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Chiral N (chiral + n)
Selected AbstractsAsymmetric Mannich-Type Reaction of a Chiral N -(tert -Butylsulfinyl) Ketimine with Imines: Application to the Synthesis of Chiral 1,3-DiaminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2006Cui-Hua Zhao Abstract Deprotonation of the chiral N -(tert -butylsulfinyl) ketimine 1 followed by trapping with imines 2 afforded the ,-aminoimines 3 as the Mannich-type products in high diastereoselectivities (99:1 dr). As versatile synthons chiral ,-amino imines 3 could be transformed into enantiomeric ,-amino ketone and chiral syn - or anti -1,3-diamines with high diastereomeric excess by hydrolysis or reduction, respectively. Moreover, the nucleophilic addition of organometallicreagents to chiral ,-amino imines 3 could provide 1,1,3-trisubstituted 1,3-diamines with high diastereoselectivities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Highly Enantioselective Allylation of Aromatic ,-Keto Phosphonates Catalyzed by Chiral N,N,- Dioxide-Indium(III) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2 2008Jinglun Huang Abstract The ramipril derivative N,N, -dioxide 3g -indium(III) complex was found to be an efficient catalyst for the allylation of the aromatic ,-keto phosphonates. The corresponding ,-hydroxy phosphonates were obtained with high yields (up to 98,%) and high enantioselectivities (up to 91,% ee). A bifunctional catalyst system was described with an N -oxide as Lewis base activating tetraallyltin and indium as Lewis acid activating aromatic ,-keto phosphonates. A possible catalytic cycle has been proposed to explain the mechanism of the reaction. [source] ChemInform Abstract: Highly Enantioselective Aza-Henry Reaction of Ketoimines Catalyzed by Chiral N,N,-Dioxide,Copper(I) Complexes.CHEMINFORM, Issue 16 2009Cheng Tan 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: Diastereoselective Cyanomethylation of Chiral N-(tert-Butylsulfinyl)imines Promoted by Lewis Bases.CHEMINFORM, Issue 9 2008Teruaki Mukaiyama 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] The Synthesis and Application of Novel C2 -Symmetric Chiral N,N,O,O Bisoxazoline Ligands with a Ferrocene Backbone.CHEMINFORM, Issue 17 2007Genghong Hua 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] Asymmetric Synthesis of trans-3-Amino-4-alkylazetidin-2-ones from Chiral N,N-Dialkylhydrazones.CHEMINFORM, Issue 48 2004Elena Diez Abstract For Abstract see ChemInform Abstract in Full Text. [source] Configurationally Stable Axially Chiral N,N,-Dialkyl-2,2,-biphenylene-N,N,-ureas.CHEMINFORM, Issue 20 2004Alexander I. Roshchin Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereoselective Formation of N-Acyliminium Ion via Chiral N,O-Acetal TMS Ether and Its Application to the Synthesis of ,-Amino Acids.CHEMINFORM, Issue 5 2004Dong-Yun Shin Abstract For Abstract see ChemInform Abstract in Full Text. [source] Enantioselective Strecker Reactions Between Aldimines and Trimethylsilyl Cyanide Promoted by Chiral N,N,-Dioxides.CHEMINFORM, Issue 5 2004Zhigang Jiao Abstract For Abstract see ChemInform Abstract in Full Text. [source] The Catalytic Asymmetric Addition of Diethylzinc to N-(Diphenylphosphinoyl) Imines Catalyzed by Cu(OTf)2 -Chiral N-(Binaphthyl-2-yl)thiophosphoramide Ligands.CHEMINFORM, Issue 46 2003Min Shi No abstract is available for this article. [source] Intermolecular Phenolic Hydroxy Methylation Occurring between Chiral N,N, -Bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamide and Co-crystallized Methanol under Electron Impact Ionization ConditionsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2004Jia-Xi Xu Abstract An intermolecular phenolic hydroxy methylation occurring between chiral N,N, -bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5dicarbamide and co-crystallized methanol under electron impact ionization conditions was observed. The result was confirmed by X-ray diffraction structural analysis of a co-crystalline of (R,R)-enantiomer and methanol. [source] New Chiral N, 5-Ligands with Thiophenyl at Benzylic Position.CHINESE JOURNAL OF CHEMISTRY, Issue 9 2002Palladium (II)-catalyzed Enantioselective Allylic Alkylation Abstract New chiral N, S-ligands with oxazoline and thiophenyl substituents at benzene ring and benzylic position have been prepared and applied in palladium-catalyzed asymmetric allylic alkylation reaction to provide the product with high yield and entantioselectivity (82%,93% ee). [source] Syntheses, Spectroscopic Studies, and Crystal Structures of Chiral [Rh(aminocarboxylato)(,4 -cod)] and Chiral [Rh(amino alcohol)(,4 -cod)](acetate) Complexes with an Example of a Spontaneous Resolution of a Racemic Mixture into Homochiral Helix-EnantiomersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2006Mohammed Enamullah Abstract The dimeric complex acetato(,4 -cycloocta-1,5-diene)rhodium(I), [Rh(O2CMe)(,4 -cod)]2 (cod = cycloocta-1,5-diene), reacts with amino acids [HAA = L -alanine, (S)-2-amino-2-phenylacetic acid (L -phenylglycine), N -methylglycine, and N -phenylglycine] and with the amino alcohol (S)-2-amino-2-phenylethanol to afford the aminocarboxylato(,4 -cycloocta-1,5-diene)rhodium(I) complexes [Rh(AA)(,4 -cod)] (AA = deprotonated amino acid = aminocarboxylato ligand) and [(S)-2-amino-2-phenylethanol](,4 -cycloocta-1,5-diene)rhodium(I) acetate, [Rh{(S)-HOCH2,CH(Ph)-NH2}(,4 -cod)](O2CMe) (V). The complexes are characterized by IR, UV/Vis, 1H/13C NMR and mass spectroscopy. The achiral N -phenylglycine ligand gives a chiral N -phenylglycinato complex [Rh(O2C,CH2,NHPh)(,4 -cod)] (IV) with the amine nitrogen atom becoming the stereogenic center upon metal coordination. Complex IV crystallizes in the tetragonal, chiral space group P43 and the crystal structure reveals twofold spontaneous resolution of a racemic mixture into homochiral helix-enantiomers. The investigated crystal contained only one type of helix, namely (left-handed or M- ) 43 -helical chains. This is traced first to an intermolecular N,H···O hydrogen bonding from the stereogenic amino group to a neighboring unligated carboxyl oxygen atom that connects only molecules of the same (R)-configuration into (left-handed or M- ) 43 -helical chains. This intrachain homochirality is supplemented, secondly, by the interlocking of adjacent chains with their corrugated van der Waals surface to allow for an interchain transmission of the sense of helicity, building the single crystal from the same homochiral helix-enantiomer. The enantiomeric amino alcohol complex V crystallizes in the monoclinic, noncentrosymmetric (Sohncke) space group P21. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Alkylzinc Complexes with Achiral and Chiral Monoanionic N,N,O Heteroscorpionate LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2003Ina Hegelmann Abstract The synthesis of the new chiral ligand (3,5-di- tertbutylpyrazol-1-yl)(3,,5,-dimethylpyrazol-1-yl)aceticacid (bpaHtBu2,Me2) (4) has been achieved. Two different synthetic routes to its precursor 3,5-di- tert -butyl-1-[(3,5-dimethyl-1H -pyrazol-1-yl)methyl]-1H -pyrazole (bpmtBu2,Me2) (3) are reported. Deprotonation at the methylene group, followed by reaction with carbon dioxide, yielded a racemic mixture of 4. The chemical behaviour of bis(3,5-di- tert -butylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) and the new chiral N,N,O scorpionate ligand 4 involving their coordination to zinc ions was studied. [Zn(bpatBu2,Me2)Cl] (5) was formed from a mixture of ZnCl2, 4 and base. Reaction of bis(3,5-di- tert -butylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) with Zn(CH3)2 or Zn(CH2CH3)2 gave the alkylzinc complexes [Zn(bdtbpza)(CH3)] (6) and [Zn(bdtbpza)(CH2CH3)] (7). [Zn(bpatBu2,Me2)(CH3)] (8) was obtained from a synthesis analogous to that of 6 with 4. The further reactions of 6 and 8 with acetic acid resulted in the acetato complexes [Zn(OAc)(bdtbpza)] (9) and [Zn(OAc)(bpatBu2,Me2)] (10). The chiral methyl complex 8 may serve as a precursor for structural model complexes of the active sites of zinc enzymes, such as thermolysin or carboxypeptidase A. [Zn(bpatBu2,Me2)2] (11) was formed from a side reaction. Crystal structures of 4, 5, 8 and 11 were obtained; 5 crystallised as the dimer [Zn(bpatBu2,Me2)Cl]2; 11 presents an unusual zinc binding geometry. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003) [source] The Use of N -Type Ligands in the Enantioselective Liquid,Liquid Extraction of Underivatized Amino AcidsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Bastiaan J. V. Verkuijl Abstract The first palladium based extraction system using chiral N -based ligands in the enantioselective liquid,liquid extraction (ELLE) of underivatized amino acids, is presented. The system shows the highest selectivity for the ELLE of methionine with metal complexes as hosts reported to date. Furthermore, the host can be prepared in situ from commercially available compounds. The dependency of the system on parameters such as pH, organic solvent, and temperature has been established. The intrinsic selectivity was deduced by determination of the association constants of the palladium complex with the tryptophan enantiomers. [source] Theoretical Study on Hetero-Diels,Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII ComplexesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2010Xiuli Cao Abstract The mechanism of the hetero-Diels,Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N, -dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ,mol,1, which is 63.0 kJ,mol,1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N, -dioxide/In(OTf)3 complex catalyzed hetero-Diels,Alder reaction at the molecular level. [source] A Temporary Stereocentre Approach for the Stereodivergent Synthesis of Either Enantiomer of ,-MethyloctanalEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2007D. Gangani Niyadurupola Abstract The aldol reaction of a chiral N -(acyl)oxazolidin-2-one with 2-methyleneoctanal or (E)-2-methyloct-2-enal affords chiral aldol products whose alkene functionalities were hydrogenated using Brown's or Wilkinson's catalyst to afford syn - or anti -selective products with excellent levels of diastereocontrol. Subsequent retro -aldol cleavage of these syn - or anti -adducts resulted in the formation of either (R)- or (S)-enantiomer of ,-methyloctanal with no racemisation occurring, which could be derivatised in-situ to afford chiral dithiane, alcohol or ,,,-unsaturated ester products in enantiopure form.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Asymmetric Mannich-Type Reaction of a Chiral N -(tert -Butylsulfinyl) Ketimine with Imines: Application to the Synthesis of Chiral 1,3-DiaminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2006Cui-Hua Zhao Abstract Deprotonation of the chiral N -(tert -butylsulfinyl) ketimine 1 followed by trapping with imines 2 afforded the ,-aminoimines 3 as the Mannich-type products in high diastereoselectivities (99:1 dr). As versatile synthons chiral ,-amino imines 3 could be transformed into enantiomeric ,-amino ketone and chiral syn - or anti -1,3-diamines with high diastereomeric excess by hydrolysis or reduction, respectively. Moreover, the nucleophilic addition of organometallicreagents to chiral ,-amino imines 3 could provide 1,1,3-trisubstituted 1,3-diamines with high diastereoselectivities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthetic Studies on Camptothecins.HELVETICA CHIMICA ACTA, Issue 11 2008Part Abstract A six-step asymmetric total synthesis of (20S)-camptothecin (1) has been accomplished in 25% overall yield starting from the known pyridone 3. The key steps in this synthesis are the chemoselective Ni-catalyzed hydrogenation of 3-cyanopyridone 6 to 3-formylpyridone 7 in AcOH/pyridine/H2O and the Davis asymmetric hydroxylation of tricyclic lactone 4 utilizing a chiral N -sulfonyloxaziridine into (4,S)-tricyclic hydroxylactone 2. [source] Highly Efficient Asymmetric Three-Component Vinylogous Mannich Reaction Catalyzed by a Chiral Scandium(III)- N,N,-Dioxide ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Qi Zhang Abstract The asymmetric three-component vinylogous Mannich reaction of an acyclic silyl dienol ester, an aldehyde and 2-aminophenol was accomplished using a chiral N,N,-dioxide-scandium(III) complex as the catalyst. A variety of aldehydes were found to be suitable substrates for the reaction and the desired ,-amino-,,,-unsaturated esters were obtained in 90,99% yields with good to excellent enantioselectivities (up to >99% ee) and complete regioselectivities. Moreover, the simple experimental procedures were air-tolerant and convenient. The present catalytic process provides the potential for large-scale syntheses of the chiral ,-amino-,,,-unsaturated esters. [source] Enantioselective Synthesis of Chiral Tetrahydroisoquinolines by Iridium-Catalyzed Asymmetric Hydrogenation of EnaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Pu-Cha Yan Abstract Chiral iridium complexes based on spiro phosphoramidite ligands are demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of unfunctionalized enamines with an exocyclic double bond. In combination with excess iodine or potassium iodide and under hydrogen pressure, the complex Ir/(Sa,R,R)- 3a provides chiral N -alkyltetrahydroisoquinolines in high yields with up to 98% ee. The L/Ir ratio of 2:1 is crucial for obtaining a high reaction rate and enantioselectivity. A deuterium labeling experiment showed that an inverse isotope effect exists in this reaction. A possible catalytic cycle including an iridium(III) species bearing two monophosphoramidite ligands is also proposed. [source] Development and Application of a New General Method for the Asymmetric Synthesis of (E)-(2-En-3-ynyl)-aminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Chao Yin Abstract The first direct approach for the asymmetric synthesis of (E)-2-arylidene-1,4-diphenylbut-3-yn-1-amines by addition of alkynylzinc to chiral N - tert -butylsulfinylimines is reported with excellent diastereoselectivity and good yield. This asymmetric addition reaction provides a practical, economical and concise synthesis of multifunctional molecules with the 1,3-enyne side chain and an amino group. In addition, this methodology can be applied to the synthesis of substituted vinyl iodide compounds, and substituted chiral dihydropyrroles. [source] An N -Linked Bidentate Phosphoramidite Ligand (N- Me-BIPAM) for Rhodium-Catalyzed Asymmetric Addition of Arylboronic Acids to N- SulfonylarylaldiminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Kazunori Kurihara Abstract A chiral N -linked C2 -symmetric bidentate phosphoramidite (N- Me-BIPAM) was newly developed for the rhodium-catalyzed enantioselective addition of arylboronic acids to N- sulfonylimines. This ligand achieved high enantioselectivities in a range of 84,99% ee in additions of arylboronic acids to N- tosyl- and N- nosylarylaldimines. [source] Bond-based 3D-chiral linear indices: Theory and QSAR applications to central chirality codificationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2008Juan A. Castillo-Garit Abstract The recently introduced non-stochastic and stochastic bond-based linear indices are been generalized to codify chemical structure information for chiral drugs, making use of a trigonometric 3D-chirality correction factor. These improved modified descriptors are applied to several well-known data sets to validate each one of them. Particularly, Cramer's steroid data set has become a benchmark for the assessment of novel quantitative structure activity relationship methods. This data set has been used by several researchers using 3D-QSAR approaches such as Comparative Molecular Field Analysis, Molecular Quantum Similarity Measures, Comparative Molecular Moment Analysis, E-state, Mapping Property Distributions of Molecular Surfaces, and so on. For that reason, it is selected by us for the sake of comparability. In addition, to evaluate the effectiveness of this novel approach in drug design we model the angiotensin-converting enzyme inhibitory activity of perindoprilate's ,-stereoisomers combinatorial library, as well as codify information related to a pharmacological property highly dependent on the molecular symmetry of a set of seven pairs of chiral N -alkylated 3-(3-hydroxyphenyl)-piperidines that bind ,-receptors. The validation of this method is achieved by comparison with earlier publications applied to the same data sets. The non-stochastic and stochastic bond-based 3D-chiral linear indices appear to provide a very interesting alternative to other more common 3D-QSAR descriptors. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Asymmetric transfer hydrogenation catalyzed by a novel planar chiral N -heterocyclic carbene,rhodium(I) complexAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2009Ru Jiang Abstract A novel chelated ferrocene-based planar chiral N-heterocyclic carbene-Rh(I) complex was synthesized by a simple method. It was applied to the asymmetric transfer hydrogenation of prochiral ketones. Enantioselectivities of up to 67% ee were observed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation of novel axially chiral NHC,Pd(II) complexes and their application in oxidative kinetic resolution of secondary alcoholsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2009Shi-Jia Liu Abstract Novel axially chiral N -heterocyclic carbene (NHC) Pd(II) complexes were prepared from optically active 1,1,-binaphthalenyl-2,2,-diamine (BINAM) and H8 -BINAM and their crystal structures were unambiguously determined by X-ray diffraction. These chiral N -heterocyclic carbene (NHC) Pd(II) complexes were applied in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant or under aerobic conditions, affording the corresponding sec -alcohols in good yields with moderate to good enantioselectivities. Copyright © 2009 John Wiley & Sons, Ltd. [source] Enantioselective Synthesis of l -Homophenylalanine by Whole Cells of Recombinant Escherichia coli Expressing l -Aminoacylase and N -Acylamino Acid Racemase Genes from Deinococcus radiodurans BCRC12827BIOTECHNOLOGY PROGRESS, Issue 6 2006Shih-Kuang Hsu l -Homophenylalanine (l -HPA) is a chiral unnatural amino acid used in the synthesis of angiotensin converting enzyme inhibitors and many pharmaceuticals. To develop a bioconversion process with dynamic resolution of N -acylamino acids for the l -HPA production, N -acylamino acid racemase (NAAAR) and l -aminoacylase (LAA) genes were cloned from Deinococcus radiodurans BCRC12827 and expressed in Escherichia coli XLIBlue. The recombinant enzymes were purified by nickel-chelate chromatography, and their biochemical properties were determined. The NAAAR had high racemization activity toward chiral N -acetyl-homophenylalanine (NAc-HPA). The LAA exhibited strict l -enantioselection to hydrolyze the NAc- l -HPA. A stirred glass vessel containing transformed E. coli cells expressing D. radiodurans NAAAR and LAA was used for the conversion of NAc- d -HPA to l -HPA. Unbalance activities of LAA and NAAAR were found in E. coli cell coexpressing laa and naaar genes, which resulted in the accumulation of an intermediate, NAc- l -HPA, in the early stage of conversion and a low productivity of 0.83 mmol l -HPA/L h. The results indicated that low activity of LAA present in the biomass is the rate-limiting factor in l -HPA production. In the case of two whole cells with separately expressed enzyme, the enzymatic activities of LAA and NAAAR could be balanced by changing the loading of individual cells. When the activities of two enzymes were fixed at 3600 U/L, 99.9% yield of l -HPA could be reached in 1 h, with a productivity of 10 mmol l -HPA/L h. The cells can be reused at least six cycles at a conversion yield of more than 96%. This is the first NAAAR/LAA process using NAc-HPA as substrate and recombinant whole cells containing Deinococcus enzymes as catalysts for the production of l -HPA to be reported. [source] Catalytic Asymmetric Synthesis of 3-(,-Hydroxy-,-carbonyl) Oxindoles by a ScIII -Catalyzed Direct Aldol-Type ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2010Ke Shen Abstract A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N, -dioxide,Sc(OTf)3 (Tf=trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93,% yield, 99:1 diastereomeric ratio (dr), and >99,% enantiomeric excess (ee)) under mild conditions, to deliver 3-(,-hydroxy-,-carbonyl) oxindoles with vicinal quaternary,tertiary or quaternary,quaternary stereocenters. Even with 1,mol,% catalyst loading or on scaleup (10,mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and ScIII -based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. [source] Highly Enantioselective Synthesis of ,-Heteroaryl-Substituted Dihydrochalcones Through Friedel,Crafts Alkylation of Indoles and PyrroleCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2010Wentao Wang Abstract A highly enantioselective Friedel,Crafts (F,C) alkylation of indoles and pyrrole with chalcone derivatives catalyzed by a chiral N,N, -dioxide,Sc(OTf)3 complex has been developed that tolerates a wide range of substrates. The reaction proceeds in moderate to excellent yields and high enantioselectivities (85,92,% enantiomeric excess) using 2,mol,% (for indole) or 0.5,mol,% (for pyrrole) catalyst loading, which showed the potential value of the catalyst system. Meanwhile, a strong positive nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible working model is proposed to explain the origin of the activation and asymmetric induction. [source] Enantioselective Addition of Phenylacetylene to Ketones Catalyzed by Titanium(IV) Complexes of N -Sulfonylated , -Amino AlcoholsCHINESE JOURNAL OF CHEMISTRY, Issue 2 2006Shao-Hua Wang Abstract The easily prepared and recoverable chiral N -sulfonylated , -amino alcohol 2 in combination with Ti(OPr- i)4was found to be an effective chiral catalyst for the enantioselective addition of alkynylzinc to ketones, which gave the useful products, i.e. chiral tertiary propargyl alcohols, with the ee up to 92%. [source] | |||||||||||||||||||||||||