Ceric ammonium nitrate mediated selective bromoalkoxylation of activated cinnamyl compounds using lithium bromide

Article abstract of DOI:10.1055/s-2001-10774

Selective bromoalkoxylation of activated cinnamyl systems has been achieved in good yield, using lithium bromide and propargyl alcohol.

Full text of DOI:10.1055/s-2001-10774

226
LETTER
Ceric Ammonium Nitrate Mediated Selective Bromoalkoxylation of Activated
Cinnamyl Compounds Using Lithium Bromide
Subhas Chandra Roy,*a Chandrani Guin,a Kalyan Kumar Rana,a Gourhari Maitib
aDepartment of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India
bDepartment of Chemistry, Jadavpur University, Jadavpur, Calcutta 700 032, India
E-mail: ocscr@mahendra.iacs.res.in
Received 16 November 2000
Table CAN mediated bromoalkoxylation of activated cinnamyl
compounds
Abstract: Selective bromoalkoxylation of activated cinnamyl sys-
tems has been achieved in good yield, using lithium bromide and
propargyl alcohol.
Key words: ceric ammonium nitrate, bromoalkoxylation, lithium
bromide, selective
In addition to the carbon-carbon bond-forming reactions,1
ceric ammonium nitrate (CAN) has also been found to be
a potential, readily available reagent for various valuable
transformations2 in organic synthesis. Because of our con-
tinued interest3 in exploring CAN as a powerful single
electron oxidant, we decided to explore its efficacy in the
bromoalkoxylation of cinnamyl compounds using LiBr as
the bromine source. Bromoalkoxylation4 is an important
transformation in organic synthesis and the bromoalkoxy
compounds can be used as versatile intermediates towards
the synthesis of various natural products.5,6 The bromo-
ethers are generally prepared by the reaction of an olefin
with N-bromosuccinimide (NBS) in the presence of an
excess of alcohol. Although several CAN mediated
organic transformations have been reported in the litera-
ture, to our knowledge, bromoalkoxylation of cinnamyl
compounds has not yet been explored. We report here a
procedure for ceric ammonium nitrate mediated selective
bromoalkoxylation of activated cinnamyl compounds us-
ing lithium bromide in good yield (Scheme).
a Yields refer to chromatographically pure isolated products.
b Stirring at room temperature for 24 h.
R1 = electron donating group
R2 = Me or Et
then the addition of alcohol provides the bromo ethers.
The reaction is only effective when there is an electron do-
nating group, e.g. a methoxy group in the aromatic moiety
either in ortho or para position. Without this aromatic ac-
tivation the reaction does not proceed at all. As a result,
simple methylcinnamate remained unaffected under the
reaction conditions.
Scheme
Thus, a series of activated cinnamyl esters or ketones were
subjected to bromoalkoxylation in the presence of CAN
and LiBr with an excess of propargyl alcohol at room tem-
perature to furnish the corresponding bromoethers.7,8 The
results are summarised in the Table.
The cation Br+ is generated by the reaction of LiBr with
CAN which reacts with the styrenoid double bond and
In conclusion, we developed a selective bromoalkoxyl-
ation of activated cinnamyl compounds mediated by ceric
ammonium nitrate using lithium bromide in good yield.
Synlett 2001, No. 2, 226–227 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Ceric Ammonium Nitrate Mediated Selective Bromoalkoxylation
227
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Acknowledgement
We thank the Department of Science and Technology, New Delhi
for financial support. C.G. thanks CSIR, New Delhi for the award
of a Junior Research Fellowship.
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References and Notes
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(7) All compounds gave satisfactory spectroscopic data and were
compared with the authentic samples.
(8) General Procedure: To a magnetically stirred solution of the
cinnamyl compound (2.08 mmol), LiBr (2.5 mmol) and
propargyl alcohol (1.44 g, 25.7 mmol) in dry acetonitrile
(5 ml), a solution of ceric(IV) ammonium nitrate (1.7 g,
3.12 mmol) in acetonotrile (10 ml) was added dropwise at
room temperature under nitrogen. The reaction mixture was
further stirred for 3 h, and then diluted with ether (15 ml). The
organic layer was separated, washed successively with
saturated aqueous NaHCO3 solution (3 10 ml), water
(10 ml) and brine (3 10 ml) and then dried over Na2SO4.
Volatiles were removed under reduced pressure and the
residue was purified by chromatography over silica gel to
furnish the pure bromoether.
Article Identifier:
1437-2096,E;2001,0,02,0226,0227,ftx,en;L20800ST.pdf
Synlett 2001, No. 2, 226–227 ISSN 0936-5214 © Thieme Stuttgart · New York