chemical stability. Furthermore, by focusing on the optimization at the C-4′ position of the thiazole ring and the C-6 position of the thieno[2,3-d]pyrimidine moiety, compound 35 has been identified with efficacy in a xenograft model of HCT116 cells. In this paper, the potency, selectivity profile, and structure-activity relationships of our synthetic compounds are discussed.
- Horiuchi, Takao,Takeda, Yasuyuki,Haginoya, Noriyasu,Miyazaki, Masaki,Nagata, Motoko,Kitagawa, Mayumi,Akahane, Kouichi,Uoto, Kouichi
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experimental part
p. 991 - 1002
(2011/10/02)
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- PREPARATION OF PRECURSORS OF CARBENES OF CAAC TYPE AND PREPARING SAID CARBENES THEREFROM
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Precursors of carbenes of CAAC type (Cyclic)(Alkyl)(Amino)(Carbenes) are prepared and carbenes are produced therefrom; novel synthesis intermediates are provided for preparing the precursors of CAAC-type carbenes.
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Page/Page column 13
(2010/05/13)
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- ANGIOTENSIN II RECEPTOR ANTAGONISTS
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A compound having the structure (Formula I), wherein R is an angiotensin receptor antagonist active group, Y is -Y1-Y2-Y3-Y4-Y5.; Y1 is C(R1R2); R1 is selected from the group consisting of hydrogen and C1-4 alkyl; R2 is selected from the group consisting of hydrogen, C1-4 alkyl, and -0C(0)C1-4 alkyl; Y2 is O or CH2; Y3 is C(O) or CH2; Y4 is O or CH2; Y5 is -(CH2) 1-2-(X)0-l-(CH2)0-l- or is absent; X is -O- or - CR3R4-; and R3 and R4 are independently selected from the group consisting of hydrogen and C1-C4 alkyl; or a pharmaceutically acceptable salt or hydrate thereof, which is useful for treating hypertension.
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Page/Page column 26
(2008/12/06)
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- Reduction of 5-(bromomethyl)-1-pyrrolinium bromides to 2-(bromomethyl)pyrrolidines and their transformation into piperidin-3-ones through an unprecedented ring expansion-oxidation protocol
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3,3-Dialkyl-5-(bromomethyl)-1-pyrrolinium bromides, prepared via bromocyclization of N-(2,2-dialkyl-4-pentenylidene)amines by means of bromine in dichloromethane, were reduced to 4,4-dialkyl-2-(bromomethyl)pyrrolidines for the first time using borane dimethyl sulfide in dichloromethane. Furthermore, the latter 2-(bromomethyl)pyrrolidines were transformed into the corresponding piperidin-3-ones through an unprecedented ring expansion-oxidation protocol in dimethylsulfoxide in the presence of potassium carbonate. Reduction of 5,5-dialkylpiperidin-3-ones by means of sodium borohydride in methanol afforded 5,5-dialkyl-3-hydroxypiperidines in good yields.
- D'hooghe, Matthias,Baele, Jan,Contreras, Jan,Boelens, Mark,Kimpe, Norbert De
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scheme or table
p. 6039 - 6042
(2009/04/11)
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- Supramolecular catalysis of unimolecular rearrangements: Substrate scope and mechanistic insights
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A cavity-containing metal-ligand assembly is employed as a catalytic host for the 3-aza Cope rearrangement of allyl enammonium cations. Upon binding, the rates of rearrangement are accelerated for all substrates studied, up to 850-fold. Activation parameters were measured for three enammonium cations in order to understand the origins of acceleration. Those parameters reveal that the supramolecular structure is able to reduce both the entropic and enthalpic barriers for rearrangement and is highly sensitive to small structural changes of the substrate. The space-restrictive cavity preferentially binds closely packed, preorganized substrate conformations, which resemble the conformations of the transition states. This hypothesis is also supported by quantitative NOE studies of two encapsulated substrates, which place the two reacting carbon atoms in close proximity. The capsule can act as a true catalyst, since release and hydrolysis facilitate catalytic turnover. The question of product hydrolysis was addressed through detailed kinetic studies. We conclude that the iminium product must dissociate from the cavity interior and the assembly exterior before hydroxide-mediated hydrolysis, and propose the intermediacy of a tight ion pair of the polyanionic host with the exiting product.
- Fiedler, Dorothea,Van Halbeek, Herman,Bergman, Robert G.,Raymond, Kenneth N.
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p. 10240 - 10252
(2007/10/03)
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- Supramolecular catalysis of a unimolecular transformation: Aza-Cope rearrangement within a self-assembled host
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Catalytic containers: A supramolecular metal-ligand assembly [M 4L6] is utilized as a catalytic host for the unimolecular carbon-carbon bond-forming rearrangement of enammonium cations (see scheme). The restricted reaction space of the supramolecular structure forces the substrate to adopt a reactive conformation upon binding to the interior. The assembly achieves up to 850-fold rate acceleration of the rearrangement.
- Fiedler, Dorothea,Bergman, Robert G.,Raymond, Kenneth N.
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p. 6748 - 6751
(2007/10/03)
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- Synthesis of functional olefin copolymers with controllable topologies using a chain-walking catalyst
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The branching topology of ethylene polar copolymers was for the first time successfully controlled by copolymerization of ethylene with polar olefins using a palladium-bisimine chain-walking catalyst, in which ethylene pressure and comonomer concentration were used to control the competition between isomerization (chain-walking) and monomer insertion processes. Although the overall branching density changes very slightly, the topology of the copolymers becomes more dendritic as the ethylene pressure and comonomer feed concentration are decreasing. This provides a straightforward one-pot synthesis to access a full range of functional copolymers having controllable branching topologies. To demonstrate the utility of this methodology, dendritic functional copolymers having hydroxyl, epoxide, and carbohydrate groups were prepared in a one-pot polymerization as potential functional materials.
- Chen, Guanghui,Ma, Xun S.,Guan, Zhibin
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p. 6697 - 6704
(2007/10/03)
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- Concise total syntheses of the bioactive mesotricyclic diterpenoids jatrophatrione and citlalitrione
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The highly functionalized [5.9.5] tricyclic framework resident in jatrophatrione (1) and citlalitrione (2) has been synthesized. The route begins with the tandem anionic oxy-Cope rearrangement/methylation/transannular ene cyclization of 21 and subsequent introduction of a conjugated enone double bond. Hydroxyl-directed 1,4-reduction of this functionality in 25 with LiAlH4/Cul/hexamethylphosphoramide/tetrahydrofuran sets the stage for the implementation of a Grob fragmentation and expedited generation of 27. Stereocontrolled intramolecular hydrosilylation allows for the subsequent introduction of a cyclic carbonate as in 53. This intermediate undergoes remarkably efficient, fully regiocontrolled Treibs reaction to generate 54, with this maneuver serving as a pivotal step for making 1 available five steps later. Treatment of 1 with m-chloroperbenzoic acid leads to 2, with attack occurring preferentially on a α-face of the double bond more remote to the carbonyl.
- Yang, Jiong,Long, Yun Oliver,Paquette, Leo A.
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p. 1567 - 1574
(2007/10/03)
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- Iodide-catalysed cyclization of unsaturated N-chloroamines: A new way to synthesise 3-chloropiperidines
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Tetrabutylammonium iodide is a very efficient catalyst for the cyclization of unsaturated N-chloroamines. The catalysis seems to proceed through N-iodoamine intermediates, which act as a source of iodonium ions. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Noack, Michael,Goettlich, Richard
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p. 3171 - 3178
(2007/10/03)
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- Synthesis of pyrrolizidines by cascade reactions of N- alkenylaziridinylmethyl radicals
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Pyrrolizidines were synthesized in a one-step-reaction from 2- (bromomethyl)aziridines via a cascade of radical reactions involving aziridinylmethyl radicals. N-allylaminyl radicals and carbon-centered pyrrolidinyl radicals.
- De Smaele, Dirk,Bogaert, Piet,De Kimpe, Norbert
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p. 9797 - 9800
(2007/10/03)
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- Synthesis of 3-alkenylamines, 4-alkenylamines and 3-allenylamines via a transamination procedure
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3-Alkenylamines, 4-alkenylamines and 3-allenylamines were synthesized conveniently by potassium t-butoxide induced transamination of α-vinylaldimines, α-allylaldimines or α-allenylaldimines followed by hydrolysis with aqueous oxalic acid.
- De Kimpe, Norbert,De Smaele, Dirk,Hofkens, Arn,Dejaegher, Yves,Kesteleyn, Bart
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p. 10803 - 10816
(2007/10/03)
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- New Method for the Selective Reduction of Amides
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A new procedure was developed for the reduction of tertiary aliphatic, olefinic, and aromatic amides to aldehydes.Reaction of the amides (1), (5), (7), (9), (11), (13), (15), and (17) with ethyl or methyl trifluoromethanesulphonate in CH2Cl2 at room temperature and then with L-Selectride at -78 deg C gave the corresponding aldehydes (2), (6), (8), (10), (12), (14), (16), and (18), respectively.A second functional group, including CO2R, C=C, CH(OCH2CH2O), and CN, in these amides was found to be inert under the conditions employed.These selective reductions gave the desired aldehydes in 50-73percent isolated yields and in >95percent yields based on converted amides.
- Tsay, Shwu-Chen,Robl, Jeffrey A.,Hwu, Jih Ru
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p. 757 - 759
(2007/10/02)
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- CYCLIZATION OF UNSATURATED ALDEHYDES CATALYZED BY (PPh3)2Co(Ph2PCH2CH2PPh2)
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Catalytic cyclization of γ,δ-unsaturated aldehydes (intramolecular hydroacylation) in the presence of (PPh3)2Co(Ph2PCH2CH2PPh2) gives four-membered and five-membered cycloalkanones.Depending on aldehyde structure the selectivity is 90-97percent at 10-100percent aldehyde conversion.
- Vinogradov, M. G.,Tuzikov, A. B.,Nikishin, G. I.
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p. 2353 - 2356
(2007/10/02)
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- PALLADIUM(II)-CATALYZED CLAISEN REARRANGEMENT OF ALLYL VINYL ETHERS
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The Claisen rearrangement of allyl vinyl ethers is catalyzed by PdCl2(CH3CN)2, provided that alkyl substituents protect the vinyl ether double bond from coordination by the metal catalyst.
- Baan, J. L. van der,Bickelhaupt, F.
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p. 6267 - 6270
(2007/10/02)
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- Conformational Analysis and Stereodynamics of Primary Acyclic Alkyl Radicals by EPR Spectroscopy
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The EPR spectra of n-alkyl, 2-methylalkyl, 2,2-dimethylalkyl, 2,2,3-trimethylbutyl, and 2,2,3,3-tetramethylbutyl radicals indicate that at 90 K they exist in "rigid" conformations with respect to rotation about the Cβ-Cγ bonds.The preferred conformations about the Cα-Cβ and Cβ-Cγ bonds were deduced by analysis of the β- and γ-H hyperfine splittings (hfs). 2,2,3,3-Tetramethylbutyl radicals, the only radicals with a CH3 group approximately all-trans with respect to the semioccupied p-orbital, were also the only radicals to show resolved δ-hfs.The barriers to internal rotation of the methyl groups in n-propyl, isobutyl, neopentyl, 2,2-bis(trideuteriomethyl)butyl, and 2,2,3,3-tetramethylbutyl radicals were obtained by line shape analysis; the ethyl rotation barrier in 2,2-bis(trideuteriomethyl)butyl and the tert-butyl rotation barrier in 2,2,3,3-tetramethylbutyl radicals were estimated in a similar way.The experimental hfs of trans γ-hydrogens were shown to fit a relationship of the form aHγ = 0.1 +7.9 cos2 Φ, where Φ is the dihedral angle between the SOMO and the plane through Cα, Cβ, and Cγ.Trends in the internal rotation barriers of the alkyl groups were adequately accounted for in terms of steric effects.
- Ingold, K. U.,Nonhebel, D. C.,Walton, J. C.
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p. 2859 - 2869
(2007/10/02)
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- ALKYLATION DIRECTE DE CETONES ET D'ALDEHYDES EN PRESENCE DE POTASSE SOLIDE EN SUSPENSION
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Dehydrated solid KOH, suspended in aprotic solvents, is used as a base for ketone and aldehyde alkylation.The best solvent as regards yields and selectivity is DME.The quantity of KOH depends on the carbonyl compound acidity.This method gives as good results as less convenient homogeneous conditions.
- Artaud, I.,Torossian, G.,Viout, P.
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p. 5031 - 5038
(2007/10/02)
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- Cyclometallation of Dialkylbis(triethylphosphine)platinum(II) Complexes: Formation of Pt,Pt-Bis(triethylphosphine)platinacycloalkanes
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The thermal decompositions of three analogues of bis(triethylphosphine)dineopentylplatinum(II) (L2Pt2 (1)) - L2Pt2 (3), L2Pt2 (5), and L2Pt2 (7) - have been examined.Compounds 3 and 7 decompose more rapidly than 1 by a factor of ca. 104 to give as products Pt,Pt-bis(triethylphosphine)-3,3-dimethylplatinacyclohexane (4) and Pt,Pt-bis(triethylphosphine)-3,3,5,5-tetramethylplatinacyclohexane (8), respectively, and 1 equiv of the corresponding alkane.Compound 5 decomposes at a rate ca. 50 times faster than 1 to yield Pt,Pt-bis(triethylphosphine)-2,4,4-trimethylplatinacyclopentane (6a), -3-methyl-3-n-propylplatinacyclobutane (6b), and -3,3-dimethylplatinacyclohexane (6c).The conversion of 3 to 4 and 5 to 6a proceeds by dissociation of triethylphosphine, intramolecular oxidative addition of a δ carbon-hydrogen bond of the alkyl groups to platinum, and reductive elimination of alkane.The decomposition of L2Pt2 (11) proceeds by β-hydride elimination rather than cleavage of a carbon-hydrogen bond and formation of platinacycloalkane.The difference in the free energies of activation for reactions which form four- and five-membered platinacycloalkanes is small (ΔΔG(excit.) ca./= 4 kcal mol-1); that for reactions wich form four- and six-membered rings is smaller (ΔΔG(excit.) ca./= 0 kcal mol-1).We identify these values of ΔΔG(excit.) with estimates of the strain energies of these rings, assuming the strain energy of the platinacyclohexane is small.The important conclusion from these studies is that the strain energy of the platinacyclobutane studied here is small (-1).
- DiCosimo, Robert,Moore, Stephen S.,Sowinski, Allan F.,Whitesides, George M.
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p. 124 - 133
(2007/10/02)
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