期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 19, 期 13, 页码 4344-4351出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201204221
关键词
benzofurans; Friedel-Crafts reaction; heterocycles; naphthofurans; nitroallylic acetate; synthetic methods
资金
- National Science Council of the Republic of China [NSC 99-2113M-003-002-MY3, NSC 99-2119M-003-001-MY2]
- National Taiwan Normal University [100-D-06]
Substituted naphthofurans and benzofurans are easily accessible by treatment of naphthols/substituted phenols with nitroallylic acetates through a substitution-elimination process promoted by cesium carbonate. Reactions between naphthols and aromatic/heteroaromatic-substituted nitroallylic acetates gave the desired functionalized naphthofurans in high to excellent chemical yields (14-97%). On the other hand, treatment of phenol derivatives (i.e., 3-dimethylamino-, 3-methoxy-, and 3,5-dimethoxyphenol) with various nitroallylic acetates afforded the corresponding benzofurans in moderate to good chemical yields (24-91%). The reaction proceeded through an interesting Friedel-Crafts S(N)2' process followed by intramolecular oxa-Michael cyclization and subsequent aromatization. A plot of log (k/k(H)) against Hammett constants sigma(P) showed satisfactory linearity with a positive rho value, indicating that the initial Friedel-Crafts-type S(N)2' process constituted the rate-determining step. This methodology has been applied to the synthesis of various novel C-2 and C-3 symmetric bis- and trisfurans by using catechol and phloroglucinol as the nucleophilic partners. The reactivity decreased when alkyl-substituted nitroallylic acetate systems were used. This might be related to the decreased electrophilic character of these substrates.
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