Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 11
    Electronic Resource
    Electronic Resource
    Cycloadditionen von Homodienen (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 829-836 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cycloadditions with HomodienesIn solvents of low polaritiy homofuran 1 reacts with tetracyanoethylene (TCNE) to form the seven-membered cycloadduct 21,2) in quantitative yields. This [(σ2 + π2) + π2] cycloaddition corresponds to a Diels-Alder reaction in which one of the double bonds is replaced by a cyclopropane ring. In solvents of high polarities, however, mainly the [π2 + π2] adduct 3 is formed, in addition to 2. In order to examine the mechanisms of both reactions, quenching experiments were carried out. With methanol, only the intermediate of the [2 + 2] addition is scavenged. The yield of the [4 + 2] adduct does not depend on the trapping reagent. In acetonitrile the half life of the 1,4-dipolar intermediate 5 of the [2 + 2] addition is almost 3 h. Thus it is substantially more stable than the intermediates of comparable cycloadditions.
    Notes: In schwach polaren Lösungsmitteln reagiert Homofuran 1 mit Tetracyanethylen (TCNE) ausschließlich und quantitativ zum Siebenring-Addukt 21,2). Diese [(σ2 + π2) + π2]-Cycloaddition entspricht einer Diels-Alder-Reaktion, bei der eine der Doppelbindungen durch einen Cyclopropanring ersetzt ist. In polaren Lösungsmitteln dagegen entsteht neben 2 vorwiegend das [π2 + π2]-Addukt 3. Zur Ermittlung des Mechanismus der Reaktionen wurden Abfangexperimente unternommen. Mit Methanol läßt sich lediglich die Zwischenstufe der [2 + 2]-Addition quantitativ abfangen. Die Bildung des [4 + 2]-Adduktes wird durch das Abfangreagenz nicht beeinflußt. In Acetonitril beträgt die Halbwertszeit der 1,4-dipolaren Zwischenstufe 5 der [2 + 2]-Addition fast 3 h. Sie ist somit wesentlich stabiler als die Zwischenstufen vergleichbarer Cycloadditionen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861190306
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 12
    Electronic Resource
    Electronic Resource
    Synthese von 6,6-Dimethylfulven-2-carbonsäure-methylester und -2,3-dicarbonsäure-dimethylester sowie deren Umsetzung zu 2,3,5,6-substituierten Nordbornadienen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1143-1145 
    Details
    ISSN: 0009-2940
    Keywords: Fulvenes ; Norbornadienes ; Cycloadditions ; Diels-Alder reactions ; Pyrolysis, flash vacuum ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Methyl 6,6-Dimethylfulvene-2-carboxylate and Dimethyl 6,6-Dimethylfulvene-2,3-dicarboxylate as well as their Reaction to 2,3,5,6-Substituted NorbornadienesFulvenes 5 and 6 were synthesized by Diels-Alder reaction of 6,6-dimethylfulvene with methyl prop-2-ynoate and dimethyl but-2-ynedioate, catalytic reduction of the unsubstituted norbornadiene double bond, and a subsequent retro Diels-Alder reaction under flash vacuum pyrolysis conditions, 5 and 6 are used as the diene component in synthesizing 2,5-, 2,3,5-, and 2,3,5,6-substituted norbornadienes 7-9 by Diels-Alder reaction with electron-deficient alkynes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270627
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 13
    Electronic Resource
    Electronic Resource
    Wissenschaft Aktuell (1998)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 32 (1998), S. 274-278 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19980320507
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 14
    Electronic Resource
    Electronic Resource
    Diels-Alder Reactions of Tetradehydrodianthracene with Electron-Rich Dienes (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1795-1800 
    Details
    ISSN: 0947-3440
    Keywords: Tetradehydrodianthracene ; Diels-Alder reactions ; Diradical ; Stretched bond ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetradehydrodianthracene (TDDA; 1) reacts with electronrich dienes such as butadiene, cyclopentadiene and o-quinodimethane under ambient conditions. Only 1:1 products 5-8 were observed even with a large excess of the diene and under drastic conditions (though two strained and highly pyramidalized double bonds are available). The enhanced reactivity of TDDA compared with its mono Diels-Alder adducts is mainly due to the through-bond and through-space interaction of the two olefinic double bonds. During the cycloaddition one of the olefinic bonds in TDDA is converted into an extremely long C-C single bond (〉 1.65 Å). Attempts to cleave the strained π-bond thermochemically to form a diradical 13 afforded product 14a that was formed via a formal intramolecular homo 1,3-sigmatropic shift.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961113
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 15
    Electronic Resource
    Electronic Resource
    Synthesis of Photoresponsive Polyethers (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 361-361 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The name of an additional author (T. W.) should be added as shown above.The elemental analysis data of several compounds were inadvertently omitted and should be added as follows: 3c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.43, H 9.16. 4c: C26H44O8 (484.3): calcd. C 64.44, H 9.15; found C 64.68, H 9.33. 5c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.95, H 9.28.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 16
    Electronic Resource
    Electronic Resource
    Matrix Isolation of 3,4-Benzocyclodeca-3,7,9-triene-1,5-diyne (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 799-803 
    Details
    ISSN: 1434-193X
    Keywords: Bergman cyclization ; Matrix isolation ; Ab initio calculations ; Flash pyrolysis ; [10]Annulenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,4-Benzocyclodeca-3,7,9-triene-1,5-diyne (3) has been synthesized from two different precursors and characterized by means of matrix-isolation spectroscopy. Energies, structures and IR spectra of the product, the intermediate 9,10-didehydroanthracene (4), and of the transition state of the Bergman cyclization 3 → 4 have been calculated at the B3LYP-6-31G* level of theory.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 17
    Electronic Resource
    Electronic Resource
    Electrophilic additions to tetradehydrodianthracene (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1283-1289 
    Details
    ISSN: 0947-3440
    Keywords: Electrophilic addition ; Tetradehydrodianthracene ; Solvent effects ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5,12:6,11-Di[1,2]benzenodibenzo[a,e]cyclooctene (tetrade-hydrodianthracene, TDDA) (1) reacts with halogens to give transannular (anti) 4, 5 and ring-opened (syn) products 6, 7. The product ratio shows a remarkable solvent dependence. Solvents of medium polarity favor anti addition, whereas syn addition is observed both with increasing and decreasing polarity. For instance, chlorine in toluene adds 100% syn, in dichloroethane 56 % anti, and in trifluorethanol again 100% syn. It is concluded that, depending on solvent polarity, three different mechanisms for electrophilic addition are operative.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507170
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 18
    Electronic Resource
    Electronic Resource
    Diels-Alder Reactions of Tetradehydrodianthracene with Electron-Deficient DienesDedicated to Professor Dr. Miha Tisler on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1473-1479 
    Details
    ISSN: 0947-3440
    Keywords: Tetradehydrodianthracene ; Diels-Alder reactions ; Cycloadditions ; Tetrazines ; Steric hindrance ; Kinetics ; Semiempirical calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical calculations and simple MO considerations predict that a coplanar and spatially close arrangement of double bonds in structures such as tetradehydrodianthracene 1, should both lower the LUMO and raise the HOMO energy of the π system. Thus the reactivity in Diels-Alder reactions towards electron-rich, as well as electron-deficient, dienes should be enhanced. The first effect has already been shown in a previous paper, the latter statement is now also confirmed by the reactivity of 1 in Diels-Alder reactions with inverse electron demand. In [4 + 2] cycloaddition reactions of 1 with 1,2,4,5-tetrazines 2 the electronic effect of 3,6 substituents in tetrazines is far outweighed by steric factors resulting in an unexpected reactivity sequence: 2a ≫ 2b ≈ 2c 〉 2d.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970726
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 19
    Electronic Resource
    Electronic Resource
    Formaldehyd-O-oxid und Colchicine: ein eleganter Zugang zu AllocolchicinenIn memoriam Dr. Howard E. Simmons (1998)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 468-471 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formaldehyde-O-oxide and Colchicine: An Elegant Route to the AllocolchicinesTropone is a structural unit of numerous natural products i.e. imerubrine, harringtonolide and colchicine (2). It is of interest to study the selectivity of formaldehyde-O-oxide (1) with respect to these polyfunctional tropone derivatives. We report about the reactions of 1 with colchicine (2) and the colchicine derivatives 5, 8, 11, 14, 17, 20 under ozone free conditions. The fragmentation of the spiroozonides 3, 6, 9, 12, 15, 18, 21 via the activated complexes 3a, 6a, 9a, 12a, 15a, 18a, 21a opens up an elegant route to the allocolchicines 4, 7, 10, 13, 16, 19.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19983400510
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 20
    Electronic Resource
    Electronic Resource
    Synthesis of Photoresponsive Polyethers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2533-2539 
    Details
    ISSN: 1434-193X
    Keywords: Photoresponsive molecular switches ; Norbornadiene ; Quadricyclane ; Polyethers ; Complex ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Diels-Alder, retro Diels-Alder sequence provides access to 2,3,5-tri- and 2,3,5,6-tetraester-substituted norbornadienes. Attempts to reduce the norbornadiene esters with LiAlH4 failed. The corresponding quadricyclanes, which are available by photoisomerization of the norbornadienes give the alcohols in 32 and 74% yield. The quadricyclane alcohols 2a-c are converted with methyl iodide to compounds 3a-c or with 2-methoxyethyl 4-toluenesulfonate to the “tentacle molecules” 4a-c. A number of catalysts were tested to reisomerize the “tentacle” quadricyclanes to the norbornadienes. Neutral aluminum oxide proved to be most effective. In preliminary studies the tentacle quadricyclanes exhibit excellent complexing properties for Na+ and K+, whereas the norbornadiene isomers are less effective complexing agents.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...