The chemoselective hydrozirconation reaction of a series of 1-ene-3-yne molecules 51a-d, using the commercially available hydride reagent, Cp₂ZrCl(H) 1, provides an efficient route to the syntheses of 1,3-dienes 55a-d, substituted at the 1-position by the Cp₂ZrCl moiety. Similar chemoselectivity was observed in the hydrozirconation reaction of α, β-unsaturated nitriles, to generate the corresponding 1-azadienyl complexes 68-71.
The complexes 55a-d were found to be useful general precursors in the preparation of other heterosubstituted 1,3-dienes. Thus, corresponding tin-, phosphorus-, boron-, selenium-and sulfur-heterosubstituted 1,3-dienes 77a-d, 79a-d, 87a-d, 88a-d and 89a-d were readily prepared in good to excellent yields by a stereoselective transfer reaction from zirconium. The 1-azadienyl complexes also served as useful starting materials in the preparation of selenium-and phosphorus-substituted 1-azadienes.
The selenium-substituted 1,3-dienes 88a-d underwent a facile isomerization reaction when exposed to fluorescent light, and when thermolysed in the dark at 80°C in unsealed reactors. Mechanistic studies of this isomerization process suggested that an intermolecular pathway involving free radical intermediates was operable. A comparable photochemical isomerization reaction of the sulfur-substituted 1,3-dienes was also observed. When the cycloaddition reactions of 88a-b and 88d with maleic anhydride were performed in the absence of light at reson able temperatures, good yields of the expected endo-cycloadducts were obtained. However, when the same reactions were repeated in room light or at temperatures in excess of those required for formation of the endo-cycloadducts an, interesting, apparent [l,3]-shift of the phenylselenenyl moiety resulted. The results of a crossover experiment indicated that this rearrangment was intermolecular in nature.
The preparation of the trialkylstannyl and phenylselenenyl 2-substituted 1,3-dienes (128 and 129) was achieved via a transmetalation reaction of the Grignard reagent 24. The Diels-Alder reactivity of 1,3-dienes 128 and 129, with a series of electron-deficient dienophiles, was successfully investigated. [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/29433 |
| Date | January 1988 |
| Creators | Stone, Charles |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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