Synthesis of 3β,3β,5-tribromoacetyl-4-hydroxy-6-methyl-2H-pyran- 2-one by bromination of dehydroacetic acid

Article abstract of DOI:10.1081/SCC-200048970

Bromination of dehydroacetic acid giving rise to 3β,3β,5- tribromoacetyl-4-hydroxy-6-methyl-2H-pyran-2-one is described. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1081/SCC-200048970

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Synthesis of
3β,3β,5‐tribromoacetyl‐4‐hydroxy‐
by Bromination of
Dehydroacetic Acid
Ajay Kumar a , Richa Prakash a & Shiv P. Singh a
a Department of Chemistry, Kurukshetra University,
Kurukshetra, 136 119, Haryana, India
Published online: 28 Jul 2007.
To cite this article: Ajay Kumar , Richa Prakash & Shiv P. Singh (2005): Synthesis
of 3β,3β,5‐tribromoacetyl‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one by Bromination of
Dehydroacetic Acid, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 35:3, 461-464
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Synthetic Communicationsw, 35: 461–464, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048970
Synthesis of 3b,3b,5-tribromoacetyl-4-
hydroxy-6-methyl-2H-pyran-2-one by
Bromination of Dehydroacetic Acid
Ajay Kumar, Richa Prakash, and Shiv P. Singh
Department of Chemistry, Kurukshetra University,
Kurukshetra, Haryana, India
Abstract: Bromination of dehydroacetic acid giving rise to 3b,3b,5-tribromoacetyl-4-
hydroxy-6-methyl-2H-pyran-2-one is described.
Keywords: Dehydroacetic acid, bromination, tribromodehydroacetic acid
3-Acetyl-4-hydroxy-6-methyl-2H-pyran-2-one (Dehydroacetic acid, DHA, 1)
and its derivatives find wider application in the synthesis of heterocyclic
compounds,[1–4] and the area has been reviewed by us.[5] As part of our
ongoing studies on the chemistry of DHA, we are now interested in the
synthesis of some novel heterocycles from the reactions of 5-bromodehydroa-
cetic acid (5-BrDHA, 2) with appropriate substrates.
During the preparation of 2 according to literature procedure[6] involving
2.5 equivalent of Br2 containing catalytic amount of I2 in CHCl3, we found
that bromination of DHA (1) leads to a new product, namely, 3b,3b,5-tribro-
moacetyl-4-hydroxy-6-methyl-2H-pyran-2-one (3) in addition to the reported
2. Since the new product 3 seems to be a potential precursor for the synthesis
of new heterocyclic compounds, e.g., synthesis of thiazoles involving
Hantzsch thiazole synthesis, it will be worthwhile to publish this note on
the preparation of 3.
Received in India October 18, 2004
Address correspondence to Shiv P. Singh, Department of Chemistry, Kurukshetra
University, Kurukshetra 136 119 Haryana, India. Fax: 01744-238628, 238277;
E-mail: shivpsingh@rediffmail.com

462
A. Kumar, R. Prakash, and S. P. Singh
Thus, DHA was treated with 2.5 equivalent of Br2 containing 1 mol% iodine
in CHCl3 for 72h at 0–58C. The 1H NMR and TLC of the crude product showed
formation of two products, including the expected product 2 as the major one.
Recrystallization of the crude mixture from alcohol afforded 2 and 3 in 60%
and 8% yields, respectively. The product 2 was identified by comparison of the
m.p. and spectral data (ir and nmr) with the reported data6, whereas the
structure of the new product 3 was confirmed by its spectral and analytical
1
data. In the H NMR spectrum of 3, a singlet at d 7.4 integrating one proton
was attributed to COCHBr2. The singlet at 2.56 integrating for three protons
was attributed C(6)-CH3.
With a view to promote 3, as a versatile precursor, attention was drawn to
increase the yield of 3. Subsequent experimentaion showed that significant
improvement in the yield of 3 was observed, when the reaction was allowed to
proceed by treating DHA with 3 equivalent of Br2 at 08C for 72h and then at
room temperature for 24h. The best result (78% yield of 3) was obtained when
2 is separately treated with 2.5 equivalent of Br2 at room temperature for 48h.
The compound 3 was treated with benzothioamide to give the pyranylthia-
zole derivative (4) in 76% yield. This method to prepare pyranylthiazole was
better than the conventional Hantzsch thiazole synthesis involvinga-haloketone.
EXPERIMENTAL
3b,3b,5-Tribromoacetyl-4-hydroxy-6-methyl-2H-pyran-2-one (3)
Method I
To a solution of 5.04 g (30 mmol) of DHA (1) in chloroform (30 mL) was
added a solution of 4.5 mL (90 mmol) of Br2 and 0.2 g of I2 in chloroform

Synthesis of 3b,3b,5-tribromoacetyl-4-hydroxy-6-methyl-2H-pyran-2-one
463
(30 mL) at 08. After 72 h at 58 and then at room temperature for 24 h, the
solution was washed with 5% sodium bisulphite solution, dried, crystallized
from ethanol to give 6.0 g (45%) of 3: m.p. 102–1038C; IR (KBr): 3400
1
(OH), 1731 (s, C55O), H NMR (CDCl3, d): 2.56 (s, 3H, CH3), 7.4 (s, 1H,
CHBr2), 16.3 (s, 1H, OH), 13C NMR (CDCl3): 192.34, 177.55, 168.75,
158.22, 97.28, 95.55, 39.65, 21.40, Mass (m/z): 405, Anal:Found C, 24.08;
H, 1.29; C8H5Br3O4 requires: C, 23.70; H, 1.23.
Method II
To a solution of 3.5 g of 5-bromoacetyl-4-hydroxy-6-methyl-2H-pyran-2-one
(2)6 in chloroform (30 mL) was added a solution of 2.5 mL of Br2 and 0.2 g of
I2 in chloroform (30 mL) at room temperature. After 48 h at room temperature,
the solution was washed with 5% sodium bisulphite solution, dried, evapor-
ated, and crystallized from ethanol to give 4.3 g (78%) of 3.
4-(5-Bromo-4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-
phenylthiazole (4)
To a solution of 0.405 g (1 mmol, 3) in ethanol (10 mL) was added 0.137 g
(1 mmol) of benzothioamide, and the reaction mixture was stirred for 15–
30 min. The resulting solid was filtered and washed from ethanol to give 4.
m.p. 1908C; Yield 76%, IR (nmax, KBr): 1706 cm21 (C55O); 1H NMR
(CDCl3, DMSO, 300 MHz, d): 2.51 (s, 3H, CH3), 7.49–7.91 (m, 5H, Ar),
8.33 (s, 1H, C5-H). 13C NMR (CDCl3, DMSO): 166.50, 165.54, 160.85,
159.73, 148.41, 131.35, 131.10, 129.31, 126.44, 115.57, 98.01, 95.52,
20.37, Mass (m/z): 364, Found C, 49.08; H, 2.02; N, 3.53; C15H10BrNO3S
requires: C, 49.00; H, 2.00, N, 3.85.
ACKNOWLEDGMENT
We are thankful to DRDO (ERIP/ER/0103294/M/01), New Delhi for
financial assistance.
REFERENCES
1. Manas, M. M.; Pleixats, R. Dehydroacetic acid, triacetic acid lactone and related
pyrones. Advances in Heterocyclic Chemistry 1992, 53, 1.
2. Prakash, O.; Kumar, A.; Sadana, A.; Singh, S. P. A facile synthesis of 3,4-dihydro-
2-pyronyl-1,5-benzodiazepine derivatives. Synth. Commun. 2002, 32, 2663.

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A. Kumar, R. Prakash, and S. P. Singh
3. Singh, S. P.; Grover, M.; Tarar, L. S.; Elguero, J.; Martinez, A. 1H and 13C
NMR study of the structure and tautomerism of 4-pyrazolylpyrazolinones.
J. Heterocycl. Chem. 1990, 27, 865.
4. Singh, S. P.; Kumar, D.; Batra, H.; Naithani, R.; Rozas, J.; Elguero, J. The reaction
between hydrazines and b-dicarbonyl compounds: proposal for a mechanism.
Can. J. Chem. 2000, 78, 1109.
5. Prakash, O.; Kumar, A.; Singh, S. P. Synthesis of heterocyclic compounds from the
reactions of dehydroacetic acid (DHA) and its derivatives. Heterocycles 2004,
63 (5), 1193.
6. Harris, T. M.; Harris, C. W.; Brush, C. K. Bromination of dehydroacetic acid.
J. Org. Chem. 1970, 35, 1329.