Lewis acid-catalyzed [4 + 2] benzannulation between enynal units and enols or enol ethers: novel synthetic tools for polysubstituted aromatic compounds including indole and benzofuran derivatives.
The reaction of enynals 1, including o-(alkynyl)benzaldehydes, and carbonyl compounds 2, such as aldehydes and ketones, 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. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds 5 afforded the corresponding aromatic compounds 3 in good yields. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(NTf2)2 and 1 equiv of H2O in (CH2Cl)2 at 100 degrees C, the decarbonylated naphthalene products 4 were obtained selectively over 3. Benzofused heteroaromatic compounds, such as indole derivatives 13 and benzofuran derivatives 15, were also synthesized by using the present benzannulation methodology.
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
D000447:Aldehydes / Q000737:chemistry*; D001572:Benzofurans / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D004987:Ethers / Q000737:chemistry*; D017612:Gold Compounds / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure
D000447:Aldehydes; D001572:Benzofurans; D004987:Ethers; D017612:Gold Compounds; D007211:Indoles; D007659:Ketones