Regioselectivity for intramolecular Diels-Alder (IMDA) reactions of 6-acetoxy-6-alkenylcyclohexa-2,4dien-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-2,4dien-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.
3-Hydroxy-3-vinylcycloalkanones, which were prepared from the corresponding cyclic 1,3-diketones by mono-vinylation, were rearranged to two-carbon ring enlarged cyclic 1,5-diketones by treatment with a catalytic amount of potassium tert-butoxide.
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