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Regio
Kinds of Regio Selected AbstractsChemo-, Regio- and Stereospecific Synthesis of Unnatural, Fluorescent Amino Acids by Condensation of L -Lysine and 1-Vinylpyrrole-2-carbaldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2010Andrey V. Ivanov Abstract A new family of unnatural, optically active amino acids containing the pyrrole moiety have been synthesized by condensation of 1-vinylpyrrole-2-carbaldehydes with L -lysine under mild conditions (EtOH, room temp., 2.5,3 h, 0.5 wt.-% of CF3CO2H) in up to 90,% yields. Unlike non-vinylated analogues, 1-vinylpyrrole-2-carbaldehydes react chemo-, regio- and stereospecifically with an ,-amino group only to afford products of exclusively (E) configuration. The amino acids synthesized containing aromatic or condensed aromatic substitutents in the pyrrole ring fluoresce in the UV/Vis region (,max = 350,382 nm, Stokes shifts 6150,7800 cm,1). [source] A Facile Synthesis of Lentiginosine Analogues Based on a Highly Regio- and Diastereoselective Allylic Amination Using Chlorosulfonyl IsocyanateEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2010In Su Kim Abstract The concise synthesis of the lentiginosine analogues pyrrolizidine alkaloid 2 and pyrroloazepine alkaloid 3 has been achieved from inexpensive and readily available D -lyxose. The key steps in the synthesis included regio- and diastereoselective amination, inter- or intramolecular olefin metathesis, and Appel cyclization. The anti -3,4-amino alcohol 6, essential for the preparation of the title compounds 2 and 3, was synthesized by the regio- and diastereoselective amination of anti -3,4-tribenzyl ether 7 using chlorosulfonyl isocyanate. The reaction of 7 with chlorosulfonyl isocyanate in toluene at 0 °C afforded 6 exclusively with a diastereoselectivity of 26:1 in 84,% yield. These results can be explained by the neighboring-group effect, which leads to retention of thestereochemistry. [source] DFT Study of Brønsted Acid Catalyzed Nitroso Aldol Reaction Between Achiral Enamines and Nitrosobenzene: The Reason for Regio- and EnantioselectivityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2008Matsujiro Akakura Abstract The regio- and enantioselectivity of the nitroso aldol reaction between achiral enamines and nitrosobenzene catalyzed by chiral Brønsted acid catalysts (TADDOL or 1-naphthylglycolic acid) were investigated in experimental and theoretical studies. The use of a model involving a simple organic acid (MeOH or AcOH) revealed that the reaction was catalyzed by two or more molecules of the organic acid and that the transition-state structure encompassed several hydrogen bonds. The role of hydrogen bonding in the regioselectivity was also examined carefully. The enantioselectivity in the reaction catalyzed by chiral organic acids (S,S)-TADDOL and (S)-1-naphthylglycolic acid was also confirmed through computational study.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Diels,Alder Reactions of Symmetrically 1,4-Disubstituted Dienes: Theoretical Study on the Influence of the Configuration of the Double Bonds on the Regio- and EndoselectivityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2008Samira Baki Abstract It was experimentally shown in Diels-Alder reactions that symmetrically 1,4-disubstituted dienes exhibit high regio- and endoselectivity induced by the (E,Z) configuration of the double bonds. In order to understand the origin of this selectivity, the transition states associated with the reaction between a series of such dienes (R = OMe, CH3, NH2, F, CN) on substituted ethylene (R, = CO2Me, CN, F, OMe) were determined by DFT calculations. If the regioselectivity confirmed by a single-point MP2 calculation is predicted to be good in most cases, its direction remains difficult to predict; the R, group of the dienophile can orient itself toward either the (Z) or the (E) side of the diene. Neither primary nor secondary frontier orbital interactions appear to be able to rationalize these results. They are more likely explained by a delicate balance between steric and electrostatic interactions. This hypothesis is further supported by the calculated reactivity of the (E,E) and (Z,Z) corresponding dienes. In any case, a standard DFT calculation, confirmed by a single-point MP2 step, is likely to provide a reliable guideline for a synthesis strategy that allows the control of up to four stereogenic centres in a single reaction step.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Highly Regio- and Stereoselective Diels,Alder Cycloaddition of Difluoro(methylene)cyclopropanesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2008Xiao-Chun Hang Abstract The Diels,Alder reactions of difluoro(methylene)cyclopropanes (F2MCPs) with cyclic dienes are described. These cycloaddition reactions exhibited complete regioselectivity and high endo -stereoselectivity. The obtained cycloadducts underwent a retro-Diels,Alder reaction to give the original dienophiles and dienes when heated, reflecting the reversible Diels,Alder reactivity of F2MCPs.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Palladium-Catalyzed Formation of Cyclic Ethers , Regio-, Stereo- and Enantioselectivity of the ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2007Anna Zawisza Abstract An efficient and stereoselective synthesis of 3-alkyl-3-hydroxymethyl-5-vinyltetrahydrofurans is described by the Pd0 -catalyzed cyclization of the methyl carbonates of ,,,-bis(hydroxymethyl)-,,,-unsaturated alcohols. The use of chiral ligands gave the corresponding THF derivatives in low to moderate enantiomeric ratios. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] An Improved Synthesis of Procyanidin Dimers: Regio- and Stereocontrol of the Interflavan BondEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Isabelle Tarascou Abstract A direct and general synthesis of procyanidin dimers B1, B2, B3 and B4 (10a,d) is presented. The approach is based on the stoichiometric coupling of two protected monomeric units (the nucleophilic 2a,b and electrophilic 4a,b partners) and deals with the regio- and stereocontrol of the C4,C8 interflavan bond as well as the control of the degree of oligomerization. The synthesis involves a five-step pathway starting from the native catechin (1a) or epicatechin (1b) to the fully deprotected dimers 10a,d. Furthermore, the process appears to be iterative as the coupling intermediates 9a,d themselves can be readily used in further selective syntheses of trimers or higher oligomers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Simultaneous Regio- and Enantiodifferentiation in Carbohydrate Coupling,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006M. Belén Cid Abstract The glycosylation of 1,2- trans -diequatorial diols derived from tetrabenzoylated and tetrabenzylated D - and L - chiro -inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The RuO4 -Catalyzed Ketohydroxylation, Part II:A Regio-, Chemo- and Stereoselectivity StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2005Bernd Plietker Abstract The direct RuO4 -catalyzed ketohydroxylation of olefins is a new and convenient method for the preparation of a wide range of symmetrical and unsymmetrical ,-hydroxy ketones. Since reactions in which two different functional groups are introduced in one step always involve regio-, chemo- and stereoselectivity issues, this paper gives a full account of investigations of various selectivity aspects in the ketohydroxylation. Stereoselectivity issues were examined in the final part of the present report. The Kishi rules, known from OsO4 -catalyzed dihydroxylations, are found to be valid for the RuO4 -catalyzed ketohydroxylation and lead to moderate to good diastereomeric ratios in the oxidation of olefins possessing an allylic center of chirality. Furthermore, competition experiments between different substituted olefins led to a reactivity profile applicable to the prediction of which is the most reactive of different C=C double bonds present in a molecule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Efficient Regio- and Stereoselective Conversions of Oxiranes and Aziridines into , -(Nitrooxy)-Substituted Alcohols and Amines by Using Bismuth Nitrate,HELVETICA CHIMICA ACTA, Issue 1 2007Biswanath Das Abstract Oxiranes and aziridines efficiently undergo ring opening with bismuth nitrate at room temperature to furnish the corresponding , -(nitrooxy)-substituted alcohols and amines respectively. The conversions are highly regio- and stereoselective and afford the nitrooxy-compounds in excellent yields within a short period of time. [source] Novel Cs -Symmetric 1,4-Diphosphine Ligands in the Copolymerization of Propene and Carbon Monoxide: High Regio- and Stereocontrol in the Catalytic PerformanceHELVETICA CHIMICA ACTA, Issue 2 2005Antonella Leone New Cs -symmetric aryl 1,4-diphosphine ligands were synthesized and tested in the copolymerization of carbon monoxide and propene. The electronic properties of the two different P-atoms did not affect the high enantioselectivity of the catalyst precursors, thus resulting in high ,regio'- and ,stereoregular' copolymers. [source] Iron-Catalysed Regio- and Stereoselective Head-to-Tail Dimerisation of StyrenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Abstract Cationic iron salts and complexes catalyse the head-to-tail dimerisation of styrene derivatives to form the corresponding dimers with good to excellent yields and stereoselectivities. In particular, the use of a phosphine-iron(III) complex allows the recovery and reuse of the catalyst. The counteranion plays an important role in both the activity and selectivity. These catalysts constitute an alternative to those based on toxic and expensive late-transition metals. [source] Regio- and Stereoselective Intermolecular Hydroalkoxylation of Alkynes Catalysed by Cationic Gold(I) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Avelino Corma Abstract Vinyl ethers and ketals are obtained from the reaction of phenylacetylene derivatives and dimethyl acetylenedicarboxylate (DMAD) with alcohols in good yields and levels of stereoselectivity by using cationic gold(I)-phosphine complexes as catalysts. By choosing the appropriate phosphine, the selective formation of the Z or the E isomer of the vinyl ether can be tuned, and the undesired formation of the ketal can be controlled. The isomerisation of fumarates (Z -isomer) to maleates (E -isomer) is a gold-catalysed process that can be conducted in one-pot. When using polyols, 5-membered cyclic ketals are easily isolated by extraction with hexane and the gold complex can be reused. [source] Michael Reaction of Nitroalkanes with ,-Nitroacrylates under a Solid Promoter: Advanced Regio- and Diastereoselective Synthesis of Nitro-Functionalized ,,,-Unsaturated Esters and 1,3-Butadiene-2-carboxylatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Alessandro Palmieri Abstract A new class of nitro-functionalized ,,,-unsaturated esters has been prepared by a regio- and diastereoselective Michael addition of nitroalkanes to ,-nitroacrylates, performed at room temperature, under carbonate on polymer as promoter, and in the presence of ethyl acetate as eco-friendly solvent. Moreover, by the modular choice of the reaction conditions the method allows the synthesis of 1,3-butadiene-2-carboxylates. [source] Aluminium Powder-Catalyzed Regio- and Stereoselective Aminobromination of ,,,-Unsaturated Carbonyl Compounds and Simple Olefins with the p -Toluenesulfonamide/ N -Bromosuccinimide (TsNH2 -NBS) SystemADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Zhan-Guo Chen Abstract The regio- and stereoselective aminobromination of ,,,-unsaturated carbonyl compounds and simple olefins catalyzed by elementary aluminium powder has been established by using p -toluenesulfonamide (TsNH2) and N -bromosuccinimide (NBS) as the nitrogen/bromine sources. The reaction was convenient to carry out with a loading of 1,mol% catalyst at room temperature without inert gas protection. This method provides an easy approach to trans vicinal haloamino derivatives of ,,,-unsaturated carbonyl compounds and simple olefins in high yields (up to 99.8%) and in excellent regio- and stereoselectivities. The electron-rich and electron-deficient olefins show significant differences in activity to the aminobromination reaction and give the opposite regioselectivities. Two possible pathways involving separately a bromonium or an aziridinium intermediate have been proposed. [source] Promiscuous Substrate Binding Explains the Enzymatic Stereo- and Regiocontrolled Synthesis of Enantiopure Hydroxy Ketones and DiolsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Marcela Kurina-Sanz Abstract Regio- and stereoselective reductions of several diketones to afford enantiopure hydroxy ketones or diols were accomplished using isolated alcohol dehydrogenases (ADHs). Results could be rationalised taking into account different (promiscuous) substrate-binding modes in the active site of the enzyme. Furthermore, interesting natural cyclic diketones were also reduced with high regio- and stereoselectivity. Some of the 1,2- and 1,3-diketones used in this study were reduced by employing a low excess of the hydrogen donor (2-propanol) due to the quasi-irreversibility of these ADH-catalysed processes. Thus, using lower quantities of co-substrate, scale-up could be easily achieved. [source] Ferric Chloride Hexahydrate-Catalyzed Highly Regio- and Stereoselective Conjugate Addition Reaction of 2,3-Allenoates with Grignard Reagents: An Efficient Synthesis of ,,,-AlkenoatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Guobi Chai Abstract Ferric chloride hexahydrate was shown to be an efficient catalyst for the conjugate addition of 2,3-allenoates with alkyl-, aryl-, or vinyl-Grignard reagents to synthesize polysubstituted ,,,-unsaturated alkenoates with high regio- and stereoselectivity. The in situ formed magnesium dienolate may readily react with different electrophilic reagents under different reaction conditions with or without a catalyst to construct an allylic quaternary carbon at the ,-position of the ester group and a stereocontrollable retention of the carbon-carbon double bond. [source] A Practical and Effective Ruthenium Trichloride-Based Protocol for the Regio- and Stereoselective Catalytic Hydroamidation of Terminal AlkynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2008Lukas Abstract A rational catalyst development based on mechanistic and spectroscopic investigations led to the discovery of a new protocol for catalytic hydroamidation reactions that draws on easily available ruthenium trichloride trihydrate (RuCl3,3,H2O) as the catalyst precursor instead of the previously employed, expensive bis(2-methylallyl)(1,5-cyclooctadiene)ruthenium(II). This practical and easy-to-use protocol dramatically improves the synthetic applicability of Ru-catalyzed hydroamidations. The catalyst, generated in situ from ruthenium(III) chloride hydrate, tri- n -butylphosphine, 4-(dimethylamino)pyridine and potassium carbonate, effectively promotes the addition of secondary amides, lactams and carbamates to terminal alkynes under formation of (E)- anti -Markovnikov enamides. The scope of the new protocol is demonstrated by the synthesis of 24 functionalized enamide derivatives, among them valuable intermediates for organic synthesis. [source] Highly Regio- and Stereoselective Iodohydroxylation of Non- Heteroatom-Substituted Allenes: An Efficient Synthesis of 4-[3,-Hydroxy-2,-iodoalk-1,(Z)-enyl]-2(5H)-furanone DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2007Zhenhua Gu Abstract An efficient protocol for the highly regio- and stereoselective synthesis of 4-(3,-hydroxy-2,-iodoalk-1,(Z)-enyl)furan-2(5H)-one derivatives via selective iodohydroxylation of non-heteroatom-substituted allenes, i.e., 4-allenyl-2(5H)furanones, has been developed. The regio- and stereoselectivity of this reaction may be controlled by the electronic and steric effects of the furanone ring. [source] Highly Regio- and Stereoselective Copper(I) Chloride-Mediated Carbometallation of 2,3-Allenols with Grignard ReagentsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007Zhan Lu Abstract An efficient highly regio- and stereoselective copper(I) chloride-mediated carbometallation of differently substituted 2,3-allenols with primary or secondary alkyl or aromatic Grignard reagents followed by iodination to synthesize fully-substituted allylic alcohols has been developed. This protocol introduces the R4 group from the Grignard reagent to the terminal position of the 2,3-allenols. [source] Allylation of Aldehydes Promoted by the Cerium(III) Chloride Heptahydrate/Sodium Iodide System: the Dependence of Regio- and Stereocontrol on the Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-13 2005G. Bartoli Abstract The cerium(III) chloride heptahydrate/sodium iodide complex (CeCl3,,,7,H2O/NaI) acts as a useful promoter in the carbon-carbon bond forming reaction by addition of allyltributylstannanes to aldehydes. The reaction of 2-butenyltributylstannane shows that the regio- and the stereochemical outcomes depend on the reaction conditions. When the promoter is adsorbed on a solid support (aluminum oxide), a highly prevalent formation of the ,-adduct is observed in solvent-free conditions. Conversely, when the reaction is carried out in acetonitrile as the solvent, the ,-adduct largely prevails. In the last case, a complete stereocontrol is observed, the less stable (Z)-isomer being obtained in high geometrical purity. [source] MgBr2 -mediated opening of 2,3-three membered heterocyclic aminesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2010Giuliana Righi Regio- and stereo-controlled opening of 2,3-epoxy amines and 2,3-aziridine amines by the commercially available MgBr2 is described. As reported, this new method could represent a general and useful approach for the preparation of promising intermediates. Moreover, in particular cases, the reaction evolves toward an interesting oxazolidin-2-one structure. J. Heterocyclic Chem., (2010). [source] Regio- and stereoselective synthesis of isoxazolidine derivatives by asymmetric 1,3-dipolar cycloaddition reaction of chiral nitrones with 1-propene-1,3-sultoneJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2008Hong-Kui Zhang Asymmetric 1,3-dipolar cycloadditions of chiral nitrones to 1-propene-1,3-sultone (1) were investigated. Chiral nitrones 6a-e reacted with sultone 1 in toluene at 90 °C for 24-36 h to give the corresponding isoxazolidines in moderate yields with high regioselectivities and stereoselectivities. The diastereoselectivity of this reaction varied with the choice of dipolarophile and the steric demands of nitrones. When sultone 1 was allowed to react chiral nitrone 6e, a much better diastereoselectivity of up to 5.1:1 was observed. [source] Regio- and stereochemistry of Michael addition of methanol to Thiele's esterJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2004David E. Minter Abstract Acid-promoted esterification of Thiele's acid with methanol was found to afford three products. In addition to the expected major product (i.e. the corresponding dimethyl ester, 2a), two minor products are obtained, one of which, 3, results from subsequent Michael addition of methanol to the norbornene CC double bond in 2a. Analysis of its one- and two-dimensional NMR spectra indicates that this minor product possesses structure 3a in which the (C-5),OCH3 and (C-6),CO2CH3 bonds are exo and endo, respectively. This conclusion is reinforced by the results of thermodynamics calculations and associated chemical shift calculations. In addition, theoretical analysis of competing transition states for Michael addition of methanol to 2a suggests that exo approach of methanol towards the (C-5)(C-6) double bond in the substrate is preferred kinetically over the corresponding endo reaction pathway. Copyright © 2004 John Wiley & Sons, Ltd. [source] Complete Regio- and Stereoselective Construction of Highly Substituted Silyl Enol Ethers by Three-Component Coupling,ANGEWANDTE CHEMIE, Issue 39 2010Dr. Akira Tsubouchi Drei Komponenten zur totalen Kontrolle: Dreifach substituierte Silylenolether wurden durch Dreikomponentenkupplung von ,,,-ungesättigten ,-Silylketonen, Organokupferreagentien und organischen Halogeniden vollständig regio- und stereoselektiv synthetisiert (siehe Schema). Die Reaktion verläuft über eine 1,3-Wanderung der Silylgruppe unter Bildung von cyclischen Silicat-Zwischenstufen, die die Konfiguration der Silylenolether festlegen. [source] Efficient Silver-Catalyzed Regio- and Stereospecific Aziridination of Dienes,ANGEWANDTE CHEMIE, Issue 39 2010Josep Llaveria Nitrentransfer: Unsymmetrische Diene mit einer endständigen Hydroxygruppe können durch Nitrentransfer von PhINTs in Gegenwart eines Silberkatalysators regio- und stereospezifisch in Vinylaziridine umgewandelt werden. Dazu wurden äquimolare Gemische aus Dien und PhINTs sowie nur 0.5,% Katalysator eingesetzt (siehe Schema). Mit dieser Methode war (±)-Sphingosin in drei Stufen mit guten Ausbeuten zugänglich. Ts=4-Toluolsulfonyl. [source] Regiodivergent Ligand-Controlled Rhodium-Catalyzed [(2+2)+2] Carbocyclization Reactions with Alkyl Substituted Methyl Propiolates,ANGEWANDTE CHEMIE, Issue 33 2010Andrew Evans Prof. Man hat die Wahl: In der Titelreaktion lässt sich die selektive Bildung der zwei Regioisomere durch sorgfältige Wahl der Hilfsliganden steuern (siehe Schema). Entscheidend war der Befund, dass Reste von Silbersalzen aus der Salzmetathese des neutralen Komplexes einen starken Einfluss auf die Regio- und Diastereoselektivität haben. [source] Nickel-Catalyzed Regio- and Enantioselective Annulation Reactions of 1,2,3,4-Benzothiatriazine-1,1(2H)-dioxides with Allenes,ANGEWANDTE CHEMIE, Issue 29 2010Tomoya Miura Dr. N2 -Abspaltung: 1,2,3,4-Benzothiatriazin-1,1(2H)-dioxide reagierten mit Allenen in Gegenwart eines Nickel(0)/(R)-Quinap-Komplexes regio- und enantioselektiv zu einer Vielzahl substituierter 3,4-Dihydro-1,2-benzothiazin-1,1(2H)-dioxide. Eine Nickelacyclus-Zwischenstufe wurde durch Aktivierung der Triazo-Einheit unter Stickstoffabspaltung erzeugt, was den intermolekularen Einbau einer Allengruppe ermöglichte. [source] Palladium-Catalyzed Arylative Ring-Opening Reactions of Norbornenols: Entry to Highly Substituted Cyclohexenes, Quinolines, and Tetrahydroquinolines,ANGEWANDTE CHEMIE, Issue 26 2010Michael Waibel Dr. Retro-Design: Palladium-katalysierte Retro-Allylierungen ausgehend von tertiären Norbornenolen ermöglichen deren Kupplung mit Aryl- oder Vinylhalogeniden unter Bildung tetrasubstituierter Cyclohexene mit hervorragender Regio- und Diastereoselektivität (siehe Schema). Dominovarianten dieser Reaktion eröffnen den Zugang zu hoch funktionalisierten Chinolinen und Tetrahydrochinolinen. [source] Phosphoramidite: privilegierte Liganden in der asymmetrischen KatalyseANGEWANDTE CHEMIE, Issue 14 2010Johannes Abstract Die asymmetrische Katalyse mit Übergangsmetallkomplexen ist die Grundlage unzähliger stereoselektiver Umwandlungen und hat damit das Bild der modernen Synthesechemie gewandelt. Der Schlüssel zum Erfolg war die Entwicklung chiraler Liganden zur Kontrolle der Regio-, Diastereo- und Enantioselektivität. Dabei haben sich Phosphoramidite als eine äußerst vielseitige und leicht zugängliche Klasse von chiralen Liganden erwiesen. Ihre modulare Struktur ermöglicht die Herstellung von Ligandenbibliotheken und erleichtert die Feinabstimmung für eine bestimmte katalytische Reaktion. Phosphoramidite bewirken oft außerordentlich hohe Stereoselektivitäten, und ihre einzähnige Natur ist in der kombinatorischen Katalyse, die gemischte Liganden verwendet, unverzichtbar. In diesem Aufsatz werden neue Entwicklungen in der asymmetrischen Katalyse mit Phosphoramiditen diskutiert, wobei der Schwerpunkt auf der Bildung von Kohlenstoff- Kohlenstoff- und Kohlenstoff-Heteroatom-Bindungen liegt. [source] | ||||||||||||||||||||||||||||