4
Tetrahedron Letters
4. (a) Meerwein, H. Ber. Dtsch. Chem. Ges. 1933, 66, 411; (b) Meerwein,
The direct amination of aromatics with NaN3 in the presence of
H.; Pannwitz, W. J. Prakt. Chem. 1934, 141, 123.
boron trifluoride monohydrate can be presumed to undergo
through a mechanism similar to the one proposed by Olah and co-
workers in earlier studies.28c In boron trifluoride monohydrate,
which acts as a strong Brønsted acid system and provides
superacidic stable ion conditions, protonation of azide A forms
hydrazoic acid B in situ that undergoes further protonation to form
aminodiazonium ion C. The aminodiazonium ion acts as the
nitrenium ion “NH2 ” source, which drives subsequent “NH2 ”
electrophilic addition to the aromatic substrate with the
elimination of nitrogen, a facile leaving group (Scheme 2).
5. Greenwood, N. N.; Martin, R. L. J. Chem. Soc. 1951, 1915-1921.
6. (a) Gillespie, R.J.; Peel, T.E.; Robinson, E.A. J. Am. Chem. Soc. 1971,
93, 5083–5087; (b) Gillespie, R.J.; Peel, T.E J. Am. Chem. Soc. 1973,
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+
+
9. (a) Oyama, T.; Hamano, T.; Nagumo, K.; Nakane, R. Bull. Chem. Soc.
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Bahrmann, H. In New Syntheses with Carbon Monoxide; Falbe, J., Ed.;
Springer: Berlin, 1980, p. 372.
+
Therefore, the nitrenium ion “NH2 ” formed by the elimination of
nitrogen from aminodiazonium ion can be envisaged as the
reactive species, as also presumed by Borodkin and co-workers.29
11. Sasaki, I.; Nikizaki, S. U.S. Patent 3574760, 1971.
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60; (b) Olah, G. A.; Wang, Q.; Trivedi, N.; Prakash, G. K. S. Synthesis
1992, 465–466; (c) Olah, G. A.; Wang, Q.; Li, X.-Y.; Bucci, I. Synthesis
1992, 1085–1086; (d) Olah, G. A.; Wang, Q.; Li, X.-Y.; Prakash, G. K.
S. Synlett 1993, 32–34; (e) Olah, G. A.; Wang, Q.; Li, X.-Y.; Prakash,
G. K. S. Synthesis 1993, 207–208.
Scheme 2. Formation of aminodiazoium ion and electrophilic
amination
Conclusion
18. (a) Wang, Q.; Li, X.; Prakash, G. K. S.; Olah, G. A. Arkivoc 2001, 8,
116-128; (b) Prakash, G. K. S.; Mathew, T.; Hoole, D.; Esteves, P. M.;
Wang, Q.; Rasul, G.; Olah, G. A. J. Am. Chem. Soc. 2004, 126, 15770–
15776; (c) Prakash, G. K. S.; Panja, C.; Mathew, T.; Olah, G. A. Catal.
Lett. 2007, 114, 24–29; (d) Prakash, G. K. S.; Paknia, F.; Chacko, S.;
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G. K. S.; Panja, C.; Shakhmin, A.; Shah, E.; Mathew, T.; Olah, G. A. J.
Org. Chem. 2009, 74, 8659–8668; (f) Prakash, G. K. S.; Paknia, F.;
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19. Rappoport, Z., Ed. The Chemistry of Anilines, Parts 1 and 2; John
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20. (a) Weissermel, K.; Arpe, H.-J. Industrial Organic Chemistry, VCH,
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2010, 39, 4130
We have described an effective protocol for the synthesis of
primary aromatic amines directly from aromatics by using
sodium azide in the presence of boron trifluoride monohydrate.
Boron trifluoride monohydrate acts as strong acid catalyst as well
as an effective solvent for sodium azide providing sufficient
acidity for the protonation of azide ion for the generation of
hydrazoic acid and subsequently the aminodiazonium ion which
+
acts as the nitrenium ion “NH2 ” source for electrophilic
amination of aromatics to give primary aromatic amines. Unlike
previous reports of electrophilic amination of aromatics which
used an excess of aromatics, in our reactions both the aminating
agent and the aromatic substrate are used in equimolar amounts.
Our study also demonstrates that for the purpose of electrophilic
amination, easily accessible, nonoxidizing and inexpensive boron
trifluoride monohydrate can be used as an effective substitute for
expensive super acids such as triflic acid.
22. Romero, M.; Harrak, Y.; Basset, J.; Orúe, J. A.; Pujol, M. D.
Tetrahedron, 2009, 65, 1951.
23. (a) Coeffard, V.; Moreau, X.; Thomassigny, C.; Greck, C. Angew.
Chem., Int. Ed. 2013, 52, 2; (b) Ou, L.; Shao, J.; Zhang, G.; Yu, Y.
Tetrahedron Lett. 2011, 52, 1430; (c) Xiao, Q.; Tian, L.; Tan, R.; Xia,
Y.; Qiu, D.; Zhang, Y.; Wang, J. Org. Lett. 2012, 14, 4230; (d)
Mlynarski, S. N.; Karns, A. S.; Morken, J. P. J. Am. Chem. Soc. 2012,
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Chem. Soc. 2012, 134, 18253; (f) Voth, S.; Hollett, J. W.; McCubbin, J.
A. J. Org. Chem., 2015, 80, 2545–2553.
Acknowledgment
Support for our work by Loker Hydrocarbon Research
Institute is gratefully acknowledged.
Supplementary Data
24. Klinkenberg, J. L.; Hartwig, J. F. Angew. Chem., Int. Ed., 2011, 50, 86.
25. (a) Becker, J.; Hölderich, W. F. Catal. Lett., 1998, 54, 125; (b) U.S.
Pat., U.S. 2948755, 1960; (c) U.S. Pat., U.S. 3919155, 1975; (d) U.S.
Pat., U.S. 4031106, 1977.
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.....
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