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Asymmetric Synthesis of 4,5,6- and 3,4,5,6-Substituted Azepanes by a Highly Diastereoselective and Enantioselective Lithiation-Conjugate Addition Sequence

Lee, Suk Joong; Beak, Peter
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 22/02/2006 EN
Relevância na Pesquisa
16.19%

Synthesis of the C3–C18 Fragment of Amphidinolides G and H

Petri, Andreas F.; Schneekloth, John S.; Mandal, Amit K.; Crews, Craig M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
16.19%
A synthesis of an amphidinolides G and H C3–C18 subunits is reported. The C10–C18 segment 4 was prepared by a Negishi cross-coupling, whereas the synthesis of the C3–C9 fragment 5 employed an asymmetric cyanosilylation as the key step. The two segments were coupled by lithiation of iodide 4 and trapping of the anion with amide 5. The allylic epoxide moiety could be synthesized from the protected anti- mesylate 22.

Electron Bottleneck in the Charge/Discharge Mechanism of Lithium Titanates for Batteries

Ventosa, Edgar; Skoumal, Marcel; Vazquez, Francisco Javier; Flox, Cristina; Arbiol, Jordi; Morante, Joan Ramon
Fonte: WILEY-VCH Verlag Publicador: WILEY-VCH Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
16.19%
The semi-solid flow battery (SSFB) is a promising storage energy technology featured by employing semi-solid fluid electrodes containing conductive additive and active Li-ion battery materials. The state of art anode material for SSFB is Li4Ti5O12 (LTO). This work shows that LTO improves drastically the performance in fluid electrode via hydrogen annealing manifesting the importance of the electrical conductivity of the active material in SSFBs. On the other hand, the properties of fluid electrodes allow the contributions of ionic and electrical resistance to be separated in operando. The asymmetric overpotential observed in Li4Ti5O12 and TiO2 is proposed to originate from the so-called electron bottleneck mechanism based on the transformation from electrically insulator to conductor upon (de-)lithiation, or vice versa, which should be considered when modelling, evaluating or designing advanced materials based on Li4Ti5O12, TiO2 or others with insulating-conducting behavior materials.

Understanding the Origin of Selectivity in the Asymmetric Lithiation Reaction of N-Heterocycles: A Theoretical Study

Taban, Keivan
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
67.16%
The natural abundance of the N-heterocycle containing compounds has pushed the synthetic community toward the invention of new synthetic methods that result in the structural diversity of N-heterocycles. Among this, is the efficient and highly selective diamine mediated asymmetric lithiation process. Amongst the diamine chiral ligands, (-)-sparterine, which is a naturally occurring alkaloid proved to be an efficient one. Many successful, good yielding and highly selective lithiation reactions have been accomplished with the mediation by this chiral diamine base. Although, there are some examples of experimental and theoretical mechanistic studies in the literature, there is a lack of detailed understanding as to how it exactly induces the chirality. In this thesis is described a systematic investigation of how (-)-sparteine influences the stereoselectivity in the course of asymmetric lithiation reaction. This led us to the establishment of the function of A-ring’s β-CH2 effect and D-ring effect. Consequently, the importance of the A-ring and D-ring portions of (-)-sparteine in the stereoselectivity is unraveled. Another part of this thesis deals with the asymmetric lithiation of BF3-activated N,N- dimethylaminoferrocene in the presence of (1R...

Diastereoselective Synthesis of Planar Chiral N-Substituted Ferrocenes Derived from Epimeric Imidazolones and their Application to Asymmetric Hydrogenation of Quinolines

John, Joshni
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
37.03%
This thesis describes the synthesis and use of an N-substituted ferrocene bearing a proline-derived chiral directing group and diastereoselective lithiation-electrophile quench of the pro-Sp hydrogen of the ferrocene to give planar chiral products in >95:5 dr. The auxiliary group is found to be stable to lithium bases of types RLi and R2NLi giving the same diastereoselectivity. The anti- epimer of the previously mentioned syn auxiliary induces lithiation of pro Rp rather than pro Sp hydrogen in >95:5 dr. Upon electrophile quench and elimination, the enantiomer of the syn-derived planar chiral imidazolone is obtained. Hence, this method provides a practical way to prepare planar chiral enantiomers in this series without the use of a more expensive D-proline derived starting material. The syn and anti epimers have β, γ-stereogenic centers and the origin of stereoselectivity in lithiation appears to be driven by the conformational bias exerted by the β-silyloxy moiety in each chiral auxiliary. In the thesis, this conclusion is supported using insensitivity of lithiation selectivity to the bulkiness of the base, comparison of enantiomers, deuteration experiments, nOe difference studies and computational modeling of the ground states and lithiation transition states for both substrates. The products are then converted to ligand precursors to make iridium and rhodium complexes. Among them...

New methods for the synthesis of diynyl, diyndiyl and bis(diyndiyl) ruthenium (II) complexes.

Scoleri, Nancy
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2008
Relevância na Pesquisa
16.42%
Chapter One outlines the different methods described in the literature for the synthesis of diynyl, symmetric and asymmetric diyndiyl complexes. The extension to complexes containing a central bridging group within the carbon chain is also introduced with the description of two different linking groups, either an organic or organometallic moiety. A brief overview of molecular electronics and one method of evaluation of electronic communication, cyclic voltammetry, are also addressed. Chapter Two describes the synthesis of novel symmetric and asymmetric bis(diyndiyl) ruthenium(II) complexes of general formula {LnM}-C≡CC≡C-{M”L”p}- C≡CC≡C-{M’L’m}, featuring two transition metal fragments linked by either a Ru(dppe)2 moiety or a trinuclear copper(I) or silver(I) cluster M3(μ-dppm)3 (M = Cu, Ag). Through the use of cyclic voltammetry, it was shown that the inclusion of these three particular bridging groups allows electronic communication between the two terminal end-groups. The chemistry of the starting material trans-Ru(C4H)2(dppe)2 (1) is also described, forming novel complexes when reacted with AuCl(PPh3) or TCNE. Chapter Three describes a new convenient synthetic route to diynyl and diyndiyl ruthenium(II) complexes. Lithiation of the ruthenium(II) diynyl complexes Ru(C≡CC≡CH)(dppe)Cp* and Ru(C≡CC≡CH)(PPh3)2Cp with n-BuLi yields the lithium complexes Ru(C≡CC≡CLi)(dppe)Cp* and Ru(C≡CC≡CLi)(PPh3)2Cp. The most favorable conditions for their formation are examined by using NMR spectroscopy and different assay reactions. These lithium species are further reacted with a range of metal halides to give new asymmetric diyndiyl complexes of general formula [Ru](C≡CC≡C){MLn} (where [Ru] = Ru(dppe)Cp*...

Stereoselective synthesis of substituted hexahydro-3a,4a-diazacyclopentaphenanthren-4-ones and aminoferrocenes

Zaifman, Joshua David
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
36.89%
This thesis explored the development of several methodologies for the stereoselective construction of ligand frameworks and some of their applications. The first segment concerns the application of an enantioselective lithiation at an Sp3_ hybridized position adjacent to nitrogen by means of the widely used and typically highly effective enantioselective lithiation with ( -)-sparteine. This investigation was intended to develop a method to install chirality into a system that would be converted into a family of diaminoylidenes for use as phosphine mimics in transition metal catalysis or as nucleophilic reagents. Molecular modeling of the system revealed some key interactions between the substrate and (-)-sparteine that provided general insight into the diamine's mode of action and should lend some predictive value to its future applications. The second portion focuses on the development of methods to access 1,2- disubstituted aminoferrocenes, an underexplored class of metallocenes possessing planar chirality. Two routes were examined involving a diastereoselective and an enantioselective pathway, where the latter method made use of the first BF3-mediated lithiation-substitution to install planar chirality. Key derivatives such as 1...

Rescaling of metal oxide nanocrystals for energy storage having high capacitance and energy density with robust cycle life

Jeong, Hyung Mo; Choi, Kyung Min; Cheng, Tao; Lee, Dong Ki; Zhou, Renjia; Ock, Il Woo; Milliron, Delia J.; Goddard, William A., III; Kang, Jeung Ku
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 30/06/2015
Relevância na Pesquisa
16.49%
Nanocrystals are promising structures, but they are too large for achieving maximum energy storage performance. We show that rescaling 3-nm particles through lithiation followed by delithiation leads to high-performance energy storage by realizing high capacitance close to the theoretical capacitance available via ion-to-atom redox reactions. Reactive force-field (ReaxFF) molecular dynamics simulations support the conclusion that Li atoms react with nickel oxide nanocrystals (NiO-n) to form lithiated core–shell structures (Ni:Li_2O), whereas subsequent delithiation causes Ni:Li_2O to form atomic clusters of NiO-a. This is consistent with in situ X-ray photoelectron and optical spectroscopy results showing that Ni^(2+) of the nanocrystal changes during lithiation–delithiation through Ni^0 and back to Ni^(2+). These processes are also demonstrated to provide a generic route to rescale another metal oxide. Furthermore, assembling NiO-a into the positive electrode of an asymmetric device enables extraction of full capacitance for a counter negative electrode, giving high energy density in addition to robust capacitance retention over 100,000 cycles.

Development of a Strategy for the Asymmetric Synthesis of Polycyclic Polyprenylated Acylphloroglucinols via N-Amino Cyclic Carbamate Hydrazones: Application to the Total Synthesis of (+)-Clusianone;

Garnsey, Michelle R.; Lim, Daniel; Yost, Julianne M.; Coltart, Dr Don
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Publicado em //2010 EN_US
Relevância na Pesquisa
36.42%
A broadly applicable asymmetric synthetic strategy utilizing N-amino cyclic carbamate alkylation that provides access to the various stereochemical permutations of a common structural motif found in many polycyclic polyprenylated acylphloroglucinols is described. The utility of this methodology is demonstrated through the first asymmetric total synthesis of the antiviral agent (+)-clusianone.