AuBr(3)-catalyzed [4 + 2] benzannulation between an enynal unit and enol |
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Authors: | Asao Naoki Aikawa Haruo Yamamoto Yoshinori |
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Affiliation: | Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. asao@mail.tains.tohoku.ac.jp |
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Abstract: | The reaction of enynals 1, including o-alkynylbenzaldehydes, and carbonyl compounds 2 in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. The AuBr3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuBr3, the formation of a pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand-type Diels-Alder addition of the enols, derived from 2, to the auric ate complex, and subsequent dehydration and bond rearrangement. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds afforded the corresponding aromatic compounds in good yields. |
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