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  • 1
    Electronic Resource
    Electronic Resource
    Stereoselective Intramolecular Hetero Diels-Alder Reactions of Cyclic Benzylidenesulfoxides and DFT Calculations on the Transition Structures (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2733-2741 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Density functional calculations ; Cycloadditions ; Dihydropyrans ; Enantioselective oxidations ; Sulfur heterocycles ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 4-benzylidene-3-oxo[1,3]oxathiolan-5-ones 13-15, which were derived from the 3-oxo[1,3]oxathiolan-5-ones 9-11 by Knoevenagel condensation with the aldehydes 12, cyclize in an intramolecular hetero Diels-Alder reaction with high yield and excellent endo/exo as well as induced diastereoselectivity to give the hetero Diels-Alder adducts 16-18. The preferred formation of the Knoevenagel products 13-15 with a (Z) configuration was predicted with DFT calculations (B3LYP-6-311+G*) using the model systems 28 and 29. In addition B3LYP-6-31G*/sB3LYP/3-21G(*) calculations on transition structures for the hetero Diels-Alder reaction of 29 and 30 allowed a good correlation with the experimental results, which show that an endo attack of the dienophile syn to the S-O group in 13-15 leads to the main products.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Enantioselective Synthesis of the Chromane Moiety of Vitamin E (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1075-1084 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Atropisomerism ; Bis(hydroxylation) ; Conformational analysis ; Palladium ; Vitamin E ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Several new approaches for the enantioselective synthesis of the chromane moiety of vitamin E are described. Sonogashira coupling of 3a with the alkyne 4 and subsequent elimination gave 6, which was bis(hydroxylated) in 93% yield and with 85% ee. Recrystallization gave enantiopure 7a, which was hydrogenated and transformed into the vitamin E precursor 11. The bis(hydroxylation) of 18 and 21 to give 9 and 22, respectively, was less than satisfactory, proceeding with ee values of 28% and 18%. In contrast, stereoselective allylation of ketone 15 followed by removal of the protecting group or ozonolysis of the allyl moiety furnished the allyl alcohol 26 and the aldehyde 27, respectively, in almost enantiopure form, which again could be used as precursors for vitamin E. Partial hydrogenation of 5a gave the alkene 32a and that of 28 the alkene 30b, both of which show interesting atropisomerism.
    Additional Material: 3 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Novel Steroid Alkaloids by Cyclization of Arylimines from Estrone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3013-3020 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Domino reactions ; Iminium ions ; Lewis acids ; Quinolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular Lewis or Brønsted acid-catalyzed cyclization reactions of steroid arylimines 6 yielded either tetrahydroquinolines condensed to the estrane skeleton 9 or N-arylamino-D-homosteroids 12-16, depending on the substituent of the arylimino group.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Efficient Biomimetic Synthesis of Indole Alkaloids of the Vallesiachotamine Group by a Domino Knoevenagel Hetero Diels-Alder Hydrogenation Sequence (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 881-886 
    Details
    ISSN: 0947-3440
    Keywords: Diels-Alder reaction ; Indole alkaloids ; Domino reactions ; Dihydroantirhine ; Strictosidine ; Cycloadditions ; Biomimetic Synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient three-step biomimetic synthesis of the four diastereomeric 18,19-dihydroantirhines 4a-d starting from the tetrahydrocarboline aldehydes 5a and 5b is described. Domino reaction of the aldehydes 5a and 5b, respectively, with Meldrum's acid (6) and the enol ethers 8a and 8b in the presence of catalytic amounts of ethylenediammonium diacetate leads to the strictosidine analogues 10a-d and 11a-h, respectively, in 74-86% yield, hydrogenation of which gives mainly 15 and 16 with the skeleton of the vallesiachotamine indole alkaloids (55-86%). In addition, small amounts of 17 and 18 with the corynanthe skeleton are also formed (10-12%). Reduction of both 15 and 16 with LiAlH4 yields the diastereomeric rac-18,19-dihydroantirhines 4a-d in 78-86% yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970515
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  • 5
    Electronic Resource
    Electronic Resource
    Intramolecular Heck Reaction for the Synthesis of Isochromanes under Ambient and High pressure (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 887-891 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, intramolecular ; Isochromane ; Palladium ; Heterocycles ; High-pressure chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iodoarenes 9 and 10, bearing (E)- and (Z)-alkene moieties, respectively, easily prepared by alkylation of the corresponding alcohols 7a-c and 8a-c with 2 iodobenzyl iodide, undergo intramolecular Heck reactions to give the isochromanes 12-15a-c in good yields. The selectivity of the reaction depends on the size of the substituent R in 9 and 10; increasing bulkiness of R leads to a decrease in diastereoselectivity and an increase in regioselectivity. High-pressure experiments confirm the proposed mechanism and show that bromoarenes such as 11, which tend to be unreactive at ambient pressure, give good results when the cyclisation is performed under high pressure.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970516
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  • 6
    Electronic Resource
    Electronic Resource
    Regioselective Silane-Terminated Intramolecular Heck Reaction with Alkenyl Triflates and Alkenyl Iodides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1959-1964 
    Details
    ISSN: 1434-193X
    Keywords: C-C coupling ; Palladium ; Silanes ; Catalysts ; Allylsilanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---One of the main problems of the Heck reaction using acyclic substrates which lead to Pd intermediates with β- and β′-hydrogens is the lack of selectivity in the formation of the double bond as the last step of the catalytic cycle. The use of allylsilanes as the alkene moiety permits control of the elimination step. Thus, the Pd0-catalysed reaction of 1a-c and 2 leads exclusively to the corresponding bicyclic compounds 11a-c. In contrast, reaction of 7 yields a mixture of 12a, (E)-12b and (Z)-12b.
    Additional Material: 1 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    Efficient Enantioselective Synthesis of Chiral Precursors for the Preparation of Vitamin E (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2221-2225 
    Details
    ISSN: 0947-3440
    Keywords: Vitamin E ; Enynes ; Bishydroxylation ; Palladium ; Asymmetric synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective bishydroxylation of the protected hydroxymethyl enynes 7a-d and 8a, b, which are easily obtained from commercially available 5 and 6, gave the triol derivatives 9a-d and 11a, b in good yields and moderate to high enantiomeric excess. Palladium-catalyzed coupling of 9a-d and 11a, b with the iodoarene 13 led to the desired precursors for the vitamin E synthesis ent-3a-d and 15a, b.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971108
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  • 8
    Electronic Resource
    Electronic Resource
    Diastereo- and Regioselective Intramolecular Heck Reaction of α-Amino Alcohol Derivatives for the Synthesis of Enantiomerically Pure Isoquinolines and Benzazepines at Ambient and High Pressure (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1407-1413 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, intramolecular ; α-Amino acids ; Isoquinolines ; Palladium ; Heterocycles ; Synthesis, enantioselective ; High pressure ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation and acylation of the alkenes 9b, c and 10a, b, which are easily prepared from the corresponding α-amino alcohols, with 2-halobenzyl and 2-halobenzoyl halides respectively, gives 11-15. These compounds cyclize with excellent diastereo- and regioselectivity to the enantiomerically pure N-heterocycles 18-20 in an intramolecular Heck reaction using 5 mol-% of Pd(OAc)2 in the presence of PPh3, TPAB and KOAc. Under the same conditions substrate 17 leads to the enantiomerically pure benzazepine 24. The reaction of the bromoarene derivatives 14-15 must be performed under high pressure to give good results.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970718
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  • 9
    Electronic Resource
    Electronic Resource
    Stereoselective Total Synthesis of a Novel D-Homosteroid by a Twofold Heck Reaction (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1827-1830 
    Details
    ISSN: 1434-193X
    Keywords: C-C coupling ; Homosteroids ; Palladium ; Steroids ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The D-homosteroid 1 was synthesized by two successive Heck reactions starting from enantiopure 3 and the bromoarene 2 containing a (Z)-bromovinyl group. The first intermolecular Pd-catalyzed reaction leads to 6 in a highly regio- and diastereoselective way which forms 1 with an unusual cis-junction of the rings B and C by a second intramolecular Heck reaction.
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  • 10
    Electronic Resource
    Electronic Resource
    Hocheffiziente Synthese von Cephalotaxin durch zweifache palladiumkatalysierte CyclisierungProfessor Peter Welzel zum 60. Geburtstag gewidmetDiese Arbeit wurde von der Deutschen Forschungsgemeinschaft (Sonderforschungsbereich 416) und vom Fonds der Chemischen Industrie gefördert. Der Degussa AG danken wir für eine großzügige Spende an Edelmetallen. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 1159-1160 
    Details
    ISSN: 0044-8249
    Keywords: Alkaloide ; Allylierungen ; Benzazepine ; Heck-Reaktionen ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971091027
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