AuBr(3)-catalyzed [4 + 2] benzannulation between an enynal unit and enol.
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.
Asao
Naoki
N
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. asao@mail.tains.tohoku.ac.jp
Aikawa
Haruo
H
Yamamoto
Yoshinori
Y
D000447:Aldehydes / Q000138:chemical synthesis* / Q000737:chemistry; D000480:Alkynes / Q000138:chemical synthesis* / Q000737:chemistry; D001547:Benzaldehydes / Q000737:chemistry; D001965:Bromides / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D006046:Gold / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure
D000447:Aldehydes; D000480:Alkynes; D001547:Benzaldehydes; D001965:Bromides; D007659:Ketones; D006046:Gold