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  • 1
    Electronic Resource
    Electronic Resource
    Drugs for chiral discrimination: Non-coded amino acids and dipeptides by asymmetric hydrogenation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 535-539 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric hydrogenation ; non-coded amino acids ; enantioselectivity ; dipeptides ; diastereoselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of Propranolol, Pindolol, and Carazolol, well-known β-blockers, have been used to prepare cationic aminophosphine phosphinite rhodium complexes. Propraphos-Rh and Pindophos-Rh are very efficient catalysts in the asymmetric hydrogenation of N-Boc-protected unusual dehydroamino acid derivatives. Carazolol-Rh is less suitable in both activity and enantioselectivity. Under the same conditions, N-Boc-protected dehydrodipeptides are hydrogenated with diastereoselectivities between 70 and 90% de. Chirality 10:535-539, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Enantioselective synthesis of α-aminophosphonic acid derivatives by hydrogenation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 564-572 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric hydrogenation ; aminophosphine phosphinites ; rhodium complexes ; dehydro aminophosphonic acids ; NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral α-aminophosphonic acid derivatives are efficiently synthesized by asymmetric hydrogenation of the prochiral N-acyl-α,β-dehydroaminophosphonates. PROPRAPHOS-Rh-catalysts from readily available (S)- and (R)-Propranolol proved to be suitable in the homogenous reaction affording an enantiomeric excess of 87-92% with high rate. The aminophosphonic acid derivatives and precursors were fully characterized by 1H, 13C, and 31P NMR spectroscopy. Chirality 10:564-572, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Unusual amino acids VI. Substituted arylamino acids by asymmetric hydrogenation of N-Cbz and N-Boc protected dehydroamino acid derivatives (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 173-188 
    Details
    ISSN: 0899-0042
    Keywords: amino acids ; chiral rhodium complexes ; aminophosphine-phosphinite ; D- and L-enantiomers ; NMR spectra ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N-Cbz and N-Boc protected arylamino acrylic acids and esters have been prepared and used in asymmetric hydrogenations catalyzed by PROPRAPHOSRh. Stereoselectivities 〉 90% ee could be achieved, the rate of which is dependent on the position of the substituent in the aromatic ring. The N-Boc derivatives provide advantages compared with the N-Cbz analogues. The amino acid derivatives were fully characterized by 19F, 13C, and 1H NMR spectroscopy. © 1996 Wiley-Liss, Inc.
    Additional Material: 12 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Allenyl Enolates - A New Class of Chiral Ambident Nucleophiles, 5Part 4: M. Laux, N. Krause, U. Koop, Synlett 1996, 87-88.. Ireland-Claisen Rearrangements of Allenic Silyl Ketene Acetals (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 725-728 
    Details
    ISSN: 0947-3440
    Keywords: Allenes ; Silyl ketene acetals ; Selectivity ; Cuprates ; Rearrangements ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Allenic silyl ketene acetals 3 formed by conjugate 1,6-addition of organocuprates to 2-propen-1-yl and 2-buten-1-yl 2-en-4-ynoates 1 and regioselective enolate capture with silyl electrophiles readily undergo [3,3]-Ireland-Claisen rearrangements to the 2-substituted methyl 3,4-dienoates 4. The simple diastereoselection of the formation of 4b could be improved by variation of the silylating agent as well as the addition of bases. in the case of product 4c, the sigmatropic rearrangement also takes place with good diastereofacial selectivity, i.e., with axis-to-center chirality transfer.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970413
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of Vinylallenes by Conjugate 1,6-, 1,8-, 1,10- and 1,12-Addition Reactions of Organocuprates with Acetylenic Michael Acceptors and Their Use as Dienes in Intermolecular Diels-Alder Reactions (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1487-1499 
    Details
    ISSN: 0947-3440
    Keywords: Vinylallenes ; Organocuprates ; Conjugate addition ; Diels-Alder reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various vinylallenes were synthesized by conjugate cuprate additions to acetylenic Michael acceptors. Thus, 1,6-addition reactions with 2-en-4-ynoates 1, 3, and 5a, respectively, furnished vinylallenes 2, 4, and 7 after regioselective electrophilic capture of the allenyl enolates formed. Likewise, 1,8-addition to 2,4-dien-6-ynoates 8a and 10 gave the vinylallenes 9 and 11, whereas the 1,10-addition of Me2CuLi to 2,4,6-trien-8-ynoate 12 provided allene 13, and the analogous 1,12-addition to 2,4,6,8-tetraen-10-ynoate 14 furnished the polyene 15. These vinylallenes are valuable dienophiles in regio- and stereoselective Diels-Alder reactions, as evidenced by the formation of the cycloaddition products 16-24. In the presence of Lewis acids, vinylallene 4a presumably rearranges to a cyclopentadiene derivative which then forms the cycloadducts 25 and 26.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961002
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  • 6
    Electronic Resource
    Electronic Resource
    Diastereoselective Protonation of Chiral Enolates with Chelating Proton Donors under Reagent Control: Scope, Mechanism, and ApplicationsDedicated to Prof. Dr. Klaus Hafner on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2409-2418 
    Details
    ISSN: 0947-3440
    Keywords: Protonations ; Enolates ; Metalations ; Stereoselectivity ; Cuprates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Endocyclic keto-enolates of type 2 can be protonated under reagent control with high diastereoselectivities when chelating proton donors with a salicylate structure are used. The stereochemical course of these protonations is hardly affected by the ring size, the substitution pattern, and the presence of additional stereogenic centers in the enolate. The substrates can be prepared by conjugate cuprate addition as well as deprotonation; in the latter case, good diastereoselectivities are obtained by removal of competing proton sources and the inclusion of transmetalation steps. The chelate complex A serves as a mechanistic model that makes the usual trial and error search for stereoselective protonating agents unnecessary. The method is applied to stereoselective syntheses of a precursor for methyl epijasmonate and of the insect pheromone (2S,3S)-diprionyl acetate.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971204
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