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Regioselectivity
Kinds of Regioselectivity Selected AbstractsSynthesis of Hafnacyclopentanes from Hafnocene Alkyne Complexes: Influence of Styrene Substituents on the C,C Coupling RegioselectivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2009Torsten Beweries Abstract The alkyne complex rac -(ebthi)Hf(,2 -Me3SiC2SiMe3) (1)[ebthi = 1,2-ethylene-1,1,-bis(,5 -tetrahydroindenyl)] reacts with styrene and p -(trifluoromethyl)styrene to give hafnacyclopentanes 2 and 3, respectively. C,C coupling proceeds in different ways: whereas for complex 2 a hafnacyclopentane with substituents in the ,,,-position is formed, in the latter case only ,,, coupling was observed. Complexes 2 and 3 can be activated with B(C6F5)3 to form active catalysts for the polymerization of ethylene.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Regioselectivity in the Addition of Grignard Reagents to Bis(2-benzothiazolyl) Ketone: C - vs.EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2010O -Alkylation Using Aryl Grignard Reagents Abstract The reaction between bis(2-benzothiazolyl) ketone (1) and a series of ring-substituted phenyl Grignard reagents gives, in considerable amount, the unexpected O -alkylation product derived from the attack of the Grignard reagent to thecarbonyl oxygen atom, thus extending the range of rarely reported cases in which O -alkylation can occur. The expected classic 1,2-addition product and that derived from O -alkylation have been obtained in a relative molar ratio dependent on the substituent on the phenyl ring. Bis(2-benzothiazolyl) aryl carbinols, the classic 1,2-addition products to the carbonyl group of 1, were obtained in high yield through an alternative synthetic route that permitted the limit imposed by O - vs. C -alkylation competition to be overcome. [source] Regioselectivity of Friedländer Quinoline Syntheses,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2008Claas Lüder Diedrich Abstract Optically active, bicyclic ketones were submitted to Friedländer quinoline syntheses with 2-aminobenzaldehyde to yield regioisomeric linear or angular products. When starting from trans -configured ketones, the linear products are the major isomers (ratios ranging from 76:24 to >98/2). With cis -configured ketones the angular products are predominantly formed, although with lower regioselectivity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Theoretical and Experimental Study of the Regioselectivity of Michael AdditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2004David C. Chatfield Abstract Nucleophilic attack at an ,,,-unsaturated carbonyl moiety usually results in conjugate addition at the ,-carbon atom (1,4 or Michael addition) or, occasionally, in addition at the carbonyl carbon atom (1,2 addition). Recently, however, addition at the ,-carbon atom has been observed when strongly electron-withdrawing groups are positioned at the carbon atom , relative to the carbonyl group [e.g., methyl 3,3-bis(trifluoromethyl)propenoate (8) and ethyl 3-(2,4-dinitrophenyl)propenoate (24)]. We have performed theoretical calculations [HF/6,31+G(d) and B3LYP//HF/6,31+G(d)] for the addition of cyanide anion to model ,,,-unsaturated carbonyl compounds to determine trends in the regioselectivity with respect to properties of the substituents. The difference between the reaction barriers for ,- vs. ,-addition decreases as the strength of electron-withdrawing groups increases until, for sufficiently strong electron-withdrawing groups, ,-addition becomes favored. The calculations are in agreement with the experimental results. We show that the regioselectivity can be predicted from partial atomic charges and properties of the frontier orbitals of the reactants. We also report new experimental evidence of ,-addition to polysubstituted cinnamates and cinnamaldehydes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Substrate-dependent hysteretic behavior in StEH1-catalyzed hydrolysis of styrene oxide derivativesFEBS JOURNAL, Issue 24 2008Diana Lindberg The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and pre-steady-state measurements on a series of styrene oxide derivatives. A preference for the (S)- or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide and trans -stilbene oxide was established, with E -values of 43, 160 and 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence, as did the rate of alkylenzyme formation in the reaction with the (R,R)-enantiomer. Such kinetic behavior is indicative of an additional, off-pathway step in the mechanism, referred to as hysteresis. On the basis of these data, a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13C-NMR spectroscopy of 18O-labeled diol products. The (S,S)-enantiomer is attacked exclusively at the C-1 epoxide carbon, whereas the (R,R)-enantiomer is attacked at either position at a ratio of 65 : 35 in favor of the C-1 carbon. On the basis of the results, we conclude that differences in efficiency in stabilization of the alkylenzyme intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans -stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency. [source] Epoxidation of Polyunsaturated Fatty Acid Double Bonds by Dioxirane Reagent: Regioselectivity and Lipid Supramolecular OrganizationHELVETICA CHIMICA ACTA, Issue 10 2006Stanislav Abstract The use of dimethyldioxirane (DMD) as the epoxidizing agent for polyunsaturated fatty acids was investigated. With fatty acid methyl esters, this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by-products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome, and the epoxidation showed interesting regioselective features. The CC bonds closest to the aqueous-micelle interface is the most favored for the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid (=,(9Z,12Z)-octadeca-9,12-dienoic acid) to the 9,10-monoepoxy derivative was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid (=,(5Z,8Z,11Z,14Z)-eicosa-5,8,11,14-tetraenoic acid) micelles, the regioselective outcome with formation of the four possible monoepoxy isomers was studied under different conditions. It resulted to be a convenient synthesis of ,cis -5,6-epoxyeicosatrienoic acid' (=,3-[(2Z,5Z,8Z)-tetradeca-2,5,8-trienyl]oxiran-2-butanoic acid), whereas in reverse micelles, epoxidation mostly gave ,cis -14,15-epoxyeicosatrienoic acid (=,(5Z,8Z,11Z)-13-(3-pentyloxiran-2-yl)trideca-5,8,11-trienoic acid). [source] Reusable Gold(I) Catalysts with Unique Regioselectivity for Intermolecular Hydroamination of AlkynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Antonio Leyva Abstract Two gold(I) phosphine complexes bearing the low-coordinating bis(trifluoromethanesulfonyl)imidate ligand, namely AuSPhosNTf2 and AuPPh3NTf2, are active catalysts for the regioselective intermolecular hydroamination of both internal and terminal alkynes under mild reaction conditions. The catalysts show a regioselectivity based on electronic rather than steric factors, which allow the preferential synthesis of regioisomers opposite to those described previously. This subtle chemo- and regioselectivity depends on the catalyst, substrates and reaction conditions employed, and allows one to perform new tandem reactions. These gold(I) complexes operate under free-solvent conditions, without exclusion of air, without addition of acidic promoters and can be quantitatively recovered and reused by simple precipitation in hexane. [source] Remote Interactions Explain the Unusual Regioselectivity of Lipase from Pseudomonas cepacia toward the Secondary Hydroxyl of 2,-DeoxynucleosidesCHEMBIOCHEM, Issue 4 2006Iván Lavandera Dr. Abstract Lipase from Pseudomonas cepacia (PCL) surprisingly favors acylation of the secondary hydroxyl at the 3,-position over the primary hydroxyl at the 5,-position in 2,-deoxynucleosides by up to >98:1. Catalytically productive tetrahedral intermediate analogues for both orientations were found by molecular modeling. However, acylation of the 3,-hydroxyl places the thymine base in the alternate hydrophobic pocket of PCL's substrate-binding site where it can hydrogen bond to the side-chain hydroxyls of Tyr23 and Tyr29 and the main chain carbonyl of Leu17. Conversely, acylation of the 5,-hydroxyl leaves the thymine base in the solvent where there is no favorable binding to the enzyme. We propose that these remote stabilizing interactions between the thymine base and PCL's substrate-binding site stabilize the 3,-acylation transition state and thus account for the unusual regioselectivity. [source] ChemInform Abstract: Unusual Regioselectivity in Pd(0)-Catalyzed Coupling of Allylic Monoacetates and Nitroalkenes: One-Pot Isomerization,Alkylation.CHEMINFORM, Issue 26 2010Pasha M. Khan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Water-Controlled Regioselectivity of Pd-Catalyzed Domino Reaction Involving a C,H Activation Process: Rapid Synthesis of Diverse Carbo- and Heterocyclic Skeletons.CHEMINFORM, Issue 26 2010Zhiyao Lu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Synthesis of Quinoxaline Quinones and Regioselectivity in Their Diels,Alder Cycloadditions.CHEMINFORM, Issue 12 2010Gitanjali Sharma Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Switching the Regioselectivity of Direct C,H Arylation of 1,3-Dimethyluracil.CHEMINFORM, Issue 50 2009Miroslava Cernova Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Nickel- and Rhodium-Catalyzed Addition of Terminal Silylacetylenes to Propargyl Amines: Catalyst-Dependent Complementary Regioselectivity.CHEMINFORM, Issue 37 2009Naoto Matsuyama Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Cycloaddition of Cyclohexa-2,4-dienones with Nitroolefins: An Unusual Regioselectivity and Expeditious Entry into Nitro-bicyclo[2.2.2]octenones.CHEMINFORM, Issue 5 2009Vishwakarma Singh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: High Regioselectivity in Electrochemical ,-Methoxylation of N-Protected Cyclic Amines.CHEMINFORM, Issue 41 2008Samuel S. Libendi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Base-Mediated Reaction of Hydrazones and Nitroolefins with a Reversed Regioselectivity: A Novel Synthesis of 1,3,4-Trisubstituted Pyrazoles.CHEMINFORM, Issue 36 2008Xiaohu Deng Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Improved Regioselectivity in Pyrazole Formation Through the Use of Fluorinated Alcohols as Solvents: Synthesis and Biological Activity of Fluorinated Tebufenpyrad Analogues.CHEMINFORM, Issue 34 2008Santos Fustero Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Regioselectivity in the Reaction of Ethyl Diethoxyphosphorylacetate with 1-Aryl-2-haloalkan-1-ones: Effective Synthesis of 4-Aryl-2-diethoxyphosphoryl-4-oxobutanoates.CHEMINFORM, Issue 41 2007Jacek F. Koszuk Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity in Lewis Acid Catalyzed X,H (O, S, N) Insertions of Methyl Styryldiazoacetate with Benzyl Alcohol, Benzyl Thiol, and Aniline.CHEMINFORM, Issue 36 2007Yongli Yue Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity in a Highly Efficient, Microwave-Assisted Epoxide Aminolysis.CHEMINFORM, Issue 29 2007Hinal Desai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Unexpected Regioselectivity in the Reaction Between Cycloalkenyl-1-diazenes and Thioamides: Useful Entry to Fused Cycloalkyl-thiazoline and Cycloalkyl-thiazoline,Pyrazole Systems.CHEMINFORM, Issue 28 2007Orazio A. Attanasi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A Study of the Scope and Regioselectivity of the Ruthenium-Catalyzed [3 + 2]-Cycloaddition of Azides with Internal Alkynes.CHEMINFORM, Issue 10 2007Max M. Majireck Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Expedient Synthesis of Chiral 1,2- and 1,4-Diamines: Protecting Group Dependent Regioselectivity in Direct Organocatalytic Asymmetric Mannich Reactions.CHEMINFORM, Issue 42 2006Naidu S. Chowdari Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity in the Formation of Small- and Medium-Sized Cyclic Ethers by Diene-Ene Ring-Closing Metathesis.CHEMINFORM, Issue 40 2006Sudipta Basu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity in Nucleophilic Addition of Siloxyalkenes to an Alkylideneallyl Cation.CHEMINFORM, Issue 35 2006Morifumi Fujita Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity of Reduction Debromination of Substituted Pentabromobenzenes with Sodium tert-Butoxide in DMSO.CHEMINFORM, Issue 34 2006V. N. Shishkin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Change in Regioselectivity in the Monoreduction of 2,4,6-Trinitrotoluene with Titanium(III) and Vanadium(II) Ions in the Presence of Iron(II) and Copper(II) Salts.CHEMINFORM, Issue 29 2006V. N. Leibzon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Mercuric Chloride and Iodide Mediated Cyclization of Tethered Alkynedithioacetals as a General Route to Five- and Six-Membered Rings: Tuning of Regioselectivity by Alkyne Substitution.CHEMINFORM, Issue 22 2006Goutam Biswas Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regioselectivity in Nickel(0)/Phosphine Catalyzed Cycloadditions of Alkynes and Isocyanates.CHEMINFORM, Issue 13 2006Hung A. Duong Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Relevance of the Glycosyl Donor to the Regioselectivity of Glycosidation of Primary-Secondary Diol Acceptors and Application of These Ideas to in situ Three-Component Double Differential Glycosidation.CHEMINFORM, Issue 4 2006Clara Uriel No abstract is available for this article. [source] | ||||||||||||||||||||||||||||