3,4,5-Trifluorobenzeneboronic acid: A mild and versatile catalyst for the one-pot synthesis of acyl azides from carboxylic acids

Article abstract of DOI:10.1016/S0040-4039(02)02256-6

Acyloxyboron intermediates generated from carboxylic acids and 3,4,5-trifluorobenzeneboronic acid react with sodium azide to furnish the corresponding acyl azides in moderate to good yields.

Full text of DOI:10.1016/S0040-4039(02)02256-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9715–9716
3,4,5-Trifluorobenzeneboronic acid: a mild and versatile catalyst
for the one-pot synthesis of acyl azides from carboxylic acids
R. H. Tale* and K. M. Patil
Organic Chemistry Research Laboratory, School of Chemical Sciences, S.R.T.M. University, Nanded-6, Maharashtra, India
Received 22 July 2002; revised 24 September 2002; accepted 4 October 2002
Abstract—Acyloxyboron intermediates generated from carboxylic acids and 3,4,5-trifluorobenzeneboronic acid react with sodium
azide to furnish the corresponding acyl azides in moderate to good yields. © 2002 Elsevier Science Ltd. All rights reserved.
There are several routes to acyl azides.1–5 In most of
these reactions, a carboxylic acid is converted into a
more reactive intermediate, e.g. an acyl chloride, which
is then allowed to react with an azide ion in either
water or a water miscible organic solvent. However,
these methods suffer from the limitation that acyl chlo-
rides or other reactive acid derivatives are not always
available. For practical reasons it is preferable to form
reactive intermediates in situ.
as exists indicates that they are of relatively low toxicity
[benzeneboronic acid:15 LD50, oral-rat=740 mg/kg] and
environmental impact. Yamamoto has found that a
boronic acid with electron withdrawing substituents, in
particular 3,4,5-trifluorobenzeneboronic acid 1 can be
an effective catalyst for amidation and esterification of
carboxylic acids.16 To our knowledge, however there
are no reports in the literature on the boronic acid-cat-
alyzed azidation of carboxylic acids.
There have been some reports in the literature on the
preparation of acyl azides directly from carboxylic
acids. These include the use of acid activators such as
ethyl chloroformate,6 SOCl2–DMF,7 diphenylphospho-
ryl azide (DPPA)8 and NCS–PPh3.9
In view of the great utility of acyl azides as synthetic
intermediates in organic chemistry,17 it is worthwhile to
explore the generality and scope of boronic acid 1 as a
catalyst for the azidation of carboxylic acids. In the
present paper we wish to describe an extremely simple
but powerful procedure for the one-pot synthesis of
acyl azides from carboxylic acids using 1 and sodium
azide which proceeds via acyloxyboron intermediates
(Scheme 1).
Attempts have also been made to prepare acyl azides
directly from aldehydes by using special types of
reagents such as chromic anhydride-trimethylsilyl
azide10 and triazidochlorosilane–manganese dioxide.11
Very recently acyl azides have been prepared from
carboxylic acids using triphosgene12 and cyanuric
chloride13 as acid activators. Although these methods
provide good yields of acyl azides, they involve the use
of hazardous reagents.
The chemistry of boronic acids continues to be a
growth area in synthetic methodology. Many
organoboron compounds,14 are air sensitive, tend to be
easily hydrolyzed and in some cases are pyrophoric.
Boronic acids, RB(OH)2, in contrast, are usually crys-
talline solids, stable to air and moisture. Such evidence
The reaction is thought to involve a six-membered
cyclic intermediate (Scheme 2).
Various structurally diverse carboxylic acids have been
successfully converted into their corresponding acyl
azides using catalytic amounts of 1 in the presence of
sodium azide in moderate to good yields (Table 1).
Mild reaction conditions, simplicity, ease of workup
and the low toxicity and environmental impact of
boronic acids15 in contrast to the hazardous reagents
Keywords: carboxylic acid; 3,4,5-trifluorobenzeneboronic acid; acyl
azide.
* Corresponding author. Fax: +91-2462-29245; e-mail: rkht2002@
yahoo.com
Scheme 1.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02256-6

9716
R. H. Tale, K. M. Patil / Tetrahedron Letters 43 (2002) 9715–9716
Scheme 2.
Table 1. Synthesis of acyl azides catalyzed by boronic
acid 1
Acknowledgements
The authors are grateful to Sudhir Dapurkar (Research
Scholar, I.I.T., Mumbai) for the gift of boronic acid 1.
Entry
Carboxylic acid
Acyl azide
Yielda,b (%)
1
2
3
Benzoic acid
Cinnamic acid
2-Chlorobenzoic
acid
Benzoyl azide
Cinnamyl azide
2-Chlorobenzoyl
azide
85
83
92
References
1. Laszio, P.; Polla, E. Tetrahedron Lett. 1984, 25, 3701.
2. Grundmmann, C. Methoden der Org. Chem. (Houben-
Weyl) 1965, 10, 777.
3. Huisgen, R.; Ugi, I. Chem. Ber. 1957, 90, 2914.
4. Sakai, K.; Anselme, J. P. J. Org. Chem. 1971, 36, 2387.
5. Surya Prakash, G. K.; Arvanaghi, M.; Olah, G. A. J.
Org. Chem. 1983, 48, 3358.
6. (a) Koyashi, S.; Kamiyama, K.; Iimori, T.; Ohno, M.
Tetrahedron Lett. 1984, 25, 2557; (b) Canone, P.; Akssira,
M.; Dahouh, A.; Kashmi, H.; Boumzebrra, M. Heterocy-
cles 1993, 36, 1305.
4
5
4-Chlorobenzoic
acid
4-Hydroxybenzoic 4-Hydroxybenzoyl
acid
Hexanoic acid
Decanoic acid
4-Iodobenzoic acid 4-Iodobenzoyl azide 95
4-Methoxybenzoic 4-Methoxybenzoyl
acid
4-Nitrobenzoic
acid
4-Chlorobenzoyl
azide
94
96
azide
Hexanoyl azide
Decanoyl azide
6
7
8
9
92
90
95
71
83
azide
4-Nitrobenzoyl
azide
10
11
12
13
Phenylacetic acid
Phenylacetyl azide
Phenoxyacetic acid Phenoxyacetyl azide 83
3,5-Dinitrobenzoic 3,5-Dinitrobenzoyl 66
acid azide
7. Arrieta, A.; Aizpurua, J. M.; Palomo, C. Tetrahedron
Lett. 1984, 25, 3365.
8. Shao, H.; Colucci, M.; Tong, S.; Zhang, H.; Castelhano,
A. L. Tetrahedron Lett. 1998, 39, 7235.
9. Froeyen, P. Phosphorus, Sulfur Silicon Relat. Elem. 1994,
89, 57.
10. (a) Lee, J. G.; Kwak, K. H. Tetrahedron Lett. 1992, 33,
3165; (b) Reddy, P. S.; Yadagiri, P.; Lumin, S.; Flack, J.
R. Synth. Commun. 1988, 18, 545.
a Yields refer to the pure isolated product.
b The products were characterized by their physical constants, spec-
troscopic data (IR, 1H NMR) and elemental microanalyses.
11. Elmorsy, S. S. Tetrahedron Lett. 1995, 36, 1341.
12. Gumaste, V. K.; Bhawal, B. M.; Deshmukh, A. R.
Tetrahedron Lett. 2002, 43, 1345.
13. Bandgar, B. P.; Pandit, S. S. Tetrahedron Lett. 2002, 43,
3413.
14. See, for example: Pelter, A.; Smith, K.; Brown, H. C.
Borane Reagents; Academic Press: London, 1988; Smith,
K. In Organometallics in Synthesis; Schlosser, M., Ed.
Organoboron Chemistry. Wiley: Chichester, 1994.
15. Boron, Metallo-Boron Compounds and Boranes; Adams,
R. M., Ed.; Wiley: New York, 1964; p. 693: data quoted
in Registry of Toxic Effects of Chemical Substances,
NIOSH, 2001.
16. (a) Ishihara, K.; Ohara, S.; Yamamoto, H. J. Org. Chem.
1996, 61, 4196; (b) Ishihara, K.; Ohara, S.; Yamamoto,
H. Macromolecules 2000, 33, 3511.
17. (a) Moore, H. W.; Goldish, D. M. In The Chemistry of
Halides, Pseudo-halides and Azides; Patai, S.; Rappoport,
Z., Eds.; Wiley: Chichester, UK, 1983; Vol. 1, p. 321; (b)
Lowski, W. In Azides Nitrenes; Scriven, E. F. V., Ed.;
Academic: Orlando, FL, 1984; p. 205.
reported in the literature12,13 are some of the notewor-
thy features of this method.
In conclusion, we have developed a mild, simple, gen-
eral and environmentally benign protocol for the one-
pot synthesis of acyl azides from carboxylic acids.
General procedure:
To a solution of the carboxylic acid (2 mmol) and
sodium azide (10 mmol) in dry acetonitrile (20 ml) was
added Na2SO4 (1 g) and boronic acid 1 (1 mol%) and
the mixture was stirred at room temperature for 10 h.
After completion of the reaction (TLC), the mixture
was filtered, washed with aqueous NaHCO3 and
extracted with chloroform (3×10 ml). After drying over
anhydrous Na2SO4, the solvent was evaporated to give
the product. The product was purified by column chro-
matography (ethyl acetate:petroleum ether, 1:9).