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Diels-Alder Reactions of tert-Butylphosphaethyne with 1,3,2-Diaza- and 1,2-Azaphosphinines (1998)

Avarvari, Narcis ; Ricard, Louis ; Mathey, François ; [et al.]

Weinheim : Wiley-Blackwell

Liebigs Annalen 1998 (1998), S. 2039-2045

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ISSN: 1434-193X

Keywords: Phosphorus heterocycles ; Nitrogen heterocycles ; Phosphinines ; Phosphaalkynes ; [4 + 2] Cycloadditions ; Chemistry ; General Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: tert-Butylphosphaethyne (2) undergoes a Diels-Alder reaction with the 1,3,2-diazaphosphinine 1 at room temperature to furnish the diazadiphosphabarrelene 3. In the presence of an excess of 2 in toluene under reflux compound 3 experiences elimination of a molecule of pivalonitrile to afford the 1-aza-2,4-diphosphinine 5 which, in turn, reacts with a further equivalent of 2 to form the transient azatriphosphabarrelene 6. Formation of the final product, the stable tetraphosphatetracyclic compound 4, is the result of a homo Diels-Alder reaction between 6 and yet another equivalent of 2. The structure of 4 has been confirmed by an X-ray crystallographic analysis of its pentacarbonyltungsten complex 7. As a consequence of the high steric overcrowding in 4, complexation occurs exclusively at its phosphaalkene phosphorus atom. The reactivity of 2 towards the four functionally substituted 1,2-azaphosphinines 8a-d has also been examined. At room temperature smooth [4 + 2] cycloaddition reactions proceed to yield the azadiphosphabarrelenes 9a-d. While thermolyses of the barrelenes 9a-c in toluene under reflux lead exclusively to the starting compounds 8a-c by a [4 + 2] cycloreversion process with concomitant elimination of 2, pyrolysis of 9d under the same conditions furnishes the 1,3-diphosphinine 10, also unambiguously identified by analysis of its tpentacarbonyltungsten complex 11.

Type of Medium: Electronic Resource

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On the Unusual Dienophilicity of Trimethylsilylphosphaacetylene (1999)

Fiedler, Wolfgang ; Löber, Oliver ; Bergsträßer, Uwe ; [et al.]

Weinheim : Wiley-Blackwell

Liebigs Annalen 1999 (1999), S. 363-371

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ISSN: 1434-193X

Keywords: Phosphaalkynes ; Diels-Alder reactions ; Ene reactions ; Homo [4 + 1] cycloaddition reactions ; Ab initio calculations ; Chemistry ; General Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: -The diphosphatricyclooctenes 8a, b are obtained from reactions of the phosphaacetylene 2 with the buta-1,3-dienes 6a, b through a reaction sequence involving Diels-Alder, ene, and intramolecular [4 + 2] cycloaddition reactions with the intermediates 7 and 9. An ab initio MO investigation at the MP2/6-31+G* level of theory has provided reasons why the postulated intermediates cannot be detected. The polycyclic products 8a, b were characterized in the form of the corresponding metal carbonyl complexes 10a, b, and 11. Reaction of the silylated phosphaalkyne 2 with cyclohexa-1,4-diene (12) furnishes the monophosphatricyclooctene 14; this reaction has also been studied by means of ab initio calculations. The result of the reaction of 2 with cyclopentadiene (15), however, is a complete surprise: the triphosphaspiropolycyclic system 17 is formed, apparently through Diels-Alder, homo-Diels-Alder, and homo [4 + 1] cycloaddition reactions with the intermediates 16 and 18.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

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