A. A. TAHERPOUR ET AL.
improved by using a new variant of the click reaction using Cu
nanoparticles in the presence of amine hydrochlorides.[50]
However, the cycloaddition takes place under the conventional,
thermal Huisgen conditions, i.e in boiling toluene for 24–48 h and
affords a mixture of the two regioisomeric addition products 26
and 27,[23] but there is a controversy in the literature concerning
the assignment of NMR spectra to the two isomers.[23,24] We have
examined this cycloaddition under microwave conditions and
find that neither of the previous assignments of 1H NMR spectra
was correct. In other words, it was still not known which isomer is
which. In order to resolve the issue, we have obtained X-ray
crystal structures of the two isomers (Fig. 4, Scheme 4) as well as
400 MHz 1H NMR spectra. This has permitted a definitive
assignment of spectra and melting points to the structures.
The bond lengths and angles of the two isomers are not
significantly different. The main structural differences are found
in their inter-ring torsional angles. In the 1,4-isomer 26, the
acridine and triazole rings are twisted by ꢂ728 relative to each
other while the phenyl and triazole rings are close to coplanar
(ꢂ68 twist angle). In the 1,5-isomer, the acridine/triazole
interplanar twist angle is again marked (ꢂ638), but in this isomer
the phenyl/triazole rings must also twist significantly (ꢂ458) to
avoid clashing between the phenyl and acridine rings. In both
structures, the space group symmetry dictates that all acridine
rings are parallel and intermolecular stacking is a feature of their
structures (see Supporting Information).
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crystal structure of 10 is described in H.-W. Winter, Doctoral Disser-
tation: Philips-Universita¨t Marburg, Germany, 1980.
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[11] A. Kuhn, C. Plu¨g, C. Wentrup, J. Am. Chem. Soc. 2000, 122, 1945.
[12] C. O. Kappe, M. W. Wong, C. Wentrup, J. Org. Chem. 1995, 60, 1686.
[13] A. Albert, B. Ritchie, Org. Synth. 1942, 22, 5.
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[15] A. C. Mair, M. F. G. Stevens, J. Chem. Soc., Perkins Trans. 1 1972, 161.
[16] C. Wentrup, Top. Curr. Chem. 1976, 62, 173.
[17] C. Wentrup, Tetrahedron 1971, 27, 367.
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1988, 53, 794.
[19] C. Mayor, C. Wentrup, J. Am. Chem. Soc. 1975, 97, 7467;
[20] A. W. Freeman, M. Urvoy, M. E. Criswell, J. Org. Chem. 2005, 70, 5014.
[21] N. C. Kaarsholm, H. B. Olsen, P. Madsen, S. Oestergaard, P. Jakobsen,
T. Moeller Tagmose, PCT Int. Appl. 2006, WO 2006082245,
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[22] A. Albert, The Acridines, Edward Arnold & Co, London, 1951.
[23] D. J. Hagan, D. Chan, C. H. Schwalbe, M. G. F. Stevens, J. Chem Soc.,
Perkin Trans. 1 1998, 915.
[24] E. Veverkova, S. Toma, Chem. Pap. 2005, 59, 350.
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reported by Stevens and colleagues.[23] This reaction, too, can be
carried out conveniently by using MW irradiation.
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CONCLUSION
Photolysis of matrix-isolated 9-azidoacridine 14 affords 9-
acridinylnitrene 15, which is characterized by its IR and ESR
spectra. The nitrene can also be generated and matrix-isolated by
FVT of 14. The nitrene is long-lived and photochemically stable in
low temperature Ar matrices. FVTof 14 causes ring contraction to
a mixture of isomeric cyanocarbazoles. Thermal reaction of 14
with diethylamine and dipropylamine in solution affords
acridinylamidines 25. Thermal cycloaddition with phenylacety-
lene affords the triazolylacridines 26 and 27. The syntheses of 9-
chloroacridine, 9-azidoacridine 14, amidines 25 and triazoles 26
and 27 were carried out conveniently and rapidly under
microwave irradiation.
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Acknowledgements
This work was supported by the Australian Research Council. A. A.
Taherpour thanks I. Azad University for leave of absence to
undertake this work.
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