Download or read book Development of Selective and Catalytic Arylation Methods for Sp2 and Sp3 C H Bonds in Complex Organic Molecules written by Bengü Sezen and published by . This book was released on 2005 with total page 926 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Sustainable C sp3 H Bond Functionalization written by Jin Xie and published by Springer. This book was released on 2016-02-29 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights major achievements made in the last five years concerning sustainable C(sp3)-H bond functionalization and offers a promising and emerging tool-kit for organic synthesis. The book is divided into three chapters demonstrating key advances in C(sp3)-H bond functionalization. Chapter 1 reviews transition-metal-catalyzed C(sp3)-H bond functionalization using different directing groups, while Chapter 2 addresses the new methods of transition-metal-catalyzed and metal-free C(sp3)-H bond functionalization without directing groups, in addition to briefly highlighting redox-neutral C(sp3)-H bond functionalization. In closing, Chapter 3 examines visible-light photoredox catalysis, an emerging and highly sustainable C(sp3)-H bond functionalization strategy. The book offers an intriguing and useful reference guide for a broad readership working and/or interested in the fields of organic, organometallic, and green chemistry.

Download or read book Amination and Formation of sp2 C N Bonds written by Marc Taillefer and published by Springer. This book was released on 2013-12-12 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: Palladium-Catalyzed sp2C–N Bond Forming Reactions: Recent Developments and Applications. Metal-catalyzed C(sp2)-N bond formation.- Recent Developments in Recyclable Copper Catalyst Systems for C−N Bond Forming Cross-Coupling Reactions Using Aryl Halides and Arylboronic Acids. Assembly of N-containing heterocycles via Pd and Cu-catalyzed C-N bond formation reactions. Copper-Catalyzed C(aryl)-N Bond Formation.

Download or read book Palladium Catalyzed C sp2 C sp3 Bond Formation written by Sophie Rousseaux and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Palladium-catalyzed reactions for carbon-carbon bond formation have had a significant impact on the field of organic chemistry in recent decades. Illustrative is the 2010 Nobel Prize, awarded for "palladium-catalyzed cross couplings in organic synthesis", and the numerous applications of these transformations in industrial settings. This thesis describes recent developments in C(sp2)-C(sp3) bond formation, focusing on alkane arylation reactions and arylative dearomatization transformations. In the first part, our contributions to the development of intramolecular C(sp3)-H arylation reactions from aryl chlorides are described (Chapter 2). The use of catalytic quantities of pivalic acid was found to be crucial to observe the desired reactivity. The reactions are highly chemoselective for arylation at primary aliphatic C-H bonds. Theoretical calculations revealed that C-H bond cleavage is facilitated by the formation of an agostic interaction between the palladium centre and a geminal C-H bond. In the following section, the development of an alkane arylation reaction adjacent to amides and sulfonamides is presented (Chapter 3). The mechanism of C(sp3)-H bond cleavage in alkane arylation reactions is also addressed through an in-depth experimental and theoretical mechanistic study. The isolation and characterization of an intermediate in the catalytic cycle, the evaluation of the roles of both carbonate and pivalate bases in reaction mechanism as well as kinetic studies are reported. Our serendipitous discovery of an arylation reaction at cyclopropane methylene C-H bonds is discussed in Chapter 4. Reaction conditions for the conversion of cyclopropylanilines to quinolines/tetrahydroquinolines via one-pot palladium(0)-catalyzed C(sp3)-H arylation with subsequent oxidation/reduction are described. Initial studies are also presented, which suggest that this transformation is mechanistically unique from other Pd catalyzed cyclopropane ring-opening reactions. Preliminary investigations towards the development of an asymmetric alkane arylation reaction are highlighted in Chapter 5. Both chiral carboxylic acid additives and phosphine ligands have been examined in this context. While high yields and enantiomeric excesses were never observed, encouraging results have been obtained and are supported by recent reports from other research groups. Finally, in part two, the use of Pd(0)-catalysis for the intramolecular arylative dearomatization of phenols is presented (Chapter 7). These reactions generate spirocyclohexadienones bearing all-carbon quaternary centres in good to excellent yields. The nature of the base, although not well understood, appears to be crucial for this transformation. Preliminary results in the development of an enantioselective variant of this transformation demonstrate the influence of catalyst activation on levels of enantiomeric excess.

Download or read book Photochemical and Electrochemical Activation Strategies of C sp3 Based Building Blocks for Organic Synthesis written by Su Yong Go and published by Springer Nature. This book was released on with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Radical Strategies for hetero benzylic C sp3 H Functionalization and Cross Coupling written by Dung Le Golden and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: C-H functionalization reactions are among the most useful and synthetically applicable approaches to access structurally complex organic molecules, including pharmaceuticals and agrochemicals. While methods promoting functionalization and cross coupling of C(sp2)-H bonds have found broad applications, a growing number of reactions have focused on functionalizing C(sp3)-H bonds to incorporate three-dimensionality and expand the chemical space. Radical C-H functionalization reactions initiated by hydrogen-atom transfer and proceeding via radical intermediates introduce strategic opportunities to functionalize C(sp3)-H bonds. In addition to the commonly seen radical-chain and biomimetic radical-rebound mechanisms, radical-relay reactions provide the basis for versatile C-H cross-coupling methods with diverse partners. This thesis discloses our recent development of radical-relay and radical-chain (hetero)benzylic C(sp3)-H functionalization and their synthetic utility in accessing three-dimensional chemical space. Chapter 2 discussed our recent development of a copper-catalyzed benzylic C-H esterification reaction enabled by a "photochemical redox buffering" strategy using tert-butyl peroxybenzoate as the oxidant. Copper(I)/peroxide (or Kharasch-Sosnovsky-typed) reactions historically require excess of C-H substrates and forcing reaction conditions, leading to poor synthetic applicability. Copper(I) catalysts interact rapidly with peroxide-based oxidants, resulting in a pool of inactive copper(II) species, which are incapable of activating oxidants. Our recent efforts in copper/NFSI-catalyzed radical relay functionalization and cross coupling of benzylic C(sp3)-H bonds revealed a ''redox buffering'' strategy enabling the controlled regeneration of copper(I). For copper/NFSI systems, we have identified that certain nucleophiles (i.e. cyanides and arylboronic acids) can promote the reduction of CuII to CuI, whereas nucleophiles like alcohols and azoles requires additional chemical reductants (i.e. dialkylphosphites) to promote ''redox buffering.'' To address the issues with copper/peroxide system, we have developed a 2,2'-biquinoline/copper-catalyzed reaction under photoirradiation to promote benzylic esterification using limiting C-H substrates. Mechanistic interrogation revealed that light promoted carboxylate-to-copper charge transfer enables the regeneration of copper(I) catalyst, similar to the aforementioned ''redox buffering'' approach. Chapter 3 disclosed our recently developed chlorination/ diversification sequence of heterobenzylic C(sp3)-H bonds in 3-alkylpyridines via radical chain. Alkylpyridines are important and prevalent classes of substrates in medicinal chemistry with the (hetero)benzylic C-H bonds having similar bond dissociation energies to alkylarenes. However, copper/NFSI-catalyzed reactions are unsuccessful in accessing these C-H bonds due to the deleterious reactivity between the pyridyl nitrogen atom and NFSI. While chlorination of 2- and 4-alkylpyridines can be achieved using a polar activation strategy, heterobenzylic C-H bonds of 3-alkylpyridines are more amenable to radical-based chlorination. Experimental and density functional theory identified an N-chlorosulfonamide reagent for selective chlorination at the heterobenzylic C-H site. Subsequent diversification of heterobenzyl chlorides with a broad scope of nucleophiles enabled facile access to complex cross-coupled products. This method should find broad application for building block modification and library synthesis in drug discovery. Chapter 4 detailed our investigation in copper/NFSI-catalyzed fluorination of benzylic C-H bonds followed by diversification with various nucleophiles. Redox buffering promoted by addition of boron-based reductants enabled successful fluorination with limiting C-H substrates. Benzyl fluorides were subsequently subjected to nucleophilic displacement catalyzed by Lewis acidic additives, affording C-O, C-N, and C-C bond formations. This method inspired later developments of other radical halogenation/diversification methods to functionalize (hetero)benzylic C-H bonds. Chapter 5 disclosed our development of a copper/NFSI-catalyzed cross couplings of benzylic C(sp3)-H bonds and azoles enabled by redox buffering. In addition to excellent benzylic selectivity, N-site selectivity of azoles was achieved by modifying the reaction conditions. Diverse N-H heterocycles were compatible coupling partners, including pyrazoles, purines, and sultams. The ability to access both regioisomers of azoles via a cross coupling array validated the synthetic utility of this method in pharmaceutical research. Collectively, radical (hetero)benzylic C(sp3)-H functionalization contributed to a growing number of methods in accessing more three-dimensional chemical space. Mechanistic insights from these reactions will enable further development of more synthetically useful methodologies. Additionally, the synthetic applications should allow chemists to assemble compound libraries with higher complexity and expand the accessible chemical space.

Download or read book Photochemical and Electrochemical Activation Strategies of C sp3 Based Building Blocks for Organic Synthesis written by Su Yong Go and published by Springer. This book was released on 2024-04-21 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book addresses novel C(sp3)-C(sp2) and C(sp3)-heteroatom bond-forming reactions. Two strategies are given in the book using photoredox or electrochemical methods. The first strategy describes that the hydroalkylation of alkynes via photoredox-mediated Ni/Ir dual catalysis produces trisubstituted alkenes as versatile synthetic building blocks for the synthesis of pharmaceutical agents and natural products. High regioselectivity and E/Z-selectivity were achieved by introducing silyl groups that can provide steric and electronic effects to these selectivities with extensive opportunities for post-functionalization. The second strategy enables the development of C(sp3)-heteroatom bond-forming reactions through the electrochemical activation of C(sp3)-B bonds. The bonding of heteroatoms to carbon atoms has been an enduring subject of investigation for organic chemists. The function of most molecules is mainly determined by heteroatoms attached to the carbon atom, althoughthe backbone structure of organic compounds comprises carbon fragments.

Download or read book C H Bond Activation and Catalytic Functionalization I written by Pierre H. Dixneuf and published by Springer. This book was released on 2015-12-18 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Topics in Organometallic Chemistry presents critical overviews of research results in organometallic chemistry. As our understanding of organometallic structure, properties and mechanisms increases, new ways are opened for the design of organometallic compounds and reactions tailored to the needs of such diverse areas as organic synthesis, medical research, biology and materials science. Thus the scope of coverage includes a broad range of topics of pure and applied organometallic chemistry, where new breakthroughs are being achieved that are of significance to a larger scientific audience. The individual volumes of Topics in Organometallic Chemistry are thematic. Review articles are generally invited by the volume editors. All chapters from Topics in Organometallic Chemistry are published OnlineFirst with an individual DOI. In references, Topics in Organometallic Chemistry is abbreviated as Top Organomet Chem and cited as a journal.

Download or read book Part 1 written by Derek Schipper and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Part 1: Transition-metal-catalyzed direct transformations of aromatic C-H bonds are emerging as valuable tools in organic synthesis. These reactions are attractive because of they allow for inherently efficient construction of organic building blocks by minimizing the pre-activation of substrates. Of these processes, direct arylation has recently received much attention due to the importance of the biaryl core in medicinal and materials chemistry. Also, alkyne hydroarylation has garnered interest because it allows for the atom-economical synthesis of functionalized alkenes directly from simple arenes and alkynes. Described in this thesis are number of advancements in these areas. First, palladium catalyzed direct arylation of azine N-oxides using synthetically important aryl triflates is described. Interesting reactivity of aryl triflates compared to aryl bromides was uncovered and exploited in the synthesis of a compound that exhibits antimalarial and antimicrobial activity. Also reported is the efficient, direct arylation enabled (formal) synthesis of six thiophene based organic electronic materials in high yields using simple starting materials. Additionally, the site-selective direct arylation of both sp2 and sp3 sites on azine N-oxide substrates is described. The arylation reactions are carried out in either a divergent manner or a sequential manner and is applied to the synthesis of the natural products, Papaverine and Crykonisine. Mechanistic investigations point towards the intimate involvement of the base in the mechanism of these reactions. Next, the rhodium(III)-catalyzed hydroarylation of internal alkynes is described. Good yields are obtained for a variety of alkynes and arenes with excellent regioselectivity for unsymmetrically substituted alkynes. Mechanistic investigations suggest that this reaction proceeds through arene metalation with the cationic rhodium catalyst, which enables challenging intermolecular reactivity. Part 2: Access to single enantiomer compounds is a fundamental goal in organic chemistry and despite remarkable advances in enantioselective synthesis, their preparation remains a challenge. Kinetic resolution of racemic products is an important method to access enantioenriched compounds, especially when alternative methods are scarce. Described in this thesis is the resolution of tertiary and secondary alcohols, which arise from ketone and aldehyde aldol additions. The method is technically simple, easily scalable, and provides tertiary and secondary alcohols in high enantiomeric ratios. A rationale for the unique reactivity/selectivity associated with (1S,2R)-N-methylephedrine in the resolution is proposed. Organocatalysis is a rapidly developing, powerful field for the construction of enantioenriched organic molecules. Described here is a complimentary class of organocatalysis using simple aldehydes as temporary tethers to perform challenging formally intermolecular reactions at room temperature. This strategy allows for the enantioselective, intermolecular cope-type hydroamination of allylic amines with hydroxyl amines. Also, interesting catalytic reactivity for dichloromethane is revealed.

Download or read book Palladium catalyzed Direct Arylation Via Sp2 and Sp3 C H Activation of Hetero aromatics and Hydrocarbons for C C Bond Formation written by Liqin Zhao and published by . This book was released on 2014 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: During this thesis, we were interested in the sp2 and sp3 C-H bond activation catalyzed by palladium catalysts for the preparation of (hetero)aryl-aryls and biaryls. This method is considered as cost effective and environmentally attractive compared to the classical couplings such as Suzuki, Heck, or Negishi. First we described the palladium-catalyzed direct C2-arylation of benzothiophene in the absence of phosphine ligand with high selectivity. We also demonstrated that it is possible to active both C2 and C5 C-H bonds for access to 2,5-diarylated compounds in one step, and also to non-symmetrically substituted 2,5-diarylpyrroles via sequential C2 arylation followed by C5 arylation. We also studied the reactivity of polychlorobenzenes via palladium-catalyzed C-H activation. We finally examined the palladium-catalysed selective sp2 and sp3 C-H bond activation of guaiazulene. The selectivity depends on the solvent and base: sp2 C2-arylation (KOAc in ethylbenzene), sp2 C3-arylation (KOAc in DMAc) and sp3 C4-Me arylation (CsOAc/K2CO3 in DMAc). Through this method, a challenging sp3 C-H bond was activated.

Download or read book C sp2 C sp3 Cross coupling of Aryl Halides and Active C sp3 H Bonds Via Dual Catalysis written by Nicholas Armada and published by . This book was released on 2019 with total page 51 pages. Available in PDF, EPUB and Kindle. Book excerpt: Convenient catalytic methodologies that can facilitate the formation of C-C bonds are undoubtedly of great interest in synthetic organic chemistry. Recent reports in literature have showcased hybrid catalytic methods that couple Ni-redox catalysis and photocatalysis to enable C-H activation of tetrahydrofuran (THF) and subsequent cross-coupling with aryl halides in appreciable yields and under relatively mild reaction conditions.1-2 However, these studies used expensive, heavy metal-containing photocatalysts and both report difficulty obtaining low-specificity across their scopes of aryl-halides. The following report will shed light on a class of photo-excitable small organic molecules that – in conjunction with a catalytic Ni-redox cycle – can be used to catalyze C-C cross-coupling reactions between THF and aryl chlorides, bromides, and iodides with yields comparable to the aforementioned reports. After screening several organic molecules with suspected photoactivity and optimization of the reaction conditions, several benzophenone derivatives were found to catalyze the cross-coupling reaction in yields up to 97%. Mechanistic investigations suggest that this reaction proceeds through a tandem catalytic pathway that involves a photocatalyzed hydrogen atom transfer/proton-coupled electron transfer (HAT/PCET) process and a Ni-mediated oxidative addition/reductive elimination cross-coupling process.

Download or read book Palladium catalyzed C H Bond Functionalization of Heterocycles and Amines written by Enrico Tapire Nadres and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Palladium-catalyzed functionalization of C-H bonds is becoming an important synthetic tool that allows the preparation of desired substances in fewer steps and higher yields compared to traditional synthetic routes. The C-H bonds can be directly converted to C-C or C-heteroatom bonds. However, the ubiquity of C-H bonds in organic compounds can lead to problems in chemo- and regioselectivity. In heterocycles, the control of regioselectivity of the reaction is governed by the difference in acidity of the heterocyclic ring C-H bonds. An economical method for the arylation of C-H bonds of pyrroles and furans by aryl chlorides was developed. The method employs a palladium acetate catalyst, 2-(dicyclohexylphosphino)biphenyl ligand, and an inorganic base. Electron-rich, electron-poor, and heterocyclic aryl chloride coupling partners can be used and arylated heterocycles are obtained in moderate to good yields. The functionalization of sp2 and sp3 C-H bonds can be promoted by the use of directing groups that coordinate the Pd catalyst and activate the desired C-H functionalities. Use of Pd(OAc)2 in conjunction with cesium acetate or potassium carbonate bases allows functionalization of sp2 and sp3 C-H bonds in amides possessing picolinic acid directing group. Stoichiometric silver additive is not required in contrast with previously published procedure. Arylations are effective for sp2 as well as primary and secondary sp3 C-H bonds. Alkylations of sp2 C-H bonds are successful in most cases. Both primary and secondary alkyl iodides are reactive but secondary alkyl iodides afford low yields. Alkylation of sp2 C-H bonds is low yielding and the reaction requires further optimization. Alkyl and aryl iodides as well as benzyl bromides are reactive. Aryl and alkyl bromides afford no product. Direct conversion of C-H bonds to C-N bonds was also developed. Pd-catalyzed method for pyrrolidine, indoline, and isoindoline formation by cyclization via C-H/N-H coupling is presented. The method employs a picolinamide directing group, PhI(OAc)2 oxidant, and toluene solvent at 80-120 °C. Cyclization is effective for sp2 as well as aliphatic and benzylic sp3 C-H bonds.

Download or read book Solvent controlled Switch of Selectivity Between Sp2 and Sp3 C H Bond Activation by Platinum II written by Alexander William Garner and published by . This book was released on 2010 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cyclometalation reactions have been studied intensely for the past few decades, especially those containing palladium. The factors that control the process of the C-H bond activation, however, are not yet completely understood. C-H bonds are ever-present in organic molecules, but the vast majority of them cannot be exploited for chemical reactions due to their inert and stable nature. Early attempts to activate these bonds led to very complicated mixtures of products, and therefore not an acceptable means of C-H activation due to poor selectivity. Controlling the selectivity of a reaction is one of the most important issues surrounding synthetic chemistry. It is generally recognized that aromatic C-H bonds are more likely to undergo activation by platinum complexes. However, recently it has been illustrated that there is a delicate balance between sp2 and sp3 C-H bond activation in a platinum (II) complex system. In this study, the solvent-controlled switch of selectivity between sp2 and sp3 C-H bond activation in platinum (II) complex systems will be discussed. Ligands L1 through L3 were designed and synthesized to test the selectivity of cycloplatination of a reaction with potassium tetrachloroplatinate (II) in two different solvents, acetonitrile and glacial acetic acid. It was found that in each of the solvents used, a different isomer was produced from the complexation reaction. Reactions of L1 through L3 with potassium tetrachloroplatinate (II) in acetonitrile produced the sp2 substituted isomer (1B-3B), while the same reaction performed in glacial acetic acid formed the sp3 substituted isomer (1A-3A). It was determined through mechanistic studies that the sp2 substituted isomer is a kinetically controlled product, while the sp3 substituted isomer is a thermodynamically controlled product. Also, it was found that the ratio of products depends on time, where as more time goes by the thermodynamically stable product begins to predominate. Other issues examined in this study were the side reactions that occurred during the complexation of ligands L2 and L3. These side products were due to C-C bond cleavage in L2 and C-N bond cleavage in L3. These side products were characterized and studied in their own right.

Download or read book Tunable Selective C sp3 h Aminations Via Silver catalyzed Nitrene Transfer Reactions written by Minxue Huang and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract The ubiquitousness of amines in pharmaceuticals, agrochemicals, ligands for transition metals, biologically active natural compounds and functional materials is the strong motivation of organic chemists to develop highly efficient yet mild reactions to install valuable C-N bonds. Transition metal-catalyzed nitrene transfer is a convenient strategy to directly functionalize a hydrocarbon substrate with amine functionality. For all means of C(sp3)−H amination, one of the core issues hampering their developments is the difficulty to differentiate multiple C-H bonds that have nearly identical electronic properties and bond strengths. As described in this work, this problem is addressed through utilizing Ag catalysts based on deliberately designed ligands, which is inspired by mechanism study, to achieve tunable site-, regio-, and stereoselectivity. Chapter 1 gives a brief introduction by providing a selected review of literature on transition metal-catalyzed C(sp3)−H aminations reactions via nitrene transfer, emphasizing the common problems associated with reactivity and selectivity. Chapter 2 demonstrates both the solid and solution-state behavior of diverse Ag(I) catalysts competent for nitrene transfor through X-ray characterization and NMR studies, and discusses our understanding of how the ligand identity manipulate those behavior of corresponding Ag(I) complexes. Chapter 3 describes both computational models and experimental probes revealing possible roles of noncovalent interactions in directing the site-selectivity of silver-catalyzed C−H aminations. Chapter 4 addresses the fluxional behavior of Ag(tpa)OTf in solution potentially hampering its site-selectivity in nitrene insertion by a rigid ligand. Finally, chapter 5 provide a novel silver catalytic system which is able to tune the selectivity between [beta] or [gamma] C-H bond amindation of an easily prepared carbamate, overriding substrate control, and amidate traditionally difficult primary aliphatic C-H bonds. Further experimental and computational studies revealed some mechanistic insights into this system. Additional, synthetic utility of this methodology was proven by the late-stage functionalization of natural products and drug-like molecules, even in gram-scale.

Download or read book Metal catalyzed Allylic Substitution Arylation with Weakly Acidic C sp3 H Bonds written by Sheng-Chun Sha and published by . This book was released on 2015 with total page 612 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation describes two methods to functionalization of weakly acidic C(sp3 )-H bonds, allylic substitution and arylation, with success on both Pd or Ni as catalyst. The first two chapters of the dissertation describe transition metal catalyzed allylic substitution with diarylmethane pronucleophiles (pka up to 32.3). Diarylmethane are among the least acidic pronucleophiles used to date in transition metal catalyzed allylic substitution reactions (Tsuji-Trost reaction). In Chapter 1, we successfully demonstrated the cut-off between soft and hard nucleophiles for Pd-catalyzed allylic substitution should be raised from pK a of 25 to at least 32. This discovery expands the scope of soft nucleophiles, and suggests the possibility of developing asymmetric allylic substitution for more weakly acidic substrates. In chapter 2, we further applied Ni catalyzed allylic substitution on diarylmethanes to develop a supplement to the Pd version. We were able to prove the same nucleophile behaves as soft nucleophile in both Pd and Ni catalyzed allylic substitution. More importantly, Ni has always been paired with hard nucleophiles to perform asymmetric allylic substitution, but we were able to identify a chiral ligand SL-J204-1 to do asymmetric allylic substitution using Ni as catalyst with soft nucleophile (diarylmethane) and got up to 91% yield with 92% e.e. This result suggests Ni catalyzed asymmetric allylic substitution can be done with both soft and hard nucleophiles, which makes Ni an appealing choice other than Pd for transition metal catalyzed allylic substitution. The second part of the dissertation focus on the arylation of weakly acidic substrates such as carboxylate and toluene (pKa = 44±1). The same strategy DCCP is applied to both types of substrates, through direct metalation and subsequent cross coupling of benzylic C(sp3 )-H bonds. Chapter 3 describes alpha arylation of carboxylic acids. Significant works on alpha arylation have been done on carbonyl group containing substrates such as ketone, aldehyde, ester and amide. However, examples on alpha arylation of carboxylic acids remain scarce due to the difficulty of generating dienolate. We successfully demonstrated the reversible deprotonation could be applied to benzyl carboxylic acids and identified a catalyst system that could further cross couple dienolate with aryl chlorides and bromides. Finally, chapter 4 describes a direct arylation of toluene derivatives benzylic C-H bond. We used an unique catalyst with deprotonatable ligand NIXANTPHOS. The deprotonated ligand would carry the counter cation (alkali metal) of the base through out the catalytic cycle. Previously, our group had developed an activation strategy using [velar nasal]6 -coordination of arenes to tricarbonylchromium to activate toluene benzylic C-H bond. In this chapter, we developed a new strategy using [velar nasal]6 -coordination of toluene to potassium to activate benzylic C-H bond to perform DCCP. The mechanistic study showed the crucial role of potassium cation. The method is valuable in two points: 1. Direct arylation of toluene derivatives provides a strong tool transforming cheap, inert molecule to useful molecule diarylmethane. 2. The unique mechanism would inspire us to design more heterobimetallic systems with deprotonatable ligands to activate different kind of molecules. (Abstract shortened by UMI.).

Download or read book C H Activation for Asymmetric Synthesis written by Françoise Colobert and published by John Wiley & Sons. This book was released on 2019-11-11 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides, in one handbook, comprehensive coverage of one of the hottest topics in stereoselective chemistry Written by leading international authors in the field, this book introduces readers to C-H activation in asymmetric synthesis along with all of its facets. It presents stereoselective C-H functionalization with a broad coverage, from outer-sphere to inner-sphere C-H bond activation, and from the control of olefin geometry to the induction of point, planar and axial chirality. Moreover, methods wherein asymmetry is introduced either during the C-H activation or in a different elementary step are discussed. Presented in two parts?asymmetric activation of C(sp3)-H bonds and stereoselective synthesis implying activation of C(sp2)-H bonds?CH-Activation for Asymmetric Synthesis showcases the diversity of stereogenic elements, which can now be constructed by C-H activation methods. Chapters in Part 1 cover: C(sp3)-H bond insertion by metal carbenoids and nitrenoids; stereoselective C-C bond and C-N bond forming reactions through C(sp3)?H bond insertion of metal nitrenoids; enantioselective intra- and intermolecular couplings; and more. Part 2 looks at: C-H activation involved in stereodiscriminant step; planar chirality; diastereoselective formation of alkenes through C(sp2)?H bond activation; amongst other methods. -Covers one of the most rapidly developing fields in organic synthesis and catalysis -Clearly structured in two parts (activation of sp3- and activation of sp2-H bonds) -Edited by two leading experts in C-H activation in asymmetric synthesis CH-Activation for Asymmetric Synthesis will be of high interest to chemists in academia, as well as those in the pharmaceutical and agrochemical industry.

Download or read book Asymmetric Functionalization of C H Bonds written by Shu-Li You and published by Royal Society of Chemistry. This book was released on 2015-08-13 with total page 433 pages. Available in PDF, EPUB and Kindle. Book excerpt: Asymmetric C-H direct functionalization reactions are one of the most active and fascinating areas of research in organic chemistry due to their significance in the construction of molecular complexity without pre-activation, and the step economy and atom economy features in potential synthetic application. Distinguishing the reactivity among numerous C–H bonds in one single molecule represents one of the most challenging issues in organic synthesis and requires precise reaction design. As such, this field is now receiving increasing attention from researchers. This book provides the first comprehensive review of this field, summarizing the origin, mechanism, scope and applications of the asymmetric C-H bond functionalization reaction. It covers organocatalytic reactions and transition-metal-catalyzed reactions, as well as asymmetric C-H functionalization reactions not described in other books. Written by a leading expert in this field, the book is ideal for postgraduates and researchers working in organic synthesis, catalysis, and organometallic chemistry.