Simple and facile method for the preparation of vinyl azides

Article abstract of DOI:10.1016/j.tetlet.2009.06.097

A synthetic utility of [bis(trifluoroacetoxy)iodo]benzene on α,β-unsaturated carboxylic acid is described. This is the first example of preparation of vinyl azide using α,β-unsaturated carboxylic acids directly by using hypervalent iodine reagent. The adv

Full text of DOI:10.1016/j.tetlet.2009.06.097

Tetrahedron Letters 50 (2009) 5056–5058
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Tetrahedron Letters
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Simple and facile method for the preparation of vinyl azides
*
Vikas N. Telvekar , Balaram S. Takale, Harshal M. Bachhav
Department of Pharmaceutical Sciences and Technology, Institute of Chemical Technology, Matunga, Mumbai 400 019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A synthetic utility of [bis(trifluoroacetoxy)iodo]benzene on
This is the first example of preparation of vinyl azide using
using hypervalent iodine reagent. The advantage of this protocol is characterized with non-toxicity of
starting material and shorter reaction times to obtain good preparative yields. The method is also useful
for the preparation of acyl azides.
a
a
,b-unsaturated carboxylic acid is described.
,b-unsaturated carboxylic acids directly by
Received 30 May 2009
Revised 17 June 2009
Accepted 22 June 2009
Available online 25 June 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
[Bis(trifluoroacetoxy)iodo]benzene
Sodium azide
Carboxylic acids
Vinyl azides
Vinyl azides have found wide applications in organic transfor-
mations such as conversions to azirine,1 indole,2 triazole,3 and
many other cyclic compounds.4 Although vinyl azides have shown
increasing importance in many aspects, synthetic studies toward
these compounds are rare. There are only a few methods reported
for the preparation of vinyl azides. A commonly used preparation
method is the elimination of b-iodo azides,5 which is based on
the addition of iodine azide to olefins. However this procedure
was characterized by unfavorable decomposition of iodine azide
in some cases. In substitution reaction, vinyl halide reacted with
for the synthesis of N-arylated and N-alkylated heterocyclic-fused
aromatic compounds,10 synthesis of pyrrolidinone and lactone
skeletons,11 oxidative deprotection of dithiane containing alka-
loids,12 direct -hydroxylation of ketones,13 and other reactions.14
a
During the course of our previous unpublished studies, we
found that treatment of ,b-unsaturated carboxylic acids with
a
NaN3 and tetraethylammonium bromide (TEAB) in dichlorometh-
ane gave vinyl azides. Initially, we carried out the reaction with
cinnamic acid as a model to explore the suitable reaction condi-
tions with sodium azide and TEAB in dichloromethane at room
temperature (Scheme 1; Table 1, entry 1). In this case, the reaction
afforded the corresponding 3-phenylprop-2-enoyl azide as a major
product in absence of TEAB instead of desired vinyl azide (Scheme
2; Table 1, entry 11). We have also found that chloroform and
dichloromethane are the best solvents. As we are working on
hypervalent iodine system, to explore the possibility of other triva-
sodium azide in presence of CuI and
inconvenient syntheses there is only one method reported which
involves the indirect conversion of ,b-unsaturated carboxylic
acids to vinyl azides. In this method, first ,b-unsaturated carbox-
L
-proline.6 Apart from these
a
a
ylic acids reacted with sodium azide in acetonitrile overnight in
presence of cerium ammonium nitrate. The elimination of formed
nitrate intermediate then affords vinyl azide using sodium ace-
tate.7 Despite the above mentioned examples, the study of novel
efficient synthesis of vinyl azides is still valuable in the field of or-
ganic chemistry.
Hypervalent iodine reagents have found widespread applica-
tions in organic synthesis because of their selectivity and simplic-
ity in use.8 Our group has been working extensively on the
development of novel methodologies under mild reaction condi-
tions using various hypervalent iodine reagents.9 [bis(trifluoro-
acetoxy)iodo]benzene is commercially available as colorless
crystalline solid. It is fairly stable and can be kept without refriger-
ation for long period of time, with protection from light. It is used
lent iodine reagents for conversion of
a,b-unsaturated carboxylic
acids to vinyl azide, we carried out the reaction with cinnamic acid
under similar as well as different reaction conditions with hyper-
valent iodine reagents such as IBX and 4,40-bis-(dichloroiodo)-
biphenyl instead of [bis(trifluoroacetoxy) iodo]benzene, no forma-
tion of vinyl azide was observed even after 48 h.
In order to explore the reaction scope, a variety of
a,b-unsatu-
rated carboxylic acids, prepared by standard reported procedures,
COOH
[bis(trifluoroacetoxy)iodo]benzene / NaN3
TEAB, CH
N3
2Cl2, rt
* Corresponding author. Tel.: +91 22 24145616; fax: +91 22 24145614.
E-mail address: vikastelvekar@rediffmail.com (V.N. Telvekar).
Scheme 1. Cinnamic acid converted into vinyl azide using [bis(trifluoroacet-
oxy)iodo]benzene and sodium azide and TEAB.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.06.097

V. N. Telvekar et al. / Tetrahedron Letters 50 (2009) 5056–5058
5057
Table 1
Carboxylic acid reaction with [bis(trifluoroacetoxy)iodo]benzene and sodium azide
Entry
Substrateb
Product
Time (min)
30
Yieldc (%)
80
N3
COOH
1a
COOH
N3
2
3
4
30
84
80
75
H3C
H3C
COOH
N3
35
Cl
Cl
N3
COOH
120
O2N
O2N
N3
COOH
5
6
7
30
87
88
70
OCH3
OCH3
COOH
N3
35
H3CO
H3CO
COOH
COOH
N3
180
H3COOC
H3COOC
N3
H3C
H3C
H3C
H3C
8
180
24 h
24 h
30
70
COOH
9
—
—
NRd
NRd
86
COOH
COOH
10
11e
H3C
CON3
COOH
CON3
12
30
88
H3C
H3C
a
Reaction conditions (entries 1–10): substrate (1.0 equiv), [bis(trifluoroacetoxy)iodo]benzene (1.2 equiv), TEAB (1.2 equiv), anhyd CH2Cl2, rt, and sodium azide (1.2 equiv).
Starting compounds were prepared by standard reported procedures.
b
c
Isolated yields after column chromatography and structures were confirmed by comparison of the IR and 1H NMR spectra with those of authentic materials.
No reaction.
d
e
Reaction conditions (entries 11 and 12): substrate (1.0 equiv), [bis(trifluoroacetoxy)iodo]benzene (1.2 equiv), sodium azide (1.2 equiv), anhyd CH2Cl2, rt.

5058
V. N. Telvekar et al. / Tetrahedron Letters 50 (2009) 5056–5058
O
Acknowledgment
COOH
N3
[bis(trifluoroacetoxy)iodo]benzene / NaN3
V.N.T. thanks All India Council for Technical Education (AICTE)
for financial support under Research Promotion Scheme (RPS).
CH2Cl2, rt
Scheme 2. Cinnamic acid converted into acyl azide using [bis(trifluoroacet-
oxy)iodo]benzene and sodium azide.
References and notes
1. Yujiro, N.; Naoto, H.; Yoshito, T. Chem. Lett. 1976, 901.
2. Kazuhiro, K.; Sachiko, M.; Masaharu, M.; Yasuoki, M. Chem. Pharm. Bull. 1999,
47, 1227.
3. Scriven, E.; Turnbull, K. Chem. Rev. 1988, 88, 304.
4. Thakorej, A. N.; Buchshriberan, D.; Oehlschlag, A. C. Can. J .Chem. 1973, 51, 2406.
5. (a) Singh, P. N. D.; Carter, C. L.; Gudmundsdottir, A. D. Tetrahedron Lett. 2003, 44,
6763; (b) Timen, A. S.; Risberg, E.; Somfai, P. Tetrahedron Lett. 2003, 44, 5339;
(c) Hassner, A.; Fowler, F. W. J. Org. Chem. 1963, 33, 2686.
were converted to corresponding vinyl azides in moderate to good
yields and the results are summarized in Table 1.15 It was found
that either electron-rich or electron-deficient a,b-unsaturated car-
boxylic acids were suitable for this reaction, giving desired vinyl
azide in moderate to good yields in short reaction times (Table 1,
entries 2–4). It was noted that a variety of functional groups toler-
ated these reaction conditions (Table 1, entries 3–7). This feature
would allow the use of the present method in the synthesis of wide
range of vinyl azides. A lower reaction rate was observed with ali-
6. Zhu, W.; Ma, D. Chem. Commun. 2004, 888.
7. Nair, V.; George, G. T. Tetrahedron Lett. 2000, 41, 3199.
8. (a) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2002, 102, 2523; (b) Zhdankin, V. V.
Curr. Org. Synth. 2005, 2, 121; (c) Wirth, T. Angew. Chem., Int. Ed. 2005, 44, 3656.
9. (a) Telvekar, V. N.; Patel, K. N.; Kundaikar, H. S.; Chaudhari, H. K. Tetrahedron Lett.
2008, 49, 2213; (b) Telvekar, V. N.; Rane, R. M. Tetrahedron Lett. 2007, 48, 6051.
10. Du, Y.; Liu, R.; Linn, G.; Zhao, K. Org. Lett. 2006, 8, 5919.
phatic a,b-unsaturated carboxylic acids (Table 1, entries 7 and 8).
11. Tellitu, I.; Serna, S. .; Herrero, M. T.; Moreno, I.; Domínguez, E.; SanMartin, R. J.
Org. Chem. 2007, 72, 1526.
Further investigations indicated that in the absence of double
bond reaction does not take place (Table 1, entries 9 and 10). In
the absence of TEAB under similar reaction conditions cinnamic
acid and p-methyl cinnamic acid readily converted into corre-
sponding acyl azides (Table 1, entries 11 and 12) without affecting
the double bond.
12. Fleming, F.; Funk, L.; Altundas, R.; Tu, Y. J. Org. Chem. 2001, 66, 6502.
13. Moriarty, R. M.; Berylund, B. A.; Penmasta, R. Tetrahedron Lett. 1992, 33, 6065.
14. Karam, O.; Jacquesy, J. C.; Jouannetand, M. P. Tetrahedron Lett. 1994, 35, 2541.
15. General procedure: To a stirred solution of [bis(trifluoroacetoxy)iodo]benzene
(1.2 equiv) in anhyd CH2Cl2 (15 mL) was added TEAB (1.2 equiv) in one portion.
The resultant reaction mixture was stirred for 5 min followed by addition of
a
,b-unsaturated carboxylic acid (1.0 equiv). After completion of addition,
In conclusion, a new reaction system using trivalent iodine re-
agents, [bis(trifluoroacetoxy)iodo]benzene, in combination with
TEAB and sodium azide has been developed, which is capable of
sodium azide (1.2 equiv) was added and the mixture was stirred at room
temperature until the starting material was completely consumed (TLC). The
reaction mixture was diluted with CH2Cl2 and washed successively with 10%
sodium bisulfate solution (2 ꢀ 20 mL), 10% sodium bicarbonate (2 ꢀ 15 mL),
and water (2 ꢀ 20 mL). The organic layer was dried over anhydrous sodium
sulfate and concentrated under reduced pressure to give crude product. Pure
product was obtained after silica gel column chromatography (10% EtOAc–
hexane). [Acyl azides were prepared using similar procedure without the
addition of TEAB].
converting various
a,b-unsaturated carboxylic acids into corre-
sponding vinyl azides, at room temperature. The method devel-
oped is mild and gives moderate to good yields of vinyl azides
and acyl azides for both aliphatic and aromatic substrates.