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  • Title: Bridged-Selective Intramolecular Diels-Alder Reactions in the Synthesis of Bicyclo[2.2.2]octanes.
    Author: Hanashima M, Matsumura T, Asaji Y, Yoshimura T, Matsuo JI.
    Journal: Chem Pharm Bull (Tokyo); 2020; 68(12):1201-1209. PubMed ID: 33268652.
    Abstract:
    Regioselectivity for intramolecular Diels-Alder (IMDA) reactions of 6-acetoxy-6-alkenylcyclohexa-2,4-dien-1-ones that were formed by oxidation of 2-alkenylphenols with lead tetraacetate in acetic acid were studied. Bridged regioselectivity was observed in the IMDA reactions of 6-acetoxy-6-alkenylcyclohexa-2,4-dien-1-ones having a dienophile part which could conjugate with an aromatic group. Bridged seven- and eight-membered rings and bicyclo[2.2.2]octane skeletons were constructed by the present IMDA reactions. Density functional theory (DFT) calculations suggested that conjugation of the dienophile with neighboring aromatic groups lowered the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap and preceded bridged [4 + 2] adducts.
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