Thermal rearrangements of heteroatom-bridged polyunsaturated hydrocarbons
Bui, Binh H
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In predicting new reactions, systematic strategies involving the classification of systems of interest and methodological applications of computational tools are used to study heterosubstituted polyunsaturated hydrocarbons. Although this is a rather “heuristic approach,” it provides qualitatively reasonable results and collective findings of reaction families. A systematic application of the BLYP/6-311+G*//BLYP/6-31G* computational scheme was utilized to study the thermal rearrangements of 4-heteroatom-1,2-hexadiene-5-ynes (Chapter 2), 3-heteroatom-pent-1-en-4-yn-1-ones (Chapter 3), and (hetero)atom-bridged diallenes (Chapter 4). It was found that the aromatization 2,6-cyclization path leading to the formally aromatic five-membered ring products are preferred and experimentally accessible. Protonation of the heteroatom X resulted in either the 1,6-Claisen-type rearrangement to form the stable acyclic product or the competitive 1,6-cyclization mode to form homoaromatic six-membered ring products. The Ã-electron-withdrawing and À-electron-donating abilities of the heteroatom (or group) X have been determined to be effective in governing the reaction barriers (TS26) but not the reaction energies.