A mild and efficient method for oxidative halodecarboxylation of α,β-unsaturated aromatic acids using lithium bromide/chloride and ceric ammonium nitrate

Article abstract of DOI:10.1016/S0040-4039(01)01936-0

A mild and efficient ecofriendly method for the halodecarboxylation of α,β-unsaturated aromatic acids has been developed by using lithium bromide/chloride and ceric ammonium nitrate in acetonitrile-water at room temperature to afford the vinyl halides in moderate to good yields.

Full text of DOI:10.1016/S0040-4039(01)01936-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 9253–9255
A mild and efficient method for oxidative halodecarboxylation of
a,b-unsaturated aromatic acids using lithium bromide/chloride
and ceric ammonium nitrate
a,
a
b
Subhas Chandra Roy, * Chandrani Guin and Gourhari Maiti
a
Department of Organic Chemistry, Indian Association for the Cultivation of Science Jadavpur, Calcutta 700 032, India
b
Department of Chemistry, Jadavpur University, Jadavpur, Calcutta 700 032, India
Received 24 August 2001; revised 1 October 2001; accepted 12 October 2001
Abstract—A mild and efficient ecofriendly method for the halodecarboxylation of a,b-unsaturated aromatic acids has been
developed by using lithium bromide/chloride and ceric ammonium nitrate in acetonitrile–water at room temperature to afford the
vinyl halides in moderate to good yields. © 2001 Elsevier Science Ltd. All rights reserved.
The decarboxylation of organic carboxylic acids accom-
panied by a simultaneous replacement by a halogen
under radical conditions is an extremely useful and
selective reaction in organic chemistry for the synthesis
of halogenated organic substances. The original method
for oxidative halodecarboxylation, known as the Huns-
diecker reaction, is the reaction of a silver salt of a1
carboxylic acid with mainly bromine as the halogen.
The efficacy of the reaction has been improved by2
several groups to include carboxylates of mercury,
demands some mild and efficient alternative reagents
for the Hunsdiecker reaction.
Lanthanide salts have been used as shift reagents and
13
reagents for organic synthesis.
Ceric ammonium
nitrate (CAN) is one such reagent, which has been used
extensively for functional group transformations in
organic synthesis. The strong oxidising power of the
ceric ion has been recognised for many decades. How-
ever, its synthetic utility to organic chemistry has only
3
4
5
14
15
thallium, lead, and manganese besides the original
silver of Hunsdiecker. In spite of that, the classical
Hunsdiecker reactions have some limitations e.g. (i) the
reaction of trans and cis cinnamic acids give b-bromo-
been explored recently. Asakura has demonstrated
that CAN can be efficiently used as a one electron
oxidant to generate electrophilic bromine from the
16
metal salts. In continuation of our efforts to explore
CAN as a one electron oxidant, we report here a simple
and efficient methodology for the halodecarboxylation
of a,b-unsaturated aromatic acids using LiBr or LiCl
and CAN, at room temperature to afford the vinyl
halides (Scheme 1). Thus, a series of trans-a,b-unsatu-
rated aromatic acids were treated with LiX (X=Cl or
6
styrene in a very low yield, (ii) generally, a high
temperature is required for the reaction (iii) the use of
toxic or hazardous reagents like molecular bromine and
salts of mercury, thallium, lead and silver.
Later, classical Hunsdiecker reactions7 have been
modified by using NBS/iodosyl benzene, NBS/lithium
Br) and CAN in acetonitrile–water (10:1) at room
8
9
0
17
acetate, NBS/tetrabutylammonium trifluoroacetate,
temperature to afford trans-b-halostyrenes.
The
1
and bis(collidine) halogen(I)hexafluorophosphate.
results are summarised in Table 1. It is noteworthy that
the amount of water in the solvent had a remarkable
effect on the yield. An increase of water content in the
solvent resulted in an increase in the yield of b-
Very recently, microwave induced Hunsdiecker reac-
tions using N-halosuccinimide/catalytic amount of
1
1
®12
lithium acetate and sodium halide/oxone
have been
reported. Although, most of these methods are quite
satisfactory, the use of expensive and complex reagents,
large amounts of solvent and prolonged reaction times
Keywords: halodecarboxylation; lithium bromide; ceric ammonium
nitrate; a,b-unsaturated aromatic acids.
*
Corresponding author.
Scheme 1.
0
040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01936-0

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S. C. Roy et al. / Tetrahedron Letters 42 (2001) 9253–9255
Table 1. Halodecarboxylation of a,b-unsaturated aromatic acids with CAN and LiBr/LiCl
1
2
halostyrene and we obtained the maximum yield using
a solvent to water ratio of 10:1. Moderate to good
yields of the corresponding halides were obtained and it
was observed that electron donating substituents in the
aromatic ring accelerated the reaction.
the Department of Science and Technology, New Delhi.
C.G. thanks CSIR, New Delhi for the award of Senior
Research Fellowship.
References
In conclusion, we have developed a simple, efficient and
environmentally friendly methodology for the halode-
carboxylation of a,b-unsaturated aromatic acids using
lithium bromide/chloride and ceric ammonium nitrate
at room temperature.
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17. General procedure: To a magnetically stirred solution
of the cinnamic acid derivative (1.68 mmol), LiBr or
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solution of ceric ammonium nitrate (3.5 mmol) in ace-
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cessively with saturated aqueous NaHCO
10 ml), water (2×10 ml), brine (3×10 ml) and then
dried (Na SO ). Volatiles were removed under reduced
pressure and the residue was purified by chromatogra-
phy over Al (2% ethylacetate in petroleum ether) to
furnish the pure vinyl halides.
solution (3×
3
1
1
2
4
O
3
2
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