Gotowe bibliografie tematyczne / N-N axially chiral molecules

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Gotowa bibliografia na temat „N-N axially chiral molecules”

Autor: Grafiati

Data publikacji: 6 września 2023

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Artykuły w czasopismach na temat "N-N axially chiral molecules"

Fukasawa, Sota, Tatsuya Toyoda, Ryohei Kasahara, Chisato Nakamura, Yuuki Kikuchi, Akiko Hori, Gary J. Richards i Osamu Kitagawa. "Catalytic Enantioselective Synthesis of N-C Axially Chiral N-(2,6-Disubstituted-phenyl)sulfonamides through Chiral Pd-Catalyzed N-Allylation". Molecules 27, nr 22 (13.11.2022): 7819. http://dx.doi.org/10.3390/molecules27227819.

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Recently, catalytic enantioselective syntheses of N-C axially chiral compounds have been reported by many groups. Most N-C axially chiral compounds prepared through a catalytic asymmetric reaction possess carboxamide or nitrogen-containing aromatic heterocycle skeletons. On the other hand, although N-C axially chiral sulfonamide derivatives are known, their catalytic enantioselective synthesis is relatively underexplored. We found that the reaction (Tsuji–Trost allylation) of allyl acetate with secondary sulfonamides bearing a 2-arylethynyl-6-methylphenyl group on the nitrogen atom proceeds with good enantioselectivity (up to 92% ee) in the presence of (S,S)-Trost ligand-(allyl-PdCl)2 catalyst, affording rotationally stable N-C axially chiral N-allylated sulfonamides. Furthermore, the absolute stereochemistry of the major enantiomer was determined by X-ray single crystal structural analysis and the origin of the enantioselectivity was considered.

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Zhang, Xiaoke, Ya-Zhou Liu, Huawu Shao i Xiaofeng Ma. "Advances in Atroposelectively De Novo Synthesis of Axially Chiral Heterobiaryl Scaffolds". Molecules 27, nr 23 (3.12.2022): 8517. http://dx.doi.org/10.3390/molecules27238517.

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Axially chiral heterobiaryl frameworks are privileged structures in many natural products, pharmaceutically active molecules, and chiral ligands. Therefore, a variety of approaches for constructing these skeletons have been developed. Among them, de novo synthesis, due to its highly convergent and superior atom economy, serves as a promising strategy to access these challenging scaffolds including C-N, C-C, and N-N chiral axes. So far, several elegant reviews on the synthesis of axially chiral heterobiaryl skeletons have been disclosed, however, atroposelective construction of the heterobiaryl subunits by de novo synthesis was rarely covered. Herein, we summarized the recent advances in the catalytic asymmetric synthesis of the axially chiral heterobiaryl scaffold via de novo synthetic strategies. The related mechanism, scope, and applications were also included.

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Shi, Lei, Jiawei Zhu, Biqiong Hong i Zhenhua Gu. "A Chiral Relay Race: Stereoselective Synthesis of Axially Chiral Biaryl Diketones through Ring-Opening of Optical Dihydrophenan-threne-9,10-diols". Molecules 28, nr 16 (8.08.2023): 5956. http://dx.doi.org/10.3390/molecules28165956.

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We report herein a point-to-axial chirality transfer reaction of optical dihydrophenanthrene-9,10-diols for the synthesis of axially chiral diketones. Two sets of conditions, namely a basic tBuOK/air atmosphere and an acidic NaClO/n-Bu4NHSO4, were developed to oxidatively cleave the C-C bond, resulting in the formation of axially chiral biaryl diketones. Finally, brief synthetic applications of the obtained chiral aryl diketones were demonstrated.

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Corti, Vasco, i Giulio Bertuzzi. "Organocatalytic Asymmetric Methodologies towards the Synthesis of Atropisomeric N-Heterocycles". Synthesis 52, nr 17 (15.06.2020): 2450–68. http://dx.doi.org/10.1055/s-0040-1707814.

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A perspective on the literature dealing with the organocatalytic asymmetric preparation of axially chiral N-heterocycles is provided. A particular focus is devoted to rationalize the synthetic strategies employed in each case. Moreover, specific classes of organocatalysts are shown to stand out as privileged motives for the stereoselective preparation of such synthetically challenging molecular architectures. Finally, an overview of the main trends in the field is given.1 Introduction2 Five-Membered Rings2.1 Arylation2.2 Dynamic Kinetic Resolution2.3 Ring Construction2.4 Central-to-Axial Chirality Conversion and Chirality Transfer2.5 Desymmetrization3 Six-Membered Rings3.1 Desymmetrization3.2 (Dynamic) Kinetic Resolution3.3 Ring Construction3.4 Central-to-Axial Chirality Conversion4 Conclusion

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Peerlings, H. W. I., i E. W. Meijer. "Synthesis and Characterization of Axially Chiral Molecules Containing Dendritic Substituents". European Journal of Organic Chemistry 1998, nr 4 (kwiecień 1998): 573–77. http://dx.doi.org/10.1002/(sici)1099-0690(199804)1998:4<573::aid-ejoc573>3.0.co;2-n.

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Zeindlhofer, Veronika, Phillip Hudson, Ádám Márk Pálvölgyi, Matthias Welsch, Mazin Almarashi, H. Lee Woodcock, Bernard Brooks, Katharina Bica-Schröder i Christian Schröder. "Enantiomerization of Axially Chiral Biphenyls: Polarizable MD Simulations in Water and Butylmethylether". International Journal of Molecular Sciences 21, nr 17 (28.08.2020): 6222. http://dx.doi.org/10.3390/ijms21176222.

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In this study, we investigate the influence of chiral and achiral cations on the enantiomerization of biphenylic anions in n-butylmethylether and water. In addition to the impact of the cations and solvent molecules on the free energy profile of rotation, we also explore if chirality transfer between a chiral cation and the biphenylic anion is possible, i.e., if pairing with a chiral cation can energetically favour one conformer of the anion via diastereomeric complex formation. The quantum-mechanical calculations are accompanied by polarizable MD simulations using umbrella sampling to study the impact of solvents of different polarity in more detail. We also discuss how accurate polarizable force fields for biphenylic anions can be constructed from quantum-mechanical reference data.

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Wang, Jiaming, Changgui Zhao i Jian Wang. "Recent Progress toward the Construction of Axially Chiral Molecules Catalyzed by an N-heterocyclic Carbene". ACS Catalysis 11, nr 20 (28.09.2021): 12520–31. http://dx.doi.org/10.1021/acscatal.1c03459.

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Suzuki, Yuya, Masato Kageyama, Ryuichi Morisawa, Yasuo Dobashi, Hiroshi Hasegawa, Satoshi Yokojima i Osamu Kitagawa. "The synthesis of optically active N–C axially chiral tetrahydroquinoline and its response to an acid-accelerated molecular rotor". Chemical Communications 51, nr 56 (2015): 11229–32. http://dx.doi.org/10.1039/c5cc03659c.

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Matsui, Ryosuke, Erina Niijima, Tomomi Imai, Hiroyuki Kobayashi, Akiko Hori, Azusa Sato, Yuko Nakamura i Osamu Kitagawa. "Intermolecular Halogen Bond Detected in Racemic and Optically Pure N-C Axially Chiral 3-(2-Halophenyl)quinazoline-4-thione Derivatives". Molecules 27, nr 7 (6.04.2022): 2369. http://dx.doi.org/10.3390/molecules27072369.

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The halogen bond has been widely used as an important supramolecular tool in various research areas. However, there are relatively few studies on halogen bonding related to molecular chirality. 3-(2-Halophenyl)quinazoline-4-thione derivatives have stable atropisomeric structures due to the rotational restriction around an N-C single bond. In X-ray single crystal structures of the racemic and optically pure N-C axially chiral quinazoline-4-thiones, we found that different types of intermolecular halogen bonds (C=S⋯X) are formed. That is, in the racemic crystals, the intermolecular halogen bond between the ortho-halogen atom and sulfur atom was found to be oriented in a periplanar conformation toward the thiocarbonyl plane, leading to a syndiotactic zig-zag array. On the other hand, the halogen bond in the enantiomerically pure crystals was oriented orthogonally toward the thiocarbonyl plane, resulting in the formation of a homochiral dimer. These results indicate that the corresponding racemic and optically pure forms in chiral molecules are expected to display different halogen bonding properties, respectively, and should be separately studied as different chemical entities.

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Krishnamurthy, M. S., i Noor Shahina Begum. "Crystal structure of ethyl 2-cyano-3-[(1-ethoxyethylidene)amino]-5-(3-methoxyphenyl)-7-methyl-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate". Acta Crystallographica Section E Crystallographic Communications 71, nr 4 (25.03.2015): o256—o257. http://dx.doi.org/10.1107/s2056989015005241.

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In the title compound, C22H24N4O4S, the central pyrimidine ring adopts a sofa conformation with the ring-junction N atom displaced by 0.2358 (6) Å from the mean plane of the remaining ring atoms. The 3-methoxyphenyl ring, at the chiral C atom opposite the other N atom, is positioned axially and is inclined to the thiazolopyrimidine ring with a dihedral angle of 83.88 (7)°. The thiazole ring is essentially planar (r.m.s. deviation = 0.0034 Å). In the crystal, pairs of weak C—H...O hydrogen bonds link molecules related by twofold rotation axes to formR22(8) rings, which in turn are linked by weak C—H...N interactions, forming ribbons along [-110]. In addition, π–π stacking interactions [centroid—centroid distance = 3.5744 (15) Å] connect the ribbons, forming slabs lying parallel to (001).

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Rozprawy doktorskie na temat "N-N axially chiral molecules"

Hulmes, David. "An axially chiral P,N ligand for asymmetric homogeneous catalysis". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359505.

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Yeung, Ka Yim. "Studies on asymmetric reactions and catalysis using axially chiral 2-substituted N, N-dialkyl-1-naphthamides and p-chiral secondary phosphine oxides /". View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202003%20YEUNG.

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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 196-207). Also available in electronic version. Access restricted to campus users.

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Bob-Egbe, Opetoritse. "Development of axially chiral 2-aryl-4-dialkylaminopyridine-N-oxide based catalysts for the sulfonylative kinetic resolution of amines". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9776.

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Lewis base catalysis has been studied extensively in recent years as a powerful tool for introducing asymmetry into a variety of reactions, avoiding the use of expensive and potentially toxic metal catalysts. There is however still ample scope for the development of procedures for the non-enzymatic catalytic kinetic resolution (KR) of amines. Unlike alcohols, the intrinsic high reactivity of amines towards acyl and sulfonyl donors makes their KR highly challenging. As a result, there are relatively few publications on non-enzymatic catalytic KR of amines via acylation1-8 and none via sulfonylation. This thesis describes the development of a new class of chiral 2-aryl-(4-dialkylamino)pyridine-N-oxides (2-Ar-(4-DAAP)-N-oxides) (A), which are chiral by virtue of atropisomerism around the biaryl axis, and their application as catalysts for the KR of amines via sulfonylation. [molecular structure diagram] The use of C-H activation was explored for the development of a concise and modular synthetic procedure to the target catalyst structure. As a result, the key step in our final synthesis is a microwave (MW) assisted C-H halogenation procedure.(9) This reaction provides facile access to a di-ortho functionalised late stage intermediate from which a subsequent Pd catalysed cross coupling with a range of activated aryl partners provides access to an array of chiral catalyst structures. [molecular structure diagram] These catalysts were synthesised for assessment in the kinetic resolution of the axially chiral amine NOBIN, a synthetically useful chiral ligand which suffers from a difficult enantioselective synthesis. [molecular structure diagram] This thesis will provide a description of the synthetic route developed to achiral and chiral catalysts, the dependence of sulfonylation rates on the electronics of the catalyst and the key role of C-H activation in achieving a successful efficient synthesis of the target chiral catalyst structures. *For molecular structure diagrams, please see the PDF of the thesis.

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Joan, Saltó de la Torre. "Development of tailor-made catalyst libraries for the construction of chiral C-X (X= C, N and O) bonds. Application to the synthesis of complex molecules". Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/673144.

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La demanda constant de compostos enantiomèricament purs (fàrmacs, agroquímics, additius...) ha impulsat el desenvolupament de la catàlisi asimétrica emprant compostos organometàl.lics quiral com a catalitzadors. En aquest context, la síntesis de nous lligands quirals és essencial per descobrir bons sistemes catalítics en catàlisi asimètrica. Aquesta tesi s'ha centrat en el desenvolupament de tres noves lligandoteques quirals heterodadores i la seva aplicació a la substitució al·lílic catalizada per paladi. Es tracta de lligandoteques estables a l'aire, de fàcil manipulació i que s'han sintetizats en poques etapes a partir de productes d'elevada disponibilitat i baix preu. Combinant estudis teòrics i espectroscòpia de RMN, hem pogut afinar racionalment els lligands, millorar l'enantioselectivitat i identificar les espècies responsables dels resultats catalítics. A més a més, els productes de substitució al·lílic resultants es van utilitzar amb èxit per a la síntesi de molècules més complexes.
La demanda constante de compuestos enantioméricamente puros (fármacos, agroquímicos, aditivos...) ha impulsado el desarrollo de la catálisis asimétrica empleando compuestos organometálicos quiral como catalizadores. En este contexto, la síntesis de nuevos ligandos quirales es esencial para descubrir buenos sistemas catalíticos en catálisis asimétrica. Esta tesis se ha centrado en el desarrollo de tres nuevas ligandotecas quirales heterodadoras y su aplicación a la sustitución alílica catalizada por paladio. Se trata de ligandotecas estables al aire, de fácil manipulación y que se han sintetizado en pocas etapas a partir de productos de elevada disponibilidad y bajo precio. Combinando estudios teóricos y espectroscopia de RMN, hemos podido afinar racionalmente a los ligandos, mejorar la enantioselectividad e identificar las especies responsables de los resultados catalíticos. Además, los productos de sustitución alílica resultantes se utilizaron exitosamente para la síntesis de moléculas más complejas.
The constant demand for enantiomerically pure compounds (drugs, agrochemicals, additives ...) has driven the development of asymmetric catalysis using chiral organometallic compounds as catalysts. In this context, the synthesis of new chiral ligands is essential to discover good catalytic systems in asymmetric catalysis. This thesis has focused on the development of three new heterodonating chiral ligand libraries and their application to Pd-catalyzed allylic substitutions. These are ligand libraries stable in the air, easy to handle and have been synthesized in a few steps from readily available products and at low price. Combining theoretical studies and NMR spectroscopy, we were able to rationally fine-tune the ligands, improve enantioselectivity, and identify the species responsible for catalytic performance. In addition, the resulting allylic substitution products were successfully used for the synthesis of more complex molecules.

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Heister, Philipp [Verfasser], Ulrich K. [Akademischer Betreuer] Heiz i Steffen Johannes [Akademischer Betreuer] Glaser. "Nonlinear Spectroscopy of Supported Size-Selected Silver Clusters (n=9-55) and Supported Chiral 2,2'-Dihydroxy-1,1'-Binaphthyl (Binol) Molecules / Philipp Heister. Gutachter: Ulrich K. Heiz ; Steffen Johannes Glaser. Betreuer: Ulrich K. Heiz". München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1054752990/34.

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Stucchi, M. "MULTICOMPONENT APPROACHES TO THE SYNTHESIS OF SMALL BIOACTIVE MOLECULES". Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/330951.

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In this PhD thesis, we exploited the potentialities of four different multicomponent reactions (MCRs), namely Ugi four-component reaction (U-4CR), N-split Ugi reaction (N-split U-4CR), van Leusen three-component reaction (vl-3CR) and Biginelli reaction (Bg-3CR), developing five different approaches to the synthesis of small bioactive molecules. In particular, we successfully applied the build/couple/pair strategy obtaining a small library of ketopiperazine-based minimalist peptidomimetics, by means of diastereoselective U-4CR/post-cyclization sequences, employing optically pure amino acid-derived α-amino aldehydes and α-isocyanoacetates as starting materials. Computer-assisted NMR NOE analysis allowed us to determine the configuration of the newly formed stereocenters, while molecular dynamics simulation and biological evaluation clearly underlined the potentiality of selected compounds to interfere with protein-protein interactions (PPIs). We also focused our attention on another class of peptide-like compounds, namely diamine-based peptidomimetics, by carefully optimizing the N-split U-4CR conditions for the introduction of N-protected amino acids and α-isocyanoacetates components, in a stereoconservative way. This methodology largely simplifies the synthesis of such compounds, opening the way to the use of more complex secondary diamines, able to induce well-defined secondary structures in the related peptidomimetic and hopefully targeting novel PPIs. Furthermore, by combining the same N-split U-4CR with common transformations, a library of dopamine receptor agonists was rapidly obtained, with biological activities in the nanomolar range. Although the desired D2/D3 selectivity was not achieved, structure-activity relationship (SAR) and docking studies allowed us to understand the key pharmacophoric elements in these novel structures, leading the way to the design of improved molecular scaffolds. By employing the vL-3CR in an iterative way, we designed a novel C2-C5’ linked polyimidazole-based minimalist framework, able to mimic the i, i+1, i+2 and i+3 amino acid residues of a β-strand motif. Its conformational behaviour was investigated through solution-phase NMR and molecular dynamics studies, allowing to demonstrate its ability to mimic a poly-alanine β-strand. Finally, we explored the possibility to combine MCRs with organocatalysis, developing the first BINOL-derived phosphoric acid catalysed Biginelli-like reaction on a ketone. In particular, employing N-substituted isatins as carbonyl substrates, we achieved the synthesis of a small library of biologically relevant enantioenriched spiro[indoline-pyrimidine]-diones derivatives. The assignment of the configuration at the new oxindole C-3 stereocenter was assessed through quantum-mechanical methods and NMR spectroscopy, while computational studies on the reaction transition state allowed us to explain the enantioselectivity and the stereochemical outcome.

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Balanna, Kuruva. "N-Heterocyclic Carbene-Catalyzed Synthesis of Oxazolones, e-Lactones and N-N Axially Chiral Molecules". Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6191.

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The diverse reactivity of N-heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modes of action. Although NHC-bound enolates and dienolates were well-known, the NHC-bound cross-conjugated aza-trienolates were undisclosed. We have demonstrated the synthesis of pyrrolooxazolones via NHC-bound azatrienolate intermediates. In the same fashion, involvement of chiral alpha-carbon center (proximal reaction centre) in dynamic kinetic resolution (DKR) via NHC-bound enolates were known. However, the gamma, gamma-disubstituted chiral carbon center (remote reaction centre) involving in DKR via NHC-bound dienolates were unknown. We have recently demonstrated the DKR of gamma,gamma-disubstituted indole 2-carboxaldehydes via NHC-Lewis acid cooperative catalysis for the synthesis of tetracyclic epsilon-lactones. Additionally, NHC-catalyzed atroposelective synthesis of C-C and C-N axially chiral molecules were known, and the asymmetric synthesis of axially chiral N-N molecules remains unknown in carbene catalysis. We have demonstrated the N-heterocyclic carbene (NHC)-catalyzed selective amidation reaction leading to the atroposelective synthesis of N-N axially chiral 3-amino quinazolinones.
UGC CSIR

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Części książek na temat "N-N axially chiral molecules"

Benkoski, Léa, i Tristan H. Lambert. "Construction of Multiple Stereocenters". W Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0039.

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Erick M. Carreira at ETH Zürich reported (Science 2013, 340, 1065) the enantioselective α-allylation of aldehyde 1 with alcohol 2 to produce 3 using a dual catalytic system involving a chiral iridium complex and amine 5. This stereodivergent method allows access to all of the possible stereoisomers of 3. In a conceptually related process, John F. Hartwig at the University of California, Berkeley reported (J. Am. Chem. Soc. 2013, 135, 2068) the highly stereoselective allylic alkylation of azlactone 6 with allylic carbonate 7 catalyzed by a combination of Ir(cod)Cl₂, ligand 9, and racemic silver phosphate 10. An enantioselective three-component Mannich-type reaction of tert-butyl diazoacetate, aniline, and imine 11 to produce α,β-bis(arylamino) acid derivative 13 under dual catalysis with Rh₂(OAc)₄ and acid 12 was developed (Synthesis 2013, 45, 452) by Wenhao Hu at the Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development. Keiji Maruoka at Kyoto University reported (Chem. Commun. 2013, 49, 1118) a one-pot cross double-Mannich reaction of acetylaldehyde 14, and imines 16 and 17 using axially chiral amino sulfonamide 15 to obtain densely functionalized 1,3-diamine 18 as a single stereoisomer. Jeffrey S. Johnson at the University of North Carolina at Chapel Hill reported (Org. Lett. 2013, 15, 2446) the asymmetric synthesis of enantioenriched anti-α-hydroxy-β-amino acid derivative 21 from 19 by treatment with oxone followed by catalytic hydrogenation using Ru(II) complex 20. Naoya Kumagai and Masakatsu Shibasaki at the Institute of Microbial Chemistry found (Org. Lett. 2013, 15, 2632) that a silver complex of bisphosphine 24 effected a syn-selective and highly enantioselective Mannich-type reaction of aldimine 22 and α-sulfanyl lactone 23 to furnish the stereodiad 25 with very high ee. The enantioselective homocrotylation of octanal 26 with cyclopropylcarbinylboronate 27 to produce alcohol 28 with high ee was disclosed (J. Am. Chem. Soc. 2013, 135, 82) by Isaac J. Krauss at Brandeis University with computational studies provided by Kendall N. Houk at UCLA. Benjamin List at the Max-Planck-Institut für Kohlenforschung reported (J. Am. Chem. Soc. 2013, 135, 6677) the enantioselective epoxidation of cyclohexenone 29 utilizing cinchona alkaloid- derived catalyst 30.

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Ying, Jun, i Lin Pu. "Axially Chiral X,X-Ligands (X = N, O) for Asymmetric Metal-Catalyzed Reactions". W Atropisomerism and Axial Chirality, 447–88. WORLD SCIENTIFIC (EUROPE), 2019. http://dx.doi.org/10.1142/9781786346469_0006.

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Rokade, Balaji V., i Patrick J. Guiry. "Axially Chiral P,X-Ligands (X = N, O, and S) for Asymmetric Metal-Catalyzed Reactions". W Atropisomerism and Axial Chirality, 379–445. WORLD SCIENTIFIC (EUROPE), 2019. http://dx.doi.org/10.1142/9781786346469_0005.

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Wu, X., Y. Liu i Z. Jin. "3 Organocatalytic Dynamic Kinetic Resolution". W Dynamic Kinetic Resolution (DKR) and Dynamic Kinetic Asymmetric Transformations (DYKAT). Stuttgart: Georg Thieme Verlag KG, 2023. http://dx.doi.org/10.1055/sos-sd-237-00019.

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AbstractThere has long been interest in obtaining optically pure molecules from racemic or non-chiral starting materials through environmentally friendly chemical transformations with high yields and enantioselectivities. Organocatalytic reactions possess the inherent advantages of non-toxicity and good efficiency and are insensitive to air and moisture. Dynamic kinetic resolution (DKR) represents one class of the most efficient strategies for the preparation of chiral molecules from racemic mixtures with up to 100% yields. Therefore, DKR reactions promoted by various organic catalysts are attractive based on their efficiencies, selectivities, and low toxicities. In this review, we introduce some representative examples of the reported DKR reactions catalyzed by typical organic catalysts, including chiral amines, Brønsted acids, N-heterocyclic carbenes, phosphines, guanidines, and isothioureas. The aim is to provide readers with a general overview of the scope and efficiency of organocatalytic DKR transformations and to inspire groundbreaking ideas for the development and applications of organocatalytic DKR reactions in future research.

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Morrow, Gary W. "Brief Organic Review". W Bioorganic Synthesis. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199860531.003.0004.

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In addition to simple hydrocarbon structures (alkanes, alkenes, alkynes, and aromatic systems) and alkyl groups (methyl, ethyl, propyl, isopropyl, etc.), this text assumes a familiarity with the most common functional groups associated with organic chemical structures and their basic reactivity patterns. Table 1.1 summarizes the names and structures of some of the more important functional groups we will be dealing with throughout the remainder of the book. It is important to remember that functional groups containing O or N with nonbonding electrons have an affinity for both protic and Lewis acids and are important participators in H-bonding. Groups containing a carbonyl (C=O) function are especially important, as these bonds are strongly polarized (δ+C=Oδ–), the C atom being electron deficient and the O atom electron excessive; this strong polarization is mainly responsible for the familiar reactivity patterns associated with carbonyl compounds. Figure 1.1 depicts the standard classification of isomers in organic chemical structures. Recall that constitutional isomers are compounds with the same molecular formula but different atom connectivity, such as 1-butanol versus 2-butanol. Stereoisomers, on the other hand, are compounds with the same formula and the same atom connectivity, differing from one another only in the three-dimensional orientation of their atoms in space. These are divided into two groups: enantiomers and diastereomers. Enantiomers are nonsuperimposable mirror image molecules whose asymmetry is usually the result of a tetrahedral carbon atom with four different atoms or groups attached to it, as in the 2-butanol enantiomers. Such chiral molecules rotate the plane of polarized light either (+) or (−) and so are said to be optically active. Achiral molecules, such as 1-butanol, do not rotate the plane of polarized light and so are optically inactive. A standard formalism for representation of a chiral center is to use bond line drawings with two of the four atoms or groups lying in the plane of the paper, a third projecting outward (wedge bond), and the fourth projecting inward (dashed bond).

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Pérez Méndez, Mercedes, José Fayos Alcañiz i Marc Meunier. "Molecular Simulation of Cholesteric Liquid-Crystal Polyesteramides: Conformational and Structure Analysis by Rietveld Refinement". W Liquid Crystals [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.100388.

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Molecular modeling techniques are applied to polyesteramides designed as PNOBDME (C34H38N2O6)n and PNOBEE (C26H22N2O6)n, synthesized and characterized as cholesteric liquid crystals -through the condensation reaction between 4 and 4′-(terephthaloyl- diaminedibenzoic chloride (NOBC) and racemic glycol: DL-1,2 dodecanediol, or DL-1,2-butanediol, respectively, being chemical modifications of precursor multifunctional cholesteric LC polyesters, adding new properties but holding their helical macromolecular structures. Although the starting raw materials were racemic, these cholesteric LC polymers exhibit unexpected optical activity and chiral morphology. For that reason, conformational analysis is studied on the monomer models of PNOBDME and PNOBEE. Four helical conformers models, experimentally observed by NMR, are proposed for each cholesteric polyesteramide: Rgg, Rgt, Sgg, Sgt. Polymerization of the monomeric conformers, with minima energies, have been simulated and used to reproduce the crystalline fraction observed by x-ray diffraction. Three orders of chirality are observed in the structure of the polymer chains: One due to the asymmetric carbon atoms, a second chirality due to the two successive rotations of the benzene groups, along the main chain, within the monomer which implies the formation of helical molecules, for both R and S chirality and still, a third chirality corresponding to the twisting of the rigid/semirigid cholesteric LC polymer chains. All these factors contributing to the net optical activity observed in these materials. Crystal packing is simulated in triclinic primitive P1cells, with molecular chains oriented parallel to the z-axis (c lattice parameter equal to the pitch length of each simulated polymer helix) and parameters a, b, α, β and γ, obtained by Pawley refinement from the known structures of precursor polyesters. The simulated x-ray diffraction patterns of the proposed crystal models fit, after successive Pawley and Rietveld refinement cycles, the experimental WAXS. Powder Quantitative Phase Analysis applied to an ideal mixture with the four possible helical conformers, for each degree of polymerization, allows to refine their relative weight and determine the major phase relative amount. These results would confirm the theory of a preferable recrystallization, among the four possible helical diastereoisomers, depending on the synthetic conditions.

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Streszczenia konferencji na temat "N-N axially chiral molecules"

Carroll, Brandon, Geoffrey Blake i Brett McGuire. "AN ALMA SEARCH FOR CHIRAL MOLECULES TOWARD SGRB2(N)". W 74th International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2019. http://dx.doi.org/10.15278/isms.2019.mg06.

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