Intramolecular cyclization of a phosphinoazide: Transformation of 1,2,3,4-triazaphosphole into 1,2,4-diazaphosphole

Article abstract of DOI:10.1080/10426507.2010.507732

Carbanion 4 generated from phosphane azide 3 undergoes intramolecular cyclization to give 1,2,3,4-triazaphosphole 5, which rearranges into 1,2,4-diazaphosphole 8. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.507732

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Intramolecular Cyclization of a
Phosphinoazide: Transformation of
1,2,3,4-Triazaphosphole into 1,2,4-
Diazaphosphole
K. V. Turcheniuk a & I. V. Shevchenko a
a Institute of Bioorganic Chemistry and Petrochemistry , Kiev ,
Ukraine
Published online: 25 Apr 2011.
To cite this article: K. V. Turcheniuk & I. V. Shevchenko (2011) Intramolecular Cyclization of a
Phosphinoazide: Transformation of 1,2,3,4-Triazaphosphole into 1,2,4-Diazaphosphole, Phosphorus,
Sulfur, and Silicon and the Related Elements, 186:4, 766-768, DOI: 10.1080/10426507.2010.507732
To link to this article: http://dx.doi.org/10.1080/10426507.2010.507732
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Phosphorus, Sulfur, and Silicon, 186:766–768, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.507732
INTRAMOLECULAR CYCLIZATION OF A
PHOSPHINOAZIDE: TRANSFORMATION
OF 1,2,3,4-TRIAZAPHOSPHOLE INTO
1,2,4-DIAZAPHOSPHOLE
K. V. Turcheniuk and I. V. Shevchenko
Institute of Bioorganic Chemistry and Petrochemistry, Kiev, Ukraine
Abstract Carbanion 4 generated from phosphane azide 3 undergoes intramolecular cycliza-
tion to give 1,2,3,4-triazaphosphole 5, which rearranges into 1,2,4-diazaphosphole 8.
Keywords Azides; carbanions; 1,2,4-diazaphosholes; 1,2,3,4-triazaphospholes; ylides
INTRODUCTION
It is known that phosphaalkynes 1 and some phosphaalkenes 1a are able to par-
ticipate in [3+2] cycloaddition reactions with azides to give 1,2,3,4-triazaphospholes 2
(Scheme 1).1,2 However, this reaction is restricted by the accessibility of phosphaalkynes
and phospaalkenes, the stabilization of which requires sterically demanding substituents.
N
Me3Si
R1
Cl
X
X-N3
X-N3
N
N
R1
P
P
P
–Me3SiCl
R1
1
2
1a
R1=bulky substituens; X=H, CH3, C6H5, CH2CN, SiMe3, CO2Me
Scheme 1
RESULTS AND DISCUSSION
We have found that generation of a carbanionic center in the α-position to the phos-
phane azide moiety may lead to the intramolecular cyclization into 1,2,3,4-triazaphospholes.
For example, the addition of DBU to phosphane azide 3 led to its intramolecular cycliza-
tion into triazaphosphole 5 in 85% yield (Scheme 2). It is possible that this is a particular
Received 1 July 2010; accepted 1 July 2010.
Address correspondence to I. V. Shevchenko, Institute of Bioorganic Chemistry and Petrochemistry, Mur-
manskaya str. 1, Kiev 02660, Ukraine. E-mail: igorshevchenko@yahoo.com
766

INTRAMOLECULAR CYCLIZATION OF A PHOSPHINOAZIDE
767
N
DBUH+
(Et2N)2P
(F3C)2HC
N
N
N3
P
N3
DBU
(Et2N)2P
(F3C)2HC
P
DBUH+
P
(Et2N)2P
(F3C)2HC
NEt2
–HNAlk2
NEt2
CN
CN
CN
3
4
5
Scheme 2
example of a more general reaction that can be used for the synthesis of other 1,2,3,4-
triazaphospholes. The presence of an activated methylene group in the α-position to the
phosphane center is the necessary condition for the generation of carbanions.
Starting phosphane azides can be easily obtained from chlorophosphanes and
trimethylsilyl azide. For example, phosphane azide 3 was quantitatively synthesized and
without purification was used for the synthesis of 5. The 31P-NMR spectrum of the reaction
mixture after addition of DBU displays two clear doublets of compound 5. The chemical
shift of 238 ppm is typical for the two-coordinate phosphorus atom in such compounds.1–4
The intramolecular cyclization of intermediate carbanion 4, which is accompanied by the
elimination of diethylamine, is probably much more rapid in comparison with the rate of
its formation. For this reason 4 cannot be registered by the 31P-NMR spectroscopy.
Triazaphosphole 5 cannot be isolated from the reaction mixture because it rear-
ranges spontaneously into 1,2,4-diazaphosphole 8. This kind of transformation has not
been experimentally observed earlier. There is one example known of the synthesis of
1,2,4-diazaphosphole by the reaction of triazaphospholes and diazo alkanes.4 The decom-
position of a 1,2,3,4-triazaphosphole with the formation of diazo alkane and polymeric
product (PN)n has also been postulated in two works.2,3 We suppose that the mechanism of
the rearrangement of triazaphosphole 5 into 1,2,4-diazaphosphole 8 should be accounted
for by the combination of these two previously described processes (Scheme 3). Triaza-
phosphole 5 decomposes first into diazo compound 6, which then adds to the starting
triazaphosphole with the formation of bicyclic intermediate 7. Due to the presence of the
cation [DBU∗H]+, intermediate 7 undergoes an interesting elimination of DBU∗HN3 yield-
ing 1,2,4-diazaphosphole 8. DBU∗HN3 and diazaphosphole 8 can be separately isolated
from the reaction mixture. The polymeric product (PN)n 6a resulting from the decompo-
sition of triazaphosphole 5 was identified in the reaction mixture as a broad signal in the
31P-NMR spectrum at +55 ppm.
2DBUH+
N
DBUH+
DBUH+
N
N
DBUH+
N
N
R1
N
N
5
N
(Et2N)2P
(F3C)2HC
P(NEt2)2
CH(CF3)2
N
N
R1
P
–DBU*HN3
P
P
N
6
R1
R1
CN
NC
N
5
7
8
P
N
6a
R1=P(NEt2)2C(CN)CH(CF3)2
Scheme 3

768
K. V. TURCHENIUK AND I. V. SHEVCHENKO
Figure 1 31P-NMR spectrum of diazaphosphole 8.
Diazaphosphole 8 was isolated in 50% yield. This compound displays the character-
istic 31P-NMR spectrum (Figure 1), consisting of a doublet at 60 ppm and a triplet at 160
ppm with a ratio of 2:1. The low field value corresponds to the two-coordinate phosphorus
atom and coincides with the literature data.1a,2,3 The high-resolution mass spectrum of di-
azaphosphole 8 with electrospray ionization displayed intensive signals of the anionic and
cationic parts of the molecule.
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