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Asymmetric Synthesis Of Bioactive Lactones And The Development Of A Catalytic Asymmetric Synthesis Of Aryl Ketones
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Book Synopsis Asymmetric Synthesis of Bioactive Lactones and the Development of a Catalytic Asymmetric Synthesis of α-Aryl Ketones by : Robert Doran
Download or read book Asymmetric Synthesis of Bioactive Lactones and the Development of a Catalytic Asymmetric Synthesis of α-Aryl Ketones written by Robert Doran and published by Springer. This book was released on 2015-06-24 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis addresses two fundamental areas in contemporary organic chemistry: synthesis of natural products and catalytic asymmetric synthesis. Firstly, a new methodology, developed by our research group, which allows the asymmetric synthesis of lactones, a structural unit ubiquitous in natural products, was utilised in the synthesis of a number of natural product analogues that showed significant biological activity. Secondly, the development of a catalytic asymmetric synthesis of a key structural motif present in a number of natural products and pharmaceuticals was accomplished. During the course of this work we discovered dual stereo control, which is significant because it allows the configuration of a new stereo centre to be controlled by a simple change of proton source.
Book Synopsis Catalytic Asymmetric Synthesis by : Takahiko Akiyama
Download or read book Catalytic Asymmetric Synthesis written by Takahiko Akiyama and published by John Wiley & Sons. This book was released on 2022-05-27 with total page 798 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytic Asymmetric Synthesis Seminal text presenting detailed accounts of the most important catalytic asymmetric reactions known today This book covers the preparation of enantiomerically pure or enriched chemical compounds by use of chiral catalyst molecules. While reviewing the most important catalytic methods for asymmetric organic synthesis, this book highlights the most important and recent developments in catalytic asymmetric synthesis. Edited by two well-qualified experts, sample topics covered in the work include: Metal catalysis, organocatalysis, photoredox catalysis, enzyme catalysis C–H bond functionalization reactions Carbon–carbon bond formation reactions, carbon–halogen bond formation reactions, hydrogenations, polymerizations, flow reactions Axially chiral compounds Retaining the best of its predecessors but now thoroughly up to date with the important and recent developments in catalytic asymmetric synthesis, the 4th edition of Catalytic Asymmetric Synthesis serves as an excellent desktop reference and text for researchers and students, from upper-level undergraduates all the way to experienced professionals in industry or academia.
Book Synopsis Asymmetric and Selective Biocatalysis by : Jose M. Palomo
Download or read book Asymmetric and Selective Biocatalysis written by Jose M. Palomo and published by MDPI. This book was released on 2019-04-12 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Issue contains one communication, six articles, and two reviews. The communication from Paola Vitale et al. represents a work where whole cells were used as biocatalysts for the reduction of optically active chloroalkyl arylketones followed by a chemical cyclization to give the desired heterocycles. Among the various whole cells screened (baker’s yeast, Kluyveromyces marxianus CBS 6556, Saccharomyces cerevisiae CBS 7336, Lactobacillus reuteri DSM 20016), baker’s yeast provided the best yields and the highest enantiomeric ratios (95:5) in the bioreduction of the above ketones. In this respect, valuable chiral non-racemic functionalized oxygen-containing heterocycles (e.g., (S)-styrene oxide, (S)-2-phenyloxetane, (S)-2-phenyltetrahydrofuran), amenable to be further elaborated on, can be smoothly and successfully generated from their prochiral precursors. Studies about pure biocatalysts with mechanistical studies, application in different reactions, and new immobilization methods for improving their stability were reported in five different articles. The article by Su-Yan Wang et al. describes the cloning, expression, purification, and characterization of an N-acetylglucosamine 2-epimerase from Pedobacter heparinus (PhGn2E). For this, several N-acylated glucosamine derivatives were chemically synthesized and used to test the substrate specificity of the enzyme. The mechanism of the enzyme was studied by hydrogen/deuterium NMR. The study at the anomeric hydroxyl group and C-2 position of the substrate in the reaction mixture confirmed the epimerization reaction via ring-opening/enolate formation. Site-directed mutagenesis was also used to confirm the proposed mechanism of this interesting enzyme. The article by Forest H. Andrews et al. studies two enzymes, benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC), which catalyze the non-oxidative decarboxylation of 2-keto acids with different specificity. BFDC from Pseudomonas putida exhibited very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Zymomonas mobilis showed virtually no activity with benzoylformate (phenylglyoxylate). After studies using saturation mutagenesis, the BFDC T377L/A460Y variant was obtained, with 10,000-fold increase in pyruvate/benzoylformate. The change was attributed to an improvement in the Km value for pyruvate and a decrease in the kcat value for benzoylformate. The characterization of the new catalyst was performed, providing context for the observed changes in the specificity. The article by Xin Wang et al. compares two types of biocatalysts to produce D-lysine L-lysine in a cascade process catalyzed by two enzymes: racemase from microorganisms that racemize L-lysine to give D,L-lysine and decarboxylase that can be in cells, permeabilized cells, and the isolated enzyme. The comparison between the different forms demonstrated that the isolated enzyme showed the higher decarboxylase activity. Under optimal conditions, 750.7 mmol/L D-lysine was finally obtained from 1710 mmol/L L-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. D-lysine yield could reach 48.8% with enantiomeric excess (ee) of 99%. In the article by Rivero and Palomo, lipase from Candida rugosa (CRL) was highly stabilized at alkaline pH in the presence of PEG, which permitted its immobilization for the first time by multipoint covalent attachment on different aldehyde-activated matrices. Different covalent immobilized preparation of the enzyme was successfully obtained. The thermal and solvent stability was highly increased by this treatment, and the novel catalysts showed high regioselectivity in the deprotection of per-O-acetylated nucleosides. The article by Robson Carlos Alnoch et al. describes the protocol and use of a new generation of tailor-made bifunctional supports activated with alkyl groups that allow the immobilization of proteins through the most hydrophobic region of the protein surface and aldehyde groups that allows the covalent immobilization of the previously adsorbed proteins. These supports were especially used in the case of lipase immobilization. The immobilization of a new metagenomic lipase (LipC12) yielded a biocatalyst 3.5-fold more active and 5000-fold more stable than the soluble enzyme. The PEGylated immobilized lipase showed high regioselectivity, producing high yields of the C-3 monodeacetylated product at pH 5.0 and 4 °C. Hybrid catalysts composed of an enzyme and metallic complex are also treated in this Special Issue. The article by Christian Herrero et al. describes the development of the Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A). The complex was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source. The two published reviews describe different subjects with interest in the fields of biocatalysis and mix metallic-biocatalysis, respectively. The review by Anika Scholtissek et al. describes the state-of-the-art regarding ene-reductases from the old yellow enzyme family (OYEs) to catalyze the asymmetric hydrogenation of activated alkenes to produce chiral products with industrial interest. The dependence of OYEs on pyridine nucleotide coenzyme can be avoided by using nicotinamide coenzyme mimetics. In the review, three main classes of OYEs are described and characterized. The review by Yajie Wang and Huimin Zhao highlights some of the recent examples in the past three years that combine transition metal catalysis with enzymatic catalysis. With recent advances in protein engineering, catalyst synthesis, artificial metalloenzymes, and supramolecular assembly, there is great potential to develop more sophisticated tandem chemoenzymatic processes for the synthesis of structurally complex chemicals. In conclusion, these nine publications give an overview of the possibilities of different catalysts, both traditional biocatalysts and hybrids with metals or organometallic complexes to be used in different processes—particularly in synthetic reactions—under very mild reaction conditions.
Book Synopsis The Asymmetric Synthesis of Beta-lactones by Catalytic Asymmetric Homodimerization of Ketoketenes by : Pei-Hsun Wei
Download or read book The Asymmetric Synthesis of Beta-lactones by Catalytic Asymmetric Homodimerization of Ketoketenes written by Pei-Hsun Wei and published by . This book was released on 2010 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Catalytic Methods in Asymmetric Synthesis by : Michelangelo Gruttadauria
Download or read book Catalytic Methods in Asymmetric Synthesis written by Michelangelo Gruttadauria and published by John Wiley & Sons. This book was released on 2011-07-05 with total page 720 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers advances in the methods of catalytic asymmetric synthesis and their applications. Coverage moves from new materials and technologies to homogeneous metal-free catalysts and homogeneous metal catalysts. The applications of several methodologies for the synthesis of biologically active molecules are discussed. Part I addresses recent advances in new materials and technologies such as supported catalysts, supports, self-supported catalysts, chiral ionic liquids, supercritical fluids, flow reactors and microwaves related to asymmetric catalysis. Part II covers advances and milestones in organocatalytic, enzymatic and metal-based mediated asymmetric synthesis, including applications for the synthesis of biologically active molecules. Written by leading international experts, this book consists of 16 chapters with 2000 References and illustrations of 560 schemes and figures.
Book Synopsis Catalytic Asymmetric Synthesis by : Iwao Ojima
Download or read book Catalytic Asymmetric Synthesis written by Iwao Ojima and published by Wiley-VCH. This book was released on 1993 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt: Covering catalytic asymmetric synthesis, this book should be of interest to organic, medicinal and pharamaceutical chemists.
Book Synopsis Asymmetric Synthesis of Pharmaceutically Important Lactones and Cyclic Ketones by : Sophie Connolly
Download or read book Asymmetric Synthesis of Pharmaceutically Important Lactones and Cyclic Ketones written by Sophie Connolly and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Asymmetric Synthesis of Non-Proteinogenic Amino Acids by : Ashot S. Saghyan
Download or read book Asymmetric Synthesis of Non-Proteinogenic Amino Acids written by Ashot S. Saghyan and published by John Wiley & Sons. This book was released on 2016-11-14 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: Authored by two internationally recognized experts with an excellent track record, this much-needed reference summarizes latest research in the rapidly developing field of stereoselective synthesis of enantiomerically enriched amino acids, particularly of non-proteinogenic origin. It highlights several different catalytic and stoichiometric asymmetric methods for their synthesis and also provides information on origin, biological properties, different synthetic strategies and important applications in medicine and pharmacology. Essential reading for synthetic chemists working in the field of asymmetric synthesis, natural products and peptide synthesis, stereochemistry, medicinal chemistry, biochemistry, pharmacology, and biotechnology.
Book Synopsis Asymmetric and Selective Biocatalysis by : Cesar Mateo
Download or read book Asymmetric and Selective Biocatalysis written by Cesar Mateo and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This Issue contains one communication, six articles, and two reviews. The communication from Paola Vitale and others represents a work where whole cells were used as biocatalysts for the reduction of optically active chloroalkyl arylketones followed by a chemical cyclization to give the desired heterocycles. Among the various whole cells screened (baker's yeast, Kluyveromyces marxianus CBS 6556, Saccharomyces cerevisiae CBS 7336, Lactobacillus reuteri DSM 20016), baker's yeast provided the best yields and the highest enantiomeric ratios (95:5) in the bioreduction of the above ketones. In this respect, valuable chiral non-racemic functionalized oxygen-containing heterocycles (e.g., (S)-styrene oxide, (S)-2-phenyloxetane, (S)-2-phenyltetrahydrofuran), amenable to be further elaborated on, can be smoothly and successfully generated from their prochiral precursors. Studies about pure biocatalysts with mechanistical studies, application in different reactions, and new immobilization methods for improving their stability were reported in five different articles. The article by Su-Yan Wang and others describes the cloning, expression, purification, and characterization of an N-acetylglucosamine 2-epimerase from Pedobacter heparinus (PhGn2E). For this, several N-acylated glucosamine derivatives were chemically synthesized and used to test the substrate specificity of the enzyme. The mechanism of the enzyme was studied by hydrogen/deuterium NMR. The study at the anomeric hydroxyl group and C-2 position of the substrate in the reaction mixture confirmed the epimerization reaction via ring-opening/enolate formation. Site-directed mutagenesis was also used to confirm the proposed mechanism of this interesting enzyme. The article by Forest H. Andrews and others studies two enzymes, benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC), which catalyze the non-oxidative decarboxylation of 2-keto acids with different specificity. BFDC from Pseudomonas putida exhibited very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Zymomonas mobilis showed virtually no activity with benzoylformate (phenylglyoxylate). After studies using saturation mutagenesis, the BFDC T377L/A460Y variant was obtained, with 10,000-fold increase in pyruvate/benzoylformate. The change was attributed to an improvement in the Km value for pyruvate and a decrease in the kcat value for benzoylformate. The characterization of the new catalyst was performed, providing context for the observed changes in the specificity. The article by Xin Wang and others compares two types of biocatalysts to produce D-lysine L-lysine in a cascade process catalyzed by two enzymes: racemase from microorganisms that racemize L-lysine to give D,L-lysine and decarboxylase that can be in cells, permeabilized cells, and the isolated enzyme. The comparison between the different forms demonstrated that the isolated enzyme showed the higher decarboxylase activity. Under optimal conditions, 750.7 mmol/L D-lysine was finally obtained from 1710 mmol/L L-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. D-lysine yield could reach 48.8% with enantiomeric excess (ee) of 99%. In the article by Rivero and Palomo, lipase from Candida rugosa (CRL) was highly stabilized at alkaline pH in the presence of PEG, which permitted its immobilization for the first time by multipoint covalent attachment on different aldehyde-activated matrices. Different covalent immobilized preparation of the enzyme was successfully obtained. The thermal and solvent stability was highly increased by this treatment, and the novel catalysts showed high regioselectivity in the deprotection of per-O-acetylated nucleosides. The article by Robson Carlos Alnoch and others describes the protocol and use of a new generation of tailor-made bifunctional supports activated with alkyl groups that allow the immobilization of proteins through the most hydrophobic region of the protein surface and aldehyde groups that allows the covalent immobilization of the previously adsorbed proteins. These supports were especially used in the case of lipase immobilization. The immobilization of a new metagenomic lipase (LipC12) yielded a biocatalyst 3.5-fold more active and 5000-fold more stable than the soluble enzyme. The PEGylated immobilized lipase showed high regioselectivity, producing high yields of the C-3 monodeacetylated product at pH 5.0 and 4 °C. Hybrid catalysts composed of an enzyme and metallic complex are also treated in this Special Issue. The article by Christian Herrero and others describes the development of the Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A). The complex was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source. The two published reviews describe different subjects with interest in the fields of biocatalysis and mix metallic-biocatalysis, respectively. The review by Anika Scholtissek and others describes the state-of-the-art regarding ene-reductases from the old yellow enzyme family (OYEs) to catalyze the asymmetric hydrogenation of activated alkenes to produce chiral products with industrial interest. The dependence of OYEs on pyridine nucleotide coenzyme can be avoided by using nicotinamide coenzyme mimetics. In the review, three main classes of OYEs are described and characterized. The review by Yajie Wang and Huimin Zhao highlights some of the recent examples in the past three years that combine transition metal catalysis with enzymatic catalysis. With recent advances in protein engineering, catalyst synthesis, artificial metalloenzymes, and supramolecular assembly, there is great potential to develop more sophisticated tandem chemoenzymatic processes for the synthesis of structurally complex chemicals. In conclusion, these nine publications give an overview of the possibilities of different catalysts, both traditional biocatalysts and hybrids with metals or organometallic complexes to be used in different processes-particularly in synthetic reactions-under very mild reaction conditions.
Book Synopsis Chiral Auxiliaries and Substrate Directable Reactions to Access Highly Functionalised Chiral Lactones by : Iwan Rhydian Davies
Download or read book Chiral Auxiliaries and Substrate Directable Reactions to Access Highly Functionalised Chiral Lactones written by Iwan Rhydian Davies and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the development of chiral auxiliary based methodologies for the asymmetric synthesis of hydroxylated!-lactones and "--Lactones containing multiple contiguous stereocentres. The first chapter introduces the concept of chirality and provides a general overview of the range of strategies available for the preparation of chiral molecules in enantiomerically pure forms. The second chapter critically reviews the range of synthetic methodology that is currently available for the asymmetric synthesis of chiral #-lactones that are either natural products or useful chiral building blocks for synthesis. The third chapter describes the development of novel methodology for the epoxidation/lactonisation of a range of #x1C;-vinyl-syn-aldols to directly afford!-lactones containing up to four contiguous stereocentres in high de. These reactions were shown to proceed via a mechanism whereby hydroxyl-directed diastereoselective epoxidation is followed by intramolecular attack of their!-acyl-oxazolidin-2- one fragment, to directly afford the desired chiral!-lactone. The?self-cleavage? aspect of these reactions was exploited to enable this methodology to be transferred to polymer-support using an immobilised Evans?-oxazolidin-2-one for asymmetric synthesis. Chapter 4 describes the development of a complementary methodology for the asymmetric synthesis of this type of hydroxylated!-lactone based on a strategy involving dihydroxylation of N-acyl-oxazolidin-2-one-#x1C;-vinyl-syn-aldols using catalytic amounts of osmium tetroxide. This methodology was developed as part of a reinvestigation of previously reported dihydroxylation reactions by Dias and coworkers, where we have clearly shown that the stereochemistry of thelactones reported in their paper have been incorrectly assigned. This diastereoselective dihydroxylation methodology has been successfully applied to the asymmetric synthesis of the natural product deoxyribonolactone. Finally, Chapter 5 describes the development of methodology for the asymmetric synthesis of chiral "-lactones containing four contiguous stereocentres of use as potential chiral building blocks for the synthesis of polyketide natural products. In this approach, cyclopropanation of N-acyl-oxazolidin-2-one-#x1C;-vinyl-syn-aldols occurs under the sterodirecting effect of the #x1C;- hydroxyl group to afford cyclopropyl-aldols in very high de. These cyclopropyl-aldols are then ring opened in the presence of mercuric ions, with their N-acyl-oxazolidin-2-one fragment acting as an internal nucleophile, to afford highly functionalised alkyl-mercury species that may be subsequently reduced to afford their corresponding "-lactones in high de.
Book Synopsis Catalytic Asymmetric Synthesis of Allylic Aryl Ethers and Progress Toward the Total Synthesis of Palau'amine, Axinellamines A-D, and Massadine by : Nicole Suzanne White
Download or read book Catalytic Asymmetric Synthesis of Allylic Aryl Ethers and Progress Toward the Total Synthesis of Palau'amine, Axinellamines A-D, and Massadine written by Nicole Suzanne White and published by . This book was released on 2009 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt: In chapter 2, the isolation, characterization, and biological activity of the pyrrole-imidazole alkaloids palau'amine, axinellamines A--D and massadine are reviewed. The proposed biosynthesis of these alkaloids is described and several synthetic approaches toward these alkaloids are discussed.
Book Synopsis Investigations Into the Catalytic Asymmetric Synthesis of Sterically Hindered Lactones and Dihydrocoumarins by : Jinju Rose James
Download or read book Investigations Into the Catalytic Asymmetric Synthesis of Sterically Hindered Lactones and Dihydrocoumarins written by Jinju Rose James and published by . This book was released on 2018 with total page 413 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of Lewis Base Catalyzed Stereoselective Methods for Synthesis of [beta]-lactones and Dyotropic Rearrangements of Tricyclic [beta]-lactones by : Vikram C. Purohit
Download or read book Development of Lewis Base Catalyzed Stereoselective Methods for Synthesis of [beta]-lactones and Dyotropic Rearrangements of Tricyclic [beta]-lactones written by Vikram C. Purohit and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent finding that the FDA-approved antiobesity agent orlistat (tetrahydrolipstatin, Xenical) is a potent inhibitor of the thioesterase domain of fatty acid synthase (FAS) led us to develop a concise and practical asymmetric route to pseudosymmetric 3,4-dialkyl-cis-beta-lactones. The well-documented upregulation of FAS in cancer cells makes this enzyme complex an interesting therapeutic target for cancer. The described route to 3,4-dialkyl- beta -lactones is based on a two-step process involving Calter's catalytic, asymmetric ketene dimerization of acid chlorides followed by a facialselective hydrogenation leading to cis-substituted- beta -lactones. Importantly, the ketene dimer intermediates were found to be stable to flash chromatography, enabling opportunities for subsequent transformations of these optically active, reactive intermediates. Subsequent R-epimerization and R-alkylation or acylation led to trans- beta - lactones and beta -lactones bearing alpha-quaternary carbons, respectively. Several of the ketene dimers and beta-lactones displayed antagonistic activity (apparent Ki in the low micromolar range) in competition with a fluorogenic substrate toward a recombinant form of the thioesterase domain of fatty acid synthase. The best antagonist, a simple phenyl-substituted cis- beta -lactone, displayed an apparent Ki (2.5 (0.5 muM) of only 10- fold lower than that of orlistat (0.28 (0.06 muM). In addition, mechanistic studies of the ketene dimerization process by Reaction View infrared spectroscopy support previous findings that ketene formation is rate determining. A highly diastereoselective, nucleophile-promoted bis-cyclization process, employing readily available and tractable keto-acid substrates, is described. This methodology provides concise access to bicyclic- and tricyclic-beta-lactones bearing tertiary carbinol centers and quaternary carbons, greatly extending the scope of previous routes to bicyclic-beta-lactones from aldehyde acid substrates. This and related processes may be revealing a subtle interplay between [2 + 2] cycloaddition and nucleophilecatalyzed aldol lactonization (NCAL) reaction manifolds. An early induction period in the bis-cyclization of keto-acids is confirmed via isolation of the complex between 4- pyrrolopyridine and Modified Mukaiyama reagent N-propyl-2-bromo pyridinium triflate. Dyotropic rearrangements of tricyclic keto beta-lactones derived in high yields and>19:1 diastereoselectivity from readily available 1, 3-dione acids is described. Zn (II) salts were found to be most efficient for affecting dyotropic 1, 2-acyl migrations where as sub stoichiometric TMSOTf was found to execute a delta-lactone migration providing bis gamma-lactone in modest yields. Enantioselective desymmetrization with inexpensive (S) - tetramisole has been demonstrated to provide direct evidence of Lewis base involvement in the Nucleophile Promoted Bis-cyclization of keto-acids. Further studies using TsCl as the carboxylate activating agent instead of modified Mukaiyama reagent and catalytic tetramisole are described for achieving practical, catalytic, enantioselective synthesis of beta-lactones from keto-acids. Preliminary studies toward conjugate addition- lactonization pathway provided a hint as to the complexity involved to affect this transformation under the bis-cyclization conditions. An alternate hypotheses concerning the possibility of isomerization-dienolate formation - lactonization is experimentally proven. Additionally, applications of these and related findings in the intramolecular Morita-Baylis-Hillman reaction with cyclic ketones have been investigated which provide new avenues of synthetic methodology development.
Book Synopsis Applications of Chiral Aluminum and Boron Catalysts in Asymmetric Synthesis by : Li Zheng
Download or read book Applications of Chiral Aluminum and Boron Catalysts in Asymmetric Synthesis written by Li Zheng and published by . This book was released on 2020 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: A potent chiral aluminum catalyst has been developed for asymmetric MPV reduction of ketones with broad substrate scope and excellent yields and enantiomeric inductions. The catalyst consists an aluminum core, a VANOL-derived chiral ligand and an isopropoxy group. Different ligands have been screened and reaction parameters have been optimized. A variety of aromatic (both electron-poor and electron-rich) and aliphatic ketones were converted to chiral alcohols in good yields with high enantioselectivities (26 examples, 70-98% yield and 82-99% ee). This method operates under mild conditions (-10 °C) and low catalyst loading (1-10 mol%). Furthermore, this process is catalyzed by the earth-abundant main group element aluminum and employs inexpensive and environmentally benign 2-propanol as hydride source. This catalyst has also been employed in resolution of racemic alcohols. The kinetic resolution of alcohols by Oppenauer oxidation has been achieved with moderate results. The formal dynamic kinetic resolution via Oppenauer oxidation/ MPV reduction sequence has also been examined and discussed, which avoided acylation and the use of enzymes.A highly efficient asymmetric heteroatom Diels-Alder reaction between diene and aldehydes for the construction of 6-membered heterocycles catalyzed by chiral boron catalysts has been developed. A BINOL-derived propeller borate is found to be effective catalyzing the reaction of aromatic aldehydes. A VANOL-derived meso-borate is found to be able to catalyze the reaction of both aromatic and aliphatic aldehydes with high asymmetric inductions. Excellent yields and enantioselectivities have been achieved after optimization. Furthermore, the skeleton of 6-carbon saccharides is synthesized in the reaction of 2-hydoxyacetaldehyde with different protecting groups, which can be derivatized into many saccharide analogs. The mechanism of this reaction is proposed to be concerted based on experiments involving different methods for the reaction quench. A reversal of direction of the asymmetric induction by switching boron to aluminum has been observed. Computational studies show that catalysts derived from boron and aluminum have different geometries at the Lewis acid center.
Book Synopsis The Development and Application of Magnesium Amide Bases in Asymmetric Synthesis by : Linsey S. Bennie
Download or read book The Development and Application of Magnesium Amide Bases in Asymmetric Synthesis written by Linsey S. Bennie and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A range of bridged bicyclic ketones were then prepared in order to probe their application in magnesium amide-mediated asymmetric deprotonation reactions. Initial studies were performed using a simple oxabicyclic substrate and our C2-symmetric bisamide. Pleasingly, after a short period of optimisation, the enantioenriched silyl enol ether was obtained in unprecedented yield and enantioselectivity. Attention was then turned to the analogous thiabicyclic ketone substrate. When performing the asymmetric deprotonation of this novel substrate under the previously optimised conditions at -78 oC, an outstanding level of enantioselection was observed (99:1 er), and the silyl enol ether product was obtained in good yield. Having achieved such impressive results at -78 oC, the efficiency of the transformation at room temperature was probed. Pleasingly, the enantioenriched silyl enol ether was obtained in excellent enantioselectivity (94:6 er) and yield, without the requirement for subambient temperatures. This is in marked contrast to the results achieved using the corresponding lithium amide, which delivered the silyl enol ether with a lower level of enantioselectivity (93:7) at -78 oC. Impressive results could also be achieved when the analogous alkylmagnesium amide was applied to the desymmetrisation of the thiabicyclic substrate. Studies within the area of magnesium base chemistry have been extended to the enantioselective total synthesis of the bicyclic eicosanoid, (-)-mucosin. The synthetic strategy which has been devised involves a magnesium base-mediated enantioselective deprotonation as the key transformation. As such, the required meso-ketone substrate has been prepared efficiently using a series of simple synthetic transformations. With the mesoketone in hand, conversion to the racemic enol silane has been achieved by utilising carboncentred magnesium base chemistry. In addition, preparation of the required allylic bromide electrophile has been completed in a short number of synthetic steps using readily available starting materials, and the racemic enol silane and allylic bromide coupling partners were reacted to give the required -substituted ketone in moderate yield. Efforts were then focused on the development of an asymmetric method for the preparation of the enol silane intermediate, delivering the optically-enriched enol silane in high enantioselectivity using our C2-symmetric magnesium bisamide (93:7 er) or the C2-symmetric lithium amide (94:6 er) at - 78 oC.
Book Synopsis Catalytic Asymmetric Synthesis of Chiral Alcohols and Amines by : Johannes Gerardus Henricus Willems
Download or read book Catalytic Asymmetric Synthesis of Chiral Alcohols and Amines written by Johannes Gerardus Henricus Willems and published by . This book was released on 1996 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of Asymmetric Organocatalysis in One-pot Strategy for Enantioselective Synthesis of Highly Functionalized Hexahydrophenanthrene Derivatives and Hajos-parrish-type Ketones by : 雷嘉
Download or read book Development of Asymmetric Organocatalysis in One-pot Strategy for Enantioselective Synthesis of Highly Functionalized Hexahydrophenanthrene Derivatives and Hajos-parrish-type Ketones written by 雷嘉 and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
![Download Development of Lewis Base Catalyzed Stereoselective Methods for Synthesis of [beta]-lactones and Dyotropic Rearrangements of Tricyclic [beta]-lactones PDF Online Free](https://books.google.com/books/content/images/frontcover/Ubt5AQAACAAJ?fife=w200-h370)
