| Ferric chloride can be used as one-electron oxidant. Because it's commerciallyavailable and environmentally friendly, we are interested to investigate its oxidationapplications. In our precious work, we realized the formation of a series ofN-alkoxyindole-3-carbonitriles via a novel FeCl3-mediated intramolecular aromaticC-N bond formation. Inspired by this finding, we were interested in investigating theconstruction of benzo[b]furan skeletons by a similar intramolecular cyclizationpathway involving direct C-H functionalization of an electron-rich aromatic ring witha side chain O-moiety.Using different substitutedα-aryl ketones and esters as starting materials,α-aryl-β-ketones,α-aryl-β-carbonyl-carboxylates and aromatic diones weresynthesized as substrates. The substrates with different substitutions at differentpositions were prepared. And in order to investigate the effect ofelectron-withdrawing group at the benzylic positionin in the cyclization step, othertypes of substrates were synthesized for comparision purpose.Usingα-aryl-β-ketones,α-aryl-β-carbonyl-carboxylates or aromatic diones assubstrates, a series of benzo[b]furan derivarives were synthesized via intramolecularcyclization in the presence of ferric chloride in 1, 2-dichloroethane. The reaction wascarried out under mild condition, and has a simple workup procedure and moderateyields. The substituents on the benzene ring could influence the cyclization. Theresults indicate that the electron-donating methoxy groups on the benzene ring werecrucial for the oxidative intramolecular cyclization to occur, and a para-methoxygroup is more determinant than a meta-methoxy group. It was also found that theelectron-withdrawing group at the benzylic position is indispensable.A series of benzofuran derivatives were synthesized by this method, and thestructures of the compounds were chracterized by 1H NMR and 13C NMR spectra,and LRMS analysis. The tentative mechanistic pathway for the reaction process wasstudied.
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