One-pot sequential synthesis of 3-carbonyl-4-arylbenzo[f]indole and 3-carbonyl-4-arylnaphthofuran fluorophores†
The development of novel methods for the construction of valuable fluorophores, 3-carbonyl-4-arylbenzo[f]indoles and 3-carbonyl-4-arylnaphthofurans, is described. In this protocol, the important polycarbonyl key intermediate was generated via the ketonization of ortho-alkynylarylketone tethered with a 1,3-dicarbonyl moiety. This intermediate reacted with an amine to selectively form a pyrrole intermediate, followed by cyclization in acetic acid to provide 3-carbonyl-4-arylbenzo[f]indole. Importantly, these conditions did not cause any epimerization of the stereogenic center in chiral amine substrates. Moreover, the polycarbonyl intermediate could also be utilized to prepare 3-carbonyl-4-arylnaphthofuran using In(OTf)3 as a catalyst for double cyclization under thermal conditions. In addition, the fluorescence properties of both fluorophores were also studied.