4244
N. Iranpoor et al. / Tetrahedron Letters 49 (2008) 4242–4244
lent yields and short reaction times are advantages worthy of
mention for the present method.
n-Bu4NNO2
- n-Bu4NBr
Ph3P + Br2
Ph3PBr / Br
I
Acknowledgements
R1R2NH
R1R2NNO
+
Ph3PO
Ph3P
ONO / Br
II
We are thankful to the Organization of Management and
Planning of Iran and the Shiraz University Research Council for
the support of this work.
R3N
R2NNO
R3NNO
Ph3P
Ph3P
ONO / Br
II
-Ph3PO
References and notes
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ArNHNH2
-Ph3PO
-H2O
ArN3
ArNHNHNO
ONO / Br
II
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Scheme 3.
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A typical procedure for this transformation is as follows. To an
efficiently stirred solution of Ph3P (1.2 mmol, 0.314 g) Br2
(1.2 mmol, 0.07 mL) and n-Bu4NNO2 (1.2 mmol, 0.348 g), in dry
CH3CN (5 mL) at 0 °C was added 4-nitrophenylhydrazine (1 mmol,
0.153 g). The reaction was monitored by TLC. After the disappear-
ance of the starting material, the solvent was evaporated. Column
chromatography of the crude mixture on silica gel using n-hexane
as eluent gave 4-nitrophenyl azide in 90% yield.
We propose a mechanism in which, in the first stage, triphenyl-
phosphine reacts with bromine to form the phosphonium bromide
I. Then, addition of n-Bu4NNO2 to I produces the intermediate II
and n-Bu4NBr. This intermediate reacts with R1R2NH, R3N or
ArNHNH2 via substitution at the nitrogen atom of II according to
Scheme 3. Generation of triphenylphosphine oxide in these reac-
tions is considered a strong driving force.
We were also interested in using another source of bromine for
these reactions, however, when we used NBS, similar reactions
with Ph3P/NBS/n-Bu4NNO2 gave no reaction even after a long reac-
tion time.
To summarize, we have described a highly efficient method for
the preparation of nitrosamines and azides. The Ph3P/Br2/n-Bu4N-
NO2 system acts as a source for the delivery of NO+ under very mild
reaction conditions. The ready availability of the reagents, excel-
19. Kim, Y. H.; Kim, K.; Shim, S. B. Tetrahedron Lett. 1986, 27, 4749.
20. Laszlo, P.; Polla, E. Tetrahedron Lett. 1984, 25, 3701.
21. Pozsgay, V.; Jennings, H. J. Tetrahedron Lett. 1987, 28, 5091.