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  • 1
    Electronic Resource
    Electronic Resource
    Intramolecular Ene and Related Reactions, 53g). Stereoselective Formation of trans-1,2-Disubstituted Cyclopentanes by Intramolecular Cyclisation of Allylsilane Alkylidene 1,3-Dioxo Compounds (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1387-1395 
    Details
    ISSN: 0009-2940
    Keywords: Cyclopentanes, trans-1,2-disubstituted ; Allylsilanes ; Knoevenagel condensation ; Ene reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkylidene 1,3-dioxo compounds 4a-d with an allylsilane moiety undergo a fluoride-, Lewis acid- and TMSOTf-induced intramolecular cyclisation to give almost exclusively the trans-1,2-disubstituted cyclopentanes 5a-d in good to excellent yields. The diastereoselectivity of the reaction was determined as a function of the 1,3-dioxo moiety and the inductor. The best results were obtained with FeCl3/Al2O3 followed by TMSOTf and Me2AlCl1 the highest selectivity was found in the cyclisation of 4b with TMSOTf leading to 5b and 6b in a ratio of 99.8:0.2. FeCl3/Al2O3 and TMSOTf have not previously been used for this type of reaction. The alkylidene 1,3-dioxo compounds 4a-d were synthesised by Knoevenagel condensation of the aldehyde 11 with the malonic acid derivatives 11a-d.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230631
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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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective Total Synthesis and Absolute Configuration of the Natural Norsesquiterpene 7-Demethyl-2-methoxycalamenene by a Silane-Terminated Intramolecular Heck Reaction (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1981-1987 
    Details
    ISSN: 0947-3440
    Keywords: Heck reaction, enantioselective ; Allylsilanes ; Norsesquiterpenes ; 7-Demethyl-2-methoxycalamenene, total synthesis, absolute configuration, and cytotoxicity of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of the norsesquiterpene 7-demethyl-2-methoxycalamenene (1) by a newly developed enantioselective silane-terminated Heck reaction is described. The Pd0-catalyzed transformation of the allylsilane 7, obtained from 3-(3-methoxyphenyl)propanol (2) in 7 steps, provides the tetralin 8 in 91% yield and with 92% ee in the presence of (R)-BINAP. Transformation of 8 via 14 and 15 gives 1. The absolute configuration of 1 which has previously not been known was deduced from a single-crystal X-ray analysis of 10, obtained from the cyclization product 8 by hydroboration and acylation with camphanic acid chloride.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961207
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Highly Selective Allylation of Alkyl Methyl Ketones in the Presence of Chiral 2-Amino Alcohol Derivatives (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1639-1644 
    Details
    ISSN: 1434-193X
    Keywords: Allylation ; Allylsilanes ; Amino alcohols ; Domino reactions ; Homoallylic alcohols ; Homoallylic ketones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The facial selective allylation of alkyl methyl ketones 1a-f in the presence of chiral 2-amino alcohol derivatives 2a-p by reaction with allylsilane 3 and a catalytic amount of TfOH to give the tertiary homoallylic ethers 8a-o and 9a-e is described. The best results were obtained with the 2-amino alcohol derivative 2p which affords a stereoselectivity of 18:1 even for the allylation of ethyl methyl ketone. The ethers 8 and 9, which contain a phenyl group at C-1 of the amino alcohol moiety, can be cleaved to give the corresponding homoallylic alcohols 5 by reduction with sodium or lithium in liquid ammonia.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of Enantiomerically Pure trans-1,2-Disubstituted Cyclopentanes and Cyclohexanes by Intramolecular Allylsilane Addition to Chiral Alkylidene-1,3-dicarbonyl Compounds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2089-2099 
    Details
    ISSN: 1434-193X
    Keywords: Allylsilanes ; Asymmetric synthesis ; Ene reactions ; Oxazolidinones ; Cyclohexanes ; Cyclopentanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure trans-1,2-disubstituted cyclopentanes 14 and cyclohexanes 15 bearing three stereogenic centers can be synthesized highly selectively by Lewis acid induced intramolecular cyclizations of chiral alkylidene-1,3-dicarbonyl compounds 8 and 9. The best results were obtained using SnCl4 and the substrates 8d and 9d, which contain an oxazolidinone moiety derived from (S)-phenylalanine. In these reactions, 10d was formed from 8d in a 98:1:1 ratio, while 11d was formed from 9d in a 99:1 ratio, both in 87 % yield. The configuration of the major products 10d and 11d was proven by X-ray analysis. Reduction of 10d and 11d with LiAlH4 led to 14 and 15, respectively, or to the diols 16 and 17. The alkylidene-1,3-dicarbonyl compounds 8 and 9 were synthesized by Knoevenagel condensation of the respective allylsilane carbaldehydes 6 and 7 with the malonic acid derivatives 5a-d.
    Type of Medium: Electronic Resource
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  • 7
    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.
    Type of Medium: Electronic Resource
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Ab Initio Molecular Orbital Calculations on Allylic 1,3-Strain of Electron-Donor- and Electron-Acceptor-Substituted Alkenes (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1575-1579 
    Details
    ISSN: 0947-3440
    Keywords: Allylic 1,3-strain ; Calculations, ab initio ; sp2-Geminal effect ; Ene reaction ; Allylsilanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations on the conformations of several electron-rich and electron-poor alkenes 2, 8-15 were performed up to the MP2/6-31G*/RHF/6-31G* level. It was proven that allylic 1,3-strain can be traced back to steric interactions between the allylic center and the (Z) substituent of the double bond. The electron density of the double bond seems to have no effect on the difference in energy between the global and the local minimum. The local minimum (180° conformation) of (Z)-methyl-substituted alkenes 2, 14 and 15 carrying a methyl, carboxyl and methoxy group, respectively, at the double bond in (E) position, lies 3.37-3.52 kcal/mol above the 0° conformation (global minimum); thus, the (E) substituent has no significant influence on this energy difference and therefore on the equilibrium distribution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961012
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  • 10
    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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