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  • Enantioselective hydrosilylation  (4)
  • Optical induction  (3)
  • Diastereoselective hydrogenation  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Enantioselektive Cyclopropanierung von 1,1-Diphenylethylen und Diazoessigester mit Kupfer-Katalysatoren (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 1237-1254 
    Details
    ISSN: 1434-4475
    Keywords: Catalytic enantioselective cyclopropanation ; Copper (II) catalysts ; Optical induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Copper(II) compounds catalyze the reaction of 1,1-diphenylethylene with diazoacetic acid ethylester. The main product is 2,2-diphenylcyclopropane carboxylic acid ethylester. The formation of the carbene dimerization products fumaric and maleic acid diethylester can be suppressed by the continuous addition of diazoacetic acid ester to 1,1-diphenylethylene. 37 optically active ligands, partly new, were combined with copper(II)-acetate to givein-situ-catalysts. In five cases isolated copper complexes were used as catalysts. The best optical inductions in the formation of 2,2-diphenylcyclopro-pane carboxylic acid ethylester with up to 65.6% ee were achieved withSchiff base ligands, which derive from salicylaldehyde and amino alcohols, obtained from amino acid esters and phenylGrignard.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809355
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of optically active michael adducts via chiral enamines (1988)
    Springer
    Monatshefte für Chemie 119 (1988), S. 1161-1167 
    Details
    ISSN: 1434-4475
    Keywords: Michael Addition ; Enamines ; 1,3-Dicarbonyl compounds ; Optical induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Chirale Enamine, durchSchiffbasenkondensation aus 1,3-Dicarbonylverbindungen und (R)-(+)-1-Phenylethylamin erhalten, gehen mit α,β-ungesättigten Carbonylverbindungen diastereoselektiveMichaelreaktionen ein. Nach hydrolytischer Abspaltung des chiralen Hilfsstoffs (R)-(+)-1-Phenylethylamin werden dieMichaeladdukte in 59–95% optischer Ausbeute isoliert.
    Notes: Abstract Chiral enamines, obtained bySchiff base condensation from 1,3-dicarbonyl compounds and (R)-(+)-1-phenylethylamine, were found to undergo diastereoselectiveMichael reactions with α,β-unsaturated carbonyl compounds. After removal of the chiral auxiliary (R)-(+)-1-phenylethylamine by hydrolysis, theMichael adducts were isolated in 59–95% optical yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809268
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  • 3
    Electronic Resource
    Electronic Resource
    Asymmetrische Katalysen, 39. Mitt.: Monohydrosilane in der enantioselektiven katalytischen Hydrosilylierung prochiraler Ketone (1988)
    Springer
    Monatshefte für Chemie 119 (1988), S. 525-532 
    Details
    ISSN: 1434-4475
    Keywords: Monohydrosilanes ; Enantioselective hydrosilylation ; Prochiral ketones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reactivity of several monohydrosilane/complex systems in the hydrosilylation of acetophenone and benzylmethylketone was investigated. The active systems were modified by addition of optically active ligands and used as enantioselectivein-situ catalysts for the hydrosilylation of the above prochiral ketones which on hydrolysis gave α-phenylethanol and α-benzylethanol in up to 18% ee.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809204
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrierung prochiraler Olefine mit Rhodium-Komplexen von optisch aktiven Amidinen (1980)
    Springer
    Monatshefte für Chemie 111 (1980), S. 275-287 
    Details
    ISSN: 1434-4475
    Keywords: Catalytic asymmetric hydrogenation ; Optical induction ; Rh/amidine complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract [RhCl(C8H14)2]2 together with the optically active amidines C6H5C(=NR)NHCH(CH3) (C6H5) I–V or their Li derivatives after activation with molecular hydrogen gives catalysts which at room temperature and 1.1 bar H2-pressure hydrogenate the prochiral substrates (Z)-α[N-acetylamino]-cinnamic acid, itaconic acid, α-methylcinnamic acid, α-methylcinnamic aldehyde, and α-methylcinnamic alcohol as well as cyclohexene, benzene and toluene. Good hydrogenation activity of the new catalysts is in contrast to low optical induction which only in the hydrogenation of α-methylcinnamic alcohol with 1.5 to 2% leads to values different from zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938734
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  • 5
    Electronic Resource
    Electronic Resource
    Asymmetric Catalysis, 105Part 104: Ref.. Stereoselective Hydrogenation of Folic Acid with Immobilized Optically Active Rhodium(I)/Diphosphane Catalysts (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 55-62 
    Details
    ISSN: 0009-2940
    Keywords: Diastereoselective hydrogenation ; Folic acid ; Immobilized optically active rhodium(I)/diphosphane catalysts ; Leucovorin ; HPLC analysis of 5-formyltetrahydrofolic acid derivatives ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the hydrogenation of the C=N bonds in the pyrazine ring of the vitamin folic acid (1) optically active rhodium(I)/diphosphane complexes immobilized on supports such as silica gel or Al2O3 were used. The reduction was carried out at 50 bar hydrogen pressure in an aqueous solution buffered to pH 7. Thus, 5,6,7,8-tetrahydrofolic acid (2) was obtained which contains a new asymmetric center at C-6 of the pterine system. Therefore, in combination with the (S) configuration of the natural L-glutamic acid part of the molecule two diastereomers with (6S,S) and (6R,S) configuration arise. The relatively unstable tetrahydrofolic acid (2) was converted into its 5-formyl derivative folinic acid (4) by treatment with methyl formate/formic acid in a 5:1 mixture of DMSO/pyridine. The Ca salt of folinic acid (4) is the widely used drug leucovorin. The diastereomers were separated by silica gel HPLC. To the column bovine serum albumine (BSA) is covalently bound. With optically active rhodium(I)/diphosphane catalysts, immobilized on silica gel supports, a diastereoselectivity of up to 90% could be achieved in the hydrogenation of folic acid (1).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300109
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  • 6
    Electronic Resource
    Electronic Resource
    Asymmetrische Katalyse, 67. Diastereoselektive Hydrierung der Folsäure mit optisch aktiven Rhodium(I)-Diphosphan-Komplexen (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2085-2093 
    Details
    ISSN: 0009-2940
    Keywords: Diastereoselective hydrogenation ; Immobilized enantioselective rhodium(I)-diphosphane catalysts ; Folic acid ; (6S,S)-Folinic acid ; 5,6,7,8-Tetrahydrofolic acid ; N-5-(menthyloxycarbonyl)- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric Catalysis, 67[1]. - Diastereoselective Hydrogenation of Folic Acid with Optically Active Rhodium(I)-Diphosphane ComplexesWith immobilized rhodium(I)-diphosphane catalysts supported on silica gel, the C = N bonds of the pyrazine ring of folic acid (1) are reduced with hydrogen in aqueous solution to give 5,6,7,8-tetrahydrofolic acid. A mixture of the two diastereomers 2a and 3a is obtained with (6S)- and (6R)-configuration, respectively, at the newly formed asymmetric center in the pterine system and (S)-configuration in the L-glutamic acid moiety. The unstable hydrogenation products are derivatized with (-)-menthyl chloroformate. An improved HPLC procedure for the analysis of the products has been developed. By using optically active chelate phosphanes as cocatalysts together with [Rh(cod)Cl]2, a diastereomeric excess of up to 24% of the natural isomer 2a with (6S,S)-configuration is attained in the heterogeneous hydrogenation of folic acid.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250917
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  • 7
    Electronic Resource
    Electronic Resource
    Asymmetrische Katalysen, 45. Enantioselektive Hydrosilylierung von Ketonen mit [Rh(COD)Cl]2/Pyridinyloxazolin-Katalysatoren (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 499-507 
    Details
    ISSN: 0009-2940
    Keywords: Enantioselective hydrosilylation ; Optically active secondary alcohols ; Rhodium/pyridinyloxazoline catalysts ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Asymmetric Catalysis, 45. - Enantioselective Hydrosilylation of Ketones with [Rh(COD)Cl]2/Pyridinyloxazoline Catalysts21 optically active 2-(2-pyridinyl)oxazolines are synthezised from 2-cyanopyridine and optically pure amino alcohols. The new pyridinyloxazolines are used as cocatalysts together with [Rh(COD)-Cl]2 as homogeneous in situ catalysts in the enantioselective hydrosilylation of prochiral ketones with diphenylsilane. After hydrolysis, 1-phenylethanol is produced in 83.4% ee from acetophenone. Another three ketones are included into these investigations. The optical purity depends on the rhodium/ligand, rhodium/ketone, and ketone/silane ratio as well as on the solvent. Compared with other organic solvents, hydrosilylations in the solvent CCl4 without exceptions result in better chemical yields and optical purities as consequence of a change in the catalytically active species due to oxidative addition of CCl4.
    Notes: 21 optisch aktive 2-(2-Pyridinyl)oxazoline werden ausgehend von 2-Cyanpyridin und optisch reinen Aminoalkoholen synthetisiert. Die neuen Pyridinyloxazoline werden als Cokatalysatoren zusammen mit [Rh(COD)Cl]2 als homogene in-situ-Katalysatoren bei der enantioselektiven Hydrosilylierung von prochiralen Ketonen mit Diphenylsilan eingesetzt. Dabei wird aus Acetophenon nach Hydrolyse 1-Phenylethanol mit bis 83.4% ee erhalten. Drei weitere prochirale Ketone werden in die Untersuchungen einbezogen. Die optischen Induktionen sind vom Rhodium/Ligand-, Rhodium/Keton- und Keton/Silan-Verhältnis sowie vom Lösungsmittel abhängig. Hydrosilylierungen im Lösungsmittel, CCl4, führen, verglichen mit anderen organischen Lösungsmitteln, ausnahmslos zu verbesserten chemischen Ausbeuten und optischen Induktionen als Folge einer Veränderung der katalytisch aktiven Spezies durch oxidative Addition von CCl4.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220318
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  • 8
    Electronic Resource
    Electronic Resource
    Rh(I)-Catalysed Asymmetric Hydrosilylation using New Oxazoline Ligands with Potential Charge-transfer Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 783-788 
    Details
    ISSN: 1434-1948
    Keywords: Enantioselective hydrosilylation ; Oxazoline ligands ; Charge-transfer ; 4,4-Bipyridine derivatives ; 2,5-Dimethoxyacetophenone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel N′-methylated 2-(oxazolin-2-yl)-4,4′-bipyridinium salts, bearing a chiral oxazoline moiety, were tested in the Rh(I)-catalysed enantioselective hydrosilylation. After coordination to rhodium these electron-attracting ligands are supposed to exhibit charge-transfer effects with electron-donating substrates. Therefore, a new catalytic hydrosilylation reaction with 2,5-dimethoxyacetophenone as an electron-rich substrate was developed. The results were compared with those of the non-methylated 2-(oxazolin-2-yl)-4,4′-bipyridine and related ligands. In addition, the new ligands and Rh(I)-complexes were tested in the hydrosilylation of acetophenone.
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  • 9
    Electronic Resource
    Electronic Resource
    Novel Chiral Oxazoline Ligands for Potential Charge-Transfer Effects in the Rh(I)-Catalysed Enantioselective Hydrosilylation (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 771-781 
    Details
    ISSN: 1434-1948
    Keywords: Oxazolines ; Charge-transfer ; 4,4′-Bipyridine ; Enantioselective hydrosilylation ; Rh(I)-complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel 2-(4,4′-bipyridin-2-yl)oxazolines, bearing a chiral oxazoline moiety, were synthesised starting from 4,4′-bipyridine and selectively monomethylated in the N′-position. After coordination to rhodium these electron-poor ligands are supposed to exhibit charge-transfer effects with electron-donating substrates in the Rh(I)-catalysed enantioselective hydrosilylation (see next publication). Similar effects were expected from 4,4′-bipyridine- and pyrazine-bisoxazolines after complexation with rhodium. For comparison 2-(4-phenylpyridin-2-yl)oxazoline ligands were synthesised. Rh(I)-complexes of selected ligands were prepared and characterised, including an X-ray structure analysis.
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