Organic Letters
Letter
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Figure 4. (a) Normalized emission spectra of 3w in different solvents;
(b) emission spectra of 3w in different ratios of water in THF; (c)
solution color of 3w under UV light, from left to right: CH, THF,
DMSO, H2O/THF(85/15).
increased to 85 to 15, bright yellow emission of 3w was seen
under UV light (Figure 4c). A similar phenomenon is observed
for compound 7e (see the SI).
In conclusion, we have developed a green methodology for the
preparation of 2-aryl-3-cyanobenzofurans by using o-hydrox-
ybenzaldehydes and arylacetonitriles in the presence of copper
acetate and sodium methoxide. Many substituents tolerate the
reaction conditions and produce 2-aryl-3-cyanobenzofurans in
moderate to good yields. The cascade process includes
Knoevenagel condensation, cyanide anion transfer, intramolec-
ular nucleophilic addition, and aromatization. Furthermore, 2-
aryl-3-cyanobenzofurans are bright blue under UV irradiation.
The highest quantum yield in dilute methylene chloride is
determined to be 88.9%. Moreover, emission depends on the
solvent polarity. When the solvent is changed from cyclohexane
to THF and finally to DMSO, an emission color of 3w is
accordingly altered from bright blue to light blue and finally to
green. It implies that compound 3w might be used as a
fluorescent probe for the detection of environmental variation,
such as solvent polarity.
(14) Huang, X.-C.; Liu, Y.-L.; Liang, Y.; Pi, S.-F.; Wang, F.; Li, J.-H.
Org. Lett. 2008, 10, 1525.
(15) X-ray crystal structure of 3a, which is numbered CCDC 1438893,
is available from the Cambridge Crystallographic Data Centre.
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37, 314.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
Detailed synthetic procedures and characterization data
UV−vis absorption and fluorescence spectra (PDF)
Crystallographic information for compound 3a (CIF)
AUTHOR INFORMATION
Corresponding Authors
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Author Contributions
†L.Z. and Z.P. contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors thank the National Natural Science Foundation of
China (Nos 21472173 and 21272203) for financial support.
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REFERENCES
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